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2 Jul 2001

Volume 79, Issue 1, pp. 1-143

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Microcavities in polymeric photonic crystals

Hong-Bo Sun, Vygantas Mizeikis, Ying Xu, Saulius Juodkazis, Jia-Yu Ye, Shigeki Matsuo, and Hiroaki Misawa

Appl. Phys. Lett. 79, 1 (2001); http://dx.doi.org/10.1063/1.1381035 (3 pages) | Cited 76 times

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We report the fabrication and characteristics of planar microcavities in a log-pile photonic crystal structure formed using light-induced photopolymerization of resin. A planar defect was introduced into the middle of the log-pile structure as a single layer with every second rod missing. The existence of confined cavity states was confirmed experimentally and by numeric simulations. The cavity resonance found at the midgap wavelength λM ∼ 4.0 μm had a quality factor of about 130. © 2001 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.70.Jk Polymers and organics
42.82.Cr Fabrication techniques; lithography, pattern transfer
82.35.-x Polymers: properties; reactions; polymerization

Efficient, narrow linewidth excitonic emission at room temperature from GaAs/AlGaAs V-groove quantum wire light-emitting diodes

H. Weman, M.-A. Dupertuis, E. Martinet, A. Rudra, and E. Kapon

Appl. Phys. Lett. 79, 4 (2001); http://dx.doi.org/10.1063/1.1380405 (3 pages) | Cited 9 times

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We report on efficient, narrow linewidth exciton recombination in GaAs/AlGaAs V-groove quantum wire light-emitting diodes at room temperature. The high efficiency is due to a selective carrier injection mechanism resulting in an estimated internal quantum efficiency of ∼20% with an electroluminescence (EL) linewidth as narrow as 15 meV. The thermal broadening contribution to the linewidth is 6 meV due to exciton scattering with optical phonons. An analysis of the EL peak shift in a magnetic field points out the typical superlinear behavior of the excitonic binding energy for a quantum wire. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.21.Hb Quantum wires
78.67.Lt Quantum wires
78.60.Fi Electroluminescence
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
63.20.kk Phonon interactions with other quasiparticles
71.35.Gg Exciton-mediated interactions

Compact holographic memory system using a one-beam geometry in a photorefractive crystal

Hideta Mitsuhashi and Minoru Obara

Appl. Phys. Lett. 79, 7 (2001); http://dx.doi.org/10.1063/1.1383061 (2 pages) | Cited 9 times

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We have demonstrated a compact holographic memory system by using a one-beam geometry, which eliminates the process of dividing the incident beam into object and reference beams, by using a 635 nm laser diode as a compact light source. As the recording media, a photorefractive crystal (Fe-doped 45° cut LiNbO3) is used. One crucial advantage of the developed system is improved mechanical stability because hologram recording is sensitive to mechanical vibrations. An image is successfully recorded and reconstructed, and the ability of the system is also discussed. © 2001 American Institute of Physics.
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42.40.Ht Hologram recording and readout methods
42.70.Gi Light-sensitive materials
42.70.Ln Holographic recording materials; optical storage media
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.30.Wb Image reconstruction; tomography

Variable-wavelength switchable Bragg gratings formed in polymer-dispersed liquid crystals

Chris C. Bowley, Pavel A. Kossyrev, Gregory P. Crawford, and Sadeg Faris

Appl. Phys. Lett. 79, 9 (2001); http://dx.doi.org/10.1063/1.1383566 (3 pages) | Cited 34 times

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We report a holographic polymer-dispersed liquid crystal cell whose reflection peak can be tuned as a function of applied voltage. Electro-optic results are presented which are in excellent agreement with our model based on coupled wave theory. © 2001 American Institute of Physics.
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42.79.Dj Gratings
42.70.Df Liquid crystals
61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems
78.20.Jq Electro-optical effects

Fabrication and optical studies of AlGaN/GaN quantum-well waveguides

T. N. Oder, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 79, 12 (2001); http://dx.doi.org/10.1063/1.1381037 (3 pages) | Cited 8 times

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We report the successful fabrication and optical study of submicron waveguide structures based on AlGaN/GaN multiple-quantum wells (MQWs). The MQW structures were grown by metalorganic chemical vapor deposition on sapphire substrates and the waveguides were fabricated by electron-beam lithography and inductively coupled plasma dry etching. The waveguides were patterned with a fixed width of 0.5 μm but with orientations varying from −30° to 60° relative to the a axis of GaN. Optical emission from these structures was studied by photoluminescence spectroscopy. The peak position and linewidth of the emission peak were found to vary systematically with the orientations of the waveguides and followed the sixfold symmetry of a wurtzite structure. This is most likely related to the anisotropy of the exciton/carrier diffusion coefficient along the different crystal orientations in the quasione-dimensional case. The implication from the results is that in proper designs of photonic and electronic devices where submicron structures are fabricated in III nitrides one must consider the orientations of the structures. © 2001 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.07.St Quantum wells
78.67.De Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Cf Surface cleaning, etching, patterning

Tunable omnidirectional reflection bands and defect modes of a one-dimensional photonic band gap structure with liquid crystals

Young-Ki Ha, Y.-C. Yang, J.-E. Kim, H. Y. Park, C.-S. Kee, H. Lim, and J.-C. Lee

Appl. Phys. Lett. 79, 15 (2001); http://dx.doi.org/10.1063/1.1381414 (3 pages) | Cited 45 times

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We have theoretically investigated the tunability of the omnidirectional reflection band (ORB) of a one-dimensional (1D) photonic crystal (PC) consisting of alternating isotropic dielectric and nematic liquid crystal layers by an external electric field. The width of the ORB becomes wide as the external voltage increases, but the center frequency is changed little. The frequency of the defect mode created by inserting a layer of liquid crystals into a 1D dielectric PC is also found to be tunable by the application of external voltage. These properties can be applied to tunable optical filters or optical switches. © 2001 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.70.Df Liquid crystals
42.79.Ci Filters, zone plates, and polarizers
61.30.Jf Defects in liquid crystals
42.79.Kr Display devices, liquid-crystal devices
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Dark pulse formation in a quantum-dot laser

J. Zimmermann, S. T. Cundiff, G. von Plessen, J. Feldmann, M. Arzberger, G. Böhm, M.-C. Amann, and G. Abstreiter

Appl. Phys. Lett. 79, 18 (2001); http://dx.doi.org/10.1063/1.1379977 (3 pages) | Cited 6 times

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The laser emission of an InAs/GaAs quantum-dot laser after injection of a nonresonant optical pulse is time resolved using femtosecond upconversion. The injected pulse burns a hole into the gain spectrum that leads to an ultrafast redistribution of carriers away from the lasing wavelength, thereby generating a spatial domain of reduced laser intensity. This domain propagates through the laser, is reflected at the facets, and thus repeats periodically in the output of the quantum-dot laser, forming a train of dark pulses. As a slower response to the optically induced perturbation, gigahertz-frequency relaxation oscillations are observed. © 2001 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Px Semiconductor lasers; laser diodes
78.67.Hc Quantum dots
42.60.Rn Relaxation oscillations and long pulse operation
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.60.Fi Electroluminescence
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
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Generation of fluxes of highly charged heavy ions from a picosecond laser-produced plasma

J. Badziak, P. Parys, A. B. Vankov, J. Wołowski, and E. Woryna

Appl. Phys. Lett. 79, 21 (2001); http://dx.doi.org/10.1063/1.1381570 (3 pages) | Cited 21 times

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The results of the investigations of ion emission from targets of medium and high atomic numbers irradiated by 1 ps laser pulse of intensity up to 5×1016 W/cm2 are presented. The generation of high energy (up to 1 MeV) highly charged heavy ions (Ta+38, Au+33), as well as Ar-like Ag ions and fully striped Al ions is demonstrated. Some properties of ion fluxes emitted from picosecond laser-produced high-z plasmas are determined. © 2001 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
07.77.Ka Charged-particle beam sources and detectors

Enhanced K-shell x-ray line emissions from aluminum plasma created by a pair of femtosecond laser pulses

Hidetoshi Nakano, Tadashi Nishikawa, and Naoshi Uesugi

Appl. Phys. Lett. 79, 24 (2001); http://dx.doi.org/10.1063/1.1383571 (3 pages) | Cited 15 times

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The influence of an ultrashort prepulse on K-shell x-ray line emissions from Al plasma produced by 100 fs Ti:sapphire laser pulses is studied. By introducing an independent 100 fs prepulse, a more than 20-fold enhancement in K-shell emission was achieved. We could experimentally optimize Kα and Heα line emissions. In case of oblique incidence, resonance absorption made it possible to maximize Kα emission while keeping pulse duration short. On the other hand, Heα line emission was maximized when a separation between two laser pulses was large, resulting in pulse broadening ( ∼ 30 ps). © 2001 American Institute of Physics.
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52.70.La X-ray and γ-ray measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
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In situ studies of electrodic materials in Li-ion cells upon cycling performed by very-high-energy x-ray diffraction

V. Rossi Albertini, P. Perfetti, F. Ronci, P. Reale, and B. Scrosati

Appl. Phys. Lett. 79, 27 (2001); http://dx.doi.org/10.1063/1.1383058 (3 pages) | Cited 19 times

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A very high-energy synchrotron radiation source (87 keV) was utilized for in situ sampling of the structural changes occurring in the electrodic materials of a Li-ion cell during charge–discharge cycling. The real-time evolution of their crystal lattice was obtained as a function of the degree of Li intercalation. As a result, new information on two electrodic materials, Li–Ti “zero strain” and Li–Ni–Co oxide, both of extreme interest for generation of rechargeable batteries, was gained. The actual change of the Li–Ti oxide lattice parameter upon cycling was observed in greater detail than before, and provided evidence of unexpected behavior in some intervals of the cycle. In the Li–Ni–Co sample, a new phase formed during the early stages of cycling that remained stable in the subsequent cycles was revealed. © 2001 American Institute of Physics.
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61.66.Fn Inorganic compounds
82.45.-h Electrochemistry and electrophoresis
82.47.-a Applied electrochemistry
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Liquid-crystal photoalignment using low-molecular-weight photo-cross-linkable composites

O. Yaroshchuk, L. G. Cada, M. Sonpatki, and L.-C. Chien

Appl. Phys. Lett. 79, 30 (2001); http://dx.doi.org/10.1063/1.1381567 (3 pages) | Cited 7 times

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A liquid-crystal (LC) photoalignment method, based on the use of low-molecular-weight photo-cross-linkable (LMWPC) composites is proposed. The basic idea of this method is that cross linking or both cross linking and polymerization of LMWPC composites are realized immediately on the substrate simultaneously with the photoalignment or as a stage of the backing process. Providing the advantages of a conventional photoalignment method, the use of LMWPC composites simplifies the synthesis and alignment procedure, makes possible wide range control of pretilt angles, and enhances the thermal stability of the LC alignment. The abilities of this method are demonstrated using a series of cinnamate-containing monomers. © 2001 American Institute of Physics.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry

Microstructural and interband transition properties of vertically stacked InAs/GaAs self-assembled quantum dots embedded in modulation-doped heterostructures

T. W. Kim, D. U. Lee, D. C. Choo, H. J. Kim, H. S. Lee, J. Y. Lee, and M. D. Kim

Appl. Phys. Lett. 79, 33 (2001); http://dx.doi.org/10.1063/1.1380239 (3 pages) | Cited 3 times

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The transmission electron microscopy image and selected area electron diffraction pattern showed that self-assembled InAs quantum-dot (QD) arrays embedded in GaAs barriers were periodically inserted in an Al0.25Ga0.75As/GaAs heterostructure. The temperature-dependent photoluminescence spectra of the InAs/GaAs quantum dots embedded in modulation-doped heterostructures showed interband transitions from the first-excited electronic subband to the first-excited heavy-hole subband together with those from the ground subband to the ground heavy-hole band (E1–HH1) while the spectra of the InAs/GaAs QDs alone showed only the peak related to the (E1–HH1) transitions. © 2001 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
73.21.La Quantum dots
81.07.Ta Quantum dots
68.35.Ct Interface structure and roughness
68.65.Hb Quantum dots (patterned in quantum wells)

Absorption of gas-phase atomic hydrogen by Si(100): Effect of surface atomic structures

Jae Yeol Maeng, Sehun Kim, S. K. Jo, W. P. Fitts, and J. M. White

Appl. Phys. Lett. 79, 36 (2001); http://dx.doi.org/10.1063/1.1379989 (3 pages) | Cited 7 times

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The atomic-scale surface structural evolution of Si(100) exposed to gas-phase thermal hydrogen atoms, H(g), has been investigated by scanning tunneling microscopy and temperature-programed desorption mass spectrometry. For the substrate temperature (Ts) between 420 and 530 K, dihydride species in 3×1:H domains were selectively etched upon extensive exposures to H(g). As a result, etch pits grew laterally along Si surface dimer rows. The presence of these pits correlates with the absorption of H(g) into the bulk of Si(100), confirming our earlier suggestion that atomic-scale surface roughening caused by etching is a prerequisite for H(g) absorption. © 2001 American Institute of Physics.
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68.43.Mn Adsorption kinetics
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.43.Vx Thermal desorption

Interfacial process of nucleation and molecular nucleation templator

X. Y. Liu

Appl. Phys. Lett. 79, 39 (2001); http://dx.doi.org/10.1063/1.1384007 (3 pages) | Cited 5 times

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Interfacial effects of nucleation inhibition and promotion were identified from the nucleation of paracetamol. Unlike the classic interfacial effects, which are caused by the change in nucleation barrier, the nonepitaxial interfacial effects are only associated with kink integration kinetics. Methylparaben inhibits nucleation by increasing the desolvation free energy barrier, which is revealed as the nonepitaxial interfacial effect of nucleation inhibition. Polysaccharide revealed its nonepitaxial interfacial effects of nucleation promotion by lowering the conformation entropic barrier via liquid molecule preordering. Polysaccharide can be regarded as an example of molecular nucleation promoter based on the nonepitaxial interfacial effects. © 2001 American Institute of Physics.
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81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
81.10.Dn Growth from solutions
68.35.Md Surface thermodynamics, surface energies
68.08.De Liquid-solid interface structure: measurements and simulations

Kinetic evidence for the structural similarity between a supercooled liquid and an icosahedral phase in Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glass

M. W. Chen, I. Dutta, T. Zhang, A. Inoue, and T. Sakurai

Appl. Phys. Lett. 79, 42 (2001); http://dx.doi.org/10.1063/1.1383060 (3 pages) | Cited 25 times

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By differential scanning calorimetric measurement, the kinetics of the phase transformation present in Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glass during continuous heating was investigated. It was found that the effective activation energy from a supercooled liquid to an icosahedral quasicrystalline phase is much lower than that from the supercooled liquid to eutectic crystalline phases. In addition, the activation energy from the icosahedral phase to the crystalline phases is almost the same as that from the supercooled liquid to the crystalline phases. Both of them support that the local atomic structure is similar for the supercooled liquid and the icosahedral phase in the bulk metallic glass. © 2001 American Institute of Physics.
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61.44.Br Quasicrystals
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
81.70.Pg Thermal analysis, differential thermal analysis (DTA), differential thermogravimetric analysis
64.70.D- Solid-liquid transitions
81.30.Fb Solidification

Magneto-optical study of electron occupation and hole wave functions in stacked self-assembled InP quantum dots

M. Hayne, J. Maes, V. V. Moshchalkov, Y. M. Manz, O. G. Schmidt, and K. Eberl

Appl. Phys. Lett. 79, 45 (2001); http://dx.doi.org/10.1063/1.1383807 (3 pages) | Cited 12 times

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We have studied the magnetophotoluminescence of doubly stacked layers of self-assembled InP quantum dots in a GaInP matrix. 4.0±0.1 monolayers of InP were deposited in the lower layer of each sample, whereas in the upper layer 3.9, 3.4, and 3.0 monolayers were used. Low-temperature photoluminescence measurements in zero magnetic field are used to show that, in each case, only one layer of dots is occupied by an electron, and imply that when the amount of InP in both layers is the same, the dots in the upper layer are larger. High-field photoluminescence data reveal that the position and extent of the hole wave function are strongly dependent on the amount of InP in the stack. © 2001 American Institute of Physics.
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73.21.La Quantum dots
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
81.07.Ta Quantum dots
78.66.Fd III-V semiconductors
78.67.Hc Quantum dots
78.20.Ls Magneto-optical effects

Role of oxygen at the grain boundary of metal oxide varistors: A potential barrier formation mechanism

P. R. Bueno, E. R. Leite, M. M. Oliveira, M. O. Orlandi, and E. Longo

Appl. Phys. Lett. 79, 48 (2001); http://dx.doi.org/10.1063/1.1378051 (3 pages) | Cited 70 times

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A model is proposed here to explain how the chemical features of metal oxide varistors can alter their nonohmic physical behavior, based on nonohmic similarities in the electrical properties of ZnO- and SnO2-based varistors. The proposed model explains the electrical properties of ZnO- and SnO2-based varistors before and after thermal treatments in oxygen- and nitrogen-rich atmospheres, which cause similar changes in the nonohmic feature of these polycrystalline ceramics with greatly differing chemical compositions and microstructures. The model is based on the key role that oxygen plays in varistor grain boundaries, independently of the type of ceramic system (ZnO-, SnO2- or even SrTiO3-based varistors) involved. © 2001 American Institute of Physics.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
61.72.Mm Grain and twin boundaries
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions

Surface plasmon propagation in microscale metal stripes

B. Lamprecht, J. R. Krenn, G. Schider, H. Ditlbacher, M. Salerno, N. Felidj, A. Leitner, F. R. Aussenegg, and J. C. Weeber

Appl. Phys. Lett. 79, 51 (2001); http://dx.doi.org/10.1063/1.1380236 (3 pages) | Cited 136 times

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Addressing the fundamental question of miniaturization of light guiding and routing towards nanoscale optics, we study experimentally surface plasmon propagation in silver and gold thin films of finite widths in the micrometer range. Spatially confined excitation of surface plasmons is realized by a prism coupling arrangement involving an opaque aluminum screen for a distinct separation of excitation and propagation (measurement) region. The surface plasmon propagation length as a function of film widths is measured by detecting stray light due to surface plasmon scattering with a conventional optical microscope. © 2001 American Institute of Physics.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
78.66.Bz Metals and metallic alloys
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Photoluminescence and photoreflectance of GaInNAs single quantum wells

Sho Shirakata, Masahiko Kondow, and Takeshi Kitatani

Appl. Phys. Lett. 79, 54 (2001); http://dx.doi.org/10.1063/1.1374221 (3 pages) | Cited 32 times

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The temperature dependence of photoluminescence (PL) and photoreflectance (PR) was studied on a 10 nm GaInNAs/GaAs single quantum well prepared by molecular-beam epitaxy using a solid As source. PL was dominated by the near-band edge PL peak with a full width at half maximum (FWHM) value of 16–28 meV for 50–280 K. This indicates that the GaInNAs epilayer was of good quality. The temperature dependence of the band gap energy was studied by the PR measurements, and the dependence was comparable to that of the GaInAs. The near-band edge PL at low temperature exhibited a blueshift with an increase in excitation intensity and temperature (8–50 K). It had a large FWHM value of 24–26 meV at 8 K. These results are discussed in terms of carrier localization. © 2001 American Institute of Physics.
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78.67.De Quantum wells
68.65.Fg Quantum wells
73.21.Fg Quantum wells
78.55.Cr III-V semiconductors
81.07.St Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Microstructural studies of top and bottom magnetic tunnel junctions

X. Portier, A. K. Petford-Long, J. H. Nickel, T. C. Anthony, and J. A. Brug

Appl. Phys. Lett. 79, 57 (2001); http://dx.doi.org/10.1063/1.1381420 (3 pages) | Cited 3 times

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High-resolution electron microscopy has been used to study the microstructural properties of top and bottom magnetic tunnel junctions. Different physical properties have been found for the two configurations, and they have been interpreted in terms of microstructural features. All physical parameters favor the bottom configuration except for the coupling field, which is higher for the bottom structure. This latter result has been explained by the more pronounced roughness at the interfaces between the electrodes and the insulator film. © 2001 American Institute of Physics.
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68.35.Ct Interface structure and roughness
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.23.Hk Coulomb blockade; single-electron tunneling
73.40.Gk Tunneling

Thermal evidence of stress-induced structural disorder of a Zr55Al10Ni5Cu30 glassy alloy in the non-Newtonian region

H. S. Chen, H. Kato, A. Inoue, J. Saida, and N. Nishiyama

Appl. Phys. Lett. 79, 60 (2001); http://dx.doi.org/10.1063/1.1381032 (3 pages) | Cited 18 times

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The evolution of specific heat near the glass transition temperature, Tg, of a Zr55Al10Ni5Cu30 glassy alloy subjected to different degrees of non-Newtonian flow conditions was investigated. At conditions in which non-Newtonian flow begins, a gradual exothermic relaxation near Tg was observed. This is attributed to the change in configuration of the long-range liquid structure of the alloy. At conditions in which a high degree of non-Newtonian flow is favored, the alloy exhibits both high-temperature and low-temperature relaxation due to a change in local short-range order. The enthalpy of relaxation is found to scale as the logarithm of the normalized viscosity and is interpreted in terms of the free volume model of viscous flow. The decrease in viscosity in the non-Newtonian flow region is associated with a highly disordered structure and induced free volume. © 2001 American Institute of Physics.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses
66.20.-d Viscosity of liquids; diffusive momentum transport
83.60.Df Nonlinear viscoelasticity
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Towards controlled production of specific carbon nanostructures— a theoretical study on structural transformations of graphitic and diamond particles

Helmut Hermann, Florin Fugaciu, and Gotthard Seifert

Appl. Phys. Lett. 79, 63 (2001); http://dx.doi.org/10.1063/1.1382852 (3 pages) | Cited 15 times

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Structural transformations of carbon nanoparticles are studied by means of molecular dynamics using a density-functional-based tight-binding method. The starting particles consist of 64 to 275 atoms arranged on a graphitic or diamond lattice. At elevated temperatures (1400 to 2800 K), the particles transform into spherical or elongated closed cages, concentric shell fullerenes, carbon nanotips, and spiraloidal and irregularly shaped clusters. The type of the final cluster depends essentially on the size and the atomic order of the starting particles, and on the temperature applied. The results show a way to proceed towards controlled preparation of specific carbon nanostructures. © 2001 American Institute of Physics.
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64.70.Nd Structural transitions in nanoscale materials
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
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Effective mass of two-dimensional electron gas in an Al0.2Ga0.8N/GaN heterojunction

D. R. Hang, C.-T. Liang, C. F. Huang, Y. H. Chang, Y. F. Chen, H. X. Jiang, and J. Y. Lin

Appl. Phys. Lett. 79, 66 (2001); http://dx.doi.org/10.1063/1.1380245 (3 pages) | Cited 17 times

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We have performed a magnetotransport study on an AlGaN/GaN heterostructure at low temperatures. The effective-mass values have been evaluated by analyzing the exact form of the temperature-dependent Shubnikov–de Haas oscillation function. The values obtained increase with the magnetic field. This mass enhancement is attributed to conduction-band nonparabolicity. The effective-mass variation with the magnetic field was extrapolated to zero field, together with further correction due to the triangular confinement of the carriers, yielding an effective mass of 0.185±0.005 of the free-electron mass. Our result is in excellent agreement with the results obtained by first-principle calculations and the tight-binding method, and suggest the significance of magnetic-field-induced nonparabolicity in transport measurements. © 2001 American Institute of Physics.  
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73.20.At Surface states, band structure, electron density of states
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Carrier relaxation dynamics for As defects in GaN

Bernard Gil, Aurélien Morel, Thierry Taliercio, Pierre Lefebvre, C. T. Foxon, I. Harrison, A. J. Winser, and S. V. Novikov

Appl. Phys. Lett. 79, 69 (2001); http://dx.doi.org/10.1063/1.1380400 (3 pages) | Cited 6 times

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Long decay times in the 50–150 ns range have been measured for the characteristic blue photoluminescence that peaks at 2.6 eV in GaN:As. We interpret these long decay times according to the theoretical predictions that this blue photoluminescence is caused by the incorporation of arsenic on the gallium site. The long decay times are characteristics of the large lattice relaxation for such a deep donor with a negative-U center behavior. © 2001 American Institute of Physics.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.47.-p Spectroscopy of solid state dynamics
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Time constant for relaxation of n = 2 excitons into n = 1 continuum states in GaAs quantum wells

Bipul Pal and A. S. Vengurlekar

Appl. Phys. Lett. 79, 72 (2001); http://dx.doi.org/10.1063/1.1382625 (3 pages) | Cited 2 times

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We resonantly excite excitons associated with the second electron and heavy hole subbands (n = 2 excitons) in 13 and 17.5 nm GaAs quantum wells (QWs) at 8 K to perform femtosecond degenerate four wave mixing measurements. We deduce the lifetime T1 of the n = 2 excitons to be ≈ 890 fs and ≈ 2.63 ps, respectively, for the 13 and 17.5 nm QWs. © 2001 American Institute of Physics.
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73.21.Fg Quantum wells
78.67.De Quantum wells
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.47.-p Spectroscopy of solid state dynamics
78.55.Cr III-V semiconductors
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
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