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24 Jan 2005

Volume 86, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 86, 043106 (2005); http://dx.doi.org/10.1063/1.1853514 (3 pages)

William L. Hughes and Zhong L. Wang
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Physical properties of liquid and undercooled tungsten by levitation techniques

Paul-François Paradis, Takehiko Ishikawa, Ryuichi Fujii, and Shinichi Yoda

Appl. Phys. Lett. 86, 041901 (2005); http://dx.doi.org/10.1063/1.1853513 (3 pages) | Cited 12 times

Online Publication Date: 18 January 2005

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Maintaining deep undercooling melts represents a formidable challenge when dealing with tungsten due to its high vapor pressure, its melting temperature (Tm = 3695 K), and the risk of contamination. Using electrostatic levitation, properties of liquid tungsten were measured above the melting temperature as well as in the undercooled phase. Over the 3125–3710 K interval, the density was measured as ρ(T) = 1.67×104−1.08(T−Tm) kg m−3. Similarly, the surface tension was measured as σ(T) = 2.478×103−0.31(T−Tm) over the 3360–3700 K range. At Tm, the data agree well with the literature values. The excellent processing conditions also offer opportunities to achieve reproducible and controlled formation of metastable phases.
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64.70.D- Solid-liquid transitions
81.30.Fb Solidification
68.03.Cd Surface tension and related phenomena

Study of band structure InxGa1−xN/GaN multiple quantum wells by high-resolution electron microscopy and electron holography

W. Lü, C. R. Li, and Z. Zhang

Appl. Phys. Lett. 86, 041902 (2005); http://dx.doi.org/10.1063/1.1856138 (3 pages)

Online Publication Date: 18 January 2005

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Two InxGaN1−x/GaN (x = 0.15 and 0.18) multiple-quantum-well samples with strained-layer thickness larger∕less than the critical thickness, respectively, were investigated by high-resolution electron microscopy, electron holography, and photoluminescence (PL). The PL intensity of the sample with strained-layer thickness larger than the critical thickness was weaker than that of the sample with strained-layer thickness less than the critical thickness by five times. Electron holography revealed that the profiles of the inner potential V0 across the quantum wells GaN/InxGaN1−x/GaN of the samples were not too different. The well feature of the sample with strained-layer thickness larger than the critical thickness was very blurry, especially near the top GaN/InGaN interface. It is suggested that the interface sharpness is most critical for optical property of quantum well devices.
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81.07.St Quantum wells
73.21.Fg Quantum wells
78.67.De Quantum wells
68.35.Gy Mechanical properties; surface strains
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Differential scanning calorimetry analysis of the linear parabolic growth of nanometric Ni silicide thin films on a Si substrate

F. Nemouchi, D. Mangelinck, C. Bergman, P. Gas, and Ulf Smith

Appl. Phys. Lett. 86, 041903 (2005); http://dx.doi.org/10.1063/1.1852727 (3 pages) | Cited 15 times

Online Publication Date: 18 January 2005

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The formation of nanometric Ni silicide films on a Si wafer is analyzed using differential scanning calorimetry (DSC) and isothermal x-ray diffraction measurements. The sensitivity of DSC is remarkable even in this experimental configuration constituted of a Ni∕Si bilayer deposited on a Si substrate. Both methods confirm the sequential growth of Ni2Si and NiSi (for T<700 °C). However the kinetics of growth of the first silicide formed (Ni2Si) cannot be fitted, for the two sets of measurements, by a simple parabolic law. Better agreement is obtained using a linear-parabolic growth law and a smaller activation energy for the linear term (0.8 eV) than for the parabolic one (1.5 eV).
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68.37.-d Microscopy of surfaces, interfaces, and thin films

Giant optical anisotropy in a single InAs quantum dot in a very dilute quantum-dot ensemble

I. Favero, G. Cassabois, A. Jankovic, R. Ferreira, D. Darson, C. Voisin, C. Delalande, Ph. Roussignol, A. Badolato, P. M. Petroff, and J. M. Gérard

Appl. Phys. Lett. 86, 041904 (2005); http://dx.doi.org/10.1063/1.1854733 (3 pages) | Cited 21 times

Online Publication Date: 18 January 2005

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We present experimental evidence of giant optical anisotropy in single InAs quantum dots. Polarization-resolved photoluminescence spectroscopy reveals a linear polarization ratio with huge fluctuations, from one quantum dot to another, in sign and in magnitude with absolute values up to 82%. Systematic measurements on hundreds of quantum dots coming from two different laboratories demonstrate that the giant optical anisotropy is an intrinsic feature of dilute quantum-dot arrays.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Magneto-controlled nonlinear optical materials

J. P. Huang and K. W. Yu

Appl. Phys. Lett. 86, 041905 (2005); http://dx.doi.org/10.1063/1.1854719 (3 pages) | Cited 14 times

Online Publication Date: 18 January 2005

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We exploit theoretically a magneto-controlled nonlinear optical material which contains ferromagnetic nanoparticles with a nonmagnetic metallic nonlinear shell in a host fluid. Such an optical material can have anisotropic linear and nonlinear optical properties and a giant enhancement of nonlinearity, as well as an attractive figure of merit.
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42.70.Mp Nonlinear optical crystals
75.50.Tt Fine-particle systems; nanocrystalline materials
42.65.An Optical susceptibility, hyperpolarizability
78.20.Ls Magneto-optical effects
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

In situ x-ray diffraction and calorimetric studies of devitrification process in Cu-based bulk glassy alloys

Dmitri V. Louzguine, Alain Reza Yavari, and Akihisa Inoue

Appl. Phys. Lett. 86, 041906 (2005); http://dx.doi.org/10.1063/1.1850589 (3 pages) | Cited 5 times

Online Publication Date: 18 January 2005

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The present work is devoted to an investigation of the formation of the nanoscale icosahedral phase in Cu55Zr30Ti10Pd5 and Cu50Zr30Ti10Pd10 bulk glassy alloys by synchrotron x-ray radiation. Calculations based on the x-ray and selected-area electron diffraction patterns indicate that this phase has a high degree of icosahedral order. Kinetics of the devitrification of Cu55Zr30Ti10Pd5 is also studied in detail.
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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
61.44.Br Quasicrystals
61.46.-w Structure of nanoscale materials

Influence of an in-plane electric field on exciton fine structure in InAs-GaAs self-assembled quantum dots

K. Kowalik, O. Krebs, A. Lemaître, S. Laurent, P. Senellart, P. Voisin, and J. A. Gaj

Appl. Phys. Lett. 86, 041907 (2005); http://dx.doi.org/10.1063/1.1855409 (3 pages) | Cited 63 times

Online Publication Date: 19 January 2005

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The influence of an in-plane electric field on the optical properties of single quantum dots is investigated. On a sample containing a plane of InAs/GaAs dots, micrometer-size electro-optical structures were produced in order to apply an external electric field in the dot plane. A large decrease of the anisotropic exchange splitting, correlated with the in-plane Stark shift, is observed.
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73.21.La Quantum dots
78.67.Hc Quantum dots
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.55.Cr III-V semiconductors
71.35.Ee Electron-hole drops and electron-hole plasma
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Continuous evolution of Ga adlayer coverages during plasma-assisted molecular-beam epitaxy of (0001) GaN

G. Koblmüller, J. Brown, R. Averbeck, H. Riechert, P. Pongratz, and J. S. Speck

Appl. Phys. Lett. 86, 041908 (2005); http://dx.doi.org/10.1063/1.1853530 (3 pages) | Cited 19 times

Online Publication Date: 20 January 2005

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We present a study of the evolution of the Ga adlayer during plasma-assisted molecular-beam epitaxy of (0001) GaN as a function of both Ga flux and growth temperature. In situ quadrupole mass spectrometry was used to quantitatively determine the adsorbed Ga coverage by monitoring its subsequent desorption after GaN growth. Independent of the growth time, the Ga adlayer was found to form steady-state coverages that increase continuously from 0 to 2.5 monolayers when raising the Ga flux from N-rich to moderate Ga-rich growth conditions. At higher Ga fluxes or lower growth temperatures, macroscopic Ga droplets form on top of the Ga adlayer (Ga droplet regime). Based on the temperature dependency for the transition between the Ga adlayer and Ga droplet regime, we determined an apparent activation energy of 3.4 eV, which is discussed with respect to previously reported values.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.43.Mn Adsorption kinetics

Surface-diffusion-controlled incorporation of nanosized voids during hydrogenated amorphous silicon film growth

A. H. M. Smets, W. M. M. Kessels, and M. C. M. van de Sanden

Appl. Phys. Lett. 86, 041909 (2005); http://dx.doi.org/10.1063/1.1853508 (3 pages) | Cited 9 times

Online Publication Date: 20 January 2005

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The incorporation of nanosized voids during hydrogenated amorphous silicon film growth is studied by measurements of the film mass density and the hydrogen present at the void surfaces. The observed dependence of the density of nanosized voids on the growth flux and substrate temperature is explained in terms of a surface-diffusion-controlled void incorporation model. From this analysis, an activation energy for surface diffusion in the range of 0.77–1.05 eV has been found, a value which is in agreement with the activation energy obtained from the analysis of the surface roughness evolution during growth in a previous study.
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61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.43.Bn Structural modeling: serial-addition models, computer simulation
68.35.Fx Diffusion; interface formation
68.35.B- Structure of clean surfaces (and surface reconstruction)
66.30.Lw Diffusion of other defects
68.55.-a Thin film structure and morphology

Correlation between yellow luminescence intensity and carrier lifetimes in GaN epilayers

J. Mickevičius, R. Aleksiejūnas, M. S. Shur, S. Sakalauskas, G. Tamulaitis, Q. Fareed, and R. Gaska

Appl. Phys. Lett. 86, 041910 (2005); http://dx.doi.org/10.1063/1.1857090 (3 pages) | Cited 7 times

Online Publication Date: 20 January 2005

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GaN epilayers grown on sapphire and SiC substrates and exhibiting yellow and blue luminescence were studied using photoluminescence spectroscopy, light-induced grating, and Kelvin probe techniques. For epilayers on sapphire substrates, we observed practically no yellow luminescence (YL) and lifetimes exceeding 100 ps in samples with the Fermi level close ( ∼ 0.5 eV) to conduction band, while samples with Fermi level close to the midgap exhibited YL. A general trend is a decrease in the intensity of yellow and blue emission bands compared to the intensity of the band-to-band recombination in the samples with longer carrier lifetimes.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.20.At Surface states, band structure, electron density of states
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

In situ pressure Raman spectroscopy and mechanical stability of superhard boron suboxide

Zhongwu Wang, Yusheng Zhao, Peter Lazor, Hans Annersten, and S. K. Saxena

Appl. Phys. Lett. 86, 041911 (2005); http://dx.doi.org/10.1063/1.1857091 (3 pages) | Cited 6 times

Online Publication Date: 20 January 2005

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In situ Raman spectroscopy was used to explore the mechanical stability and electronic properties of superhard boron suboxide (B6O) under nonhydrostatic pressure. B6O stabilizes in a rhombohedral structure (Rmathm) to the peak pressure of 90 GPa. The icosahedra-chain (B–O) phonon at 274 cm−1 exhibits a negative pressure dependent profile of −0.21 cm−1/GPa, while the intraicosahedral vibrations (B–B) between 400 and 1100 cm−1 and the intericosahedral phonon at 1141 cm−1 display 0.7–2.3 and 3.8 cm−1/GPa, respectively. The small pressure dependencies of intraicosahedral modes resulting from the crystal lattice are significant indications of the low compressibility of B6O. Upon decompression to 3.3 GPa, crystalline B6O transforms to the amorphous boron oxide and glassy boron. The structure instability of superhard B6O upon release of pressure implies its critical weakness for applications in harsh environments of dynamic impacts and high stress concentrations.
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78.30.Hv Other nonmetallic inorganics
61.66.Fn Inorganic compounds
64.70.K- Solid-solid transitions
62.50.-p High-pressure effects in solids and liquids
61.43.Er Other amorphous solids
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Stability of shuffle and glide dislocation segments with increasing misfit in Ge/Si1−xGex(001) epitaxial layers

A. Marzegalli, F. Montalenti, and Leo Miglio

Appl. Phys. Lett. 86, 041912 (2005); http://dx.doi.org/10.1063/1.1856145 (3 pages)

Online Publication Date: 21 January 2005

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Using molecular dynamics simulations, based on Tersoff potentials, we show that at typical experimental temperatures high compressive strain regimes suppress the formation of partial glide dislocations, while enhancing the gliding of the shuffle segments. Despite being qualitative in nature, these results suggest that strain relaxation in thin virtual substrates at high misfit may occur with a different modality than in thick graded layers, as indicated by preliminary experimental results by low-energy plasma enhanced chemical vapor deposition.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Bb Theories and models of crystal defects
68.55.-a Thin film structure and morphology
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Control of silicidation in HfO2/Si(100) interfaces

Deok-Yong Cho, Kee-Shik Park, B.-H. Choi, S.-J. Oh, Y. J. Chang, D. H. Kim, T. W. Noh, Ranju Jung, Jae-Cheol Lee, and S. D. Bu

Appl. Phys. Lett. 86, 041913 (2005); http://dx.doi.org/10.1063/1.1856140 (3 pages) | Cited 26 times

Online Publication Date: 21 January 2005

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The interfacial states of the HfO2 thin film grown on the Si(100) substrate by the pulsed laser deposition method is investigated in situ using x-ray photoelectron spectroscopy. They are found to depend on the HfO2 film thickness, oxygen pressure during the pulsed laser deposition growth, and the deposition process. The hafnium silicide is formed in an oxygen-deficient condition, and it can be most effectively controlled by the ambient oxygen pressure during film growth. The close relation between the silicide formation and abundance of the silicon suboxides at the interface is presented.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
79.60.Dp Adsorbed layers and thin films
73.20.At Surface states, band structure, electron density of states
68.35.Fx Diffusion; interface formation
77.55.-g Dielectric thin films
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology

Fatigue failure in thin-film polycrystalline silicon is due to subcritical cracking within the oxide layer

D. H. Alsem, E. A. Stach, C. L. Muhlstein, and R. O. Ritchie

Appl. Phys. Lett. 86, 041914 (2005); http://dx.doi.org/10.1063/1.1856689 (3 pages) | Cited 17 times

Online Publication Date: 21 January 2005

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It has been established that microelectromechanical systems created from polycrystalline silicon thin films are subject to cyclic fatigue. Prior work by the authors has suggested that although bulk silicon is not susceptible to fatigue failure in ambient air, fatigue in micron-scale silicon is a result of a “reaction-layer” process, whereby high stresses induce a thickening of the post-release oxide at stress concentrations such as notches, which subsequently undergoing moisture-assisted cracking. However, there exists some controversy regarding the post-release oxide thickness of the samples used in the prior study. In this letter, we present data from devices from a more recent fabrication run that confirm our prior observations. Additionally, new data from tests in high vacuum show that these devices do not fatigue when oxidation and moisture are suppressed. Each of these observations lends credence to the “reaction-layer” mechanism.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.65.Mq Oxidation
62.20.M- Structural failure of materials
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