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9 Oct 2000

Volume 77, Issue 15, pp. 2271-2423

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Evidence of a two-dimensional nucleation and growth mechanism for metastable nanocrystals embedded in Pd40.5Ni40.5P19 glass

K. F. Yao and H. W. Kui

Appl. Phys. Lett. 77, 2313 (2000); http://dx.doi.org/10.1063/1.1316067 (3 pages) | Cited 5 times

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Nanocrystals, with a body-centered-cubic crystal structure of lattice parameter 18.2525 Å , were found in amorphous Pd40.5Ni40.5P19 specimens that had been annealed at 628 K for 30 min. The crystal surfaces are smooth and dislocations are absent, suggesting that the growth of these nanocrystals is through a two-dimensional nucleation and growth mechanism (formation of surface nuclei of critical size and their subsequent growth). © 2000 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.05.Bx Metals, semimetals, and alloys
64.60.Q- Nucleation
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
61.66.Dk Alloys
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena
61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments

Anisotropic polarization memory in thermally oxidized porous silicon

Hideki Koyama and Philippe M. Fauchet

Appl. Phys. Lett. 77, 2316 (2000); http://dx.doi.org/10.1063/1.1316068 (3 pages) | Cited 5 times

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Visible photoluminescence (PL) from thermally oxidized porous silicon (PSi) has been investigated in terms of polarization memory (PM). The PSi samples were prepared by anodization of (100)p+-Si wafers in a HF/ethanol solution, followed by thermal oxidation at 700–1000 °C. These oxidized PSi samples show significantly anisotropic PM which depends largely on the polarization direction of the excitation light with respect to their crystallographic axes. In addition, the anisotropic PM from samples oxidized at 800 and 900 °C shows an anomalous emission-energy dependence. It is also observed that thermal oxidation at 1000 °C results in a significant decrease in the degree of PM, although it increases with increasing oxidation temperatures for ⩽900 °C. These experimental results suggest that the PL from oxidized PSi cannot be explained as a simple extension of the PL from as-anodized PSi and should be attributed to several different origins. © 2000 American Institute of Physics.
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78.55.Ap Elemental semiconductors
81.65.Mq Oxidation
81.05.Rm Porous materials; granular materials
81.05.Cy Elemental semiconductors

Investigation of the thermal conductivity of the mixed pentatellurides Hf1−xZrxTe5

B. M. Zawilski, R. T. Littleton, and Terry M. Tritt

Appl. Phys. Lett. 77, 2319 (2000); http://dx.doi.org/10.1063/1.1316065 (3 pages) | Cited 5 times

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Transition-metal pentatellurides (HfTe5 and ZrTe5) exhibit a promising power factor (electronic properties) for possible use as a thermoelectric material. For complete characterization of these crystals, thermal conductivity measurements are necessary. In this letter, we report measurements of the thermal conductivity for this group of materials using the parallel thermal conductance technique which is well adapted for needle-like samples. Thermal conductivity is presented as a function of temperature and composition of the pentatelluride solid solution HfxZr1−xTe5 with 0 ⩽ x ⩽ 1 in which the magnitude of the room temperature thermal conductivity varies from 5 to 8 W/(m K). Dependence on the cross-sectional area and possible size effects (or sample quality) is also presented and discussed. These results also indicate the importance of sample quality on the low-temperature thermal conductance maximum λmax. © 2000 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
81.05.Hd Other semiconductors
72.20.Pa Thermoelectric and thermomagnetic effects
07.20.-n Thermal instruments and apparatus
72.80.Ga Transition-metal compounds

Excitonic gain and stimulated ultraviolet emission in nanocrystalline zinc-oxide powder

Y. Sun, J. B. Ketterson, and G. K. L. Wong

Appl. Phys. Lett. 77, 2322 (2000); http://dx.doi.org/10.1063/1.1316069 (3 pages) | Cited 45 times

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We have studied ultraviolet photoluminescence from high-purity zinc-oxide powder over a wide temperature range (2–293 K). At low temperatures, the spontaneous emission is due to radiative recombination of excitons bound to donors and acceptors. At high temperature (>90 K), it mainly consists of recombination of free excitons, with exciton–exciton collision-induced recombination dominating the spectrum at higher pumping intensities. Emission from the exciton–exciton collision process shows clear stimulated-emission behavior. At sufficiently high pumping intensity, the stimulated emission band shifts abruptly to a longer wavelength due to the formation of an electron–hole plasma. Sharp emission peaks are observed in the stimulated emission bands. The possible origins of these sharp peaks are discussed. © 2000 American Institute of Physics.
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78.45.+h Stimulated emission
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
61.46.-w Structure of nanoscale materials
42.50.-p Quantum optics
71.35.Ee Electron-hole drops and electron-hole plasma
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.30.+q High-frequency effects; plasma effects

Mechanism for rapid thermal annealing improvements in undoped GaNxAs1−x/GaAs structures grown by molecular beam epitaxy

I. A. Buyanova, G. Pozina, P. N. Hai, N. Q. Thinh, J. P. Bergman, W. M. Chen, H. P. Xin, and C. W. Tu

Appl. Phys. Lett. 77, 2325 (2000); http://dx.doi.org/10.1063/1.1315632 (3 pages) | Cited 51 times

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A systematic investigation of the effect of rapid thermal annealing (RTA) on optical properties of undoped GaNAs/GaAs structures is reported. Two effects are suggested to account for the observed dramatic improvement in the quality of the GaNxAs1−x/GaAs quantum structures after RTA: (i) improved composition uniformity of the GaNxAs1−x alloy, deduced from the photoluminescence (PL), PL excitation and time-resolved measurements; and (ii) significant reduction in the concentration of competing nonradiative defects, revealed by the optically detected magnetic resonance studies. © 2000 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
61.82.Fk Semiconductors
76.70.Hb Optically detected magnetic resonance (ODMR)
78.47.-p Spectroscopy of solid state dynamics
61.72.-y Defects and impurities in crystals; microstructure
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Structural transition of Ge dots induced by submonolayer carbon on Ge wetting layer

Yutaka Wakayama, Gerhard Gerth, Peter Werner, Ulrich Gösele, and Leonid V. Sokolov

Appl. Phys. Lett. 77, 2328 (2000); http://dx.doi.org/10.1063/1.1316778 (3 pages) | Cited 8 times

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We have investigated the influence of carbon on Ge dot growth on Si(100) substrates. To modify the Ge dot structure, submonolayers of carbon were deposited on Ge wetting layers. The Ge deposited on the carbon-covered wetting layer tends to form dome structures instead of hut structures even at a substrate temperature of 500 °C. The main effect of C is to enhance a structural transition from huts to domes by influencing the configurational energy of the Ge dots. The dominant factor to determine the dot size is the substrate temperature. Accordingly, small domes with 10–20 nm in diameter were formed by combining techniques of the submonolayer C on the Ge wetting layer and low-temperature deposition. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.05.Cy Elemental semiconductors
68.08.Bc Wetting
68.35.Rh Phase transitions and critical phenomena
68.35.B- Structure of clean surfaces (and surface reconstruction)

Scanning second-harmonic/third-harmonic generation microscopy of gallium nitride

Chi-Kuang Sun, Shih-Wei Chu, Shi-Peng Tai, Stacia Keller, Umesh K. Mishra, and Steven P. DenBaars

Appl. Phys. Lett. 77, 2331 (2000); http://dx.doi.org/10.1063/1.1316776 (3 pages) | Cited 21 times

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Scanning second-harmonic generation and third-harmonic generation microscopy of a gallium nitride (GaN) sample was demonstrated using a femtosecond Cr:forsterite laser. Taking advantage of the electric-field enhanced second-harmonic generation effect and bandtail state resonance effect, the obtained second-harmonic and third-harmonic generation microscopic images revealed the piezoelectric field and bandtail state distributions in a GaN sample. © 2000 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
71.20.Nr Semiconductor compounds
77.65.Ly Strain-induced piezoelectric fields
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Spectroscopic imaging of nanoparticles in laser ablation plume by redecomposition and laser-induced fluorescence detection

Junichi Muramoto, Takahiro Inmaru, Yoshiki Nakata, Tatsuo Okada, and Mitsuo Maeda

Appl. Phys. Lett. 77, 2334 (2000); http://dx.doi.org/10.1063/1.1316780 (3 pages) | Cited 12 times

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We propose and demonstrate an imaging technique to observe clusters formed in a laser ablation plume, which are difficult to be detected by conventional laser-induced fluorescence (LIF) and ultraviolet Rayleigh scattering techniques. The clusters were decomposed by the irradiation of another laser beam, and the disintegrated atoms were visualized by a two-dimensional LIF technique. This technique was applied to visualize the formation process of clusters in a laser ablation plume. Based on this imaging diagnostics, the onset time of the clustering in the plume is discussed. © 2000 American Institute of Physics.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
79.20.Ds Laser-beam impact phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Solid–liquid interface velocity and diffusivity in laser-melt amorphous silicon

Luigi Brambilla, Luciano Colombo, Vittorio Rosato, and Fabrizio Cleri

Appl. Phys. Lett. 77, 2337 (2000); http://dx.doi.org/10.1063/1.1317535 (3 pages) | Cited 18 times

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We studied the microscopic kinetics of the amorphous-liquid interface in supercooled laser-melt silicon by means of molecular dynamics computer simulations. The interface velocity was obtained as a function of temperature by direct simulation of the interface motion in an amorphous-liquid model system. The temperature dependence of the kinetic prefactor was extracted from the interface velocity function and compared to the values of self-diffusivity obtained from independent molecular dynamics simulations of bulk amorphous Si. The kinetic prefactor for interfacial diffusion shows a distinctly non-Arrhenius behavior which is attributed to Fulcher–Vogel kinetics in the supercooled liquid. © 2000 American Institute of Physics.
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64.70.D- Solid-liquid transitions
61.43.Dq Amorphous semiconductors, metals, and alloys
68.35.Fx Diffusion; interface formation
61.43.Bn Structural modeling: serial-addition models, computer simulation
61.20.Ja Computer simulation of liquid structure

Heat capacity of hydrogenated diamond-like carbon films

M. Hakovirta, J. E. Vuorinen, X. M. He, M. Nastasi, and R. B. Schwarz

Appl. Phys. Lett. 77, 2340 (2000); http://dx.doi.org/10.1063/1.1290387 (3 pages) | Cited 9 times

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We have used differential scanning calorimetry to measure the heat capacity of diamond-like carbon (DLC) film prepared by a plasma immersion ion processing method. The same calorimeter was used to measure the heat capacity of single crystal natural diamond and of high purity graphite. The amount of atomic hydrogen trapped in the DLC films was determined by elastic-recoil-detection spectrometry. The present data and literature values were used to deduce an expression for the specific heat that factors out the contribution from the sp3/sp2 bonding and from the atomic hydrogen trapped in the carbon. The data shows that the hydrogen contribution to the specific heat of carbon is independent of the sp3/sp2 bonding and amounts to about 0.63kB per hydrogen atom. We propose a simple method to determine the sp3/sp2 bonding ratio in hydrogenated DLC films based on measuring the specific heat and the hydrogen content of the sample. © 2000 American Institute of Physics.
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65.40.-b Thermal properties of crystalline solids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
61.43.Dq Amorphous semiconductors, metals, and alloys
68.60.Dv Thermal stability; thermal effects
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