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Journal of Applied Physics

Issue 5 • Date Mar 1991

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Displaying Results 1 - 25 of 110
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Analysis of signals from superposed relaxation processes

    Page(s): 2759 - 2767
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    System functions of many linear physical systems or autocorrelation functions of their output signals are often a sum of relaxator terms with different relaxation times and amplitudes. In the time domain a superposition of exponential decays e-γt is observed, while in the frequency domain a sum of relaxator terms of structure 1/(γ+iω) is measured. Thus, the response is either the Laplace transform of the system function or its Stieltjes transform, respectively. In both cases it is the task of an analyst to gain the relaxation times and weights from the measured signal. An exact reconstruction of the system function is limited by the noise, measuring time, and number of points measured. In this paper procedures for the approximate reconstruction of the system function are introduced. The equivalence of most of them is shown and their properties are discussed. An expression for the limit of resolution is derived for a given signal‐to‐noise ratio. The results are applicable to experimental data from various physical systems. For illustration the autocorrelation function of the light scattered from polymer solutions and the response of photoconductors are used. View full abstract»

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  • Analytic potential in a linear radio‐frequency quadrupole trap with cylindrical electrodes

    Page(s): 2768 - 2775
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    We have analyzed a linear radio‐frequency ion trap of finite length employing a four‐sectored hollow cylinder enclosed between two end caps. Solutions to Laplace’s equation determine the effective potential inside the trap due to the rf trapping field, the static confining potential from dc‐biased end caps, and the potential arising when a dc bias is present on the cylinder sectors. The finite length of a linear trap results in field distortion at the trap ends due to fringing effects. We have demonstrated that near the ends, the effective potential arising from the rf fields acts to propel ions out of the trap. We have further shown that the addition of a dc bias on two neighboring cylinder sectors generates an inhomogeneous field in the trap which produces a force on the ions along the trap’s long axis in a direction dependent on the sign of the bias. An exact analytic determination of the potential can be used to determine the profile of the trapped ion cloud. View full abstract»

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  • Influence of Te concentration on the infrared cathodoluminescence of GaAs:Te wafers

    Page(s): 2776 - 2779
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    Cathodoluminescence (CL) scanning electron microscopy has been used to investigate the nature and distribution of defects involved in the infrared emission of GaAs:Te wafers. Spectral and CL‐contrast changes as a function of doping level have been found. Profiles of infrared CL intensity across the wafers show an inverted U shape. View full abstract»

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  • Frequency pulling by hyperfine σ transitions in cesium beam atomic frequency standards

    Page(s): 2780 - 2792
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    It is demonstrated that frequency pulling by Δm=±1 hyperfine σ transitions, here called Ramsey pulling, is a real calculable effect in atomic beam frequency standards. An analytic expression for the effects of Ramsey pulling is derived using perturbative techniques for the driving σ transitions, while treating the primary π transitions exactly. It is shown that these Ramsey pulling effects are intrinsically different from Rabi pulling in origin, manifestation, and elimination. These predictions are compared to measurements performed on a cesium beam atomic frequency standard, giving good quantitative verification of the theory and a clear demonstration of the existence of these effects. View full abstract»

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  • Calibration of the nitrogen vibron pressure scale for use at high temperatures and pressures

    Page(s): 2793 - 2799
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    Coherent anti‐Stokes Raman scattering (CARS) and spontaneous Raman spectroscopy have been used to obtain vibrational spectra of shock‐compressed and static high‐pressure fluid nitrogen, respectively. Vibrational frequencies were obtained from the CARS data using a semiclassical model for these spectra. Spontaneous Raman vibrational frequencies were determined by fitting data using a Lorentz‐shape line. A functional form was found for the dependence of the vibrational frequency on pressure and temperature to 40 GPa and 5000 K, respectively. By fitting the vibrational data to this form, a pressure scale based on the fluid nitrogen vibron has been calibrated for use at very high temperature. The nitrogen vibron pressure scale was used to determine the fluid‐δ nitrogen phase boundary up to 20 GPa and 900 K. View full abstract»

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  • Induced multipole strengths for two dielectric spheres in an external electric field

    Page(s): 2800 - 2804
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    Two nonidentical spheres are immersed in a uniform external electric field. Induced multipoles through hexadecapole are found along the mutually perpendicular axes of the system. These multipoles are expressed directly in terms of the coefficients that appear in the infinite series representation of the potential. View full abstract»

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  • Chemical generation of optical gain at 471 nm

    Page(s): 2805 - 2809
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    Stimulated emission on the P(43) and R(70) transitions of the BiF (A‐X, v’=1 to v‘=4) band was demonstrated, using the reaction of premixed FN3 and Bi(CH3)3. The transient chemistry was thermally initiated by a pulsed CO2 laser, using SF6 as a sensitizer, while amplification was detected using an étalon‐tuned pulsed dye laser probe and a sensitive cavity ringdown technique. The magnitude of the peak gain, estimated at 3.6×10-4/cm, was consistent with a negligible concentration of the terminal BiF(X, v‘=4) state, based on the calculated optical cross section and the peak concentration of the BiF (A, v’=1) state, as measured by absolute photometry. View full abstract»

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  • A novel three‐guide optical coupler using a taper‐formed waveguide

    Page(s): 2810 - 2814
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    A novel taper‐formed three‐guide coupler is presented. Its unique power coupling characteristics are experimentally demonstrated. By virtue of adopting the taper‐formed waveguide, the severe restrictions imposed on the device fabrication process are greatly relaxed. This makes the coupler advantageous to application in a variety of integrated optics, such as power splitters and combiners, and as constituent elements of devices like optical isolators. View full abstract»

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  • Scaling of the electron‐beam‐pumped xenon chloride laser

    Page(s): 2815 - 2825
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    A comprehensive kinetics and extraction model of electron‐beam‐excited xenon chloride lasers is used to examine the feasibility of constructing a megajoule‐class excimer laser. The ratio of small‐signal gain to absorption scales nearly logarithmically with pump rate over the range studied, 10 kW/cm3 to 1 MW/cm3, and limits extraction efficiency to 20%–50%. Active volume dimensions are practically constrained to 1–2 m in length and to ∼2 m in width, with efficient extraction possible for pulse lengths of 2 μs or less. Single modules operating in the technologically conservative, low‐pump‐power (≤100 kW/cm3 ) regime should be capable of producing pulse energies of 40 kJ. View full abstract»

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  • Universal dispersion and power curves for transverse magnetic waves propagating in slab waveguides with a nonlinear self‐focusing substrate

    Page(s): 2826 - 2834
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    For TM‐polarized waves, a mode‐power measure is applied to characterize optical waveguides with a nonlinear self‐focusing substrate, producing a concise overview of the waveguiding properties at a given power for various designs. We also show how birefringence varies between the TE and TM modes as a function of the total power carried by the waveguide. Since our description is based on universal parameters, our results are applicable to different geometries of waveguide through simple scaling rules. View full abstract»

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  • Photovoltaic spatial light modulator

    Page(s): 2835 - 2840
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    A novel concept for implementing a high‐resolution spatial light modulator using a thin slab of photorefractive LiNbO3 crystal is described. This method uses the photovoltaic effect to impress phase information onto the crystal without the use of holography where coherent reference beams are required. Experimental demonstration as well as an analysis of the operation and performance of the device are given. View full abstract»

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  • Thermal effects on cavity stability of chromium‐ and neodymium‐doped gadolinium scandium gallium garnet laser under solar‐simulator pumping

    Page(s): 2841 - 2848
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    A chromium‐ and neodymium‐codoped gadolinium scandium gallium garnet (Cr:Nd:GSGG) crystal was tested for pulsed‐ and continuous‐wave (cw) laser operations with a flashlamp and solar simulator as pumping sources. The crystal has been considered as a good candidate for a solar‐pumped laser because of its broad absorption bands over the solar spectrum. However, it was observed experimentally and theoretically that its cw laser operation is difficult at high pump powers because too many thermal lensing effects are induced. Only at low solar‐simulator beam intensities of up to 1500 solar constants (203 W/cm2 ) was cw laser operation lasting longer than 10 min achieved. For higher pump beam intensities of up to 2500 solar constants (338 W/cm2 ), a quasi‐cw‐laser operation was obtained with continuously chopped pumping with a duty cycle of 0.5 and a repetition rate of 13 Hz. The experimental result was compared with the calculated stability condition of the laser resonator for various pump powers and showed that the thermal focusing of the Cr:Nd:GSGG is 15–8 times greater than that of the neodymium‐doped yttrium aluminum garnet (Nd:YAG) laser for the pump beam intensities from 1000 to 3000 solar constants. View full abstract»

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  • Rapid‐phase transitions of GeTe‐Sb2Te3 pseudobinary amorphous thin films for an optical disk memory

    Page(s): 2849 - 2856
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    Amorphous films having a component of the stoichiometric GeTe‐Sb2Te3 pseudobinary alloy system, GeSb2Te4 or Ge2Sb2Te5 representatively, were found to have featuring characteristics for optical memory material presenting a large optical change and enabling high‐speed one‐beam data rewriting. The material films being sandwiched by heat‐conductive ZnS layers can be crystallized (low power) or reamorphized (high power) by laser irradiation of very short duration, less than 50 ns. The cooling speed of the sandwiched film is extremely high: more than 1010 deg/s, which permits the molten material to convert to the amorphous state spontaneously; whereas, a low‐power pulse irradiation of the same duration changed the exposed portion into the crystalline state. The optical constant changes between the amorphous state and the crystalline state of them were measured to be large: from 4.7+i1.3 to 6.9+i2.6 and from 5.0+i1.3 to 6.5+i3.5, respectively. The crystallized portion was known to have a GeTe‐like fcc structure by an analytical experiment using transmission electron microscopy, differential scanning calorimetry, and x‐ray and electron diffraction methods. The high crystallization speed is ascribed to (1) the pseudobinary system which can form crystalline compositions without any phase separation, (2) the high symmetry of the fcc structure which is the nearest to the random amorphous structure, (3) the high‐energy difference between the amorphous state and the fcc crystal state. View full abstract»

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  • Analysis and optimization of graded‐index separate‐confinement heterostructure waveguides for quantum well lasers

    Page(s): 2857 - 2861
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    Waveguide structures for quantum well (QW) lasers are analyzed numerically by a straightforward 2×2 matrix approach. It is shown that this approach is capable of analyzing separate‐confinement heterostructure (SCH) waveguides, having any arbitrarily graded‐index (GRIN) profile in the waveguide layers and any number of QWs in the active layer, to any desired level of accuracy. Using this waveguide analysis, general GRIN‐SCH waveguide structures of QW lasers can be optimized for maximum confinement factors. It is estimated that the laser threshold current density can be reduced typically by 10% as a result of this waveguide optimization. View full abstract»

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  • On the normal acceleration sensitivity of contoured quartz resonators with the mode shape displaced with respect to rectangular supports

    Page(s): 2862 - 2870
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    It is shown that the normal acceleration sensitivity of contoured quartz resonators with rectangular supports vanishes when the centers of the mode shape and support rectangle coincide. This result is a consequence of symmetry and applies to many other shapes. Since it is essentially impossible to realize this situation in practice, an analysis of the influence of an offset of the centers on the normal acceleration sensitivity is performed. The biasing deformation is determined by means of a variational approximation procedure using the variational principle with all natural conditions for anisotropic static flexure. The very important accompanying strains varying quadratically across the thickness are determined recursively, as in earlier work. The resulting flexural biasing states are employed in an existing perturbation equation along with the equivalent trapped‐energy‐mode shapes of the contoured resonators to calculate the normal acceleration sensitivities. It is shown that for small offsets the acceleration sensitivity increases linearly with offset, and orientations for which this effect is minimized are found. View full abstract»

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  • Temperature distribution during heating using a high repetition rate pulsed laser

    Page(s): 2871 - 2876
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    A general equation has been derived for computing the temperature distribution produced in a substrate heated by a high repetition rate pulsed laser. The theoretical predictions have been compared with experimental results obtained for etching of Mn‐Zn ferrite in KOH solution using a copper vapor laser. The effects of the laser power and substrate scan speed on the temperature distribution have been investigated, and the predicted melt‐zone boundaries have been compared with the experimentally observed width, depth, and shape of the etched grooves. View full abstract»

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  • Measurement of electrical avalanches and optical radiation near solid insulators in high pressure (up to 0.3 MPa) nitrogen gas

    Page(s): 2877 - 2884
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    Electron and ion avalanches have been recorded near a variety of insulators (plexiglas, teflon, high‐density polyethylene, low‐density polyethylene, polypropylene, delrin, polyvinyl chloride, and nylon) in nitrogen gas at pressures of 0.1, 0.2, and 0.3 MPa. With the exception of nylon, suppression of avalanches has been observed in the presence of insulators. In addition to electron and ion avalanches, simultaneous measurement of optical radiation associated with an electron avalanche was successfully carried out. Qualitative explanations have been provided for the suppression of avalanches near most insulators and an anomalous growth of avalanches near nylon insulators. Photoemission from nylon surfaces appears to be responsible for the enhanced growth of avalanches near nylon insulators. More precise measurements of optical radiation are needed to better understand the electron‐photon interactions near a solid insulator in a gaseous dielectric medium. View full abstract»

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  • Chamber material effects on actinometric measurements in rf glow discharges

    Page(s): 2885 - 2888
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    The relative concentration of atomic fluroine was measured in a CF4 rf glow discharge using the actinometric technique. The dependence of fluorine concentration on power, pressure and flow are presented and shown to be dependent upon reactor wall material and electrode material. View full abstract»

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  • Electric field induced emission as a diagnostic tool for measurement of local electric field strengths

    Page(s): 2889 - 2895
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    The phenomenon of electric field induced (EFI) emission is examined in several diatomic and polyatomic molecules. The possibility of using this phenomenon as a diagnostic tool to measure, nonintrusively, the strength and direction of local electric fields in plasmas is discussed. An estimate of the EFI signal emitted in a typical application plasma is given. This yields a lower bound on the detector sensitivity necessary to exploit EFI emission in practical applications. It is concluded that, at present, the EFI signal could be measured by some very sensitive infrared detection schemes available. Current progress in infrared detector technology, if maintained, could result in the possibility of utilizing EFI emission on a more routine basis. This would allow measurement of electric fields in plasmas of species that are not suitable candidates for any of the other currently available schemes which measure such fields. View full abstract»

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  • A boundary‐layer model for a plane free‐burning high‐pressure gas‐discharge arc

    Page(s): 2896 - 2903
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    A boundary‐layer model for a plane free‐burning high‐pressure gas‐discharge arc is given. For the dependence on the temperature, a rule given by Elenbaas [The High Pressure Mercury Vapour Discharge (North‐Holland, Amsterdam, 1951)]is used for the electrical conductivity and power‐law rules for the dynamic viscosity and the thermal conductivity. The specific heat is assumed to be constant. It is shown that a similarity transformation can be applied. The upward velocity increases with the square root of the core temperature. Graphs are given which show how the temperature rise in the arc depends upon the applied current. View full abstract»

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  • Measurements of spatial and temporal sheath evolution for spherical and cylindrical geometries in plasma source ion implantation

    Page(s): 2904 - 2908
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    A comparison of experimental measurements and numerical calculations of temporal and spatial sheath evolution is presented. Spherical targets of copper and stainless steel (radius=2 cm) and a cylindrical target (radius=0.95 cm, height=18 cm) were immersed in an argon plasma with plasma densities of 2×108–8×109 cm-3 and biased negatively (20–50 kV). A Langmuir probe was used to detect the propagating sheath edge. Experimental measurements of sheath edge position were in good agreement with those determined by numerical calculations. View full abstract»

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  • Ion and electron dynamics in the sheath of radio‐frequency glow discharges

    Page(s): 2909 - 2922
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    The distribution of ion energies and the temporal modulation of ion and electron currents were measured at the cathode of an asymmetric, capacitively coupled rf discharge system operated at 13.56 MHz. The ion energy distributions (IEDs) were found to exhibit pronounced features, namely a characteristic series of peaks and double peaks, their position and intensity depending strongly on process parameters such as self‐bias voltage and pressure. Those structured IEDs have been observed for a variety of gases including argon, oxygen, hydrogen, and benzene. The IED features are explained by the rf modulation of the sheath potential in combination with the creation of thermal ions by charge‐exchange processes in the sheath. A model for the ion transport through collisional rf sheaths is presented which satisfactorily explains the observed IEDs. It will be shown that the observed features are an inherent property of capacitively coupled rf discharges. By analyzing these structures detailed information about the spatial field distribution in the sheath and the transport of ions through rf plasma sheaths is obtained. The time‐resolved measurements revealed that the ion current behind the cathode is strongly modulated. This temporal modulation has been described by the same theory confirming the applicability of the present model. Finally the electron current was found to be confined to short periodic pulses of 2–3 ns width. View full abstract»

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  • Angular ion and neutral energy distribution in a collisional rf sheath

    Page(s): 2923 - 2930
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    A numerical study on the ion and neutral angular impact energy distribution at the rf‐driven electrode of a reactive ion etcher is presented. The calculations for the ions are performed using a Monte Carlo method that includes charge exchange and elastic scattering. The contribution of both collision processes to the angular ion impact energy distribution is studied. For the case that charge exchange is the only collision process, the Monte Carlo results can be checked against those of a method based on a spatially uniform and time independent collision rate. In that case, both methods yield the same ion impact energy distribution. The position, velocity, and propagation angle of the energetic neutrals created in collisions of ions with the background gas are stored. These are used as input data for a separate code that follows the evolution of the angular neutral energy distribution, taking into account (multiple) neutral elastic scattering. From the ion and neutral distributions, the number of neutrals per ion, the average impact energy, and the energy‐weighted average impact angle have been derived. It is shown that these parameters are well described by simple expressions. Finally, the sputter yield is calculated. The results show that the contribution of the angular distributions of both ions and neutrals to the yield can be neglected. View full abstract»

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  • The effect of implant energy, dose, and dynamic annealing on end‐of‐range damage in Ge+‐implanted silicon

    Page(s): 2931 - 2937
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    A study of the effect of Ge+ implantation energy, dose, and temperature on the concentration of atoms bound by the extrinsic end‐of‐range dislocation loops in Si 〈100〉 wafers is presented. Plan‐view and cross‐sectional transmission electron microscopy observations of both the as‐implanted and annealed (900 °C, 30 min) morphology were made. The implant energy was varied from 30 to 150 keV, the dose varied from 2×1014 to 1×1016/cm2, and the temperature was varied by using three different wafer‐cooling methods during the implantation. Increasing the implant energy, dose, or wafer temperature all resulted in significant increases (as much as two orders of magnitude) in the concentration of atoms bound by the end‐of‐range loops. Recent models have suggested that the concentration of end‐of‐range defects is related to the integrated recoil concentration beyond the amorphous/crystalline (a/c) interface. Correlation of trim‐88 calculations with measured a/c depths show that the integrated recoil concentration beyond the a/c interface can explain both qualitatively and quantitatively the dependence of the ‘‘trapped interstitials’’ on the implant energy. However, this model can only qualitatively explain the temperature dependence of the defects, and it fails to account for the strong dose dependence when wafer heating is suppressed. 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