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1 Jun 2009

Volume 94, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 221101 (2009); http://dx.doi.org/10.1063/1.3143652 (3 pages)

Gangyi Xu, Virginie Moreau, Yannick Chassagneux, Adel Bousseksou, Raffaele Colombelli, G. Patriarche, G. Beaudoin, and I. Sagnes
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Surface-emitting quantum cascade lasers with metallic photonic-crystal resonators

Gangyi Xu, Virginie Moreau, Yannick Chassagneux, Adel Bousseksou, Raffaele Colombelli, G. Patriarche, G. Beaudoin, and I. Sagnes

Appl. Phys. Lett. 94, 221101 (2009); http://dx.doi.org/10.1063/1.3143652 (3 pages) | Cited 9 times

Online Publication Date: 1 June 2009

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Surface emitting photonic-crystal quantum cascade lasers operating at λ ≈ 7.3 μm are demonstrated. The photonic crystal resonator is written solely on the top metallization layer. The mismatch between the modes supported by metallized and nonmetallized regions yields enough optical feedback to achieve laser action. The devices exhibit single-mode emission with a side mode suppression ratio of ≈ 20 dB, the wavelength is lithographically tunable across a range of almost 70 cm−1, and the radiation is emitted from the surface. The maximum operating temperature is 220 K. The divergence of the output beam, which is doughnut-shaped, is approximately 9°.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Exact surface plasmon dispersion relations in a linear-metal-nonlinear dielectric structure of arbitrary nonlinearity

Haiping Yin, C. Xu, and P. M. Hui

Appl. Phys. Lett. 94, 221102 (2009); http://dx.doi.org/10.1063/1.3144273 (3 pages) | Cited 8 times

Online Publication Date: 1 June 2009

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Exact analytic expression for obtaining the surface plasmon (SP) dispersion relations in a system consisting of a thin metallic film sandwiched between a linear dielectric and a nonlinear dielectric of arbitrary nonlinearity is derived, based on a generalized first integral approach. The changes in SP dispersion relations on film thicknesses and nonlinearity are studied by model calculations. The thick-film limit generalizes previous results on metal/Kerr-type nonlinear interface to arbitrary nonlinearity. An analytic expression is obtained for the limiting SP frequency at large wave vectors with previous result recovered as a special case.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
77.22.Ch Permittivity (dielectric function)
78.20.Jq Electro-optical effects
68.55.A- Nucleation and growth

Resonantly probing micropillar cavity modes by photocurrent spectroscopy

C. Kistner, S. Reitzenstein, C. Schneider, S. Höfling, and A. Forchel

Appl. Phys. Lett. 94, 221103 (2009); http://dx.doi.org/10.1063/1.3147162 (3 pages) | Cited 4 times

Online Publication Date: 1 June 2009

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We demonstrate electrical readout of high quality quantum dot micropillars by means of photocurrent (PC) spectroscopy under resonant excitation. Applying this technique enables a high spectral resolution mapping of the optical mode spectrum of the micropillar revealing quality factors of up to 11 000 for a 3 μm diameter device. PC spectroscopy also shows that the contacted micropillars can act as light sensors with highly wavelength selective and photon sensitive detection capabilities down to 20 nW incident power. Moreover, bias voltage dependent PC studies provide an effective tool to study the competition between carrier tunneling out of the quantum dots and the radiative recombination.
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81.07.Ta Quantum dots
73.21.La Quantum dots
72.40.+w Photoconduction and photovoltaic effects
73.40.Gk Tunneling
78.67.Hc Quantum dots
79.60.-i Photoemission and photoelectron spectra

Electronic properties of nanocrystalline LaNiO3 and La0.5Sr0.5CoO3 conductive films grown on silicon substrates determined by infrared to ultraviolet reflectance spectra

Z. G. Hu, W. W. Li, Y. W. Li, M. Zhu, Z. Q. Zhu, and J. H. Chu

Appl. Phys. Lett. 94, 221104 (2009); http://dx.doi.org/10.1063/1.3148339 (3 pages) | Cited 4 times

Online Publication Date: 1 June 2009

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Electronic band structures of nanostructured LaNiO3 (LNO) and La0.5Sr0.5CoO3 (LSCO) films have been investigated by near-normal incident optical reflectance at room temperature. Dielectric constants of the conductive films in the photon energy range of 0.47–6.5 eV have been extracted with the Drude–Lorentz function. It is found that four interband electronic transitions can be uniquely assigned for the perovskite-type metallic oxides. Moreover, optical conductivity is approximately varied from 100 to 450 Ω−1 cm−1 and shows a different variation trend for the LNO and LSCO layers. The discrepancy could be ascribed to diverse electronic structure, grain size, and crystalline formation.
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73.22.-f Electronic structure of nanoscale materials and related systems
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
77.22.Ch Permittivity (dielectric function)
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics

Time-resolved characterization of external-cavity quantum-cascade lasers

Borislav Hinkov, Quankui Yang, Frank Fuchs, Wolfgang Bronner, Klaus Köhler, and Joachim Wagner

Appl. Phys. Lett. 94, 221105 (2009); http://dx.doi.org/10.1063/1.3142875 (3 pages) | Cited 4 times

Online Publication Date: 1 June 2009

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We report on the temporal and spectral evolution of the lasing spectrum of an external-cavity quantum-cascade (QC) laser operated in pulsed mode. Time-resolved lasing spectra, recorded on nanosecond time scale, revealed that after turn-on of the 100 ns current pulse multiple-mode lasing starts at the gain maximum of the QC laser controlled by the cavity formed by the chip facets. Depending on the spectral tuning after a time delay of 15–35 ns, the QC laser couples to the external cavity as seen from a change in lasing wavelength to that defined by the external grating as wavelength selective element.
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42.55.Px Semiconductor lasers; laser diodes

Observation of stimulated Raman scattering in silicon nanocomposites

L. Sirleto, M. A. Ferrara, G. Nicotra, C. Spinella, and I. Rendina

Appl. Phys. Lett. 94, 221106 (2009); http://dx.doi.org/10.1063/1.3148669 (3 pages) | Cited 3 times

Online Publication Date: 2 June 2009

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In this paper, we report on the observation of stimulated Raman scattering in silicon nanocomposites, consisting of silicon nanoparticles dispersed in SiO2 matrix prepared by sol-gel method. Using a 1427 nm cw pump laser, amplification of Stokes signal, at 1542.2 nm, up to 1.4 dB/cm is demonstrated. A preliminary valuation of approximately a fivefold enhancement of the gain coefficient in Raman amplifier based on silicon nanocomposites with respect to silicon and a significant reduction of threshold power are also reported. These results have a potential interest for silicon-based Raman lasers.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
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)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.55.Ye Raman lasers
42.55.Wd Fiber lasers

Distortion of the intense terahertz signal measured by spectral-encoding technique

Xiao-Yu Peng, Ralph Jung, Toma Toncian, Oswald Willi, and Jing-Hua Teng

Appl. Phys. Lett. 94, 221107 (2009); http://dx.doi.org/10.1063/1.3148674 (3 pages) | Cited 3 times

Online Publication Date: 2 June 2009

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We demonstrate that a distortion of the terahertz signal measured by spectral-encoding technique occurs when the original signal is too intense. We found that the stronger the original signal is, the more severe the distortion of the retrieved signal will be. Our simulation reproduces this phenomenon and suggests that this distortion, which affects the application of the single-shot terahertz detection technique, comes from the neglect of the quadratic term of the modulation depth which reflects the strength of the terahertz signal in the retrieving process. A possible simple method is proposed to eliminate this distortion.
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84.40.Ua Telecommunications: signal transmission and processing; communication satellites
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High-speed liquid lens with 2 ms response and 80.3 nm root-mean-square wavefront error

H. Oku and M. Ishikawa

Appl. Phys. Lett. 94, 221108 (2009); http://dx.doi.org/10.1063/1.3143624 (3 pages) | Cited 19 times

Online Publication Date: 2 June 2009

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A liquid lens structure with a step response time of 2 ms, a refractive power range of 52 D, and a root-mean-square (rms) wavefront error of 80.3 nm is reported. This lens uses a liquid-liquid interface with a pinned contact line as a variable refractive surface, and its shape is controlled by a piezostack actuator via a built-in hydraulic amplifier. The measured wavefront error suggests that the method of pinning the contact line to a precise shape is an important factor in achieving higher optical performance.
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42.79.Bh Lenses, prisms and mirrors
07.07.Tw Servo and control equipment; robots
07.05.Dz Control systems
42.15.Fr Aberrations

Low-noise GaN ultraviolet p-i-n photodiodes on GaN substrates

Yun Zhang, Shyh-Chiang Shen, Hee Jin Kim, Suk Choi, Jae-Hyun Ryou, Russell D. Dupuis, and Bravishma Narayan

Appl. Phys. Lett. 94, 221109 (2009); http://dx.doi.org/10.1063/1.3148812 (3 pages) | Cited 6 times

Online Publication Date: 4 June 2009

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We report low-noise GaN visible-blind homojunction p-i-n photodiodes. The devices are grown on a freestanding bulk GaN substrate and are fabricated using a “ledged” surface depletion technique to suppress the mesa sidewall leakage. For an 80-μm-diameter photodetector, the dark current density is lower than 40 pA/cm2. A room-temperature noise equivalent power of 4.27×10−17 W Hz−0.5 and a detectivity of 1.66×1014 cm Hz0.5 W−1 are achieved at a reverse bias of 20 V. The noise performance of the reverse-biased GaN p-i-n photodiodes are among the best values reported to date and demonstrate the potential of GaN photodiodes for low-noise high-speed UV detection.
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85.60.Dw Photodiodes; phototransistors; photoresistors
81.05.Ea III-V semiconductors

High power efficiency in Si-nc/SiO2 multilayer light emitting devices by bipolar direct tunneling

A. Marconi, A. Anopchenko, M. Wang, G. Pucker, P. Bellutti, and L. Pavesi

Appl. Phys. Lett. 94, 221110 (2009); http://dx.doi.org/10.1063/1.3147164 (3 pages) | Cited 34 times

Online Publication Date: 4 June 2009

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We demonstrate experimentally bipolar (electrons and holes) current injection into silicon nanocrystals in thin nanocrystalline-Si/SiO2 multilayers. These light emitting devices have power efficiency of 0.17% and turn-on voltage of 1.7 V. The high electroluminescence efficiency and low onset voltages are attributed to the radiative recombination of excitons formed by both electron and hole injection into silicon nanocrystals via the direct tunneling mechanism. To confirm the bipolar character, different devices were grown, with and without a thick silicon oxide barrier at the multilayer contact electrodes. A transition from bipolar tunneling to unipolar Fowler–Nordheim tunneling is thus observed.
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78.66.Db Elemental semiconductors and insulators
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
73.40.Gk Tunneling
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Impact of disorder on surface plasmons in two-dimensional arrays of metal nanoparticles

J. B. Khurgin and G. Sun

Appl. Phys. Lett. 94, 221111 (2009); http://dx.doi.org/10.1063/1.3152292 (3 pages) | Cited 5 times

Online Publication Date: 5 June 2009

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We study the impact of disorder on the properties of surface plasmons (SP) in metal nanoparticle arrays and develop analytical expressions enabling us to ascertain the degree of localization and mixing between the SP states. We show that it might be advantageous to intentionally introduce a certain degree of disorder in order to engineer the improved sensors and detectors.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.22.Lp Collective excitations
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Enhanced directional lasing by the interference between stable and unstable periodic orbits

Yuan Yao Lin, Chih-Yao Chen, Wei Chien, Jin-Shan Pan, Tsin-Dong Lee, and Ray-Kuang Lee

Appl. Phys. Lett. 94, 221112 (2009); http://dx.doi.org/10.1063/1.3148682 (3 pages) | Cited 2 times

Online Publication Date: 5 June 2009

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We demonstrate the idea of surface-assisted microstructures to tailor the modes and resulting emission from a dynamical localized vertical cavity surface emitting laser at room temperature. With a slightly mismatch between the surface structure and the native oxide cavity layer, near field intensity images corresponding to the spontaneous emission patterns, whispering-gallery modes (WGMs), dynamical localized modes (DLMs), and unidirectional light emissions are measured and identified in experiments and simulations. Moreover, the coherent superposition of WGM and DLM, i.e., stable and unstable periodic orbits, respectively, is reported to provide an alternative and general method to control lasing characteristics as well as to study quantum chaos in mesoscopic system.
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42.55.Px Semiconductor lasers; laser diodes
42.25.Hz Interference
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Optimal electro-optic sensor configuration for phase noise limited, remote field sensing applications

A. Garzarella, S. B. Qadri, and Dong Ho Wu

Appl. Phys. Lett. 94, 221113 (2009); http://dx.doi.org/10.1063/1.3152792 (3 pages) | Cited 3 times

Online Publication Date: 5 June 2009

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Electro-optic (EO) sensors, used for the nonperturbative detection of electric fields, are typically configured to modulate an optical probe beam along a crystal direction in which the EO tensor coefficient is largest. However in fiber optic EO sensors, such configurations can be strongly limited by phase noise and cumbersome compensation optics. Our results demonstrate that a greater signal to noise ratio can be achieved by modulating along a crystal direction of low static birefringence, even when the active EO tensor coefficient is several times smaller.
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42.81.Pa Sensors, gyros
42.79.-e Optical elements, devices, and systems
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Local, submicron, strain gradients as the cause of Sn whisker growth

M. Sobiech, M. Wohlschlögel, U. Welzel, E. J. Mittemeijer, W. Hügel, A. Seekamp, W. Liu, and G. E. Ice

Appl. Phys. Lett. 94, 221901 (2009); http://dx.doi.org/10.1063/1.3147864 (3 pages) | Cited 21 times

Online Publication Date: 2 June 2009

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It has been shown experimentally that local in-plane residual strain gradients occur around the root of spontaneously growing Sn whiskers on the surface of Sn coatings deposited on Cu. The strain distribution has been determined with synchrotron white beam micro Laue diffraction measurements. The observed in-plane residual strain gradients in combination with recently revealed out-of-plane residual strain-depth gradients [ M. Sobiech et al., Appl. Phys. Lett. 93, 011906 (2008) ] provide the driving forces for whisker growth.
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68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
81.65.-b Surface treatments
68.60.Bs Mechanical and acoustical properties

A reliable method of manufacturing metallic hierarchical superhydrophobic surfaces

Roman Pogreb, Gene Whyman, Reuven Barayev, Edward Bormashenko, and Doron Aurbach

Appl. Phys. Lett. 94, 221902 (2009); http://dx.doi.org/10.1063/1.3148363 (3 pages) | Cited 9 times

Online Publication Date: 2 June 2009

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A method of manufacturing hierarchical metallic surfaces demonstrating superhydrophobic properties is presented. The surfaces showed apparent contact angles as high as 153° and sliding angles of 10° for 50–100 μl droplets. The Cassie-like model [ A. B. D. Cassie and S. Baxter, Trans. Faraday Soc. 40, 546 (1944) ], considering the hierarchical topography of the relief, predicts apparent contact angles in a satisfactory agreement with the measured values.
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68.03.Cd Surface tension and related phenomena
81.05.Bx Metals, semimetals, and alloys
68.35.bd Metals and alloys

Characterizing size-dependent effective elastic modulus of silicon nanocantilevers using electrostatic pull-in instability

H. Sadeghian, C. K. Yang, J. F. L. Goosen, E. van der Drift, A. Bossche, P. J. French, and F. van Keulen

Appl. Phys. Lett. 94, 221903 (2009); http://dx.doi.org/10.1063/1.3148774 (3 pages) | Cited 26 times

Online Publication Date: 2 June 2009

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This letter presents the application of electrostatic pull-in instability to study the size-dependent effective Young’s Modulus math ( ∼ 170–70 GPa) of [110] silicon nanocantilevers (thickness ∼ 1019–40 nm). The presented approach shows substantial advantages over the previous methods used for characterization of nanoelectromechanical systems behaviors. The math is retrieved from the pull-in voltage of the structure via the electromechanical coupled equation, with a typical error of ≤ 12%, much less than previous work in the field. Measurement results show a strong size-dependence of math. The approach is simple and reproducible for various dimensions and can be extended to the characterization of nanobeams and nanowires.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli

Interface structure and the chemical states of Pt film on polar-ZnO single crystal

T. Nagata, J. Volk, Y. Yamashita, H. Yoshikawa, M. Haemori, R. Hayakawa, M. Yoshitake, S. Ueda, K. Kobayashi, and T. Chikyow

Appl. Phys. Lett. 94, 221904 (2009); http://dx.doi.org/10.1063/1.3149701 (3 pages) | Cited 7 times

Online Publication Date: 3 June 2009

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The interface structures and the chemical states between the Pt layer and polar-ZnO single crystal were investigated. Two-dimensional x-ray diffraction images revealed that Zn-polar ZnO had less mosaicity than the O-polar one. Angle-resolved hard x-ray photoelectron spectroscopy was used to investigate the chemical states of the interface. At the interface of the Pt/Zn-polar ZnO, zinc diffusion into the Pt layer, forming PtZn and ZnPtO bonds, was found. For the O-polar ZnO, in contrast, PtO was predominantly formed at the interface. Zinc diffusion prevented oxidization of the Pt layer and affected the mosaicity of the interface.
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68.35.Ct Interface structure and roughness
73.40.Ns Metal-nonmetal contacts
81.65.Mq Oxidation
66.30.H- Self-diffusion and ionic conduction in nonmetals
68.55.at Other materials
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Hydrogen sorption in Pd-decorated Mg–MgO core-shell nanoparticles

E. Callini, L. Pasquini, E. Piscopiello, A. Montone, M. Vittori Antisari, and E. Bonetti

Appl. Phys. Lett. 94, 221905 (2009); http://dx.doi.org/10.1063/1.3147205 (3 pages) | Cited 10 times

Online Publication Date: 3 June 2009

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Mg nanoparticles with metal-oxide core-shell morphology were synthesized by inert-gas condensation and decorated by in situ Pd deposition. Transmission electron microscopy and x-ray diffraction underline the formation of a noncontinuous layer with Pd clusters on top of the MgO shell. Even in the presence of a thick MgO interlayer, a modest (2 at. %) Pd decoration deeply enhances the hydrogen sorption properties: previously inert nanoparticles exhibit metal-hydride transformation with fast kinetics and gravimetric capacity above 5 wt %.
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68.43.Nr Desorption kinetics
68.37.Og High-resolution transmission electron microscopy (HRTEM)
82.60.Nh Thermodynamics of nucleation

Influence of structural changes on diffusion in liquid germanium

S. M. Chathoth, B. Damaschke, T. Unruh, and K. Samwer

Appl. Phys. Lett. 94, 221906 (2009); http://dx.doi.org/10.1063/1.3139753 (3 pages) | Cited 1 time

Online Publication Date: 4 June 2009

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Liquid germanium exhibits a change in the bonding character from being more covalent to more metallic while heating. We used quasielastic neutron scattering to measure the absolute value of self-diffusion coefficients in this liquid. Compared to other monoatomic liquids, such as liquid Ni or Ti, the self-diffusivity is an order faster near the melting temperature and shows a non-Arrhenius-like behavior. Above 1325 K, the activation energy for self-diffusion is low and obeys Stokes–Einstein relation. Even though the packing density of liquid germanium is less than that of simple metallic melts such as Pb or Sn, the temperature dependence of self-diffusivity does not exhibit D∝Tn(n ≃ 2) form, which is observed for uncorrelated binary collisions of hard-spheres.
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61.25.Mv Liquid metals and alloys
66.10.C- Diffusion and thermal diffusion
64.70.dj Melting of specific substances

Doping selective lateral electrochemical etching of GaN for chemical lift-off

Joonmo Park, Kwang Min Song, Seong-Ran Jeon, Jong Hyeob Baek, and Sang-Wan Ryu

Appl. Phys. Lett. 94, 221907 (2009); http://dx.doi.org/10.1063/1.3153116 (3 pages) | Cited 16 times

Online Publication Date: 5 June 2009

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An electrochemical etching based on oxalic acid was developed for use in the chemical lift-off of GaN epitaxial structures. It was shown that only the Si-doped n-GaN layer was etched away, while the p-type and undoped GaN layers were not etched at all. The etch rate and the remaining structure were analyzed for various doping concentrations and etching voltages. A lateral etch rate of 12 μm/min was achieved under 60 V for n-type doping concentration of 8×1018 cm−3. This doping selective etching was used to lift-off a GaN epitaxial layer patterned into 300×300 μm2 squares.
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81.65.Cf Surface cleaning, etching, patterning
61.72.uj III-V and II-VI semiconductors
82.45.Vp Semiconductor materials in electrochemistry
68.55.ag Semiconductors

InN nanocolumns grown by plasma-assisted molecular beam epitaxy on A-plane GaN templates

J. Grandal, M. A. Sánchez-García, E. Calleja, E. Gallardo, J. M. Calleja, E. Luna, A. Trampert, and A. Jahn

Appl. Phys. Lett. 94, 221908 (2009); http://dx.doi.org/10.1063/1.3151824 (3 pages)

Online Publication Date: 5 June 2009

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This work reports on the growth of wurtzite InN nanocolumns on A-plane GaN templates and on their structural and optical characterization by scanning and transmission electron microscopy, photoluminescence, and Raman spectroscopy. InN nanocolumns grown on A-plane substrates show sharp and pyramidal-like top surfaces that could be attributed to A-plane and M-plane facets, instead of the hexagonal top surfaces observed in nanocolumns grown on C-plane surfaces. The results of these characterization techniques show that the nanocolumns preserve the nonpolar growth orientation of the GaN templates. Good crystal quality is expected from the low temperature (13 K) photoluminescence dominant peak at 0.69 eV.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Og High-resolution transmission electron microscopy (HRTEM)
78.40.Ha Other nonmetallic inorganics
78.55.Cr III-V semiconductors

Proximity gettering of Cu at a (110)/(001) grain boundary interface formed by direct silicon bonding

X. Yu, J. Lu, K. Youssef, and G. Rozgonyi

Appl. Phys. Lett. 94, 221909 (2009); http://dx.doi.org/10.1063/1.3151914 (3 pages) | Cited 2 times

Online Publication Date: 5 June 2009

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We have demonstrated that a direct silicon bonded (110)/(001) interface, fabricated using hybrid orientation technology (HOT), acts as a proximity gettering center for Cu during quench annealing. The Cu gettering efficiency, which increases with annealing temperature, can reach more than 99%. Gettered Cu impurities tend to form colonylike precipitates at the (110)/(001) grain boundary (GB) interface when quenched from an elevated temperature. It is believed that interfacial GB imperfections initiate the Cu precipitation, and then, due to the release of a large number of self-interstitials, dislocation loops form and become new gettering centers which enhance the Cu gettering efficiency. These results are of interest for the defect engineering of the HOT wafer in advanced microelectronics and for enhancing our understanding of GBs in multicrystalline photovoltaic silicon.
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61.72.Mm Grain and twin boundaries
81.40.Gh Other heat and thermomechanical treatments
61.72.jj Interstitials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
72.40.+w Photoconduction and photovoltaic effects

Hydrogen diffusion in bulk and nanoclusters of MgH2 and the role of catalysts on the basis of ab initio molecular dynamics

M. Ramzan, T. Hussain, and R. Ahuja

Appl. Phys. Lett. 94, 221910 (2009); http://dx.doi.org/10.1063/1.3152250 (3 pages) | Cited 3 times

Online Publication Date: 5 June 2009

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We present ab initio molecular dynamics calculations based on density functional theory to study the hydrogen-deuterium exchange in bulk and nanoclusters of MgH2. Our calculations reveal the important role of catalysts to diffuse the hydrogen at low temperatures and increase the diffusion rate. We determine the diffusion constants, 〈D〉 of deuterium, and show the single hydrogen-deuterium exchange in bulk and nanocluster of MgH2. Our calculated value of diffusion constant of deuterium in bulk MgH2 is in excellent agreement with the experimental value. Furthermore, we show the edge site importance of catalysts in the fast diffusion of hydrogen.
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66.30.Pa Diffusion in nanoscale solids
84.60.-h Direct energy conversion and storage
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
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Modeling single-particle energy levels and resonance currents in a coherent electronic quantum dot mixer

C. Payette, B. Partoens, G. Yu, J. A. Gupta, D. G. Austing, S. V. Nair, S. Amaha, and S. Tarucha

Appl. Phys. Lett. 94, 222101 (2009); http://dx.doi.org/10.1063/1.3147196 (3 pages) | Cited 2 times

Online Publication Date: 1 June 2009

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We present model calculations based on a coherent tunneling picture, which reproduce well both the single-particle energy level position and the resonant current strength at two typical anticrossings, one involving two levels and the other three levels in a coherent mixer composed of two weakly coupled vertical quantum dots. An essential ingredient is the inclusion of higher degree terms to account for deviations from an ideal elliptical parabolic confining potential in realistic dots. We also calculate density plots of the mixed states for the modified potential.
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73.21.La Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling
73.63.Kv Quantum dots
73.40.Gk Tunneling

Enhancement of responsivity in solar-blind β-Ga2O3 photodiodes with a Au Schottky contact fabricated on single crystal substrates by annealing

Rikiya Suzuki, Shinji Nakagomi, Yoshihiro Kokubun, Naoki Arai, and Shigeo Ohira

Appl. Phys. Lett. 94, 222102 (2009); http://dx.doi.org/10.1063/1.3147197 (3 pages) | Cited 8 times

Online Publication Date: 1 June 2009

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We fabricated β-Ga2O3 photodiodes with a Au Schottky contact on a single crystal substrate and investigated the effect of postannealing on the electrical and optical properties of the photodiodes. The ideality factor improved to near unity by annealing at temperatures above 200 °C; however, the reverse leakage current remained nearly unchanged. The responsivity in the wavelength region below 260 nm was enhanced dramatically by a factor of more than 102 after annealing at 400 °C resulting in maximum responsivity of 103 A/W, accompanied with a contrast ratio of about six orders of magnitude between the responsivities at 240 and 350 nm.
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85.60.Dw Photodiodes; phototransistors; photoresistors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
73.30.+y Surface double layers, Schottky barriers, and work functions
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