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9 Jun 2008

Volume 92, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 92, 231901 (2008); http://dx.doi.org/10.1063/1.2938921 (3 pages)

N. A. Mara, D. Bhattacharyya, P. Dickerson, R. G. Hoagland, and A. Misra
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Deformability of ultrahigh strength 5 nm Cu/Nb nanolayered composites

N. A. Mara, D. Bhattacharyya, P. Dickerson, R. G. Hoagland, and A. Misra

Appl. Phys. Lett. 92, 231901 (2008); http://dx.doi.org/10.1063/1.2938921 (3 pages) | Cited 55 times

Online Publication Date: 9 June 2008

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In this work, micropillar compression testing has been used to obtain stress-strain curves for sputter-deposited Cu–Nb nanolaminate composites with nominal bilayer thickness of 10 nm. In addition to the extremely high flow strength of 2.4 GPa, the 5 nm Cu/5 nm Nb nanolaminate exhibits significant ductility, in excess of 25% true strain.
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62.25.-g Mechanical properties of nanoscale systems
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Improved a-plane GaN quality grown with flow modulation epitaxy and epitaxial lateral overgrowth on r-plane sapphire substrate

Jeng-Jie Huang, Kun-Ching Shen, Wen-Yu Shiao, Yung-Sheng Chen, Tzu-Chi Liu, Tsung-Yi Tang, Chi-Feng Huang, and C. C. Yang

Appl. Phys. Lett. 92, 231902 (2008); http://dx.doi.org/10.1063/1.2942391 (3 pages) | Cited 9 times

Online Publication Date: 9 June 2008

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The authors demonstrate superior crystal quality of a-plane GaN grown on r-plane sapphire substrate based on the flow modulation epitaxy (FME) technique, in which the Ga atom supply is alternatively switched on and off with continuous nitrogen supply. With the FME technique, a high growth rate of 2.3 μm/h can still be achieved. With or without epitaxial lateral overgrowth (ELOG), either c- or m-mosaic condition is significantly improved in the samples of using FME. With ELOG, the surface roughness can be reduced from 1.58 to 0.647 nm in an area of 10×10 μm2 microns by using the FME technique. Based on the results of photoluminescence measurement, one can also conclude the better optical property of the FME-grown a-plane GaN thin films. Besides, it is shown that tensile strain is more relaxed in the FME samples.
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68.55.ag Semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Advanced x-ray stress analysis method for a single crystal using different diffraction plane families

Muneyuki Imafuku, Hiroshi Suzuki, Kazuyuki Sueyoshi, Koichi Akita, and Shin-ichi Ohya

Appl. Phys. Lett. 92, 231903 (2008); http://dx.doi.org/10.1063/1.2912030 (3 pages)

Online Publication Date: 10 June 2008

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Generalized formula of the x-ray stress analysis for a single crystal with unknown stress-free lattice parameter was proposed. This method enables us to evaluate the plane stress states with any combination of diffraction planes. We can choose and combine the appropriate x-ray sources and diffraction plane families, depending on the sample orientation and the apparatus, whenever diffraction condition is satisfied. The analysis of plane stress distributions in an iron single crystal was demonstrated combining with the diffraction data for Fe{211} and Fe{310} plane families.
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07.85.-m X- and γ-ray instruments
61.05.-a Techniques for structure determination

Surface chemistry of plasma-assisted atomic layer deposition of Al2O3 studied by infrared spectroscopy

E. Langereis, J. Keijmel, M. C. M. van de Sanden, and W. M. M. Kessels

Appl. Phys. Lett. 92, 231904 (2008); http://dx.doi.org/10.1063/1.2940598 (3 pages) | Cited 22 times

Online Publication Date: 10 June 2008

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The surface groups created during plasma-assisted atomic layer deposition (ALD) of Al2O3 were studied by infrared spectroscopy. For temperatures in the range of 25–150 °C, –CH3 and –OH were unveiled as dominant surface groups after the Al(CH3)3 precursor and O2 plasma half-cycles, respectively. At lower temperatures more –OH and C-related impurities were found to be incorporated in the Al2O3 film, but the impurity level could be reduced by prolonging the plasma exposure. The results demonstrate that –OH surface groups rule the surface chemistry of the Al2O3 process and likely that of plasma-assisted ALD of metal oxides from organometallic precursors in general.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
52.77.Dq Plasma-based ion implantation and deposition
78.30.Hv Other nonmetallic inorganics

Thermal properties of calcium doped strontium barium niobate crystal

Ch. Y. Gao, H. R. Xia, J. Q. Xu, C. L. Zhou, H. J. Zhang, and J. Y. Wang

Appl. Phys. Lett. 92, 231905 (2008); http://dx.doi.org/10.1063/1.2943187 (2 pages) | Cited 4 times

Online Publication Date: 11 June 2008

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Calcium doped strontium barium niobate is a tungsten-bronze ferroelectric crystal with a tetragonal unit cell. Thermophysical properties including specific heat, thermal expansion, and thermal diffusion were performed on a single crystal (Ca0.28Ba0.75)0.25(Sr0.60Ba0.40)0.75Nb2O6 (CSBN25) to determine thermal behaviors along the a and c axes. Negative thermal expansion was observed along the c axes below the Curie temperature. Isotropic thermal behavior (thermal diffusion and thermal conductivity) was observed around Curie temperature. The abnormal thermal behaviors are considered as arising due to the geometry of the dope-affected crystal.
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65.40.Ba Heat capacity
65.40.De Thermal expansion; thermomechanical effects
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
66.30.Xj Thermal diffusivity
77.80.-e Ferroelectricity and antiferroelectricity

Experimental verification and theoretical analysis of the relationships between hardness, elastic modulus, and the work of indentation

Rong Yang, Taihua Zhang, Peng Jiang, and Yilong Bai

Appl. Phys. Lett. 92, 231906 (2008); http://dx.doi.org/10.1063/1.2944138 (3 pages) | Cited 4 times

Online Publication Date: 11 June 2008

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The relationship between hardness (H), reduced modulus (Er), unloading work (Wu), and total work (Wt) of indentation is examined in detail experimentally and theoretically. Experimental study verifies the approximate linear relationship. Theoretical analysis confirms it. Furthermore, the solutions to the conical indentation in elastic-perfectly plastic solid, including elastic work (We), H, Wt, and Wu are obtained using Johnson’s expanding cavity model and Lamé solution. Consequently, it is found that the We should be distinguished from Wu, rather than their equivalence as suggested in ISO14577, and (H/Er)/(Wu/Wt) depends mainly on the conical angle, which are also verified with numerical simulations.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Lm Deformation, plasticity, and creep
62.20.de Elastic moduli
62.20.F- Deformation and plasticity

Dislocation network at InN/GaN interface revealed by scanning tunneling microscopy

Y. Liu, Y. Cai, Lixin Zhang, M. H. Xie, N. Wang, S. B. Zhang, and H. S. Wu

Appl. Phys. Lett. 92, 231907 (2008); http://dx.doi.org/10.1063/1.2944145 (3 pages) | Cited 5 times

Online Publication Date: 11 June 2008

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For heteroepitaxy of InN on GaN(0001) by molecular-beam epitaxy, the lattice misfit strain is relieved by misfit dislocations (MDs) formed at the interface between InN and GaN. Imaging by scanning tunneling microscopy (STM) of the surfaces of thin InN epifilms reveals line feature parallel to 〈11math0〉. Their contrast becomes less apparent for thicker epifilms. From the interline spacing as well as a comparison with transmission electron microscopy studies, it is suggested that they correspond to the MDs beneath the surface. The STM contrast originates from both the surface distortion caused by the local strain at MDs and the electronic states of the defects.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.20.At Surface states, band structure, electron density of states
68.35.Dv Composition, segregation; defects and impurities
68.55.ag Semiconductors

Elastic property of fcc metal nanowires via an atomic-scale analysis

Li Qiao and Xiaojing Zheng

Appl. Phys. Lett. 92, 231908 (2008); http://dx.doi.org/10.1063/1.2924310 (3 pages) | Cited 3 times

Online Publication Date: 12 June 2008

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A simple atomic-scale model based on the distortion of the unit cell generating the nanowire is proposed to predict the elastic characteristics of fcc metal nanowires. It allows for an analytical study on the mechanical behavior of nanomaterials from the perspective of atomic interactions. Bond-strength enhancing arising from the spontaneous bond relaxation has significant effects on the elastic properties of metal nanowires, which can be described by a scale function. Contribution from effects related to surface roughness and surface oxidation to the elastic modulus of nanostructures is also considered. There is good qualitative agreement between theoretical predictions and experimental observations.
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62.23.Hj Nanowires
62.20.de Elastic moduli
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.35.bd Metals and alloys
81.65.Mq Oxidation
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

Nonradiative recombination at threading dislocations in n-type GaN: Studied by cathodoluminescence and defect selective etching

M. Albrecht, J. L. Weyher, B. Lucznik, I. Grzegory, and S. Porowski

Appl. Phys. Lett. 92, 231909 (2008); http://dx.doi.org/10.1063/1.2928226 (3 pages) | Cited 14 times

Online Publication Date: 12 June 2008

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Dislocations in GaN single crystal were studied by means of spectral cathodoluminescence (CL) mapping and defect selective etching. We show that the c-type screw dislocations are not recombination active. The recombination strength of the a- and (a+c)-type dislocations is influenced by impurity gettering. While fresh dislocations exhibit a CL contrast of 0.01–0.05 in accordance with intrinsic dislocation states, grown in dislocations show a contrast of 0.25. From the analysis of spectral CL maps, we find that impurities such as oxygen and silicon are depleted in the surrounding of the dislocations. We explain the increased contrast by a reduced screening of the electrical field of the dislocation.
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78.60.Hk Cathodoluminescence, ionoluminescence
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.65.Cf Surface cleaning, etching, patterning
61.72.Yx Interaction between different crystal defects; gettering effect
81.65.Tx Gettering
68.47.Fg Semiconductor surfaces

Superior hydrogen desorption kinetics of Mg(NH2)2 hollow nanospheres mixed with MgH2 nanoparticles

Lei Xie, Yaoqi Li, Rong Yang, Yang Liu, and Xingguo Li

Appl. Phys. Lett. 92, 231910 (2008); http://dx.doi.org/10.1063/1.2943284 (3 pages) | Cited 5 times

Online Publication Date: 12 June 2008

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Mg3N2 nanocubes were prepared by vaporized bulk magnesium in ammonia atmosphere associated with plasma metal reaction. Then the product transformed to Mg(NH2)2 hollow nanospheres after it was reacted with NH3 based on the Kirkendall effect. The electron microscopy results suggested that the obtained hollow nanospheres were around 100 nm and the shell thickness was about 10 nm. Because of its short distance for Mg2+ diffusion and large specific surface area for interaction between Mg(NH2)2 and MgH2, the structure dramatically enhanced the hydrogen desorption kinetics of Mg(NH2)2–2MgH2.
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68.43.Nr Desorption kinetics
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
52.77.-j Plasma applications
66.30.Ny Chemical interdiffusion; diffusion barriers
81.07.-b Nanoscale materials and structures: fabrication and characterization

Optical properties and morphology of InAs/InP (113)B surface quantum dots

A. Nakkar, H. Folliot, A. Le Corre, F. Doré, I. Alghoraibi, C. Labbé, G. Elias, S. Loualiche, M.-E. Pistol, P. Caroff, and C. Ellström

Appl. Phys. Lett. 92, 231911 (2008); http://dx.doi.org/10.1063/1.2943651 (3 pages)

Online Publication Date: 12 June 2008

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We report on long-wavelength photoluminescence (PL) emission at room temperature from self-organized InAs surface quantum dots grown by gas-source molecular beam epitaxy on a GaInAsP/InP (113)B substrate. The influence of arsenic pressure conditions during growth on the PL emission of surface quantum dots is detailed as well as oxide/contamination layer formation after growth. Experimental results are in good agreement with six-band k⋅p theory in the envelope function approximation.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Tensile properties of carbon nanotubes grown on ultrahigh strength polyacrylonitrile-based and ultrahigh modulus pitch-based carbon fibers

Kimiyoshi Naito, Jenn-Ming Yang, Yoshihisa Tanaka, and Yutaka Kagawa

Appl. Phys. Lett. 92, 231912 (2008); http://dx.doi.org/10.1063/1.2944258 (3 pages) | Cited 6 times

Online Publication Date: 12 June 2008

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The tensile properties and fracture behavior of carbon nanotubes (CNTs) grown on ultrahigh tensile strength polyacrylonitrile (PAN)-based (T1000GB) and ultrahigh modulus pitch-based (K13D) carbon fibers have been investigated. The CNTs were grown on the carbon fiber surface using chemical vapor deposition. The statistical scattering of the tensile strength was also evaluated. The results clearly show that grafting of CNTs improves the mechanical properties and the Weibull modulus of ultrahigh tensile strength PAN-based and ultrahigh modulus pitch-based carbon fibers.
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62.25.Mn Fracture/brittleness
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.46.Fg Nanotubes
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Photoluminescence in heavily doped ZnO:N:In films

Z. Z. Ye, L. L. Chen, B. H. Zhao, and H. P. He

Appl. Phys. Lett. 92, 231913 (2008); http://dx.doi.org/10.1063/1.2945630 (3 pages) | Cited 3 times

Online Publication Date: 12 June 2008

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Temperature-dependent photoluminescence is used to investigate ZnO films codoped with In and N at different doping levels. Conversion from exciton recombination to band-to-band transition with increasing both doping level and temperature is observed. We suggest that ionization of the N acceptors and dissociation of excitons by impurity-induced local field are responsible for such conversion. For the film with N concentration of 4×1020 cm−3, the excitonic emission intensity shows anomalous temperature dependence due to localized carriers. The localization energy and the N acceptor level is determined to be about 5 and 164 meV, respectively.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
71.55.Gs II-VI semiconductors
71.35.-y Excitons and related phenomena

Effects of diffraction and dispersion on acoustic radiation-induced static pulses

John H. Cantrell

Appl. Phys. Lett. 92, 231914 (2008); http://dx.doi.org/10.1063/1.2937474 (3 pages) | Cited 4 times

Online Publication Date: 13 June 2008

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It is shown that the shapes of acoustic radiation-induced static strain and displacement pulses are defined locally by the energy density of the generating waveform and that diffraction and attenuation produce dramatic changes in the shape of static displacement pulses when using laser detection. The effects of dispersion on static pulses are obtained by including a dispersive term in the phase of the particle velocity solution to the nonlinear wave equation. The dispersion causes an evolutionary change in the shape of the energy density profile that leads to the generation of solitons experimentally observed in fused silica.
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62.65.+k Acoustical properties of solids
43.25.Dc Nonlinear acoustics of solids
43.25.Rq Solitons, chaos

Linear and nonlinear optical properties of multifunctional PbVO3 thin films

Amit Kumar, Nikolas J. Podraza, Sava Denev, Jian Li, Lane W. Martin, Ying-Hao Chu, R. Ramesh, Robert W. Collins, and Venkatraman Gopalan

Appl. Phys. Lett. 92, 231915 (2008); http://dx.doi.org/10.1063/1.2943283 (3 pages) | Cited 6 times

Online Publication Date: 13 June 2008

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Lead vanadate (PbVO3) is a multifunctional material which is both polar and magnetic. Its optical properties, important for linear and nonlinear optical spectroscopy of the material, are presented. Using spectroscopic ellipsometry, the refractive index and absorption versus wavelength of lead vanadate thin films at 295 K is reported. Using optical second harmonic generation, the nonlinear optical coefficients were determined to be d15/d31 = 0.20±0.02, d33/d31 = 316.0±4.4, and ∣d33∣ = 10.40±0.35 pm/V at a fundamental wavelength of 800 nm.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Ek Optical activity
77.55.-g Dielectric thin films
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Growth of highly strain-relaxed Ge1−xSnx/virtual Ge by a Sn precipitation controlled compositionally step-graded method

Shotaro Takeuchi, Yosuke Shimura, Osamu Nakatsuka, Shigeaki Zaima, Masaki Ogawa, and Akira Sakai

Appl. Phys. Lett. 92, 231916 (2008); http://dx.doi.org/10.1063/1.2945629 (3 pages) | Cited 24 times

Online Publication Date: 13 June 2008

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We have investigated Sn precipitation and strain relaxation behaviors in the growth of Ge1−xSnx layers on virtual Ge substrates (v-Ge) for strain engineering of Ge. By varying misfit strain at Ge1−xSnx/v-Ge and Ge1−ySny/Ge1−xSnx interfaces, we found that a critical misfit strain controls the onset of Sn precipitation at a given thickness of the Ge1−xSnx layer. A compositionally step-graded method, in which the critical misfit strain is taken into account, was applied to the growth of strain-relaxed Ge1−xSnx layers on v-Ge. Postdeposition annealing at each growth step led to lateral propagation of threading dislocations preexisting in the layer and originating from v-Ge, which resulted in high degree of strain relaxation. An epitaxial Ge layer was grown on the strain-relaxed Ge1−xSnx layer and an in-plane tensile strain of 0.68% was achieved.
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68.55.ag Semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.60.Bs Mechanical and acoustical properties

Single-crystalline B12As2 on m-plane (1math00) 15R-SiC

Hui Chen, Guan Wang, Michael Dudley, Zhou Xu, J. H. Edgar, Tim Batten, Martin Kuball, Lihua Zhang, and Yimei Zhu

Appl. Phys. Lett. 92, 231917 (2008); http://dx.doi.org/10.1063/1.2945635 (3 pages) | Cited 4 times

Online Publication Date: 13 June 2008

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Single crystal, heteroepitaxial growth of icosahedral B12As2 (IBA, a boride semiconductor) on m-plane 15R-SiC is demonstrated. Previous studies of IBA on other substrates, i.e., (111)Si and (0001)6H-SiC, produced polycrystalline and twinned epilayers. In contrast, single-crystalline and untwinned IBA was achieved on m-plane 15R-SiC. Synchrotron white beam x-ray topography, Raman spectroscopy, and high resolution transmission electron microscopy confirm the high quality of the films. High quality growth is shown to be mediated by ordered nucleation of IBA on (474) substrate facets. This work demonstrates that m-plane 15R-SiC is a good substrate choice to grow high-quality untwinned IBA epilayers for future device applications.
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68.55.ag Semiconductors
78.30.Hv Other nonmetallic inorganics

Ar gas discharge lamp with heated LiF window: A monochromatized light source for photoemission

M. Budke and M. Donath

Appl. Phys. Lett. 92, 231918 (2008); http://dx.doi.org/10.1063/1.2945641 (3 pages) | Cited 1 time

Online Publication Date: 13 June 2008

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We present a simple, inexpensive, and highly effective method for monochromatizing the vacuum ultraviolet light emitted from an Ar gas discharge for use, e.g., in photoemission experiments. By using a slightly heated window of LiF acting as low-pass filter, the emission spectrum of the Ar gas discharge is reduced to the Ar line at 11.62 eV (106.7 nm). The performance of the low-pass filter is demonstrated by photoemission measurements on Cu(111). Furthermore, we compare our light source with an unmonochromatized He gas discharge, which represents the most widely used laboratory photon source in photoemission.
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42.72.Bj Visible and ultraviolet sources
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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