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20 Dec 2004

Volume 85, Issue 25, pp. 6083-6293

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 6281 (2004); http://dx.doi.org/10.1063/1.1834720 (3 pages)

M. P. Rao, M. F. Aimi, and N. C. MacDonald
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Direct observations of dislocation half-loops inserted from the surface of the GeSi heteroepitaxial film

Yu. B. Bolkhovityanov, A. S. Deryabin, A. K. Gutakovskii, M. A. Revenko, and L. V. Sokolov

Appl. Phys. Lett. 85, 6140 (2004); http://dx.doi.org/10.1063/1.1839271 (3 pages) | Cited 6 times

Online Publication Date: 15 December 2004

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The initial stage of relaxation of mechanical stresses in the Ge0.32Si0.68∕Si(001) heterostructure grown by low-temperature (300 °C) molecular-beam epitaxy is studied by means of transmission electron microscopy. Dislocation half-loops propagating from the film surface and generating misfit dislocations during expansion are visualized.
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81.05.Hd Other semiconductors
81.05.Cy Elemental semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.37.Lp Transmission electron microscopy (TEM)
61.72.Cc Kinetics of defect formation and annealing
68.55.-a Thin film structure and morphology

Atomic arrangement at the Au∕p-GaN interface in low-resistance contacts

H. Omiya, F. A. Ponce, H. Marui, S. Tanaka, and T. Mukai

Appl. Phys. Lett. 85, 6143 (2004); http://dx.doi.org/10.1063/1.1840105 (3 pages) | Cited 10 times

Online Publication Date: 15 December 2004

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The atomic arrangement of Ni∕Au contacts on p-type GaN has been studied by transmission electron microscopy (TEM). The initial Au∕Ni∕GaN structure transforms upon annealing at 400–600 °C into Ni∕Au∕GaN. The Au layer consists of thin platelets with uniform thickness. High-resolution TEM reveals an atomically sharp interface between GaN and Au, with no intermediate phases present. The epitaxial relationship between the Au layer and the GaN film is (111)Au∥(0002)GaN, and [1math0]Au∥[11math0]GaN. Analysis of TEM images shows that Au is directly in contact with Ga atoms, with no evidence of presence of Ni. The interface separation corresponds to covalent Ga and metallic Au, with a bond length of ∼2.5 math. This corresponds to an atomically abrupt transition between covalently bonded Ga and metallic bonded Au.
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68.35.Ct Interface structure and roughness
71.55.Eq III-V semiconductors
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.Mm Grain and twin boundaries
68.37.Lp Transmission electron microscopy (TEM)

Epitaxial thin film growth of Ca2RuO4+δ by pulsed laser deposition

X. Wang, Y. Xin, P. A. Stampe, R. J. Kennedy, and J. P. Zheng

Appl. Phys. Lett. 85, 6146 (2004); http://dx.doi.org/10.1063/1.1841451 (3 pages) | Cited 2 times

Online Publication Date: 15 December 2004

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Epitaxial Ca2RuO4+δ thin films have been grown on (001) LaAlO3 substrate by pulsed laser deposition. X-ray diffraction and transmission electron microscopy studies show that the films are single crystal with good structural quality. The films are determined to have quasitetragonal structure with a=5.352(8) math, c=12.20(9) math and epitaxially grown on the substrate with in-plane tensile strains. C plane of the film is parallel to the substrate surface and its 〈100〉 is along 〈110〉 of the pseudocubic LaAlO3 cell. Resistivity versus temperature measurement reveals that the thin film has metallic-like behavior with low resistivity (<0.002 Ω cm) and no metal-to-insulator transition between 2 and 300 K, different from its bulk material property.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
75.50.Ee Antiferromagnetics
81.15.Np Solid phase epitaxy; growth from solid phases
81.15.Fg Pulsed laser ablation deposition
72.60.+g Mixed conductivity and conductivity transitions
73.61.Ng Insulators
68.55.A- Nucleation and growth
68.37.Lp Transmission electron microscopy (TEM)
68.55.-a Thin film structure and morphology

Electron-beam-induced surface quasimelting of Co granular nanowires

Seung H. Huh and Atsushi Nakajima

Appl. Phys. Lett. 85, 6149 (2004); http://dx.doi.org/10.1063/1.1839278 (3 pages) | Cited 5 times

Online Publication Date: 15 December 2004

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Electron-beam-induced surface quasimelting of Co granular nanowires (GNWs) of 6–10 nm in diameter and ∼30 nm in length has been studied using a high-resolution electron microscope. From the time evolution of electron microscope images as a function of the irradiation time, it has been revealed that the morphological change in the Co GNW is quite different from that in a Co nanocluster (NC) in terms of structures and phase transitions. For example, the allotropic β→α transition, inhibited in the Co NC, can proceed in the Co GNW through the lattice softening of fcc (111) facets without dimensional collapse.
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81.07.Bc Nanocrystalline materials
61.80.Fe Electron and positron radiation effects
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
61.82.Bg Metals and alloys
64.70.K- Solid-solid transitions
61.46.-w Structure of nanoscale materials

Tailoring the Ti∕4H–SiC Schottky barrier by ion irradiation

Fabrizio Roccaforte, Corrado Bongiorno, Francesco La Via, and Vito Raineri

Appl. Phys. Lett. 85, 6152 (2004); http://dx.doi.org/10.1063/1.1841476 (3 pages) | Cited 4 times

Online Publication Date: 15 December 2004

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The effects of ion irradiation on the Ti∕4H–SiC Schottky barrier are discussed. The Ti∕SiC interfacial region was modified by irradiating Schottky diodes with 8 MeV Si+4 ions at fluences between 1×109 and 1×1012 ions∕cm2. By increasing the ion fluence, an increase of the Schottky barrier ΦB occurs, from the value of 1.05 eV after preparation to the value of 1.21 eV after irradiation at a fluence of 1×1012 ions∕cm2, without substantial changes in the ideality factor (n=1.09). Along with the barrier height increase, a decrease of the leakage current of about two orders of magnitude was observed after irradiation. The results were interpreted in terms of the structural and electrical modification of the interfacial region.
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61.80.Jh Ion radiation effects
73.40.Ns Metal-nonmetal contacts
61.82.Fk Semiconductors
61.82.Bg Metals and alloys
85.30.Kk Junction diodes
73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Hi Surface barrier, boundary, and point contact devices

Photoemission study of energy-band alignment for RuOx∕HfO2∕Si system

Q. Li, S. J. Wang, K. B. Li, A. C. H. Huan, J. W. Chai, J. S. Pan, and C. K. Ong

Appl. Phys. Lett. 85, 6155 (2004); http://dx.doi.org/10.1063/1.1839287 (3 pages) | Cited 22 times

Online Publication Date: 15 December 2004

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Conductive oxides RuOx as alternative electrode on high-κ HfO2 gate dielectric have been fabricated by ultrahigh-vacuum sputtering and subsequently oxidized using oxygen plasma. The energy-band alignment for the RuOx∕HfO2∕Si system and the oxidation-state dependence of barrier height for RuOx contacting to HfO2 dielectrics has been analyzed by x-ray photoemission spectroscopy. The valence- and conduction-band offsets of HfO2∕Si are determined to be 3.05±0.1 and 1.48±0.1 eV, respectively. The barrier heights for the RuOx contacting to HfO2 are oxidation-state dependent, in the range of 1.95–2.73 eV.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
73.20.At Surface states, band structure, electron density of states
81.15.Cd Deposition by sputtering
81.65.Mq Oxidation
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Dp Adsorbed layers and thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Cw Elemental semiconductors

Electron-irradiation enhanced photoluminescence from GaInNAs∕GaAs quantum wells subject to thermal annealing

E.-M. Pavelescu, A. Gheorghiu, M. Dumitrescu, A. Tukiainen, T. Jouhti, T. Hakkarainen, R. Kudrawiec, J. Andrzejewski, J. Misiewicz, N. Tkachenko, V. D. S. Dhaka, H. Lemmetyinen, and M. Pessa

Appl. Phys. Lett. 85, 6158 (2004); http://dx.doi.org/10.1063/1.1834997 (3 pages) | Cited 8 times

Online Publication Date: 15 December 2004

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Electron irradiation of a 1.3‐μm‐GaInNAs∕GaAs multi-quantum-well heterostructure, grown by molecular beam epitaxy and subsequently rapid-thermal annealed, is found to induce much stronger photoluminescence than what is observed for an identical as-grown sample upon annealing. Annealing of the irradiated sample also causes a small additional spectral blueshift and reduces alloy potential energy fluctuations at the conduction band minimum. These irradiation-related phenomena are accompanied by small but discernable changes in x-ray diffraction features upon annealing, which indicate compositional and∕or structural changes in the quantum wells.
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61.82.Fk Semiconductors
61.80.Fe Electron and positron radiation effects
78.55.Cr III-V semiconductors
78.67.De Quantum wells
61.72.Cc Kinetics of defect formation and annealing

Determination of elastic properties of a film-substrate system by using the neural networks

Baiqiang Xu, Zhonghua Shen, Xiaowu Ni, Jijun Wang, Jianfei Guan, and Jian Lu

Appl. Phys. Lett. 85, 6161 (2004); http://dx.doi.org/10.1063/1.1841472 (3 pages) | Cited 3 times

Online Publication Date: 15 December 2004

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An inverse method based on artificial neural network (ANN) is presented to determine the elastic properties of films from laser-genrated surface waves. The surface displacement responses are used as the inputs for the ANN model; the outputs of the ANN are the Young’s modulus, density, Poisson’s ratio, and thickness of the film. The finite element method is used to calculate the surface displacement responses in a film-substrate system. Levenberg Marquardt algorithm is used as numerical optimization to speed up the training process for the ANN model. In this method, the materials parameters are not recovered from the dispersion curves but rather directly from the transient surface displacement. We have also found that this procedure is very efficient for determining the materials parameters of layered systems.
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81.05.Bx Metals, semimetals, and alloys
07.05.Mh Neural networks, fuzzy logic, artificial intelligence
68.60.Bs Mechanical and acoustical properties
02.60.Pn Numerical optimization
43.60.Np Acoustic signal processing techniques for neural nets and learning systems
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
02.70.Dh Finite-element and Galerkin methods
02.30.Zz Inverse problems

In situ measurements of the critical thickness for strain relaxation in AlGaN∕GaN heterostructures

S. R. Lee, D. D. Koleske, K. C. Cross, J. A. Floro, K. E. Waldrip, A. T. Wise, and S. Mahajan

Appl. Phys. Lett. 85, 6164 (2004); http://dx.doi.org/10.1063/1.1840111 (3 pages) | Cited 33 times

Online Publication Date: 15 December 2004

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Using in situ wafer-curvature measurements of thin-film stress, we determine the critical thickness for strain relaxation in AlxGa1−xN∕GaN heterostructures with 0.14⩽x⩽1. The surface morphology of selected films is examined by atomic force microscopy. Comparison of these measurements with critical-thickness models for brittle fracture and dislocation glide suggests that the onset of strain relaxation occurs by surface fracture for all compositions. Misfit-dislocations follow initial fracture, with slip-system selection occurring under the influence of composition-dependent changes in surface morphology.
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81.05.Ea III-V semiconductors
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.37.Ps Atomic force microscopy (AFM)
68.60.Bs Mechanical and acoustical properties
62.20.M- Structural failure of materials
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Optical characteristics of arsenic-doped ZnO nanowires

Woong Lee, Min-Chang Jeong, and Jae-Min Myoung

Appl. Phys. Lett. 85, 6167 (2004); http://dx.doi.org/10.1063/1.1840124 (3 pages) | Cited 34 times

Online Publication Date: 15 December 2004

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The effect of arsenic doping on optical characteristics of ZnO nanowires was investigated by photoluminescence spectroscopy carried out at 13–290 K. In as-grown nanowires, emission due to acceptor-bound excitons predominated at low temperatures; as temperatures increased, emission due to recombination of free excitons prevailed. Arsenic-doped nanowires exhibited emission due to acceptor-bound excitons with no free exciton emission in the whole temperature range, indicating the formation of the acceptor level within the ZnO nanowire by arsenic doping.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
73.22.Lp Collective excitations

Microstructural change near the martensitic transformation in a ferromagnetic shape memory alloy Ni51Fe22Ga27 studied by electron holography

Y. Murakami, D. Shindo, K. Oikawa, R. Kainuma, and K. Ishida

Appl. Phys. Lett. 85, 6170 (2004); http://dx.doi.org/10.1063/1.1841471 (3 pages) | Cited 16 times

Online Publication Date: 15 December 2004

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Temperature dependence of the magnetic microstructure in a ferromagnetic shape memory alloy Ni51Fe22Ga27 has been studied by electron holography, by which the distribution of magnetic flux is clearly imaged. Although the magnetic flux is quite even in the parent phase near room temperature, it undergoes considerable modulation when the temperature approaches Ms (martensitic transformation start temperature). The magnetization distribution in the martensite appears to be inherited from that in the parent phase. The observations shed further light on the precursor phenomenon of martensitic transformations.
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81.05.Bx Metals, semimetals, and alloys
75.50.Bb Fe and its alloys
81.30.Kf Martensitic transformations
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
64.70.K- Solid-solid transitions

A simple approach to determine five thermomechanical properties of thin ductile films on an elastic substrate

W. M. Huang, Y. Y. Hu, and L. An

Appl. Phys. Lett. 85, 6173 (2004); http://dx.doi.org/10.1063/1.1840125 (3 pages) | Cited 8 times

Online Publication Date: 15 December 2004

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We present a simple approach to determine five thermomechanical properties of linear strain hardening thin films, namely, the Young’s modulus, coefficient of thermal expansion, yield start stress, strain hardening, and Poisson’s ratio. The approach is based on the conventional curvature test on bilayer structures upon temperature variation. Three tests, which result in three curvature versus temperature curves, are enough to determine the values of these properties. Both the closed-form solutions and estimations are obtained.
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65.40.De Thermal expansion; thermomechanical effects
68.60.Bs Mechanical and acoustical properties
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.F- Deformation and plasticity
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