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Journal of Applied Physics

Issue 9 • Date Nov 2000

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Displaying Results 1 - 25 of 98
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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  • Plasma heating and ultrafast semiconductor laser modulation through a terahertz heating field

    Page(s): 4933 - 4940
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    Electron-hole plasma heating and ultrafast modulation in a semiconductor laser under a terahertz electrical field are investigated using a set of hydrodynamic equations derived from the semiconductor Bloch equations. The self-consistent treatment of lasing and heating processes leads to the prediction of a strong saturation and degradation of modulation depth even at moderate terahertz field intensity. This saturation places a severe limit to bandwidth achievable with such scheme in ultrafast modulation. Strategies for increasing modulation depth are discussed. © 2000 American Institute of Physics. View full abstract»

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  • Conditions of single guided mode in two-dimensional triangular photonic crystal slab waveguides

    Page(s): 4941 - 4946
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    Photonic band structure analyses are applied to study the effect of slab thickness in two-dimensional photonic crystal slab waveguides. For transverse electric-like modes of a triangular lattice of air holes, the band gap of the asymmetric photonic crystal slab with a drilled low-index cladding do not differ significantly from that of the photonic crystal suspended in air over a wide range of slab thickness. The condition of single guided mode operation is also studied and it is found that the single mode cutoff thickness changes only by a small amount as an air-hole filling ratio varies once the center of the band gap is fixed. © 2000 American Institute of Physics. View full abstract»

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  • Longitudinal and transverse polarizability of the conducting double sphere

    Page(s): 4947 - 4952
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    Exact expressions are derived for the longitudinal and transverse polarizability of two overlapping conducting spheres of arbitrary radii and with arbitrary angle of intersection. The transverse polarizability is expressed as a single integral, which can be performed if the angle of intersection is a rational fraction of π, i.e., the angle of intersection can be expressed as mπ/n, with m and n integers. The longitudinal polarizability can be expressed as a single integral if the two spheres are equal. For unequal spheres it involves two integrals, as well as the capacity, which itself was expressed as a single integral earlier. For equal spheres the second integral vanishes by symmetry, and the capacity is not needed. Both integrals can be performed if the angle of intersection is a rational fraction of π. In earlier work by the authors the longitudinal and transverse polarizability were found only for discrete angles of intersection π/n with n integer. Our result for the longitudinal polarizability of two equal overlapping conducting spheres shows that an earlier result of Radchik etal [J. Appl. Phys. 76, 4827 (1994)] for overlapping dielectric spheres is incorrect. © 2000 American Institute of Physics. View full abstract»

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  • Vacuum-ultraviolet resonant photoabsorption imaging of laser produced plasmas

    Page(s): 4953 - 4960
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    We present results from a vacuum-ultraviolet (VUV) “photoabsorption imaging” technique based on the measurement of the time and space resolved absorption of a quasimonochromatic VUV beam from a laser plasma light source. The use of VUV radiation as a probe beam permits direct access to resonance lines of (singly and more highly charged) ions and also to the resonant and nonresonant continua of atoms and ions. In this experiment we have confined ourselves to measurements using the 3p–3d resonances of Ca, Ca+, and Ca2+ as markers of the temporal and spatial distribution of ground state atoms and ions in an expanding laser plasma plume. We show how time resolved column density maps may be extracted from such images. In addition we have extracted plasma plume velocities from the data, which compare well with an analytical laser ablation model. © 2000 American Institute of Physics. View full abstract»

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  • Modeling of incident particle energy distribution in plasma immersion ion implantation

    Page(s): 4961 - 4966
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    Plasma immersion ion implantation is an effective surface modification technique. Unlike conventional beam-line ion implantation, it features ion acceleration/implantation through a plasma sheath in a pulsed mode and non-line-of-sight operation. Consequently, the shape of the sample voltage pulse, especially the finite rise time due to capacitance effects of the hardware, has a large influence on the energy spectra of the incident ions. In this article, we present a simple and effective analytical model to predict and calculate the energy distribution of the incident ions. The validity of the model is corroborated experimentally. Our results indicate that the ion energy distribution is determined by the ratio of the total pulse duration to the sample voltage rise time but independent of the plasma composition, ion species, and implantation voltage, subsequently leading to the simple analytical expressions. The ion energy spectrum has basically two superimposed components, a high-energy one for the majority of the ions implanted during the plateau region of the voltage pulse as well as a low-energy one encompassing ions implanted during the finite rise time of the voltage pulses. The lowest-energy component is attributed to a small initial expanding sheath obeying the Child-Langmuir law. Our model can also deal with broadening of the energy spectra due to molecular ions such as N2+ or O2+, in which case each implanted atom only carries a fraction (in this case, half) of the total acceleration energy. © 2000 American Institute of Physics. View full abstract»

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  • Spatiotemporal behaviors of excited Xe atoms in unit discharge cell of ac-type plasma display panel studied by laser spectroscopic microscopy

    Page(s): 4967 - 4974
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    Two-dimensional spatiotemporal behaviors of excited Xe atoms in the 1s4 resonance state and the 1s5 metastable state were measured in a unit discharge cell of an ac-type plasma display panel by a laser absorption technique combined with an optical microscope. The measured density of Xe(1s5) has two large peaks on both the temporal anode and cathode sides. The peak at the anode has a narrower spatial distribution while the peak at the cathode is distributed over the electrode area. In its temporal behavior, the anode peak rises slightly faster than the peak at the cathode and decays faster at the beginning of afterglow, but both peaks tend to have the same decay rate in the later period. The behavior of Xe(1s4) shows similar features, but the decay rate is much larger, corresponding to the effective lifetime of imprisoned resonance radiation. The maximum densities of Xe(1s5) and Xe(1s4) are 5×1013 and 2×1013 cm-3, respectively. Emission from Xe(2p) atoms was also observed, and this nearly followed the current wave form. With these results, we estimated the efficiency of vacuum ultraviolet emissions from excited Xe(1s4) atoms and Xe2* excimers formed from Xe(1s5) atoms. © 2000 American Institute of Physics. View full abstract»

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  • Raman scattering studies on silver nanoclusters in a silica matrix formed by ion-beam mixing

    Page(s): 4975 - 4979
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    The formation and growth of nanoscale silver clusters in silica matrices are studied by means of optical absorption and Raman scattering spectroscopy. The metallic silver layer of the Ag/SiO2 couple was irradiated by argon ions for ion-beam mixing of silver with the silica matrix. Postannealing of the embedded Ag atoms in silica matrices results in the growth of Ag nanoclusters. The quadrupolar surface acoustic vibrational mode of the Ag nanoclusters has been observed in low-frequency Raman scattering experiments. The average size of these Ag nanoclusters is estimated from the quadrupolar mode frequency. Systematic growth of Ag nanoclusters embedded in silica matrices is observed with the increase of postannealing temperature. We have estimated the activation energy for the diffusion of Ag atoms in irradiated a-SiO2 from the coarsening of these embedded Ag atoms. Development of a peak at about 3 eV in the optical absorption spectra for the samples postannealed at higher temperatures corroborates further the growth of Ag nanoclusters in the silica matrices. New Raman modes at 1368 and 1573 cm-1 are observed in Ag embedded silica samples and the possible origin of these modes is discussed. © 2000 American Institute of Physics. View full abstract»

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  • Effects of end-of-range dislocation loops on transient enhanced diffusion of indium implanted in silicon

    Page(s): 4980 - 4984
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    Transient enhanced diffusion of indium implanted in silicon is studied in the presence of the end-of-range (EOR) damage layer. To investigate the effect of EOR defects on the indium diffusion, the samples that were implanted with indium at a high dose (1×1013–5×1014/cm2) sufficient to produce the amorphous layer were prepared. Transmission electron microscopy measurements and Rutherford backscattering spectrometry reveal the amorphization threshold of indium implantation is around 5×1013/cm2 for 200 keV, 115In+ implanted with 100 μA/cm2 beam current density at room temperature. These results are consistent with Monte Carlo simulation of implantation. Monte Carlo simulations indicate the deviation from the plus one model due to the mass effect of indium. After amorphization, following both RTA at 1000 °C and furnace anneal at low temperature (650 and 850 °C) in nitrogen ambient showed the formation of extrinsic EOR dislocation loops below the original amorphous/crystalline interface. During this process, strong segregation of indium toward the EOR dislocation loops is clearly observed. The profile shift of indium at a concentration of 1×1017 atoms/cm3 is not proportional to the implanted dose. Since most interstitials condense into EOR dislocation loops, diffusivity enhancement of indium is not proportional to the implant dose above amorphization threshold. © 2000 American Institute of Physics. View full abstract»

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  • Structure and luminescence of annealed nanoparticles of ZnS:Mn

    Page(s): 4985 - 4993
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    Structural and light-emitting properties of nanoparticles of ZnS:Mn annealed in vacuum at temperatures up to 525 °C are presented. Annealing the 3.5 nm particles at temperatures up to 350 °C caused growth of some particles without substantial change in the luminescence or ZnS lattice. After annealing at 400–525 °C, the high-temperature wurtzite phase of ZnS appeared, accompanied by an increase of the average particle diameter to approximately 100 nm and a rearrangement of the Mn ions. Dramatic increase in cathodoluminescence emission was also observed and is compared to the structural information obtained from electron microscopy, x-ray diffraction, x-ray absorption fine structure, and electron paramagnetic resonance measurements. © 2000 American Institute of Physics. View full abstract»

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  • Relationship between fluence gradient and lateral grain growth in spatially controlled excimer laser crystallization of amorphous silicon films

    Page(s): 4994 - 4999
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    In order to clarify the relationship between excimer laser fluence gradient and the length of lateral grain growth, the excimer laser fluence used for crystallization is modulated by a beam mask. The crystallized 50-nm-thick a-Si films are secco etched in order to observe the lateral grain growth by scanning electron microscope. The fluence distribution across the pattern is measured by a negative photoresist that has a linear relationship between laser fluence and resist thickness after development. This mapped fluence distribution is utilized to deduce the fluence gradient for each laser energy output. It is shown that lateral growth length increases and the directionality of the grains improves as the fluence gradient increases. Lateral growth length as long as 1.5 μm can be driven in a 50-nm-thick a-Si film by a single excimer laser pulse without any substrate heating. Electrical conductance measurement is used to probe the solidification dynamics. The lateral solidification velocity is estimated to be 7 m/s. A model is proposed to explain the formation of grain microstructure. © 2000 American Institute of Physics. View full abstract»

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  • Lateral gettering of iron by cavities induced by helium implantation in silicon

    Page(s): 5000 - 5003
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    Lateral gettering has been studied by introducing cavities in the periphery of large active devices. Cavities were induced by helium implantation followed by a thermal treatment on samples previously contaminated by iron. Those cavities are known to be efficient to trap metallic impurities in silicon by chemisorption. The iron distribution in samples of 6×6 mm2 area has been monitored by measuring current versus voltage characteristics and interstitial iron concentrations by deep level transient spectroscopy on Schottky diodes uniformly distributed. A symmetrical iron distribution has been observed with a decreasing concentration close to the gettering region. This lateral gettering is enhanced with increasing thermal budget. Extensions of several millimeters can be obtained allowing applications in power device technology. © 2000 American Institute of Physics. View full abstract»

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  • Effect of polyatomic ion structure on thin-film growth: Experiments and molecular dynamics simulations

    Page(s): 5004 - 5016
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    The experiments described here examine 25–100 eV CF3+ and C3F5+ ion modification of a polystyrene (PS) surface, as analyzed by x-ray photoelectron spectroscopy. The molecular dynamics computer simulations probe the structurally and chemically similar reactions of 20–100 eV CH3+ and C3H5+ with PS. CF3+ and C3F5+ each form a distribution of different fluorocarbon (FC) functional groups on PS in amounts dependent upon the incident ion energy, structure, and fluence. Both ions deposit mostly intact upon the surface at 25 eV, although they also undergo some crosslinking upon deposition. Fragmentation of the two ions increases as the ion energies are increased to 50 eV. Both ions show increases in total fluorine and fluorinated carbon content when changing the ion energy from 25 to 50 eV. The simulations predict that CH3+ and C3H5+ behave in a similar fashion to their FC analogs, remaining mostly intact and either embedding or scattering from the surface without reacting at 20 eV. At 50 and 100 eV, the simulations predict fragmentation most or all of the time. The simulations also show that the chemical products of the collisions depend significantly on the structure of the incident isomer. The simulations further illustrate how the maximum penetration depth of ion fragments depends on ionic structure, incident energy, and the identity of the penetrating fragment. These ion–surface results are discussed in - terms of their possible role in plasmas. © 2000 American Institute of Physics. View full abstract»

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  • EL2, EL3, and EL6 defects in GaAs highly implanted with sulfur

    Page(s): 5017 - 5021
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    Sulfur ions were implanted into a semi-insulating GaAs wafer at 50 keV at a dose of 1×1015cm-2. The implanted GaAs wafer was annealed at temperatures of 650–1000 °C for 15 min. Deep levels were measured in regions with carrier concentrations lower than 3×1017cm-3, after layers of various thicknesses were removed from the surface of the wafer. The dominant defects in samples annealed at temperatures lower than 850 °C were EL2 and EL6, while 1000 °C annealed samples exhibited isolated EL2 and EL3 defects. Isolated EL2 defects were observed in regions of carrier concentrations lower than 1×1017cm-3, and EL3 defects were observed in regions of carrier concentrations higher than 2×1017cm-3. © 2000 American Institute of Physics. View full abstract»

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  • Transmittance in irradiated poly(methyl methacrylate) at elevated temperatures

    Page(s): 5022 - 5027
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    The transient transmittance of gamma-ray irradiated poly(methyl methacrylate) at elevated temperatures is investigated. The transmittance in the ultraviolet and visible range decreases with an increase of radiation dose. We propose that the color center is responsible for the reduction of transmittance in the irradiated specimen. Then the concentration of the color center decreases with increasing annealing time at elevated temperatures. The transmittance data at 407 nm are in excellent agreement with the theoretical model in which the color center is annihilated by a second order kinetic process. The rate constant follows the Arrhenius equation. The activation energy in the range of 44.27–51.52 kJ/mol decreases with increased dose. © 2000 American Institute of Physics. View full abstract»

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  • Ab initio study of structure in boron nitride, aluminum nitride and mixed aluminum boron nitride amorphous alloys

    Page(s): 5028 - 5032
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    Car–Parrinello molecular dynamics is applied to the liquid quench simulation of the amorphous networks of BN, AlN and AlBN2. Structural and elastic properties were determined. It is found that AlN has a stronger tendency to chemical order than BN, driven by the greater energy penalty for “wrong bonds.” AlN, however, has a stronger tendency to form an amorphous structure as judged by the energy difference between the crystalline and amorphous states. There is some experimental evidence for an amorphous form of AlN. BN was simulated at two densities, 2.0 and 3.0 g/cm3. Even at the higher density, the fraction of tetrahedral coordination remained low, in contrast to AlN, enabling us to predict that the tetrahedral amorphous form of BN does not form under liquid quench conditions. The amorphous network with the formula AlBN2 has an intermediate tendency to form a tetrahedral structure and has a relatively high elastic modulus. This material is predicted to be of value for application as a wear resistant coating. © 2000 American Institute of Physics. View full abstract»

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  • Multiphonon hopping conduction in nonconventional chromium-doped Bi3Pb1Sr3Ca3Cu4-nCrnOx (n=0.025–0.2) glasses with nanocrystalline particles and clusters

    Page(s): 5033 - 5042
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    Transport properties of Cr containing multicomponent oxide glasses Bi3Pb1Sr3Ca3Cu4-nCrnOx (n=0.025, 0.05, 0.1, and 0.2) dispersed with nanocrystalline particles (5–20 nm depending on the values of n) have been reported in the temperature range of 250–450 K. Conductivity of this glass-nanocrystal composite system shows little decrease with increasing Cr content. Above θD/2 D is the Debye temperature), conductivity data can be analyzed with small polaron hopping models. Interestingly, unlike undoped Bi4Sr3Ca3Cu4Ox (or Bi-4334) glasses [showing nonadiabatic small polaron hopping (SPH) conduction at T≫θD/2], the Cr doped glasses supports adiabatic SPH conduction mechanism above θD/2 indicating change of glass network structure due to partial substitution of Cu by Cr. But below this temperature Mott’s or Greaves’ variable range hopping models can be consistently used to fit the experimental conductivity data only with larger (compared to the usual transition metal oxide glasses) values of the density of states at the Fermi level N(EF). The most probable transport mechanism for the entire range of temperature and glass compositions is concluded to be due to multiphonon tunneling of large polarons between the nanoclusters present in the glasses which is also in sharp contrast t- o the behavior of the undoped (Bi-4334) glass. All the glass samples (except n≥0.2) are found to become superconductors by annealing at higher temperatures. © 2000 American Institute of Physics. View full abstract»

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  • Near edge x-ray absorption fine structure of thermally annealed amorphous nitrogenated carbon films

    Page(s): 5043 - 5049
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    The change of structure of tetrahedral amorphous carbon (ta-C) films after nitrogen incorporation, particularly at a high concentration, was studied by near edge x-ray absorption fine structure (NEXAFS) spectroscopy and it was found to be very close to pyridine. The π* peak at the N K (nitrogen K) edge was decomposed into three components corresponding to different resonances. From a detailed analysis of N K edge by NEXAFS spectroscopy it was revealed that as the nitrogen concentration in the films increases, the σ** intensity ratio decreases, indicating that there is an increase of the amount of CN relative to the C–N bonds. By thermal annealing at different temperatures, up to 800 °C, the nitrogen concentration in the films is reduced. Intensity as well as the position of the π* peak at the C K edge changed with annealing temperature. At the same time, a decrease of the intensity of the π* peak at the N K edge and a very interesting change of the relative intensities of the three split components of this π* peak have been observed. The possible changes of structure of nitrogenated carbon films by annealing and thermal stability of the films have been thoroughly emphasized. © 2000 American Institute of Physics. View full abstract»

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  • Three-dimensional strain field calculations in coupled InAs/GaAs quantum dots

    Page(s): 5050 - 5055
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    A detailed calculation of the three-dimensional strain field in and around InAs/GaAs quantum dots is presented. The strain field is calculated by minimizing the elastic strain energy on a cubic grid. Surface boundary conditions are incorporated to enable the strain field at the surface of the cap layer to be examined in detail. This has important implications for the vertical and lateral ordering of subsequent layers of dots. Results are presented for a single dot as well as two and four coupled dots. It is found that the elastic energy density at the surface of the epilayer above a layer of seed dots exhibits strong minima directly above the seed dots, facilitating vertical ordering. An intriguing result is that, under certain conditions, satellite minima also occur at interstitial points, raising the possibility that a second layer of dots above the seed layer can have significantly more dots than the seed layer because of lateral ordering. © 2000 American Institute of Physics. View full abstract»

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  • Stiffness of compressed fiber mats

    Page(s): 5056 - 5061
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    We investigate, using an analytical and a numerical model, the in-plane stiffness of fiber mats. A mat is modeled by randomly depositing thin linear-elastic fibers on top of each other under the influence of an external pressure. The external pressure has the effect of bending the fibers over each other. The fibers are assumed rigidly bonded at contacts. For a low external pressure the stiffness of the mat deviates from that of its two-dimensional projection only by a geometrical factor, and the effective Poisson contraction is close to zero. For higher pressures, stiffness is governed by two competing effects and a maximum appears in the stiffness. The effective Poisson ratio is clearly negative in this range. An approximative analytical description is developed for the stiffness of mats formed under low external pressure. The stiffness is given as a function of only a few parameters: the degree of bonding, the dimensions of the fibers, the elastic constants of the fiber material, and the density of fibers. © 2000 American Institute of Physics. View full abstract»

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  • Coupled-flux nucleation modeling of oxygen precipitation in silicon

    Page(s): 5062 - 5070
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    Experimental data for oxygen precipitation densities in Czochralski-grown silicon following multistep annealing treatments are compared with predictions from a coupled-flux model for time-dependent nucleation. This is a more correct model for diffusion-controlled nucleation processes than is the classical theory of nucleation since it directly couples the two stochastic fluxes of interfacial attachment and long-range diffusion. Quantitative agreement is obtained between the measured and calculated densities for nucleation temperatures greater than 650 °C. Good agreement is obtained for lower temperatures if the oxygen diffusion rate is taken to be larger than is predicted from high-temperature diffusion data. The fit values for the diffusion coefficient from the nucleation data are in good agreement with recent results from dislocation-unlocking experiments. The oxygen loss calculated by coupled-flux nucleation and diffusion-limited growth agrees with the experimental observations. Classical theory nucleation calculations predict a much greater oxygen loss, signaling the failure of the theory to correctly treat nucleation when long-range diffusion is important, true in most solid-state precipitation processes. © 2000 American Institute of Physics. View full abstract»

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  • Elliptically-deformed spherulitic crystallization observed in the formation of μm-sized periodic grating structures in photopolymerized prepolymer/liquid crystal material systems

    Page(s): 5071 - 5078
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    This paper reports the effects of an artificially introduced μm-sized periodic grating structure on the growth of spherulites in prepolymer/liquid crystal material systems between two glass substrates. The authors use the technique of forming the volume holographic grating to create well-defined obstacles having periodic structures. Spherulites grown in an ordinary polymer-dispersed liquid crystal (PDLC) environment are compared with spherulites in the holographic grating environment, and differences in shape are presented. Although spherulites grown under ordinary conditions for the formation of PDLC are characterized by a circular shape and well-developed radial striations, those grown in volume holographic gratings are elliptically deformed, oriented so that the long axis is in the direction of the gratings, and the major striations tend to be either parallel or perpendicular to the grating walls. These findings have been observed for different material systems, suggesting that the features are not simply material specific but more common to prepolymer/liquid crystal mixtures. Compared with other factors affecting the growth and shape of spherulites, a μm-sized periodic grating structure made of polymer-based materials acts not as a complete barrier but as a retarder, which causes directional variation in the movement of the growth front and leads to elliptical deformation in the growing spherulite. Based on the results of this study, the authors have proposed a model of the growth process of a spherulite in the grating environment. © 2000 American Institute of Physics. View full abstract»

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  • Contrast enhancement in the detection of defects in transparent layered structures: The use of optothermal interference technique in solar cell investigation

    Page(s): 5079 - 5086
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    This article shows the enhanced sensitivity of the optothermal interference technique in the detection of local differences (nonhomogeneity in thickness and optothermal parameters), compared to the conventional optical interference, when investigating layered transparent structures. The measured signal is sensitive to the reflectance variation at the distinct interfaces, function of temperature, as well as to the optical phase lag between the reflected beams. Measurements made on solar cells show contrast of the order of 100% in the optothermal interference, while the conventional optical interference presents a contrast of only 15%. A model based on the reflectance variation at each interface describes the signal behavior as a function of modulation frequency. Theoretical calculation based on this model evidences the influence of the optothermal parameters in the signal contrast. © 2000 American Institute of Physics. View full abstract»

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  • Annealing effect on electron field-emission properties of diamond-like nanocomposite films

    Page(s): 5087 - 5092
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    The field-emission properties of a Si–O bond-containing diamond-like nanocomposite (DLN) film were investigated as a function of annealing temperature (Ta). It was found that with increasing Ta the emission threshold voltage decreased gradually. After annealing at Ta=500 °C, the emission current decreased significantly. At Ta=700 °C, however, the field-emission properties of the DLN film improved greatly, the threshold field became very low (∼1.5 Vm), and the emission current rather high (e.g., ∼2.3 μA/mm2 at an electric field of 22 Vm). The structural variation of the film after annealing at different temperatures was monitored by ultraviolet Raman spectroscopy, spectroscopic ellipsometry, atomic-force microscopy, and electrical resistivity measurements. By using a three-step model: (i) electron injection from the substrate, (ii) electron transport through the film, and (iii) electron emission at the film surface, the annealing effect on field-emission properties of the DLN film were qualitatively interpreted. It is believed that the threshold electric field is determined by the local electron affinity on the film surface, while the emission current is mainly limited by electron injection and transport processes. © 2000 American Institute of Physics. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory