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• Compare and contrast as microscopes get up close and personal
  - UNKNOWN 6(4):191-193 (2011)
  Nature Nanotechnology | Thesis Compare and contrast as microscopes get up close and personal * Chris Toumey1Journal name:Nature NanotechnologyVolume: 6,Pages:191–193Year published:(2011)DOI:doi:10.1038/nnano.2011.55Published online06 April 2011 To explore the meaning of inter-instrumentality, provided samples of his blood and hair to be imaged by four different types of microscope. Here he describes the results. View full text Subject terms: * Nanometrology and instrumentation * Surface patterning and imaging Figures at a glance * Figure 1: Image of red blood cells taken with a scanning electron microscope at a magnification of ×20,000. The original image (with scale bar and other experimental data) is available as Fig. S1 in the Supplementary Information. * Figure 2: Images of red blood cells (top) and a human hair (bottom) taken with (from left to right) a confocal microscope, an atomic force microscope and a scanning electron microscope. Red blood cells can be seen in the background of confocal microscope image of the human hair (bottom left), and a white blood cell can be seen in the image of the red blood cells (top left). The original images are available as Figs S2–S7 in the Supplementary Information. * Figure 3: Images of red blood cells (top) and a human hair (bottom) taken with a tunnelling electron microscope. The original images are available as Figs S8 and S9 in the Supplementary Information. Author information * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * Chris Toumey is at the University of South Carolina NanoCenter. Corresponding author Correspondence to: * Chris Toumey Author Details * Chris Toumey Contact Chris Toumey Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Author information * Supplementary information PDF files * Supplementary information (1,193 KB) Supplementary information Additional data
• Our choice from the recent literature
  - UNKNOWN 6(4):194 (2011)
  Nature Nanotechnology | Research Highlights Our choice from the recent literature Journal name:Nature NanotechnologyVolume: 6,Page:194Year published:(2011)DOI:doi:10.1038/nnano.2011.59Published online06 April 2011 Read the full article * Instant access to this article: US$32Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Science doi:10.1126/science.1201938 (2011) FENG XIONG AND ALEX JEREZ The surface of a rewritable digital video disk is covered in a material that can reversibly switch between crystalline and amorphous phases when irradiated by a laser. An electronic memory based on such a phase-change material would have numerous advantages, including non-volatility. However, electronic phase-change memories have required high programming currents to generate the heat necessary for a phase transformation. Now, Eric Pop and colleagues at the University of Illinois at Urbana-Champaign have constructed an electronic phase-change memory that can be programmed with currents 100 times smaller than those required by state-of-the-art devices. View full text Read the full article * Instant access to this article: US$32Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Additional data
• Nanobiotechnology: A new look for nanopore sensing
  - UNKNOWN 6(4):195-196 (2011)
  Nature Nanotechnology | News and Views Nanobiotechnology: A new look for nanopore sensing * Tim Albrecht1Journal name:Nature NanotechnologyVolume: 6,Pages:195–196Year published:(2011)DOI:doi:10.1038/nnano.2011.52Published online06 April 2011 Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Coating solid-state nanopores with fluid lipid bilayers can reduce the translocation speeds of molecules and prevent the nanopores from clogging. View full text Subject terms: * Nanobiotechnology * Nanosensors and other devices Author information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * Tim Albrecht is in the Department of Chemistry, Imperial College London, Exhibition Road, London SW7 2AZ, UK. Corresponding author Correspondence to: * Tim Albrecht Author Details * Tim Albrecht Contact Tim Albrecht Search for this author in: * NPG journals * PubMed * Google Scholar Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Additional data
• Nanoelectronics: Making light of electrons
  - UNKNOWN 6(4):196-197 (2011)
  Nature Nanotechnology | News and Views Nanoelectronics: Making light of electrons * David Goldhaber-Gordon1Journal name:Nature NanotechnologyVolume: 6,Pages:196–197Year published:(2011)DOI:doi:10.1038/nnano.2011.53Published online06 April 2011 Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Electrons have been channelled through graphene wires using the principles of optical guiding by fibre optic cables. View full text Subject terms: * Electronic properties and devices * Nanomaterials Author information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * David Goldhaber-Gordon is in the Department of Physics and Geballe Laboratory for Advanced Materials, Stanford University, 476 Lomita Mall, Stanford, California 94305, USA, and at the Weizmann Institute of Science, Rehovot 76100, Israel. Corresponding author Correspondence to: * David Goldhaber-Gordon Author Details * David Goldhaber-Gordon Contact David Goldhaber-Gordon Search for this author in: * NPG journals * PubMed * Google Scholar Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Additional data
• Nanoelectronics: A topological twist for transistors
  - UNKNOWN 6(4):197-198 (2011)
  Nature Nanotechnology | News and Views Nanoelectronics: A topological twist for transistors * Qi-Kun Xue1Journal name:Nature NanotechnologyVolume: 6,Pages:197–198Year published:(2011)DOI:doi:10.1038/nnano.2011.47Published online06 April 2011 Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. A nanoribbon of a material with topological surface states has been used as the channel in a field-effect transistor. View full text Subject terms: * Electronic properties and devices Author information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * Qi-Kun Xue is in the Department of Physics, Tsinghua University, Beijing, 100084 China. Corresponding author Correspondence to: * Qi-Kun Xue Author Details * Qi-Kun Xue Contact Qi-Kun Xue Search for this author in: * NPG journals * PubMed * Google Scholar Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Additional data
• Spin physics: DNA spintronics sees the light
  - UNKNOWN 6(4):198-199 (2011)
  Nature Nanotechnology | News and Views Spin physics: DNA spintronics sees the light * Massimiliano Di Ventra1 * Yuriy V. Pershin2 * Affiliations * Corresponding authorsJournal name:Nature NanotechnologyVolume: 6,Pages:198–199Year published:(2011)DOI:doi:10.1038/nnano.2011.48Published online06 April 2011 Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. A thin layer of double-stranded DNA on a gold surface can act as a spin filter. View full text Subject terms: * Nanomagnetism and spintronics * Nanomaterials Author information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * Massimiliano Di Ventra is in the Department of Physics, University of California, San Diego, La Jolla, California 92093, USA * Yuriy V. Pershin is in the Department of Physics and Astronomy and the USC Nanocenter, University of South Carolina, Columbia, South Carolina 29208, USA. Corresponding authors Correspondence to: * Massimiliano Di Ventra or * Yuriy V. Pershin Author Details * Massimiliano Di Ventra Contact Massimiliano Di Ventra Search for this author in: * NPG journals * PubMed * Google Scholar * Yuriy V. Pershin Contact Yuriy V. Pershin Search for this author in: * NPG journals * PubMed * Google Scholar Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Additional data
• Random materials: Localization on the nanoscale
  - UNKNOWN 6(4):199-200 (2011)
  Nature Nanotechnology | News and Views Random materials: Localization on the nanoscale * Takeshi Egami1Journal name:Nature NanotechnologyVolume: 6,Pages:199–200Year published:(2011)DOI:doi:10.1038/nnano.2011.51Published online06 April 2011 Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. What happens when the size of a metallic particle becomes smaller than the characteristic length scale for electron diffusion in that material? View full text Subject terms: * Electronic properties and devices * Nanomaterials Author information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * Takeshi Egami is at the University of Tennessee, Knoxville, Tennessee 37996, USA, and the Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA. Corresponding author Correspondence to: * Takeshi Egami Author Details * Takeshi Egami Contact Takeshi Egami Search for this author in: * NPG journals * PubMed * Google Scholar Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Additional data
• Nanomaterials: Exfoliating the inorganics
  - UNKNOWN 6(4):200-201 (2011)
  Nature Nanotechnology | News and Views Nanomaterials: Exfoliating the inorganics * Dmitri Golberg1Journal name:Nature NanotechnologyVolume: 6,Pages:200–201Year published:(2011)DOI:doi:10.1038/nnano.2011.57Published online06 April 2011 Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. A versatile method for the production of sheets of inorganic compounds with atomic thickness has been demonstrated. View full text Subject terms: * Nanomaterials * Synthesis and processing Author information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Affiliations * Dmitri Golberg is in the International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 3050044, Japan. Corresponding author Correspondence to: * Dmitri Golberg Author Details * Dmitri Golberg Contact Dmitri Golberg Search for this author in: * NPG journals * PubMed * Google Scholar Read the full article * Instant access to this article: US$18Buy now * Subscribe to Nature Nanotechnology for full access: SubscribeLogin for existing subscribers Additional access options: * Use a document delivery service * Login via Athens * Purchase a site license * Institutional access * British Library Document Supply Centre * Infotrieve * Thompson ISI Document Delivery * You can also request this document from your local library through inter-library loan services. Additional data
• Comparative advantages of mechanical biosensors
  - UNKNOWN 6(4):203-215 (2011)
  Nature Nanotechnology | Review Comparative advantages of mechanical biosensors * J.L. Arlett1 * E.B. Myers1 * M.L. Roukes1 * Affiliations * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:203–215Year published:(2011)DOI:doi:10.1038/nnano.2011.44Published online27 March 2011 Abstract * Abstract * Author information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Mechanical interactions are fundamental to biology. Mechanical forces of chemical origin determine motility and adhesion on the cellular scale, and govern transport and affinity on the molecular scale. Biological sensing in the mechanical domain provides unique opportunities to measure forces, displacements and mass changes from cellular and subcellular processes. Nanomechanical systems are particularly well matched in size with molecular interactions, and provide a basis for biological probes with single-molecule sensitivity. Here we review micro- and nanoscale biosensors, with a particular focus on fast mechanical biosensing in fluid by mass- and force-based methods, and the challenges presented by non-specific interactions. We explain the general issues that will be critical to the success of any type of next-generation mechanical biosensor, such as the need to improve intrinsic device performance, fabrication reproducibility and system integration. We also discuss the ne! ed for a greater understanding of analyte–sensor interactions on the nanoscale and of stochastic processes in the sensing environment. View full text Subject terms: * Nanobiotechnology * Nanosensors and other devices * NEMS Figures at a glance * Figure 1: Fluidic detection limits for protein sensing. The limit of detection in moles (left axis) and grams per millilitre (right axis) versus the analysis time for the different types of biosensor (both mechanical and non-mechanical) shown in the panels at the top of the figure and listed in Table 1. Note that both axes are logarithmic. The black dashed line shows the present state-of-the-art (with longer analysis times leading to lower limits of detection); the ideal biosensor would offer low limits of detection and short analysis time (that is, it would be found in the bottom left region of this graph). For many biomarkers the diagnostic level of significance is within the picomolar to nanomolar range, which can be accessed by conventional immunofluorescence assays (IFAs): the challenge for new biosensors is to achieve this sensitivity while also achieving shorter analysis times than the IFA approach. However, detector performance is frequently limited by non-specific binding effects rather than the intrinsic biosensor perfo! rmance (see text). Non-specific binding effects lead to a 'biological noise floor' below which the analyte of interest cannot be detected. The figure shows the biological noise floors (horizontal blue lines) for target–receptor affinities of 1 nM−1 and 100 nM−1 and a non-specific binding association rate of 104 M−1; this noise floor is less of a problem when the target–receptor affinity is high. Such limitations do not apply to sandwich-type assays (see text). Many microfluidic sensors are now approaching the level of sensitivity that will permit real-time measurements on proteins secreted from individual cells. The figure shows the biosensor performance (solid black sloping lines) needed to detect the secretion of TNF-α from a single human monomyelocytic cell in a 1-nl volume121 for both native single cell (SC) secretion and stimulated SC secretion (in which the rate of secretion is increased by a factor of ~80); a mass of 34 kDa was used to relate concentration! to density. SPR: surface-plasmon resonance; SMR: suspended mi! crochannel resonantor; NW: nanowire; LFA: lateral flow assay129; MRR: microring resonantor; QCM: quartz crystal microbalance; BBA: biobarcode amplification assay; IFA: immunofluorescent assay; MC: microcantilever. Panels at top of figure reproduced with permission from: SMR, ref. 37, © 2007 NPG; NW, ref. 128, © 2005 NPG; MRR, ref. 130 © 2009 ACS; IFA, ref. 61, © 2004 RSC. * Figure 2: Fluidic micromechanical biosensors. , Schematic of static-mode surface-stress sensing MEMS device. Binding of target molecules generates a surface stress, which leads to a quasistatic deflection of the cantilever (bottom)7. , Scanning electron micrograph (SEM) of a dynamic mode MEMS device. Target molecules are detected through their influence on the resonance frequency of the cantilever: when the molecules land on the cantilever, they increase its mass and therefore reduce its resonance frequency25. , Suspended microchannel resonator (SMR). The fluid containing the target molecules flows through a channel inside the device (the top of the device is not shown in this cutaway schematic) and bind to the inner flow-channel walls, while the resonator oscillates in air or vacuum3. , Resonance spectrum (oscillation amplitude versus frequency) of a SMR. The quality factor of the device is normally unaffected when the channel is filled with water (red line)37. Figure reproduced with permission from: , ref. 7, © 2001 ! NPG; , ref. 30, © 2004 RSC; , ref. 3, © 2010 ACS; , ref. 37, © 2007 NPG. * Figure 3: Depletion in microfluidic structures. The length needed for 50% depletion L* versus the rate of association kon in an open-loop fluidic configuration for five different combinations of flow rate and microchannel geometry: details of four of these combinations are shown in Table 2; for the fifth combination (black line) t = 700 nm, w = 4 μm and l = 2.05 cm. The dotted vertical lines show the values of kon for the six target–receptor pairs listed in Table 2. Significant depletion can be achieved for lengths of hundreds of nanometres for very small channels (in which the flow rate is reduced) for the highest values of kon (such as for biotin–streptavidin binding), but tens of micrometres or more are needed to achieve significant depletion for larger channels (with much greater flow rates), even for the highest values of kon. For much lower values of kon (such as IL-6 binding to its receptor) it is not possible to achieve significant depletion within practical length scales for microfluidic sensors, implying th! at the kinetics are always reaction limited. Depletion length scales shown here are for short timescales, that is, far from equilibrium. Near equilibrium the kinetics are always dominated by reaction kinetics (see Table 2). Depletion is strongly dependent on the flux of molecules to the surface, which depends on both the flow rate and the channel geometry; here depletion has the greatest role for the combination shown by the black line. * Figure 4: Effect of surface-area:volume ratio on bulk target depletion. The fraction of receptors bound at 10 min versus the surface-area:volume ratio for the six target–receptor pairs listed in Table 2 under reaction-limited conditions (Box 1): the affinity Ka of the pairs decreases from top to bottom. The fraction of bound receptors can be increased by reducing the surface-area:volume ratio. However, below a threshold (determined by Ka), there is no further gain. * Figure 5: Fluidic nanomechanical biosensors. Demonstration of reduction in force noise through the overall reduction of cantilever dimensions. , Noise versus time for a large cantilever (length = 200 μm; spring constant k = 0.060 N m−1; top trace) and a small cantilever (length = 10 μm; k = 0.060 N m−1; bottom trace)131. , Theoretical predictions for total force sensitivity (including thermomechanical Brownian noise, Johnson noise and typical read-out amplifier noise) on a logarithmic scale versus frequency for a silicon piezoresistive cantilever immersed in water and operating at room temperature for three different sets of conditions; the thermodynamic limit (that is, just Brownian noise) is also shown for reference. The sensitivity depends on the maximum tolerable temperature rise both at the tip ΔTtip and the position of maximum heating ΔTmax. As the bias voltage Vdev and bias current I increase, both ΔTtip and ΔTmax also increase, and the sensitivity improves, approaching the thermodynamic limit. The can! tilever device dimensions are: t = 130 nm, w = 2.5 μm, l = 15 μm. , Analogous plot to for a smaller cantilever132 showing qualitatively similar behaviour but substantially higher sensitivity (note that the scale on the y-axis is different): t = 30 nm, w = 100 nm, l = 3 μm. At frequencies below 1 MHz, the system approaches the thermodynamic limit, and the sensitivity remains within about 20% of the fluidic noise floor at the relatively low bias voltage of 0.5 V. Below 0.25 MHz, the total sensitivity is ~5 fN √Hz−1 (for reasonable bias voltages). Figure reproduced with permission from: , ref. 131, © 1999 AIP; ,, ref. 132, © 2007 Springer. * Figure 6: NEMS arrays and system integration. , False-colour SEM image of an array of 20 silicon nitride nanomechanical resonators (in two separately biased banks) with capacitive readout and actuation101; the resonant frequencies of the resonators are ~12 MHz. , Resonance spectrum (oscillation amplitude (S11) versus frequency) of the array in . It is possible to read out the array with a single radiofrequency read-out circuit101. Seven resonators in bank 1 (blue trace) and three resonators in bank 2 (red trace) were detected in this frequency range. , Array of silicon cantilevers: each cantilever is 2.8-μm long and 0.7-μm wide, with the 'legs' being 200-nm wide. A piezoresistive approach was used for readout. Image courtesy of P. Andreucci (Minatec, Leti, CEA). , SEM of a section of a 4,096 silicon cantilever array, transferred onto a wiring wafer. The transfer is done on the 100-mm wafer scale, with approximately 50 such arrays per wafer114. These cantilevers were designed for memory storage applications, with resis! tors at the base to induce (the write step) and measure (read step) the deflection. , Multiplexed microfluidics. PDMS microvalves enable independent compartmentalization, purging and pairwise mixing for each of the 256 chambers on the chip115. Figure reproduced with permission from: ,, ref. 101, © 2007 ACS; , ref. 114, © 2004 IEEE; , ref. 115, © 2002 AAAS. Author information * Abstract * Author information Affiliations * Kavli Nanoscience Institute and Departments of Physics, Applied Physics, and Bioengineering, California Institute of Technology, MC 149-33 Pasadena, California 91125, USA. * J.L. Arlett, * E.B. Myers & * M.L. Roukes Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * M.L. Roukes Author Details * J.L. Arlett Search for this author in: * NPG journals * PubMed * Google Scholar * E.B. Myers Search for this author in: * NPG journals * PubMed * Google Scholar * M.L. Roukes Contact M.L. Roukes Search for this author in: * NPG journals * PubMed * Google Scholar Additional data
• Manipulating surface states in topological insulator nanoribbons
  - UNKNOWN 6(4):216-221 (2011)
  Nature Nanotechnology | Letter Manipulating surface states in topological insulator nanoribbons * Faxian Xiu1, 4 * Liang He1, 4 * Yong Wang1, 2, 4 * Lina Cheng2, 4 * Li-Te Chang1 * Murong Lang1 * Guan Huang1 * Xufeng Kou1 * Yi Zhou1 * Xiaowei Jiang1 * Zhigang Chen2 * Jin Zou2 * Alexandros Shailos3 * Kang L. Wang1 * Affiliations * Contributions * Corresponding authorsJournal name:Nature NanotechnologyVolume: 6,Pages:216–221Year published:(2011)DOI:doi:10.1038/nnano.2011.19Received16 November 2010Accepted21 January 2011Published online13 February 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Topological insulators display unique properties, such as the quantum spin Hall effect, because time-reversal symmetry allows charges and spins to propagate along the edge or surface of the topological insulator without scattering1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14. However, the direct manipulation of these edge/surface states is difficult because they are significantly outnumbered by bulk carriers9, 15, 16. Here, we report experimental evidence for the modulation of these surface states by using a gate voltage to control quantum oscillations in Bi2Te3 nanoribbons. Surface conduction can be significantly enhanced by the gate voltage, with the mobility and Fermi velocity reaching values as high as ~5,800 cm2 V−1 s−1 and ~3.7 × 105 m s−1, respectively, with up to ~51% of the total conductance being due to the surface states. We also report the first observation of h/2e periodic oscillations, suggesting the presence of time-reversed paths with the same relative! zero phase at the interference point16. The high surface conduction and ability to manipulate the surface states demonstrated here could lead to new applications in nanoelectronics and spintronics. View full text Subject terms: * Electronic properties and devices Figures at a glance * Figure 1: Structural characterizations of a Bi2Te3 nanoribbon. , Low-magnification TEM image of a Bi2Te3 nanoribbon on a holey carbon grid. The nanoribbon in this image is ~230 nm wide and ~3.5 µm long. , Selected area diffraction pattern taken along the Bi2Te3 [0001] direction. Sharp diffraction spots indicate high-quality single crystals. , High-resolution TEM image taken along the Bi2Te3 [0001] direction, revealing a perfect crystalline structure. The spacing between the atomic planes is measured to be 0.22 nm (marked by two pairs of parallel lines in ). * Figure 2: Electrical transport measurements of a nanoribbon FET. , Schematic of a typical back-gate FET device. The nanoribbon has a width of ~185 nm, thickness of ~30 nm and channel length of ~2 µm. A constant current geometry was used during transport measurements. , Channel resistance R on a logarithmic scale versus the inverse of temperature, 1/T. Inset: R versus T. , Channel conductance G versus gate voltage Vg at five different temperatures; the magnetic field is zero. Arrows indicate a systematic shift of the Fermi level when applying gate biases at different temperatures. All curves are vertically shifted for clarification. , Sketch of surface-state dispersion near the Γ point showing surface states (SS), valence band (VB) and conduction band (CB) of the bulk states (from refs. 6 and 18). The Fermi level (horizontal lines) shifts towards the middle of the bandgap as the gate voltage is increased from −60 V to +80 V, resulting in the bulk making a smaller contribution to the overall conduction of the system. * Figure 3: SdH oscillations in a nanoribbon FET. –, Shubnikov–de Haas oscillations at different temperatures and gate voltages. The oscillations become more pronounced as the gate voltage increases from −60 V to +80 V at T = 1.4 K () and 4 K (). Purple arrows in the corresponding FFT spectra (,) indicate the frequency of the SdH oscillations, which represent the surface states. Green solid dots suggest the presence of other oscillation frequencies, which are developed when the bulk carrier concentration increases under negative gate voltages. The oscillations also become more pronounced as the temperature decreases from 8 K to 1.4 K at gate voltages of +80 V () and +40 V (). , Normalized conductivity amplitude versus temperature at gate voltages of +80 V and +40 V. A magnetic field of 7.4 T was used to extract the cyclotron effective mass: ~0.131m0 (+80 V) and ~0.119m0 (+40 V). ,, Dingle plots at three different temperatures at gate voltages of +80 V () and +40 V (). Transport lifetime, mean free path and mobility ca! n be extracted from the best fit to log [(ΔR/R0)Bsinh λ]. * Figure 4: Gate-modulated AB oscillations. , Magnetoresistance plots (resistance R versus applied magnetic field B) with superimposed Aharonov–Bohm oscillations at five different temperatures between 1.4 and 8 K, and no gate voltage. , AB oscillations can be clearly seen when the smooth magnetoresistance background is subtracted from the plots in . A detailed description of the subtraction method can be found in Supplementary Fig. S2a. , Magnetoresistance plots at seven different gate voltages between −60 and 60 V, at 1.4 K. , Significant enhancement of the AB oscillation for positive gate voltages can be clearly seen when the smooth magnetoresistance background is subtracted from the plots in , FFT of the magnetoresistance plots in reveals AB oscillations with periods of h/e and h/2e, suggesting different interference paths during in-plane transport. The peaks at h/e and h/2e are most pronounced at 1.4 K. , Amplitude of the FFT spectra in versus temperature: the amplitude, fitted to T−1/2 (red line), suggests ! the absence of inelastic phonon scattering. , AB oscillations with periods of h/e and h/2e can also be seen in the FFT of the magnetoresistance plots in . The peaks at h/e and h/2e are most pronounced at a gate voltage of +60 V. Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Faxian Xiu, * Liang He, * Yong Wang & * Lina Cheng Affiliations * Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA * Faxian Xiu, * Liang He, * Yong Wang, * Li-Te Chang, * Murong Lang, * Guan Huang, * Xufeng Kou, * Yi Zhou, * Xiaowei Jiang & * Kang L. Wang * Materials Engineering and Centre for Microscopy and Microanalysis, The University of Queensland, Brisbane, Queensland 4072, Australia * Yong Wang, * Lina Cheng, * Zhigang Chen & * Jin Zou * California Nanosystems Institute, University of California, Los Angeles, California 90095, USA * Alexandros Shailos Contributions F.X. and L.H. designed and fabricated the devices. F.X., L-T.C., M.L. and A.S. carried out the measurements. L-N.C., Y.W., Z.G.C. and J.Z. synthesized the Bi2Te3 nanoribbons and performed structural analysis. Y.W., G.H., X.K., X.J. and Y.Z. contributed to the measurements and analysis. K.W. supervised the research. F.X., Y.W., L.H., J.Z. and K.W. wrote the paper, with help from all other co-authors. Competing financial interests The authors declare no competing financial interests. Corresponding authors Correspondence to: * Faxian Xiu or * Kang L. Wang Author Details * Faxian Xiu Contact Faxian Xiu Search for this author in: * NPG journals * PubMed * Google Scholar * Liang He Search for this author in: * NPG journals * PubMed * Google Scholar * Yong Wang Search for this author in: * NPG journals * PubMed * Google Scholar * Lina Cheng Search for this author in: * NPG journals * PubMed * Google Scholar * Li-Te Chang Search for this author in: * NPG journals * PubMed * Google Scholar * Murong Lang Search for this author in: * NPG journals * PubMed * Google Scholar * Guan Huang Search for this author in: * NPG journals * PubMed * Google Scholar * Xufeng Kou Search for this author in: * NPG journals * PubMed * Google Scholar * Yi Zhou Search for this author in: * NPG journals * PubMed * Google Scholar * Xiaowei Jiang Search for this author in: * NPG journals * PubMed * Google Scholar * Zhigang Chen Search for this author in: * NPG journals * PubMed * Google Scholar * Jin Zou Search for this author in: * NPG journals * PubMed * Google Scholar * Alexandros Shailos Search for this author in: * NPG journals * PubMed * Google Scholar * Kang L. Wang Contact Kang L. Wang Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (10,793 KB) Supplementary information Additional data
• Gate-controlled guiding of electrons in graphene
  - UNKNOWN 6(4):222-225 (2011)
  Nature Nanotechnology | Letter Gate-controlled guiding of electrons in graphene * J. R. Williams1, 3, 4 * Tony Low2 * M. S. Lundstrom2 * C. M. Marcus3 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:222–225Year published:(2011)DOI:doi:10.1038/nnano.2011.3Received06 December 2010Accepted06 January 2011Published online13 February 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Ballistic semiconductor structures have allowed the realization of optics-like phenomena in electronic systems, including the magnetic focusing1 and electrostatic lensing2 of electrons. An extension that appears unique to graphene is to use both n and p carrier types to create electronic analogues of optical devices with both positive and negative indices of refraction3. Here, we use the gate-controlled density of both p and n carrier types in graphene to demonstrate the electronic analogue of fibre-optic guiding4, 5, 6, 7, 8. Two basic effects are investigated: bipolar p–n junction guiding, based on the principle of angle-selective transmission through the interface between the graphene and the p–n junction; and unipolar fibre-optic guiding, using total internal reflection controlled by carrier density. We also demonstrate modulation of the guiding efficiency through gating, and comparison of these data with numerical simulations indicates that guiding performance is li! mited by the roughness of the interface. The development of p–n and fibre-optic guiding in graphene may lead to electrically reconfigurable wiring in high-mobility devices. View full text Subject terms: * Electronic properties and devices * Nanomaterials Figures at a glance * Figure 1: Schematics of the device and guiding in unipolar and bipolar regimes. , Schematic of a top-gated electron guiding device with four contacts (i, c, g1 and g2) used to measure resistances Rii, Riif and Ricf. Voltages on the top gate, VTG, and the back gate, VBG (not shown) independently control carrier densities (including sign), which serve as effective indices of refraction. Graphene lattice orientation is schematic and is not controlled. , OPG is based on reflection above a critical angle when the density in the channel (under the top gate) is higher than outside the channel (controlled by the back gate), similar to the operation of a fibre optic. , Alternatively, PNG is based on exponentially suppressed transmission through a p–n interface at oblique angles of incidence. * Figure 2: Simulated optical and p–n guiding in gated graphene. , Guiding regimes (OPG (blue), PNG and OPG/PNG (pink)) as a function of density under the top gate (n1) and outside the top gate (n2). The midpoint of the diagram is zero density in Regions 1 and 2. –, Simulations of the current density J in the three regimes for fixed effective index of refractions ε1 and ε2. The x- and y-axes represent the 100 nm × 100 nm size scale of the device. The guiding efficiency is γ = 0.53, 0.03 and 0.24 (Ω = 0.58, 0.18 and 0.29) in the OPG, PNG and OPG/PNG regimes, respectively. Green lines in – are lines of constant current density. * Figure 3: Effects of gating and disorder on guiding efficiency . Inset: experimental guiding efficiency Ωexp (colour scale) as a function of top-gate voltage, VTG, and back-gate voltage, VBG, extracted from the resistances Rii, Riif and Rfic, with three guiding regimes indicated (black dashed lines). Cut line (white dashed line) through the OPG regime indicates where experimental and numerical guiding efficiencies are compared in the main figure. Main panel: experimental guiding efficiency γexp along constant Fermi energy (effective index of refraction) in Region 1, ε1 = 0.3 eV. The value of γexp rises from 0 at VBG = −50 V (the point where the density is a constant in the device) to ~0.20 at VBG = 0 V. Numerical guiding efficiencies are plotted for interface roughnesses of 0 (black circles), 1 nm (green squares) and 2 nm (blue diamonds). , γexp extracted along VBG = −10 V (red crosses) shows the extracted guiding in the OPG, PNG and OPG/PNG regimes along with γ from simulation with disorder of 0 (black) and 2 nm (blue) in th! e OPG regime and 0 (black), 2 (blue) and 4 nm (purple) in the PNG and OPG/PNG regimes. Good agreement between experiment is observed for 2 nm in the OPG regime and 4 nm for the PNG and OPG/PNG regimes. * Figure 4: Magnetic field improves gate-defined guiding. , Inset: Rfic as a function of VTG and B at VBG = −10 V. Main panel: plot of Rfic at B = 0 T and B = 5 T. The increase in B corresponds to an increase in Ricf and the ratio Ricf(bipolar)/Ricf(unipolar), indicating a magnetic-field enhancement of the PNG contribution to Ricf. In the inset, Rfic(VTG,B) demonstrates enhancement of Ricf for fields B > 2 T. , Simulation of J in the OPG/PNG regime at B = 5 T. γ is enhanced from 0.24 (Fig. 2d) to 0.50 (Ω is enhanced from 0.29 to 0.55). Author information * Abstract * Author information * Supplementary information Affiliations * School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA * J. R. Williams * School of Electrical & Computer Engineering, Purdue University, West Lafayette, Indiana 47906, USA * Tony Low & * M. S. Lundstrom * Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA * J. R. Williams & * C. M. Marcus * Present address: Department of Physics, Stanford University, Stanford, California 94305, USA * J. R. Williams Contributions Experiments were performed by J.W. and C.M, and numerics/theory by T.L. and M.L. All authors contributed to writing the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * C. M. Marcus Author Details * J. R. Williams Search for this author in: * NPG journals * PubMed * Google Scholar * Tony Low Search for this author in: * NPG journals * PubMed * Google Scholar * M. S. Lundstrom Search for this author in: * NPG journals * PubMed * Google Scholar * C. M. Marcus Contact C. M. Marcus Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (597 KB) Supplementary information Additional data
• Controlling single-molecule conductance through lateral coupling of π orbitals
  - UNKNOWN 6(4):226-231 (2011)
  Nature Nanotechnology | Letter Controlling single-molecule conductance through lateral coupling of π orbitals * Ismael Diez-Perez1, 2 * Joshua Hihath1 * Thomas Hines1 * Zhong-Sheng Wang3 * Gang Zhou3 * Klaus Müllen4 * Nongjian Tao1 * Affiliations * Contributions * Corresponding authorsJournal name:Nature NanotechnologyVolume: 6,Pages:226–231Year published:(2011)DOI:doi:10.1038/nnano.2011.20Received03 December 2010Accepted25 January 2011Published online20 February 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg In recent years, various single-molecule electronic components have been demonstrated1. However, it remains difficult to predict accurately the conductance of a single molecule and to control the lateral coupling between the π orbitals of the molecule and the orbitals of the electrodes attached to it. This lateral coupling is well known to cause broadening and shifting of the energy levels of the molecule; this, in turn, is expected to greatly modify the conductance of an electrode–molecule–electrode junction2, 3, 4, 5, 6. Here, we demonstrate a new method, based on lateral coupling, to mechanically and reversibly control the conductance of a single-molecule junction by mechanically modulating the angle between a single pentaphenylene molecule bridged between two metal electrodes. Changing the angle of the molecule from a highly tilted state to an orientation nearly perpendicular to the electrodes changes the conductance by an order of magnitude, which is in qualitative! agreement with theoretical models of molecular π-orbital coupling to a metal electrode. The lateral coupling is also directly measured by applying a fast mechanical perturbation in the horizontal plane, thus ruling out changes in the contact geometry or molecular conformation as the source for the conductance change. View full text Subject terms: * Electronic properties and devices Figures at a glance * Figure 1: Lateral coupling. , Schematic of lateral coupling experiment. As the two electrodes are separated or modulated within the horizontal plane, the angle θ decreases and the conductance G falls. , Change in conductance, ΔG, versus electrode–electrode distance (bottom x-axis) and θ (top x-axis): ΔG ∝ sin4θ. , Structure of the ladder-type pentaphenylene molecule used to study the effects of lateral coupling in a single-molecule junction. * Figure 2: Break junction and blinking experiments on a pentaphenylene molecular junction. , Three individual conductance decays (current versus time), showing a long transition between tunnelling and plateau regions. , Conductance histogram of 2,000 decays similar to those in , showing a peak centred at 4.5 × 10−6G0. –, Blinking events in individual conductance decays for four electrode–electrode separations. As the separation increases from 1.1 nm () to 2 nm (), the tilt angle becomes smaller and the conductance decreases. The sketches on the right show approximate angles for each configuration. * Figure 3: Blink-and-pull experiments on a tetraphenyl junction. ,, Current versus time traces for single tetraphenyl molecules at separations of 0.9 nm () and 1.25 nm (). The amplitudes of the blinking events are the same for the two separations, indicating that there is only poor coupling to the electrodes or no coupling at all. , Average of 15 blink-and-pull experiments (current versus electrode separation or tilt angle) on a tetraphenyl junction (solid squares) showing that the conductance does not change appreciably within the range of accessible angles. Grey background indicates standard deviation. The 'softening' effect in the breakdown region is due to the averaging process. The blue line is an individual pulling trace showing a sharp event during the junction breakdown. Inset: tetraphenyl molecule. * Figure 4: Blink-and-pull experiments on a pentaphenylene junction. , Three blink-and-pull traces (current versus electrode separation or tilt angle). The blinking events occur at an initial separation of 1.2 nm, and the conductance falls during the pulling process. The junctions typically break down at a separation of ~1.9 nm. , Two blink-and-pull traces for experiments in which the initial separation is ~2 nm. Almost no change is seen in the conductance because the angle (and the lateral coupling) is already small. , Average of ~40 pulling (filled squares)–pushing (open circles) cycles where the junction is not broken. There is an obvious change in conductance, and no hysteresis in the curves. Inset: time evolution of the experiments. , Average of 10 long pulling curves where the junction breaks down at very low angles. The decrease follows the same trend as the theoretical model, I ∝ sin4θ (red curve). Dashed blue line: best fit of the averaged curve to y = I0 sinn(θ–θ0). Best fit occurs for n = 4.4 ± 0.01. Open blocks are value! s from the blinking events in Fig. 2. Inset: pentaphenylene molecule. Grey shadow in and indicates standard deviation. * Figure 5: Blinking experiments coupled with a.c. horizontal and vertical distance modulation. –, Blinking events (red curves) at progressively larger electrode–electrode separations. Left insets: FFTs of parts of the blinking curves for open junctions (no bridging molecule). Right insets: FFTs of blinking curves for single-molecule junctions; the x, y and z amplitudes of the three a.c. modulation components are indicated. For molecular tilt angles of more than 50°, the x and/or y components can be seen. Sketches on the right show the approximate configuration. * Figure 6: Total lateral coupling magnitude. , , Plots of r = √(x2 + y2) versus tilt angle for tetraphenyl () and pentaphenylene () junctions, where x and y are determined by FFT analysis of multiple individual blinking traces (see Fig. 5). A plot of I ∝ sin4θ (red line) has been added to for guidance. Author information * Abstract * Author information * Supplementary information Affiliations * Center for Biosensors and Bioelectronics, Biodesign Institute, Arizona State University, Tempe, Arizona 85287, USA * Ismael Diez-Perez, * Joshua Hihath, * Thomas Hines & * Nongjian Tao * Institute for Bioengineering of Catalonia (IBEC), University of Barcelona (UB), Barcelona 08028, Spain * Ismael Diez-Perez * Laboratory of Advanced Materials, Fudan University, Shanghai 200438, China * Zhong-Sheng Wang & * Gang Zhou * Max-Planck-Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany * Klaus Müllen Contributions N.J.T. conceived the transport experiment. I.D.-P., J.H. and T.H. conducted the experiments and analysed the data. K.M. supervised the design and synthesis of the molecule. Z.-S.W. and G.Z. synthesized the molecule. Competing financial interests The authors declare no competing financial interests. Corresponding authors Correspondence to: * Nongjian Tao or * Gang Zhou or * Klaus Müllen Author Details * Ismael Diez-Perez Search for this author in: * NPG journals * PubMed * Google Scholar * Joshua Hihath Search for this author in: * NPG journals * PubMed * Google Scholar * Thomas Hines Search for this author in: * NPG journals * PubMed * Google Scholar * Zhong-Sheng Wang Search for this author in: * NPG journals * PubMed * Google Scholar * Gang Zhou Contact Gang Zhou Search for this author in: * NPG journals * PubMed * Google Scholar * Klaus Müllen Contact Klaus Müllen Search for this author in: * NPG journals * PubMed * Google Scholar * Nongjian Tao Contact Nongjian Tao Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (1,323 KB) Supplementary information Additional data
• Nanoporous metal/oxide hybrid electrodes for electrochemical supercapacitors
  - UNKNOWN 6(4):232-236 (2011)
  Nature Nanotechnology | Letter Nanoporous metal/oxide hybrid electrodes for electrochemical supercapacitors * Xingyou Lang1 * Akihiko Hirata1 * Takeshi Fujita1 * Mingwei Chen1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:232–236Year published:(2011)DOI:doi:10.1038/nnano.2011.13Received16 November 2010Accepted14 January 2011Published online20 February 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Electrochemical supercapacitors can deliver high levels of electrical power and offer long operating lifetimes1, 2, 3, 4, 5, 6, 7, 8, but their energy storage density is too low for many important applications2, 3. Pseudocapacitive transition-metal oxides such as MnO2 could be used to make electrodes in such supercapacitors, because they are predicted to have a high capacitance for storing electrical charge while also being inexpensive and not harmful to the environment9, 10. However, the poor conductivity of MnO2 (10–5–10–6 S cm–1) limits the charge/discharge rate for high-power applications10, 11. Here, we show that hybrid structures made of nanoporous gold and nanocrystalline MnO2 have enhanced conductivity, resulting in a specific capacitance of the constituent MnO2 (~1,145 F g–1) that is close to the theoretical value9. The nanoporous gold allows electron transport through the MnO2, and facilitates fast ion diffusion between the MnO2 and the electrolytes while! also acting as a double-layer capacitor. The high specific capacitances and charge/discharge rates offered by such hybrid structures make them promising candidates as electrodes in supercapacitors, combining high-energy storage densities with high levels of power delivery. View full text Subject terms: * Nanomaterials * Synthesis and processing Figures at a glance * Figure 1: Nanoporous gold/MnO2-based supercapacitors. , Schematic showing the fabrication process for nanoporous gold/MnO2 hybrid materials by directly growing MnO2 (orange) onto nanoporous gold. , Supercapacitor device constructed with nanoporous gold/MnO2 films as electrodes, aqueous Li2SO4 as electrolyte, and tissue paper as separator. , Photograph of a nanoporous gold/MnO2-based supercapacitor. * Figure 2: Microstructure characterization. , SEM image of as de-alloyed nanoporous gold films with a characteristic length of ~40 nm. , SEM image of a nanoporous gold/MnO2 film with a MnO2 plating time of 10 min. MnO2 nanocrystals were uniformly plated onto the gold without changing the nanoporosity. , Bright-field TEM image of the nanoporous gold/MnO2 hybrid with a MnO2 plating time of 20 min. The hybrid nanostructure can be identified by the contrast between the bright MnO2 filler and the dark gold skeleton. , HRTEM image of a nanoporous gold/MnO2 sample (plating time, 20 min) showing nanocrystalline MnO2 with a grain size of ~5 nm. , High-angle annular dark-field STEM image taken from a gold/MnO2 interface region. Nanocrystalline MnO2 epitaxially grows on the gold surface, forming a chemically bonded metal/oxide interface. , EELS profile image from a region across the interface. The horizontal axis shows the electron energy loss in the range 586–705 eV. EELS spectra were obtained from 30 points with an interval ! of 0.28 nm and an exposure time of 1.6 s for each spectrum acquisition. The Mn L3 (642 eV) and L2 (653 eV) edges shift by ~0.5–1 eV to lower energies near the interface between the MnO2 and the gold. The brighter contrast in the nanoporous gold region comes from the higher background caused by multiple electron scattering with the increased thickness of the gold regions. * Figure 3: Electrochemical performance. , Cyclic voltammograms (current density versus voltage) for bare nanoporous gold electrodes and nanoporous gold/MnO2 electrodes for three different plating times. Scan rate, 50 mV s−1. , Volumetric capacitances of both nanoporous gold/MnO2 and Ag65Au35/MnO2 electrodes as a function of plating time. Inset: volumetric capacitance versus mass ratio for nanoporous gold/MnO2 electrodes. Capacitance was estimated from the cyclic voltammograms at a scan rate of 50 mV s−1. The slightly higher volumetric capacitance of Ag65Au35/MnO2 at 5 min is due to faster electrochemical plating (and hence higher MnO2 loadings) for this material system. ,, Charge-discharge (voltage versus time) curves at a current density of 0.5 A g−1 () and specific capacitance (Cs) versus discharge current density () for bare nanoporous gold electrodes and for nanoporous gold/MnO2 electrodes for three different plating times. Cs is calculated from the discharge curves according to Cs = i/[–(ΔV/Δt)m], w! ith i being the applied current, –ΔV/Δt the slope of the discharge curves after the voltage drop at the beginning of each discharge, and m is the mass of nanoporous gold or nanoporous gold/MnO2 on one electrode. All data are taken in a 2 M Li2SO4 solution at room temperature. * Figure 4: Scan rate dependence of electrochemical properties , Cyclic voltammograms (current density versus voltage) for a nanoporous gold/MnO2 electrode (plating time, 20 min) at six different scan rates between 10 and 100 mV s−1. , Corresponding specific capacitance of the plated MnO2 versus scan rate. The large errors bar (~20%) on the measurement at the lowest scan rate is thought to be a result of the higher internal resistance of the hybrid electrodes at low discharge current densities and scan rates (Supplementary Fig. S3) and possible error in the MnO2 measurement by X-ray energy-dispersive spectroscopy (Supplementary Fig. S1). All data are taken in a 2 M Li2SO4 solution at room temperature. Author information * Abstract * Author information * Supplementary information Affiliations * WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan * Xingyou Lang, * Akihiko Hirata, * Takeshi Fujita & * Mingwei Chen Contributions X.Y.L. and M.W.C. conceived and designed the experiments. X.Y.L. carried out the fabrication of materials and performed electrochemical characterization. A.H. and T.F. contributed to microstructural characterization. X.Y.L. and M.W.C. wrote the paper, and all authors discussed the results and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Mingwei Chen Author Details * Xingyou Lang Search for this author in: * NPG journals * PubMed * Google Scholar * Akihiko Hirata Search for this author in: * NPG journals * PubMed * Google Scholar * Takeshi Fujita Search for this author in: * NPG journals * PubMed * Google Scholar * Mingwei Chen Contact Mingwei Chen Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (1,194 KB) Supplementary information Additional data
• A size-dependent nanoscale metal–insulator transition in random materials
  - UNKNOWN 6(4):237-241 (2011)
  Nature Nanotechnology | Letter A size-dependent nanoscale metal–insulator transition in random materials * Albert B. K. Chen1, 3 * Soo Gil Kim1, 2, 3 * Yudi Wang1, 3 * Wei-Shao Tung1 * I-Wei Chen1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:237–241Year published:(2011)DOI:doi:10.1038/nnano.2011.21Received24 September 2010Accepted28 January 2011Published online27 February 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Insulators and conductors with periodic structures can be readily distinguished, because they have different band structures, but the differences between insulators and conductors with random structures are more subtle1, 2. In 1958, Anderson provided a straightforward criterion for distinguishing between random insulators and conductors, based on the 'diffusion' distance ζ for electrons at 0 K (ref. 3). Insulators have a finite ζ, but conductors have an infinite ζ. Aided by a scaling argument, this concept can explain many phenomena in disordered electronic systems, such as the fact that the electrical resistivity of 'dirty' metals always increases as the temperature approaches 0 K (refs 4–6). Further verification for this model has come from experiments that measure how the properties of macroscopic samples vary with changes in temperature, pressure, impurity concentration and applied magnetic field4, 5, but, surprisingly, there have been no attempts to enginee! r a metal–insulator transition by making the sample size less than or more than ζ. Here, we report such an engineered transition using six different thin-film systems: two are glasses that contain dispersed platinum atoms, and four are single crystals of perovskite that contain minor conducting components. With a sample size comparable to ζ, transitions can be triggered by using an electric field or ultraviolet radiation to tune ζ through the injection and extraction of electrons. It would seem possible to take advantage of this nanometallicity in applications. View full text Subject terms: * Electronic properties and devices * Nanomaterials Figures at a glance * Figure 1: Optical evidence of metallic clusters and free carriers. , UV reflectivity of 40 nm SiO2:Pt films; the peak at 270 nm characteristic of metallic Pt nanoparticles is completely absent at f = 0.2. Inset: transmission electron micrograph of 12 nm SiO2:0.2 Pt film with a worm-like random structure without apparent segregation. , Infrared reflectivity (200 nm films) featuring, at f = 0, only the vibrational peaks (at 9.5, 12.5, 22.5 nm) of SiO2, and at f > 0 the same peaks plus a background due to dissipative conducting electrons. Electron contribution increases with wavelength, causing an increase of peak intensity at 22.5 nm with Pt content, in agreement with the Drude model fitting the data (shown as solid curves for f = 0.2 and 0.3). Inset: electron diffraction pattern of 12 nm SiO2:0.2 Pt film with a diffuse ring typical of amorphous material27. * Figure 2: R–V dependence on thickness, composition and temperature. , Cycle from 0 V, to (–) V, to (+) V, to (–) V, to 0 V traces a R–V loop for SiO2:0.2 Pt of various thickness. These are 'first loops'; that is, samples were not subject to any previous electrical stimulus/forming. When δ ≈ ζ, the hysteresis loop provides non-volatile memory. Top electrode, Pt; bottom electrode, Mo. , δ–f map for SiO2:f Pt delineating boundaries for conductors (open circles) and insulators (filled circles) separated by switchable films (triangles), abruptly rising at f ≈ 0.4 near the bulk percolation limit. Top electrode, Pt; bottom electrode, SrRuO3 and Mo (same results). The bisector (broken line) between the boundaries is taken as ζ. Inset: f–δ independent Vset for samples along the horizontal red arrow (same δ, increasing f, as red squares) and vertical blue arrow (same f, decreasing δ, as blue squares). , R–V loops at two temperatures for 20 nm SiO2:0.25 Pt. Top electrode, Pt; bottom electrode, Mo. Note that f in is higher tha! n in . * Figure 3: UV-triggered HR-to-LR transitions. , HR of a fatigue-damaged cell promptly decreases when UV is turned on at room temperature. (The low resistance stayed permanently after the light was turned off. The outcome was identical, whether the cell was shorted to the ground or under a small positive/negative bias voltage.) 20 nm SiO2:0.25 Pt; top electrode, Pt; bottom electrode, Mo. ,, Further examples of UV-triggered HR-to-LR transitions in CaZrO3:0.055 SrRuO3 () and LaAlO3:0.125 LaNiO3 () films. (For other examples see Supplementary Fig. S4.). * Figure 4: Random perovskite solid solution. Cross-sectional high-resolution TEM image along the [010] direction of a 3:1 mixture of CaZrO3 and LaNiO3 film (30 nm) on a (100) SrTiO3 substrate with a 30 nm buffer of SrRuO3. Inset: fast Fourier transform of the same region. * Figure 5: R–δ and R–T dependencies. , HR, multiplied by cell area A, increases exponentially with film thickness. SiO2:0.25 Pt; top electrode, Pt; bottom electrode, Mo. , Logarithmic temperature dependence of resistance of the LR state (4) and four intermediate states (0–3) shown in the inset. Also shown are data (*) from another sample with a more resistive HR. Curves 0–3 are model fit using FIT: tunnelling along a metallic channel with one gap of spacing ~0.4–1.2 nm and effective gap capacitor area ~(0.2 nm)2–(0.8 nm)2. LaAlO3:0.13 LaNiO3; top electrode, Pt; bottom electrode, SrRuO3. Author information * Abstract * Author information * Supplementary information Primary authors * These authors contributed equally to this work * Albert B. K. Chen, * Soo Gil Kim & * Yudi Wang Affiliations * Department of Materials Science & Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA * Albert B. K. Chen, * Soo Gil Kim, * Yudi Wang, * Wei-Shao Tung & * I-Wei Chen * Present address: Hynix Semiconductor Inc., Icheon-Si, Korea * Soo Gil Kim Contributions I-W.C. conceived and designed the experiments and wrote the paper. A.B.C. performed the SiO2:Pt and SiN:Pt experiments. S.G.K. and Y.D.W. performed the perovskite experiments. W.S.T. performed the optical experiments. All authors analysed the data, discussed the results and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * I-Wei Chen Author Details * Albert B. K. Chen Search for this author in: * NPG journals * PubMed * Google Scholar * Soo Gil Kim Search for this author in: * NPG journals * PubMed * Google Scholar * Yudi Wang Search for this author in: * NPG journals * PubMed * Google Scholar * Wei-Shao Tung Search for this author in: * NPG journals * PubMed * Google Scholar * I-Wei Chen Contact I-Wei Chen Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (1,274 KB) Supplementary information Additional data
• Atomic-scale magnetometry of distant nuclear spin clusters via nitrogen-vacancy spin in diamond
  - UNKNOWN 6(4):242-246 (2011)
  Nature Nanotechnology | Letter Atomic-scale magnetometry of distant nuclear spin clusters via nitrogen-vacancy spin in diamond * Nan Zhao1 * Jian-Liang Hu1 * Sai-Wah Ho1 * Jones T. K. Wan1 * R. B. Liu1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:242–246Year published:(2011)DOI:doi:10.1038/nnano.2011.22Received02 December 2010Accepted28 January 2011Published online27 February 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg The detection of single nuclear spins is an important goal in magnetic resonance spectroscopy1, 2. Optically detected magnetic resonance can detect single nuclear spins that are strongly coupled to an electron spin3, 4, 5, 6, 7, 8, 9, but the detection of distant nuclear spins that are only weakly coupled to the electron spin has not been considered feasible. Here, using the nitrogen–vacancy centre in diamond3, 4, 5, 6, 7, 8 as a model system, we numerically demonstrate that it is possible to detect two or more distant nuclear spins that are weakly coupled to a centre electron spin if these nuclear spins are strongly bonded to each other in a cluster. This cluster will stand out from other nuclear spins by virtue of characteristic oscillations imprinted onto the electron spin decoherence profile10, 11, which become pronounced under dynamical decoupling control12. Under many-pulse dynamical decoupling, the centre electron spin coherence can be used to measure nuclear magnet! ic resonances of single molecules. This atomic-scale magnetometry should improve the performance of magnetic resonance spectroscopy for applications in chemical, biological, medical and materials research13, 14, and could also have applications in solid-state quantum computing3, 4, 5, 6, 7, 8. View full text Subject terms: * Nanomagnetism and spintronics * Nanometrology and instrumentation * Nanosensors and other devices * Surface patterning and imaging Figures at a glance * Figure 1: NV centre spin decoherence due to nuclear spin pair dynamics in diamond. , Diamond lattice containing randomly distributed 13C nuclei with a natural abundance (1.1%). A 13C dimer is located ~1.3 nm away from an NV centre. The NV axis is along the crystal axis [111]. , Precession of a pseudo-spin, which represents the flip-flop between the two states and of a nuclear spin pair ( ), along the red and blue trajectories about the pseudo-fields and for the electron spin state and , respectively. With the electron spin-flip , the pseudo-spin trajectories exchange their precession directions. The distance between the two trajectories determines the electron spin decoherence contributed by the pair. , Probability (red line) of finding any dimer within a given distance from the NV centre, and the probability density (blue line) of finding the nearest dimer at a given distance. , Gradient along the z-axis ([111] direction) of the z-component of the hyperfine field around an NV centre, , where dCC = 0.154 nm is the C–C bond length. The field has rotationa! l symmetry about the z-axis. , Spin coherence of the NV centre shown in as functions of time (black lines) under the one- to five-pulse UDD control (UDD1-5). A magnetic field B = 0.25 T is applied along the NV axis. The coherent oscillations match the contributions solely from the dimer (red lines). * Figure 2: Fingerprint features of nuclear spin dimers. , Contour plots of NV centre spin coherence under five-pulse UDD control, as functions of time and azimuth angle ϕ (relative to the crystal axis [ ]) of a 0.25 T magnetic field tilted from the NV axis ([111] direction) by a polar angle θ = 10°, for a 13C dimer in different positions and orientations within the same unit cell (indicated in insets of ). The unit cell centre position is 1.1 nm away from the NV centre. , As in , but contributed solely by the dimer. , Cross-sectional plots of (red lines) and (black lines) for a fixed azimuth angle (ϕ = 15°). * Figure 3: Double-blind numerical experiment for identifying a hidden dimer. Step 0: team 1 randomly configures 13C nuclei with natural abundance. A dimer is located 1.3 nm away from the NV centre, which is too far to be detected using a conventional ODMR approach. Team 2 has no information about the 13C positions. ,, Step 1: team 1 calculates the signal under UDD5 control for a magnetic field B = 0.03 T tilted away from the NV axis by θ = 10° with an azimuth angle ϕ = 0°. The signal presents coherent modulations due to the dimer superimposed on the rapid electron spin echo envelope modulation (ESEEM) due to a few closely located single 13C spins and the 14N spin. Team 2 compares the signals from Team 1 (shadows) with the fingerprint library of about 20,000 dimers within 2.5 nm of the NV centre. The 216 dimers that have compatible oscillation features (five examples are shown in as green lines) are passed for the next step of screening, and the others are rejected (four examples are shown in as discrete red lines). ,, Step 2: repeat step 1, but w! ith θ = 50° and ϕ = 60°. Seven dimers pass the screening. ,, Step 3: repeat step 1, but with θ = 70° and ϕ = 90°. Only one dimer has compatible oscillation features (), which is indeed the hidden dimer. * Figure 4: Nuclear magnetic resonances of single molecules. , C60 molecule (labelled by two 13C separated by d1 = 0.4 nm or d2 = 0.5 nm) on a diamond surface with an NV centre (blue arrow) located D = 4 nm below. Abundance of 13C (red arrows) is 0.03%. , NV centre spin coherence under seven-pulse UDD control, as functions of time and position (or rotation angle) of the molecule for the two cases indicated in . A magnetic field B = 0.2 T is applied along the NV axis. , Spin coherence of an NV centre located 10 nm below the surface of natural-abundance diamond under a zero magnetic field and 100-pulse CPMG control. On the surface there are five 12C1H4 (middle panel) or 1H216O (lower panel) molecules (separated from each other by 1 nm) just above the NV centre. The red and blue curves are decoherence caused solely by the molecules. Insets: decoherence in longer timescales. Upper panel: noise spectra due to nuclear spin transitions in the molecules, labelled by the letters indicated in and . The relative strengths of the transitions A–! F and K are amplified by a factor of 3. Times tC/K, t′C/K and t″C/K correspond in turn to the first, second and third dips induced by the transition C/K. ,, Nuclear spin transitions in 12C1H4 and 1H216O, respectively. Integers in indicate the level degeneracy. Transitions that are too weak are not shown. Author information * Abstract * Author information * Supplementary information Affiliations * Department of Physics and Center for Quantum Coherence, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China * Nan Zhao, * Jian-Liang Hu, * Sai-Wah Ho, * Jones T. K. Wan & * R. B. Liu Contributions R.B.L. conceived the idea. R.B.L. and N.Z. designed the project, formulated the theory, and wrote the paper. N.Z., J.L.H. and S.W.H. calculated electron spin decoherence. J.T.K.W. did the first-principles calculation of the hyperfine constants. All authors read and commented on the manuscript. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * R. B. Liu Author Details * Nan Zhao Search for this author in: * NPG journals * PubMed * Google Scholar * Jian-Liang Hu Search for this author in: * NPG journals * PubMed * Google Scholar * Sai-Wah Ho Search for this author in: * NPG journals * PubMed * Google Scholar * Jones T. K. Wan Search for this author in: * NPG journals * PubMed * Google Scholar * R. B. Liu Contact R. B. Liu Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (3,435 KB) Supplementary information Additional data
• Transforming C60 molecules into graphene quantum dots
  - UNKNOWN 6(4):247-252 (2011)
  Nature Nanotechnology | Article Transforming C60 molecules into graphene quantum dots * Jiong Lu1 * Pei Shan Emmeline Yeo1, 2 * Chee Kwan Gan2 * Ping Wu2 * Kian Ping Loh1 * Affiliations * Contributions * Corresponding authorJournal name:Nature NanotechnologyVolume: 6,Pages:247–252Year published:(2011)DOI:doi:10.1038/nnano.2011.30Received01 December 2010Accepted15 February 2011Published online20 March 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg The fragmentation of fullerenes using ions, surface collisions or thermal effects is a complex process that typically leads to the formation of small carbon clusters of variable size. Here, we show that geometrically well-defined graphene quantum dots can be synthesized on a ruthenium surface using C60 molecules as a precursor. Scanning tunnelling microscopy imaging, supported by density functional theory calculations, suggests that the structures are formed through the ruthenium-catalysed cage-opening of C60. In this process, the strong C60–Ru interaction induces the formation of surface vacancies in the Ru single crystal and a subsequent embedding of C60 molecules in the surface. The fragmentation of the embedded molecules at elevated temperatures then produces carbon clusters that undergo diffusion and aggregation to form graphene quantum dots. The equilibrium shape of the graphene can be tailored by optimizing the annealing temperature and the density of the carbon clu! sters. View full text Subject terms: * Carbon nanotubes and fullerenes * Surface patterning and imaging Figures at a glance * Figure 1: STM images of GQDs formed by decomposition of 0.08 ML C60 on Ru(0001). , A 0.08 ML C60/Ru sample after annealing at 725 K for 2 min. Inset: magnified view of mushroom-shaped dots. –, Magnified views of triangular (2.7 nm, ), parallelogram-shaped (2.7 × 4.2 nm, ), trapezoid-shaped (2.7 × 4.8 nm, ) GQDs. Inset to : line contour taken along the green line in . ,, Hexagon-shaped GQDs (5 nm and 10 nm) obtained after further annealing the sample at 825 K for 2 min. , Representative local STS data for differential conductances dI/dV of the GQDs in (I), (II), (III), (IV) and for giant monolayer graphene on Ru(0001) (V). Tunnelling parameters: V = 0.5 V, I = 0.1 nA; V = 0.3 V, I = 0.2 nA for the inset images in and ; V = 0.3 V, I = 0.2 nA (,); V = 0.3 V, I = 0.1 nA (,). * Figure 2: STM images of the C60-derived clusters after annealing a 0.03 ML film of C60 on Ru(0001). , 0.03 ML C60 on Ru (0001). Inset: magnified view of one C60 molecule after annealing the sample at 450 K. ,,, Bright dots observed after flash annealing at 725 K for 2 min: mushroom-shaped dots () and flower-shaped dot (); and three flower-shaped dots obtained at 825 K (). Insets (,,): magnified views of these dots. Top inset of : line contour of an individual C60 molecule (green curve) and bright dots in (white curve). , Surface diffusion and combination of C60-derived fragments (STM image size, 4.5 × 4.2 nm). , Histogram of dot size distribution at different annealing temperatures: 725 K for 2 min and 825 K for 1 min. Tunnelling parameters: V = 1.2 V, I = 0.08 nA, V = 100 mV, I = 0.3 nA for the inset image in ; V = 0.3 V, I = 0.2 nA (); V = 1.2 V, I = 0.1 nA (); V = 0.3 V, I = 0.25 nA (); V = 0.3 V, I = 0.16 nA (). * Figure 3: Three-dimensional STM images of a carbon cluster derived from the decomposition of embedded C60 molecules on Ru(0001), and the simulated 'on-top_vac' configuration of a C60 molecule on Ru(0001). , Constant-current image at 600 K (e-C60, embedded C60; i-C60, intact C60; image size, 5 × 3 nm2). , Constant current image at 650 K (d-C60, decomposition of embedded C60; image size, 5 × 3 nm2). , On-top_vac configuration of the C60 molecule. The single-sided arrow indicates the top-down point of view, from which is derived. , C–C bond lengths of the bottom hemisphere of the C60 in . The top hemisphere is not shown for clarity. * Figure 4: Comparison of the growth mechanism of graphene nanoislands and quantum dots using C2H4 and C60. –, Mechanisms using C2H4. Highly mobile carbon adatoms from the dehydrogenation of C2H4 (). Nucleation of the C adatom occurs at the step edges (at <1 L dose of C2H4) (). Large-sized, irregular shaped graphene islands are generated readily (at 1 L < Θ < 10 L dose of C2H4). (1 Langmuir (L) = 1 × 10−6 torr s.) Corresponding STM images for the growth of graphene islands from C2H4 (,). –, Mechanisms using C60. The majority of C60 molecules adsorb on the terrace, and these decompose to produce carbon clusters with restricted mobility (). Temperature-dependent growth of GQDs with different equilibrium shape from the aggregation of the surface diffused carbon clusters (). Corresponding STM images for the well-dispersed triangular and hexagonal equilibrium shaped GQDs produced from C60-derived carbon clusters (,). Tunnelling parameters (,, ,): V = 0.5 V, I = 1 nA. * Figure 5: Series of STM images monitoring the transformation of trapezium-shaped GQDs to triangular-shaped GQDs at 1,000 K. The numbers in the images indicate the time lapse in seconds. Tunnelling parameters (–): V = 1.4 V, I = 0.3 nA; image size, 25 × 12 nm2. Author information * Abstract * Author information * Supplementary information Affiliations * Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543 * Jiong Lu, * Pei Shan Emmeline Yeo & * Kian Ping Loh * Institute of High Performance Computing, 1 Fusionopolis Way, #16-16 Connexis, Singapore 138632 * Pei Shan Emmeline Yeo, * Chee Kwan Gan & * Ping Wu Contributions J.L. and K.P.L. conceived and designed the experiments. J.L. performed the STM and STS measurement. P.S.E.Y. carried out theoretical calculations. C.K.G and W.P contributed analysis tools. K.P.L supervised the project. All authors discussed the results and analysed the data. Competing financial interests The authors declare no competing financial interests. Corresponding author Correspondence to: * Kian Ping Loh Author Details * Jiong Lu Search for this author in: * NPG journals * PubMed * Google Scholar * Pei Shan Emmeline Yeo Search for this author in: * NPG journals * PubMed * Google Scholar * Chee Kwan Gan Search for this author in: * NPG journals * PubMed * Google Scholar * Ping Wu Search for this author in: * NPG journals * PubMed * Google Scholar * Kian Ping Loh Contact Kian Ping Loh Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information Movies * Supplementary information (741 KB) Supplementary movie 1 * Supplementary information (796 KB) Supplementary movie 2 PDF files * Supplementary information (1,206 KB) Supplementary information Additional data
• Controlling protein translocation through nanopores with bio-inspired fluid walls
  - UNKNOWN 6(4):253-260 (2011)
  Nature Nanotechnology | Article Controlling protein translocation through nanopores with bio-inspired fluid walls * Erik C. Yusko1 * Jay M. Johnson1 * Sheereen Majd1 * Panchika Prangkio1 * Ryan C. Rollings2 * Jiali Li2 * Jerry Yang3 * Michael Mayer1, 4 * Affiliations * Contributions * Corresponding authorsJournal name:Nature NanotechnologyVolume: 6,Pages:253–260Year published:(2011)DOI:doi:10.1038/nnano.2011.12Received28 July 2010Accepted17 January 2011Published online20 February 2011 Abstract * Abstract * Author information * Supplementary information Article tools * Full text * Print * Email * Download PDF * Download citation * Order reprints * Rights and permissions * Share/bookmark * Connotea * CiteULike * Facebook * Twitter * Delicious * Digg Synthetic nanopores have been used to study individual biomolecules in high throughput, but their performance as sensors does not match that of biological ion channels. Challenges include control of nanopore diameters and surface chemistry, modification of the translocation times of single-molecule analytes through nanopores, and prevention of non-specific interactions with pore walls. Here, inspired by the olfactory sensilla of insect antennae, we show that coating nanopores with a fluid lipid bilayer tailors their surface chemistry and allows fine-tuning and dynamic variation of pore diameters in subnanometre increments. Incorporation of mobile ligands in the lipid bilayer conferred specificity and slowed the translocation of targeted proteins sufficiently to time-resolve translocation events of individual proteins. Lipid coatings also prevented pores from clogging, eliminated non-specific binding and enabled the translocation of amyloid-beta (Aβ) oligomers and fibrils. T! hrough combined analysis of their translocation time, volume, charge, shape and ligand affinity, different proteins were identified. View full text Subject terms: * Nanobiotechnology * Nanosensors and other devices Figures at a glance * Figure 1: Bio-inspired synthetic nanopores with bilayer-coated fluid walls. , Drawing showing a cross-section through one sensillum in the antenna of the silk moth Bombyx mori. Capture, pre-concentration, and translocation of pheromones through the exoskeleton of these sensilla towards dendrites of olfactory neurons is thought to occur via lipid-coated nanopores32, 33, 34. , Drawing, to scale, showing a synthetic, lipid-coated (yellow) nanopore in a silicon nitride substrate (grey) and the interstitial water layer (blue). , Nanopore resistance and corresponding open pore diameter (indicated to the right of the curve, in nm) as a function of the thickness of the bilayer coating59. The red curve is a best fit of the data to equation (1). Numbers underneath the lipid schematics refer to the number of carbons in their acyl chains (Table 1). , Actuation of nanopore diameters by a change in the thickness of the bilayer coating, Δd, in response to a thermal phase transition of DMPC lipids (Supplementary Section S1). The blue dotted line and grey shaded re! gion represent the mean value and range of phase transition temperatures reported for DMPC lipids44. Inset: cycling the temperature between 13 °C and 27 °C varied the pore diameter dynamically, as indicated by the larger changes in electrical resistance through a pore with a bilayer (green squares) than without a bilayer (black squares). * Figure 2: Capture, affinity-dependent pre-concentration and translocation of specific proteins after binding to ligands on mobile lipid anchors. , Drawing, to scale, illustrating binding of streptavidin (large red) to specific lipid-anchored biotin-PE (blue circles) followed by single-molecule translocation of the anchored complex through the nanopore. , Current versus time traces illustrating capture, pre-concentration and reduced translocation speed of streptavidin. In the absence of biotin groups, only rare translocation events with short translocation times, td, could be detected in electrolytes containing 6 pM streptavidin (top current trace). In contrast, 0.4 mol% of biotinylated lipids in the lipid coating strongly increased the event frequency and slowed down the translocation speed sufficiently to enable complete time resolution of translocation events (bottom current trace). , Minimum bulk concentrations of streptavidin (SA), polyclonal anti-biotin Fab fragments (Fab) and monoclonal anti-biotin IgG antibodies (mAb) required to observe at least 30–100 translocation events per second. * Figure 3: Controlling the translocation times, td, of single lipid-anchored proteins by the viscosity of the bilayer coating and distinguishing proteins by their most probable td values. , Distribution of translocation times of streptavidin. Insets: current versus time traces illustrating that td could be prolonged more with intermediate-viscosity POPC bilayers (blue current traces) than with low-viscosity DΔPPC bilayers (red current traces). , Translocation of anti-biotin Fab fragments through nanopores with bilayers of intermediate viscosity (POPC) or high viscosity (~49 mol% cholesterol and 50 mol% POPC). , Translocation of anti-biotin antibodies through a pore with a coating of intermediate viscosity (POPC). Red, blue and green curves represent a best fit of the corresponding data to a biased diffusion first passage time model14 (equation (S10) in Supplementary Section S5). All bilayers contained 0.15–0.4 mol% biotin-PE. See Supplementary Sections S7 and S9 for binning methods, errors of td and measurement errors. * Figure 4: Distribution of ΔI values and corresponding molecular volumes and shape factors of individual proteins translocating through bilayer-coated nanopores with biotinylated lipids. , Translocation of streptavidin (), anti-biotin Fab fragments () and anti-biotin antibodies (); dashed red lines indicate ΔI values that would be expected for IgG antibodies with a volume of 347 nm3 and different shape factors γ (see Supplementary Section S6 for a schematic illustration and discussion of shape factors)51, 54. * Figure 5: Comparison of experimental and theoretical values of charge-dependent translocation times of streptavidin. Experimental values are shown in black squares and the red curve represents the theoretical prediction by equation (3). Dashed black line corresponds to the expected translocation time for streptavidin assuming a translocation event due purely to diffusion in one dimension without an electrophoretic effect that is, td = lP 2/ (2DL). The valence |z| of the net charge of streptavidin was varied by the pH of the electrolyte55. The length of the pore with the bilayer coating was 28 ± 0.2 nm. Note that the red curve is not a best fit to the data; it is the prediction of td as a function of |z| according to equation (3) when all parameters were fixed to their known values. * Figure 6: Bilayer-coated nanopores resist clogging and enable monitoring of the aggregation of Aβ peptides. , Representation of clogging of uncoated nanopores and a typical current versus time trace during clogging of a nanopore by Aβ aggregates. This concatenated current trace shows several 1 s recordings and one 5 min recording. , Representation of translocation of individual Aβ aggregates through a bilayer-coated nanopore with a fluid wall (white arrow in the inset) and a typical current versus time trace of translocation events. The bilayer coating confers non-fouling properties to these pores and enables resistive pulse recordings over at least 40 min without clogging. Both recordings are 5 s long; one was taken immediately after addition of the Aβ sample and the other, 40 min later. Aβ (1–40) samples were aggregated for 72 h. Author information * Abstract * Author information * Supplementary information Affiliations * Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA * Erik C. Yusko, * Jay M. Johnson, * Sheereen Majd, * Panchika Prangkio & * Michael Mayer * Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA * Ryan C. Rollings & * Jiali Li * Department of Chemistry and Biochemistry, University of California, San Diego, California 92093, USA * Jerry Yang * Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA * Michael Mayer Contributions E.C.Y., J.Y., and M.M. conceived and designed the experiments. E.C.Y., J.M.J., S.M. and P.P. performed the experiments. R.C.R. and J.L. fabricated the nanopores. E.C.Y., J.L., J.Y. and M.M. co-wrote the manuscript and Supplementary Information. Competing financial interests The authors declare no competing financial interests. Corresponding authors Correspondence to: * Jerry Yang or * Michael Mayer Author Details * Erik C. Yusko Search for this author in: * NPG journals * PubMed * Google Scholar * Jay M. Johnson Search for this author in: * NPG journals * PubMed * Google Scholar * Sheereen Majd Search for this author in: * NPG journals * PubMed * Google Scholar * Panchika Prangkio Search for this author in: * NPG journals * PubMed * Google Scholar * Ryan C. Rollings Search for this author in: * NPG journals * PubMed * Google Scholar * Jiali Li Search for this author in: * NPG journals * PubMed * Google Scholar * Jerry Yang Contact Jerry Yang Search for this author in: * NPG journals * PubMed * Google Scholar * Michael Mayer Contact Michael Mayer Search for this author in: * NPG journals * PubMed * Google Scholar Supplementary information * Abstract * Author information * Supplementary information PDF files * Supplementary information (2,643 KB) Supplementary information Additional data