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1 Aug 2000

Volume 88, Issue 3, pp. 1201-1704

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Silica glass: A material for photonics

A. J. Ikushima, T. Fujiwara, and K. Saito

J. Appl. Phys. 88, 1201 (2000); http://dx.doi.org/10.1063/1.373805 (13 pages) | Cited 28 times

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Recent studies on two aspects of silica glass as a photonic material will be described. Part A of this review will be focused on structural disorder and structural relaxations in silica glass. With regard to the structural disorder, investigations have been made to improve transparency and to shift the optical absorption edge in the ultraviolet towards shorter wavelengths. Remarkable advances have been achieved in the understanding of both light scattering, which is a dominant factor in the optical losses in silica fibers, and the absorption edge. Freezing of the structural disorder was observed, and structural relaxations are found to be important for improving the transparency, whereas for the absorption edge thermal vibration effects seem to be more predominant than the structural disorder. From the results, the present authors have tried to control the structural relaxation for developing silica glass with an ultimate optical transparency, finding that a very tiny amount of the proper impurity species gives rise to structural subrelaxations, which are effective in reducing the Rayleigh scattering. The scattering was reduced by 13% by addition of only 10 wt ppm Na2O, for example. In part B of this review the second-order optical nonlinearity induced in Ge-doped silica glass will be described based on recent experiments carried out by the group of present authors. A large second-order optical nonlinearity has been successfully induced in the glass by simultaneous applications of a high dc electric field and ultraviolet (UV) irradiation, so-called UV poling. The nonlinearity induced by UV poling in bulk and film samples has achieved a magnitude of χ(2), comparable to or even larger than those of LiNbO3 and other crystals. Surprisingly enough, the nonlinearity induced by this method then decays after the UV poling as an exact single-exponential function of time, very much unlike the usual decay processes observed in glasses. Evidence is presented associating the nonlinearity with GeE′ defect centers created from oxygen deficient vacancies through photochemical reactions. The decay or degradation can be made much slower with the addition of proper impurities which work as electron scavengers. In addition, we have found that crystallites are generated in the glass by the UV poling, which leads to an increase in the third-order nonlinearity, χ(3), approximately 15 times larger than before the treatment. As a whole, the evidence strongly suggests that a major origin of the second-order nonlinearity induced in the glass is a combined effect of a large third-order nonlinearity associated with the crystallites and an internal space-charge field, where the charges to build up the field are produced during the formation of GeE′ centers. © 2000 American Institute of Physics.
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61.43.Fs Glasses
01.30.Rr Surveys and tutorial papers; resource letters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.-k Nonlinear optics
42.70.Qs Photonic bandgap materials
77.22.Ej Polarization and depolarization
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Thermal cross-track cross talk in phase-change optical disk data storage

Chubing Peng and M. Mansuripur

J. Appl. Phys. 88, 1214 (2000); http://dx.doi.org/10.1063/1.373806 (7 pages) | Cited 5 times

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We have investigated the temperature distribution in land/groove phase-change optical disks. The incident beam is linearly polarized either parallel to track (E∥ polarization) or tangential to track (E⊥ polarization). Calculations have shown that temperature profiles in the medium are dependent on the wavelength of light, the state of polarization, the geometry of the grooved structure, and the multilayer stack. The temperature profiles are quite different between the land track and the groove track. Thermal cross-track cross talk from a land track to its neighboring groove tracks is higher than that from a groove track to its neighboring land tracks. The interaction between the E⊥ electric field and the grooved structure is mainly responsible for thermal cross-track cross talk. © 2000 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks

Energy transfer and upconversion studies in yttrium–aluminum–garnet crystal doped with thulium and holmium under near-infrared laser excitation

Wenyan Tian and B. Rami Reddy

J. Appl. Phys. 88, 1221 (2000); http://dx.doi.org/10.1063/1.373876 (4 pages) | Cited 10 times

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Upconversion emission from Tm3+ and Ho3+ ions in a yttrium–aluminum–garnet crystal was observed on resonant excitation of the 3H4 level of Tm3+ and the 5I4 level of Ho3+ with a Ti:sapphire laser at room temperature and 10 K. The upconversion and the energy transfer mechanisms between Tm3+ and Ho3+ ions are discussed. A rate equation model is developed which supported the energy transfer mechanism. © 2000 American Institute of Physics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Optical nonlinearities of inorganic metal cluster μ3-MoSe4Ag3(PPh3)3Cl

Yuenan Xiong, Wei Ji, Qianfeng Zhang, and Xinquan Xin

J. Appl. Phys. 88, 1225 (2000); http://dx.doi.org/10.1063/1.373807 (5 pages) | Cited 2 times

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Optical nonlinearity and dynamic response of a novel inorganic metal cluster (μ3-MoSe4)Ag3(PPh3)3Cl were studied. Large optical limiting effect was observed with the inorganic metal cluster (μ3-MoSe4)Ag3(PPh3)3Cl dissolved in CH2Cl2. We also proved that nonlinear scattering contributes much to its optical limiting performance, which counts for nearly 75% of the total nonlinear energy loss used. The dynamic response of the cluster when pumped at high fluence was tested by a standard time-resolved pump-probe technique. The effective third-order susceptibility χ(3) for this sample was determined in a standard backward degenerate four wave mixing experiment with pump fluence lower than limiting threshold Fth. The conjugate signal intensity tends to saturate when the incident fluence rolls over this value (Fth) in spite of the fact that large optical limiting effect was observed in this fluence region, which implies that the nonlinearity mechanism is different for these two regions. © 2000 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.An Optical susceptibility, hyperpolarizability
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

Dynamic probe of pyroelectricity of nonlinear optical polymer and theoretical analysis of its temporal response

G. J. Zhang, J. Yoshida, and T. Sugita

J. Appl. Phys. 88, 1230 (2000); http://dx.doi.org/10.1063/1.373808 (6 pages)

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The light pulsing technique was used for detecting the pyroelectricity of poled nonlinear optical polymer. We provided a simple experiment setup and an analytical model for theoretical analysis. Based on the results of our experiment, according to a model that was given in this study, we have calculated the temperature field distribution in the sample caused by the flash lamp irradiation in the polymer by means of numerical analysis, and further, the pyroelectric signal response was obtained. The model could be used for precisely investigating the response from a finite duration of light pulse. This numerical analytical method applied to the thermal pulse method yields unique relations between the time-dependent pyroelectric response and time-dependent temperature distribution for a thin nonlinear optical polymer film. The experimental results compared quite favorably with theoretical analysis. © 2000 American Institute of Physics.
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42.70.Jk Polymers and organics
77.70.+a Pyroelectric and electrocaloric effects
77.22.Ej Polarization and depolarization
77.84.Jd Polymers; organic compounds
42.65.-k Nonlinear optics

A photo-oxidation mechanism for patterning and hologram formation in conjugated polymer/glass composites

Ofer Levi, Galina Perepelitsa, Dan Davidov, Shoshy Shalom, Iris Benjamin, Ronny Neumann, Aharon J. Agranat, and Yair Avny

J. Appl. Phys. 88, 1236 (2000); http://dx.doi.org/10.1063/1.373809 (8 pages) | Cited 8 times

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Improved diffraction efficiency was observed in holograms stored in disordered conjugated polymer/glass composites. The conjugated polymers used were alkoxy substituted poly(phenylenevinylne) analogs and the glass matrices were zirconia-organosilica xerogels. Investigation of the mechanism of hologram formation revealed evidence of a photochromic process consisting of light induced photo-oxidation (bleaching) of the embedded conjugated polymer resulting in the formation of an absorption grating and a phase grating. Investigation of the hologram formation revealed that the process was oxygen dependent. Oxygen removal increases hologram formation time by more than an order of magnitude and halves the total hologram efficiency. The oxygen dependence was also highly correlated with photobleaching of the samples and beam interaction of the writing beams. The chemical transformations upon photobleaching were shown by infrared and Raman spectroscopy to involve chain scission and oxidation of the polymer at the vinylic position of the conjugated polymer. Film preparation of the composites was optimized showing a tenfold improvement in the holographic properties compared to our previous results. The optimized treatment method allows for a high, >20%, diffraction efficiency, η, to be obtained for the 2.5-μm-thick polymer/glass films. Light sensitivity was compared for several polymer/glass composites and was correlated to the absorption curves and holographic diffraction efficiency showing that the new composites and film preparation techniques are promising for holographic materials sensitive in the blue and ultraviolet spectral regions. A method of information fixing by preventing oxygen entry to the composite film resulted in a fourfold increase of the erasure time. These findings suggest that holograms can be fixed for a long term by nonoxygen permeable coating, applied after hologram formation. © 2000 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
81.65.Mq Oxidation
78.30.-j Infrared and Raman spectra

Wavelength dependence of photoreduction of Ag+ ions in glasses through the multiphoton process

Yuki Kondo, Hideyuki Inouye, Seiji Fujiwara, Toshio Suzuki, Tsuneo Mitsuyu, Toshinobu Yoko, and Kazuyuki Hirao

J. Appl. Phys. 88, 1244 (2000); http://dx.doi.org/10.1063/1.373810 (7 pages) | Cited 12 times

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We have investigated the wavelength dependence of the photoreduction of Ag+ ions in glass irradiated by visible femtosecond pulses. These pulses, issued at wavelengths ranging from 400 to 800 nm, were nonresonant with the glass absorption. In this article, a relationship between threshold powers, wavelengths, and linear and nonlinear refractive indices is described. The nonlinear refractive index of Ag+-doped glass was measured by an optical Kerr shutter method. The wavelength dependence of threshold powers of the photoreduction is explained by considering linear and nonlinear refractive indices. The mechanism of the photoreduction is also discussed. © 2000 American Institute of Physics.
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82.50.-m Photochemistry
42.70.Ce Glasses, quartz
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.-k Nonlinear optics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
82.20.Hf Product distribution
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X-ray emission from 30 J Blumlein operated compact diode

M. Zakaullah and J. Worley

J. Appl. Phys. 88, 1251 (2000); http://dx.doi.org/10.1063/1.373811 (6 pages) | Cited 7 times

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An x-ray emitting diode of impedance 2.3 Ω with a knife-edge cathode energized by a 90 kV, 30 J, solid dielectric Blumlein driver of pulse length 10 ns is studied. X-ray emission from titanium, copper, molybdenum, tin, tantalum, and lead anodes was investigated. The radiation yield from titanium and copper is low. Molybdenum and tin emit a significant part as Kα line radiation, whereas the emission with tantalum and lead anode is essentially continuum radiation. The ratio of line to continuum with molybdenum target is estimated 17%±10%. © 2000 American Institute of Physics.
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52.59.Mv High-voltage diodes
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors

Vacuum ultraviolet emission characteristics from He–Ne–Xe gas discharge in an alternating current plasma display panel cell

Jeong Hyun Seo, Heui Seob Jeong, Joo Yul Lee, Cha Keun Yoon, Joong Kyun Kim, and Ki-Woong Whang

J. Appl. Phys. 88, 1257 (2000); http://dx.doi.org/10.1063/1.373812 (6 pages) | Cited 36 times

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We measured the time integrated vacuum ultraviolet (VUV) emission spectra of He–Ne–Xe gas mixture from a surface type alternating current (ac) plasma display panel cell. The measured emission lines are the resonance line (147 nm) from Xe∗(1s4), the first continuum (150 nm) and the second continuum (173 nm) from Xe dimer excited states. The relative intensities of VUV spectral lines from Xe∗ and Xe2∗ are dependent on the He/Ne mixing ratio as well as the Xe partial and total pressure. The intensity of 147 nm VUV increases with the Ne content increase and Xe2∗ molecular emission increases with the He content increase. Infrared (IR) spectra and the time variation of VUV were measured to explain the reaction pathway and the effect of the mixing ratio of He/Ne on the spectral intensity. A detailed study for the decay time shows that the decay time of 147 nm has two time constants and the radiation of 150 and 173 nm results mainly from Xe∗(1s5). The IR spectra shows that the contribution from Xe∗∗(>6 s) to Xe∗(1s5) and Xe∗(1s4) in He–Xe is different from that of Ne–Xe. The change of IR intensity explains the spectral intensity variations of He–Xe and Ne–Xe discharge. © 2000 American Institute of Physics.
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52.75.-d Plasma devices
85.60.Pg Display systems
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
31.50.Df Potential energy surfaces for excited electronic states
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Plume reduction in segmented electrode Hall thruster

Y. Raitses, L. A. Dorf, A. A. Litvak, and N. J. Fisch

J. Appl. Phys. 88, 1263 (2000); http://dx.doi.org/10.1063/1.373813 (8 pages) | Cited 42 times

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A segmented electrode, which is placed at the thruster exit, is shown to affect thruster operation in several ways, whether the electrode produces low emission current or no emission current, although there appear to be advantages to the more emissive segmented electrode. Measured by plume divergence, the performance of Hall thruster operation, even with only one power supply, can approach or surpass that of nonsegmented operation over a range of parameter regimes. In particular, the low gas flow rate can exhibit low plume divergence. This allows flexibility in operation of segmented electrode thrusters in variable thrust regimes. © 2000 American Institute of Physics.
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52.75.Di Ion and plasma propulsion
52.30.-q Plasma dynamics and flow

Electrode-sheath voltages in high-pressure mercury arcs

A. Kloss, H. Schneidenbach, H. Schöpp, H. Hess, L. Hitzschke, and B. Schalk

J. Appl. Phys. 88, 1271 (2000); http://dx.doi.org/10.1063/1.373814 (5 pages) | Cited 28 times

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Electrode-sheath voltages (ESVs) were determined as a function of time in high-pressure ac mercury arcs running at different frequencies in the range 50 Hz–5 kHz with sinusoidal wave forms. Besides the experimental investigations, a one-dimensional model was used to describe the arc-column properties. Measurements of the voltage across the arcs were compared with model calculations for the arc-column voltage only. The calculated voltages are mostly smaller than the measured ones, and it was concluded that the difference should correspond to the ESV. This voltage drop was compared with values obtained in a completely different way, namely, by measuring the voltage at different lengths of the arcs which were otherwise identic, and extrapolating it to zero length. As had been shown before, at 50 Hz this voltage drop has a very pronounced time behavior during a half cycle. The investigations were extended to higher frequencies, and the obtained differences are discussed. The field strengths were derived from the rise of the measured voltage versus the discharge lengths; a quantitative agreement with the calculated field strengths was obtained by choosing an appropriate pressure. © 2000 American Institute of Physics.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.40.Hf Plasma-material interactions; boundary layer effects
52.70.Ds Electric and magnetic measurements

Dust charging and levitating in cathode sheath of glow discharges with energetic electron beam

Dezhen Wang, Deyong Liu, and Jinyuan Liu

J. Appl. Phys. 88, 1276 (2000); http://dx.doi.org/10.1063/1.373815 (5 pages) | Cited 4 times

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The dust charging and levitating in a collisionless cathode sheath of dc glow discharges with energetic electron beam released from a plane cathode are investigated with a self-consistent theoretical model. The dust charging associated with the electron beam including secondary emission of dust can dominate the dust surface potential in the close cathode region. In this case, dusts of the same size can levitate at two different positions in the cathode sheath. © 2000 American Institute of Physics.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Fi Transport properties
52.80.Hc Glow; corona
52.25.Kn Thermodynamics of plasmas
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Microscopic mechanisms of laser ablation of organic solids in the thermal and stress confinement irradiation regimes

Leonid V. Zhigilei and Barbara J. Garrison

J. Appl. Phys. 88, 1281 (2000); http://dx.doi.org/10.1063/1.373816 (18 pages) | Cited 130 times

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The results of large-scale molecular dynamics simulations demonstrate that the mechanisms responsible for material ejection as well as most of the parameters of the ejection process have a strong dependence on the rate of the laser energy deposition. For longer laser pulses, in the regime of thermal confinement, a phase explosion of the overheated material is responsible for the collective material ejection at laser fluences above the ablation threshold. This phase explosion leads to a homogeneous decomposition of the expanding plume into a mixture of liquid droplets and gas phase molecules. The decomposition proceeds through the formation of a transient structure of interconnected liquid clusters and individual molecules and leads to the fast cooling of the ejected plume. For shorter laser pulses, in the regime of stress confinement, a lower threshold fluence for the onset of ablation is observed and attributed to photomechanical effects driven by the relaxation of the laser-induced pressure. Larger and more numerous clusters with higher ejection velocities are produced in the regime of stress confinement as compared to the regime of thermal confinement. For monomer molecules, the ejection in the stress confinement regime results in broader velocity distributions in the direction normal to the irradiated surface, higher maximum velocities, and stronger forward peaking of the angular distributions. The acoustic waves propagating from the absorption region are much stronger in the regime of stress confinement and the wave profiles can be related to the ejection mechanisms. © 2000 American Institute of Physics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Pv Polymers, organic compounds
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
62.65.+k Acoustical properties of solids

Electrical behavior of ultra-low energy implanted boron in silicon

V. Privitera, E. Schroer, F. Priolo, E. Napolitani, and A. Carnera

J. Appl. Phys. 88, 1299 (2000); http://dx.doi.org/10.1063/1.373817 (8 pages) | Cited 24 times

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In this paper an extensive characterization of the electrical activation of ultra-low energy implanted boron in silicon is reported. The Spreading Resistance Profiling technique has been used, in a suitable configuration, for measuring doped layers shallower than 100 nm, in order to extract the carrier concentration profiles. The dependence on the implant energy, dose, and annealing temperature allowed us to gain more insight into the mechanisms responsible for the electrical activation at implant energies below 1 keV. By measuring the electrical activation as a function of time for several annealing temperatures, the thermal activation energy for the electrical activation of the dopant was achieved. It slightly depends on the implant dose and it is in the range of 2–3 eV. In particular, for an implant dose of 1×1014/cm2 it is 2.0 eV, close therefore to the 1.7 eV activation energy found [Napolitani et al., Appl. Phys. Lett. 75, 1869 (1999)] for the enhanced diffusion of ultra-low energy implanted boron. The best conditions to maximize electrical activation, while minimizing diffusion, are identified and junction depths of ∼50 nm with sheet resistance below 500 Ω reported. These data are reported and their implication for the fabrication of future generation devices is discussed. © 2000 American Institute of Physics.
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71.55.Cn Elemental semiconductors
81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
66.30.J- Diffusion of impurities
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors

Investigation of threading dislocation blocking in strained-layer InGaAs/GaAs heterostructures using scanning cathodoluminescence microscopy

J. J. Russell, J. Zou, A. R. Moon, and D. J. H. Cockayne

J. Appl. Phys. 88, 1307 (2000); http://dx.doi.org/10.1063/1.373818 (5 pages) | Cited 1 time

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Threading dislocation glide relieves strain in strained-layer heterostructures by increasing the total length of interface misfit dislocations. The blocking theory proposed by Freund [J. Appl. Phys. 68, 2073 (1990)] predicts the thickness above which gliding threading dislocations are able to overcome the resistance force produced by existing orthogonal misfit dislocations. A set of wedge-shaped samples of InxGa1−xAs/GaAs (x=0.04) strained-layer heterostructures was grown using molecular-beam epitaxy in order to test the theory of dislocation blocking over a range of thicknesses within one sample. Scanning cathodoluminescence microscopy techniques were used to image the misfit dislocations. The cathodoluminescence results confirm the model proposed by Freund. © 2000 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology

Transmission electron microscopy characterization of secondary defects created by MeV Si, Ge, and Sn implantation in silicon

J. Wong-Leung, S. Fatima, C. Jagadish, J. D. Fitz Gerald, C. T. Chou, J. Zou, and D. J. H. Cockayne

J. Appl. Phys. 88, 1312 (2000); http://dx.doi.org/10.1063/1.373819 (7 pages) | Cited 5 times

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Extended defects created in Si by ion implantation to doses below the amorphization threshold have been studied after annealing at 800 °C for 15 min. The implant species were the group IV elements Si, Ge, and Sn, and structural defects created by similar damage distribution were compared. The mass of the implanted ion influences the type of defect observed. For all three implant species, rod-like {311} planar defects were observed. Additionally, in Ge and Sn implanted samples, small {111} interstitial faulted dislocation loops were observed. © 2000 American Institute of Physics.
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61.72.uf Ge and Si
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
61.72.Nn Stacking faults and other planar or extended defects
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing

Emission channeling studies of Pr in GaN

U. Wahl, A. Vantomme, G. Langouche, J.P. Araújo, L. Peralta, and J. G. Correia

J. Appl. Phys. 88, 1319 (2000); http://dx.doi.org/10.1063/1.373820 (6 pages) | Cited 29 times

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We report on the lattice location of Pr in thin film, single-crystalline hexagonal GaN using the emission channeling technique. The angular distribution of β− particles emitted by the radioactive isotope 143Pr was monitored by a position-sensitive electron detector following 60 keV room temperature implantation of the precursor isotope 143Cs at a dose of 1×1013 cm−2 and annealing up to 900 °C. Our experiments provide direct evidence that Pr is thermally stable at substitutional Ga sites. © 2000 American Institute of Physics.
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61.85.+p Channeling phenomena (blocking, energy loss, etc.)
61.72.S- Impurities in crystals

Characterization of defects in (ZnMg)Se compounds by positron annihilation and photoluminescence

F. Plazaola, K. Saarinen, L. Dobrzynski, H. Reniewicz, F. Firszt, J. Szatkowski, H. Meczynska, S. Legowski, and S. Chabik

J. Appl. Phys. 88, 1325 (2000); http://dx.doi.org/10.1063/1.373821 (8 pages) | Cited 12 times

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Defect characterization of as-grown Zn1−xMgxSe mixed crystals (0⩽x<0.6) and the effect of Zn vapor annealing has been studied by positron lifetime and photoluminescence measurements. We obtain both experimental and theoretical evidence that the bulk lifetime of free positrons increases linearly with Mg alloying. The average positron lifetime increases with temperature indicating that both vacancies and negative ions trap positrons. The decompositions of the lifetime spectra show that the vacancy has the characteristic positron lifetime of 325 ps. The comparison with theoretical calculations indicate that the lifetime 325 ps corresponds either to divacancies relaxed inwards or to monovacancies strongly relaxed outwards. We consider the latter identification more likely and attribute the positron lifetime 325 ps to Zn vacancy or a complex involving VZn. The vacancy concentration is almost independent of Mg content above x=0.2 but decreases strongly at x=0.56. The Zn vapor annealing decreases the concentration of Zn vacancies. The intensity of the green photoluminescence correlates with the concentration of VZn both as a function of Mg alloying and Zn vapor annealing. We thus conclude that the electron levels of the Zn vacancy are involved in the optical transition leading to the green photoluminescence. © 2000 American Institute of Physics.
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78.70.Bj Positron annihilation
78.55.Hx Other solid inorganic materials
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
71.55.Ht Other nonmetals

Electron beam stimulated formation of CdS nanoparticles within calixarene Langmuir–Blodgett films

A. V. Nabok, A. K. Ray, and A. K. Hassan

J. Appl. Phys. 88, 1333 (2000); http://dx.doi.org/10.1063/1.373877 (6 pages) | Cited 9 times

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Two possible types of cadmium sulphide (CdS) nanostructures can be formed within Langmuir–Blodgett (LB) films of calixarene Cd salt as a result of exposure to H2S gas: nanoclusters with the size of about 1.5 nm or two-dimensional planes with the thickness of about 1.7 nm. Transmission electron microscopy and electron diffraction studies on calixarene/CdS LB films show that CdS particles are not present in the fresh samples at the beginning, but they are gradually formed under exposure to a high energy electron beam. A blueshift of the first exciton absorption band and an increase of the extinction coefficient, caused by exposure to H2S gas, were found with UV-visible optical spectroscopy and surface plasmon resonance, respectively. © 2000 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
78.66.Hf II-VI semiconductors
61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.18.-g Langmuir-Blodgett films on liquids
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.40.Fy Semiconductors

Self-trapped exciton luminescence induced in alpha quartz by swift heavy ion irradiations

J. M. Costantini, F. Brisard, G. Biotteau, E. Balanzat, and B. Gervais

J. Appl. Phys. 88, 1339 (2000); http://dx.doi.org/10.1063/1.373822 (7 pages) | Cited 3 times

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Natural quartz single crystals (α-SiO2) have been exposed to pulsed heavy ion beams (12C, 19F, 32S) with energies of 1 MeV amu−1 in the electronic slowing down regime. The simultaneous recording of the ion fluence and emitted photons with time-resolved spectroscopy experiments allowed the measurement of the “blue luminescence” time decay at 85 K as a function of the fluence at the various electronic stopping power, Se=(−dE/dx)e, of the ions. For all ions, regardless of fluence, the spectra are similar and have two broad bands centered at 1.60 and 2.75 eV with full widths at half maximum around 0.30 and 0.75 eV, respectively. Single-exponential time decay curves are found regardless of Se increasing from 1.4 keV nm−1 (12 MeV 12C) to 5.2 keV nm−1 (32 MeV 32S) across the amorphous track-formation threshold at 2.5±0.5 keV nm−1. At low damaged fractions (⩽22%), the decay-time constant ranges between 1.0 and 1.6 ms. The luminescence intensities at zero delay time approximately decrease in an exponential fashion versus fluence with a decay cross section increasing by around one order-of-magnitude at the track-formation threshold, as found in the previous experiments with continuous beams. We analyze to which extent the luminescence decay versus fluence could be due to the quenching of the self-trapped exciton (STE) radiative recombinations by interactions with the ion-induced defects. For this, a STE diffusion model is devised where the STEs recombine nonradiatively at the neighboring cylindrical tracks. The model gives luminescence decay curves versus fluence in good agreement with the experimental data by varying the STE diffusion constant and the amorphous track-core radius in a reasonable range of values. © 2000 American Institute of Physics.
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42.70.Ce Glasses, quartz
61.80.Jh Ion radiation effects
78.55.Hx Other solid inorganic materials
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.47.-p Spectroscopy of solid state dynamics
61.82.Ms Insulators

Uncertainty limits for the macroscopic elastic moduli of random polycrystalline aggregates

Pham Duc Chinh

J. Appl. Phys. 88, 1346 (2000); http://dx.doi.org/10.1063/1.373823 (10 pages) | Cited 17 times

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Practical polycrystalline aggregates are expected to have macroscopic properties that depend upon the properties of constituent crystals and the aggregate geometry. Since that microgeometry is usually random, there will be some uncertainty in the observed macroscopic behavior of the aggregates. The general shape-independent upper and lower estimates for those uncertainty intervals for the elastic moduli of completely random polycrystals are constructed from the minimum energy and complementary energy principles. Applications to aggregates of cubic crystals are presented. © 2000 American Institute of Physics.
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46.25.Cc Theoretical studies

General susceptibility functions for relaxations in disordered systems

R. Bergman

J. Appl. Phys. 88, 1356 (2000); http://dx.doi.org/10.1063/1.373824 (10 pages) | Cited 46 times

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A general equation for the susceptibility of disordered systems is proposed. It is based on the experimental observation of power laws at frequencies far from the peak frequency of the imaginary part of the frequency dependent relaxation function, the susceptibility. The obtained general expression contains the equations of other proposed relaxation functions as special cases and, thus, it might be considered as a generalization of these. From this general equation we derive an equation specially adapted for the α relaxation in glass-forming materials. This equation contains only three fit parameters and it is thus very suitable for fitting real experimental data. It is shown that this equation is a good frequency domain representation of the time domain Kohlrausch–Williams–Watts stretched exponential. From the general equation we also derive a four-parameter “universal” equation that describes most types of responses and even inverted response data, i.e., response peaks more stretched on the low frequency side than on the (as is normal) high frequency side. The physical significance of the different parameters is qualitatively discussed and the proposed functions are shown to satisfactorily describe typical experimental data. © 2000 American Institute of Physics.
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77.22.Gm Dielectric loss and relaxation
78.20.-e Optical properties of bulk materials and thin films

Diffusion of Ge in Si1-xGex/Si single quantum wells in inert and oxidizing ambients

Michelle Griglione, Timothy J. Anderson, Yaser M. Haddara, Mark E. Law, Kevin S. Jones, and Alex van den Bogaard

J. Appl. Phys. 88, 1366 (2000); http://dx.doi.org/10.1063/1.373825 (7 pages) | Cited 16 times

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The interdiffusion of Si/Si0.85Ge0.15/Si single quantum well (SQW) structures subjected to inert- and oxidizing-ambient annealing was investigated as a function of temperature (900–1200 °C) and time. Point defect injection allowed modification of the vacancy and interstitial mediated components of interdiffusion, DV and DI. Diffusion profiles of samples processed in inert and oxidizing ambients were similar, which indicates a vacancy-dominated mechanism. Activation energies of diffusion in inert and oxidizing ambients were found to be 5.8 and 5.0 eV, respectively. A fractional interstitial component fI of ∼0.10 was estimated for the lower temperatures, while a significantly smaller fI of ∼0.02 was estimated for the higher temperatures. Experiments using SQWs with buried boron marker layers showed that dislocations in the Si1-xGex trap point defects and affect interdiffusion behavior. © 2000 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.30.Ny Chemical interdiffusion; diffusion barriers
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters

Excimer laser induced diffusion in magnetic semiconductor quantum wells

H. Howari, D. Sands, J. E. Nicholls, J. H. C. Hogg, T. Stirner, and W. E. Hagston

J. Appl. Phys. 88, 1373 (2000); http://dx.doi.org/10.1063/1.373826 (7 pages) | Cited 2 times

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Studies of pulsed laser annealing (PLA) of CdTe/CdMnTe quantum well structures are made in order to examine depth dependent effects in laser irradiated semiconductors. Since diffusion coefficients are strongly dependent on the temperature, depth resolution is achieved because the diffusion of Mn from the barriers into the quantum wells is depth dependent. Multiple quantum well (MQW) structures of CdTe/CdMnTe were annealed with single pulses from an XeCl laser at 308 nm. At a threshold of 90 mJ cm−2 two new emission bands are observed that are attributed to the diffusion of Mn from barrier layers to QWs. The diffusion associated with these bands, measured as the integrated product of the diffusion constant and time, is found to be 300 and 30 Å2. Calculations of the temperature, reached within the surface following PLA, using an analytical solution of the heat diffusion equation coupled with known high temperature diffusion coefficients predict the diffusion to decrease by one order of magnitude within one period at the top of the MQW stack. It is suggested that at the threshold surface melting occurs and that these emission bands arise from the QWs immediately beneath the melt front. The diffusion of Mn ions into the QWs is confirmed by magneto-optical data. A further emission band occurs at this same threshold with a Mn concentration above that of the concentration in the barrier layers of the MQW stack. This emission is attributed tentatively to the segregation of the Mn ion within the molten region following recrystallization. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors

Composition, residual stress, and structural properties of thin tungsten nitride films deposited by reactive magnetron sputtering

Y. G. Shen, Y. W. Mai, D. R. McKenzie, Q. C. Zhang, W. D. McFall, and W. E. McBride

J. Appl. Phys. 88, 1380 (2000); http://dx.doi.org/10.1063/1.373827 (9 pages) | Cited 28 times

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Thin tungsten nitride (WNx) films were produced by reactive dc magnetron sputtering of tungsten in an Ar–N2 gas mixture. The effects of the variation of nitrogen partial pressure on the composition, residual stress, and structural properties of these films as well as the influence of postdeposition annealing have been studied. The films were analyzed in situ by a cantilever beam technique, and ex situ by x-ray photoelectron spectroscopy, electron energy-loss spectroscopy, x-ray diffraction, and transmission electron microscopy (TEM). It was found that at N concentrations below 8 at. %, the films (typical 150 nm in thickness) were essentially bcc α-W. An amorphous phase was observed in the range of about 12–28 at. % N. When N concentrations reached ∼32 at. % or above, a single-phase structure of W2N was formed. Annealing of the as-deposited films resulted in crystallization of the amorphous or an improved crystallinity of the W2N structure, which was related to the N concentration. Stresses of all W and WNx films were compressive. As the N concentration was increased, the stress decreased and reached its lowest value for amorphous samples near 20 at. % N. Past this point, the compression of films rose again. These results can be ascribed to structural changes induced by the pressure-dependent variation in the average energy of particles bombarding the film during deposition. Cross-sectional TEM studies showed that all crystalline WNx films had columnar microstructures. The average column width near stoichiometry of W2N was ∼20±5 nm near the film surface. © 2000 American Institute of Physics.
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68.55.Nq Composition and phase identification
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
68.60.Bs Mechanical and acoustical properties
61.72.Cc Kinetics of defect formation and annealing
61.66.Bi Elemental solids
61.66.Dk Alloys
61.43.Er Other amorphous solids
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.20.Kz Other electron-impact emission phenomena
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