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18 Oct 2004

Volume 85, Issue 16, pp. 3343-3639

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 3570 (2004); http://dx.doi.org/10.1063/1.1807953 (2 pages)

X. N. Zhang, C. R. Li, Z. Zhang, and Z. X. Cao
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Hysteretic behavior of the charge injection in single silicon nanoparticles

H. Diesinger, T. Mélin, D. Deresmes, D. Stiévenard, and T. Baron

Appl. Phys. Lett. 85, 3546 (2004); http://dx.doi.org/10.1063/1.1808889 (3 pages) | Cited 7 times

Online Publication Date: 22 October 2004

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Charge injection in individual silicon nanoparticles has been investigated by electric force microscopy (EFM). Stored charges injected from the EFM tip have been counted using a quantitative method. Injection kinetics reveals the setting-up of an equilibrium regime. Equilibrium charge–voltage characteristics are analyzed, and display an overall linear behavior corresponding to successive tunneling through the nonequivalent tip–nanoparticle and nanoparticle–substrate oxide barriers. A hysteretic behavior is observed in the equilibrium charge–voltage characteristics, and attributed to a secondary charge injection process associated with the nanoparticle oxide surface.
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73.63.Bd Nanocrystalline materials
73.40.Gk Tunneling

Interface effect on thermal conductivity of carbon nanotube composites

Ce-Wen Nan, Gang Liu, Yuanhua Lin, and Ming Li

Appl. Phys. Lett. 85, 3549 (2004); http://dx.doi.org/10.1063/1.1808874 (3 pages) | Cited 144 times

Online Publication Date: 22 October 2004

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A simple formula for the thermal conductivity enhancement in carbon nanotube composites is presented by incorporating the interface thermal resistance with an effective medium approach. This model well describes the thermal conductivity enhancement observed recently in nanotube suspensions. In particular, this simple formula predicts that a large interface thermal resistance across the nanotube-matrix interface causes a significant degradation in the thermal conductivity enhancement, even for the case with ultrahigh intrinsic thermal conductivity and aspect ratio of the carbon nanotubes embedded.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Electrochemical nanopatterning of Ag on solid-state ionic conductor RbAg4I5 using atomic force microscopy

Minhwan Lee, Ryan O’Hayre, Fritz B. Prinz, and Turgut M. Gür

Appl. Phys. Lett. 85, 3552 (2004); http://dx.doi.org/10.1063/1.1807964 (3 pages) | Cited 20 times

Online Publication Date: 22 October 2004

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This report introduces an electrochemical nanopatterning technique performed under ambient conditions without involving a liquid vessel or probe-to-sample material transfer. Patterning is accomplished by solid-state electrochemical nanodeposition of Ag clusters on the surface of the solid ionic conductor RbAg4I5 using an atomic force microscopy probe. Application of negative voltage pulses on the probe relative to an Ag film counter electrode on an RbAg4I5 sample induces nanometer-sized Ag deposition on the ion conductor around the probe. The patterned Ag particles are 0.5–70 nm high and 20–700 nm in diameter. The effect of the amplitude and duration of bias voltage on the size and shape of deposited Ag clusters is also shown.
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81.16.Nd Micro- and nanolithography
82.45.Fk Electrodes
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
68.37.Ps Atomic force microscopy (AFM)

Size effect on Young’s modulus of thin chromium cantilevers

S. G. Nilsson, X. Borrisé, and L. Montelius

Appl. Phys. Lett. 85, 3555 (2004); http://dx.doi.org/10.1063/1.1807945 (3 pages) | Cited 39 times

Online Publication Date: 22 October 2004

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Thin chromium cantilevers with sub-100 nm thickness have been characterized by an atomic force microscope operating in contact mode. A continuous determination of the local mechanical properties at all lengths was accomplished by applying force along the length of the cantilevers. The result show a decrease of the Young’s modulus as the cantilevers get thinner.
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68.37.Ps Atomic force microscopy (AFM)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Multiple layer local oxidation for fabricating semiconductor nanostructures

M. Sigrist, A. Fuhrer, T. Ihn, K. Ensslin, D. C. Driscoll, and A. C. Gossard

Appl. Phys. Lett. 85, 3558 (2004); http://dx.doi.org/10.1063/1.1809273 (3 pages) | Cited 2 times

Online Publication Date: 22 October 2004

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Coupled semiconductor nanostructures with a high degree of tunability are fabricated using local oxidation with a scanning force microscope. Direct oxidation of the GaAs surface of a Ga[Al]As heterostructure containing a shallow two-dimensional electron gas is combined with the local oxidation of a thin titanium film evaporated on top. A four-terminal quantum dot and a double quantum dot system with integrated charge readout are realized. The structures are tunable via in-plane gates formed by isolated regions in the electron gas and by mutually isolated regions of the Ti film acting as top gates. Coulomb blockade experiments demonstrate the high quality of this fabrication process.
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81.07.Ta Quantum dots
81.16.Nd Micro- and nanolithography
68.65.Hb Quantum dots (patterned in quantum wells)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.65.Mq Oxidation
68.37.Ps Atomic force microscopy (AFM)
73.23.Hk Coulomb blockade; single-electron tunneling

Bond length contraction in Au nanocrystals formed by ion implantation into thin SiO2

P. Kluth, B. Johannessen, V. Giraud, A. Cheung, C. J. Glover, G. de M. Azevedo, G. J. Foran, and M. C. Ridgway

Appl. Phys. Lett. 85, 3561 (2004); http://dx.doi.org/10.1063/1.1803619 (3 pages) | Cited 18 times

Online Publication Date: 22 October 2004

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Au nanocrystals (NCs) fabricated by ion implantation into thin SiO2 and annealing were investigated by means of extended x-ray absorption fine structure (EXAFS) spectroscopy and transmission electron microscopy. A bond length contraction was observed and can be explained by surface tension effects in a simple liquid-drop model. Such results are consistent with previous reports on nonembedded NCs implying a negligible influence of the SiO2 matrix. Cumulant analysis of the EXAFS data suggests surface reconstruction or relaxation involving a further shortened bond length. A deviation from the octahedral closed shell structure is apparent for NCs of size 25 math.
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81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
78.70.Dm X-ray absorption spectra
61.80.Jh Ion radiation effects
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.up Other materials

Formation of highly transmissive liquid metal contacts to carbon nanotubes

Mehdi M. Yazdanpanah, S. Chakraborty, S. A. Harfenist, R. W. Cohn, and B. W. Alphenaar

Appl. Phys. Lett. 85, 3564 (2004); http://dx.doi.org/10.1063/1.1807946 (3 pages) | Cited 5 times

Online Publication Date: 22 October 2004

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We have developed a method to produce liquid metal contacts to carbon nanotubes that allows direct measurement of the influence of the contact on the nanotube conductance. Gallium is deposited onto standard gold nanotube contacts, where it gradually spreads to coat the contact region. The two-terminal multiwall nanotube conductance increases by as much as 1.2e2∕h during the transition from gold to gallium contacts, and approaches 2e2∕h at room temperature, with a current density of 2×108 A∕cm2. Surprisingly, the conductance is independent of the contact area or contact separation, providing evidence that transport is ballistic in multiwall nanotubes.
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85.35.Kt Nanotube devices
73.40.Ns Metal-nonmetal contacts
73.63.Rt Nanoscale contacts
73.23.Ad Ballistic transport

Negative capacitance in polymer-nanocrystal composites

L. Bakueva, G. Konstantatos, S. Musikhin, H. E. Ruda, and A. Shik

Appl. Phys. Lett. 85, 3567 (2004); http://dx.doi.org/10.1063/1.1807947 (3 pages) | Cited 11 times

Online Publication Date: 22 October 2004

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The effect of negative capacitance (NC) was observed and investigated in conducting polymers with embedded PbS nanocrystals. NC occurred for signal frequencies up to 1 MHz and was absent in control samples without nanocrystals. The amplitude of NC increased with the applied bias and was accompanied by a superlinear current–voltage characteristic. A theoretical description of NC is presented based on a voltage-induced redistribution of carriers in a nonuniform sample with nanocrystals playing the role of potential wells for carriers. The characteristic time of carrier capture by nanocrystals, determined from the frequency dispersion of NC, was ∼3×10−5 s.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Ph Polymers; organic compounds
72.80.Tm Composite materials

Self-assembly of Ag∕SiOx spherules in triangular pattern on strained surface of primary particles

X. N. Zhang, C. R. Li, Z. Zhang, and Z. X. Cao

Appl. Phys. Lett. 85, 3570 (2004); http://dx.doi.org/10.1063/1.1807953 (2 pages) | Cited 6 times

Online Publication Date: 22 October 2004

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Spontaneous emergence of nanoscaled structures provides a potential alternative to the conventional bottom-up and top-down fabrication techniques. By a two-step thermal evaporation of mixed Ag2O and SiO2 powder onto sapphire substrate, concentric Ag∕SiOx spherules were assembled into a triangular pattern upon cooling on the spherical surface of large particles, which, of generally a few microns in dimension, were primarily grown with the substrate held at 1270 K. The occasional presence of pentagon or heptagon defect, as required by the spherical geometry of the primary particle, was also recognized. Strain field in the oxide shell arising from expansion mismatch with the silver core seeds the subsequent nucleation events. The triangular pattern of the secondary nanoparticles can be accounted for with a minimized strain energy in the spherical surface. The self-assembled structure of striking uniformity is promising for the generation of a large family of building blocks for device production.
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81.07.Wx Nanopowders
81.16.Dn Self-assembly
61.46.-w Structure of nanoscale materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Third-order optical nonlinearities of carbon nanotubes in the femtosecond regime

J-S. Lauret, C. Voisin, G. Cassabois, J. Tignon, C. Delalande, Ph. Roussignol, O. Jost, and L. Capes

Appl. Phys. Lett. 85, 3572 (2004); http://dx.doi.org/10.1063/1.1808226 (3 pages) | Cited 21 times

Online Publication Date: 22 October 2004

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Femtosecond pump–probe experiments have been carried out on an ensemble of single-wall carbon nanotubes deposited on a glass substrate. Measurements of transient changes of transmission and reflection provide an estimate of the real and imaginary parts of the second-order hyperpolarizability of carbon nanotubes. These values are compared with previous measurements and are discussed in the light of a simple model of the optical nonlinearities near the optical band-gap.
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81.07.De Nanotubes
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.An Optical susceptibility, hyperpolarizability
78.47.-p Spectroscopy of solid state dynamics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Quantitative force measurements in liquid using frequency modulation atomic force microscopy

Takayuki Uchihashi, Michael J. Higgins, Satoshi Yasuda, Suzanne P. Jarvis, Seiji Akita, Yoshikazu Nakayama, and John E. Sader

Appl. Phys. Lett. 85, 3575 (2004); http://dx.doi.org/10.1063/1.1803932 (3 pages) | Cited 15 times

Online Publication Date: 22 October 2004

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The measurement of short-range forces with the atomic force microscope (AFM) typically requires implementation of dynamic techniques to maintain sensitivity and stability. While frequency modulation atomic force microscopy (FM-AFM) is used widely for high-resolution imaging and quantitative force measurements in vacuum, quantitative force measurements using FM-AFM in liquids have proven elusive. Here we demonstrate that the formalism derived for operation in vacuum can also be used in liquids, provided certain modifications are implemented. To facilitate comparison with previous measurements taken using surface forces apparatus, we choose a model system (octamethylcyclotetrasiloxane) that is known to exhibit short-ranged structural ordering when confined between two surfaces. Force measurements obtained are found to be in excellent agreement with previously reported results. This study therefore establishes FM-AFM as a powerful tool for the quantitative measurement of forces in liquid.
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68.15.+e Liquid thin films
68.37.Ps Atomic force microscopy (AFM)

Gallium diffusion into self-assembled InAs quantum dots grown on indium phosphide substrates

T. Raz, N. Shuall, G. Bahir, D. Ritter, D. Gershoni, and S. N. G. Chu

Appl. Phys. Lett. 85, 3578 (2004); http://dx.doi.org/10.1063/1.1806277 (3 pages) | Cited 7 times

Online Publication Date: 22 October 2004

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The photoluminescence spectrum of small self-assembled In(Ga)As quantum dots grown on InP substrates is composed of distinct spectral lines. These lines correspond to monolayer variations in the dots smallest dimension: their heights. We use this phenomenon in order to study the diffusion of gallium atoms into the self-assembled quantum dots. We demonstrate that substantial amounts of gallium atoms diffuse from a strained GaInP layer underneath the quantum dots into the quantum dots.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Three-dimensional mapping of the strain anisotropy in self-assembled quantum-wires by grazing incidence x-ray diffraction

H. R. Gutiérrez, R. Magalhães-Paniago, J. R. R. Bortoleto, and M. A. Cotta

Appl. Phys. Lett. 85, 3581 (2004); http://dx.doi.org/10.1063/1.1808493 (3 pages) | Cited 11 times

Online Publication Date: 22 October 2004

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Three-dimensional strain mapping of InAs self-assembled nanowires on an InP substrate using grazing incidence x-ray diffraction is reported. A remarkable anisotropy was observed for the strain components, parallel [−220] and perpendicular [220] to the wire axis. The highest strain relaxation was measured along the [220] direction. The relationship between the interatomic distances along the [−220] and [220] directions, for each z position (height) in the nanostructure, was obtained by angular scans in the vicinity of the (040) reciprocal lattice point.
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61.46.-w Structure of nanoscale materials
68.65.La Quantum wires (patterned in quantum wells)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Inhomogeneous electronic structure of copper phthalocyanine film measured with microspot photoemission spectroscopy

T. Munakata, T. Sugiyama, T. Masuda, M. Aida, and N. Ueno

Appl. Phys. Lett. 85, 3584 (2004); http://dx.doi.org/10.1063/1.1808494 (3 pages) | Cited 15 times

Online Publication Date: 22 October 2004

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We have applied photoemission microspectroscopy to copper phthalocyanine film grown on a polycrystalline copper with a lateral resolution of 0.3 μm and an energy resolution of 30 meV. The photoemission band due to the highest occupied molecular orbital peaked at the binding energy of either 1.6 or 1.2 eV depending on the sample positions, while the work functions were 4.3 and 4.5 eV for the respective positions. The band was intense when the binding energy was low. The results demonstrate that a large inhomogeneity exists in the interface electronic structure.
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79.60.Fr Polymers; organic compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.At Surface states, band structure, electron density of states
71.20.Rv Polymers and organic compounds

A controllable nanomechanical memory element

Robert L. Badzey, Guiti Zolfagharkhani, Alexei Gaidarzhy, and Pritiraj Mohanty

Appl. Phys. Lett. 85, 3587 (2004); http://dx.doi.org/10.1063/1.1808507 (3 pages) | Cited 45 times

Online Publication Date: 22 October 2004

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We report the realization of a completely controllable high-speed nanomechanical memory element fabricated from single-crystal silicon wafers. This element consists of a doubly clamped suspended nanomechanical beam structure, which can be made to switch controllably between two stable and distinct states at a single frequency in the megahertz range. Because of their submicron size and high normal-mode frequencies, these nanomechanical memory elements offer the potential to rival the current state-of-the-art electronic data storage and processing.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.30.Sk Pulse and digital circuits

Photodegradation of porous silicon induced by photogenerated singlet oxygen molecules

D. Kovalev, E. Gross, J. Diener, V. Yu. Timoshenko, and M. Fujii

Appl. Phys. Lett. 85, 3590 (2004); http://dx.doi.org/10.1063/1.1804241 (3 pages) | Cited 17 times

Online Publication Date: 22 October 2004

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We report on the mechanism of photodegradation of porous silicon luminescence in ambient containing molecular oxygen. Energy transfer from excitons confined in silicon nanocrystallites to molecular oxygen results in the generation of highly chemically reactive singlet oxygen molecules. The subsequent interaction of singlet oxygen molecules with the hydrogenated surface of silicon nanocrystals results in its photooxidation and the creation of additional nonradiative defects, i.e., the luminescence fatigue effect.
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78.55.Mb Porous materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
81.05.Rm Porous materials; granular materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
81.65.Mq Oxidation

Si∕ZnS and Si∕ZnSe core/shell nanocrystal structures

J. Q. Hu, Y. Bando, J. H. Zhan, and D. Golberg

Appl. Phys. Lett. 85, 3593 (2004); http://dx.doi.org/10.1063/1.1808472 (3 pages) | Cited 7 times

Online Publication Date: 22 October 2004

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We report on the synthesis of the Si∕ZnS and Si∕ZnSe core/shell nanocrystal structures produced via a two-stage thermal evaporation of SiO and ZnS or SiO and ZnSe powder mixtures. These core/shell structures display spherical and elliptical polycrystalline particles. Most of the Si∕ZnS core/shell nanocrystal structures have diameters of ∼90–160 nm; the diameters of the cores and the thicknesses of the shells vary in a range of ∼50–100 nm. The diameters of the Si∕ZnSe core/shell nanocrystal structures range from ∼150 to ∼200 nm; the thicknesses of the shells are rather uniform, ∼30 nm, and the diameters of the cores are thus in the range of ∼120–170 nm. Room-temperature photoluminescence was also investigated from as-synthesized Si/ZnS and Si/ZnSe core/shell nanocrystal structures, respectively.
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81.05.Dz II-VI semiconductors
81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
78.55.Ap Elemental semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Self-consistent simulation of quantum shot noise in nanoscale electron devices

X. Oriols, A. Trois, and G. Blouin

Appl. Phys. Lett. 85, 3596 (2004); http://dx.doi.org/10.1063/1.1806546 (3 pages)

Online Publication Date: 22 October 2004

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An approach for studying shot noise in mesoscopic systems that explicitly includes the Coulomb interaction among electrons, by self-consistently solving the Poisson equation, is presented. As a test, current fluctuations on a standard resonant tunneling diode are simulated in agreement with previous predictions and experimental results. The present approach opens a new path for the simulation of nanoscale electron devices, where pure quantum mechanical and Coulomb blockade phenomena coexist.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.35.Ds Quantum interference devices
73.23.Hk Coulomb blockade; single-electron tunneling
72.70.+m Noise processes and phenomena
85.30.De Semiconductor-device characterization, design, and modeling

Metal heterowaveguides for nanometric focusing of light

Bing Wang and Guo Ping Wang

Appl. Phys. Lett. 85, 3599 (2004); http://dx.doi.org/10.1063/1.1807020 (3 pages) | Cited 47 times

Online Publication Date: 22 October 2004

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Based on the different propagation characteristics of surface plasmon polaritons (SPPs) excited on different metallic surfaces and on the tendency of SPPs to the region in which SPPs possess lower phase velocity, we design a kind of metal heterowaveguide for nanometric focusing of light. Finite-difference time-domain simulations demonstrate that, by converting light into SPPs, such heterowaveguides constructed with both Ag and Al can focus incident light into about a 20 nm×30 nm (λ∕27×λ∕18≈0.002λ2) domain with higher than 15% coupling efficiency.
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42.79.Gn Optical waveguides and couplers
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.68.+m Optical properties of surfaces
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