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10 Mar 2008

Volume 92, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 102101 (2008); http://dx.doi.org/10.1063/1.2890735 (3 pages)

Qing Wan, Jin Huang, Zhong Xie, Taihong Wang, Eric N. Dattoli, and Wei Lu
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Grain boundary disordering in binary alloys

Jian Luo and Xiaomeng Shi

Appl. Phys. Lett. 92, 101901 (2008); http://dx.doi.org/10.1063/1.2892631 (3 pages) | Cited 13 times

Online Publication Date: 10 March 2008

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This letter reports a grain boundary (GB) premelting/prewetting model based on the Miedema model and computational thermodynamics, predicting that GB disordering can start at as low as 60%–85% of the bulk solidus temperatures in selected systems. This model quantitatively explains the long-standing mystery of subsolidus activated sintering in W–Pd, W–Ni, W–Co, W–Fe and W–Cu, and it has broad applications for understanding GB-controlled transport kinetics and physical properties. Furthermore, this study demonstrates the necessity of developing GB “phase” diagrams as a tool for material design.
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61.72.Mm Grain and twin boundaries
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

A study of Al1−xInxN growth by reflection high-energy electron diffraction—incorporation of cation atoms during molecular-beam epitaxy

B. M. Shi, Z. Y. Wang, M. H. Xie, and H. S. Wu

Appl. Phys. Lett. 92, 101902 (2008); http://dx.doi.org/10.1063/1.2894191 (3 pages) | Cited 3 times

Online Publication Date: 10 March 2008

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Molecular-beam epitaxy of Al1−xInxN alloys with different indium (In) contents, x, were studied by in situ reflection high-energy electron diffraction (RHEED). Growth rates of the alloys were measured by the RHEED intensity oscillations for different source flux conditions, while the lattice parameters were derived from the diffraction patterns. It was found that under the excess nitrogen growth regime, incorporation of aluminum was complete whereas incorporation of In atoms was incomplete even at temperatures below 400 °C.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology

On-axis microbeam wide- and small-angle scattering experiments of a sectioned poly(p-phenylene terephthalamide) fiber

Richard J. Davies, Christian Koenig, Manfred Burghammer, and Christian Riekel

Appl. Phys. Lett. 92, 101903 (2008); http://dx.doi.org/10.1063/1.2891069 (3 pages) | Cited 9 times

Online Publication Date: 10 March 2008

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Poly(p-phenylene terephthalamide) fiber sections of ∼ 15 μm length were prepared by a laser microdissection system. On-axis mesh scans by combined small- and wide-angle x-ray scattering using a micron-sized synchrotron radiation beam confirms a radial texture of crystalline domains with orientational order differing for skin, central core and intermediate layers. A skin-core variation in small-angle scattering demonstrates the evolution of fiber structure due to the heat-treatment process.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
61.41.+e Polymers, elastomers, and plastics
81.40.Gh Other heat and thermomechanical treatments
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
78.70.Ck X-ray scattering

Volume dependence of the magnetic coupling in LaFe13−xSix based compounds

L. Jia, J. R. Sun, F. W. Wang, T. Y. Zhao, H. W. Zhang, B. G. Shen, D. X. Li, S. Nimori, Y. Ren, and Q. S. Zeng

Appl. Phys. Lett. 92, 101904 (2008); http://dx.doi.org/10.1063/1.2894194 (3 pages) | Cited 11 times

Online Publication Date: 10 March 2008

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The effects of pressure and hydrogenation, the former causes a lattice contraction while the latter causes an expansion of the sample, have been systematically studied for LaFe13−xSix (x = 1.3–2.1). It is found that the typical change of the Curie temperature is ∼ 150 K when ∼ 1.6 H/f.u. is absorbed and ∼ −106 K as the pressure sweeps from 0 to 1 GPa. One of the most remarkable results of the present work is the presence of a universal relation between Curie temperature and phase volume. The former linearly grows with the increase of lattice constant ( ∼ 1510 K/Å), irrespective of how the phase volume is modified. This result implies the exclusive dependence of the magnetic coupling in LaFe13−xSix on the Fe–Fe distances and the interstitial hydrogen does not affect the electronic structure of the compounds.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.jj Interstitials
61.66.Dk Alloys
71.20.Gj Other metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Theoretical investigation of shock wave stability in metals

I. V. Lomonosov and N. A. Tahir

Appl. Phys. Lett. 92, 101905 (2008); http://dx.doi.org/10.1063/1.2894197 (3 pages) | Cited 12 times

Online Publication Date: 10 March 2008

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Shock adiabats of metals with different initial volumes and pressures have been calculated with the use of multiphase equation of state. The stability of shock wave has been investigated using the known criteria. We found two types of instabilities occurring in the vicinity and inside two-phase liquid-gas region. They are the specific sound instability arising as a spontaneous sound emission from the shock discontinuity and two-wave configuration. The position of the instability region and its dependence on initial pressure and volume has been analyzed. Discussed are regularities obtained for 30 metals.
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62.50.Ef Shock wave effects in solids and liquids
64.30.Ef Equations of state of pure metals and alloys

Growth and thermal properties of Ga3PO7 bulk single crystals

Guogang Xu, Jing Li, Jiyang Wang, Hongyang Zhao, Xiufeng Cheng, and Wenlan Gao

Appl. Phys. Lett. 92, 101906 (2008); http://dx.doi.org/10.1063/1.2890733 (3 pages) | Cited 6 times

Online Publication Date: 10 March 2008

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Ga3PO7 crystal with large size and good optical quality has been grown by the top-seeded solution growth slow-cooling method from a Li2O–3MoO3 flux system. Thermal properties of the as-grown Ga3PO7 crystal have been carefully studied by measuring the anisotropic thermal expansion, specific heat, thermal diffusion, and thermal conductivity. The results show that Ga3PO7 crystal possesses low thermal expansion coefficients and good thermal conductivity. The calculated average thermal expansion coefficients along a and c axes are αa = 1.66×10−6 and αc = 3.53×10−6 K−1 from 293.15 to 773.15 K. The thermal conductivities along a and c axes are up to 6.34 and 6.18 W m−1 K−1 at the temperature of 303.15 K.
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81.10.Dn Growth from solutions
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
65.40.De Thermal expansion; thermomechanical effects

High pressure polymorph of MgTe predicted by first principles

Yan Li, Yanming Ma, Tian Cui, Yumei Yan, and Guangtian Zou

Appl. Phys. Lett. 92, 101907 (2008); http://dx.doi.org/10.1063/1.2895641 (3 pages) | Cited 12 times

Online Publication Date: 10 March 2008

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Ab initio phonon calculations on NiAs-type (B8) MgTe are performed to probe the structural behaviors of MgTe under high pressure. We predicted an unstable transverse acoustic mode and a phase transition of B8→orthorhombic Pnma (B31) driven by this soft mode is thus identified. The polymorph of B31 in MgTe adopts MnP-type structure containing chains of metal atoms and is stable above 42.7 GPa through the enthalpy calculations. With the discovery of the B31 phase, the previously theoretical high pressure structures of the tetragonal P4/nmm (PH4I) and the CsCl (B2) are ruled out.
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62.50.-p High-pressure effects in solids and liquids
64.70.kg Semiconductors
63.20.dk First-principles theory
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Rapid crystallization of GeTe–Bi2Te3 mixed layer

Tae-Yon Lee, Cheolkyu Kim, Younseon Kang, Dong-Seok Suh, Kijoon H. P. Kim, and Yoonho Khang

Appl. Phys. Lett. 92, 101908 (2008); http://dx.doi.org/10.1063/1.2895640 (3 pages) | Cited 7 times

Online Publication Date: 11 March 2008

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We report rapid crystallization of GeTe–Bi2Te3 mixed layers. The as-deposited (GeTe)1−x(Bi2Te3)x (GBT) layers with x>0.5 are fcc crystalline, while the layers with x<0.5 are amorphous, for cosputter deposition at room temperature. We found that Bi2Te3 significantly enhances the crystallization of the GBT layers. Furthermore, both temperature and minimum time required for crystallization (Tc and tc,min) of GBT layers are smaller than those of (GeTe)1−x(Sb2Te3)x (GST) layers. For example, crystallization of GBT layer with x = 0.12 occurs at 155.0 °C within 30.9 ns, which is around 1/3 of 95.7 ns for Ge2Sb2Te5 with Tc = 168.5 °C.
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64.70.dg Crystallization of specific substances
81.05.Gc Amorphous semiconductors

Anisotropic lattice behavior in elasticoluminescent material SrAl2O4:Eu2+

Hiroshi Yamada, Hajime Kusaba, and Chao-Nan Xu

Appl. Phys. Lett. 92, 101909 (2008); http://dx.doi.org/10.1063/1.2896296 (3 pages) | Cited 5 times

Online Publication Date: 11 March 2008

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We report that the elasticoluminescent (elastico-L) material SrAl2O4:Eu2+ (SAO-E) shows an extraordinarily anisotropic thermal expansion: the linear thermal expansion coefficient in the c axis was one order of magnitude smaller than those in the a and b axes in the monoclinic phase. This anisotropic lattice behavior was attributed to the development of the spontaneous shear strain e5 upon lowering the temperature, indicating that SAO-E is preferentially deformed by a shear stress. This suggests that controlling the crystal orientation is important for developing elastico-L devices.
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61.50.-f Structure of bulk crystals
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.20.F- Deformation and plasticity
78.60.-b Other luminescence and radiative recombination
65.40.De Thermal expansion; thermomechanical effects

Diffusion of nickel and tin in p-type (Bi,Sb)2Te3 and n-type Bi2(Te,Se)3 thermoelectric materials

Y. C. Lan, D. Z. Wang, G. Chen, and Z. F. Ren

Appl. Phys. Lett. 92, 101910 (2008); http://dx.doi.org/10.1063/1.2896310 (3 pages) | Cited 15 times

Online Publication Date: 11 March 2008

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The diffusion and spatial distribution of tin from solder, and nickel from diffusion barrier in p-type (Bi,Sb)2Te3 and n-type Bi2(Te,Se)3 thermoelectric materials were investigated using electron microscopy. The results indicate that nickel is a suitable diffusion-barrier material for tin in both (Bi,Sb)2Te3 and Bi2(Te,Se)3. However, even though it is not an issue in the (Bi,Sb)2Te3, the nickel diffuses several microns into the Bi2(Te,Se)3 during the soldering processing and degrades its performance. Diffusion coefficients of nickel in p-type (Bi,Sb)2Te3 and in n-type Bi2(Te,Se)3 were also quantitatively studied.
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68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
81.20.Vj Joining; welding

X-ray investigation of subsurface interstitial oxygen at Nb/oxide interfaces

M. Delheusy, A. Stierle, N. Kasper, R. P. Kurta, A. Vlad, H. Dosch, C. Antoine, A. Resta, E. Lundgren, and J. Andersen

Appl. Phys. Lett. 92, 101911 (2008); http://dx.doi.org/10.1063/1.2889474 (3 pages) | Cited 16 times

Online Publication Date: 11 March 2008

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We have investigated the dissolution of a natural oxide layer on a Nb(110) surface upon heating, combining x-ray reflectivity, grazing incidence diffuse scattering, and core-level spectroscopy. The natural oxide reduces after heating to 145 °C partially from Nb2O5 to NbO2, and an enrichment in subsurface interstitial oxygen by ∼ 70% in a depth of 100 Å is observed. After heating to 300 °C, the oxide reduces to NbO and the surplus subsurface oxygen gets dissolved into the bulk. Our approach can be applied for further investigation of the effect of subsurface interstitial oxygen on the performance of niobium rf cavities.
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64.75.Bc Solubility
61.72.jj Interstitials
81.40.Gh Other heat and thermomechanical treatments

A scaling method to enhance detection of a nonlinear elastic response

M. Scalerandi, A. S. Gliozzi, C. L. E. Bruno, D. Masera, and P. Bocca

Appl. Phys. Lett. 92, 101912 (2008); http://dx.doi.org/10.1063/1.2890031 (3 pages) | Cited 15 times

Online Publication Date: 11 March 2008

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The signature of nonlinearity in the elastic response of a specimen to an impingent ultrasonic wave is usually determined through Fourier analysis, which provides low amplitude signals, often below noise level. We suggest here an alternative, based on the amplitude dependence of the response of the system. Our procedure is conceptually simple and easy to implement. In addition, it keeps simultaneously into account the nonlinear signature effects on phases, amplitudes, and frequencies of the response. The sensitivity of the approach to the presence of nonlinearity is proven experimentally.
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81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
43.35.Yb Ultrasonic instrumentation and measurement techniques

Direct structural evidences of Mn11Ge8 and Mn5Ge2 clusters in Ge0.96Mn0.04 thin films

Yong Wang, Jin Zou, Zuoming Zhao, Xinhai Han, Xiaoyu Zhou, and Kang L. Wang

Appl. Phys. Lett. 92, 101913 (2008); http://dx.doi.org/10.1063/1.2884527 (3 pages) | Cited 25 times

Online Publication Date: 11 March 2008

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Mn-rich clusters in Mn-doped Ge thin films epitaxially grown on Ge (001) have been investigated by various transmission electron microscopy techniques. Both the mysterious Mn11Ge8 and the hexagonal Mn5Ge2 (a = 0.72 nm and c = 1.3 nm) clusters were confirmed to coexist in the thicker Ge0.96Mn0.04 film (80 nm). Their possible formation mechanism is attributed to the existence of ordered stacking faults. The fact that no Mn-rich clusters found in thinner films (< = 40 nm) suggests that, for a given Mn concentration and growth/annealing condition, a critical thickness exists for the formation of Mn-rich clusters.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.ag Semiconductors
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)

Role of Mn and H in formation of cubic and hexagonal GaMnN

V. K. Lazarov, S. H. Cheung, Y. Cui, L. Li, and M. Gajdardziska-Josifovska

Appl. Phys. Lett. 92, 101914 (2008); http://dx.doi.org/10.1063/1.2894190 (3 pages) | Cited 1 time

Online Publication Date: 11 March 2008

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Electron microscopy studies are carried out to determine the structure of GaMnN films grown on 6H-SiC(0001) and MgO(111) substrates by plasma-assisted molecular beam epitaxy. For the Mn/GaN multilayer growth, cubic zinc blende GaMnN is observed in the nominal Mn/GaN multilayer region and surface microprotrusions, indicative of high Mn mobility. In contrast, for the H-assisted growth of Mn-doped GaN, single phase hexagonal wurtzite GaMnN is obtained, but with columnar structure, indicative of reduced Mn mobility during growth.
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68.55.ag Semiconductors
61.72.uj III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Ac Multilayers
52.77.-j Plasma applications

Hydrogenated amorphous silicon a-Si:Hx/a-Si:Hy compositional superlattices: Profiling the lattice-constant-scale spatial change of the designed Si–H bonding configurations

Yeu-Long Jiang, Pei-Tzong Shih, and Tai-Chao Kuo

Appl. Phys. Lett. 92, 101915 (2008); http://dx.doi.org/10.1063/1.2839610 (3 pages)

Online Publication Date: 11 March 2008

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Hydrogenated amorphous silicon a-Si:Hx/a-Si:Hy compositional superlattices are produced by periodic switching two pulse-wave modulation plasmas. Simply varying the on and off times of pulse waves selectively controls the Si–H bonding configurations and yields a-Si:Hx/a-Si:Hy superlattices with spatial periodic change of the designed monohydride (SiH) bonds and polyhydride (SiH2)n bonds over ultrathin periods (4.5–2.5 nm) with lattice-constant sublayer thicknesses (2.5–0.75 nm). The superlattice structures are identified by the observation of x-ray Bragg’s diffraction peaks. The bandgap and refractive index are controlled by the spatial distribution of different Si–H bonds and changing sublayer thickness in superlattice structure.
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68.65.Cd Superlattices
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Acoustic monitoring of microplasma formation and filamentation of tightly focused femtosecond laser pulses in silica glass

Sergey I. Kudryashov, Vladimir D. Zvorykin, Andrei A. Ionin, Vygantas Mizeikis, Saulius Juodkazis, and Hiroaki Misawa

Appl. Phys. Lett. 92, 101916 (2008); http://dx.doi.org/10.1063/1.2894506 (3 pages) | Cited 9 times

Online Publication Date: 11 March 2008

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Contact acoustic technique has been employed to perform spatially resolved in situ detection of microplasma formation and filamentation of tightly focused femtosecond laser pulses with supercritical pulse powers in bulk dielectrics, via corresponding acoustic emission. Investigation of acoustic generation mechanisms related to the plasma formation and filamentation effects reveals the critical character of the opaque microplasma and provides estimates of its gigapascal-level pressures and energy densities of a few kJ/cm3. The acoustic measurement enables real-time in situ monitoring and revealing of basic mechanisms of ionization and filamentation in bulk dielectrics.
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62.65.+k Acoustical properties of solids
52.38.Hb Self-focussing, channeling, and filamentation in plasmas
52.50.-b Plasma production and heating
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Bulk moduli of wurtzite, zinc-blende, and rocksalt phases of ZnO from chemical bond method and density functional theory

Changzeng Fan, Qiang Wang, Lixiang Li, Suhong Zhang, Yan Zhu, Xinyu Zhang, Mingzhen Ma, Riping Liu, and Wenkui Wang

Appl. Phys. Lett. 92, 101917 (2008); http://dx.doi.org/10.1063/1.2895635 (3 pages) | Cited 2 times

Online Publication Date: 12 March 2008

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The density functional theory based first-principles calculations and a recently proposed chemical bond method are used to investigate the elastic and compressibility properties of the rocksalt, wurtzite, and zinc-blende phases of ZnO. The calculated bulk moduli from these two means explain the discrepancy between the theoretical and experimental values of the bulk modulus of wurtzite ZnO as well as the scattered experimental data. The results suggest that further experimental efforts are needed in order to obtain the intrinsic bulk moduli of the three phases of ZnO.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Growth of M-plane MnAs on GaAs(111)B by molecular beam epitaxy

Y. Takagaki, C. Herrmann, B. Jenichen, J. Herfort, and O. Brandt

Appl. Phys. Lett. 92, 101918 (2008); http://dx.doi.org/10.1063/1.2896616 (3 pages) | Cited 5 times

Online Publication Date: 12 March 2008

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We describe a growth procedure utilizing molecular beam epitaxy that produces a (1math00)-oriented MnAs layer on GaAs(111)B despite the incompatible unit mesh symmetry. An amorphous MnAs layer is deposited at a low temperature beyond the critical thickness for coherent growth. When solid-phase epitaxy is initiated by reducing the background As4 pressure, the layer crystalizes in the M-plane orientation with its c axis being along the {11math} directions of the substrate. The magnetization components associated with the coexisting c-axis orientations are independent of each other, suggesting that the structural domains are much larger in size than the atomic scales.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.aj Insulators
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Room temperature photoluminescence from the amorphous Si structure generated under keV Ar-ion-induced surface rippling condition

T. K. Chini, D. P. Datta, S. Facsko, and A. Mücklich

Appl. Phys. Lett. 92, 101919 (2008); http://dx.doi.org/10.1063/1.2896644 (3 pages) | Cited 6 times

Online Publication Date: 12 March 2008

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We observe room temperature (RT) visible and infrared (IR) photoluminescence (PL) bands peaked around 680 and 1020 nm, respectively, from a silicon (Si) surface amorphized and patterned with ripples by 60 keV Ar+ bombardment at 60° angle of ion incidence. However, the Si surface amorphized but not patterned under normal bombardment (0° angle of ion incidence) condition shows a drastic reduction in the intensity of the visible PL along with the complete suppression of IR emission. The present work demonstrates that Ar ion irradiation at rippling condition may yield a porouslike light emitting amorphous silicon (a-Si) nanostructure.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
78.55.Ap Elemental semiconductors
78.55.Qr Amorphous materials; glasses and other disordered solids
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Electrokinetic separation of co-solutes into bimodal fibers by electrospinning

Chunya Wu, Shinobu Nagata, Gary C. Tepper, and James T. McLeskey, Jr.

Appl. Phys. Lett. 92, 101920 (2008); http://dx.doi.org/10.1063/1.2894512 (3 pages)

Online Publication Date: 12 March 2008

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Composite and chemically/physically distinct fibers of sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate] (PTEBS) and polyethylene oxide (PEO) were formed by electrospinning from a homogeneous aqueous solution containing PTEBS and PEO co-solutes. Composite nanofibers of diameter of ∼ 60 nm were electrospun from an aqueous solution. The addition of ammonium hydroxide (NH4OH) to the water solution resulted in “bimodal” electrospun fibers consisting of distinct large diameter white PEO fiber segments and small diameter black PTEBS fiber segments. The optical absorption spectrum of the composite PTEBS/PEO nanofibers did not exhibit the characteristic peak around 460 nm, which is present in the bulk spectrum.
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78.66.Qn Polymers; organic compounds
81.05.Qk Reinforced polymers and polymer-based composites
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials

Structural disorder in the cubic Ce0.5Zr0.5O2 catalyst: A possible factor of the high catalytic activity

Takahiro Wakita and Masatomo Yashima

Appl. Phys. Lett. 92, 101921 (2008); http://dx.doi.org/10.1063/1.2890718 (3 pages) | Cited 9 times

Online Publication Date: 12 March 2008

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Nuclear-density distribution of cubic Ce0.5Zr0.5O2 compound has been studied at 1832 K by the maximum-entropy method (MEM) and MEM-based pattern fitting combined with the Rietveld method using in situ neutron powder diffraction data. The oxygen ions show a large positional disorder and shift to the ⟨111⟩ directions. Possible bulk diffusion paths of the oxygen ions can be seen along the ⟨100⟩ and ⟨110⟩ directions. The spatial distribution of oxygen ions in Ce0.5Zr0.5O2 is greater than that of CeO2, which is consistent with the higher bulk diffusivity of oxygen ions in Ce0.5Zr0.5O2. It is suggested that the greater disorder of Ce0.5Zr0.5O2 is a factor of its higher catalytic activity.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Phonon confinement and strain in CuInS2

C. Camus, E. Rudigier, D. Abou-Ras, N. A. Allsop, T. Unold, Y. Tomm, S. Schorr, S. E. Gledhill, T. Köhler, J. Klaer, M. C. Lux-Steiner, and Ch.-H. Fischer

Appl. Phys. Lett. 92, 101922 (2008); http://dx.doi.org/10.1063/1.2894519 (3 pages) | Cited 6 times

Online Publication Date: 12 March 2008

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Single crystalline and polycrystalline CuInS2 samples prepared by different methods are characterized by Raman spectroscopy. The measured spectra are fitted according to the phonon confinement model. Correlation lengths were obtained, which correspond to the size of domains of perfect crystallinity. These correlation lengths are in good agreement with distances between twin defects observed by transmission electron microscopy in polycrystalline CuInS2. Additionally, the strain present in the samples was determined from the Raman spectra. A tensile strain was obtained for the polycrystalline CuInS2 thin films, which agrees well with published values for the same material.
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63.20.-e Phonons in crystal lattices
61.72.Mm Grain and twin boundaries
78.30.Hv Other nonmetallic inorganics
68.60.Bs Mechanical and acoustical properties

Ab initio determination of Ehrlich–Schwoebel barriers on Cu{111}

S. K. Xiang and Hanchen Huang

Appl. Phys. Lett. 92, 101923 (2008); http://dx.doi.org/10.1063/1.2891106 (3 pages) | Cited 10 times

Online Publication Date: 13 March 2008

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Using the density-functional-theory based ab initio method, the authors determine the Ehrlich–Schwoebel barrier as a function of step thickness. The prototype material system is a Cu⟨110⟩ step of B type on a {111} surface. The calculation results show that the diffusion barrier of an adatom is 0.06 eV on a flat Cu{111} surface, 0.16 eV down a monolayer step, 0.39 eV down a two-layer step, and 0.40 eV down a multiple-layer step. The results, particularly the transition from 0.16  to 0.40 eV, will have major impacts on the design of surface facets during synthesis of thin films and nanorods.
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68.35.Fx Diffusion; interface formation
81.16.-c Methods of micro- and nanofabrication and processing
81.07.-b Nanoscale materials and structures: fabrication and characterization

Dynamic elastic properties and magnetic susceptibility across the austenite-martensite transformation in site-disordered ferromagnetic Ni–Fe–Al alloy

P. K. Mukhopadhyay and S. N. Kaul

Appl. Phys. Lett. 92, 101924 (2008); http://dx.doi.org/10.1063/1.2896649 (3 pages) | Cited 3 times

Online Publication Date: 13 March 2008

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ac susceptibility, sound velocity, and internal friction study of the martensitic transformation in melt-quenched (site-disordered) Ni55Fe20Al25 alloy unravels the irreversible thermoelastic changes (thermal hysteresis) that occur in the austenite phase in the premartensitic regime. In the heating cycle, the system retains the “memory” of the initiation and subsequent growth of the martensitic phase (at the expense of the parent austenite phase) that had taken place during the cooling cycle in the austenite-martensite phase coexistence region. These and other findings are discussed in this communication.
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75.50.Bb Fe and its alloys
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
75.30.Cr Saturation moments and magnetic susceptibilities
64.70.K- Solid-solid transitions
81.30.Kf Martensitic transformations

Assessing plastic shear resistance of bulk metallic glasses under nanoindentation

L. Wang, S. X. Song, and T. G. Nieh

Appl. Phys. Lett. 92, 101925 (2008); http://dx.doi.org/10.1063/1.2897301 (3 pages) | Cited 7 times

Online Publication Date: 13 March 2008

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Show Abstract
Nanoindentation tests were conducted on three different bulk metallic glasses (BMGs) using both the Berkovich and cube-corner tips. Larger displacement and more pronounced pop ins were observed under cube-corner tip in all three materials. Pop-in distance and indentation depths were used to determine the plastic shear resistance of different BMGs under nanoindentation. The plastic shear resistance was found to be independent of the shape of the indenter and dependent only on material; it is linearly scaled with the shear modulus of a material.
Show PACS
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
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