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10 Jul 2006

Volume 89, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 023901 (2006); http://dx.doi.org/10.1063/1.2219984 (3 pages)

Nikhil Ganesh, Ian D. Block, and Brian T. Cunningham
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Pressure effects on grain boundary plasticity in nanophase metals

E. M. Bringa, A. Caro, and E. Leveugle

Appl. Phys. Lett. 89, 023101 (2006); http://dx.doi.org/10.1063/1.2217188 (3 pages) | Cited 4 times

Online Publication Date: 10 July 2006

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Grain boundary sliding is often the picture that explains computer simulation results and experiments on plasticity of nanophase materials. Using atomistic computer simulations we perform a detailed study of the effects of high hydrostatic pressure on nanophase Cu plasticity and find that it can be understood in terms of pressure dependent grain boundary sliding controlled by a Mohr-Coulomb law. This result explains recent findings on pressure-induced ultrahigh strength observed in computer simulations of shocks in nanophase Cu reported by Bringa et al. [Science 309, 1838 (2005) ].
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62.25.-g Mechanical properties of nanoscale systems
81.40.Lm Deformation, plasticity, and creep
81.40.Vw Pressure treatment
62.50.-p High-pressure effects in solids and liquids
62.20.F- Deformation and plasticity
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Lithium doping of pentacene for electrochemical hydrogen storage

Baizeng Fang, Haoshen Zhou, and Itaru Honma

Appl. Phys. Lett. 89, 023102 (2006); http://dx.doi.org/10.1063/1.2221386 (3 pages) | Cited 8 times

Online Publication Date: 10 July 2006

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This study reports in detail the practical realization of electrochemical hydrogen storage in porous metal-incorporated nanostructured organic compounds, Li-doped pentacene, which has been synthesized by potentiostatic electrolysis and characterized by x-ray diffraction, Fourier transform infrared spectra analysis, and galvanostatic current charge-discharge measurements. Although the lithium doping is at a very low level the conductivity of pentacene increases considerably after the doping, which makes the ordered layer-stacked Li-doped pentacene very promising as electrode material for electrochemical hydrogen storage, and a discharge capacity of ca. 239 mA h/g (corresponding to 0.89 wt % hydrogen storage) has been achieved for the Li-doped pentacene electrode.
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82.45.Fk Electrodes
82.45.Hk Electrolysis
84.60.Ve Energy storage systems, including capacitor banks

Enhancement of free-carrier screening due to tunneling in coupled asymmetric GaN/AlGaN quantum discs

Kwan H. Lee, Jong H. Na, Robert A. Taylor, Sam N. Yi, Stefan Birner, Young S. Park, Chang M. Park, and Tae W. Kang

Appl. Phys. Lett. 89, 023103 (2006); http://dx.doi.org/10.1063/1.2220482 (3 pages) | Cited 10 times

Online Publication Date: 11 July 2006

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We present an investigation of free-carrier screening in coupled asymmetric GaN quantum discs with embedded AlGaN barriers using time-integrated and time-resolved microphotoluminescence measurements, supported by three-dimensional multiband k∙p computational modeling. We observe that with increasing optical excitation the carrier lifetime decreases and emission energy blueshifts. This originates from the screening of built-in piezo- and pyroelectric fields in the quantum discs by photogenerated free carriers. Due to nonresonant tunneling of carriers from the smaller disk to the larger disk, free-carrier screening is enhanced in the larger disk. Computational modeling was in good agreement with the experimental results.
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78.67.Hc Quantum dots
78.47.-p Spectroscopy of solid state dynamics
73.23.Hk Coulomb blockade; single-electron tunneling
73.21.La Quantum dots
73.63.Kv Quantum dots

Uniaxial-stress effects on electronic properties of silicon carbide nanowires

Binghai Yan, Gang Zhou, Wenhui Duan, Jian Wu, and Bing-Lin Gu

Appl. Phys. Lett. 89, 023104 (2006); http://dx.doi.org/10.1063/1.2221388 (3 pages) | Cited 17 times

Online Publication Date: 11 July 2006

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First-principles calculations are performed to study the mechanical properties, electronic structure, and uniaxial-stress effects of β-SiC nanowires (NWs). It is found that the band gap of SiC NWs becomes larger as their diameter decreases because of the quantum confinement effect, but increases (decreases) slightly with increasing tensile (compressive) stress up to about 12 GPa. The calculated Young’s modulus and tensile strength of SiC NWs are about 620 and 52 GPa, respectively, in accordance with the experimental data. The characteristics of their mechanical and electronic properties suggest that β-SiC NWs may be used in electronic composites as reinforcement nanomaterials or in nanoscale electronic/photoelectric devices under harsh environments.
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73.22.-f Electronic structure of nanoscale materials and related systems
62.25.-g Mechanical properties of nanoscale systems
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.F- Deformation and plasticity

Error signal artifact in apertureless scanning near-field optical microscopy

L. Billot, M. Lamy de la Chapelle, D. Barchiesi, S.-H. Chang, S. K. Gray, J. A. Rogers, A. Bouhelier, P.-M. Adam, J.-L. Bijeon, G. P. Wiederrecht, R. Bachelot, and P. Royer

Appl. Phys. Lett. 89, 023105 (2006); http://dx.doi.org/10.1063/1.2219134 (3 pages) | Cited 11 times

Online Publication Date: 12 July 2006

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Apertureless scanning near-field optical microscopy is a method for obtaining subwavelength optical images of nanostructures. However, great care must be taken to avoid artifactual images. We report on one artifact related to the error signal in cantilever vibration amplitude when operating in tapping mode atomic force microscopy. The artifact is described experimentally and modeled by electromagnetic calculations based on the finite element method. We report specific steps to identify and avoid this artifact with experimental results on gold nanostructures. It is suggested that future apertureless scanning near-field optical microscopy studies verify that optical image does not correlate with error signal.
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07.79.Fc Near-field scanning optical microscopes
68.37.Uv Near-field scanning microscopy and spectroscopy

Stark-shift microscopy of single emitters

S. Karotke, A. Lieb, and B. Hecht

Appl. Phys. Lett. 89, 023106 (2006); http://dx.doi.org/10.1063/1.2219137 (3 pages) | Cited 1 time

Online Publication Date: 12 July 2006

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We study the interaction of a biased, metallized tip in close proximity to single fluorescent molecules at cryogenic temperature. By scanning over the sample, the tip’s inhomogeneous electric field induces Stark shifts of the zero-phonon lines of nearby molecules. When illuminated with an off-resonant laser, molecules are tuned into resonance for specific tip positions located on circular patterns around the molecules’ spatial positions. The origins of circles belonging to different molecules can be determined with high precision. We demonstrate a spatial resolution of neighboring individual molecules of ∼ 50 nm using a tip scanned in a distance of ∼ 3 μm above the sample.
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33.57.+c Magneto-optical and electro-optical spectra and effects
07.60.Pb Conventional optical microscopes
33.50.Dq Fluorescence and phosphorescence spectra
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

La0.7Sr0.3MnO3 nanoparticles coated with fatty amine

Rajashree Rajagopal, J. Mona, S. N. Kale, Tanushree Bala, Renu Pasricha, P. Poddar, M. Sastry, B. L. V. Prasad, Darshan C. Kundaliya, and S. B. Ogale

Appl. Phys. Lett. 89, 023107 (2006); http://dx.doi.org/10.1063/1.2210080 (3 pages) | Cited 12 times

Online Publication Date: 12 July 2006

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We report on the synthesis of La0.7Sr0.3MnO3 (LSMO) nanoparticles having perovskite structure and particle size of the order of 30 nm. The process involves citrate-gel synthesis, size filtering, and surface coating with a shell of octadecyl amine (ODA) using electrostatic interaction-assisted novel chemical route. Magnetic measurements show the Curie temperature of ∼ 360 K establishing the desired stoichiometry and phase. Fourier transform infrared studies bring out that the amine group of ODA interacts with the LSMO surface. Refluidization yields uniform redispersion of the coated and dried powder.
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75.50.Tt Fine-particle systems; nanocrystalline materials
81.16.Be Chemical synthesis methods
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.30.-j Infrared and Raman spectra

Enhanced voltage-current characteristics of GaN nanowires treated by a selective reactive ion etching

D. Y. Jeon, K. H. Kim, S. J. Park, J. H. Huh, H. Y. Kim, C. Y. Yim, and G. T. Kim

Appl. Phys. Lett. 89, 023108 (2006); http://dx.doi.org/10.1063/1.2220538 (3 pages) | Cited 3 times

Online Publication Date: 12 July 2006

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In characterizing the electrical properties of individual NWs (nanowires), the amorphous oxide layer on the surface of NWs is known to limit the electrical conductivity owing to the contact barriers between metal electrodes and NWs. To remove the native oxide layer, a systematic reactive ion etching (RIE) was performed, resulting in a gradual decrease of the diameters of NWs. Voltage-current characteristics of the GaN NW devices treated by tuning the RIE process were improved as reflected by a 1000 times increase in conductance, which was in turn attributed to the removal of the thick (d ∼ 3.5 nm) contact barrier formed by the native oxide layer.
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81.07.Bc Nanocrystalline materials
81.05.Ea III-V semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
81.65.Cf Surface cleaning, etching, patterning
73.63.Bd Nanocrystalline materials
73.40.Ns Metal-nonmetal contacts

Combinatorial-mold imprint lithography: A versatile technique for fabrication of three-dimensional polymer structures

Hong Yee Low, Wei Zhao, and Jarrett Dumond

Appl. Phys. Lett. 89, 023109 (2006); http://dx.doi.org/10.1063/1.2219148 (3 pages) | Cited 2 times

Online Publication Date: 12 July 2006

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A two-step fabrication technique based on nanoimprint lithography is described for the fabrication of three-dimensional micro- and nanostructures. By combining simple two-dimensional geometries from two molds, complex and useful three-dimensional structures are obtained. The careful selection of mold geometries constitutes a simplified and efficient approach toward building up desirable three-dimensional structures without resorting to the use of a sacrificial process or components. Three-dimensional structures fabricated for a variety of specific applications are presented using both thermoplastic and cross-linked polymer materials.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.16.Nd Micro- and nanolithography
68.55.A- Nucleation and growth
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
81.10.Fq Growth from melts; zone melting and refining

Tuning the optical absorption properties of Ag nanorods by their topologic shapes: A discrete dipole approximation calculation

Z.-Y. Zhang and Y.-P. Zhao

Appl. Phys. Lett. 89, 023110 (2006); http://dx.doi.org/10.1063/1.2221403 (3 pages) | Cited 18 times

Online Publication Date: 12 July 2006

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The optical extinction spectra of four topologically different Ag nanorod structures, needle, periodic, L, and Y shapes, have been calculated by the discrete dipole approximation. Both the needle and periodic shaped nanorods can be used to effectively tune plasmon resonant peaks, while the L- and Y-shaped nanorods influence the shape of the extinction spectra. This study shows that the topologic defects of nanorods have significant effects on the optical properties, and provides an alternative way to tune the plasmonic characteristics of metallic nanorods.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
61.46.-w Structure of nanoscale materials
78.40.Kc Metals, semimetals, and alloys
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Si-based Coulomb blockade device for spin qubit logic gate

S. D. Lee, S. J. Shin, S. J. Choi, J. J. Lee, J. B. Choi, S. Park, S.-R. Eric Yang, S. J. Lee, and T. H. Zyung

Appl. Phys. Lett. 89, 023111 (2006); http://dx.doi.org/10.1063/1.2221513 (3 pages) | Cited 5 times

Online Publication Date: 12 July 2006

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A lateral gate-controlled double dot structure in Si has been fabricated for studying coupled two qubits. Nonequilibrium single-electron tunneling measurements at 1.4 K show that the second Coulomb peak, associated with a two-electron occupation, splits into two side peaks, and that their separation displays a strong magnetic-field dependence for various interdot coupling constants. Moreover, for some fixed magnetic fields, the separation of the side peaks decays exponentially as a function of the interdot coupling. We attribute this behavior to electron spin exchange and spin swapping between singlet and triplet states in the coupled double dot in the presence of a magnetic field.
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85.35.Ds Quantum interference devices
85.35.Gv Single electron devices

Electron holography for improved measurement of microfields in nanoelectrode assemblies

Li-Jen Chou, Mu-Tung Chang, Yu-Lun Chueh, Joong Jung Kim, Hyun Soon Park, and Daisuke Shindo

Appl. Phys. Lett. 89, 023112 (2006); http://dx.doi.org/10.1063/1.2221748 (3 pages) | Cited 3 times

Online Publication Date: 13 July 2006

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An approach to investigate the electric field distribution and field-emission property of a single crystal tungsten oxide (WO3) nanowire by electron holography technique is presented, which solves the problems encountered in the traditional reconstruction of the holograms, the so-called perturbed reference wave. We proposed this unique method to meticulously illustrate the status of the surroundings of a single crystal nanowire under biased conditions. This paves the way to precisely quantifying the electric and magnetic field distributions for nanostructures as well as nanodevices.
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42.40.Kw Holographic interferometry; other holographic techniques
41.85.-p Beam optics
79.70.+q Field emission, ionization, evaporation, and desorption

Mechanical atom manipulation with small amplitude dynamic force microscopy

Shigeki Kawai and Hideki Kawakatsu

Appl. Phys. Lett. 89, 023113 (2006); http://dx.doi.org/10.1063/1.2220539 (3 pages) | Cited 4 times

Online Publication Date: 13 July 2006

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We demonstrate atom manipulations of the Si(111)-(7×7) surface with small amplitude dynamic force microscopy at room temperature. Adatoms could not only be extracted and attached but also laterally manipulated in and over the half unit cell with a repulsive interaction force caused between the tip and the sample. In the case of a tip condition that gave a strong image contrast, an adatom beside a vacancy could be pulled to the neighboring stable site with a strong attractive force. Enhanced detection sensitivity due to the small amplitude of 4 Å could avoid accidental modifications of the surface during imaging.
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81.05.Cy Elemental semiconductors
81.16.Ta Atom manipulation
68.47.Fg Semiconductor surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)

High-density InGaN nanodots grown on pretreated GaN surfaces

P. Chen, S. J. Chua, and J. N. Tan

Appl. Phys. Lett. 89, 023114 (2006); http://dx.doi.org/10.1063/1.2218312 (3 pages) | Cited 2 times

Online Publication Date: 13 July 2006

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High-density InGaN nanodots are successfully grown on pretreated GaN surfaces. The GaN surfaces were covered by SiO2 layers firstly, and then the SiO2 layers were removed before the growth of InGaN on the GaN. After this process, the growth of InGaN on the GaN surfaces changed to a three-dimensional mode. However, on the GaN surface without the SiO2 treatment, the growth of InGaN maintained a two-dimensional growth mode as usual. The InGaN nanodots are 26 to 68 nm in diameter, 3.6–15 nm in height, and up to 9×1010 cm−2 in density, which can be controlled by growth duration and substrate temperature. Comparing with the InGaN thin film grown on untreated GaN surface with the same growth conditions, the InGaN nanodots showed stronger photoluminescence in longer wavelength range at room temperature. The formation mechanism of the nanodots is described based on the GaN surface states changed by SiO2 coverage. This approach enables fabrication of dense and controllable InGaN nanodots.
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81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
78.55.Cr III-V semiconductors
73.20.At Surface states, band structure, electron density of states
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Atomic force microscopy and x-ray photoelectron spectroscopy studies of ZnO nanoparticles on SiO2 fabricated by ion implantation and thermal oxidation

H. Amekura, O. A. Plaksin, M. Yoshitake, Y. Takeda, N. Kishimoto, and Ch. Buchal

Appl. Phys. Lett. 89, 023115 (2006); http://dx.doi.org/10.1063/1.2221507 (3 pages) | Cited 7 times

Online Publication Date: 13 July 2006

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The morphology and chemical composition of the surface of SiO2 that had been implanted with Zn ions of 60 keV and annealed in two different atmospheres, i.e., oxygen gas and a vacuum, were compared. In the as-implanted state, the surface mainly consisted of SiO2 with low roughness due to radiation-induced smoothing. A large number of domelike structures of ZnO appeared on the surface of the SiO2 after annealing in oxygen gas at 600 °C for 1 h, and the size increased with the annealing temperature up to 800 °C. After annealing at 900 °C, the surface roughness steeply decreased and the composition changed to Zn2SiO4.
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81.07.Bc Nanocrystalline materials
81.05.Dz II-VI semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
68.37.Ps Atomic force microscopy (AFM)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.47.Fg Semiconductor surfaces

Local silicon-gate carbon nanotube field effect transistors using silicon-on-insulator technology

Min Zhang, Philip C. H. Chan, Yang Chai, Qi Liang, and Z. K. Tang

Appl. Phys. Lett. 89, 023116 (2006); http://dx.doi.org/10.1063/1.2221515 (3 pages) | Cited 9 times

Online Publication Date: 13 July 2006

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A local silicon-gate carbon nanotube field effect transistor (CNFET) configuration has been proposed and implemented for integration purpose. By combining the advantages of in situ carbon nanotube growth technology and the silicon-on-insulator technology, we have realized the CNFETs with individual device operation, low parasitic capacitance, high yield fabrication, and better compatibility to the complementary-metal-oxide-semiconductor (CMOS) process. The CNFETs show up-to-date electrical performance. The scaling effect of gate oxide is also explored. This configuration makes CNFET a step closer to the CMOS integrated circuit application.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices

Heat conduction in graphite-nanoplatelet-reinforced polymer nanocomposites

M.-T. Hung, O. Choi, Y. S. Ju, and H. T. Hahn

Appl. Phys. Lett. 89, 023117 (2006); http://dx.doi.org/10.1063/1.2221874 (3 pages) | Cited 28 times

Online Publication Date: 14 July 2006

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Heat transport in polymer nanocomposites reinforced with graphite nanoplatelets (GNPs) is studied using high-precision thermal conductivity measurements. The resistance to heat conduction across interfaces between GNPs and the polymer matrix has a strong effect on energy transport in the nanocomposites. The thermal conductivity is observed to increase when GNPs are pretreated with nitric acid to improve interfacial bonding. The improvement in the thermal conductivity, however, is much smaller than the corresponding improvement in mechanical properties. The thermal interface resistance extracted from the present thermal conductivity data is comparable to that obtained from the previously reported data on carbon nanotube suspensions.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
81.05.Qk Reinforced polymers and polymer-based composites

Field emission study of SiC nanowires/nanorods directly grown on SiC ceramic substrate

S. Z. Deng, Z. B. Li, W. L. Wang, N. S. Xu, Jun Zhou, X. G. Zheng, H. T. Xu, Jun Chen, and J. C. She

Appl. Phys. Lett. 89, 023118 (2006); http://dx.doi.org/10.1063/1.2220481 (3 pages) | Cited 25 times

Online Publication Date: 14 July 2006

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Single crystalline silicon carbide (SiC) nanowires were grown directly on the surface of bulk SiC ceramic substrate in a catalyst-assisted thermal heating process. The morphology of the nanowire film and the diameter of nanowires were found to be sensitive to the thickness of catalyst film and both of them had a strong effect on field emission performance. Very low turn-on and threshold fields for electron emission were observed with SiC nanowires of small diameter. A model is proposed to qualitatively explain the field emission findings, which assumes the occurrence of an insulator-to-metal-like transition in a field emitting nanowire.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials
81.40.Gh Other heat and thermomechanical treatments
81.16.-c Methods of micro- and nanofabrication and processing
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.07.-b Nanoscale materials and structures: fabrication and characterization

Capping of InAs quantum dots grown on (311)B InP studied by cross-sectional scanning tunneling microscopy

C. Çelebi, J. M. Ulloa, P. M. Koenraad, A. Simon, A. Letoublon, and N. Bertru

Appl. Phys. Lett. 89, 023119 (2006); http://dx.doi.org/10.1063/1.2221884 (3 pages) | Cited 10 times

Online Publication Date: 14 July 2006

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Cross-sectional scanning tunneling microscopy was used to study at the atomic scale the impact of the capping material on the structural properties of self-assembled InAs quantum dots (QDs) grown on a high index (311)B InP substrate. Important differences were found in the capping process when InP or lattice matched InGaAs(P) alloys are used. The QDs capped with InP have a smaller height due to As/P exchange induced decomposition. This effect is not present when InGaAs is used as the capping material. However, in this case a strong strain driven phase separation appears, creating In rich regions above the QDs and degrading the dot/capping layer interface. If the InAs dots are capped by the quaternary alloy InGaAsP the phase separation is much weaker as compared to capping with InGaAs and well defined interfaces are obtained.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
68.55.A- Nucleation and growth
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.Ct Interface structure and roughness

Gold nanorods grown from HgTe nanoparticles directly on various surfaces

S. I. Shopova, C. W. Blackledge, A. T. Rosenberger, and N. F. Materer

Appl. Phys. Lett. 89, 023120 (2006); http://dx.doi.org/10.1063/1.2221889 (3 pages) | Cited 6 times

Online Publication Date: 14 July 2006

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Gold nanorods (NRs) are nucleated by HgTe semiconductor nanoparticles. Growth of ∼ 200×50 nm2 NRs directly on various surfaces is achieved by using an intermediary polyelectrolyte layer. X-ray photoelectron spectroscopy confirms the deposition of gold. An increase in the intensity of the Au NR plasmon resonance is observed with optical extinction spectroscopy. This seeding technique, amenable to many different surfaces, suggests a simple synthetic route to composite materials with interesting electronic and optical properties.
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81.16.-c Methods of micro- and nanofabrication and processing
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
82.45.Gj Electrolytes
82.45.Wx Polymers and organic materials in electrochemistry
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Scanning transmission electron microscope study on vertically correlated InGaAs/GaAs quantum dots

A. Sauerwald, T. Kümmell, D. Peskes, G. Bacher, A. Löffler, J. P. Reithmaier, and A. Forchel

Appl. Phys. Lett. 89, 023121 (2006); http://dx.doi.org/10.1063/1.2221890 (3 pages) | Cited 2 times

Online Publication Date: 14 July 2006

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Vertically stacked self-organized InGaAs/GaAs quantum dots have been investigated by chemically sensitive scanning transmission electron microscopy combined with electron energy loss spectroscopy. While the probability of a laterally correlated growth is strongly enhanced with decreasing spacer layer thickness, no measurable variation of both the size and the average In alloy concentration of the quantum dots within the stacks is found, making the structures ideally suited for potential applications in quantum information processing.
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68.65.Hb Quantum dots (patterned in quantum wells)
68.37.Lp Transmission electron microscopy (TEM)

Self-assembled ZnO quantum dots with tunable optical properties

J. G. Lu, Z. Z. Ye, Y. Z. Zhang, Q. L. Liang, Sz. Fujita, and Z. L. Wang

Appl. Phys. Lett. 89, 023122 (2006); http://dx.doi.org/10.1063/1.2221892 (3 pages) | Cited 26 times

Online Publication Date: 14 July 2006

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Self-assembled ZnO quantum dots (QDs) were achieved by a vapor phase transport process. ZnO nanodots were naturally formed on solid substrates in the Volmer-Weber growth mode. Size control of nanodots could be readily realized by varying the growth time. The as-prepared ZnO QDs are of high quality and very stable after formation. The blueshift of band gap energies derived from quantum confinement effects was confirmed by optical absorption spectra. Photoluminescence spectra revealed the tunable behavior of ultraviolet luminescence due to exciton localization. The realization of size-tuned color from ZnO QDs makes them more promising for practical applications.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.67.Hc Quantum dots
73.21.La Quantum dots
78.55.Et II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Effects of nanoparticle clustering and alignment on thermal conductivities of Fe3O4 aqueous nanofluids

Haitao Zhu, Canying Zhang, Shiquan Liu, Yaming Tang, and Yansheng Yin

Appl. Phys. Lett. 89, 023123 (2006); http://dx.doi.org/10.1063/1.2221905 (3 pages) | Cited 13 times

Online Publication Date: 14 July 2006

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Thermal conductivities of Fe3O4 aqueous nanofluids were studied. The results show that Fe3O4 nanofluids have higher thermal conductivities than other oxide aqueous nanofluids at the same volume fraction. The experimental values are higher than those predicted by the existing models. The abnormal thermal conductivities of Fe3O4 nanofluids are attributed to the observed nanoparticle clustering and alignment.
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66.25.+g Thermal conduction in nonmetallic liquids
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Band-gap opening in metallic carbon nanotubes adsorbed on H/Si(001)

Jung-Yup Lee and Jun-Hyung Cho

Appl. Phys. Lett. 89, 023124 (2006); http://dx.doi.org/10.1063/1.2221909 (3 pages) | Cited 10 times

Online Publication Date: 14 July 2006

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A recent scanning tunneling microscope nanolithography technique can fabricate one-dimensional “dangling-bond (DB) wire” by the selective removal of H atoms from a H-passivated Si(001) surface along the Si dimer row. We here theoretically investigate the bonding geometry, band structure, and binding mechanism of an armchair (3,3) single-walled carbon nanotube (CNT) adsorbed on the DB wire. We find that the formation of C–Si bonds between the CNT and the DB wire gives rise to hybridization between the carbon π-bond states and the Si dangling-bond states. This hybridization breaks the rotational symmetry of the (3,3) CNT whose π-bonding and π-antibonding bands cross at the Fermi level. As a result, the adsorbed CNT opens an energy gap of ∼ 0.1 eV, yielding a metal-to-semiconductor transition.
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71.20.Tx Fullerenes and related materials; intercalation compounds
61.46.Fg Nanotubes
71.30.+h Metal-insulator transitions and other electronic transitions
68.43.Mn Adsorption kinetics

Ballisticity of nanotube field-effect transistors: Role of phonon energy and gate bias

Siyuranga O. Koswatta, Sayed Hasan, Mark S. Lundstrom, M. P. Anantram, and Dmitri E. Nikonov

Appl. Phys. Lett. 89, 023125 (2006); http://dx.doi.org/10.1063/1.2218322 (3 pages) | Cited 23 times

Online Publication Date: 14 July 2006

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Show Abstract
We investigate the role of electron-phonon scattering and gate bias in degrading the drive current of nanotube field-effect transistors (FETs). Optical phonon scattering significantly decreases the drive current only when gate voltage is higher than a well-defined threshold. For comparable electron-phonon coupling, a lower phonon energy leads to a larger degradation of drive current. Thus in semiconductor nanowire FETs, the drive current will be more sensitive than in carbon nanotube FETs because of the smaller phonon energies in semiconductors. Acoustic phonons and other elastic scattering mechanisms are most detrimental to nanotube FETs irrespective of biasing conditions.
Show PACS
85.35.Kt Nanotube devices
85.30.Tv Field effect devices
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