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Journal of Applied Physics

Issue 5 • Date Mar 1998

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Displaying Results 1 - 25 of 77
  • Issue Cover

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

    Page(s): toc1
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    Freely Available from IEEE
  • Transparent, metallo-dielectric, one-dimensional, photonic band-gap structures

    Page(s): 2377 - 2383
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    We investigate numerically the properties of metallo-dielectric, one-dimensional, photonic band-gap structures. Our theory predicts that interference effects give rise to a new transparent metallic structure that permits the transmission of light over a tunable range of frequencies, for example, the ultraviolet, the visible, or the infrared wavelength range. The structure can be designed to block ultraviolet light, transmit in the visible range, and reflect all other electromagnetic waves of lower frequencies, from infrared to microwaves and beyond. The transparent metallic structure is composed of a stack of alternating layers of a metal and a dielectric material, such that the complex index of refraction alternates between a high and a low value. The structure remains transparent even if the total amount of metal is increased to hundreds of skin depths in net thickness. © 1998 American Institute of Physics. View full abstract»

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  • Role of internal loss in limiting type-II mid-IR laser performance

    Page(s): 2384 - 2391
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    We report an experimental and theoretical investigation of internal losses in optically pumped type-II lasers with InAs/GaSb/Ga1-xInxSb/GaSb superlattice active regions. Whereas the losses are found to be moderate at 100 K (11–14 cm-1), they increase rapidly with increasing temperature (to 50–120 cm-1 at 200 K). Comparison with a detailed numerical simulation shows that the internal losses play a much more important role than Auger recombination or carrier/lattice heating in limiting the laser performance at high temperatures. Calculations of the temperature-dependent intervalence absorption cross sections show that losses of the magnitude observed experimentally can easily occur if one does not take special care to avoid resonances in all regions of the Brillouin zone. Practical design guidelines are presented. The superlattice lasers yield maximum peak output powers of up to 6.5 W per facet at 100 K and 3.5 W per facet at 180 K, threshold incident pump intensities as low as 340 W/cm2 at 100 K, and Shockley–Read lifetimes ≫30 ns at 100 K. The Auger coefficients are suppressed (≤1.6×10-27cm6/s at T=260 K) despite the intervalence resonances which produce the high internal losses. © 1998 American Institute of Physics. View full abstract»

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  • Large second-order optical nonlinearity in a molecular crystal formed from a chiral smectic liquid crystal

    Page(s): 2392 - 2398
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    A new approach to achieving a large second-order nonlinear optical susceptibility in a chiral liquid crystal is described. This approach uses an aligned smectic-C* liquid crystal as a template for forming a molecular crystal, which freezes out the rotation of the molecular dipoles and thereby greatly enhances the noncentrosymmetric order of the structure. Analysis of the measured second harmonic generation gives maximum values of individual susceptibility components of ∼25 pm/V, which are stable when the field is removed. © 1998 American Institute of Physics. View full abstract»

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  • Field solutions for bidirectional high-gain laser amplifiers and oscillators

    Page(s): 2399 - 2407
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    General analytical solutions are obtained for the amplitude, phase, and intensity of the electromagnetic waves in bidirectional homogeneously broadened high-gain laser amplifiers and oscillators. These solutions are important as increasingly high-gain lasers are being employed in practical systems. Expressions are derived relating the output power to the input, including the effects of arbitrary mirror reflectivities and frequency detunings from the line center. For negligible reflectivities, these regenerative amplifier results reduce to earlier expressions for single-pass high-gain amplifiers. Multivalued outputs also occur, and in the limit of low gain per pass the results are consistent with earlier studies of single-frequency laser oscillators. © 1998 American Institute of Physics.   View full abstract»

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  • Ultrasonic beam reflection from fluid-loaded cylindrical shells

    Page(s): 2408 - 2419
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    The interaction of ultrasonic acoustic transducers with cylindrical shells in pitch-catch mode has been measured and predicted using a two-dimensional theoretical model. The measurements of the received voltage amplitude at selected frequencies and incidence angles are presented as a function of scanned angular position at fixed radius and beam launch angle. In the forward model, the received voltage is expressed in terms of a spectral integral whose integrand contains the spectral amplitudes of the transmitter and the receiver, and a spectral global reflection coefficient that accounts for the pressure wave interaction with the fluid- or air-loaded shell. The transmitter and receiver are modeled using the complex-transducer-point technique to simulate emitting and receiving electro-acoustic transducers with Gaussian profiles. The receiver voltage integral is reduced by uniform high-frequency saddle point asymptotics to closed form solutions for the dominant contributions from the specular reflected and (excited) leaky wave fields. We find generally good agreement between the model prediction and the experimental results, particularly near the voltage maximum. Experimental data are also shown for a solid cylinder, demonstrating in a time-angle plot the existence of whispering gallery modes, which is verified analytically. © 1998 American Institute of Physics. View full abstract»

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  • Small-scale laboratory measurement and simulation of a thermal precursor shock

    Page(s): 2420 - 2427
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    A shock precursor in a thin thermal layer above a 3000 K hot surface is measured in a small-scale laboratory experiment. Precursor and thermal layer characteristics are diagnosed using spectroscopy, interferometry, and dark-field shadowgraphy. The experiment is successfully simulated with a code previously validated using large-scale high-explosive tests, thereby demonstrating its applicability to events that differ in energy by 12 orders of magnitude. The simulation shows that a small-scale laboratory experiment can be a good surrogate for infrequent, expensive, and hard to diagnose large-scale tests. © 1998 American Institute of Physics. View full abstract»

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  • On the current emitted by Taylor cone-jets of electrolytes in vacuo: Implications for liquid metal ion sources

    Page(s): 2428 - 2434
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    Approximate scaling laws for the charge and size of the drops ejected from the apex of Taylor cones run in the cone-jet mode (electrospray) are now available for highly conducting electrolytes (10-4S/m≪K≪1 S/m) electrosprayed at atmospheric pressure. In order to confirm that such laws do also apply to Taylor cones in vacuo, the current versus liquid flow rate curves I(Q) characteristic of a given liquid are investigated both in vacuum and in atmospheric pressure air. Although the sprays of drops differ profoundly in both cases, the two corresponding I(Q) curves are nearly identical for relatively involatile liquids such as tributyl phosphate. A discussion on the possible relation between the behavior of Taylor cones of electrolytes of organic liquids and liquid metal ion sources (K∼106S/m) is attempted, yielding insights on the role of space charge. However, the electrical conductivity variable which dominates the behavior of liquid cones of electrolytes appears to be irrelevant in liquid metals. © 1998 American Institute of Physics. View full abstract»

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  • A gliding discharge applied to H2S destruction

    Page(s): 2435 - 2441
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    The destruction of foul smelling gases is an important subject involving a number of industrial applications. Increased interest is being devoted to technologies based on the properties of cold plasmas, which are the subject of a large body of research. Among all possible techniques, the sliding discharge is one of the simplest to utilize. We present a study of the destruction of H2S diluted in air by this type of discharge. We first describe the electric power supply, its characteristics and the design of the reactor. The properties of the discharge and its changes are then described using measurements of voltage, current, and different characteristic parameters: temperatures, velocities, and length of the discharge. After describing the instrumentation used for chemical diagnoses, the main experimental results are presented. They show the changes in the conversion rate as a function of the flow rate of the gas to treat and the dimensions of the reaction chamber, enabling a model of discharge changes to be defined. The model defines a zone of transformation corresponding to a volume swept by the plasma. It was thus possible to determine how destruction efficiency is affected by construction parameters, reactor dimensions, voltage, and flow rates. The energy cost per molecule destroyed is relatively high because the pollutant is diluted. With several improvements, the possibility of processing high flow rates with a simplified implementation could enable immediate industrial application to be envisaged. © 1998 American Institute of Physics. View full abstract»

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  • Carbon encapsulated nanoparticles of Ni, Co, Cu, and Ti

    Page(s): 2442 - 2448
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    Despite intensive research on the encapsulation of metal nanoparticles into carbon clusters deposited by arc discharge, the detailed pathways of the formation of these novel forms of materials remain unclear. The growth of a rich variety of morphologies is not well understood. Studies are reported here on the growth phenomena of different metals encapsulated into carbon cages that emphasize the effect of carbon and metal supply on the size of particles. Post-deposition annealing was introduced as a process that induces structural rearrangements, and thus enables changes in morphologies. A set of carbon encapsulated Ni, Co, Cu, and Ti particles were prepared by an arc discharge process modified in the geometry of the anode and flow pattern of helium or methane gas. The samples were then annealed under flowing argon gas. Three annealing temperatures were used (600, 900, and 1100 °C). Samples were characterized by transmission and scanning electron microscopy. Particles made under the same experimental conditions are of roughly the same size. When the supply of metal in the reactor space was increased by using a larger diameter of the metal pool, the average diameter of the particles is bigger than those of produced from the smaller metal pool. The thickness of the carbon cages of Ni and Co particles increased during the annealing. The carbon cages of Cu particles, however, did not change their thickness, while some carbon coatings of Ti particles disappeared under annealing. This suggests that the addition of layers for the Ni and Co cages results from a precipitation of carbon previously dissolved in the metal, while the much lower solubility of C in Cu prevents this possibility. The Ti of high reactivity, on the other hand, may further react with the available carbon under annealing to form TiC. It is suggested that annealing provides additional thermal energy that makes structural re-arrangement possible long after the initial deposition process was t- erminated. This may explain the rich variety of morphologies of deposit obtained at different locations of the reaction chamber. © 1998 American Institute of Physics. View full abstract»

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  • Electron spin resonance features of interface defects in thermal (100)Si/SiO2

    Page(s): 2449 - 2457
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    Electron spin resonance (ESR) on thermal (100)Si/SiO2 predominantly exhibiting either the Pb0 or Pb1 interface defect confirms the Pb1 point symmetry as monoclinic-I with g1=2.0058, g2=2.00 735±0.00 010, and g3=2.0022, where the g2 direction is at 3°±1° (towards the interface) with a <111> direction at 35.3° with the interface plane. Its line width is found weakly dependent on magnet angle, exhibiting a strain induced spread σg∼0.00 035 in g about 2–3 times less than typical for Pb in (111)Si/SiO2. For Pb0, an axially symmetric g matrix is observed, with g||=2.0018 and g=2.0081, and σg∼0.0009. From comparison of salient ESR data, it is concluded that Pb and Pb0 are chemically identical; however, systematic fabrication-induced variations in defect environment will lead to second order systematic shifts in average properties. The Pb1 defect is provisionally pictured as an unpaired Si bond on a defect Si atom at slightly subinterface plane position in the Si substrate, possibly facing an oxygen atom. © 1998 American Institute of Physics. View full abstract»

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  • Structural characterization of BaTiO3 thin films grown by molecular beam epitaxy

    Page(s): 2458 - 2461
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    Epitaxial ultrathin films of BaTiO3 were prepared using molecular beam epitaxy. For the substrate, (001)-oriented SrTiO3 single crystals were used. Controlling the growth conditions of these films as well as the semiconductor thin films, led to the successful growth of the BaTiO3 films as single crystals, characterized by x-ray diffraction even in the ultrathin range. The ultrathin BaTiO3 films are highly c-axis-oriented tetragonal phaselike bulk BaTiO3 crystals. The tetragonality of the thin film crystals is much larger than bulk crystal’s. We also measured the saturated polarization (Ps) of the BaTiO3 films at temperatures ranging from room temperature to 600 °C. The results confirmed again that the films are ferroelectric tetragonal phase crystals. Moreover, they showed that the transition temperature for the ferroelectric-paraelectric phase transition of the films is higher than bulk crystal’s. © 1998 American Institute of Physics. View full abstract»

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  • Ultrasonic damping in pure aluminum at elevated temperatures

    Page(s): 2462 - 2468
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    Ultrasonic resonant damping was measured in polycrystalline 99.999% pure aluminum spheres between 22 and 465 °C at frequencies between 0.4 and 2.0 MHz. In fully annealed samples, the damping increases monotonically with temperature in a manner similar to that reported in numerous lower-frequency studies of a variety of materials. However, the activation energy of this increase is significantly less than values reported for aluminum at lower frequencies, and the frequency dependence is much different; these facts suggest that a different physical mechanism dominates the damping in the higher frequency range. The dependences on temperature, frequency, and vibrational amplitude are consistent with an anelastic dislocation mechanism. During recovery and recrystallization of cold-worked material, the damping drops irreversibly with a time dependence matching that expected for the dislocation density. View full abstract»

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  • Theoretical investigation of the apparent spectral radiance from the metal/window interface in shock temperature experiments

    Page(s): 2469 - 2472
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    When a shock wave passes through an ideal metal/window interface, the interface temperature is time independent; accordingly, the apparent spectral radiance at the interface is also regarded as time independent. However, each material has a definite transparency, so that the apparent spectral radiance at the interface must be the total radiance of a thin layer rather than the surface. In this article, the relationship among the optical absorption coefficient of a metal and its pressure and temperature is studied based on classical electromagnetics. It is obtained that the absorption coefficient decreases and the optical depth increases as shock pressure increases. By using the radiative transport equation, the apparent spectral radiance at the ideal iron/sapphire interface following shock compression is calculated, which shows that the apparent spectral radiance is time dependent, although the interface temperature is time independent. As an example, the apparent spectral radiance history at the iron/sapphire interface under shock pressure of about 230 GPa is presented. © 1998 American Institute of Physics. View full abstract»

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  • Terahertz radiation from coherent phonons excited in semiconductors

    Page(s): 2473 - 2477
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    Terahertz radiation emitted by coherent phonons in Te, PbTe, and CdTe has been investigated by using an ultrafast photoconductive sampling detector. Pronounced coherent radiation originating from the longitudinal optical (LO) phonon oscillations of infrared-active modes was observed for all samples, irrespective of the different crystal structures. In addition, spectral dips at the transverse optical (TO) phonon frequencies, which could not be explained by absorption in the emitting volume, were observed for all samples. The model calculations indicate that the emission rate of the radiation into the air to that into the dielectric (semiconductor) side is scaled by 1/{1+(nd2d2)nd3} (nd and κd are the real and imaginary part of the complex refractive index, respectively). Thus, the enhanced emission of radiation by the coherent LO phonons and the spectral dips at the TO phonon frequencies can be explained by the respective increase and reduction of the emission efficiency of the radiation to the air due to the small and large value of the dielectric constant d(ω)|=nd2d2 near the LO and TO phonon frequencies, respectively. © 1998 American Institute of Physics. View full abstract»

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  • Ab initio molecular dynamics simulation of laser melting of graphite

    Page(s): 2478 - 2483
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    The method of ab initio molecular dynamics, based on finite temperature density functional theory, is used to simulate laser heating of graphite. We find that a sufficiently high concentration of excited electrons dramatically weakens the covalent bond. As a result the system undergoes an ultrafast melting transition to a metallic state. This process appears to be similar to, although considerably faster than, laser melting of silicon. The properties of the laser-induced liquid phase of carbon are found to depend crucially on the level of electronic excitation. All these features are in qualitative agreement with the experimental behavior. © 1998 American Institute of Physics. View full abstract»

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  • High concentration diffusivity and clustering of arsenic and phosphorus in silicon

    Page(s): 2484 - 2490
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    The As diffusion coefficient as a function of its concentration was determined by Boltzmann–Matano analysis of the profiles of the dopant diffusing out of its conjugate phase precipitates during furnace annealing at 900 and 1050 °C of samples heavily doped by ion implantation. This method allowed to assure a constant diffusion source of As and to investigate a doping range attaining 3×1021cm-3. Along the same lines, the diffusivity versus concentration of specimens heavily implanted with P was determined at 900 and 1000 °C. Dopant profiles were determined by secondary neutral mass spectroscopy. The diffusivity of both As and P increases with dopant content, attaining a maximum at a concentration which closely corresponds to the saturation value of the carrier density, ne, which we previously determined by equilibration annealing of specimens with excess dopant. This finding demonstrates that ne represents the limiting value of the concentration of unclustered dopant at the diffusion temperature. On the contrary, a diffusivity monotonically increasing with dopant concentration up to its solubility limit, was observed in the case of B and Sb, which do not cluster. Finally, we report the results of a simulation model which can accurately describe the evolution of the As profile upon annealing, by using our diffusivity data and taking into account both the precipitation and clustering phenomena. © 1998 American Institute of Physics. View full abstract»

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  • Nitrogen-induced modifications in microstructure and wear durability of ultrathin amorphous-carbon films

    Page(s): 2491 - 2499
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    A systematic experimental investigation was carried out to understand the effects of nitrogenation on the microstructure and wear durability of thin amorphous-carbon films. The films were fabricated with 0%, 10%, 15%, 20%, 30%, 40%, and 50% N2 in the sputter gas. Microstructure properties were characterized using Rutherford backscattering spectroscopy, electrical resistance, Raman spectroscopy, and x-ray photoelectron spectroscopy. Nanohardness and scratch wear resistance of the films were studied with an atomic force microscope equipped with a diamond tip. The head–disk interface tribological properties of the films were tested with industrial standard contact–start–stop wear instrumentation. The results indicate that the introduction of nitrogen into the carbon film increases the film lattice disorder and allows for the formation of carbon–nitrogen single, double, and triple bonds. The nitrogen atomic concentration in the film, electrical resistance, and the ratio of carbon–nitrogen bonds to carbon–carbon bonds increase with increasing N2 in the sputter gas. A significant addition in CN bond percentage is observed when the N2 exceeds 30% in the sputter gas. Both the nanohardness and scratch wear resistance of the carbon film can be significantly improved by incorporating an optimized nitrogen concentration in the film. In this study, the film processed with 30% N2 showed the highest nanohardness and wear resistance. The degraded nanowear resistance for the films processed with 40% and 50% N2 is attributed to the significant addition of CN- bonds. Within a wide process range (15%–30% N2), the films exhibit excellent tribological performances at the head–disk interface. The wear mechanisms from the contact–start–stop wear tests are interpreted based on the understanding of film structures and film mechanical properties. © 1998 American Institute of Physics. View full abstract»

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  • Scanning tunneling microscope induced nanostructuring of a Si(111)/
    Ag(
     3
    ×
     3
    )
    R30° surface

    Page(s): 2500 - 2503
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    An atomically flat Si(111)/Ag

    (
     3
    ×
     3
    )
    R30° surface has been modified using a scanning tunneling microscope in ultrahigh vacuum. Mesoscopic pits have been created by applying negative voltage pulses to the sample, while at opposite voltage polarity mounds were formed. Moreover, lines could be written by moving the scanner at elevated voltages. The threshold voltage for pit formation increases almost linearly with the distance of the tip to the surface and drops to a value below 2 V for the closest approach. At sufficiently high voltages the depth extends beyond the silver layer height. The lateral pit size is well below 8 nm and can be reduced to values between 2 nm and 5 nm for voltages slightly above the threshold. Even selective top layer Ag atom removal has been achieved. © 1998 American Institute of Physics. View full abstract»

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  • Strain and surface morphology in lattice-matched ZnSe/InxGa1-xAs heterostructures

    Page(s): 2504 - 2510
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    Lattice-matched ZnSe/InxGa1-xAs heterostructures were fabricated by molecular beam epitaxy on GaAs(001)2×4 surfaces. We find that the partial character of the strain relaxation within the ternary layer can be compensated by a suitable excess in the In concentration to match the free-surface lattice parameter to ZnSe. The surface of the II–VI epilayer, however, exhibits a cross-hatched pattern of surface corrugations oriented along orthogonal <110> directions. This complex surface morphology reflects the formation of surface slip steps during the nucleation of dislocation half-loops at the surface and the establishment of the misfit dislocation network at the InxGa1-xAs/GaAs interface. © 1998 American Institute of Physics. View full abstract»

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  • Coalescence and overgrowth of diamond grains for improved heteroepitaxy on silicon (001)

    Page(s): 2511 - 2518
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    Heteroepitaxial [001]-oriented diamond films with considerably increased lateral grain size and strongly improved orientational perfection could be prepared by microwave plasma-assisted chemical vapor deposition using a [001]-textured growth process on Si (001) substrates followed by a [110] step-flow growth process. The diamond films were characterized by atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. The results indicate that the diamond crystals increase their lateral dimensions at the (001) film surface either by coalescence of grains combined with a termination of the propagation of grain boundaries or by changing the grain boundary plane orientations from preferentially vertical to preferentially parallel directions with respect to the (001) growth faces. In the second case, the grains with relatively large angle deviation from the ideal epitaxial orientation are overgrown by those with relatively small angle deviation. As a result, the degree of orientational perfection of the films improves considerably in comparison to that of films prepared by the established process of [001]-textured growth. The presence of boron in the gas phase was found to strongly enhance the step-flow lateral grain growth. It was possible to achieve deposition of a thin boron-doped diamond film characterized by a full width at half maximum value of the measured tilt angle distribution of only 2.1°. © 1998 American Institute of Physics. View full abstract»

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  • Effect of atomic bond structure on crystallographic orientation dependence of carbon doping in GaAs

    Page(s): 2519 - 2523
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    The effect of atomic bond structure at the deposition surface on the crystallographic orientation dependence of carbon doping in GaAs was studied. Carbon doping into GaAs epilayers was performed by atmospheric pressure metalorganic chemical vapor deposition using extrinsic carbon sources of carbon tetrachloride (CCl4) and carbon tetrabromide (CBr4). Epitaxial growths were done on the exact (100) and four different misoriented GaAs substrates with orientations of (511)A, (311)A, (211)A, and (111)A. The electrical properties were measured by van der Pauw Hall analysis at room temperature. Electrically active concentrations in excess of 1×1019 cm-3 were obtained so that 4 and CBrCCl4 were demonstrated as efficient p-type dopant sources for carbon doping into GaAs. The dependence of hole concentration on the offset angle of CCl4-doped and CBr4-doped GaAs shows the same tendency, whereas the trend of carbon doping from intrinsic carbon doping technique is different from our results. In particular, the hole concentration on the (100) surface is higher than that on the (111)A surface in the cases of CCl4 and CBr4. The result is opposite to that of the intrinsic doping case. A model based on the atomic bond structure of an adsorption site of carbon-containing species is proposed to explain the difference. © 1998 American Institute of Physics. View full abstract»

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  • The coexistence of pressure waves in the operation of quartz-crystal shear-wave sensors

    Page(s): 2524 - 2532
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    It is demonstrated that an AT-cut quartz crystal driven in the thickness-shear-wave mode and typically used as a sensor to monitor the viscoelastic shear-wave properties of a fluid also produce longitudinal pressure waves. Unlike the shear wave, these waves are capable of long-range propagation through the fluid and of reflection at its boundaries, notably at an outer fluid–air interface. They introduce a component into the measured electrical impedance and resonance frequency shift of the crystal, which reflects the setting up of cyclic pressure-wave resonances in the fluid. This has important implications for the practical employment of these crystal as sensors. Under appropriate conditions, as demonstrated for water and n-octane, it is possible to determine the propagating properties of sound waves in a fluid simultaneously with the viscoelastic shear-wave properties. These experiments are supported by an analysis of the appropriate hydrodynamic equations for waves in the crystal–fluid system, which predicts electrical characteristics in close agreement with those found experimentally. © 1998 American Institute of Physics. View full abstract»

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  • A combined scanning tunneling microscopy and electron energy loss spectroscopy study on the formation of thin, well-ordered β-Ga2O3 films on CoGa(001)

    Page(s): 2533 - 2538
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    The formation of thin, well-ordered β-Ga2O3 films on CoGa(001) was studied by means of high resolution electron energy loss spectroscopy (EELS), scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and Auger electron spectroscopy. The crystalline β-Ga2O3 films on CoGa(001) are prepared upon adsorption of O2 at 300 K and subsequent annealing at 700 K or by oxidation of the sample directly at 700 K, respectively. EEL spectra of these films exhibit Fuchs–Kliewer modes at 305, 455, 645, and 785 cm-1 in good agreement with calculated spectra using the IR parameters of Ga2O3. The band gap was determined to be 4.5±0.2 eV. In addition, a gap state at 3.3 eV was found. The observed LEED pattern of β-Ga2O3/CoGa(001) can be explained by a (2×1) structure in two perpendicularly oriented domains. STM images exhibit atomically flat and large oxide terraces (up to 2500×700 Å2) mainly of rectangular shape. STM pictures with atomic resolution confirm the (2×1) structure. In addition, a square substructure can be observed which is related to the closed-packed oxygen lattice of β-Ga2O3. © 1998 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