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Journal of Applied Physics

Issue 10 • Date May 1986

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Displaying Results 1 - 25 of 56
  • Fundamental stability limits for the diode‐laser‐pumped rubidium atomic frequency standard

    Page(s): 3313 - 3317
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    Recently, there has been considerable interest in the use of single‐mode diode lasers in atomic frequency standards. In the present paper theoretical calculations are performed in order to quantify the expected performance improvement upon incorporation of diode lasers in rubidium gas cell atomic frequency standards. We assume that clock signal shot noise, the diode laser’s quantum noise, and diode laser frequency locking noise all contribute to the atomic frequency standard’s stability. Our results indicate that white‐noise Allan variances of ∼6×10-15/(τ)1/2 are possible if enhanced cavity Q diode lasers are employed, whereas for presently available commercial diode lasers we predict white‐noise Allan variances of ∼3×10-14/(τ)1/2. These variances represent a 2–3 orders of magnitude improvement in frequency stability over that currently obtained with rubidium gas cell atomic clocks. View full abstract»

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  • Near‐field optical‐scanning microscopy

    Page(s): 3318 - 3327
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    Near‐field optical‐scanning (NFOS) microscopy or ‘‘optical stethoscopy’’ provides images with resolution in the 20‐nm range, i.e., a very small fraction of an optical wavelength. Scan images of metal films with fine structures presented in this paper convincingly demonstrate this resolution capability. Design of an NFOS microscope with tunnel distance regulation, its theoretical background, application potential, and limitations are discussed. View full abstract»

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  • Real‐time characterization of the photoresist/substrate interface

    Page(s): 3328 - 3331
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    The use of a piezoelectric crystal as the substrate for a photoresist film provides unique resist characterization capabilities. In particular, the photoresist near the substrate is probed in real time. The basis of this measurement technique is described, emphasizing the physical phenomena responsible for observed piezoelectric crystal response behavior. Demonstration of this analysis to a gelatin‐based resist is given. The influence of solvent drying is readily distinguishable from the effects of photohardening reactions. View full abstract»

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  • Dark‐field stigmatic ion microscopy for structural contrast enhancement

    Page(s): 3332 - 3338
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    Dark‐field images are observed with a stigmatic (immersion objective lens) secondary ion mass spectroscopic ion microscope by means of an eccentric objective aperture, and are a useful extension of shadow contrast imaging. The spatial resolution in these images is comparable with conventional bright‐field imaging, provided that a narrow energy bandpass is selected to minimize chromatic aberrations. It is demonstrated that the dark‐field method is useful for correlating surface relief with chemical contrast in the compositional secondary ion mass spectroscopic mapping of conventional ion microscopy. Further, based on the information acquired in the dark‐field imaging mode, digital techniques to compensate for asperity artifacts in conventional ion microscopy are proposed. View full abstract»

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  • Signal processing in optothermal spectroscopy

    Page(s): 3339 - 3343
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    The usefulness of optothermal spectroscopy for quantitative analysis is discussed. It is shown theoretically and experimentally that optothermal spectroscopy is comparable to ordinary transmission spectroscopy for the determination of optical absorption coefficients. View full abstract»

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  • Optical superlattices for modulation and deflection of light

    Page(s): 3344 - 3355
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    A novel kind of doubly resonant light scattering involving the Floquet–Bloch waves of a fine‐period stratified structure is discussed. These waves can be Bragg scattered by a weak coarse‐period superlattice provided a certain Bragg‐like resonant condition is satisfied. Included among the unique properties of this kind of scattering are wavelength selective wide‐angle beam deflection by acoustic waves in the 10 MHz–1 GHz range, the ability to enhance or impair the efficiency of Bragg reflection by a conventional fine‐period grating, and, in one particular case, very wide‐band modulation of light. Coupled‐wave equations describing this interaction are solved for a variety of different geometries, and some potential applications proposed. View full abstract»

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  • Transmission characteristics of the birefringent filter system, where a retarder‐rotator combination is used at each stage

    Page(s): 3356 - 3359
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    Polarizers and retarders have long been known as the basic building blocks of Lyot and Solc filters. Recently the use of an optically active medium along with polarizers and retarders has been found to be useful for modifying the transmission characteristics of the birefringent filter system. In this paper, the effect of using an optically active medium as the interstage element of a Solc filter has been studied. The idea of a birefringent band suppression filter has been found and the tuning procedures of these fixed‐type filters have also been discussed. View full abstract»

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  • Theory of a variable aperture phase conjugate mirror with application to an optical cavity

    Page(s): 3360 - 3362
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    A new model for phase conjugate mirror reflectivity is derived and applied to a laser cavity with phase conjugate mirror. We find that by matching the phases of transverse cavity and phase conjugate mirror modes, the phase aberration correction ability of the mirror can be significantly improved. View full abstract»

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  • Simultaneous electron/hole transport in photorefractive materials

    Page(s): 3363 - 3366
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    The steady‐state space‐charge field and the response time of a photorefractive material illuminated with a sinusoidal interference pattern are derived for two models in which both electron and hole transport are important. In the first model in which electrons and holes are produced from a single set of recombination centers, the sign of the steady‐state space‐charge field depends on the relative value of the conductivities and/or absorption coefficients of the electrons and holes, and a single response time proportional to irradiance is obtained. In the second model in which electrons are photoionized from one set of recombination centers and holes from another, the sign of the space‐charge field depends on the relative concentrations of the empty hole and electron traps, and two time constants, each inversely proportional to irradiance, are obtained. View full abstract»

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  • Observation of the Biot slow wave in a plastic foam of high flow resistance at acoustical frequencies

    Page(s): 3367 - 3370
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    The surface impedance of a plastic foam with high flow resistance has been measured with a new method at acoustical frequencies. The Biot theory provides a description of the behavior of this surface impedance from the contributions of the fast and the slow compressional waves to pressure and acoustical velocity at the surface of the foam. The contribution of the slow wave can be observed in spite of its strong damping. View full abstract»

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  • Modeling of heat flow in multilayer cw laser‐annealed structures

    Page(s): 3371 - 3374
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    The three‐dimensional heat diffusion equation has been solved numerically for scanning cw laser‐annealed multilayer structures. The computational method can be applied to laser beams with either circular or elliptical symmetry. The temperature dependence of relevant optical and thermal properties has been included and good agreement with experimental results is obtained. The dynamics of melting are examined and discussed. It is found that the presence of a thin buried oxide in a silicon wafer substantially increases the sensitivity of the maximum melt depth to laser power. View full abstract»

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  • Rate of heat conduction from a heated sphere to a matrix containing passive spheres of a different conductivity

    Page(s): 3375 - 3382
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    Using a multipole expansion scheme, we calculate the rate of heat conduction Q from a heated sphere with constant surface temperature to a matrix of conductivity k, containing a dilute dispersion of equal‐sized passive spheres of conductivity αk, and whose temperature far away from the heated sphere vanishes. Values are presented for Q for various choices of α and λ, the ratio of the radius of a passive sphere to that of the heated sphere, and asymptotic expressions are derived for the cases λ≪1 and λ≫1, respectively. When the passive spheres are very small compared to the heated sphere, the composite can be viewed as an effective continuum on the length scale of the latter with an effective thermal conductivity relative to the matrix given by Maxwell’s expression, k*=1+3βc, where β=(α-1)/(α+2) and c is the inclusion volume fraction assumed to be small. We find, however, that this effective continuum approach can still be applied with a surprising degree of accuracy over the whole range of α even when λ is as large as O(10), provided that the effective thermal conductivity is allowed to vary with r, the distance from the center of the heated sphere, according to the expression k*≡1+3βρ(r), where ρ(r) denotes the probability that a point in the composite lies within a passive sphere. It is shown, furthermore, that this effective continuum approach becomes exact to O(α-1) for all λ. View full abstract»

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  • Kinetics of hydrogen thyratron plasmas during the conduction phase

    Page(s): 3383 - 3396
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    A study of the conduction‐phase characteristics of hydrogen thyratron plasmas is presented. A self‐consistent analysis is performed through simultaneous numerical solutions of the Boltzmann equation, the rate equations for the various ionic and neutral particle densities, and the radiative transfer equation. The electron kinetic properties, chemical composition, and radiative properties of the plasma are derived for a wide range of current densities. Moreover, the role of the various collisional processes in shaping the electron energy distribution for various values of E/N (electric field/total gas number density), fractional ionization, and dissociation degree is elucidated. Implications of the obtained plasma properties on the analysis and diagnosis of hydrogen thyratron plasmas are discussed. View full abstract»

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  • Analytical studies of an ablation mass driver system

    Page(s): 3397 - 3401
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    The electromagnetic acceleration of projectiles with an ablator using sequential Z pinches in a cylindrical electrode array is studied analytically under an assumption that every stage of the Z pinches, except the first one, is triggered automatically by the Z pinch following after the projectile. The effect of ablation on the acceleration of the projectiles is considered in detail, as well. The force distribution on the base of the projectile changes significantly when the contribution of the ablation to the total acceleration is taken into account. A method of equalizing the stress in the projectile in order to overcome the stress barrier of hypervelocities is also discussed. View full abstract»

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  • Mono‐ and disilicon radicals in silane and silane‐argon dc discharges

    Page(s): 3402 - 3411
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    Measurements of monosilicon (SiHn) and disilicon (Si2Hn) radicals at the cathode surface of dc discharges in silane and silane‐argon mixtures are reported. Silyl radical density per decomposed silane was constant for fixed flow conditions over a range of powers and silane‐argon ratios. The relative densities for other monosilicon radicals SiHn/SiH3 decreased with increased fraction of silane in silane‐argon mixtures. The density of disilicon radicals was observed to be comparable to some of the monosilicon radicals, with Si2H2 and Si2H4 the dominant Si2Hn species. Formation and destruction reactions are discussed for these radicals, disilane, and the deposited film. We deduce that disilane is formed primarily on surfaces and that sputtering is a significant source for radicals near the cathode. View full abstract»

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  • Physical and optical properties of R‐Zn‐Ba‐Yb‐Th fluoride glasses

    Page(s): 3412 - 3416
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    The effect of glass composition on the density, refractive index, thermal expansion coefficient, glass transformation temperature, viscosity, and crystallization temperatures of R‐Zn‐Ba‐Yb‐Th fluoride glasses (R=Li or Na) was measured as BaF2 was replaced by RF. The optical spectra of these glasses were also measured. Values of each of the physical properties decreased with increasing alkali fluoride concentration. In every case, lithium had a larger effect than did sodium on the value measured for a given property. These results indicate that the substitution of an alkali fluoride for barium fluoride results in a decrease in the degree of linkage of the vitreous network. View full abstract»

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  • Depth distribution of secondary defects in 2‐MeV boron‐implanted silicon

    Page(s): 3417 - 3420
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    Annealing behavior of secondary defects in 2‐MeV boron ion‐implanted (100) silicon has been investigated mainly through cross‐sectional TEM observations. The maximum defect density is located at a mean depth of 3.2 μm from the surface and the location is 0.3 μm deeper than that of the projected range of boron ions. This defect position in the crystal is constant under all annealing conditions (e.g., a temperature range of between 700 and 1000 °C, annealing time of up to 6780 min at 1000 °C), although the vertical distribution width of defects changes with both annealing temperature and time. View full abstract»

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  • Elastic interaction between general parallel screw dislocations and a surface crack

    Page(s): 3421 - 3429
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    The dislocation‐modeling technique and complex variable method are used to analyze the interaction between the general parallel screw dislocations and a surface crack. For the case of one dislocation, the dislocation distribution in the crack, the stress field, the strain energy, the image force, the stress intensity factor, and the crack extension force are obtained. The results are compared with various special cases of other papers. Under the applied stress without the frictional force, there are two metastable points and no stable point in the strain energy diagram. Therefore, the dislocation will move to the free surface, crack surface, or infinity depending on its location. The two‐dislocation system or the even dislocation dipole is analyzed. Although this approach gets the same results as the conformal mapping method, the former is superior in analyzing two or more dislocations. View full abstract»

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  • Aluminum or phosphorus co‐doping effects on the fluorescence and structural properties of neodymium‐doped silica glass

    Page(s): 3430 - 3436
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    To utilize the excellent properties of silica (SiO2) glass for a glass laser host, neodymium‐aluminum (Nd–Al) and neodymium‐phosphorous (Nd–P) co‐doped SiO2 glasses were studied. They were prepared by plasma‐torch chemical vapor deposition (CVD). It was found that a doping level less than ten times the number of Nd for the Al co‐dopant and less than about fifteen times for the P co‐dopant was enough to remove undesirable fluorescence properties of Nd‐doped SiO2 glasses and make them suitable for laser application. The clustering Nd ions disperse well in a glass matrix and lasing fluorescence increases. The effects of the Al dopant on the density and Raman spectra were also studied to obtain structural information. On the basis of glass science and solution chemistry, the marked effects of both dopants were explained by the following model. Nd ions can be well incorporated into a SiO2 glass network through co‐dopant oxide forming a solvation shell around the Nd ions. This model leads to an expansible method for coordination control around active ions in SiO2 glass. A preliminary experiment on laser oscillation using Nd–Al co‐doped SiO2 glass was also carried out. View full abstract»

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  • High‐temperature thermodynamic properties of alpha and gamma lanthanum sesquisulfides and related compounds

    Page(s): 3437 - 3440
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    The high‐temperature heat contents of La2S3(α), La2S3(γ), La3S4, and La2.65Eu0.35S4 were measured from 400 to 1800 K by using a copper block drop calorimeter. The heat and entropy of transition of the α‐to‐γ transformation of La2S3 was determined. Equations for the thermodynamic functions H0T-H0298.15, Cp, S0T-S0298.15 and -(F0T-H0298.15)/T were derived in terms of the least‐squares fit parameters of the heat content data. View full abstract»

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  • Defect structure in III‐V compound semiconductors: Generation and evolution of defect structures in InGaAs and InGaAsP epitaxial layer grown by hydride transport vapor‐phase epitaxy

    Page(s): 3441 - 3447
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    The generation and evolution of a novel defect structure in InGaAs single‐layer and InGaAsP/InP multilayer laser structures grown by hydride transport vapor‐phase epitaxy on (001)InP substrate has been studied in detail using both cross‐section and plan‐view transmission electron microscopy. Under certain growth conditions, a unique defect structure consisting of a dislocation tangle initiated at the InGaAs/InP interface, having the shape of a pyramid, followed by a bundle of straight dislocations propagating through the InGaAs epitaxial layer near [001] growth direction and along 〈112〉 orientations, is formed. Such defect structure is universal to these materials grown from vapor sources. The pyramidal‐dislocation tangles, or PDT defects, are formed as a result of the agglomeration of fine precipitates (500 Å in size) which generate a special type of edge dislocation lying in the (110) plane with the line direction oriented close to the [001] growth direction. X‐ray microanalysis indicates that the interfacial precipitate, which induces the generation of the PDT defect, contains excess Ga and P. At the InGaAsP/InP interface, the agglomeration of fine precipitates does not occur even at a density as high as 4×1012 cm2. The possible causes of the formation of the fine interfacial precipitate and PDT defect are discussed. The evolution of the defect structure across successive layers is further investigated in a multilayer structure. The result indicates that the major defects in the quaternary layers are the [001]‐oriented dislocations generated from the precipitates at the quaternary/binary interfaces. These dislocations recombine at the second interface after propagating through the layer. The 60° slip‐type dislocation is also observed. The replication of dislocations from the substrate is negligible. View full abstract»

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  • An atomistic study of the GaAs–Pd interface

    Page(s): 3448 - 3453
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    The interface of GaAs–Pd was investigated on an atomic scale by a time‐of‐flight (TOF) atom‐probe field ion microscope (FIM). It was found that Pd reacts strongly with Ga even at room temperature to form a stable PdGa compound. Depending upon heat treatment conditions, several types of Pd–(Ga, As) ternary compounds were also formed. A thin layer (less than a few monolayers) of As was quite often detected at the outermost surface layer when the interface was heated up to 400 °C. Above 400 °C only the most stable PdGa phase was observed at the interface. At a temperature range between 200 and 400 °C, the segregated Ga phase was also found beneath the As layer. The interfacial reactions can be understood by the following two processes: (1) Pd atoms diffuse into the GaAs substrate to form a stable Pd–Ga bond and (2) As, whose bonding with Ga is broken, becomes loose and migrates to the surface and desorbs. View full abstract»

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  • Computer simulation of thin‐film nucleation and growth: The multilayer mode

    Page(s): 3454 - 3457
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    The computer simulation of thin‐film nucleation and growth, which was previously performed for the case of single monolayer, has been extended to the case of multilayer growth. The simulation results show that the kinetics of multilayer growth is nearly identical to that of monolayer growth. The cluster density resulting from the multilayer mode is similar to that resulting from the monolayer mode at low coverage. At high coverage, multilayer growth results in substantially higher cluster density than that resulting from monolayer growth. View full abstract»

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  • Formation of intermediate phases, Ni3Si2 and Pt6Si5: Nucleation, identification, and resistivity

    Page(s): 3458 - 3466
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    The formation of Ni3Si2 from the reaction of Ni2Si with NiSi, and that of Pt6Si5 from the reaction of Pt2Si with PtSi have been investigated by Rutherford backscattering, x‐ray diffraction, resistance measurements, and optical and electronic microscopy. Standard x‐ray diffraction patterns were calculated for Pt6Si5 and for the high‐temperature form (hexagonal) of Pt2Si. These are shown to match experimental diffraction patterns. Both Ni3Si2 and Pt6Si5 form quite suddenly (at 470 and 535 °C, respectively) according to the pattern of nucleation‐controlled reactions which are anticipated when the free energies of formation of the new phases are sufficiently small. These observations are discussed with respect to the absence of both Ni3Si2 and Pt6Si5 from the sequence of phases which form when Ni and Pt thin films react with Si. Resistivity measurements are reported for Ni3Si2, Pt6Si5, and for the two forms (low and high temperature) of Pt2Si. View full abstract»

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  • Kinetics of Pd2Si layer growth measured by an x‐ray diffraction technique

    Page(s): 3467 - 3474
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    An x‐ray diffraction approach has been developed for determination of the kinetics of growth of Pd2Si layers. Epitaxial Pd2Si films were grown on Si(111) substrates over a temperature range of 160–222 °C by a solid‐state reaction between the substrates and the Pd overlayers. The parabolic rate equation was verified and rate constants showed Arrhenius behavior with an activation energy Ea=1.06 eV and prefactor k0=7×10-4 cm2/s. The low value of Ea suggests a short‐circuit diffusion mechanism. It is reasonable to expect that impurities and microstructure may play important roles in the growth process. Impurity levels in the specimens were evaluated by analytic techniques suited to thin‐film study: Rutherford backscattering spectrometry, secondary ion mass spectrometry, and Auger electron spectrometry. No impurities were present at concentrations approaching 1 at. %. Some O, C, and F were detected at the Pd2Si/Si interfaces. The annealing ambient was the major source of further contamination. Upon emergence of the growth interface through the sample surface (some Pd2Si on surface), impurity pickup was detected. Interfacial roughness was indicated by all the techniques to be on the order of 20 nm. 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