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6 May 2002

Volume 80, Issue 18, pp. 3247-3450

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Initiation and evolution of phase separation in heteroepitaxial InAlAs films

B. Shin, A. Lin, K. Lappo, R. S. Goldman, M. C. Hanna, S. Francoeur, A. G. Norman, and A. Mascarenhas

Appl. Phys. Lett. 80, 3292 (2002); http://dx.doi.org/10.1063/1.1476386 (3 pages) | Cited 12 times

Online Publication Date: 29 April 2002

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We have investigated the initiation and evolution of phase separation in heteroepitaxial InAlAs films. In misfit-free InAlAs layers, cross-sectional scanning tunneling microscopy (XSTM) reveals the presence of isotropic nanometer-sized clusters. For lattice-mismatched InAlAs layers with 1.2% misfit, quasiperiodic contrast modulations perpendicular to the growth direction are apparent. Interestingly, these lateral modulations are apparently initiated within the first few bilayers of film growth, and both the amplitude and wavelength of the modulations increase with film thickness. The saturation value of the modulation wavelength determined from XSTM coincides with the lateral superlattice period determined from (002) x-ray reciprocal space maps, suggesting that the lateral modulation wavelength represents a periodic composition variation. Together, these results suggest that phase separation in the heteroepitaxial InAlAs thin-film system is a misfit-driven kinetic process initiated by random compositional nonuniformities, which later develop into coupled compositional and surface morphological variations. © 2002 American Institute of Physics.
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68.55.Nq Composition and phase identification
64.75.-g Phase equilibria
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Schwoebel-Ehrlich barrier: from two to three dimensions

S. J. Liu, Hanchen Huang, and C. H. Woo

Appl. Phys. Lett. 80, 3295 (2002); http://dx.doi.org/10.1063/1.1475774 (3 pages) | Cited 43 times

Online Publication Date: 29 April 2002

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The Schwoebel-Ehrlich barrier—the additional barrier for an adatom to diffuse down a surface step—dictates the growth modes of thin films. The conventional concept of this barrier is two dimensional (2D), with the surface step being one monolayer. We propose the concept of a three-dimensional (3D) Schwoebel-Ehrlich barrier, and identify the 2D to 3D transition, taking aluminum as a prototype and using the molecular statics method. Our results show that: (1) substantial differences exist between the 2D and 3D barriers; (2) the transition completes in four monolayers; and (3) there is a major disparity in the 3D barriers between two facets; further, alteration of this disparity using surfactants can lead to the dominance of surface facet against thermodynamics. © 2002 American Institute of Physics.
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68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
68.35.Md Surface thermodynamics, surface energies
68.35.B- Structure of clean surfaces (and surface reconstruction)

Nondestructive defect delineation in SiC wafers based on an optical stress technique

Xianyun Ma, Mathew Parker, and Tangali S. Sudarshan

Appl. Phys. Lett. 80, 3298 (2002); http://dx.doi.org/10.1063/1.1469659 (3 pages) | Cited 12 times

Online Publication Date: 29 April 2002

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The potential of using the optical stress technique to delineate the various defects in silicon carbide (SiC) wafers has been fully demonstrated. The observed defects include micropipes, dislocations, stress striations, grain boundary or dislocation walls, and regions of polytype nonuniformity. Revealed dislocation density is in the range 104–105 cm−2. © 2002 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.-y Defects and impurities in crystals; microstructure
61.72.Mm Grain and twin boundaries

Study of photoluminescence at 3.310 and 3.368 eV in GaN/sapphire(0001) and GaN/GaAs(001) grown by liquid-target pulsed-laser deposition

K. W. Mah, J.-P. Mosnier, E. McGlynn, M. O. Henry, D. O’Mahony, and J. G. Lunney

Appl. Phys. Lett. 80, 3301 (2002); http://dx.doi.org/10.1063/1.1476058 (3 pages) | Cited 8 times

Online Publication Date: 29 April 2002

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Epitaxial GaN films of thickness ∼1 μm have been grown on sapphire(0001) and GaAs(001) substrates using the liquid-target pulsed-laser-deposition technique in a 5 Torr nitrogen atmosphere. Detailed x-ray diffraction and photoluminescence studies were carried out for both types of samples. Significantly enhanced low-temperature photoluminescence emissions at 3.368 eV (I3) and 3.310 eV (I4) were observed for the material deposited on a GaAs(001) substrate at ∼800 °C. We propose a model to explain the emission mechanism for both lines in which the electrons and holes are confined in cubic inclusions within the hexagonal material, analogously to a type-I quantum well. © 2002 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Fg Pulsed laser ablation deposition

Quantum chemical study of the mechanism of aluminum oxide atomic layer deposition

Yuniarto Widjaja and Charles B. Musgrave

Appl. Phys. Lett. 80, 3304 (2002); http://dx.doi.org/10.1063/1.1473237 (3 pages) | Cited 52 times

Online Publication Date: 29 April 2002

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The atomic layer deposition of alumina using water and trimethylaluminum is investigated using the density functional theory. The atomistic mechanisms of the two deposition half-cycles on Al–CH3∗ and Al–OH∗ surface sites are investigated. Both half-cycle reactions proceed through the formation of an Al–O Lewis acid-base complex followed by CH4 formation. The Al–O complexes are relatively stable, with formation energies between 0.57 and 0.74 eV. The CH4 formation activation energies range from 0.52 to 0.91 eV and both half-cycle reactions are exothermic with overall enthalpies of reaction between 1.30 and 1.70 eV. © 2002 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.33.Ya Chemistry of MOCVD and other vapor deposition methods
82.60.Cx Enthalpies of combustion, reaction, and formation
81.15.Aa Theory and models of film growth
68.55.A- Nucleation and growth
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Manipulation of the equilibrium between diamond growth and renucleation to form a nanodiamond/amorphous carbon composite

X. T. Zhou, Q. Li, F. Y. Meng, I. Bello, C. S. Lee, S. T. Lee, and Y. Lifshitz

Appl. Phys. Lett. 80, 3307 (2002); http://dx.doi.org/10.1063/1.1476721 (3 pages) | Cited 25 times

Online Publication Date: 29 April 2002

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Composite films of ∼10 nm nanodiamond particles embedded in an amorphous carbon matrix were formed using a double bias assisted hot filament chemical vapor deposition system with a feeding gas mixture of 1% CH4:99% H2. The structure was obtained via the equilibrium of a multistage process including: (1) bias enhanced nucleation of diamond in an amorphous carbon matrix, (2) growth of both amorphous carbon and diamond, (3) suppression of the diamond growth by the surrounding amorphous carbon matrix, and (4) bias enhanced renucleation of diamond on the new amorphous carbon boundaries. The work adds insight to the diamond nucleation and growth processes. © 2002 American Institute of Physics.
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81.05.U- Carbon/carbon-based materials
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.20.-n Methods of materials synthesis and materials processing

Recovery of microindents in a nickel–titanium shape-memory alloy: A “self-healing” effect

Wangyang Ni, Yang-Tse Cheng, and David S. Grummon

Appl. Phys. Lett. 80, 3310 (2002); http://dx.doi.org/10.1063/1.1476064 (3 pages) | Cited 48 times

Online Publication Date: 29 April 2002

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The thermally induced recovery of microscopic deformation in a nickel–titanium shape-memory alloy was examined. Surface deformation was simulated by indenting the alloy in the martensite phase at room temperature using both spherical and pyramidal indenters. We show that deformation in spherical microindents can be almost completely reversed by moderate heating. Partial recovery was observed for pyramidal impressions formed by a Vickers indenter and the recovery ratio was independent of the indentation depth. The observations were rationalized using the concept of representative strain and maximum stress under the spherical and pyramidal indenters. © 2002 American Institute of Physics.
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81.40.Lm Deformation, plasticity, and creep
81.30.Kf Martensitic transformations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.05.Bx Metals, semimetals, and alloys
62.20.F- Deformation and plasticity
64.70.K- Solid-solid transitions
62.20.Qp Friction, tribology, and hardness
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Thin film alloy mixtures for high speed phase change optical storage: A study on (Ge1Sb2Te4)1−x(Sn1Bi2Te4)x

Tae-Yon Lee, Ki-Bum Kim, Byung-ki Cheong, Taek Sung Lee, Sung Jin Park, Kyeong Seok Lee, Won Mok Kim, and Soon Gwang Kim

Appl. Phys. Lett. 80, 3313 (2002); http://dx.doi.org/10.1063/1.1476705 (3 pages) | Cited 20 times

Online Publication Date: 29 April 2002

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An approach is proposed to develop recording materials for high speed phase change optical data storage. It utilizes a thin film alloy mixture between a stoichiometric GeSbTe alloy and an additive ternary telluride alloy. Selection rules for an additive alloy are suggested. For a test, (Ge1Sb2Te4)1−x(Sn1Bi2Te4)x thin films are deposited by co-sputtering and their structural and thermal properties are studied. Ge1Sb2Te4 and Sn1Bi2Te4 are found to form a completely soluble pseudo-binary system, whose crystalline lattice parameters obey Vegard’s rule over the entire range of x (0<x<1). Furthermore, the alloy mixtures display an increasing tendency for crystallization with Sn1Bi2Te4 content. Dynamic tests of disk samples are made to show the effectiveness of the approach for high speed erasure. © 2002 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
78.66.Li Other semiconductors
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
61.66.Bi Elemental solids
61.66.Dk Alloys
64.70.K- Solid-solid transitions
61.50.Lt Crystal binding; cohesive energy
61.66.Fn Inorganic compounds

Time-resolved photoluminescence studies of free excitons in CuInS2 crystals

Kazuki Wakita, Kazuhito Nishi, Yoshihiko Ohta, and Naoji Nakayama

Appl. Phys. Lett. 80, 3316 (2002); http://dx.doi.org/10.1063/1.1476960 (3 pages) | Cited 6 times

Online Publication Date: 29 April 2002

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The time-resolved photoluminescence of free excitons in bulk single-crystal CuInS2 grown by the traveling heater method is examined. The decay of free exciton emission exhibits a double exponential curve at low temperature. The decay-time constant of the fast component increases monotonically with excitation density, whereas that of the slow component appears to be independent of excitation density. From this result, the fast and slow components are attributed to nonradiative and radiative recombination processes, respectively. The radiative lifetime of free excitons is estimated to be 320±30 ps at 10 K. © 2002 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.47.-p Spectroscopy of solid state dynamics
71.35.-y Excitons and related phenomena

Identification of nanocrystal nucleation and growth in Al85Ni5Y8Co2 metallic glass with quenched-in nuclei

J. Q. Wang, H. W. Zhang, X. J. Gu, K. Lu, F. Sommer, and E. J. Mittemeijer

Appl. Phys. Lett. 80, 3319 (2002); http://dx.doi.org/10.1063/1.1476388 (3 pages) | Cited 7 times

Online Publication Date: 29 April 2002

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The crystallization kinetics of an Al85Ni5Y8Co2 metallic glass, with quenched-in nuclei and a well-defined glass transition temperature (Tg) upon heating, was monitored by x-ray diffraction, differential scanning calorimetry, in situ electrical resistance measurement, and high-resolution transmission electron microscopy. It was found that the formation and the evolution of the primary Al nanocrystals proceed at largely separated stages. The growth of a few quenched-in nuclei of Al occurs predominantly well below Tg. In the vicinity of Tg (T<Tg), an additional large number of nanoscale Al particles appear, prior to the primary crystallization temperature above Tg. Subsequently, the growth of the Al nanocrystals, both the quenched-in ones and those formed upon heating, dominates the primary crystallization reaction. © 2002 American Institute of Physics.
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61.43.Fs Glasses
61.46.-w Structure of nanoscale materials
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
72.15.Cz Electrical and thermal conduction in amorphous and liquid metals and alloys

Phonons on GaN(110)

H. M. Tütüncü, R. Miotto, G. P. Srivastava, and J. S. Tse

Appl. Phys. Lett. 80, 3322 (2002); http://dx.doi.org/10.1063/1.1476401 (3 pages) | Cited 1 time

Online Publication Date: 29 April 2002

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We present results of adiabatic bond-charge model calculations for the vibrational properties of the GaN(110) surface using electronic and structural data obtained from a first-principles pseudopotential method. It is found that in order to relate the energy locations of optical phonon modes on this surface with corresponding modes on nonnitride III–V(110) and II–VI(110) surfaces, it is necessary to consider scaling of results with the lattice constant in addition to the reduced mass. © 2002 American Institute of Physics.
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68.35.Ja Surface and interface dynamics and vibrations

In situ ordering of FePt thin films with face-centered-tetragonal (001) texture on Cr100−xRux underlayer at low substrate temperature

Yingfan Xu, J. S. Chen, and J. P. Wang

Appl. Phys. Lett. 80, 3325 (2002); http://dx.doi.org/10.1063/1.1476706 (3 pages) | Cited 114 times

Online Publication Date: 29 April 2002

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In situ ordered FePt thin films with face-centered-tetragonal (fct)-(001) texture have been prepared by magnetron sputtering the FePt layer onto the Cr100−xRux underlayer at relatively low temperature. The dependence of FePt texture on the Ru content in the Cr underlayer and the substrate temperature is investigated. Addition of Ru in Cr underlayer results in the formation of the FePt ordered phase in a lower substrate temperature (350 °C) with c-axis orientation perpendicular to the film plane. Good perpendicular magnetic properties are obtained in films with Cr91Ru9 underlayer. A thin Pt intermediate layer is introduced between the FePt layer and the CrRu underlayer, which is found to effectively resist the Cr diffusion from the CrRu underlayer into the FePt layer and results in better FePt fct-(001) texture and improved magnetic properties. © 2002 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ss Magnetic recording materials
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
75.30.Gw Magnetic anisotropy
68.35.Fx Diffusion; interface formation

Lattice distortions and the transmuted-Ge related luminescence in neutron-transmutation-doped GaN

K. Kuriyama, T. Tokumasu, Jun Takahashi, H. Kondo, and M. Okada

Appl. Phys. Lett. 80, 3328 (2002); http://dx.doi.org/10.1063/1.1477269 (3 pages) | Cited 12 times

Online Publication Date: 29 April 2002

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The lattice distortion and the transmuted-Ge related luminescence in neutron-transmutation-doped (NTD) GaN are studied by combining Rutherford backscattering spectroscopy/channeling, Raman scattering, and photoluminescence methods. The lattice displacement of Ga atoms of ∼ 0.12 Å from the 〈0001〉 row is estimated from the normalized angular yield profiles, preserving the single crystallinity in as-irradiated GaN with a minimum yield (χmin) of 7%. A 2.84 eV emission band observed in 600 °C annealed NTD-GaN is associated with the Ga interstitial, supporting the lattice distortion. Two emission bands at 2.90 eV and 2.25 eV observed in 1000 °C annealed NTD-GaN are assigned to a negatively charged DX-like center of Ge at Ga site and a complex defect attributed to Ge at Ga site and Ga vacancy, respectively. © 2002 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
61.82.Fk Semiconductors
78.55.Cr III-V semiconductors
61.80.Hg Neutron radiation effects
71.55.Eq III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
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