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16 Jul 2007

Volume 91, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 033106 (2007); http://dx.doi.org/10.1063/1.2757609 (3 pages)

S. Ingole, P. Aella, Sean J. Hearne, and S. T. Picraux
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Scanning photovoltage microscopy of potential modulations in carbon nanotubes

Marcus Freitag, James C. Tsang, Ageeth Bol, Phaedon Avouris, Dongning Yuan, and Jie Liu

Appl. Phys. Lett. 91, 031101 (2007); http://dx.doi.org/10.1063/1.2757100 (3 pages) | Cited 14 times

Online Publication Date: 16 July 2007

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We use the locally generated photovoltage in carbon nanotubes to image potential modulations produced by defects. The correlation with spatially resolved spectroscopy of the disorder-enhanced Raman band allows us to locate the defects and to determine their effect on band bending. The defects produce local potential maxima, which are consistent with trapped electrons near the tube. An offset photovoltage is generated when the laser populates metastable traps in the oxide. Previously uncharged defects can thus be imaged. To demonstrate the versatility of the technique, we show that tube-tube junction at the base of nanotube loops can be electronically characterized.
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73.63.Fg Nanotubes
78.67.Ch Nanotubes
72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.30.Hv Other nonmetallic inorganics
71.55.Ht Other nonmetals

Frequency-dependent refractive index of one-dimensionally structured thick metal film

Young-Min Shin, Jin-Kyu So, Jong-Hyo Won, and Gun-Sik Park

Appl. Phys. Lett. 91, 031102 (2007); http://dx.doi.org/10.1063/1.2753115 (3 pages) | Cited 6 times

Online Publication Date: 16 July 2007

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The authors have studied the frequency-dependent dielectric response of thick metal film one-dimensionally perforated by a subwavelength slit waveguide array. Our theoretical approach based on a three-dimensional homogenization of the periodic metallic structure shows that an effective refractive index chromatically varying due to TE waveguide mode formation gives rise to dense Fabry-Pérot resonance population near the cutoff, which leads to an energy level continuum in the transmission spectrum. Finite difference time domain simulation numerically demonstrates the transmission spectrum and spatial field distributions of even and odd resonance modes.
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78.66.Bz Metals and metallic alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Enhanced Pockels effect in GaN/AlxGa1−xN superlattice measured by polarization-maintaining fiber Mach-Zehnder interferometer

P. Chen, X. G. Tu, S. P. Li, J. C. Li, W. Lin, H. Y. Chen, D. Y. Liu, J. Y. Kang, Y. H. Zuo, L. Zhao, S. W. Chen, Y. D. Yu, J. Z. Yu, and Q. M. Wang

Appl. Phys. Lett. 91, 031103 (2007); http://dx.doi.org/10.1063/1.2759267 (3 pages) | Cited 3 times

Online Publication Date: 17 July 2007

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Six-period 4 nm GaN/10 nm AlxGa1−xN superlattices with different Al mole fractions x were prepared on (0001) sapphire substrates by low-temperature metal-organic chemical vapor deposition. The linear electro-optic (Pockels) effect was studied by a polarization-maintaining fiber-optical Mach-Zehnder interferometer system with an incident light wavelength of 1.55 μm. The measured electro-optic coefficients, γ13 = 5.60±0.18 pm/V, γ33 = 19.24±1.21 pm/V (for sample 1, x = 0.3), and γ13 = 3.09±0.48 pm/V, γ33 = 8.94±0.36 pm/V (for sample 2, x = 0.1), respectively, are about ten times larger than those of GaN bulk material. The enhancement effect in GaN/AlxGa1−xN superlattice can be attributed to the large built-in field at the interfaces, depending on the mole fraction of Al.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.20.Jq Electro-optical effects

Monitoring ultrashort pulses by transverse frequency doubling of counterpropagating pulses in random media

Robert Fischer, Dragomir N. Neshev, Solomon M. Saltiel, Andrey A. Sukhorukov, Wieslaw Krolikowski, and Yuri S. Kivshar

Appl. Phys. Lett. 91, 031104 (2007); http://dx.doi.org/10.1063/1.2751583 (3 pages) | Cited 18 times

Online Publication Date: 19 July 2007

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The authors study experimentally the transverse second-harmonic generation of counterpropagating pulses by a quasi-phase-matching in a medium with a random ferroelectric domain structure. The authors show that this parametric process results in a direct realization of the cross correlation of two optical signals and, therefore, it can be employed for direct characterizations of ultrashort pulses including their temporal structure and pulse front tilt.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

The nonlinear effect from the interplay between the nonlinearity and the supercollimation of photonic crystal

Xunya Jiang, Chuanhong Zhou, Xiaofang Yu, Shanhui Fan, Marin Soljačić, and J. D. Joannopoulos

Appl. Phys. Lett. 91, 031105 (2007); http://dx.doi.org/10.1063/1.2739413 (3 pages) | Cited 5 times

Online Publication Date: 19 July 2007

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The authors theoretically and numerically investigate the beam propagation near the supercollimation frequency ωs0 in a photonic crystal made of nonlinear material. Since the value and sign of the equal-frequency-contour curvature which dominates the beam behaviors can be nonlinearly tuned near ωs0, a kind of nonlinear effect is generated. The envelope equation with unique form is also obtained. Beam-control mechanisms are theoretically predicted and observed in numerical experiments, such as tunable collimation, tunable beam-divergence angle, and self-lock of collimation. These mechanisms can be utilized to function as fiber, lens and coupler, or to design photonic devices.
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42.70.Qs Photonic bandgap materials
42.65.-k Nonlinear optics

Single-photon experiments at telecommunication wavelengths using nanowire superconducting detectors

C. Zinoni, B. Alloing, L. H. Li, F. Marsili, A. Fiore, L. Lunghi, A. Gerardino, Yu. B. Vakhtomin, K. V. Smirnov, and G. N. Gol’tsman

Appl. Phys. Lett. 91, 031106 (2007); http://dx.doi.org/10.1063/1.2752108 (3 pages) | Cited 27 times

Online Publication Date: 19 July 2007

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The authors report fiber-coupled superconducting single-photon detectors with specifications that exceed those of avalanche photodiodes, operating at telecommunication wavelength, in sensitivity, temporal resolution, and repetition frequency. The improved performance is demonstrated by measuring the intensity correlation function g(2)(τ) of single-photon states at 1300 nm produced by single semiconductor quantum dots.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
42.81.Pa Sensors, gyros
42.82.Gw Other integrated-optical elements and systems

Terahertz photomixing in high energy oxygen- and nitrogen-ion-implanted GaAs

I. Cámara Mayorga, E. A. Michael, A. Schmitz, P. van der Wal, R. Güsten, K. Maier, and A. Dewald

Appl. Phys. Lett. 91, 031107 (2007); http://dx.doi.org/10.1063/1.2753738 (3 pages) | Cited 12 times

Online Publication Date: 19 July 2007

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In this letter, the authors elaborate a detailed study of ion-implanted GaAs terahertz photomixers. The authors implanted several GaAs samples with oxygen and nitrogen ions with energies between 2 and 3 MeV and doses ranging from 2×1011 to 3×1013 cm−2. The samples were processed by patterning metal-semiconductor-metal structures on the feed point of self-complementary log-periodic spiral broadband antennas. From dc measurements and analysis of frequency roll-off in the 100 GHz–1 THz range under variable bias conditions, the authors studied systematically the carrier trapping time, terahertz power, and photocurrent dependence on applied voltage and frequency for the different samples.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources

Evolution of the onset of coherence in a family of photonic crystal nanolasers

Y.-S. Choi, M. T. Rakher, K. Hennessy, S. Strauf, A. Badolato, P. M. Petroff, D. Bouwmeester, and E. L. Hu

Appl. Phys. Lett. 91, 031108 (2007); http://dx.doi.org/10.1063/1.2751131 (3 pages) | Cited 11 times

Online Publication Date: 19 July 2007

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The authors report on the systematic variation of the onset of lasing in high-β photonic crystal nanolasers. A series of nanocavities has been designed to systematically approach the high-β devices by controlling the number of modes in the s-shell spectrum of InAs quantum dots at 4 K. The lasing action is confirmed by the observation of coherent-state transition to Poissonian photon statistics. The quantitative analysis reveals the high β of 0.69, 0.44, and 0.19 for the nanocavities with one, two, and three modes, respectively. By mapping the observed lasing transitions to β factors, the authors demonstrate the interplay of β and lasing performance.
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42.55.Tv Photonic crystal lasers and coherent effects
42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Amplified spontaneous emission from dye-doped polymer film sandwiched by two opal photonic crystals

Feng Jin, Yang Song, Xian-Zi Dong, Wei-Qiang Chen, and Xuan-Ming Duan

Appl. Phys. Lett. 91, 031109 (2007); http://dx.doi.org/10.1063/1.2766652 (3 pages) | Cited 11 times

Online Publication Date: 20 July 2007

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The authors observed amplified spontaneous emission (ASE) from dye-doped polymer film sandwiched by two opal photonic crystals (PhCs). The ASE effect occurred at 599 nm with a full width at half maximum of about 5.1 nm, which corresponds to the L-point gap edge of the opal PhCs. Photoluminescence lifetimes of both dye-doped polymer films with and without opal PhCs were measured and corroborated that the ASE of the dye-doped polymer film emission is due to the presence of the photonic stop band.
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78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds
78.45.+h Stimulated emission
78.20.Bh Theory, models, and numerical simulation
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High strength ultrafine/nanostructured aluminum produced by back pressure equal channel angular processing

W. Xu, T. Honma, X. Wu, S. P. Ringer, and K. Xia

Appl. Phys. Lett. 91, 031901 (2007); http://dx.doi.org/10.1063/1.2755923 (3 pages) | Cited 11 times

Online Publication Date: 16 July 2007

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High strength ultrafine/nanograined aluminum materials with ultimate strength up to 740 MPa and Vickers microhardness up to 2285 MPa were produced using back pressure equal channel angular processing of ultrafine-sized aluminum powder at 400 °C. Microstructure analyses revealed that the attained high strength and microhardness were derived from the presence of nanosized aluminum and γ-alumina grains (5–10 nm) as well as residual amorphous alumina. The interaction between the severe shear deformation and the preexisting amorphous alumina, concurrent oxidation, and amorphous to γ-alumina transition was considered to be responsible for the formation of such a refined and complex nanostructure.
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81.07.Bc Nanocrystalline materials
81.10.Fq Growth from melts; zone melting and refining
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
64.70.K- Solid-solid transitions
81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Microstructure and strain relaxation of epitaxial PrScO3 thin films grown on (001) SrTiO3 substrates

Y. B. Chen, M. B. Katz, X. Q. Pan, C. M. Folkman, R. R. Das, and C. B. Eom

Appl. Phys. Lett. 91, 031902 (2007); http://dx.doi.org/10.1063/1.2756359 (3 pages) | Cited 2 times

Online Publication Date: 16 July 2007

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We have studied the microstructure and strain relaxation of epitaxial PrScO3 films grown on miscut (001) SrTiO3 substrates by transmission electron microscopy. PrScO3 films grown on highly miscut (>1°) SrTiO3 substrates are single domain films, fully strain relaxed via interfacial misfit dislocations, small angle tilt boundaries, and antiphase boundaries bounded by partial dislocation. In contrast, strain in PrScO3 films on low miscut (<0.2°) SrTiO3 substrates is relaxed by misfit dislocation as well as the formation of six different crystallographic domains. The formation of single domain PrScO3 films on high angle miscut substrates could be due to interfacial strain-energy minimization.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.37.Lp Transmission electron microscopy (TEM)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Modified Eshelby tensor modeling for elastic property prediction of carbon nanotube reinforced ceramic nanocomposites

Yao Chen, Kantesh Balani, and Arvind Agarwal

Appl. Phys. Lett. 91, 031903 (2007); http://dx.doi.org/10.1063/1.2756360 (3 pages) | Cited 9 times

Online Publication Date: 16 July 2007

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A modified model using the Eshelby equivalent tensor is developed to evaluate overall elastic properties of carbon nanotube (CNT) reinforced aluminum oxide nanocomposites. This model accounts for the effect of carbon nanotube geometry and porosity on the effective elastic modulus. Experimental results are compared with the computed predictions. Computed results show higher elastic modulus values, which are attributed to the perfect bonding between the reinforcement and the matrix. It is concluded that the modified Eshelby model can predict the elastic property of CNT reinforced ceramic nanocomposites.
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62.25.-g Mechanical properties of nanoscale systems
81.05.Mh Cermets, ceramic and refractory composites
61.46.Fg Nanotubes
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Fine structure and chemical shifts in nonresonant inelastic x-ray scattering from Li-intercalated graphite

M. Balasubramanian, C. S. Johnson, J. O. Cross, G. T. Seidler, T. T. Fister, E. A. Stern, C. Hamner, and S. O. Mariager

Appl. Phys. Lett. 91, 031904 (2007); http://dx.doi.org/10.1063/1.2752755 (3 pages) | Cited 18 times

Online Publication Date: 16 July 2007

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The authors report measurements of hard x-ray nonresonant inelastic x-ray scattering (IXS) from the Li and C 1s electrons of fully staged LiC6 Li-intercalated graphite prepared by both chemical and electrochemical methods. They find that the Li 1s orbital shifts to higher energies relative to Li metal. Relative to graphite, the C 1s IXS for LiC6 shows a shift for the σ-orbital threshold to lower energies, but no shift for the π* resonance. The findings provide bulk-sensitive evidence for substantial charge transfer from the Li intercalant to the carbon host and establish important groundwork for future in situ electrochemical studies.
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82.45.Aa Electrochemical synthesis
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
76.60.Cq Chemical and Knight shifts
78.70.Ck X-ray scattering

Evolution of boron-interstitial clusters in crystalline Si studied by transmission electron microscopy

S. Boninelli, S. Mirabella, E. Bruno, F. Priolo, F. Cristiano, A. Claverie, D. De Salvador, G. Bisognin, and E. Napolitani

Appl. Phys. Lett. 91, 031905 (2007); http://dx.doi.org/10.1063/1.2757145 (3 pages) | Cited 14 times

Online Publication Date: 16 July 2007

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The thermal evolution of large boron-interstitials clusters (BICs) in crystalline Si has been studied by transmission electron microscopy (TEM). After ion implantation (20 keV and 1×1014 Si/cm2) and annealing (815 °C and 5 min), large clusters (6–8 nm) have been observed in correspondence of a narrow, highly doped Si:B layer (2×1020 B/cm3). Under prolonged annealing, such clusters dissolve, progressively shrinking their mean size below the TEM detection limit. The time evolution of such a BIC shrinking is fully compatible with the slow path dissolution kinetics recently published. These data suggest the identification of the slow dissolving BICs with the large observed clusters.
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61.72.J- Point defects and defect clusters
68.37.Lp Transmission electron microscopy (TEM)
61.72.uf Ge and Si
81.40.Gh Other heat and thermomechanical treatments

First principles studies of ideal strength and bonding nature of AlN polymorphs in comparison to TiN

R. F. Zhang, S. H. Sheng, and S. Veprek

Appl. Phys. Lett. 91, 031906 (2007); http://dx.doi.org/10.1063/1.2759265 (3 pages) | Cited 22 times

Online Publication Date: 17 July 2007

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The stress-strain relationships under tensile and shear loads and bonding nature of fcc (rocksalt)-, hcp (wurtzite)-AlN, and fcc (rocksalt)-TiN are calculated by first principles method. Compared to fcc-TiN, fcc-AlN shows similar anisotropy of tensile strengths, but lower shear strength is found in both AlN polymorphs. Based on the calculated electronic density of states, bonding nature for both AlN polymorphs is discussed. The hardness enhancement in TiN/AlN heterostructures and nanocomposites cannot be attributed to the difference of the ideal strength and bonding nature between fcc-AlN and hcp-AlN, but to the formation of semicoherent fcc-TiN/fcc-AlN interface.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.F- Deformation and plasticity
62.20.Qp Friction, tribology, and hardness
61.50.Lt Crystal binding; cohesive energy

Correlation between fragility and glass-forming ability/plasticity in metallic glass-forming alloys

E. S. Park, J. H. Na, and D. H. Kim

Appl. Phys. Lett. 91, 031907 (2007); http://dx.doi.org/10.1063/1.2759266 (3 pages) | Cited 27 times

Online Publication Date: 17 July 2007

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In the present study, the authors draw attention to the relationship among fragility index (m), glass-forming ability (GFA), and plasticity in various metallic glass-forming alloys (MGAs), and show that the m value is closely related to both characteristics. In particular, m can be formulated with ν (Poisson’s ratio): ν = −0.179+0.312 log m, which means that high m as well as large ν values might be regarded as indicators of the MGAs ductility. As an example, it can be rationalized that the lowest m value (21.5 at 5 K/min) of Ca65Mg15Zn20 supports both outstanding GFA and extreme brittleness.
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81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity
62.20.M- Structural failure of materials
62.20.D- Elasticity

Structural evidence of secondary phase segregation from the Raman vibrational modes in Zn1−xCoxO (0<x<0.6)

Xuefeng Wang, Jianbin Xu, Xiaojiang Yu, Kun Xue, Jiaguo Yu, and Xiujian Zhao

Appl. Phys. Lett. 91, 031908 (2007); http://dx.doi.org/10.1063/1.2759272 (3 pages) | Cited 31 times

Online Publication Date: 17 July 2007

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Micro-Raman measurements were performed to study the influence of Co doping on the lattice dynamic properties of the host ZnO. The structural evidence of secondary phase segregation was detected from two distinct phonon vibrational modes at around 472 and 678 cm−1 in Zn1−xCoxO (0<x<0.6) ternary alloys with x above 0.098. In addition, an intense, broad, and symmetric phonon vibration was apparent at about 530 cm−1 for alloys with x not more than 0.155. The authors suggest the shallow donor defects bound on the Co sites rather than the local vibrational mode involving Co motion as the origin.
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64.75.-g Phase equilibria
63.20.Pw Localized modes
78.30.Fs III-V and II-VI semiconductors
61.72.uj III-V and II-VI semiconductors

Visualization of photoassisted polarization switching and its consequences in BiFeO3 thin films probed by terahertz radiation

D. S. Rana, K. Takahashi, K. R. Mavani, I. Kawayama, H. Murakami, and M. Tonouchi

Appl. Phys. Lett. 91, 031909 (2007); http://dx.doi.org/10.1063/1.2759259 (3 pages) | Cited 4 times

Online Publication Date: 18 July 2007

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The principle of terahertz radiation emission from multiferroic BiFeO3 thin films was employed to acquire high-resolution images of their photoassisted ferroelectric polarization switching. These images are evidence that poling in “electric-field assisted by illumination of band gap light” enhances the terahertz-emission amplitude by creating additional switchable ferroelectric dipoles.
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77.80.Fm Switching phenomena
77.22.Ej Polarization and depolarization
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Fabrication and optical properties of two-dimensional ZnO hollow half-shell arrays

Y. Gao, A. D. Li, Z. B. Gu, Q. J. Wang, Y. Zhang, D. Wu, Y. F. Chen, N. B. Ming, S. X. Ouyang, and T. Yu

Appl. Phys. Lett. 91, 031910 (2007); http://dx.doi.org/10.1063/1.2759268 (3 pages) | Cited 5 times

Online Publication Date: 18 July 2007

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Two-dimensional optically active ZnO shells on polystyrene (PS) templates have been fabricated using a sputtering technique. Periodic ZnO hollow half-shell structure has been obtained by removing PS templates. It exhibits several anomalous dips in transmission spectra that have not been reported. The dips can be tuned up by changing the shell thickness and PS sphere size. The PL spectra confirm that the structure has enhanced defect emission of ZnO.
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81.16.-c Methods of micro- and nanofabrication and processing
81.15.Cd Deposition by sputtering
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors

On the lattice parameters of GaN

V. Darakchieva, B. Monemar, and A. Usui

Appl. Phys. Lett. 91, 031911 (2007); http://dx.doi.org/10.1063/1.2753122 (3 pages) | Cited 15 times

Online Publication Date: 19 July 2007

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The lattice parameters of low-defect density, undoped bulk GaN fabricated by hydride vapor phase epitaxy (HVPE) on (0001) sapphire and subsequent substrate removal, are precisely determined using high-resolution x-ray diffraction. The obtained values, c = 5.18523 Å and a = 3.18926 Å, are compared with the lattice parameters of freestanding HVPE GaN from different sources and found to be representative for state-of-the-art undoped HVPE bulk GaN material. A comparison with bulk GaN fabricated by the high-pressure technique and homoepitaxial GaN is made, and significant differences in the lattice parameters are found. The observed differences are discussed and a possible explanation is suggested.
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68.55.-a Thin film structure and morphology

AsS: Bulk inorganic molecular-based chalcogenide glass

V. V. Brazhkin, A. G. Gavrilyuk, A. G. Lyapin, Yu. A. Timofeev, Y. Katayama, and S. Kohara

Appl. Phys. Lett. 91, 031912 (2007); http://dx.doi.org/10.1063/1.2759261 (3 pages) | Cited 8 times

Online Publication Date: 19 July 2007

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The authors have developed a high pressure method to produce bulk chalcogenide glasses of a unique AsS composition. The structure, optical properties, and stability of the obtained glasses have been studied. Glasses have an intrinsic deep-red color, optical pseudogap Eg ≈ 1.75 eV, a broad Urbach absorption tail WU ≈ 120 meV, and high temperature stability up to 130 °C. AsS glasses show photoinduced transformations, including photocrystallization. The glass structure is largely based on the quasimolecular As4S4 units with partial polymerization providing an example of an inorganic molecular-based glass.
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61.43.Fs Glasses
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
64.70.K- Solid-solid transitions
82.35.-x Polymers: properties; reactions; polymerization

Grain boundary fine structure of ultrananocrystalline diamond thin films measured by Raman scattering

M. Veres, S. Tóth, and M. Koós

Appl. Phys. Lett. 91, 031913 (2007); http://dx.doi.org/10.1063/1.2757122 (3 pages) | Cited 12 times

Online Publication Date: 20 July 2007

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Structural units of the grain boundaries in ultrananocrystalline diamond thin films with different grain sizes were investigated using Raman spectroscopy. Characteristic peaks of well-defined molecular structural building blocks were detected in the near-infrared excited Raman spectra of these materials by limiting the excitation volume to the size of the crystallites using an optical microscope and surface enhanced Raman spectroscopy. The analysis of the spectra provides evidence for the presence of aromatic hydrocarbons and different sp3 CHx groups in grain boundaries of these materials.
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68.55.-a Thin film structure and morphology
61.72.Mm Grain and twin boundaries
61.46.Hk Nanocrystals
78.30.Na Fullerenes and related materials

Density-functional theory calculations of bare and passivated triangular-shaped ZnO nanowires

Hu Xu, A. L. Rosa, Th. Frauenheim, R. Q. Zhang, and S. T. Lee

Appl. Phys. Lett. 91, 031914 (2007); http://dx.doi.org/10.1063/1.2757147 (3 pages) | Cited 20 times

Online Publication Date: 20 July 2007

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The authors employ density functional theory within the generalized-gradient approximation to investigate infinitely long [0001] ZnO nanowires. The authors report on atomic relaxations, formation energies, and electronic structure of bare and hydrogen passivated ZnO wires with triangular cross sections. The authors find that surface reconstruction plays an important role in stabilizing the nanowires. The authors have shown that the band gap can be tuned by changing the wire diameter and by passivating with hydrogen. While bare and completely passivated wires are semiconducting, wires with intermediate hydrogen passivation exhibit metallic behavior.
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73.21.Hb Quantum wires
73.20.At Surface states, band structure, electron density of states
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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Surface-depletion controlled gas sensing of ZnO nanorods grown at room temperature

C. C. Li, Z. F. Du, L. M. Li, H. C. Yu, Q. Wan, and T. H. Wang

Appl. Phys. Lett. 91, 032101 (2007); http://dx.doi.org/10.1063/1.2752541 (3 pages) | Cited 56 times

Online Publication Date: 16 July 2007

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The authors report on surface-depletion controlled gas sensing ZnO nanorods. These nanorods were synthesized through a simple wet chemical route at room temperature. The diameter of nanorods is about 15 nm, which is close to two times of the Debye length of ZnO. In contrast to the previous report, the sensing is surface-depletion controlled rather than contact controlled and the sensitivity is up to 29.7 against 100 ppm ethanol. Such high sensitivity is due to an almost complete depletion of the rods in air, which is confirmed from photoluminescence spectrum and x-ray photoelectron spectroscopy. The gas sensing mechanism controlled by surface depletion provides another approach to realize high-performance gas sensors.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.-w Structure of nanoscale materials
78.55.Et II-VI semiconductors
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Demonstration of a quantum cellular automata cell in a GaAs/AlGaAs heterostructure

F. Perez-Martinez, I. Farrer, D. Anderson, G. A. C. Jones, D. A. Ritchie, S. J. Chorley, and C. G. Smith

Appl. Phys. Lett. 91, 032102 (2007); http://dx.doi.org/10.1063/1.2759257 (3 pages) | Cited 6 times

Online Publication Date: 17 July 2007

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The authors report on the experimental demonstration of a GaAs/AlGaAs-based quantum cellular automata cell fabricated using electron beam lithographically defined gates. These surface metallic gates form a pair of double quantum dots, as well as a pair of quantum point contacts (QPCs) that act as noninvasive voltage probes. Measurements at cryogenic temperatures show that an electron transfer in the input dots induces the relocation of a single electron in the output dots. Using the QPCs they were also able to determine the operating limits of the cell.
Show PACS
85.35.Ds Quantum interference devices
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