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23 Mar 2009

Volume 94, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 122502 (2009); http://dx.doi.org/10.1063/1.3100783 (3 pages)

Junhua Wang, Yisheng Shi, Juexian Cao, and Ruqian Wu
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Direct-gap exciton and optical absorption in the Ge/SiGe quantum well system

Yu-Hsuan Kuo and Yin-Shun Li

Appl. Phys. Lett. 94, 121101 (2009); http://dx.doi.org/10.1063/1.3106621 (3 pages) | Cited 9 times

Online Publication Date: 23 March 2009

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The ground-level direct-gap excitons and quantum-confined Stark effect (QCSE) electroabsorption in the Ge/SiGe quantum well structures are studied using the tunneling resonance modeling and the variational method. The exciton radius, transition energy, binding energy, and optical oscillator strength are calculated for various quantum well thicknesses (5–35 nm) and vertical electric fields (0–105 V/cm) simultaneously. The relative direct-gap-to-indirect-gap absorption ratios are compared. A quantum well implementation scheme with relatively broad thickness range of ∼ 5–15 nm can provide moderate excitonic absorption and contrast ratio for long wavelength operation. This investigation will improve the QCSE electroabsorption efficiency in the Ge quantum well system.
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73.21.Fg Quantum wells
73.40.Gk Tunneling
78.67.De Quantum wells
78.20.Jq Electro-optical effects
71.35.-y Excitons and related phenomena
68.65.Fg Quantum wells

Scalable implementation of strongly coupled cavity-quantum dot devices

A. Dousse, J. Suffczyński, R. Braive, A. Miard, A. Lemaître, I. Sagnes, L. Lanco, J. Bloch, P. Voisin, and P. Senellart

Appl. Phys. Lett. 94, 121102 (2009); http://dx.doi.org/10.1063/1.3100781 (3 pages) | Cited 15 times

Online Publication Date: 23 March 2009

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Using low temperature in situ optical lithography, we fabricate pillar microcavities with quality factors around 2×104. Each pillar embeds a spatially and spectrally resonant single InGaAs quantum dot (QD). Light-matter strong coupling regime is reached for 100% of the fabricated pillars for which the resonance can be tuned through temperature. This is a demonstration of scalable and deterministic implementation of strongly coupled cavity-QD devices.
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81.07.Ta Quantum dots
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.40.Hp Lithography, masks and pattern transfer

Acoustoelectric luminescence from a field-effect n-i-p lateral junction

Giorgio De Simoni, Vincenzo Piazza, Lucia Sorba, Giorgio Biasiol, and Fabio Beltram

Appl. Phys. Lett. 94, 121103 (2009); http://dx.doi.org/10.1063/1.3106108 (3 pages) | Cited 4 times

Online Publication Date: 23 March 2009

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A surface-acoustic-wave (SAW) driven light-emitting-diode structure that can implement a single-photon source for quantum-cryptography applications is demonstrated. Our lateral n-i-p junction is realized starting from an undoped GaAs/AlGaAs quantum well by gating. It incorporates interdigitated transducers for SAW generation and lateral gates for current control. We demonstrate acoustoelectric transport and SAW-driven electroluminescence. The acoustoelectric current can be controlled down to complete pinch-off by means of the lateral gates.
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78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.60.Fi Electroluminescence
07.07.Mp Transducers
73.21.Fg Quantum wells
78.67.De Quantum wells
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High-speed switching of spin polarization for proposed spin-photon memory

V. Zayets and K. Ando

Appl. Phys. Lett. 94, 121104 (2009); http://dx.doi.org/10.1063/1.3106637 (3 pages) | Cited 3 times

Online Publication Date: 24 March 2009

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Nonvolatile high-speed optical memory is proposed, which utilizes the magnetization reversal of nanomagnet by spin-polarized photoexcited electrons. It was demonstrated experimentally that one selected pulse from the train of two optical data pulses with interval of 450 fs can solely excite the spin-polarized electrons without a disturbance from the unselected optical data pulse. That proves feasibility for operation of the memory with speed of 2.2 Tbits/s.
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84.30.Sk Pulse and digital circuits
75.60.Jk Magnetization reversal mechanisms
72.25.Fe Optical creation of spin polarized carriers

Mid-infrared tunable two-dimensional Talbot array illuminator

P. Maddaloni, M. Paturzo, P. Ferraro, P. Malara, P. De Natale, M. Gioffrè, G. Coppola, and M. Iodice

Appl. Phys. Lett. 94, 121105 (2009); http://dx.doi.org/10.1063/1.3109794 (3 pages) | Cited 5 times

Online Publication Date: 26 March 2009

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We report the realization and characterization of a tunable, two-dimensional Talbot array illuminator for mid-infrared (MIR) wavelengths. A phase array, prepared by deposing tin-doped indium oxide electrodes on a square-lattice-geometry poled LiNbO3 sample, is illuminated by a difference-frequency generator emitting at 3 μm. Then, combining the electro-optic with the Talbot effect allows generation of a variety of light patterns under different values of distance and external electric field. Several potential applications with great relevance to the MIR spectral region are discussed.
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42.30.-d Imaging and optical processing
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Dj Gratings

High quality factor photonic crystal nanobeam cavities

Parag B. Deotare, Murray W. McCutcheon, Ian W. Frank, Mughees Khan, and Marko Lončar

Appl. Phys. Lett. 94, 121106 (2009); http://dx.doi.org/10.1063/1.3107263 (3 pages) | Cited 89 times

Online Publication Date: 27 March 2009

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We investigate the design, fabrication, and experimental characterization of high quality factor photonic crystal nanobeam cavities in silicon. Using a five-hole tapered one-dimensional photonic crystal mirror and precise control of the cavity length, we designed cavities with theoretical quality factors as high as 1.4×107. By detecting the cross-polarized resonantly scattered light from a normally incident laser beam, we measure a quality factor of nearly 7.5×105. The effect of cavity size on mode frequency and quality factor was simulated and then verified experimentally.
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42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
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Influence of a transverse magnetic field on arc root movements in a dc plasma torch: Diamagnetic effect of arc column

Keun Su Kim

Appl. Phys. Lett. 94, 121501 (2009); http://dx.doi.org/10.1063/1.3109782 (3 pages) | Cited 1 time

Online Publication Date: 27 March 2009

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The effect of a transverse magnetic field on the anodic arc root movement inside a dc plasma torch has been investigated. The arc voltage fluctuation, which represents the degree of the arc instability, was reduced to 28.6% of the original value and the high frequency components in the voltage signal also decreased in their magnitudes. The inherent arc instability in a dc thermal plasma torch seems to be suppressed by a diamagnetic effect of the arc column. Furthermore, the measured voltage wave forms indicated that the arc root attachment mode would be controllable by a transverse magnetic field.
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52.75.Hn Plasma torches
52.25.Xz Magnetized plasmas
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An acoustic emission study of the effect of a magnetic field on the martensitic transition in Ni2MnGa

Benno Ludwig, Christian Strothkaemper, Uwe Klemradt, Xavier Moya, Lluís Mañosa, Eduard Vives, and Antoni Planes

Appl. Phys. Lett. 94, 121901 (2009); http://dx.doi.org/10.1063/1.3103289 (3 pages) | Cited 3 times

Online Publication Date: 23 March 2009

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Acoustic emission measurements during the martensitic transition of a Ni–Mn–Ga magnetic shape-memory alloy reveal the intermittent and jerky character of the transition. The distribution of the amplitude of the acoustic emission events shows power law behavior, which reflects the absence of characteristic scales in the process. In this paper we show that the distribution is affected by an applied magnetic field, which proves that the transition dynamics is strongly influenced by magnetostructural coupling taking place at multiple length scales. The martensitic start temperature and the power law exponent of the amplitude distribution are measured in dependence of the applied field.
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62.65.+k Acoustical properties of solids
81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions

Pulsed metal-organic chemical vapor deposition of high-quality AlN/GaN superlattices for near-infrared intersubband transitions

C. Bayram, N. Péré-laperne, R. McClintock, B. Fain, and M. Razeghi

Appl. Phys. Lett. 94, 121902 (2009); http://dx.doi.org/10.1063/1.3104857 (3 pages) | Cited 15 times

Online Publication Date: 23 March 2009

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A pulsed metal-organic chemical vapor deposition technique is developed for the growth of high-quality AlN/GaN superlattices (SLs) with intersubband (ISB) transitions at optical communications wavelengths. Tunability of the AlN and GaN layers is demonstrated. Indium is shown to improve SL surface and structural quality. Capping thickness is shown to be crucial for ISB transition characteristics. Effects of barrier- and well-doping on the ISB absorption are reported.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.Cd Superlattices
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

On the anisotropic shear resistance of hard transition metal nitrides TMN (TM = Ti, Zr, Hf)

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

Appl. Phys. Lett. 94, 121903 (2009); http://dx.doi.org/10.1063/1.3105990 (3 pages) | Cited 9 times

Online Publication Date: 23 March 2009

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The anisotropic shear moduli and strengths of hard fcc-TMN (TM = Ti, Zr, Hf) have been calculated by ab initio density functional theory in order to better understand their shear resistance. TiN shows the largest shear strength among the three nitrides, being consistent with the known facts that TiN is harder than HfN which is harder than ZrN. The electronic origin is further addressed. Based on the smooth shapes of the stress-strain curves and on the variation of electronic structure during shear deformations, the abrupt lattice instability mode reported previously for TiN (110)〈1math0〉 shear deformation is not supported by our data.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Correlations between elastic moduli and molar volume in metallic glasses

J. Q. Wang, W. H. Wang, H. B. Yu, and H. Y. Bai

Appl. Phys. Lett. 94, 121904 (2009); http://dx.doi.org/10.1063/1.3106110 (3 pages) | Cited 7 times

Online Publication Date: 23 March 2009

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We report clear correlations between bulk modulus (K) and average molar volume Vm, and between Poisson’s ratio ν and Vm for various bulk metallic glasses. The origin for the correlations between elastic moduli and Vm are discussed. The established correlation, associated with Poisson’s ratio ν, and since the ν correlates with plasticity of metallic glasses, indicates that the average molar volume is important factor to be considered for plastic metallic glasses searching. The found correlations also suggest a close relation between the mechanical properties and the short-range atomic bonding, and assist in understanding deformation behavior in metallic glasses.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dj Poisson's ratio
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity

Conditions to cancel the laser polarization dependence of a subwavelength tip

J. Houard, A. Vella, F. Vurpillot, and B. Deconihout

Appl. Phys. Lett. 94, 121905 (2009); http://dx.doi.org/10.1063/1.3095829 (3 pages) | Cited 6 times

Online Publication Date: 23 March 2009

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Using laser assisted atom probe tomography, we investigate the polarization dependence of the absorption coefficient of a subwavelength Al tip illuminated by an ultrashort laser pulse. In practice, we find an equilibrium condition as a function of the incident wavelength for which the atom evaporation rate becomes independent of the wave polarization. It is experimentally shown that this condition only depends on the ratio between the tip radius and the laser wavelength. Furthermore, our calculations demonstrate that a transverse local plasmon polariton mode can be resonantly excited at the tip apex.
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07.60.Pb Conventional optical microscopes
07.79.Cz Scanning tunneling microscopes
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.22.Lp Collective excitations
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Lateral epitaxial overgrowth of (0001) AlN on patterned sapphire using hydride vapor phase epitaxy

Scott A. Newman, Derrick S. Kamber, Troy J. Baker, Yuan Wu, Feng Wu, Zhen Chen, Shuji Namakura, James S. Speck, and Steven P. DenBaars

Appl. Phys. Lett. 94, 121906 (2009); http://dx.doi.org/10.1063/1.3089253 (3 pages) | Cited 3 times

Online Publication Date: 24 March 2009

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Coalesced, crack-free (0001) AlN films were grown on stripe patterned sapphire substrates without AlN seed layers using hydride vapor phase epitaxy. Using templates with stripes oriented in the 〈11math0〉sapphire direction, lateral epitaxial overgrowth AlN films were coalesced over trench regions as wide as 10 μm despite parasitic sidewall and trench growth. Using transmission electron microscopy, a reduction in the dislocation density from 1.6×109 cm−2 in the seed region to less than 1.0×108 cm−2 in the wing region was demonstrated. Atomic force microscopy and cathodoluminescence measurements were also performed to assess the material quality.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Lk Linear defects: dislocations, disclinations
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence
81.05.Ea III-V semiconductors

Growth of deformation twins in room-temperature rolled nanocrystalline nickel

X. Y. Zhang, X. L. Wu, and A. W. Zhu

Appl. Phys. Lett. 94, 121907 (2009); http://dx.doi.org/10.1063/1.3104858 (3 pages) | Cited 6 times

Online Publication Date: 24 March 2009

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Deformation twinning has been observed in room-temperature rolled nanocrystalline Ni. The growth of the deformation twins via the emission of partial dislocations from a grain boundary has been examined in detail. Partial dislocations on neighboring slip planes may migrate for different distances and then remain in the grain interior, leading to the formation of a steplike twin boundary (TB). With continued twin growth, the TBs become gradually distorted and lose their coherent character due to accumulated high stresses. Moreover, we propose that microtwins may form near such TBs due to the emission of partial dislocations from the TB.
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61.72.Mm Grain and twin boundaries
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.-c Methods of micro- and nanofabrication and processing
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Introduction of molecular scale porosity into semicrystalline polymer thin films using supercritical carbon dioxide

Peter Gin, Mitsunori Asada, Maya K. Endoh, Cynthia Gedelian, Toh-Ming Lu, and Tadanori Koga

Appl. Phys. Lett. 94, 121908 (2009); http://dx.doi.org/10.1063/1.3104851 (3 pages) | Cited 3 times

Online Publication Date: 26 March 2009

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We report supercritical carbon dioxide (scCO2) technology used for forming a large degree of molecular scale porosity in semicrystalline polymer thin films. The following three steps were integrated: (i) pre-exposure to an organic solvent which melted crystalline structures but did not cause a decrease in thickness, (ii) scCO2 exposure under the unique conditions where the anomalous absorption of CO2 occurred, and (iii) subsequent quick evaporation of CO2 to preserve the swollen structures. This unified process resulted in homogenous low-density polyphenylene vinylene films (a 15% reduction in density) with the sustained structure for at least 6 months at room temperature.
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61.43.Gt Powders, porous materials
64.70.F- Liquid-vapor transitions
61.41.+e Polymers, elastomers, and plastics
68.55.am Polymers and organics

Polarization field mapping of Al0.85In0.15N/AlN/GaN heterostructure

Lin Zhou, David A. Cullen, David J. Smith, Martha R. McCartney, Anas Mouti, M. Gonschorek, E. Feltin, J. F. Carlin, and N. Grandjean

Appl. Phys. Lett. 94, 121909 (2009); http://dx.doi.org/10.1063/1.3108084 (3 pages) | Cited 9 times

Online Publication Date: 27 March 2009

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Off-axis electron holography has been used to measure the built-in potential profile across an Al0.85In0.15N/AlN/GaN high electron mobility transistor heterostructure. Profile measurements indicated a polarization-induced electric field of 6.9 MV/cm within the AlN layer. A two-dimensional electron gas with a density of ∼ 2.1×1013 cm−2 was located in the GaN layer at ∼ 0.8 nm away from the AlN/GaN interface in reasonable agreement with the reported simulations. Electron microscopy confirmed that the Al0.85In0.15N layer was uniform and that Al0.85In0.15N/AlN and AlN/GaN interfaces were abrupt and well defined.
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85.30.Tv Field effect devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Formation energies of antisite defects in Y3Al5O12: A first-principles study

Bo Liu, Mu Gu, Xiaolin Liu, Shiming Huang, and Chen Ni

Appl. Phys. Lett. 94, 121910 (2009); http://dx.doi.org/10.1063/1.3109799 (3 pages) | Cited 6 times

Online Publication Date: 27 March 2009

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We perform the first-principles calculations for the formation energies of cation antisite defects in Y3Al5O12. This method provides precise values of formation energy and thus allows us to estimate the defect concentration. The calculations show that YAl,16a is the most predominant antisite defects at high temperature for the single crystal growth and its concentration significantly decreases at low temperature for the single-crystalline film preparation. The calculated defect concentrations are quantitatively accord with the experimental estimation. AlY has high formation energy even with excess Al2O3, which indicates AlY is energetically unfavorable and the defect process is not intrinsic but nonstoichiometry.
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61.72.J- Point defects and defect clusters
61.72.Bb Theories and models of crystal defects
71.55.Ht Other nonmetals
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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Electron transport properties of irradiated polyimide thin films in single track regime

Pandiyan Murugaraj, David Mainwaring, and Rainer Siegele

Appl. Phys. Lett. 94, 122101 (2009); http://dx.doi.org/10.1063/1.3106602 (3 pages) | Cited 1 time

Online Publication Date: 23 March 2009

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We have prepared a suite of polyimide thin films containing spatially separated one-dimensional conductive-nanowires by ion-beam irradiation exhibiting temperature dependent electrical resistance consistent with thermally activated electron hopping with activation energies about 1 eV arising from localized states spatially distributed along the ion tracks. Dielectric measurements showed the formation of high dielectric constant interphase regions surrounding each ion track generated during the irradiation process, responsible for space-charge accumulation which influences electron transport within the ion tracks. This behavior suggests a role for space-charge effects and dielectric properties in this interphase region in the control of electron transport within single track nanowires.
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73.61.Ph Polymers; organic compounds
61.80.Jh Ion radiation effects
77.22.Ch Permittivity (dielectric function)
77.22.Jp Dielectric breakdown and space-charge effects
61.41.+e Polymers, elastomers, and plastics
73.63.Nm Quantum wires

Polarity-dependent photoemission spectra of wurtzite-type zinc oxide

Naoki Ohashi, Yutaka Adachi, Takeo Ohsawa, Kenji Matsumoto, Isao Sakaguchi, Hajime Haneda, Shigenori Ueda, Hideki Yoshikawa, and Keisuke Kobayashi

Appl. Phys. Lett. 94, 122102 (2009); http://dx.doi.org/10.1063/1.3103271 (3 pages) | Cited 10 times

Online Publication Date: 23 March 2009

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Electronic structures of the polar and nonpolar surfaces of ZnO were investigated by hard x-ray photoelectron spectroscopy (HXPES) using synchrotron radiation. The profile of HXPES spectra in the valence band region varied with the crystalline orientation (polarity) of the surface. This polarity dependence was always found in the HXPES spectra regardless of sample conditions such as surface treatment and doping. The possible origin of the polarity dependence of HXPES spectra is discussed in terms of spontaneous polarization.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.At Surface states, band structure, electron density of states
71.20.Nr Semiconductor compounds

Thermoelectric properties of tetrahedrally bonded wide-gap stannite compounds Cu2ZnSn1−xInxSe4

X. Y. Shi, F. Q. Huang, M. L. Liu, and L. D. Chen

Appl. Phys. Lett. 94, 122103 (2009); http://dx.doi.org/10.1063/1.3103604 (3 pages) | Cited 27 times

Online Publication Date: 23 March 2009

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It is usually accepted that good thermoelectric (TE) materials should be narrow-gap semiconductors. Here we show an example that the tetrahedrally bonded stannite compound Cu2ZnSnSe4 with a band gap of 1.44 eV can also exhibit a high figure of merit at intermediate temperature. The highly distorted structure strives for the relatively low thermal conductivity, and the tunability of the electrical properties were demonstrated through doping. The maximum ZT of Cu2ZnSn0.90In0.10Se4 reaches 0.95 at 850 K. This work may open a way for exploring high-performance TE materials with the family of widely existing tetrahedrally bonded semiconductors.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
66.70.Df Metals, alloys, and semiconductors
71.20.Nr Semiconductor compounds
61.72.up Other materials

Solid state nanogaps for differential measurements of molecular properties

Benjamin Moody and Gregory S. McCarty

Appl. Phys. Lett. 94, 122104 (2009); http://dx.doi.org/10.1063/1.3103616 (3 pages) | Cited 3 times

Online Publication Date: 23 March 2009

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This paper demonstrates the production and probing of solid state nanogaps. These nanogaps can be inexpensively and controllably produced using a combination of molecular and standard photolithography. These nanogaps are implemented for chemical monitoring by using surface enhanced Raman spectroscopy to collect molecular information at the nanogap and current-voltage traces to probe the charge transport of the nanogap. These data show that the oligonucleotides used as the molecular resist are degraded, that some of the degraded oligonucleotides are removed, and then new oligonucleotides are adsorbed.
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78.30.Jw Organic compounds, polymers

Fabrication and characterization of low temperature polycrystalline silicon thin film transistors by ink-jet printed nickel-mediated lateral crystallization

Jang-Sik Lee, Min-Sun Kim, Dongjo Kim, Yong-Mu Kim, Jooho Moon, and Seung-Ki Joo

Appl. Phys. Lett. 94, 122105 (2009); http://dx.doi.org/10.1063/1.3105983 (3 pages) | Cited 2 times

Online Publication Date: 23 March 2009

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High-performance polycrystalline silicon thin film transistors (poly-Si TFTs) were fabricated by using ink-jet printed nickel on large area glass substrates. Direct-printed Ni dots were used as a catalyst to crystallize the amorphous silicon into poly-Si for use in the channel region of TFT devices by metal-induced lateral crystallization. The fabricated poly-Si TFTs showed high field-effect mobility and on-off ratio that are comparable to the TFTs prepared using conventional semiconductor processes. The method presented here is a combination of bottom-up and top-down approaches and has a potential to be used in next generation high-performance poly-Si TFT fabrication.
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85.30.Tv Field effect devices
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Electrical spin injection into Si: A comparison between Fe/Si Schottky and Fe/Al2O3 tunnel contacts

G. Kioseoglou, A. T. Hanbicki, R. Goswami, O. M. J. van ‘t Erve, C. H. Li, G. Spanos, P. E. Thompson, and B. T. Jonker

Appl. Phys. Lett. 94, 122106 (2009); http://dx.doi.org/10.1063/1.3099049 (3 pages) | Cited 14 times

Online Publication Date: 25 March 2009

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We compare electrical spin injection from Fe into Si n-i-p heterostructures using different tunnel barriers—a reversed biased Fe/Si Schottky contact and a Fe/Al2O3 barrier. The electroluminescence (EL) spectra are dominated by transverse acoustic and optical phonon emission for both types of structures. The circular polarization of the EL tracks the Fe magnetization, confirming that the spin-polarized electrons originate from the Fe in each case. However, the polarization is lower for the Fe/Si contact than for the Fe/Al2O3 contact. Transmission electron microscopy reveals a complex interface and intermixing for Fe/Si that is absent in Fe/Al2O3/Si.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Gk Tunneling
73.30.+y Surface double layers, Schottky barriers, and work functions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.25.-b Spin polarized transport

Epitaxial ZnO films on (111) Si substrates with Sc2O3 buffer layers

W. Guo, M. B. Katz, C. T. Nelson, T. Heeg, D. G. Schlom, B. Liu, Y. Che, and X. Q. Pan

Appl. Phys. Lett. 94, 122107 (2009); http://dx.doi.org/10.1063/1.3095506 (3 pages) | Cited 9 times

Online Publication Date: 25 March 2009

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Epitaxial (0001) ZnO films were grown on (111) Si substrates using epitaxial (111) Sc2O3 buffer layers. The quality of the ZnO epilayers is manifested by a Hall mobility of 77 cm2/V s at room temperature, x-ray diffraction rocking curve full widths at half maximum of 300–400 arc sec, and optical properties comparable to ZnO single crystals. Transmission electron microscopy studies reveal that a thin layer of SiOx was formed at the Sc2O3/Si interface not during the Sc2O3 growth, but during the growth of the ZnO films. The thermal-mismatch induced residual strain in the films causes an energy shift of the exciton resonances in the photoluminescence spectrum. The redshifts are smaller than those of GaN films, indicating that the optical properties of ZnO are less strain sensitive.
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73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
71.35.-y Excitons and related phenomena
78.55.Et II-VI semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
68.55.ag Semiconductors

Nucleation mechanism of dislocation half-loop arrays in 4H-silicon carbide homoepitaxial layers

N. Zhang, Y. Chen, Y. Zhang, M. Dudley, and R. E. Stahlbush

Appl. Phys. Lett. 94, 122108 (2009); http://dx.doi.org/10.1063/1.3105944 (3 pages) | Cited 3 times

Online Publication Date: 25 March 2009

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A model is presented for the formation mechanism of dislocation half-loop arrays formed during the homoepitaxial growth of 4H-SiC. The reorientation during glide of originally screw oriented threading segments of basal plane dislocation (BPD) renders them susceptible to conversion into sessile threading edge dislocations (TEDs), which subsequently pin the motion of the BPD. Continued glide during further growth enables parts of the mobile BPD to escape through the surface leaving arrays of half loops comprising two TEDs and a short BPD segment with significant edge component. The faulting behavior of the arrays under UV excitation is consistent with this model.
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68.55.ag Semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
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