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1348 records returned

Template-Assisted Three-Dimensional Nanolithography via Geometrically Irreversible Processing.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
An innovative and versatile nanofabrication technique based on template assisted three-dimensional (3D) nanolithography is presented that takes advantage of the irreversibility of conformal growth and conformal etching at locations with negative surface curvatures in 3D templates. Using colloidal crystals as templates, nanoring particles are generated with quantity much higher than conventional methods. Relying on the same principle, metallodielectric photonic crystals with discrete metal elements are fabricated that show strong absorption in the near-IR and transmission at longer wavelengths. PMID: 19921779 [PubMe...
Source: Nano Letters - November 18, 2009 Category: Nanotechnology Authors: Yu X, Zhang H, Oliverio JK, Braun PV Tags: Nano Lett Source Type: journals

Long-Range Fluorescence Quenching by Gold Nanoparticles in a Sandwich Immunoassay for Cardiac Troponin T.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We report the first homogeneous sandwich immunoassay with gold nanoparticles (AuNPs) as fluorescence quenchers. The sandwich assay is designed for the detection of the protein cardiac troponin T (cTnT) by its simultaneous interaction with two different antibodies, one attached to AuNPs and the other labeled with fluorescent dyes. We demonstrate the working principle of the assay and using time-resolved fluorescence spectroscopy, we determine the quenching efficiency of the gold nanoparticles. In spite of the relatively large separation distance between dye molecules and AuNPs, ranging from 3 to 22 nm, the AuNPs quench the ...
Source: Nano Letters - November 18, 2009 Category: Nanotechnology Authors: Mayilo S, Kloster MA, Wunderlich M, Lutich A, Klar TA, Nichtl A, Kürzinger K, Stefani FD, Feldmann J Tags: Nano Lett Source Type: journals

Charge Carrier Motion in Disordered Conjugated Polymers: A Multiscale Ab Initio Study.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We developed an ab initio multiscale method for simulation of carrier transport in large disordered systems, based on direct calculation of electronic states and electron-phonon coupling constants. It enabled us to obtain the never seen before rich microscopic details of carrier motion in conjugated polymers, which led us to question several assumptions of phenomenological models, widely used in such systems. The macroscopic mobility of disordered poly(3-hexylthiophene) (P3HT) polymer, extracted from our simulation, is in agreement with experimental results from the literature. PMID: 19908900 [PubMed - as supplied ...
Source: Nano Letters - November 13, 2009 Category: Nanotechnology Authors: Vukmirović N, Wang LW Tags: Nano Lett Source Type: journals

Pd-Sensitized Single Vanadium Oxide Nanowires: Highly Responsive Hydrogen Sensing Based on the Metal-Insulator Transition.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Exceptionally sensitive hydrogen sensors were produced using Pd-nanoparticle-decorated, single vanadium dioxide nanowires. The high-sensitivity arises from the large downward shift in the insulator to metal transition temperature following the adsorption on and incorporation of atomic hydrogen, produced by dissociative chemisorption on Pd, in the VO(2), producing approximately 1000-fold current increases. During a rapid initial process, the insulator to metal transition temperature is decreased by >10 degrees C even when exposed to trace amounts of hydrogen gas. Subsequently, hydrogen continues to diffuse into the V...
Source: Nano Letters - November 13, 2009 Category: Nanotechnology Authors: Baik JM, Kim MH, Larson C, Yavuz CT, Stucky GD, Wodtke AM, Moskovits M Tags: Nano Lett Source Type: journals

An Upper Bound to Carrier Multiplication Efficiency in Type II Colloidal Quantum Dots.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This study indicates that, while CM is probably present in type II QD heterostructures below the CM threshold for each constituent separately, it exhibits only a modest yield. PMID: 19911830 [PubMed - as supplied by publisher] (Source: Nano Letters)
Source: Nano Letters - November 13, 2009 Category: Nanotechnology Authors: Gachet D, Avidan A, Pinkas I, Oron D Tags: Nano Lett Source Type: journals

Subthreshold Regime has the Optimal Sensitivity for Nanowire FET Biosensors.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Nanowire field-effect transistors (NW-FETs) are emerging as powerful sensors for detection of chemical/biological species with various attractive features including high sensitivity and direct electrical readout. Yet to date there have been limited systematic studies addressing how the fundamental factors of devices affect their sensitivity. Here we demonstrate that the sensitivity of NW-FET sensors can be exponentially enhanced in the subthreshold regime where the gating effect of molecules bound on a surface is the most effective due to the reduced screening of carriers in NWs. This principle is exemplified in both p...
Source: Nano Letters - November 12, 2009 Category: Nanotechnology Authors: Gao XP, Zheng G, Lieber CM Tags: Nano Lett Source Type: journals

Heterogenous Catalysis Mediated by Plasmon Heating.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We introduce a new method for performing and miniaturizing many types of heterogeneous catalysis involving nanoparticles. The method makes use of the plasmon resonance present in nanoscale metal catalysts to provide the necessary heat of reaction when illuminated with a low-power laser. We demonstrate our approach by reforming a flowing, liquid mixture of ethanol and water over gold nanoparticle catalysts in a microfluidic channel. Plasmon heating of the nanoparticles provides not only the heat of reaction but the means to generate both water and ethanol vapor locally over the catalysts, which in turn allows the chip a...
Source: Nano Letters - November 12, 2009 Category: Nanotechnology Authors: Adleman JR, Boyd DA, Goodwin DG, Psaltis D Tags: Nano Lett Source Type: journals

Metal-Driven Hierarchical Self-Assembled One-Dimensional Nanohelices.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Sophisticated helical structure has been an attractive subject due to its significance in understanding of biological self-assembly and appealing application in nanoscience. In this work, a facile route toward one-dimensional helical nanostructure is presented based on metal-cholate supramolecular self-assembly. Well-defined right-handed helical nanoribbons in calcium-cholate systems are systematically investigated and a series of metal ions are exploited to drive metal-cholate supramolecular helix. It is anticipated that the incorporation of metal ions may endow versatile functionalities and merits to the self-assembl...
Source: Nano Letters - November 12, 2009 Category: Nanotechnology Authors: Qiao Y, Lin Y, Wang Y, Yang Z, Liu J, Zhou J, Yan Y, Huang J Tags: Nano Lett Source Type: journals

Chemical Fabrication of Heterometallic Nanogaps for Molecular Transport Junctions.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We report a simple and reproducible method for fabricating heterometallic nanogaps, which are made of two different metal nanorods separated by a nanometer-sized gap. The method is based upon on-wire lithography, which is a chemically enabled technique used to synthesize a wide variety of nanowire-based structures (e.g., nanogaps and disk arrays). This method can be used to fabricate pairs of metallic electrodes, which exhibit distinct work functions and are separated by gaps as small as 2 nm. Furthermore, we demonstrate that a symmetric thiol-terminated molecule can be assembled into such heterometallic nanogaps to form m...
Source: Nano Letters - November 12, 2009 Category: Nanotechnology Authors: Chen X, Yeganeh S, Qin L, Li S, Xue C, Braunschweig AB, Schatz GC, Ratner MA, Mirkin CA Tags: Nano Lett Source Type: journals

Fabrication and Electrical Properties of Si Nanowires Synthesized by Al Catalyzed Vapor-Liquid-Solid Growth.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The synthesis of epitaxially oriented Si nanowires at high growth rates (>1 mum/min) was demonstrated on (111) Si substrates using Al as the catalyst. The use of high H(2) and SiH(4) partial pressures was found to be effective at reducing problems associated with Al oxidation and nanowire nucleation, enabling growth of high aspect ratio structures at temperatures ranging from 500 to 600 degrees C with minimal tapering of the diameter. Because of the high growth rate observed, the Al catalyst is believed to be in the liquid state during the growth. Four-point resistance measurements and back-gated current-voltage mea...
Source: Nano Letters - November 11, 2009 Category: Nanotechnology Authors: Ke Y, Weng X, Redwing JM, Eichfeld CM, Swisher TR, Mohney SE, Habib YM Tags: Nano Lett Source Type: journals

Spatial Resolution of a Type II Heterojunction in a Single Bipolar Molecule.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Bipolar molecules incorporating donor and acceptor components within a single molecule create exciting device opportunities due to their possible use as nanoscale p-n heterojunctions. Here we report a direct characterization of the internal electronic structure of a single bipolar molecular heterojunction, including subnanometer features of the intramolecular donor-acceptor interface. Angstrom-resolved scanning tunneling spectroscopy was used to map the energy levels and spatial extent of molecular orbitals across the surface of an individual bipolar molecule, bithiophene naphthalene diimide (BND). We find that individ...
Source: Nano Letters - November 11, 2009 Category: Nanotechnology Authors: Tao C, Sun J, Zhang X, Yamachika R, Wegner D, Bahri Y, Samsonidze G, Cohen ML, Louie SG, Tilley TD, Segalman RA, Crommie MF Tags: Nano Lett Source Type: journals

Photo-Targeted Nanoparticles.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We report a novel and simple proof-of-concept of a nanoparticulate system that targets any tissue selectively upon illumination. Nanoparticles were covalently functionalized with the amino acid sequence YIGSR, which adheres to the beta1 integrins present on most cell surfaces. This peptide was masked with a caging group, rendering it biologically inert. Illumination with UV light released the caging group from the YIGSR, allowing binding to cells. PMID: 19904979 [PubMed - as supplied by publisher] (Source: Nano Letters)
Source: Nano Letters - November 11, 2009 Category: Nanotechnology Authors: Dvir T, Banghart MR, Timko BP, Langer R, Kohane DS Tags: Nano Lett Source Type: journals

Templated Self-Assembly of Square Symmetry Arrays from an ABC Triblock Terpolymer.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Self-assembly provides the ability to create well-controlled nanostructures with electronic or chemical functionality and enables the synthesis of a wide range of useful devices. Diblock copolymers self-assemble into periodic arrays of microdomains with feature sizes of typically 10-50 nm, and have been used to make a wide range of devices such as silicon capacitors and transistors, photonic crystals, and patterned magnetic media(1-3). However, the cylindrical or spherical microdomains in diblock copolymers generally form close-packed structures with hexagonal symmetry, limiting their device applications. Here we demon...
Source: Nano Letters - November 11, 2009 Category: Nanotechnology Authors: Chuang VP, Gwyther J, Mickiewicz RA, Manners I, Ross CA Tags: Nano Lett Source Type: journals

Endosomal Leakage and Nuclear Translocation of Multiwalled Carbon Nanotubes: Developing a Model for Cell Uptake.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We report our findings on cellular membrane penetration, endocytosis, endosomal leakage, and nuclear translocation of multiwalled carbon nanotubes (MWCNTs). Our data is consistent with a working model for MWCNTs' cell uptake and cellular translocations. PMID: 19902917 [PubMed - as supplied by publisher] (Source: Nano Letters)
Source: Nano Letters - November 10, 2009 Category: Nanotechnology Authors: Mu Q, Broughton DL, Yan B Tags: Nano Lett Source Type: journals

Direct Correlation of Structural Domain Formation with the Metal Insulator Transition in a VO(2) Nanobeam.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The electrical resistance of single VO(2) nanobeams was measured while simultaneously mapping the domain structure with Raman spectroscopy to investigate the relationship between structural domain formation and the metal-insulator transition. With increasing temperature, the nanobeams transformed from the insulating monoclinic M(1) phase to a mixture of the Mott-insulating M(2) and metallic rutile phases. Domain fractions were used to extract the temperature dependent resistivity of the M(2) phase, which showed an activated behavior consistent with the expected Mott-Hubbard gap. Metallic monoclinic phases were also pro...
Source: Nano Letters - November 10, 2009 Category: Nanotechnology Authors: Zhang S, Chou JY, Lauhon LJ Tags: Nano Lett Source Type: journals

Detection of Local Protein Structures along DNA Using Solid-State Nanopores.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Nanopores have been successfully employed as a new tool to rapidly detect single biopolymers, in particular DNA. When a molecule is driven through a nanopore by an externally applied electric field, it causes a characteristic temporary change in the trans-pore current. Here, we examine the translocation of DNA with discrete patches of the DNA-repair protein RecA attached along its length. Using the fact that RecA-coated DNA and bare DNA yield very different current-blockade signatures, we demonstrate that it is possible to map the locations of the proteins along the length of a single molecule using a solid-state nanop...
Source: Nano Letters - November 10, 2009 Category: Nanotechnology Authors: Kowalczyk SW, Hall AR, Dekker C Tags: Nano Lett Source Type: journals

Wafer-Scale Fabrication of Separated Carbon Nanotube Thin-Film Transistors for Display Applications.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Preseparated, semiconductive enriched carbon nanotubes hold great potential for thin-film transistors and display applications due to their high mobility, high percentage of semiconductive nanotubes, and room-temperature processing compatibility. Here in this paper, we report our progress on wafer-scale processing of separated nanotube thin-film transistors (SN-TFTs) for display applications, including key technology components such as wafer-scale assembly of high-density, uniform separated nanotube networks, high-yield fabrication of devices with superior performance, and demonstration of organic light-emitting diode ...
Source: Nano Letters - November 10, 2009 Category: Nanotechnology Authors: Wang C, Zhang J, Ryu K, Badmaev A, De Arco LG, Zhou C Tags: Nano Lett Source Type: journals

Manipulating Nanoscale Light Fields with the Asymmetric Bowtie Nano-Colorsorter.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We present a class of devices called Asymmetric Bowtie nano-Colorsorters. These devices are specifically engineered to not only capture and confine optical fields, but also to spectrally filter and steer them while maintaining nanoscale field distributions. We show that spectral properties and localized spatial mode distributions can be readily tuned by controlled asymmetry. Nano-Colorsorters can control light's spatial and spectral distributions at the nanoscale and thus significantly impact applications ranging from broadband light harvesting to ultrafast wavelength-selective photodetection. PMID: 19899744 [PubMed - ...
Source: Nano Letters - November 9, 2009 Category: Nanotechnology Authors: Zhang Z, Weber-Bargioni A, Wu SW, Dhuey S, Cabrini S, Schuck PJ Tags: Nano Lett Source Type: journals

Alignment Controlled Growth of Single-Walled Carbon Nanotubes on Quartz Substrates.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Single-walled carbon nanotubes (SWNTs) possess extraordinary electrical properties, with many possible applications in electronics. Dense, horizonally aligned arrays of linearly configured SWNTs represent perhaps the most attractive and scalable way to implement this class of nanomaterial in practical systems. Recent work shows that templated growth of tubes on certain crystalline substrates yields arrays with the necessary levels of perfection, as demonstrated by the formation of devices and full systems on quartz. This paper examines advanced implementations of this process on crystalline quartz substrates with diffe...
Source: Nano Letters - November 9, 2009 Category: Nanotechnology Authors: Xiao J, Dunham S, Liu P, Zhang Y, Kocabas C, Moh L, Huang Y, Hwang KC, Lu C, Huang W, Rogers JA Tags: Nano Lett Source Type: journals

Identification of Surface Structures on 3C-SiC Nanocrystals with Hydrogen and Hydroxyl Bonding by Photoluminescence.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
SiC nanocrystals (NCs) exhibit unique surface chemistry and possess special properties. This provides the opportunity to design suitable surface structures by terminating the surface dangling bonds with different atoms thereby boding well for practical applications. In this article, we report the photoluminescence properties of 3C-SiC NCs in water suspensions with different pH values. Besides a blue band stemming from the quantum confinement effect, the 3C-SiC NCs show an additional photoluminescence band at 510 nm when the excitation wavelengths are longer than 350 nm. Its intensity relative to the blue band increases...
Source: Nano Letters - November 6, 2009 Category: Nanotechnology Authors: Wu XL, Xiong SJ, Zhu J, Wang J, Shen JC, Chu PK Tags: Nano Lett Source Type: journals

Toughening through Nature-Adapted Nanoscale Design.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The extraordinary combination of strength and toughness attained by nature's highly sophisticated structural design in nacre has inspired the synthesis of novel nanocomposites. In this context, the organic-inorganic hierarchical design of nacre has been mimicked. However, two key features of nacre, namely the scaling of the structural components and the low content of the organic phase, have not been replicated yet. Here, we present thin nanocomposite films with properly adjusted thicknesses of the organic and inorganic layers, as well as a microstructure that closely resembles that of nacre. These films, which are obt...
Source: Nano Letters - November 6, 2009 Category: Nanotechnology Authors: Burghard Z, Zini L, Srot V, Bellina P, Aken PA, Bill J Tags: Nano Lett Source Type: journals

Bacterial Motility and Clustering Guided by Microcontact Printing.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Type IV pili are bacterial nanomotors that mediate two opposing behaviors on surfaces, spreading and clustering. Here we show that the velocity of motile Neisseria gonorrhoeae depends quantitatively on the fluidity of the phospholipid membrane surface. Using microcontact printing, we confined the surface motility to nonfluid islands within a fluid lipid membrane. On an array of islands, the transition from spreading to clustering was analyzed in real time and at the single cell level, showing that it was triggered by the number of bacteria (7.5 +/- 0.3) for small islands and by the surface density (56 +/- 2%) when the ...
Source: Nano Letters - November 5, 2009 Category: Nanotechnology Authors: Holz C, Opitz D, Mehlich J, Ravoo BJ, Maier B Tags: Nano Lett Source Type: journals

Nanodome Solar Cells with Efficient Light Management and Self-Cleaning.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Here for the first time, we demonstrate novel nanodome solar cells, which have periodic nanoscale modulation for all layers from the bottom substrate, through the active absorber to the top transparent contact. These devices combine many nanophotonic effects to both efficiently reduce reflection and enhance absorption over a broad spectral range. Nanodome solar cells with only a 280 nm thick hydrogenated amorphous silicon (a-Si:H) layer can absorb 94% of the light with wavelengths of 400-800 nm, significantly higher than the 65% absorption of flat film devices. Because of the nearly complete absorption, a very large sh...
Source: Nano Letters - November 5, 2009 Category: Nanotechnology Authors: Zhu J, Hsu CM, Yu Z, Fan S, Cui Y Tags: Nano Lett Source Type: journals

Efficient CdSe Quantum Dot-Sensitized Solar Cells Prepared by an Improved Successive Ionic Layer Adsorption and Reaction Process.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In pursuit of efficient quantum dot (QD)-sensitized solar cells based on mesoporous TiO(2) photoanodes, a new procedure for preparing selenide (Se(2-)) was developed and used for depositing CdSe QDs in situ over TiO(2) mesopores by the successive ionic layer adsorption and reaction (SILAR) process in ethanol. The sizes and density of CdSe QDs over TiO(2) were controlled by the number of SILAR cycles applied. After some optimization of these QD-sensitized TiO(2) films in regenerative photoelectrochemical cells using a cobalt redox couple [Co(o-phen)(3)(2+/3+)], including addition of a final layer of CdTe, over 4% overal...
Source: Nano Letters - November 5, 2009 Category: Nanotechnology Authors: Lee H, Wang M, Chen P, Gamelin DR, Zakeeruddin SM, Grätzel M, Nazeeruddin MK Tags: Nano Lett Source Type: journals

Surface-Assisted Assembly of Discrete Porphyrin-Based Cyclic Supramolecules.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We employed de novo synthesized porphyrin modules to construct discrete cyclic supramolecular architectures supported on a copper surface. The programmed geometry and functionality of the molecular modules together with their conformational flexibility and substrate interaction yields symmetric discrete assemblies, including dimers and chains as well as three- to six-membered cyclic structures. The area of the molecular cavities is extended by creating bicomponent structures combining building blocks with different symmetry. PMID: 19888718 [PubMed - as supplied by publisher] (Source: Nano Letters)
Source: Nano Letters - November 4, 2009 Category: Nanotechnology Authors: Heim D, Seufert K, Auwärter W, Aurisicchio C, Fabbro C, Bonifazi D, Barth JV Tags: Nano Lett Source Type: journals

Supramolecular Protein Cage Composite MR Contrast Agents with Extremely Efficient Relaxivity Properties.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A DTPA-Gd containing polymer was grown in the interior of a heat shock protein cage resulting in T(1) particle relaxivities of 4200 mM(-1) sec(-1) for the 12 nm particle. Relaxivity parameters were determined, and this analysis suggests that the rotational correlation time has been optimized while the water exchange lifetime is longer than optimal. This synthetic approach holds much promise for the development of next generation contrast agents and this report will aid in their design. PMID: 19888720 [PubMed - as supplied by publisher] (Source: Nano Letters)
Source: Nano Letters - November 4, 2009 Category: Nanotechnology Authors: Liepold LO, Abedin MJ, Buckhouse ED, Frank JA, Young MJ, Douglas T Tags: Nano Lett Source Type: journals

Resolution and Enhancement in Nanoantenna-Based Fluorescence Microscopy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Single gold nanoparticles can act as nanoantennas for enhancing the fluorescence of emitters in their near fields. Here we present experimental and theoretical studies of scanning antenna-based fluorescence microscopy as a function of the diameter of the gold nanoparticle. We examine the interplay between fluorescence enhancement and spatial resolution and discuss the requirements for deciphering single molecules in a dense sample. Resolutions better than 20 nm and fluorescence enhancement up to 30 times are demonstrated experimentally. By accounting for the tip shaft and the sample interface in finite-difference time-...
Source: Nano Letters - November 3, 2009 Category: Nanotechnology Authors: Eghlidi H, Lee KG, Chen XW, Götzinger S, Sandoghdar V Tags: Nano Lett Source Type: journals

Patterning Graphene at the Nanometer Scale via Hydrogen Desorption.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We have demonstrated the reversible and local modification of the electronic properties of graphene by hydrogen passivation and subsequent electron-stimulated hydrogen desorption with an scanning tunneling microscope tip. In addition to changing the morphology, we show that the hydrogen passivation is stable at room temperature and modifies the electronic properties of graphene, opening a gap in the local density of states. This insulating state is reversed by local desorption of the hydrogen, and the unaltered electronic properties of graphene are recovered. Using this mechanism, we have "written" graphene patterns on...
Source: Nano Letters - November 2, 2009 Category: Nanotechnology Authors: Sessi P, Guest JR, Bode M, Guisinger NP Tags: Nano Lett Source Type: journals

Utilization of a Buffered Dielectric to Achieve High Field-Effect Carrier Mobility in Graphene Transistors.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We utilize an organic polymer buffer layer between graphene and conventional gate dielectrics in top-gated graphene transistors. Unlike other insulators, this dielectric stack does not significantly degrade carrier mobility, allowing for high field-effect mobilities to be retained in top-gate operation. This is demonstrated in both two-point and four-point analysis and in the high-frequency operation of a graphene transistor. Temperature dependence of the carrier mobility suggests that phonons are the dominant scatterers in these devices. PMID: 19883119 [PubMed - as supplied by publisher] (Source: Nano Letters)
Source: Nano Letters - November 2, 2009 Category: Nanotechnology Authors: Farmer DB, Chiu HY, Lin YM, Jenkins KA, Xia F, Avouris P Tags: Nano Lett Source Type: journals

Plasmonic Lens Made of Multiple Concentric Metallic Rings under Radially Polarized Illumination.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Optimal plasmonic focusing can be achieved through matching the rotational symmetry of the plasmonic lens to the polarization symmetry of a radially polarized illumination. In this letter, we report the experimental confirmation of the focusing properties and field enhancement effect of plasmonic lens made of multiple concentric annular rings using a collection mode near field scanning optical microscope. Surface plasmons excited at all azimuthal directions propagate toward the geometric center and constructively interfere at the focus to create a strongly enhanced evanescent optical "needle" field that is substantiall...
Source: Nano Letters - October 30, 2009 Category: Nanotechnology Authors: Chen W, Abeysinghe DC, Nelson RL, Zhan Q Tags: Nano Lett Source Type: journals

Tuning the Electronic Coupling and Magnetic Moment of a Metal Nanoparticle Dimer in the Nonlinear Dielectric-Response Regime.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We show that the electronic coupling and magnetic moment of a silver nanoparticle dimer can be readily tuned by applying an electric field in the nonlinear dielectric-response regime. For a given interparticle separation, the electronic coupling becomes tunable as soon as the system crosses over from the linear to nonlinear regime. Remarkably, this transition takes place for modest strengths of the electric field. Further increase of the field strength may close the HOMO-LUMO gap of the dimer due to Stark shifts, accompanied by the emergence of a net magnetic moment from two nonmagnetic building blocks. These findings,...
Source: Nano Letters - October 30, 2009 Category: Nanotechnology Authors: Troparevsky MC, Zhao K, Xiao D, Zhang Z, Eguiluz AG Tags: Nano Lett Source Type: journals

Capturing Electrochemically Evolved Nanobubbles by Electroless Deposition. A Facile Route to the Synthesis of Hollow Nanoparticles.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Gas evolution during electrochemical deposition has long been regarded as undesired and deliberately suppressed. Here, we show a new role of electrochemically evolved hydrogen bubbles, serving as both templates and reducing agent to form hollow Au nanoparticles via electroless deposition. Hollow gold nanoparticles with a complete nanocrystalline shell and a 50 nm hollow core were fabricated. By controlling the shell thickness, particle size can be varied from 100 to 150 nm. The process is very simple, scalable, and with a high throughput. Using this method, more complicated hollow nanostructures such as double nanoshel...
Source: Nano Letters - October 29, 2009 Category: Nanotechnology Authors: Huang C, Jiang J, Lu M, Sun L, Meletis EI, Hao Y Tags: Nano Lett Source Type: journals

Plasmonic Ratchet Wheels: Switching Circular Dichroism by Arranging Chiral Nanostructures.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We demonstrate circular dichroism (CD) in the second harmonic generation (SHG) signal from chiral assemblies of G-shaped nanostructures made of gold. The arrangement of the G shapes is crucial since upon reordering them the SHG-CD effect disappears. Microscopy reveals SHG "hotspots" assemblies, which originate in enantiomerically sensitive plasmon modes, having the novel property of exhibiting a chiral geometry themselves in relation with the handedness of the material. These results open new frontiers in studying chirality. PMID: 19863052 [PubMed - as supplied by publisher] (Source: Nano Letters)
Source: Nano Letters - October 28, 2009 Category: Nanotechnology Authors: Valev VK, Smisdom N, Silhanek AV, De Clercq B, Gillijns W, Ameloot M, Moshchalkov VV, Verbiest T Tags: Nano Lett Source Type: journals

Anomalous Dissipation in Single-Walled Carbon Nanotube Resonators.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We observe a new anomalous and transient process of intrinsic dissipation in simulations of the ring-down of flexural modes in single-walled carbon nanotube (CNT) resonators. The effect is pronounced, causing the quality factor of the mode to be reduced by more that 95% for tens of picoseconds. The anomalous dissipation depends on the CNT temperature and the energy in the mode, and remarkably increasing the excitation energy in the resonator causes it to decay to zero faster. By tracking the cascade of energy as it dissipates we identify "gateway" modes that provide important channels for dissipation. The processes we ...
Source: Nano Letters - October 28, 2009 Category: Nanotechnology Authors: Greaney PA, Lani G, Cicero G, Grossman JC Tags: Nano Lett Source Type: journals

Transfer-Free Batch Fabrication of Single Layer Graphene Transistors.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We report the synthesis of large scale single layer graphene directly onto an evaporated copper film. A novel fabrication method was used to directly pattern these graphene sheets into devices by simply removing the underlying copper film. Raman and conductance measurements show that the mechanical and electrical properties of our single layer graphene are uniform over a large area, ( Ferrari , A. C. et al. Phys. Rev. Lett. 2006 , 97 , 187401. ) which leads to a high device yield and successful fabrication of ultra long (>0.5 mm) graphene channels. Our graphene based devices present excellent electrical properties inclu...
Source: Nano Letters - October 27, 2009 Category: Nanotechnology Authors: Levendorf MP, Ruiz-Vargas CS, Garg S, Park J Tags: Nano Lett Source Type: journals

Intracellular Processing of Proteins Mediated by Biodegradable Polyelectrolyte Capsules.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Multilayer polyelectrolyte capsules made by layer-by-layer assembly of oppositely charged biodegradable polyelectrolytes were filled with a model of a nonactive prodrug, a self-quenched fluorescence-labeled protein. After capsule uptake by living cells, the walls of the capsules were actively degraded and digested by intracellular proteases. Upon capsule wall degradation, intracellular proteases could reach the protein cargo in the cavity of the capsules. Enzymatic fragmentation of the self-quenched fluorescence-labeled protein by proteases led to individual fluorescence-labeled peptides and thus revoked self-quenching...
Source: Nano Letters - October 27, 2009 Category: Nanotechnology Authors: Rivera-Gil P, De Koker S, De Geest BG, Parak WJ Tags: Nano Lett Source Type: journals

Kinetically Induced Kinking of Vapor-Liquid-Solid Grown Epitaxial Si Nanowires.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Epitaxial Si nanowires grown from Au seeds using the vapor-liquid-solid method begin growing normal to the Si(111) substrate atop a tapered base. After a kinetically determined length, the NWs may kink away from [111] to another crystallographic direction. The smallest NWs prefer growth along 110 while larger Si NWs choose either 111 or 112 based on whether growth conditions favor Au-free sidewalls. "Vertical" growth normal to the Si(111) substrate is obtained only for slowly growing NWs with Au-decorated sidewalls. At the fastest growth rates, single-crystal Si NWs smoothly, continuously, and randomly vary their growt...
Source: Nano Letters - October 27, 2009 Category: Nanotechnology Authors: Madras P, Dailey E, Drucker J Tags: Nano Lett Source Type: journals

Fate of Excitations in Conjugated Polymers: Single-Molecule Spectroscopy Reveals Nonemissive "Dark" Regions in MEH-PPV Individual Chains.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Single chains of the conjugated polymer MEH-PPV (poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene)) were studied with wide-field fluorescence microscopy (dispersion in inert polymer matrices) and with fluorescence correlation spectroscopy (chloroform solution). The fluorescence yield of individual molecules in matrices was found to be 1-2 orders of magnitude lower than that in solution and it decreased substantially with increasing chain length. It suggests that isolation of MEH-PPV molecules in polymer matrices creates favorable conditions for photogeneration of nonemissive primary excited states. PMID: 1...
Source: Nano Letters - October 27, 2009 Category: Nanotechnology Authors: Lin H, Tian Y, Zapadka K, Persson G, Thomsson D, Mirzov O, Larsson PO, Widengren J, Scheblykin IG Tags: Nano Lett Source Type: journals

Angle-Resolved Photoemission Spectra of Graphene from First-Principles Calculations.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Angle-resolved photoemission spectroscopy (ARPES) is a powerful experimental technique for directly probing electron dynamics in solids. The energy versus momentum dispersion relations and the associated spectral broadenings measured by ARPES provide a wealth of information on quantum many-body interaction effects. In particular, ARPES allows studies of the Coulomb interaction among electrons (electron-electron interactions) and the interaction between electrons and lattice vibrations (electron-phonon interactions). Here, we report ab initio simulations of the ARPES spectra of graphene including both electron-electron ...
Source: Nano Letters - October 26, 2009 Category: Nanotechnology Authors: Park CH, Giustino F, Spataru CD, Cohen ML, Louie SG Tags: Nano Lett Source Type: journals

Direct Observation of Martensitic Phase-Transformation Dynamics in Iron by 4D Single-Pulse Electron Microscopy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The in situ martensitic phase transformation of iron, a complex solid-state transition involving collective atomic displacement and interface movement, is studied in real time by means of four-dimensional (4D) electron microscopy. The iron nanofilm specimen is heated at a maximum rate of approximately 10(11) K/s by a single heating pulse, and the evolution of the phase transformation from body-centered cubic to face-centered cubic crystal structure is followed by means of single-pulse, selected-area diffraction and real-space imaging. Two distinct components are revealed in the evolution of the crystal structure. The f...
Source: Nano Letters - October 26, 2009 Category: Nanotechnology Authors: Park HS, Kwon OH, Baskin JS, Barwick B, Zewail AH Tags: Nano Lett Source Type: journals

Photocurrent Induced by Nonradiative Energy Transfer from Nanocrystal Quantum Dots to Adjacent Silicon Nanowire Conducting Channels: Toward a New Solar Cell Paradigm.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We report the observation of photocurrent in silicon nanowires induced by nonradiative resonant energy transfer (NRET) from adjacent layers of lead sulfide nanocrystal quantum dots using time-resolved photocurrent measurements. This demonstration supports the feasibility of a new solar cell paradigm ( Lu , S. ; Madhukar , A. Nano Lett. 2007 , 7 , 3443 - 3451 ) that exploits NRET between efficient photon absorbers and adjacent nanowire/quantum well high-mobility charge transport channels and could offer a viable alternative to the limitations of carrier transport and collection faced by excitonic solar cells. PMID: 1985...
Source: Nano Letters - October 26, 2009 Category: Nanotechnology Authors: Lu S, Lingley Z, Asano T, Harris D, Barwicz T, Guha S, Madhukar A Tags: Nano Lett Source Type: journals

Nanodroplet Activated and Guided Folding of Graphene Nanostructures.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We demonstrate by molecular dynamics simulations that water nanodroplets can activate and guide the folding of planar graphene nanostructures. Once the nanodroplets are deposited at selected spots on the planar nanostructure, they can act as catalytic elements that initiate conformational changes and help to overcome deformation barriers associated with them. Nanodroplets can induce rapid bending, folding, sliding, rolling, and zipping of the planar nanostructures, which can lead to the assembly of nanoscale sandwiches, capsules, knots, and rings. PMID: 19852466 [PubMed - as supplied by publisher] (Source: Nano Letters)
Source: Nano Letters - October 23, 2009 Category: Nanotechnology Authors: Patra N, Wang B, Král P Tags: Nano Lett Source Type: journals

Hybrid Heterojunction and Photoelectrochemistry Solar Cell Based on Silicon Nanowires and Double-Walled Carbon Nanotubes.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A hybrid solar cell model composed of a heterojunction cell and a photoelectrochemical (PEC) cell has been proposed and characterized. In the hybrid cell, a thin film of double-walled carbon nanotubes forms a heterojunction with the silicon nanowire (SiNW) array and also functions as the transparent counter electrode of the PEC cell. The cell performance can be readily tuned by controlling the SiNW density. Under AM 1.5G illumination, a power conversion efficiency of 1.29%, higher than those reported for SiNW array-based PEC cells, has been obtained. PMID: 19852483 [PubMed - as supplied by publisher] (Source: Nano Letters)
Source: Nano Letters - October 23, 2009 Category: Nanotechnology Authors: Shu Q, Wei J, Wang K, Zhu H, Li Z, Jia Y, Gui X, Guo N, Li X, Ma C, Wu D Tags: Nano Lett Source Type: journals

Scanning Tunneling Microscopy Characterization of the Electrical Properties of Wrinkles in Exfoliated Graphene Monolayers.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We report on the scanning tunneling microscopy study of a new class of corrugations in exfoliated monolayer graphene sheets, that is, wrinkles approximately 10 nm in width and approximately 3 nm in height. We found such corrugations to be ubiquitous in graphene and have distinctly different properties when compared to other regions of graphene. In particular, a "three-for-six" triangular pattern of atoms is exclusively and consistently observed on wrinkles, suggesting the local curvature of the wrinkle provides a sufficient perturbation to break the 6-fold symmetry of the graphene lattice. Through scanning tunneling spectr...
Source: Nano Letters - October 23, 2009 Category: Nanotechnology Authors: Xu K, Cao P, Heath JR Tags: Nano Lett Source Type: journals

Transparent Metal Nanowire Thin Films Prepared in Mesostructured Templates.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The preparation of conductive and transparent gold/silver nanowire mesh films is reported. The nanowires formed after the reduction of the metal ions was triggered and a thin growth solution film was spread on a substrate. Metal reduction progressed within a template of a highly concentrated surfactant liquid crystalline mesostructure formed on the substrate during film drying to form ordered bundles of ultrathin nanowires. The films exhibited metallic conductivity over large areas, high transparency, and flexibility. PMID: 19852500 [PubMed - as supplied by publisher] (Source: Nano Letters)
Source: Nano Letters - October 23, 2009 Category: Nanotechnology Authors: Azulai D, Belenkova T, Gilon H, Barkay Z, Markovich G Tags: Nano Lett Source Type: journals

Transfer of Large-Area Graphene Films for High-Performance Transparent Conductive Electrodes.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Graphene, a two-dimensional monolayer of sp(2)-bonded carbon atoms, has been attracting great interest due to its unique transport properties. One of the promising applications of graphene is as a transparent conductive electrode owing to its high optical transmittance and conductivity. In this paper, we report on an improved transfer process of large-area graphene grown on Cu foils by chemical vapor deposition. The transferred graphene films have high electrical conductivity and high optical transmittance that make them suitable for transparent conductive electrode applications. The improved transfer processes will al...
Source: Nano Letters - October 20, 2009 Category: Nanotechnology Authors: Li X, Zhu Y, Cai W, Borysiak M, Han B, Chen D, Piner RD, Colombo L, Ruoff RS Tags: Nano Lett Source Type: journals

Screening in Nanowires and Nanocontacts: Field Emission, Adhesion Force, and Contact Resistance.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The explanations of several nanoscale phenomena such as the field enhancement factor in field emission, the large decay length of the adhesion force between a metallic tip and a surface, and the contact resistance in a nanowire break junction have been elusive. Here we develop an analytical theory of Thomas-Fermi screening in nanoscale structures. We demonstrate that nanoscale dimensions give rise to an effective screening length that depends on the geometry and physical boundary conditions. The above phenomena are shown to be manifestations of the effective screening length. PMID: 19845331 [PubMed - as supplied by...
Source: Nano Letters - October 20, 2009 Category: Nanotechnology Authors: Zhang XG, Pantelides ST Tags: Nano Lett Source Type: journals

Nanowire Biocompatibility in the Brain - Looking for a Needle in a 3D Stack.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We investigated the brain-tissue response to nanowire implantations in the rat striatum after 1, 6, and 12 weeks using immunohistochemistry. The nanowires could be visualized in the scar by confocal microscopy (through the scattered laser light). For the nanowire-implanted animals, there is a significant astrocyte response at week 1 compared to controls. The nanowires are phagocytized by ED1 positive microglia, and some of them are degraded and/or transported away from the brain. PMID: 19845389 [PubMed - as supplied by publisher] (Source: Nano Letters)
Source: Nano Letters - October 20, 2009 Category: Nanotechnology Authors: Eriksson Linsmeier C, Prinz CN, Pettersson LM, Caroff P, Samuelson L, Schouenborg J, Montelius L, Danielsen N Tags: Nano Lett Source Type: journals

Nanoporous Pt-Co Alloy Nanowires: Fabrication, Characterization, and Electrocatalytic Properties.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Nanoporous Pt-Co alloy nanowires were synthesized by electrodeposition of Co-rich Pt(1)Co(99) alloy into anodic aluminum oxide (AAO) membranes, followed by a dealloying treatment in a mild acidic medium. These nanowires consist of porous skeletons with tiny pores of 1-5 nm and crystalline ligaments of 2-8 nm. Morphological and compositional evolutions of the porous Pt-Co nanowires upon dealloying were investigated, and their formation mechanism is discussed. The nanoporous Pt-Co alloy nanowires are found to exhibit distinctly enhanced electrocatalytic activities toward methanol oxidation as compared to the current stat...
Source: Nano Letters - October 19, 2009 Category: Nanotechnology Authors: Liu L, Pippel E, Scholz R, Gösele U Tags: Nano Lett Source Type: journals

Polymeric Nanoparticle-Based Activatable Near-Infrared Nanosensor for Protease Determination In Vivo.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We report here a new protease activatable strategy based on a polymer nanoparticle platform. This nanosensor delivers chemically labeled matrix metalloproteinase (MMP)-activatable fluorogenic peptides to the specific MMPs of interest in vivo. Intravenous administration of the nanosensor in an MMP-positive SCC-7 xenograft tumor and a colon cancer mouse model verified the enzyme specificity of the nanosensor in vivo. The design platform of the nanosensor is flexible and can be fine-tuned for a wide array of applications such as the detection of biomarkers, early diagnosis of disease, and monitoring therapeutic efficacy. ...
Source: Nano Letters - October 19, 2009 Category: Nanotechnology Authors: Lee S, Ryu JH, Park K, Lee A, Lee SY, Youn IC, Ahn CH, Yoon SM, Myung SJ, Moon DH, Chen X, Choi K, Kwon IC, Kim K Tags: Nano Lett Source Type: journals