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25 Sep 2006

Volume 89, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 89, 131108 (2006); http://dx.doi.org/10.1063/1.2356892 (3 pages)

Paul E. Barclay, Kartik Srinivasan, Oskar Painter, Benjamin Lev, and Hideo Mabuchi
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Complex morphology of laser-induced bulk damage in K2H(2−x)DxPO4 crystals

C. W. Carr, M. D. Feit, M. A. Johnson, and A. M. Rubenchik

Appl. Phys. Lett. 89, 131901 (2006); http://dx.doi.org/10.1063/1.2345254 (3 pages) | Cited 14 times

Online Publication Date: 25 September 2006

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We present a detailed study of the morphology of laser-induced bulk damage in K2H(2−x)DxPO4 crystals. We see three distinct regions of the internal damage sites: a rubble filled core, a shell that has probably been melted and compacted, and a larger outer region of slightly modified shocked material. The nature of these regions is important for understanding the impact of laser-induced damage on light scattering, which can be significant for high-power laser operation. We propose a simple model to explain the morphology and light scattering we observe.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.66.Fn Inorganic compounds

Elastic softening of zircon by radiation damage

Ekhard K. H. Salje

Appl. Phys. Lett. 89, 131902 (2006); http://dx.doi.org/10.1063/1.2348768 (3 pages) | Cited 6 times

Online Publication Date: 25 September 2006

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The bulk modulus and the shear modulus of zircon soften by ca. 50% when zircon is amorphized by radiation damage. A theoretical description of the experimental findings is presented which shows that the elastic response on a zircon ceramics with radiation damage follows Hashin-Shtrikman [ J. Mech. Phys. Solids 11, 127 (1963) ] behavior with very narrow bounds. The elastic response depends, in good approximation, on the square of the volume fraction fa of the amorphized regions. In a slightly coarser approximation one finds an almost linear interpolation of the bulk and the shear modulus between those of the crystalline state and those of the fully amorphous state.
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61.82.Ms Insulators
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
61.80.Az Theory and models of radiation effects

Midinfrared intersubband absorption in ZnxCd1−xSe/Znx′Cdy′Mg1−x′−y′Se multiple quantum well structures

H. Lu, A. Shen, M. C. Tamargo, C. Y. Song, H. C. Liu, S. K. Zhang, R. R. Alfano, and M. Muñoz

Appl. Phys. Lett. 89, 131903 (2006); http://dx.doi.org/10.1063/1.2354578 (3 pages) | Cited 15 times

Online Publication Date: 25 September 2006

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The authors report the observation of intersubband absorption in ZnxCd(1−x)Se/Znx′Cdy′Mg(1−x′−y′)Se multiple quantum wells. Lattice-matched samples were grown by molecular beam epitaxy on InP (001) substrates. Photoluminescence measurements indicate that the samples have excellent material quality. The peak absorption wavelengths measured by Fourier transform infrared spectroscopy are 3.99 and 5.35 μm for two samples with ZnxCd(1−x)Se well widths of 28 and 42 Å, respectively. These values fall within the 3–5 μm wavelength range, which is of interest for midinfrared intersubband devices, such as quantum cascade lasers and quantum well infrared photodetectors. Their experimental results fit well with theoretical predictions based on the envelope function approximation. The results indicate that these wide band gap II-VI materials are very promising for midinfrared intersubband device applications.
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78.67.De Quantum wells
78.30.Fs III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
73.21.Fg Quantum wells
71.20.Nr Semiconductor compounds

Glass formation mechanism of minor yttrium addition in CuZrAl alloys

Y. Zhang, J. Chen, G. L. Chen, and X. J. Liu

Appl. Phys. Lett. 89, 131904 (2006); http://dx.doi.org/10.1063/1.2357160 (3 pages) | Cited 10 times

Online Publication Date: 25 September 2006

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Effects of yttrium additions on glass-forming ability of the model system (Cu0.48Zr0.48Al0.04)100−xYx (x = 0–7 at. %) were studied in detail by using a “perturbation theory” approach. Introduction of the atomic-level strain energy into the driving force for the crystal nucleation well explained the beneficial effects of yttrium additions. It was found that the atomic-level strain energy is related closely to the atomic packing efficiency of the precipitated crystals and less yttrium amount is needed to suppress the precipitation of crystal phase with a higher atomic packing efficiency, which is consistent with the experimental observations.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses
81.30.Mh Solid-phase precipitation
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Tuning of the electronic properties of self-assembled InAs/InP(001) quantum dots using grown-in defect mediated intermixing

C. Dion, P. J. Poole, S. Raymond, P. Desjardins, and F. Schiettekatte

Appl. Phys. Lett. 89, 131905 (2006); http://dx.doi.org/10.1063/1.2357162 (3 pages) | Cited 10 times

Online Publication Date: 25 September 2006

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This paper examines the influence of rapid thermal annealing on the photoluminescence spectra of self-assembled InAs/InP(001) quantum dots capped with 760 nm InP deposited at a reduced temperature. The capping layer contained a large concentration of point defects that can promote interdiffusion upon annealing. The onset temperature for measurable blueshift in the emission spectra was found to be ∼ 600 °C whereas shifts of 270 meV were obtained after annealing at 750 °C for 300 s. Gradual etching of the InP capping layer enabled to progressively quench energy shifts upon annealing, a promising result for spatially selective emission tuning.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.65.Cf Surface cleaning, etching, patterning
61.72.J- Point defects and defect clusters

Stress relaxation during the growth of 3C-SiC/Si thin films

M. Zielinski, A. Leycuras, S. Ndiaye, and T. Chassagne

Appl. Phys. Lett. 89, 131906 (2006); http://dx.doi.org/10.1063/1.2357569 (3 pages) | Cited 15 times

Online Publication Date: 25 September 2006

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In this work the authors study the strain of 3C-SiC thin films grown on (001) on-axis silicon substrates. They use ex situ wafer curvature measurements to monitor the residual strain of silicon carbide film. At high temperature creep effects take place and modify the intrinsic strain of silicon carbide film. From the time and temperature dependences of these effects, they determine the creep exponent and the creep activation energy for 3C-SiC. Obtained values of N = 2.6±0.3 and Q = 5.6±1.0 eV are similar to those reported in literature for hexagonal polytypes of silicon carbide.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.-x Mechanical properties of solids
68.60.Bs Mechanical and acoustical properties
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Temperature dependence of the band gap of colloidal CdSe/ZnS core/shell nanocrystals embedded into an ultraviolet curable resin

Abhishek Joshi, K. Y. Narsingi, M. O. Manasreh, E. A. Davis, and B. D. Weaver

Appl. Phys. Lett. 89, 131907 (2006); http://dx.doi.org/10.1063/1.2357856 (3 pages) | Cited 18 times

Online Publication Date: 25 September 2006

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Optical absorption and photoluminescence techniques were used to investigate the energy band gap of CdSe/ZnS core/shell nanocrystals matrixed into a resin. The band gap is measured as a function of temperature for several samples with different nanocrystal diameters. Debye and Einstein temperatures were obtained by fitting the energy band gap using two different empirical expressions. Stokes shift was estimated by taking the difference between the first exciton and emission peaks. The Stokes shift was found to increase as the nanocrystal diameter is decreased suggesting a stronger electron-phonon coupling in smaller size nanocrystals.
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78.55.Et II-VI semiconductors
82.70.Dd Colloids
71.20.Nr Semiconductor compounds
63.20.K- Phonon interactions
71.38.-k Polarons and electron-phonon interactions

Local environment surrounding S and Cd in CdS:O thin film photovoltaic materials probed by x-ray absorption fine structures

Y. L. Soo, W. H. Sun, S. C. Weng, Y. S. Lin, S. L. Chang, L. Y. Jang, X. Wu, and Y. Yan

Appl. Phys. Lett. 89, 131908 (2006); http://dx.doi.org/10.1063/1.2356995 (3 pages) | Cited 2 times

Online Publication Date: 26 September 2006

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Local environments surrounding Cd and S in CdS:O thin films have been determined using extended x-ray absorption fine structure (EXAFS) and near-edge x-ray absorption fine structure (NEXAFS). As indicated by the Cd EXAFS, Cd atoms remain predominantly bonded with S. The S EXAFS and NEXAFS clearly demonstrate the presence of S–O bonds. The oxygen atoms actually combine with S to form SO3 and SO4 complexes. Combined with the transmission electron micrograph, these x-ray results suggest formation of oxygen-free CdS nanocrystals and provide an unambiguous explanation for the mystery of increased band gap that appears to violate the band anticrossing model.
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78.70.Dm X-ray absorption spectra
71.20.Nr Semiconductor compounds
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ga II-VI semiconductors

Thermal boundary conductance response to a change in Cr/Si interfacial properties

Patrick E. Hopkins and Pamela M. Norris

Appl. Phys. Lett. 89, 131909 (2006); http://dx.doi.org/10.1063/1.2357585 (3 pages) | Cited 11 times

Online Publication Date: 26 September 2006

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With continued size reduction in microelectronic devices, the boundary conductance between two materials becomes the main channel for thermal dissipation. While many efforts have been directed in studying this interfacial transport, these works have focused on the materials forming the boundary, not the boundary itself. This study focuses on the dependence of thermal boundary conductance on the properties of the region at the Cr/Si interface. The interfacial region of the Cr/Si samples is characterized with Auger electron spectroscopy depth profiling and the boundary conductance is measured with a pump-probe technique. Changes in interfacial properties are shown to significantly affect conductance.
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72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
79.20.Fv Electron impact: Auger emission

Near ultraviolet emission from nonpolar cubic AlxGa1−xN/GaN quantum wells

J. Schörmann, S. Potthast, D. J. As, and K. Lischka

Appl. Phys. Lett. 89, 131910 (2006); http://dx.doi.org/10.1063/1.2357587 (3 pages) | Cited 5 times

Online Publication Date: 26 September 2006

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In this contribution the authors studied the optical properties of cubic AlxGa1−xN/GaN single and multiple quantum wells. The well widths ranged from 2.5 to 7.5 nm. Samples were grown by rf-plasma assisted molecular beam epitaxy on free standing 3C-SiC (001) substrates. During growth of Al0.15Ga0.85N/GaN quantum wells clear reflection high energy electron diffraction oscillations were observed indicating a two dimensional growth mode. They observe strong room temperature, ultraviolet photoluminescence at about 3.3 eV with a minimum linewidth of 90 meV. The peak energy of the emission versus well width is reproduced by a square-well Poisson-Schrödinger model calculation.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.07.St Quantum wells
52.77.Dq Plasma-based ion implantation and deposition
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

In situ formation of Cu–Sn–Ni intermetallic nanolayer as a diffusion barrier in preplated lead frames

Ran Fu, Lilin Liu, Deming Liu, and Tong-Yi Zhang

Appl. Phys. Lett. 89, 131911 (2006); http://dx.doi.org/10.1063/1.2352803 (3 pages) | Cited 2 times

Online Publication Date: 26 September 2006

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A technique for impeding Cu outdiffusion in Cu alloy based preplated lead frames has been developed by electroplating a 3–4 nm thick Sn layer on a Cu alloy base prior to electroplating a Ni layer. A 10–14 nm thick epitaxylike and dense (Cu,Ni)3Sn intermetallic-compound (IMC) layer is automatically formed en route of diffuse reaction, which leads to a drastic reduction in Cu outdiffusion and hence improves significantly the protection of the lead frames against oxidation and corrosion attack. The estimated Cu diffusion coefficient in the IMC interlayer is about 1.6×10−22 m2/s at 250 °C.
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68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
81.15.Pq Electrodeposition, electroplating
81.65.Kn Corrosion protection

Cathodoluminescence of rare earth implanted AlInN

K. Wang, R. W. Martin, E. Nogales, P. R. Edwards, K. P. O’Donnell, K. Lorenz, E. Alves, and I. M. Watson

Appl. Phys. Lett. 89, 131912 (2006); http://dx.doi.org/10.1063/1.2357343 (3 pages) | Cited 12 times

Online Publication Date: 27 September 2006

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AlInN layers implanted with europium and erbium ions are systematically studied and compared with similarly implanted GaN. Cathodoluminescence from four series of annealed samples shows that the Eu/Er emissions from AlInN are considerably broader than those from GaN, while the peak positions only change slightly. The rate of increase of cathodoluminescence intensity with annealing temperature, up to 1300 °C, is analyzed for all four series. For Eu the increase exceeds 10× in both hosts. Although some decomposition is observed for annealing at 1200 °C, well above the growth temperature, AlInN is shown to be a surprisingly robust host for rare earth ions.
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78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing

Concentration dependence of carrier localization in InN epilayers

G. W. Shu, P. F. Wu, M. H. Lo, J. L. Shen, T. Y. Lin, H. J. Chang, Y. F. Chen, C. F. Shih, C. A. Chang, and N. C. Chen

Appl. Phys. Lett. 89, 131913 (2006); http://dx.doi.org/10.1063/1.2357545 (3 pages) | Cited 11 times

Online Publication Date: 27 September 2006

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The authors studied the concentration dependence of carrier localization in InN epilayers using time-resolved photoluminescence (PL). Based on the emission-energy dependence of the PL decays and the PL quenching in thermalization, the localization energy of carriers in InN is found to increase with carrier concentration. The dependence of carrier concentration on the localization energy of carriers in InN can be explained by a model based on the transition between free electrons in the conduction band and localized holes in the deeper tail states. They suggest that carrier localization originates from the potential fluctuations of randomly located impurities.
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71.20.Nr Semiconductor compounds
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Silver nanocrystal superlattice coating for molecular sensing by surface-enhanced Raman spectroscopy

T. Qiu, X. L. Wu, J. C. Shen, and Paul K. Chu

Appl. Phys. Lett. 89, 131914 (2006); http://dx.doi.org/10.1063/1.2357548 (3 pages)

Online Publication Date: 27 September 2006

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A nanotechnique to assemble silver nanocrystals and control the gaps precisely in the sub-10 nm regime is demonstrated on an active coating exhibiting surface-enhanced Raman scattering (SERS). The silver nanocrystal superlattice coating boasts a high SERS enhancement factor, large dynamic range, and universal SERS activity. The observed SERS efficiency can be explained in terms of interparticle-coupling-induced Raman enhancement.
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81.16.Dn Self-assembly
81.10.Dn Growth from solutions
68.65.Cd Superlattices
61.46.Hk Nanocrystals
78.30.Er Solid metals and alloys
87.80.-y Biophysical techniques (research methods)

Analysis of the factors governing the enhanced photoluminescence brightness of Li-doped Y2O3:Eu thin-film phosphors

Jun Yeol Cho, Young Rag Do, and Young-Duk Huh

Appl. Phys. Lett. 89, 131915 (2006); http://dx.doi.org/10.1063/1.2357561 (3 pages) | Cited 25 times

Online Publication Date: 27 September 2006

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The authors studied the Li concentration dependence of the internal efficiency and extraction efficiency contributions to the enhanced photoluminescence (PL) brightness of the Li-doped Y2O3:Eu thin films. Experiments conducted with excitation at a wavelength of 254 nm showed that adding 20 mol % Li2CO3 to conventional Y2O3:Eu thin films improved their PL brightness by a factor of over 7.0. This improvement is attributed to enhanced internal factors (crystallinity, grains, and substitution of interstitial oxygen) and the increased optical volume (thickness), as well as the reduction of photon trapping in the high-index guiding layers of the Y2O3:Eu thin films. They also discuss how to quantitatively determine the contributions of the internal efficiency, the extraction efficiency, and the optical volume to the enhanced PL brightness of the Li-doped Y2O3:Eu thin-film phosphors.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.J- Point defects and defect clusters
68.55.-a Thin film structure and morphology

Wavelength dependence of thermo-optic coefficient of organically modified SiO2–ZrO2 hybrid films

Eun-Seok Kang, Masahide Takahashi, Yomei Tokuda, and Toshinobu Yoko

Appl. Phys. Lett. 89, 131916 (2006); http://dx.doi.org/10.1063/1.2355469 (3 pages) | Cited 2 times

Online Publication Date: 27 September 2006

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Thermo-optic characteristics of organically modified SiO2–ZrO2 films prepared by a nonhydrolytic reaction have been investigated. The thermo-optic coefficient (dn/dT) is negative on the order of −10−4/K and varies with the wavelength as a function of the ZrO2 content in organically modified SiO2 material. As the amount of ZrO2 increases, the wavelength dependence of dn/dT gradually varies from positive to negative. The magnitude and wavelength dependence of dn/dT for organically modified SiO2–ZrO2 hybrid materials make these materials highly flexible for application in thermo-optic integrated devices.
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78.66.-w Optical properties of specific thin films
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Microwave transmission through metallic hole arrays: Surface electric field measurements

Bo Hou, Zhi Hong Hang, Weijia Wen, C. T. Chan, and Ping Sheng

Appl. Phys. Lett. 89, 131917 (2006); http://dx.doi.org/10.1063/1.2357942 (3 pages) | Cited 26 times

Online Publication Date: 27 September 2006

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The authors investigate the enhanced microwave transmission through a metal plate perforated by a square lattice of subwavelength holes, predicted to occur as a structure factor resonance phenomenon [ F. J. Gracía de Abajo and J. J. Sáenz, Phys. Rev. Lett. 95, 233901 (2005) ]. By probing the surface electric field on the metallic plate at the peak transmission frequency, they establish the similarities and differences between the structure factor resonance and surface plasmon.
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06.30.Ka Basic electromagnetic quantities
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Hydrogen incorporation processes in nanodiamond films studied by isotopic induced modifications of Raman spectra

Sh. Michaelson, O. Ternyak, A. Hoffman, and Y. Lifshitz

Appl. Phys. Lett. 89, 131918 (2006); http://dx.doi.org/10.1063/1.2358104 (3 pages) | Cited 9 times

Online Publication Date: 28 September 2006

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The effect of replacing H by D and C-12 by C-13 in the gas species used to grow different types of nanodiamond films on the Raman spectra of these films was studied. The modifications of the Raman spectra were investigated in submicron sized diamond films grown by hot filament chemical vapor deposition and in nanodiamond films prepared by energetic glow discharge plasma. The latter are nanocomposites of nanodiamond crystallites embedded in an a-C:H matrix. The different spectra of the two film types add insight to the hydrogen incorporation processes in nanodiamond films responsible for the C–H related (assigned to trans-polyacetylene) Raman peaks.
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81.07.Bc Nanocrystalline materials
81.05.U- Carbon/carbon-based materials
68.55.A- Nucleation and growth
78.66.-w Optical properties of specific thin films
78.30.Hv Other nonmetallic inorganics
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Observation of carbon-containing nanostructured mixed titania phases for visible-light photocatalysts

P.-W. Chou, S. Treschev, P.-H. Chung, C.-L. Cheng, Y.-H. Tseng, Y.-J. Chen, and M. S. Wong

Appl. Phys. Lett. 89, 131919 (2006); http://dx.doi.org/10.1063/1.2357879 (3 pages) | Cited 20 times

Online Publication Date: 28 September 2006

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This research analyzed a visible-light-responsive carbon-containing titania photocatalysts prepared by sol-gel method using confocal Raman spectral mapping, transmission electron microscopy, and UV/visible spectroscopy. The incorporation of carbons in the initial titania powder of anatase and amorphous phases was found to facilitate the formation of rutile or brookite phases from the amorphous phase in the 150–250 °C temperature range, resulting in nanostructured mixed titania phases which create interface states and effectively shift the band gap to ∼ 2.7 eV. The further shift in the absorption tails up to 800 nm was attributed to carbon species-covered and/or defected titania powders.
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81.07.Bc Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.50.-m Photochemistry
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)
78.30.Hv Other nonmetallic inorganics

Simultaneous growth of Ni5Ge3 and NiGe by reaction of Ni film with Ge

F. Nemouchi, D. Mangelinck, C. Bergman, G. Clugnet, P. Gas, and J. L. Lábár

Appl. Phys. Lett. 89, 131920 (2006); http://dx.doi.org/10.1063/1.2358189 (3 pages) | Cited 13 times

Online Publication Date: 29 September 2006

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The reaction between nanometric Ni films and Ge is analyzed using isothermal x-ray diffraction measurements and transmission electron microscopy. It is found that NiGe is formed during deposition at room temperature. The metal rich phase that grows during heat treatment has been clearly identified to be Ni5Ge3. The simultaneous growths of Ni5Ge3 and NiGe have been observed on amorphous and polycrystalline germanium. This is in contrast with the usual sequential growth reported in thin films.
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68.55.A- Nucleation and growth
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.37.Lp Transmission electron microscopy (TEM)
61.72.Cc Kinetics of defect formation and annealing

Quantification of multicomponent droplet evaporation through optical resonances

H. Tu and A. K. Ray

Appl. Phys. Lett. 89, 131921 (2006); http://dx.doi.org/10.1063/1.2358105 (3 pages) | Cited 2 times

Online Publication Date: 29 September 2006

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The evaporation dynamics of a binary droplet is established by aligning resonances observed in light scattering with those calculated from an evaporation model. For an ideal solution droplet the size and composition as functions of time are determined with high precision from the observed resonances, and the underlying evaporation model is unquestionably validated by accurately recovering the properties of the individual components of the droplet. The results suggest that experimental resonances, each containing a unique relation between the size parameter and the refractive index, can be used to accurately quantify multicomponent droplet evaporation through complex models.
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64.70.F- Liquid-vapor transitions
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Growth and photoluminescence studies of Al-rich AlN/AlxGa1−xN quantum wells

T. M. Al Tahtamouni, N. Nepal, J. Y. Lin, H. X. Jiang, and W. W. Chow

Appl. Phys. Lett. 89, 131922 (2006); http://dx.doi.org/10.1063/1.2358107 (3 pages) | Cited 12 times

Online Publication Date: 29 September 2006

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A set of AlN/AlxGa1−xN (x ∼ 0.65) quantum wells (QWs) with well width Lw varying from 1 to 3 nm has been grown by metal organic chemical vapor deposition. Low temperature photoluminescence (PL) spectroscopy has been employed to study the Lw dependence of the PL spectral peak position, emission efficiency, and linewidth. These results have shown that these AlN/AlGaN QW structures exhibit polarization fields of ∼ 4 MV/cm. Due to effects of quantum confinement and polarization fields, AlN/AlGaN QWs with Lw between 2 and 2.5 nm exhibit the highest quantum efficiency. The dependence of the emission linewidth on Lw yielded a linear relationship. The implications of our results on deep ultraviolet optoelectronic device applications are also discussed.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
68.65.Fg Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Buckling and competition of energy and entropy lead conformation of single-walled carbon nanocones

Shengli Zhang, Zhenwei Yao, Shumin Zhao, and Erhu Zhang

Appl. Phys. Lett. 89, 131923 (2006); http://dx.doi.org/10.1063/1.2358109 (3 pages)

Online Publication Date: 29 September 2006

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Using a continuum model, expressions for the elastic energy, defect energy, structure entropy, and mixing entropy of carbon nanocones are proposed analytically. The optimal conformation of carbon nanocones is studied by imposing minimization of free energy and analyzing the effects that the buckling of a nanocone’s walls have during formation. The model explains the experimentally observed preference of 19.2° for the cone angle of carbon nanocone. Furthermore, it predicts the optimal conformation of carbon nanocones to result in a cone angle of 19.2°, radius of 0.35 nm, and critical length of 24 nm, all of which agree very well with experimental observations.
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62.25.-g Mechanical properties of nanoscale systems
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity
62.20.D- Elasticity

Simulating temperature effects in the growth of tetrahedral amorphous carbon: The importance of infrequent events

N. A. Marks, M. F. Cover, and C. Kocer

Appl. Phys. Lett. 89, 131924 (2006); http://dx.doi.org/10.1063/1.2358116 (3 pages) | Cited 16 times

Online Publication Date: 29 September 2006

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This thin-film deposition study of tetrahedral amorphous carbon shows that including infrequent processes on the millisecond scale substantially improves the accuracy of molecular dynamics simulations. Elevated temperature between energetic impacts is used to activate processes which are typically ignored. In agreement with experiment, the simulations show an abrupt transition in which diamondlike carbon transforms into vertically oriented graphitic sheets. The simulations also highlight the importance of infrequent events in combination with energetic impact. In the absence of the latter, the transition temperature is significantly higher, in good correlation with experiment.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.A- Nucleation and growth
61.43.Bn Structural modeling: serial-addition models, computer simulation
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
61.43.-j Disordered solids

Mechanisms of dislocation reduction in an Al0.98Ga0.02N layer grown using a porous AlN buffer

J. Bai, T. Wang, P. J. Parbrook, and A. G. Cullis

Appl. Phys. Lett. 89, 131925 (2006); http://dx.doi.org/10.1063/1.2358123 (3 pages) | Cited 6 times

Online Publication Date: 29 September 2006

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Greatly improved optical properties of Al0.55Ga0.45N/Al0.65Ga0.35N multiple quantum well (MQW) structures grown on the low dislocation density Al0.98Ga0.02N layer grown using a porous AlN buffer have been observed by photoluminescence measurement, in comparison with a MQW grown on a normal AlN layer. The mechanism for the dislocation reduction has been explored by transmission electron microscopy. Due to an attraction towards lateral growth fronts, the threading dislocations in the AlN layer bend during the overgrowth, but mainly by small angles, which is different from the 90° bending generally observed in classic epitaxial lateral overgrowth method. The dislocation reduction is realized through two main pathways: enhanced dislocation annihilation due to the small-angle line bending and the termination of dislocations at local free surfaces introduced by the nanoscale voids, produced around the interface between the Al0.98Ga0.02N and AlN layers.
Show PACS
68.65.Fg Quantum wells
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.67.De Quantum wells
78.55.Cr III-V semiconductors
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