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24 Jul 2000

Volume 77, Issue 4, pp. 463-603

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Influence of sample oxidation on the nature of optical luminescence from porous silicon

I. Coulthard, W. J. Antel, J. W. Freeland, T. K. Sham, S. J. Naftel, and P. Zhang

Appl. Phys. Lett. 77, 498 (2000); http://dx.doi.org/10.1063/1.127023 (3 pages) | Cited 12 times

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Site-selective luminescence experiments were performed upon porous-silicon samples exposed to varying degrees of oxidation. The source of different luminescence bands was determined to be due to either quantum confinement in nanocrystalline silicon or defective silicon oxide. Of particular interest is the defective silicon-oxide luminescence band found at 2.1 eV, which was found to frequently overlap with a luminescence band from nanocrystalline silicon. Some of the historical confusion and debate with regards to the source of luminescence from porous silicon can be attributed to this overlap. © 2000 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.55.Mb Porous materials
81.65.Mq Oxidation

Friction contrast in resonant cantilever vibration mode

A. Spychalski-Merle, K. Krischker, T. Göddenhenrich, and C. Heiden

Appl. Phys. Lett. 77, 501 (2000); http://dx.doi.org/10.1063/1.127024 (3 pages) | Cited 6 times

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The dynamic scanning friction microscopy technique is based on a well-known lateral sample modulation technique combined with a lock-in amplifier. In this paper, we describe a modified detection scheme in the resonant regime of a cantilever’s bending mode. This resonant mode leads to a couple of advantages in the imaging mode especially applicable under ultrahigh vacuum conditions, as well as an additional spectroscopy mode by measuring the resonance curve. An interpretation of the resonance curves and the images in terms of the friction losses is given, taking into account the cantilever vibration and the observed nonlinear characteristic of the stick–slip interaction. © 2000 American Institute of Physics.
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07.79.Sp Friction force microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
62.20.Qp Friction, tribology, and hardness

Size-dependent picosecond energy relaxation in PbSe quantum dots

Tsuyoshi Okuno, Yasuaki Masumoto, Michio Ikezawa, Tomoyasu Ogawa, and Andrey A. Lipovskii

Appl. Phys. Lett. 77, 504 (2000); http://dx.doi.org/10.1063/1.127025 (3 pages) | Cited 17 times

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We measured the size dependence of the energy relaxation time of PbSe quantum dots at room temperature. The radius of the dots was evaluated by small-angle x-ray scattering. We found a monotonic decrease of the relaxation time from 25 to 1 ps with a decrease of the radius r from 2.9 to 1.4 nm. The 1/r3 dependence of the relaxation rate was indicated. © 2000 American Institute of Physics.
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78.66.Li Other semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.70.Ck X-ray scattering
78.47.-p Spectroscopy of solid state dynamics

Direct evidence of spontaneous quantum dot formation in a thick InGaN epilayer

L. Nistor, H. Bender, A. Vantomme, M. F. Wu, J. Van Landuyt, K. P. O’Donnell, R. Martin, K. Jacobs, and I. Moerman

Appl. Phys. Lett. 77, 507 (2000); http://dx.doi.org/10.1063/1.127026 (3 pages) | Cited 29 times

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We report a direct observation of quantum dots formed spontaneously in a thick InGaN epilayer by high resolution transmission electron microscopy. Investigation of a (280 nm thick) In0.22Ga0.78N single layer, emitting in the blue/green spectral region, reveals quantum dots with estimated sizes in the range of 1.5–3 nm. Such sizes are in very good agreement with calculations based on the luminescence spectra of this specimen. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Saturation of THz-frequency intraband absorption in InAs/GaAs quantum dot molecules

P. Boucaud, K. S. Gill, J. B. Williams, M. S. Sherwin, W. V. Schoenfeld, and P. M. Petroff

Appl. Phys. Lett. 77, 510 (2000); http://dx.doi.org/10.1063/1.127027 (3 pages) | Cited 15 times

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We have investigated the far-infrared absorption in InAs/GaAs quantum dot molecules. The quantum dot molecules consist of two vertically coupled InAs self-assembled quantum dots separated by a GaAs barrier. The electronic coupling between the dot states results in an intraband absorption at THz frequencies. We show that this absorption can be bleached under high excitation intensity delivered by a free-electron laser. The saturation intensity is found to be on the order of 1 W cm−2. The electron relaxation time T1 is estimated from the saturation intensity. A lower limit for T1 of the order of 30 ps is deduced. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.47.-p Spectroscopy of solid state dynamics
73.61.Ey III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Effect of multidirection rubbing on the alignment of nematic liquid crystal

Young Jin Kim, Zhizhong Zhuang, and Jay S. Patel

Appl. Phys. Lett. 77, 513 (2000); http://dx.doi.org/10.1063/1.127028 (3 pages) | Cited 9 times

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We have investigated the alignment properties of liquid crystals induced by multiple rubbing of the surfaces in different directions. Experiments were carried out using homeotropic and hybrid-aligned samples. It is experimentally found that the alignment of the liquid crystals is along neither of the rubbing directions, but instead lies along an axis intermediate between these two directions, and that the direction depended on the relative strength of rubbing along the two axes. A model that assumed the grooves along two rubbing directions is proposed, and the relation between the orientation of the liquid crystal and the relative rubbing strength is analyzed. We found that this model can explain the observed experimental results. © 2000 American Institute of Physics.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures

Morphological instability of growth fronts due to stress-induced mobility variations

Jennifer F. Sage, William Barvosa-Carter, and Michael J. Aziz

Appl. Phys. Lett. 77, 516 (2000); http://dx.doi.org/10.1063/1.127029 (3 pages) | Cited 17 times

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We report a comparison between theory and experiment for a general stress-induced morphological growth instability that is kinetically rather than energetically driven. Stress variations along a perturbed planar growth front result in variations in interfacial mobility in a manner that is destabilizing under one sign of the stress state and stabilizing under the opposite sign, even for a pure material. Investigation of solid-phase epitaxial growth at a corrugated Si(001) interface under both compression and tension results in good agreement between experiment and theory with no adjustable parameters, demonstrating that this mobility-based mechanism is dominant in determining morphological evolution in this system. © 2000 American Institute of Physics.
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81.05.Cy Elemental semiconductors
68.35.Gy Mechanical properties; surface strains
68.55.-a Thin film structure and morphology
81.15.Np Solid phase epitaxy; growth from solid phases
68.35.Ct Interface structure and roughness

Raman study of ZnxBe1−xSe alloy (100) epitaxial layers

O. Pagès, M. Ajjoun, J. P. Laurenti, D. Bormann, C. Chauvet, E. Tournié, and J. P. Faurie

Appl. Phys. Lett. 77, 519 (2000); http://dx.doi.org/10.1063/1.127030 (3 pages) | Cited 16 times

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Long wavelength longitudinal optical (LO) and transverse optical (TO) phonons of BeSe and ZnxBe1−xSe layers are identified in a wide composition range by using Raman spectroscopy. A two-mode behavior is clearly evidenced. As predicted by the dielectric model of Hon and Faust, the eigenfrequencies of the BeSe- and ZnSe-like LO modes correspond to the maxima of Im〈−ε(ω, x)−1〉. Excellent agreement is obtained with a model where the calculations are performed by using the equations of motion and polarization derived from the modified random element isodisplacement model. Besides, the TO and LO frequencies for BeSe are determined to be 501 and 579 cm−1, respectively. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
81.05.Dz II-VI semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Optical microcavities based on amorphous silicon–nitride Fabry–Pérot structures

Fabrizio Giorgis

Appl. Phys. Lett. 77, 522 (2000); http://dx.doi.org/10.1063/1.127031 (3 pages) | Cited 26 times

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All amorphous silicon–nitride (a-Si1−xNx:H) optical microcavities have been grown by plasma-enhanced chemical vapor deposition. The basic structure is a Fabry–Pérot resonator with a N-rich a-Si1−xNx:H layer as optical active medium. By controlling layer thickness and composition, homogeneous structures have been obtained on a large area. Tunable narrow emission bands (few nm) and a strong resonant enhancement of the luminescence yield (more than 1 order of magnitude) have been demonstrated. These results, which can be accounted for by a light intensity spatial redistribution owing to the anisotropic phonon density of states in the cavities, open up new possibilities for applications in thin film flat panel displays. © 2000 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.55.Hx Other solid inorganic materials
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
81.05.Gc Amorphous semiconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Crystallization of bulk amorphous Zr–Ti(Nb)–Cu–Ni–Al

Jörg F. Löffler, Sven Bossuyt, Stephen C. Glade, William L. Johnson, Werner Wagner, and P. Thiyagarajan

Appl. Phys. Lett. 77, 525 (2000); http://dx.doi.org/10.1063/1.127032 (3 pages) | Cited 38 times

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Small-angle neutron scattering (SANS) and transmission electron microscopy were used to resolve the crystallization of the bulk amorphous alloys Zr52.5Ti5Cu17.9Ni14.6Al10 (Vit105) and Zr57Nb5Cu15.4Ni12.6Al10 (Vit106). Decomposition and nanocrystallization were observed in both alloy compositions in the temperature regime from the glass transition, Tg, up to at least 90 K above Tg. From in situ SANS measurements on Vit105, chemical diffusion data were obtained whose temperature dependence follows an Arrhenius law. Normalizing the temperature to Tg, the diffusion data of Vit105 are very similar to those of the well-investigated bulk amorphous alloy Zr41.2Ti13.8Cu12.5Ni10Be22.5. © 2000 American Institute of Physics.
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81.10.Jt Growth from solid phases (including multiphase diffusion and recrystallization)
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization

Precipitation of icosahedral quasicrystalline phase in Hf65Al7.5Ni10Cu12.5Pd5 metallic glass

Chunfei Li, Junji Saida, Mitsuhide Matsushita, and Akihisa Inoue

Appl. Phys. Lett. 77, 528 (2000); http://dx.doi.org/10.1063/1.127033 (3 pages) | Cited 26 times

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An icosahedral quasicrystalline phase was found in a Hf65Al7.5Ni10Cu12.5Pd5 metallic glass annealed in the supercooled liquid region. Upon annealing at high temperature, the quasicrystalline phase was found to decompose to regular crystalline phases, indicating that it is a metastable phase. The present alloy was compared with the previously reported Zr- and Ti-based alloys with the formation of icosahedral quasicrystalline phases. Hf, Zr, and Ti belong to the same 4A column in the element periodical table. Based on the above comparison, conditions in terms of atomic radius and alloy composition which favor the formation of icosahedral quasicrystalline phase in 4A element based alloys, were suggested. © 2000 American Institute of Physics.
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81.30.Mh Solid-phase precipitation
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
64.75.-g Phase equilibria
61.44.Br Quasicrystals
81.40.Gh Other heat and thermomechanical treatments

A formation mechanism of carbon nanotube films on SiC(0001)

M. Kusunoki, T. Suzuki, T. Hirayama, N. Shibata, and K. Kaneko

Appl. Phys. Lett. 77, 531 (2000); http://dx.doi.org/10.1063/1.127034 (3 pages) | Cited 69 times

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We report a remarkable difference of decomposed structures on the Si(0001) and C(0001) faces of a SiC single crystal observed by using a cross-sectional high-resolution electron microscopy. An aligned carbon nanotube (CNT) film was fabricated on the C face perpendicular to the surface after heating at 1700 °C for half an hour in a vacuum. On the contrary, a very thin layer of graphite sheets parallel to the surface was formed on the Si face under the same condition. It is proposed that the growth of CNTs is determined by the generation of nanocaps at the initial stage, by comparing the difference of the decomposition mechanisms on the both faces. © 2000 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.05.ub Fullerenes and related materials
68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Stacking fault energies in Si doped GaN: A first principles study

J. A. Chisholm and P. D. Bristowe

Appl. Phys. Lett. 77, 534 (2000); http://dx.doi.org/10.1063/1.127035 (3 pages) | Cited 4 times

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The variation of stacking fault energy in GaN as a function of silicon doping is calculated using density functional theory. It is found that the stacking fault energy reduces with increasing silicon concentration in agreement with experimental observations of higher stacking fault densities in Si doped GaN compared to undoped GaN. The result is explained in terms of a decrease in the magnitude of the Mulliken charges on the atoms as silicon is incorporated into the lattice and an increase in the overlap populations. We propose that Mulliken charges can be used to predict how any substitutional impurity will influence the stacking fault formation energy. © 2000 American Institute of Physics.
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61.72.Nn Stacking faults and other planar or extended defects
61.72.Bb Theories and models of crystal defects
81.05.Ea III-V semiconductors

Biexciton emission from high-quality ZnO films grown on epitaxial GaN by plasma-assisted molecular-beam epitaxy

H. J. Ko, Y. F. Chen, T. Yao, K. Miyajima, A. Yamamoto, and T. Goto

Appl. Phys. Lett. 77, 537 (2000); http://dx.doi.org/10.1063/1.127036 (3 pages) | Cited 77 times

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We have investigated the optical and structural properties of high-quality ZnO films grown on epitaxial GaN (epi-GaN) by plasma-assisted molecular-beam epitaxy employing low-temperature buffer layers. High-resolution x-ray diffraction for both symmetric and asymmetric reflexes shows that crystalline defects in ZnO films have a similarity to epi-GaN used as a substrate. The quality of ZnO epilayers grown on epi-GaN is basically determined by epi-GaN. The photoluminescence (PL) spectrum at 10 K exhibits very sharp exciton emission with a linewidth of 1.5 meV, while deep-level emission is negligible, indicative of small residual strain. At 77 K, PL is dominated by a free-exciton emission line in the low-excitation regime, while it is overtaken by a new emission band due to biexcitons at its low-energy side as the excitation intensity increases. This biexciton emission band emerges even under the intermediate excitation regime of 100 W/cm2, which is 100 times smaller than the previously reported threshold for bulk ZnO. The biexciton binding energy is estimated to be 15 meV, in agreement with previous results. At the higher excitation regime, the emission line due to exciton–exciton scattering dominates the PL spectrum. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
68.55.-a Thin film structure and morphology
61.72.-y Defects and impurities in crystals; microstructure
71.35.-y Excitons and related phenomena

Real-time measurements of the pseudodielectric function of low-temperature-grown GaAs

Donald A. Gajewski, Jonathan E. Guyer, and Joseph G. Pellegrino

Appl. Phys. Lett. 77, 540 (2000); http://dx.doi.org/10.1063/1.127037 (3 pages) | Cited 1 time

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We present real-time in situ spectroscopic ellipsometry (SE) measurements of the pseudodielectric function of low-temperature-grown GaAs as a function of growth temperature Tg, As2:Ga flux ratio R, and thickness. We show that the interband critical point E1 amplitude and sharpness decrease monotonically with decreasing Tg and/or increasing R for layers thinner than the critical epitaxial thickness hepi. We used in situ SE to reveal distinct signatures of the onset of polycrystalline or amorphous growth above hepi, which depends strongly on Tg. We revealed these systematic trends using in situ SE in conjunction with diffuse reflectance spectroscopy for active feedback temperature control. © 2000 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
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