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28 Mar 2011

Volume 98, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 132101 (2011); http://dx.doi.org/10.1063/1.3570660 (3 pages)

F. Deon, V. Pellegrini, F. Giazotto, G. Biasiol, L. Sorba, and F. Beltram
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Full band structure calculation of two-photon indirect absorption in bulk silicon

J. L. Cheng, J. Rioux, and J. E. Sipe

Appl. Phys. Lett. 98, 131101 (2011); http://dx.doi.org/10.1063/1.3570654 (3 pages) | Cited 2 times

Online Publication Date: 28 March 2011

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Degenerate two-photon indirect absorption in silicon is an important limiting effect on the use of silicon structures for all-optical information processing at telecommunication wavelengths. We perform a full band structure calculation to investigate two-photon indirect absorption in bulk silicon, using a pseudopotential description of the energy bands and an adiabatic bond charge model to describe phonon dispersion and polarization. Our results agree well with some recent experimental results. The transverse acoustic/optical phonon-assisted processes dominate.
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42.65.-k Nonlinear optics
14.70.Bh Photons

Tunable ultraviolet vertically-emitting organic laser

Sébastien Forget, Hadi Rabbani-Haghighi, Nordine Diffalah, Alain Siove, and Sébastien Chénais

Appl. Phys. Lett. 98, 131102 (2011); http://dx.doi.org/10.1063/1.3571558 (3 pages) | Cited 6 times

Online Publication Date: 28 March 2011

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A solid-state organic thin-film laser with intracavity frequency doubling is reported. Tunable ultraviolet emission from 309 to 322 nm is achieved from a vertical external cavity surface-emitting organic laser, with 2% efficiency (1 μJ at 315 nm). The laser comprises a poly(methyl methacrylate) layer doped with Rhodamine 640, spun-cast onto a plane mirror, a remote concave mirror, a nonlinear crystal, and a dichroic separator. The output is spectrally narrow (<0.5 nm full width at half maximum) and tunable through phase-matching selection of the fundamental radiation lasing modes. These results highlight a low-cost and portable alternative to tunable UV laser sources, useful for spectroscopic applications.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Robust gigahertz fiber quantum key distribution

Patrick J. Clarke, Robert J. Collins, Philip A. Hiskett, Paul D. Townsend, and Gerald S. Buller

Appl. Phys. Lett. 98, 131103 (2011); http://dx.doi.org/10.1063/1.3571561 (3 pages) | Cited 1 time

Online Publication Date: 28 March 2011

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We present recent results on an innovative fiber based short wavelength gigahertz clock rate quantum key distribution system operating over a standard telecommunications optical fiber quantum channel. This system is designed to be robust against environmentally induced changes in the polarization evolution of the photons in the optical fiber quantum channel and against path-length drift in the interferometers which could otherwise compromise system performance. Experimental results are presented for error rate, net bit rate and stability for different silicon single-photon avalanche diode detector types.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
03.67.Dd Quantum cryptography and communication security
03.67.Hk Quantum communication

Narrow spectral linewidth from single site-controlled In(Ga)As quantum dots with high uniformity

A. Huggenberger, S. Heckelmann, C. Schneider, S. Höfling, S. Reitzenstein, L. Worschech, M. Kamp, and A. Forchel

Appl. Phys. Lett. 98, 131104 (2011); http://dx.doi.org/10.1063/1.3568890 (3 pages) | Cited 17 times

Online Publication Date: 28 March 2011

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We present narrow spectral linewidth from single site-controlled In(Ga)As quantum dots (QDs) grown on nanoholes, which were defined by electron beam lithography on a (100) GaAs substrate. The long-range ordering of uncapped QDs is confirmed by electron microscopy whereas the ordering of capped QDs is visualized by atomic force microscopy. We find a small inhomogeneous broadening of 14.4 meV for the ensemble emission of site-controlled QDs with 300 nm lattice period. The photoluminescence from the excitonic transitions of single site-controlled QDs exhibits linewidth values down to 43 μeV, which is promising for the investigation of pronounced cavity quantum electrodynamic effects in scalable QD-microresonator systems.
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81.16.-c Methods of micro- and nanofabrication and processing
78.67.Hc Quantum dots
73.21.La Quantum dots
81.07.Ta Quantum dots
78.55.Cr III-V semiconductors
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Resonance tuning behavior in closely spaced inhomogeneous bilayer metamaterials

M. T. Reiten, D. Roy Chowdhury, J. Zhou, A. J. Taylor, J. F. O’Hara, and A. K. Azad

Appl. Phys. Lett. 98, 131105 (2011); http://dx.doi.org/10.1063/1.3566978 (3 pages) | Cited 5 times

Online Publication Date: 28 March 2011

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We have measured the interaction between closely spaced bilayer split ring resonators (SRRs) by varying separation layer and orientation. Terahertz time domain measurements match closely to simulations for arrays separated by a thin micron-scale polyimide layer. Experimental results indicate that bilayer SRRs resonances strongly depend on interlayer coupling tunable by separation and orientation. Simulation shows a relatively high Q resonance (Q ≈ 30) is associated with the “antialigned” SRR pair at separations of λ/500. Metamaterials tuned through interlayer coupling allows resonances at frequencies lower than the natural resonance of individual SRRs which has implications for electrically small antenna design.
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42.79.Wc Optical coatings
42.70.-a Optical materials

Power scalability and frequency agility of compact terahertz source based on frequency mixing from solid-state lasers

Pu Zhao, Srinivasa Ragam, Yujie J. Ding, and Ioulia B. Zotova

Appl. Phys. Lett. 98, 131106 (2011); http://dx.doi.org/10.1063/1.3572337 (3 pages) | Cited 5 times

Online Publication Date: 28 March 2011

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We investigate power scalability and frequency agility of a terahertz (THz) source by mixing two frequencies generated by solid-state lasers in a nonlinear crystal. They are made possible by introducing two solid-state laser crystals sharing the same Q switch and output coupler with the same laser beams decoupled to each other by a polarizer. Following the optimization, we have improved the THz output power nearly fivefold at 1.64 THz. By replacing one of the neodymium-doped lithium yttrium fluoride crystals with a neodymium-doped yttrium aluminum garnet crystal, we have produced 2.1 μW at 2.98 THz.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.55.Px Semiconductor lasers; laser diodes

Lasing in a metal-clad microring resonator

Min W. Kim and P.-C. Ku

Appl. Phys. Lett. 98, 131107 (2011); http://dx.doi.org/10.1063/1.3573818 (3 pages) | Cited 2 times

Online Publication Date: 29 March 2011

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Metal cladding was experimentally demonstrated to be a feasible method to further scale down the size of a microring laser. Shrinking the physical dimensions of semiconductor microring resonators has been difficult due to a large waveguide bending loss. We experimentally show that light can be better confined into a much tighter space by using the plasmonic metal structure, thereby enabling miniaturization of a microring laser.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Carrier capture delay and modulation bandwidth in an edge-emitting quantum dot laser

Levon V. Asryan, Yuchang Wu, and Robert A. Suris

Appl. Phys. Lett. 98, 131108 (2011); http://dx.doi.org/10.1063/1.3571295 (3 pages) | Cited 7 times

Online Publication Date: 30 March 2011

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We show that the carrier capture from the optical confinement layer into quantum dots (QDs) can strongly limit the modulation bandwidth ω−3 dB of a QD laser. As a function of the cross-section σn of carrier capture into a QD, ω−3 dB asymptotically approaches its highest value when σn→∞ (the case of instantaneous capture). With reducing σn, ω−3 dB decreases and becomes zero at a certain nonvanishing σnmin. The use of multiple-layers with QDs significantly improves the laser modulation response—ω−3 dB is considerably higher in a multilayer structure as compared to a single-layer structure at the same dc current.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Photonic crystal microdisk lasers

Yi-Hao Chen, Yi-Kuei Wu, and L. Jay Guo

Appl. Phys. Lett. 98, 131109 (2011); http://dx.doi.org/10.1063/1.3567944 (3 pages) | Cited 4 times

Online Publication Date: 30 March 2011

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A photonic crystal (PC) microdisk laser cavity was introduced and demonstrated. The microlaser utilizes lossless surface modes within the PC forbidden band for vertical confinement and whispering gallery modes for lateral confinement. Analysis showed that this type of cavity mode has a smaller mode volume and a larger confinement factor than other resonant modes in the microdisk stacks. Initial experiments demonstrated lasing of optically pumped wavelength-size microdisks with four period GaAs/AlGaAs PCs and InGaAs quantum dots as gain media.
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42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Lasing in metal-coated GaN nanostripe at room temperature

Yow-Gwo Wang, Cheng-Chang Chen, Ching-Hsueh Chiu, Ming-Yen Kuo, M. H. Shih, and Hao-Chung Kuo

Appl. Phys. Lett. 98, 131110 (2011); http://dx.doi.org/10.1063/1.3572023 (3 pages) | Cited 1 time

Online Publication Date: 30 March 2011

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This study demonstrated a metal-coated GaN nanostripe laser operable at room temperature. The ultraviolet lasing mode was observed at a wavelength of approximately 370 nm with a low threshold power density of 0.042 kW/cm2. The lasing mode of the metal-coated nanostripe was characterized using finite-element method simulation. The results showed the significance of metal coatings in this nanocavity structure for lasing at room temperature.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Enhancement of the near-band-edge photoluminescence of ZnO nanowires: Important role of hydrogen incorporation versus plasmon resonances

A. Dev, J. P. Richters, J. Sartor, H. Kalt, J. Gutowski, and T. Voss

Appl. Phys. Lett. 98, 131111 (2011); http://dx.doi.org/10.1063/1.3569951 (3 pages) | Cited 5 times

Online Publication Date: 30 March 2011

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We investigated the photoluminescence properties of ZnO nanowires coated with Au, Ag, and Pt nanoparticles deposited by dc sputtering. A strong enhancement of the near-band-edge emission was observed in all metal-coated samples but also if the samples were treated with Ar plasma without any nanoparticle deposition. High-resolution photoluminescence spectroscopy revealed hydrogen-donor-bound-exciton emission in all samples indicating unintentional hydrogen incorporation. A shorter decay time of the near-band-edge emission was observed in all cases. The results indicate that unintentional hydrogen incorporation plays a dominant role when metal deposition is performed by sputtering.
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78.67.Uh Nanowires
81.07.Gf Nanowires
81.07.Vb Quantum wires
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Cd Deposition by sputtering

Ge/SiGe multiple quantum well photodiode with 30 GHz bandwidth

Papichaya Chaisakul, Delphine Marris-Morini, Giovanni Isella, Daniel Chrastina, Xavier Le Roux, Samson Edmond, Eric Cassan, Jean-René Coudevylle, and Laurent Vivien

Appl. Phys. Lett. 98, 131112 (2011); http://dx.doi.org/10.1063/1.3574539 (3 pages) | Cited 8 times

Online Publication Date: 31 March 2011

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We demonstrate high speed Ge/SiGe multiple quantum wells photodiodes using a surface-illuminated vertical p-i-n structure. The device, with a mesa diameter of 12 μm, exhibits a low dark current of 231 nA at −1 V bias. An optical bandwidth of 10 and 26 GHz is measured at −1 and −4 V reverse bias, respectively, and reaches over 30 GHz at a reverse bias of −7 V. These results prove the suitability of Ge/SiGe multiple quantum well structures for high performance optoelectronic devices required for optical interconnection applications.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Broad gain bandwidth injectorless quantum-cascade lasers with a step well design

H. Li, Simeon Katz, Gerhard Boehm, and Markus-Christian Amann

Appl. Phys. Lett. 98, 131113 (2011); http://dx.doi.org/10.1063/1.3571562 (3 pages) | Cited 3 times

Online Publication Date: 31 March 2011

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The authors present a broad gain bandwidth injectorless quantum-cascade laser (QCL) with a “short period superlattice” design which provides an equivalent GaInAlAs alloy quantum step well in each active module. Devices employing the proposed step well design demonstrate an ultrabroadband gain spectrum of 480 cm−1 ( ∼ 4 μm) around the threshold at room temperature in pulsed mode. The fabricated 30 μm wide and 4 mm long laser shows the lowest room temperature threshold current density of 1.1 kA/cm2 among the broad gain QCLs emitting at similar wavelengths and a high slope efficiency of 1.6 W/A at room temperature in pulsed mode.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Solar-blind photodiodes composed of a Au Schottky contact and a β-Ga2O3 single crystal with a high resistivity cap layer

Rikiya Suzuki, Shinji Nakagomi, and Yoshihiro Kokubun

Appl. Phys. Lett. 98, 131114 (2011); http://dx.doi.org/10.1063/1.3574911 (3 pages) | Cited 4 times

Online Publication Date: 31 March 2011

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We fabricated Ga2O3 photodiodes composed of a Au Schottky contact and a β-Ga2O3 single-crystal substrate with a sol–gel prepared high resistivity cap layer. The photodiodes with the cap layer showed solar-blind photosensitivity under both forward and reverse biases in contrast to conventional Schottky photodiodes. Finally, we proposed energy band diagram of the i-n junction to determine the photodetection mechanism of our photodiodes. The photoconductive device model explained the high responsivity of over 1 A/W at forward bias. In this model, the cap layer behaves like a photoconductor, and the substrate behaves like an electrode that replenishes electrons.
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85.60.Dw Photodiodes; phototransistors; photoresistors
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
85.60.Gz Photodetectors (including infrared and CCD detectors)

High external quantum efficiency and fill-factor InGaN/GaN heterojunction solar cells grown by NH3-based molecular beam epitaxy

J. R. Lang, C. J. Neufeld, C. A. Hurni, S. C. Cruz, E. Matioli, U. K. Mishra, and J. S. Speck

Appl. Phys. Lett. 98, 131115 (2011); http://dx.doi.org/10.1063/1.3575563 (3 pages) | Cited 12 times

Online Publication Date: 1 April 2011

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High external quantum efficiency (EQE) p-i-n heterojunction solar cells grown by NH3-based molecular beam epitaxy are presented. EQE values including optical losses are greater than 50% with fill-factors over 72% when illuminated with a 1 sun AM0 spectrum. Optical absorption measurements in conjunction with EQE measurements indicate an internal quantum efficiency greater than 90% for the InGaN absorbing layer. By adjusting the thickness of the top p-type GaN window contact layer, it is shown that the short-wavelength (<365 nm) quantum efficiency is limited by the minority carrier diffusion length in highly Mg-doped p-GaN.
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88.40.jm Thin film III-V and II-VI based solar cells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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Plasma confinement by hemispherical cavity in laser-induced breakdown spectroscopy

L. B. Guo, C. M. Li, W. Hu, Y. S. Zhou, B. Y. Zhang, Z. X. Cai, X. Y. Zeng, and Y. F. Lu

Appl. Phys. Lett. 98, 131501 (2011); http://dx.doi.org/10.1063/1.3573807 (3 pages) | Cited 4 times

Online Publication Date: 29 March 2011

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An aluminum hemispherical cavity (diameter: 11.1 mm) was used to confine plasmas produced by a KrF excimer laser in air from a steel target with a low concentration manganese in laser-induced breakdown spectroscopy. A significant enhancement (factor >12) in the emission intensity of Mn lines was observed at a laser fluence of 7.8 J/cm2 when the plasma was confined by the hemispherical cavity, leading to an increase in plasma temperature about 3600 K. The maximum emission enhancement increased with increasing laser fluence. The spatial confinement mechanism was discussed using shock wave theory.
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52.58.-c Other confinement methods
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.35.Tc Shock waves and discontinuities
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Elucidating the asymmetric behavior of the discharge in a dual magnetron sputter deposition system

M. Yusupov, E. Bultinck, D. Depla, and A. Bogaerts

Appl. Phys. Lett. 98, 131502 (2011); http://dx.doi.org/10.1063/1.3574365 (3 pages)

Online Publication Date: 31 March 2011

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A magnetron discharge is characterized by drifts of the charged particles’ guiding center, caused by the magnetic field, in contrast to unmagnetized discharges. Because of these drifts, a pronounced asymmetry of the discharge can be observed in a dual magnetron setup. In this work, it is found that the shape of the discharge in a dual magnetron configuration depends on the magnetic field configuration. In a closed configuration, strong drifts were observed in one preferential direction, whereas in a mirror configuration the deflection of the discharge was not so pronounced. Our calculations confirm experimental observations.
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52.77.Dq Plasma-based ion implantation and deposition
81.15.Cd Deposition by sputtering
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.80.Sm Magnetoactive discharges (e.g., Penning discharges)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Kt Drift waves

Influence of gap width on discharge asymmetry in atmospheric pressure glow dielectric barrier discharges

D. Dai (戴栋), H. X. Hou (侯皓星), and Y. P. Hao (郝艳捧)

Appl. Phys. Lett. 98, 131503 (2011); http://dx.doi.org/10.1063/1.3574017 (3 pages) | Cited 4 times

Online Publication Date: 1 April 2011

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In this letter, a one-dimensional fluid model is used to investigate the mechanism of discharge asymmetry in atmospheric pressure helium glow dielectric barrier discharges (GDBDs). By observing the evolutionary process between the successive peak currents, the effect of the gap width on the discharge asymmetry is thoroughly discussed. It is shown that when the gap width is too large, the very severe nonuniformity of electric field distribution over the gas gap leads to the discharge asymmetry.
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52.80.Hc Glow; corona
52.65.-y Plasma simulation
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Identification of the double acceptor levels of the mercury vacancies in HgCdTe

F. Gemain, I. C. Robin, M. De Vita, S. Brochen, and A. Lusson

Appl. Phys. Lett. 98, 131901 (2011); http://dx.doi.org/10.1063/1.3570637 (3 pages) | Cited 2 times

Online Publication Date: 28 March 2011

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Photoluminescence and temperature-dependent Hall measurements of nonintentionally doped HgCdTe epilayers were compared. These films were grown by liquid phase epitaxy and postannealed under different conditions as follows: a p-type annealing was used to control the mercury vacancy concentration and a n-type annealing under saturated Hg atmosphere was used to fill the mercury vacancies. The comparison of the photoluminescence measurements with Hall effect measurements allows us to identify the two acceptor energy levels of the mercury vacancy and to evidence its “negative-U” property corresponding to a stabilization of the ionized state V− of the mercury vacancy compared to its neutral state V0.
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71.55.Ht Other nonmetals
61.72.jd Vacancies
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Hd Other semiconductors
78.66.Li Other semiconductors
73.61.Le Other inorganic semiconductors

Sb-doping of ZnO: Phase segregation and its impact on p-type doping

F. Friedrich, I. Sieber, C. Klimm, M. Klaus, Ch. Genzel, and N. H. Nickel

Appl. Phys. Lett. 98, 131902 (2011); http://dx.doi.org/10.1063/1.3570691 (3 pages) | Cited 2 times

Online Publication Date: 28 March 2011

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The incorporation of antimony (Sb) in pulsed-laser deposited ZnO thin-films was investigated employing scanning electron microscopy, Raman spectroscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction (XRD) measurements. It is shown that an increase in the Sb concentration in the target leads to a significant deterioration of the sample structure which is accompanied by a decrease in the deposition rate. Furthermore, the dopant transfer factor depends strongly on the deposition temperature and exhibits a steplike behavior above 600 °C. XRD measurements clearly show that significant Sb–O phase precipitations occur. The implications of our data on p-type doping of ZnO are discussed.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Gs II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition

Thermal quenching of single localized excitons in GaInNAs layers

M. Latkowska, R. Kudrawiec, G. Sęk, J. Misiewicz, J. Ibáñez, M. Henini, and M. Hopkinson

Appl. Phys. Lett. 98, 131903 (2011); http://dx.doi.org/10.1063/1.3571287 (3 pages) | Cited 9 times

Online Publication Date: 28 March 2011

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The authors applied the temperature-dependent microphotoluminescence to study the thermal quenching of exciton lines related to localized emission from GaInNAs. It has been observed that the dispersion of localization energy is very strong ( ∼ 0–150 meV) whereas the activation energy of each individual line is the same within the experimental error ( ∼ 6 meV). This suggests that the main source of sharp line features are excitons localized on deep donor(acceptor)like states. At low temperatures these states can participate in radiative recombination due to the coulomb attraction between electrons and holes whereas at higher temperatures they still trap carriers but these carriers recombine nonradiatively.
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71.35.-y Excitons and related phenomena
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
81.40.Gh Other heat and thermomechanical treatments

Thermodynamics of multiferroic BiFeO3: Applications for the deposition of BiFeO3 thin films

Zhi-Gang Mei, ShunLi Shang, Yi Wang, and Zi-Kui Liu

Appl. Phys. Lett. 98, 131904 (2011); http://dx.doi.org/10.1063/1.3573809 (3 pages) | Cited 1 time

Online Publication Date: 29 March 2011

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The formation enthalpy of BiFeO3 from oxides is studied by density-functional theory. It is predicted to be a small negative value by local density approximation plus U calculations, which is used to study the phase equilibria and chemical potential-temperature phase diagram of BiFeO3 by the calculation of phase diagram approach. The predicted processing window for BiFeO3 agrees well with experimental oxygen partial pressure-temperature conditions. We further predict that Bi chemical potential represented by its partial pressure can be used to adjust the stability window of BiFeO3. This opens another dimension in tailoring processing conditions for optimal growth of BiFeO3 films.
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75.85.+t Magnetoelectric effects, multiferroics
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.55.fp Other ferroelectric films
81.30.Dz Phase diagrams of other materials
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Fast electro-optic switching in liquid crystal blue phase II

Hyunseok Choi, Hiroki Higuchi, and Hirotsugu Kikuchi

Appl. Phys. Lett. 98, 131905 (2011); http://dx.doi.org/10.1063/1.3564896 (3 pages) | Cited 14 times

Online Publication Date: 30 March 2011

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Electro-optic switching based on the Kerr effect was investigated in detail for liquid crystal blue phase II (BPII) with different chiral pitch. The Kerr constant of BPII was found to be proportional to the cube of the chiral pitch, although the theoretical expectation was the square of the chiral pitch. In addition, there was little hysteresis in the voltage-transmittance curve of BPII. The response of BPII was found to be very fast, at less than 1 ms, in both the regions of local director reorientation and electrostriction by applied electric field.
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78.20.Jq Electro-optical effects
77.65.-j Piezoelectricity and electromechanical effects
42.70.Df Liquid crystals
61.30.-v Liquid crystals
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Epitaxial refractory-metal buffer layers with a chemical gradient for adjustable lattice parameter and controlled chemical interface

O. Fruchart, A. Rousseau, D. Schmaus, A. L’Hoir, R. Haettel, and L. Ortega

Appl. Phys. Lett. 98, 131906 (2011); http://dx.doi.org/10.1063/1.3567793 (3 pages)

Online Publication Date: 30 March 2011

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We have developed and characterized the structure and composition of nanometers-thick solid-solution epitaxial layers of (V,Nb) on sapphire (11math0), displaying a continuous lateral gradient of composition from one to another pure element. Further covered with an ultrathin pseudomorphic layer of W, these provide a template for the fast combinatorial investigation of growth or physical properties depending of strain.
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61.66.Dk Alloys
68.55.-a Thin film structure and morphology
64.75.Nx Phase separation and segregation in solid solutions
81.16.-c Methods of micro- and nanofabrication and processing

Metal-insulator transition without structural phase transition in V2O5 film

Manil Kang, Inkoo Kim, Sok Won Kim, Ji-Wook Ryu, and Hyo Yeol Park

Appl. Phys. Lett. 98, 131907 (2011); http://dx.doi.org/10.1063/1.3571557 (3 pages) | Cited 7 times

Online Publication Date: 30 March 2011

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Spectroscopic ellipsometry and x-ray diffraction are used to investigate the metal-insulator transition in V2O5 films. Below and above Tc no significant change in the (001) peak is observed, but both n and k spectra undergo remarkable changes over the entire photon energy range. The SE and XRD results indicate that the V2O5 film undergoes a MIT without a structural phase transition near 280 °C. Further the MIT is confirmed by measurement of the resistance with temperature.
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73.61.Ng Insulators
71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions
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