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28 May 2007

Volume 90, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 221101 (2007); http://dx.doi.org/10.1063/1.2743884 (3 pages)

Siyka I. Shopova, Hongying Zhou, Xudong Fan, and Po Zhang
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Effects of supercritical CO2 fluid on sputter-deposited hafnium oxide

Po-Tsun Liu, Chih-Tsung Tsai, and Po-Yu Yang

Appl. Phys. Lett. 90, 223101 (2007); http://dx.doi.org/10.1063/1.2743747 (3 pages) | Cited 7 times

Online Publication Date: 29 May 2007

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Low-temperature supercritical fluid (SCF) technology is employed to improve the dielectric characteristics of metal oxide film deposited at low temperature. In this investigation, hafnium oxide (HfO2) film was sputter deposited at room temperature and post-treated with SCF at 150 °C, replacing typical high-temperature annealing process. From Fourier transformation infrared and thermal desorption spectroscopy measurement, the absorption peaks of Hf–O–Hf bonding and the oxygen content in HfO2 film have, respectively, shown apparent raise. The leakage current density of the low-temperature deposited HfO2 film is reduced significantly, and the conduction mechanism is modified from trap-assisted quantum tunneling to thermionic emission process, since SCF treatment effectively reduces the number of traps in HfO2 film.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
81.40.Gh Other heat and thermomechanical treatments
68.43.Mn Adsorption kinetics
79.40.+z Thermionic emission
78.66.Nk Insulators

First-principles study on ZnO nanoclusters with hexagonal prism structures

Chun Li, Wanlin Guo, Yong Kong, and Huajian Gao

Appl. Phys. Lett. 90, 223102 (2007); http://dx.doi.org/10.1063/1.2743934 (3 pages) | Cited 13 times

Online Publication Date: 29 May 2007

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Size-dependent ground state energies and electronic structures of ZnO nanoclusters with wurtzite structures are investigated using density-functional theory calculations. After structural optimizations, the initial Zn–O double layers merge into single layers. Particularly, a phase transition from the four-coordinate wurtzite to the six-coordinate rocksalt structure is found in the ZnO cluster with 48 atoms, which indicates that clusters with too many dangling bonds will significantly change their configurations during the relaxations. The calculations also show that on the whole both the energy gap and the binding energy approach to the corresponding bulk values with increasing cluster size.
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61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
73.22.-f Electronic structure of nanoscale materials and related systems
64.70.K- Solid-solid transitions
71.55.Gs II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations

Ni–Cr alloy to enhance single- and double-walled carbon nanotube synthesis for field-effect transistor fabrication

Tsung-Yeh Yang, Wei-Chang Yang, Tzu-Chun Tseng, Chung-Min Tsai, and Tri-Rung Yew

Appl. Phys. Lett. 90, 223103 (2007); http://dx.doi.org/10.1063/1.2743946 (3 pages)

Online Publication Date: 29 May 2007

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Single- and double-walled carbon nanotubes were synthesized between predefined Ti/Ni/Cr/Ti multilayer stacks for field-effect transistor fabrication by thermal chemical vapor deposition at 900 °C. The Ni nanoprecipitates were induced from Cr matrix because of phase segregation during high temperature process of carbon nanotube growth. The Ni–Cr catalyst was shown to significantly enhance the synthesis of single- and double-walled carbon nanotubes compared to those using pure Ni catalyst, which was demonstrated by both physical and electrical characteristics of the carbon nanotube field-effect transistor fabricated.
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81.07.De Nanotubes
85.35.Kt Nanotube devices
85.30.Tv Field effect devices
64.75.-g Phase equilibria
81.16.Hc Catalytic methods
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Hydrogen adsorption by tungsten carbide nanotube

Hui Pan, Yuan Ping Feng, and Jianyi Lin

Appl. Phys. Lett. 90, 223104 (2007); http://dx.doi.org/10.1063/1.2744479 (3 pages) | Cited 12 times

Online Publication Date: 29 May 2007

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First-principles calculations based on density functional theory were carried out to investigate single-wall tungsten carbide nanotubes and their applications to energy storage, such as hydrogen storage and fuel cell. The pristine tungsten carbide nanotube was metallic. The W atop site is the most stable adsorption site for hydrogen atom, with a binding energy of 3.94 eV and a binding distance of 1.7 Å. Hydrogen molecule also favors the W atop site energetically. The calculated binding energy and distance are 0.44 eV and 1.85 Å, respectively. The authors’ studies demonstrate that the tungsten carbide nanotube could be a promising material for energy storage.
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84.60.Ve Energy storage systems, including capacitor banks
68.43.Mn Adsorption kinetics
61.46.Fg Nanotubes

Highly dispersive thermo-optical properties of gold nanoparticles

Bruno Palpant, Majid Rashidi-Huyeh, Bruno Gallas, Stéphane Chenot, and Serge Fisson

Appl. Phys. Lett. 90, 223105 (2007); http://dx.doi.org/10.1063/1.2743936 (3 pages) | Cited 9 times

Online Publication Date: 30 May 2007

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The experimental study of the effect of temperature on the complex optical response of matrix-embedded noble metal nanoparticles has been carried out. A thin silica film containing gold nanoparticles with 7% volume fraction has been elaborated. Its thermo-optical refraction and absorption coefficients have then been extracted from temperature-dependent spectroscopic ellipsometry measurements in the visible range. The results, in agreement with our theoretical approach, exhibit strong dispersion, with amplitude and sign changes due to the local electromagnetic field enhancement associated with the surface plasmon resonance in gold nanoparticles.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Polarization and plasmon effects in nanowire arrays

H. E. Ruda and A. Shik

Appl. Phys. Lett. 90, 223106 (2007); http://dx.doi.org/10.1063/1.2744481 (3 pages) | Cited 4 times

Online Publication Date: 30 May 2007

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The charge distribution and dipole moment in a system of interacting metallic nanowires in external electric field were found and used to calculate the plasmon energies governing optical properties of these nanostructures. The in-line alignment of nanowires caused a redshift of the plasmon peak while their parallel arrangement caused a blueshift. The dependence of these shifts on the separation between nanowires was calculated and compared with the recent experimental data on linear chains of Au nanorods.
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71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.-w Structure of nanoscale materials

Improvement in conductive and photovoltaic properties of layer-by-layer poly(p-phenylenevinylene) thin films by low-temperature conversion

Michihiro Ogawa, Naomi Kudo, Hideo Ohkita, Shinzaburo Ito, and Hiroaki Benten

Appl. Phys. Lett. 90, 223107 (2007); http://dx.doi.org/10.1063/1.2744484 (3 pages) | Cited 13 times

Online Publication Date: 30 May 2007

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Poly(p-phenylenevinylene) (PPV) thin films were fabricated with poly(sodium 4-styrenesulfonate) (PSS) anion by the layer-by-layer (LbL) deposition technique. A precursor PPV was thermally converted into PPV even at 100 °C in the presence of PSS. By the low-temperature conversion, the photoluminescence efficiency from the PPV/PSS LbL films increased significantly and the hole mobility was improved to 2×10−5 cm2 V−1s−1. Consequently, the power conversion efficiency of PPV/PSS LbL photovoltaic films increased by one order of magnitude compared with that converted at 220 °C.
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73.61.Ph Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance
78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds
73.50.Pz Photoconduction and photovoltaic effects

Infrared detection with silicon nano-field-effect transistors

K. Nishiguchi, Y. Ono, A. Fujiwara, H. Yamaguchi, H. Inokawa, and Y. Takahashi

Appl. Phys. Lett. 90, 223108 (2007); http://dx.doi.org/10.1063/1.2744488 (3 pages) | Cited 5 times

Online Publication Date: 30 May 2007

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The authors fabricated nanoscale silicon metal-oxide-semiconductor field-effect transistors (MOSFETs) to detect an infrared (IR) signal at room temperature. The IR signal excites conduction-band electrons in an undoped channel of a MOSFET and some of them are injected through an energy barrier into a storage node (SN) electrically formed by the MOSFET. Small signals, originating from electrons, stored in the SN are detected by an electrometer with a single-electron resolution. Additionally, the MOSFET controls the number and energy of electrons injected into the SN. This enables electrical control of the sensitivity and cutoff wavelengths of IR signals, suggesting the possibility of highly functional IR sensors.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Tv Field effect devices

Photon enhanced aggregation of single walled carbon nanotube dispersions

H. Chaturvedi and J. C. Poler

Appl. Phys. Lett. 90, 223109 (2007); http://dx.doi.org/10.1063/1.2744489 (3 pages) | Cited 2 times

Online Publication Date: 30 May 2007

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The authors describe a photon enhanced aggregation of dispersed single walled carbon nanotubes in the presence of electron transfer reagents. A recently synthesized metallodendrimer strongly and specifically binds to the ends of the nanotubes. Upon optical excitation, of the metal to ligand charge transfer absorption, of various ruthenium complexes, the nanotubes rapidly coagulate. The electron transfer mechanism is consistent with observed photon enhancement process. These results support a directed self-assembly paradigm for nanostructured materials.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.60.-s Chemical thermodynamics
61.46.Fg Nanotubes
78.67.Ch Nanotubes

Nanophotonic switch using ZnO nanorod double-quantum-well structures

Takashi Yatsui, Suguru Sangu, Tadashi Kawazoe, Motoichi Ohtsu, Sung Jin An, Jinkyoung Yoo, and Gyu-Chul Yi

Appl. Phys. Lett. 90, 223110 (2007); http://dx.doi.org/10.1063/1.2743949 (3 pages) | Cited 29 times

Online Publication Date: 30 May 2007

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The authors report on time-resolved near-field spectroscopy of ZnO/ZnMgO nanorod double-quantum-well structures (DQWs) for a nanometer-scale photonic device. They observed nutation of the population between the resonantly coupled exciton states of DQWs. Furthermore, they demonstrated switching dynamics by controlling the exciton excitation in the dipole-inactive state via an optical near field. The results of time-resolved near-field spectroscopy of isolated DQWs described here are a promising step toward designing a nanometer-scale photonic switch and related devices.
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42.82.Gw Other integrated-optical elements and systems
42.65.Pc Optical bistability, multistability, and switching, including local field effects
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Sticky superhydrophobic surface

Zhi-Guang Guo and Wei-Min Liu

Appl. Phys. Lett. 90, 223111 (2007); http://dx.doi.org/10.1063/1.2745251 (3 pages) | Cited 39 times

Online Publication Date: 31 May 2007

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The authors present a simple and inexpensive method for fabricating a stable superhydrophobic engineering material surface using aluminum alloy and a suitable aqueous solution and time to control the surface roughness, which has a large water contact angle (>150°) and a large water sliding angle (>90°). The as-prepared surface can be large-scale produced and used in industry quickly, such as a barrier material, self-cleaning material, and lubricating material. This finding will enhance further understanding of the wettability of solid surfaces with special surface morphologies.
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68.47.De Metallic surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)

I-V characteristics of single electron tunneling from symmetric and asymmetric double-barrier tunneling junctions

R. Negishi, T. Hasegawa, K. Terabe, M. Aono, H. Tanaka, T. Ogawa, and H. Ozawa

Appl. Phys. Lett. 90, 223112 (2007); http://dx.doi.org/10.1063/1.2745252 (3 pages) | Cited 14 times

Online Publication Date: 31 May 2007

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I-V characteristics of single electron tunneling from a symmetric and an asymmetric double-barrier tunneling junction (DBTJ) were examined. A single Au nanoparticle was trapped in nanogap whose size was precisely controlled using a combination of electron beam lithography and molecular ruler technique. Though the symmetric junction showed a monotonic rise with a bias beyond the Coulomb gap voltage, the asymmetric junction showed Coulomb staircases. The capacitance of the junction estimated from the fitting curves using the Coulomb conventional theory was consistent with the capacitance calculated from the observed structure. The authors quantitatively found the correlation between the electrical and structural properties of DBTJ.
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73.40.Gk Tunneling
73.40.Ns Metal-nonmetal contacts
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Giant optical gyrotropy due to electromagnetic coupling

E. Plum, V. A. Fedotov, A. S. Schwanecke, N. I. Zheludev, and Y. Chen

Appl. Phys. Lett. 90, 223113 (2007); http://dx.doi.org/10.1063/1.2745203 (3 pages) | Cited 64 times

Online Publication Date: 31 May 2007

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The authors demonstrate a chiral photonic metamaterial with chirality provided by electromagnetic coupling between mutually twisted unconnected layers. In the visible and near-IR spectral ranges, the material exhibits polarization rotatory power of up to 2500°/mm and shows relatively low losses and negligible circular dichroism, making it a promising candidate for the development of chiral negative index media.
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42.70.-a Optical materials
78.20.Ek Optical activity
78.20.Fm Birefringence
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Solvatochromism in single-walled carbon nanotubes

Jong Hyun Choi and Michael S. Strano

Appl. Phys. Lett. 90, 223114 (2007); http://dx.doi.org/10.1063/1.2745228 (3 pages) | Cited 37 times

Online Publication Date: 31 May 2007

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The optical transition energies (Eii) of single-walled carbon nanotubes (SWCNT) are influenced by the local environment created by solvents and adsorbed molecules. Analysis of SWCNT photoluminescence (PL) energies in various dielectric media is used to elucidate a semiempirical scaling relation for Eii shifts and nanotube structural properties from a classical solvatochromic formalism. The SWCNT Kataura plot is corrected for a dielectric constant of unity and used in conjunction with the scaling to accurately describe PL energy shifts in a broad range of dielectric media.
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78.67.Ch Nanotubes
61.46.Fg Nanotubes
68.43.Mn Adsorption kinetics
77.22.Ch Permittivity (dielectric function)
78.55.Hx Other solid inorganic materials
73.63.Fg Nanotubes

Elementary building blocks of graphene-nanoribbon-based electronic devices

Zhiping Xu, Quan-Shui Zheng, and Guanhua Chen

Appl. Phys. Lett. 90, 223115 (2007); http://dx.doi.org/10.1063/1.2745268 (3 pages) | Cited 39 times

Online Publication Date: 1 June 2007

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Graphene nanoribbon junction based electronic devices are proposed in this letter. Nonequilibrium Green’s function calculations show that nanoribbon junctions tailored from single layer graphene with different edge shapes and widths can act as metal/semiconductor junctions and quantum dots can be implemented. In virtue of the possibilities of patterning monolayer graphene down to atomic precision, these structures, quite different from the previously reported two-dimensional bulk graphene or carbon nanotube devices, are expected to be used as the building blocks of the future nanoelectronics.
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71.20.Tx Fullerenes and related materials; intercalation compounds
71.55.Ht Other nonmetals
72.80.Rj Fullerenes and related materials

Fabrication of high performance top-gate complementary inverter using a single carbon nanotube and via a simple process

Y. F. Hu, K. Yao, S. Wang, Z. Y. Zhang, X. L. Liang, Q. Chen, L.-M. Peng, Y. G. Yao, J. Zhang, W. W. Zhou, and Y. Li

Appl. Phys. Lett. 90, 223116 (2007); http://dx.doi.org/10.1063/1.2745646 (3 pages) | Cited 10 times

Online Publication Date: 1 June 2007

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High performance complementary inverters have been fabricated using single-walled carbon nanotubes. The Al2O3 top-gate dielectric is grown via first depositing an Al film followed by complete oxidation of the film. It is shown that the quality of the Al2O3 film can be significantly improved by annealing at 400 °C, and stable p-type and n-type carbon nanotube field-effect transistors (CNTFETs) may be fabricated using either Pd (p-type) or Al (n-type) electrodes. High performance complementary inverter is demonstrated by integrating the p-type and n-type CNTFETs on the same carbon nanotube, and a gain of about 3.5 is achieved.
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85.30.Tv Field effect devices
81.65.Mq Oxidation
85.35.Kt Nanotube devices

Contact to ZnO and intrinsic resistances of individual ZnO nanowires with a circular cross section

Yen-Fu Lin, Wen-Bin Jian, C. P. Wang, Yuen-Wuu Suen, Zhong-Yi Wu, Fu-Rong Chen, Ji-Jung Kai, and Juhn-Jong Lin

Appl. Phys. Lett. 90, 223117 (2007); http://dx.doi.org/10.1063/1.2745648 (3 pages) | Cited 18 times

Online Publication Date: 1 June 2007

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Single crystalline ZnO nanowires (NWs) with a circular cross section and ∼ 40 nm in diameter have been synthesized and utilized to fabricate two-contact ZnO NW devices. The electrical properties of the NW devices can be categorized into two classes according to the magnitude of their room-temperature resistances. I-V curves of low-resistance devices exhibit downward bending features and their temperature dependent resistances demonstrate thermal activation transport in the ZnO NWs. The high-resistance NW devices can be modeled as back-to-back Schottky contacts and the electron transport through the contacts reveals a variable-range-hopping mechanism.
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85.30.De Semiconductor-device characterization, design, and modeling
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Fast radiative quantum dots: From single to multiple photon emission

E. Peter, S. Laurent, J. Bloch, J. Hours, S. Varoutsis, I. Robert-Philip, A. Beveratos, A. Lemaître, A. Cavanna, G. Patriarche, P. Senellart, and D. Martrou

Appl. Phys. Lett. 90, 223118 (2007); http://dx.doi.org/10.1063/1.2744475 (3 pages) | Cited 7 times

Online Publication Date: 1 June 2007

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Photon correlation measurements are performed on single GaAs quantum dots with various excitonic radiative lifetimes. A continuous increase of the probability that the quantum dot emits more than one photon per excitation pulse is observed when decreasing the exciton radiative lifetime. The authors show that this increase is due to recapture processes into the quantum dot. A model for the second-order autocorrelation function including relaxation processes is developed and gives good description of the experimental observations.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
78.47.-p Spectroscopy of solid state dynamics

Plasma based platinum nanoaggregates deposited on carbon nanofibers improve fuel cell efficiency

Amaël Caillard, Christine Charles, Rod Boswell, Pascal Brault, and Christophe Coutanceau

Appl. Phys. Lett. 90, 223119 (2007); http://dx.doi.org/10.1063/1.2745210 (3 pages) | Cited 23 times

Online Publication Date: 1 June 2007

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Improved platinum catalytic utilization has been achieved by creating an open support structure based on aligned carbon nanofibers (CNFs) attached to carbon loaded carbon cloth electrodes [known as gas diffusion layer (GDL)]. The nickel catalyst used to initiate the CNFs growth; the CNFs themselves and the 5 nm Pt nanoaggregates were deposited sequentially in the same low pressure plasma reactor. This oriented catalyst structure was incorporated into a membrane electrode assembly and tested with and without CNFs and on carbon paper or GDL. The performance of the fuel cells based on CNFs and GDL was better over the entire range of operating current.
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82.47.Gh Proton exchange membrane (PEM) fuel cells
82.45.Fk Electrodes
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