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3 Feb 2003

Volume 82, Issue 5, pp. 665-834

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 775 (2003); http://dx.doi.org/10.1063/1.1541091 (3 pages)

Sebastiaan van Dijken, Xin Jiang, and Stuart S. P. Parkin
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Lattice parameters of GaN layers grown on a-plane sapphire: Effect of in-plane strain anisotropy

V. Darakchieva, P. P. Paskov, T. Paskova, E. Valcheva, B. Monemar, and M. Heuken

Appl. Phys. Lett. 82, 703 (2003); http://dx.doi.org/10.1063/1.1542931 (3 pages) | Cited 14 times

Online Publication Date: 28 January 2003

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We have studied GaN films grown on a-plane sapphire by hydride vapor phase epitaxy and metalorganic vapor phase epitaxy. The in-plane lattice parameter was determined from sets of equivalent interplanar distances measured for six different directions in order to examine the effect of strain anisotropy. It is found that, in both types of films, the obtained six values of the in-plane lattice parameter can be grouped around two values. The strain anisotropy is estimated to have different value in the films grown by the two techniques and possible explanations are suggested. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors
68.60.Bs Mechanical and acoustical properties
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Observation of light polarization-dependent structural changes in chalcogenide glasses

Gang Chen, Himanshu Jain, Miroslav Vlcek, Syed Khalid, Jun Li, David A. Drabold, and Stephen R. Elliott

Appl. Phys. Lett. 82, 706 (2003); http://dx.doi.org/10.1063/1.1541942 (3 pages) | Cited 33 times

Online Publication Date: 28 January 2003

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The atomistic origin of photoinduced vector (polarization-dependent) phenomena in As–Se films is determined by extended x-ray absorption fine structure with in situ exposure to polarized laser light. A vector structural change is observed directly for any material: there is an expansion of the nearest-neighbor distance around the Se atoms, the magnitude of which depends on the direction of light polarization; the effect around As atoms is relatively smaller. The results point to the origin of scalar as well as vector changes in properties, which either persist after the light is removed, or exist only when light is incident on the sample. © 2003 American Institute of Physics.
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61.43.Fs Glasses
68.55.-a Thin film structure and morphology
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
78.70.Dm X-ray absorption spectra

Elastic instability of nanomechanical beams

S. M. Carr and M. N. Wybourne

Appl. Phys. Lett. 82, 709 (2003); http://dx.doi.org/10.1063/1.1539924 (3 pages) | Cited 19 times

Online Publication Date: 28 January 2003

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We report on elastic instability of nanomechanical SiO2 beams with widths 20 nm<d<110 nm and lengths 5 μm<L<10 μm. The beams are fabricated from a silicon substrate with a 500 nm thermal oxide layer. After release from the silicon substrate by reactive ion etching the beams buckle due to the residual Si/SiO2 strain. The measured buckling displacements of the beams are compared with the predictions of nonlinear continuum elasticity theory. We observe a continuous buckling transition, qualitatively different than the critical transition predicted by Euler buckling theory, which we attribute to system asymmetry. Finally, we determine the effective potential energy of the fundamental buckling mode. © 2003 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.07.Bc Nanocrystalline materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
61.46.-w Structure of nanoscale materials
46.32.+x Static buckling and instability

Compensation mechanisms in low-temperature-grown Ga1−xMnxAs investigated by scanning tunneling spectroscopy

G. Mahieu, P. Condette, B. Grandidier, J. P. Nys, G. Allan, D. Stiévenard, Ph. Ebert, H. Shimizu, and M. Tanaka

Appl. Phys. Lett. 82, 712 (2003); http://dx.doi.org/10.1063/1.1522821 (3 pages) | Cited 20 times

Online Publication Date: 28 January 2003

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Ga1−xMnxAs layers with Mn composition of up to 6.2% are investigated by cross-sectional scanning tunneling microscopy and spectroscopy. We identify in the tunneling spectra contributions from MnGa− acceptor states, compensating AsGa2+ donor states, and additional compensating donor states, which we suggest to be Mni2+ interstitials. On basis of the observed Fermi level shift and a charge carrier compensation analysis, we deduce the concentration of Mni2+ interstitials. Furthermore, scanning tunneling microscopy images suggest an inhomogeneous distribution of Mn dopant atoms. © 2003 American Institute of Physics.
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71.55.Eq III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.20.Nr Semiconductor compounds
61.72.J- Point defects and defect clusters
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.50.Pp Magnetic semiconductors

Atomic-scale strain field and In atom distribution in multiple quantum wells InGaN/GaN

K. Watanabe, N. Nakanishi, T. Yamazaki, J. R. Yang, S. Y. Huang, K. Inoke, J. T. Hsu, R. C. Tu, and M. Shiojiri

Appl. Phys. Lett. 82, 715 (2003); http://dx.doi.org/10.1063/1.1542930 (3 pages) | Cited 29 times

Online Publication Date: 28 January 2003

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We present an atomic-scale structural and compositional analysis of ultrathin layers in multiple quantum well InGaN/GaN, by high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). A high-quality HAADF STEM image processed by two-dimensional smoothing and deconvolution provides precise atomic-column positions and clear contrast, thereby allowing us to map the strain field and In atom distribution in successive GaN and InGaN layers. We conclude from these maps that there is a local fluctuation of In atoms in the InGaN layers and the In-rich regions, considered as quantum dots, cause large expansion only along the [0001] direction. © 2003 American Institute of Physics.
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68.65.Fg Quantum wells
68.37.Lp Transmission electron microscopy (TEM)
07.05.Pj Image processing

Formation and structure of inverted hexagonal pyramid defects in multiple quantum wells InGaN/GaN

K. Watanabe, J. R. Yang, S. Y. Huang, K. Inoke, J. T. Hsu, R. C. Tu, T. Yamazaki, N. Nakanishi, and M. Shiojiri

Appl. Phys. Lett. 82, 718 (2003); http://dx.doi.org/10.1063/1.1542683 (3 pages) | Cited 27 times

Online Publication Date: 28 January 2003

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We have determined the structure of inverted hexagonal pyramid defects (IHPs) in multiple quantum wells InGaN/GaN by high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM). HAADF STEM images reveal definitely that the IHP nucleates at a threading dislocation and grows in the form of a thin six-walled structure with InGaN/GaN {10math1} layers. It has been found that IHPs start even at In-rich dots under adverse growth conditions. © 2003 American Institute of Physics.
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68.65.Fg Quantum wells
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)
61.72.Lk Linear defects: dislocations, disclinations

Random anisotropy and domain-wall pinning process in the magnetic properties of rapidly quenched Nd60Fe30Al10

A. Bracchi, K. Samwer, S. Schneider, and J. F. Löffler

Appl. Phys. Lett. 82, 721 (2003); http://dx.doi.org/10.1063/1.1544430 (3 pages) | Cited 13 times

Online Publication Date: 28 January 2003

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The magnetic properties and microstructure of glassy Nd60Fe30Al10 splat-quenched samples have been investigated by small-angle neutron scattering, Mössbauer spectroscopy, and vibrating sample magnetometry. The presence of chemical inhomogeneities in the amorphous sample is evidenced by small-angle neutron scattering which indicates a complex network of atom clusters with an average diameter of 15 nm. These results are confirmed by the magnetization measurements which show the coexistence of two magnetic phases with different ordering temperatures and indicate phases separation in rapidly quenched Nd60Fe30Al10 samples. Magnetic neutron scattering analysis reveals magnetic correlation volumes in the ferromagnetic phase of about 34 nm in diameter. Random anisotropy and a domain-wall pinning process within the two phases are discussed to explain the magnetic properties of amorphous Nd60Fe30Al10. © 2003 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure
75.50.Kj Amorphous and quasicrystalline magnetic materials
76.80.+y Mössbauer effect; other γ-ray spectroscopy
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
64.75.-g Phase equilibria
75.50.Bb Fe and its alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Vv High coercivity materials
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