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Journal of Applied Physics

Issue 2 • Date Jan 2001

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Displaying Results 1 - 25 of 106
  • Issue Cover

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

    Page(s): toc1
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  • Threshold gain and gain-enhancement due to distributed-feedback in two-dimensional photonic-crystal lasers

    Page(s): 815 - 823
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    The threshold gain (gth) of a two-dimensional (2D) photonic crystal distributed-feedback (DFB) laser composed of 8×8 dielectric cylinders was one order of magnitude smaller than that of an 8-pair 1D DFB laser with the identical refractive indexes. In the 2D finite-width photonic crystal laser, gth using the 1st photonic band was smaller than that using the higher photonic band, contrary to the expectation from the flatness of the photonic band structures. This unexpected gth is probably due to the longer optical path caused by the reflection at the side boundary. Moreover, gth using the 1st photonic band was the smallest in the Γ–X direction of the square-lattice photonic crystal. The gain-enhancement using the 1st–3rd photonic bands were 10–30 in the 2D photonic crystal and that using the 3rd band was the largest. The gain-enhancement using the 1st photonic band of the 2D photonic crystal consisting of dielectric cylinders was larger than that of air cylinders. © 2001 American Institute of Physics. View full abstract»

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  • In- and out-of-plane propagation of electromagnetic waves in low index contrast two dimensional photonic crystals

    Page(s): 824 - 830
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    Propagation of electromagnetic waves through a two-dimensional triangular lattice has been studied for different values of refractive index contrast between the constituent dielectrics, and for angles of incidence both in and out of the plane of periodicity. Transmission results have been obtained both experimentally and with the transfer matrix technique, and good agreement has been found between the two. Comparison with band structure calculations has also been made. © 2001 American Institute of Physics. View full abstract»

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  • Characterization and minimization of flicker in silicon light valves

    Page(s): 831 - 837
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    We have performed systematic characterizations of flicker in silicon light valves. It was found that there were four conduction mechanisms accounting for the flicker. These four mechanisms were residual dc charge on the silicon surface, voltage holding capability of the liquid crystal cell, voltage holding capability of the silicon panel, and parasitic capacitor coupling of the pixel. Major causes of these four mechanisms were identified. Solutions of flicker minimization were obtained for each mechanism. Among these solutions, offset of common voltage was found very useful to compensate for residual dc charge and parasitic capacitor coupling. Frame rate multiplication was found very useful for the minimization of flicker due to low voltage holding capabilities of the liquid crystal cell and silicon panel. © 2001 American Institute of Physics. View full abstract»

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  • Viscoelastic liquid crystal colloids for the continuous processing of twisted nematic electro-optical cells

    Page(s): 838 - 842
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    Liquid crystal colloid materials are described based on the liquid crystal (LC) E7 and submicron sized poly(methyl methacrylate-co-divinylbenzene) particles. Application of a thermal treatment to the composite material produces a finely dispersed network of the internally crosslinked polymeric inclusions in the LC-E7. Dynamic rheological measurements on the LC colloids show that the presence of this network imposes pronounced viscoelastic behavior on the material, which may be exploited in the manufacturing of large-area twisted nematic (TN) electro-optical cells via continuous methods as an alternative to the currently available batchwise routes. The electro-optical characteristics of TN cells based on the composite material are approximately comparable to the electro-optical characteristics of a reference cell filled with pure LC E7, which ensures that the largely increased viscoelasticity of the composite does not lead to a degradation of electro-optical properties. © 2001 American Institute of Physics. View full abstract»

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  • CuH and CuBr absorption measurements and consequences on copper seeding in a Cu–HBr laser medium

    Page(s): 843 - 848
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    Molecular absorption measurements have been made across the tube radius and with respect to time in a Cu–HBr laser media. CuBr and CuH relative densities in their fundamental levels are found from spectra around 428 and 434 nm. CuBr density decreases from the wall to zero absorption on the axis with a steep gradient at 15 mm from the axis. Inversely, CuH is present on the axis and its absorption decreases toward the wall. Dissociation of the CuH molecules in different excited levels can explain the temporal and radial increase of the copper ground-state density in our operating conditions in a Cu–HBr laser. © 2001 American Institute of Physics. View full abstract»

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  • Second order nonlinear optical properties of In-doped lithium niobate

    Page(s): 849 - 854
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    Second order nonlinear optical properties of In-doped lithium niobate crystals have been quantitatively studied from the chemical bond viewpoint. The results show that the second order nonlinear optical response of In-doped lithium niobate crystals at 1079 nm decreases remarkably with increasing In concentration in the crystal. This approximately linear composition-property correlation in In-doped lithium niobate crystals is quantitatively expressed in the current work. Furthermore, the different influences of Mg, Zn, and In dopants, respectively, on the nonlinear susceptibility of lithium niobate single crystals are also compared in the present work. © 2001 American Institute of Physics. View full abstract»

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  • Observation of light propagation in two-dimensional photonic crystal-based bent optical waveguides

    Page(s): 855 - 858
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    An observation of light propagation in a two-dimensional photonic crystal-based (2D–PC) optical waveguide is reported. Bent waveguides with a bending angle of 60° embedded in a 2D–PC triangular lattice with air columns were fabricated on a molecular-beam epitaxially grown AlGaAs/GaAs structure. The light-propagation characteristics were examined by observing scattered light from PC regions with incident light in the 850–950 nm range under an optical microscope using a charge coupled device camera. The incident light was strongly guided for wavelengths corresponding to the photonic band gap. © 2001 American Institute of Physics. View full abstract»

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  • Simultaneous measurement of absorption coefficient, thermal diffusivity, and flow velocity in a gas jet with pulsed photothermal deflection spectroscopy

    Page(s): 859 - 868
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    Simultaneous measurement of the absolute optical absorption coefficient or species concentration, thermal diffusivity, and flow velocity in a gaseous medium has been demonstrated by using pulsed photothermal deflection spectroscopy (PTDS) and a multiparameter fitting procedure. The spatial distribution of the three parameters in a laminar flow has been simultaneously determined and the influence of velocity gradient on the measurement has been discussed. Saturation behavior of the PTDS signals was observed and found to influence significantly the fitted results. The saturation influences most significantly the absorption coefficient determination, somewhat less significantly the thermal diffusivity determination, and only negligibly the flow velocity determination. For an absolute and accurate measurement of the absorption coefficient or species concentration, the saturation-induced error has to be corrected by using a model taking into account the effects of the saturation. The influence of saturation on the thermal diffusivity determination can be significantly accounted for by using a simple model in which the pump beam radius is set as a free parameter in the multiparameter fitting procedure. Both multipulse and single-pulse measurements are performed. For multipulse measurement, the estimated measurement uncertainties are ±2% for the flow velocity, and ±5% for the thermal diffusivity and absorption coefficient, while for single-pulse measurement, the estimated uncertainties are ±2% and ±10%, respectively. © 2001 American Institute of Physics. View full abstract»

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  • Photoresist etching in an inductively coupled, traveling wave driven, large area plasma source

    Page(s): 869 - 877
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    We report on experimental and modeling results for photoresist etching with oxygen gas in an inductively coupled large area plasma source (LAPS). The source is driven by a 13.56 MHz traveling wave launched along a serpentine antenna embedded in the plasma and has a processing area as large as 40 cm×50 cm. We describe a new series-parallel antenna coil configuration, and we present experimental observations for oxygen plasma density profiles, photoresist etch rates, and etch profiles. We introduce a simplified spatially varying oxygen discharge model corresponding to a two-dimensional LAPS geometry in order to account for the generation and loss of both etchant atoms (O atoms) and bombarding ions. The model and experimental results on plasma density are compared. A simplified photoresist etch kinetics model combined with the spatially varying oxygen discharge model is then described. The ion flux and O-atom density predicted by the model are compared with the etch rate data. In order to gain insight into the underlying physical mechanism, we also compare the data with the scaling behavior of the etch rates predicted by a volume-averaged (global) oxygen discharge model. The models and experimental results are generally in good agreement. © 2001 American Institute of Physics. View full abstract»

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  • Inflight electron impact excitation in ionized metal physical vapor deposition

    Page(s): 878 - 882
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    Ionized metal physical vapor deposition (IMPVD) is a process in which sputtered metal atoms from a magnetron target are ionized by a secondary plasma before depositing onto the substrate. The sputtered metal atoms and neutralized ions reflected from the target have higher kinetic energies than the buffer gas and so are not in thermal equilibrium. These nonthermal (inflight) species can dominate the total metal species density at low pressures (≪5 mTorr). As a result, electron impact of the inflight species may significantly contribute to excitation and ionization. To investigate these processes, a model was developed to include the inflight electron impact excitation (IEIE) of sputtered species during IMPVD. Results for Cu IMPVD indicate that the predicted Cu+ density at low pressure (2 mTorr) significantly increased when IEIE was taken into account. As the pressure increases, the rate of thermalization increases and the importance of IEIE decreases. © 2001 American Institute of Physics. View full abstract»

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  • Corona discharge supersonic free-jet for III–V nitride growth via A 3Σu+ metastable nitrogen molecules

    Page(s): 883 - 892
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    A corona discharge supersonic free-jet is shown to be a nearly pure source of A 3Σu+ metastable molecular nitrogen, an electronically excited and chemically active form of N2 that is ideally suited to nitride semiconductor growth. Optical emission spectroscopy at various distances downstream of the supersonic nozzle reveals a cascade through the excited state manifold of N2 triplet states to populate the A 3Σu+ state. Appearance potential spectroscopy (mass spectrometer electron bombardment ionization yield, measured as a function of electron impact energy) delivers the composition of the terminal molecular beam. A 3Σu+ molecules are the dominant activated species in the beam, which otherwise contains only nonreactive X 1Σg+ ground state nitrogen molecules plus a minor amount of 4S0 nitrogen atoms. Up to 1.56% number fraction of the beam is A 3Σu+, providing 1.0×1017 metastables sr-1 s-1. © 2001 American Institute of Physics. View full abstract»

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  • Molecular composition of films and solid particles polymerized in fluorocarbon plasmas

    Page(s): 893 - 899
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    In fluorocarbon (C4F8) plasmas, formation mechanisms of polymers were investigated by the characterization with x-ray photoelectron spectroscopy (XPS) and gel permeation chromatography (GPC). The molecular compositions of the polymers in the films deposited on the substrate and in the particles formed in the gas phase were elucidated by these chemical analyses. The XPS results showed that the particles were carbon-rich and composed of highly branched molecules in contrast to the film composition. From the GPC measurements, the particles were found to contain ultrahigh mass polymers, whose molecular weights were around 100 000. On the contrary, the deposited film contained polymers with molecular weights distributed below 2000, in which oligomers, monomers, and fragmented products were included. Present study suggests that these polymers are involved in the formation of crosslinked networks of the films and the particles via surface reactions, where the crosslinking is enhanced by the ion bombardment. © 2001 American Institute of Physics. View full abstract»

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  • CF, CF2, and SiF densities in inductively driven discharges containing C2F6, C4F8, and CHF3

    Page(s): 900 - 910
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    Laser induced fluorescence was used to measure the spatially resolved CF, CF2, and SiF radical density in inductively driven discharges containing fluorocarbon gases. Measurements of the spatially resolved CF density were performed in C2F6, and CHF3 containing discharges as functions of inductive power, pressure and bias condition on a silicon substrate. In addition, CF rotational temperatures were calculated, assuming saturated spectra. Measurements of the spatially resolved CF2 and SiF density were performed in C4F8, C2F6, and CHF3 containing discharges as functions of inductive power, pressure and bias condition. SiF rotational temperatures were also estimated. As the induction coil power was increased, the SiF density in the center (r=0 cm) increased while the CF2 density decreased and the CF density slightly decreased. In all cases, the radical density in the center of the glow increased with pressure changes from 5 to 30 mTorr while changes in the bias power had little influence on any of the measured radical densities. The spatial distribution of the CF and SiF density peaked in the center of the discharge. The CF2 density had a local maximum in the center of the plasma with a decreasing density at the edge of the glow. However, the CF2 density outside the glow region was a factor of 2- 013;6 higher than the density inside the glow region, depending on the gas. CF and SiF rotational temperatures were between 450 and 750 K. © 2001 American Institute of Physics. View full abstract»

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  • Spatial profiles of neutral, ion, and etch uniformity in a large-area high-density plasma reactor

    Page(s): 911 - 914
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    Spatial profiles of neutral density, ion density, and etch rate have been measured in a large-area high-density plasma reactor. Blanket photoresist films on 200 mm wafers are etched by oxygen plasmas in a magnetized inductively coupled plasma reactor. Ion density and relative neutral density are measured by a scanning Langmuir probe and optical probe, respectively. Spatially resolved atomic oxygen density is then measured by optical emission spectroscopy and spatially resolved actinometry. The etch rate is calculated from film thickness measurements taken before and after the wafer is exposed to the oxygen plasma. Ion energy and wafer surface temperature were also measured. The mechanism linking neutral density, ion density, and etching rate is discussed. © 2001 American Institute of Physics. View full abstract»

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  • Time resolved ultraviolet absorption spectroscopy of pulsed fluorocarbon plasmas

    Page(s): 915 - 922
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    Ultraviolet absorption spectroscopy has been used to quantitatively measure CF2 transients in 1 Torr capacitively coupled pulsed plasmas. Time resolved concentrations were obtained for both tetrafluoroethylene (TFE) and hexafluoropropylene oxide (HFPO) feed gases. In the TFE plasma, the CF2 production kinetics follow a first order rise to concentrations of ∼1014/cm3. In the plasma afterglow, a net production of CF2 is observed for a few milliseconds before the transient becomes dominated by a second order recombination process. In the HFPO plasma, three distinct regimes are observed in the plasma on time. Two production regimes exist, one presumably due to HFPO dissociation and the second due to an unknown source, beginning about 5 ms into the on time. Finally, the CF2 concentration passes through a maximum and decreases to steady state. The afterglow processes are similar to those observed for TFE. The production observed in the off time is believed to be related to surface processes. © 2001 American Institute of Physics. View full abstract»

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  • Effect of sheath evolution on metal ion implantation in a vacuum arc plasma source

    Page(s): 923 - 927
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    Plasma immersion ion implantation is a surface modification technique in which ions to be implanted are drawn directly from surrounding plasma by a pulse biased substrate. Ion acceleration occurs in the electric sheath that forms around the substrate. The technique is most often used to implant ions, such as nitrogen, from plasmas formed by excitation of a gas. More recently it has been applied with cathodic vacuum arc plasmas in order to implant metal ions. These plasmas have a directed ion drift velocity and generally a higher density than gas based plasmas. Both of these differences influence the development of the electric sheath, which determines the implantation profile and the overall stability of the process. If the sheath expands too much during the pulse, the plasma is depleted and implantation ceases. If, however, the sheath is too thin at any point in space breakdown occurs also stopping the implantation process. The major parameters affecting the sheath formation are plasma density, ion drift velocity, and substrate curvature. The influence of each of these factors is discussed and strategies for forming optimum sheath structures are identified. © 2001 American Institute of Physics. View full abstract»

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  • Investigation of two infrared bands at 1032 and 1043 cm-1 in neutron irradiated silicon

    Page(s): 928 - 932
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    We report on infrared (IR) studies of defects in Czochralski-grown silicon (Cz-Si) subjected to fast neutron irradiation and subsequent thermal anneals. We focus mainly on the investigation of the VO4 defect which, in the literature, has been correlated with the pair of bands (1032 and 1043 cm-1) in neutron-irradiated Si and another pair of bands (983 and 1004 cm-1) in oxygen-implanted Si. Semiempirical calculations of the localized vibrational mode frequencies of the VO4 structure support its correlation with the second pair of bands. This correlation is consistent with the ascertainment that the zero point energy of each VOn (n=1,2,3,4) defect is smaller than the zero point energy of the constituent defects VOn-1, Oi, that is: EVOn≪EVOn-1+EOi. © 2001 American Institute of Physics. View full abstract»

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  • Structure and distribution of secondary defects in high energy ion implanted 4H-SiC

    Page(s): 933 - 941
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    The structure, size, and distribution of the secondary defects in high-energy B+ or Al+ implanted 4H-SiC were investigated by cross-sectional transmission electron microscope observations and secondary ion mass spectrometry analyses. Three types of defect structure were detected. The first (type I) is an extrinsic Frank partial dislocation loop parallel to {0001} and is same as that observed in kilo-electron-volt energy B+ or Al+ implanted SiC. The second (type II) is also an extrinsic dislocation loop with an extra Si–C bilayer parallel to {0001} but it has not been previously reported. The last type (type III) has no extra Si–C bilayer. The type of defect is correlated to the size of it. When the size is larger than about 12 nm, the defect becomes type I or type II and the defects which are smaller than about 12 nm are type III. The range of the secondary defect size depends on implanted ions and its dose. The maximum size of defects grows with dopant concentration and that in B+ implanted sample is larger than that in Al+ implanted one at the same volume concentration of dopant. But the minimum size of defects seems independent of dopant concentration and ion species. It is 2–4 nm in any case. These defects are distributed in the deeper region of projected range for low dose implantation. On the contrary, they are distributed from near surface for high dose implanted samples. © 2001 American Institute of Physics. View full abstract»

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  • Modeling laser texturing of silicate glass

    Page(s): 942 - 950
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    A refined model of a glass laser texturing process used on computer disk substrates is presented. Field equations for fictive temperature and elasto-viscoplastic strain in the glass are numerically integrated over the thermal cycle created with a microsecond CO2 laser pulse. Calculating the fictive temperature change as part of the solution provides for a consistent treatment of glass properties that depend on fictive temperature. The short time scale of the thermal cycle causes the final altered state of fictive temperature in the heat affected zone to be relatively constant over the depth of change, and higher than the initial value by more than 300 K. Plastic strain resulting from thermomechanical stresses and the fictive temperature rise are considered in this description. The model illustrates the rise in the compressive stress caused by initial heating, the relaxation process that occurs in the molten region above the transition temperature, and the subsequent introduction of tensile stress during cooling. At the end of the thermal cycle, the region of glass with altered fictive temperature is left in a state of high tensile stress. The time evolution of surface topography is studied with the model, and shows good agreement with measured dimensions of the final bump geometry over a range of laser pulse energies. © 2001 American Institute of Physics. View full abstract»

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  • Combined electron diffraction/microanalysis investigation of crystallography and cation distributions in the transparent conductive oxide Cd1+xIn2-2xSnxO4

    Page(s): 951 - 954
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    The distribution of Cd, In, and Sn cations on the spinel lattice was investigated across the solid solution, Cd1+xIn2-2xSnxO4. Convergent beam electron diffraction was used to establish the presence of the spinel crystallography throughout the solid solution. Atom location by channeling enhanced microanalysis was employed to determine the distributions of cations on the octahedral and tetrahedral lattice sites. CdIn2O4 was observed to be a normal-type spinel. As x was increased, the cation distribution became more random as Cd and Sn filled the octahedral sublattice. These observations may correlate with previously observed changes in optical gap and conductivity across the solution. © 2000 American Institute of Physics. View full abstract»

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  • Intrinsic point defects in oxidized 3C epitaxial layers on Si substrates

    Page(s): 955 - 959
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    We have used electron paramagnetic resonance to study two intrinsic defects in oxidized epitaxial layers of 3C SiC, a potential substitute for Si in high speed, high power electronics. One center can be described by an isotropic g value of 2.0044. The defect is distinguished by a strong temperature dependence and is located throughout the 3C epitaxial layer. Although the detailed structure has not been determined, the g value is consistent with theoretical predictions for a Si dangling bond surrounded by carbon atoms. The second Si-related center, induced by post oxidation dry heat treatment, is characterized by an axial g tensor with g||=2.0023 and g=2.0082. The spectroscopic and chemical properties of the latter defect are consistent with those of the Si Pb center, a Si dangling bond located at a Si/insulator interface. Experiments show that in our 3C samples, the Pb signal is probably located on the Si side of a SiO2/Si interface between the SiC epilayer and the Si substrate. © 2001 American Institute of Physics. View full abstract»

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  • Mechanism of liquid crystal alignment on submicron patterned surfaces

    Page(s): 960 - 964
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    The alignment mechanism of liquid crystals on polymeric surfaces that were patterned using an atomic force microscope (AFM) tip was studied by polarizing optical microscopy. Depending on the thickness of the polymer, polymer chain alignment or grooves appear to be responsible for the liquid crystal alignment. In thick polymer films (above 100 nm) the polymer chains will align in the direction of the scan due to the large lateral force exerted by the tip. In thin polymer films (5–20 nm) the polymer chains are strongly fixed to the surface and will not realign by the tip; instead grooves will be formed. The azimuthal surface anchoring the energy of thick polymer films does not depend on the scan line separation and scan force, is of the same order of magnitude as for conventionally rubbed polyimide surfaces, but increases by the number of scans. AFM patterned pixels do not show a pretilt angle. © 2001 American Institute of Physics. View full abstract»

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  • Raman investigation of ion beam synthesized β-FeSi2

    Page(s): 965 - 972
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    The Raman spectra of ion beam synthesized (IBS) β-FeSi2 are investigated and evidence for the presence of a net tensile stress is presented. Possible origins of the observed stress are suggested and a simple model is proposed in order to calculate a value of the observed stress. A correlation between the tensile stress, the nature of the band gap, and the resulting light emitting properties of IBS β-FeSi2 is suggested. © 2001 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