Showing papers in "Applied physics in 1980"

Mechanism and kinetics of the diffusion of gold in silicon

Abstract: The diffusion of Au in Si is known to take place via the interchange of Au atoms between substitutional (Au s ) and interstitial (Au i ) sites. So far it has generally been believed that this interchange involves lattice vacancies (V) and that it occurs via the Frank-Turnbull mechanism V+Au i ⇆Au s . It is stated in the literature that this model explains the observation that the Au s concentrationC s m in the centre of Au-diffused Si wafers increases with timet according to $$C_s^m \propto \sqrt t $$ . We show that this statement is incorrect, i.e., the Frank-Turnbull model cannot account for the $$C_s^m \propto \sqrt t $$ law. Such a dependence is expected in the case of Si wafers with a sufficiently low density of internal sinks for self-interstitials if the Au i −Au s interchange is controlled by the so-called kick-out mechanism Au i ⇆Au s +1. Since this mechanism involves self-interstitials (I) the present result is in accordance with the fact that under high-temperature equilibrium conditions the dominating intrinsic point defects in Si are self-interstitials and not vacancies as in Ge or metals.

Brightness enhancement of slow positron beams

Abstract: The brightness of slow positron beams can be enhanced significantly by repeated stages of moderation, acceleration and focusing. Presently available data suggest that the source spot area should decrease by 10−4 after each stage with only a modest loss of intensity. Beams with very small angular divergence, which could be made with this technique, would be useful for characterizing surfaces by positron diffraction and microscopy. Using such beams it is possible to envision the study of new exotic systems such as thee +-e − plasma and the positronium molecule.

High- Resolution Optical Spectra of Laser Cooled Ions

Abstract: We obtain essentially Doppler free spectra of the naturally occuring isotopes of Mg+, which are bound in a Penning trap, by using a frequency stabilized laser to continuously cool the ions, while the scatter rate from a second, frequency swept laser is, monitored. We show that the magnetron motion as well as the cyclotron and axial motion can be minimized. Line position measurements yielding resonance transition energy, isotope and hyperfine shifts are reported.

Epitaxial growth of ferroelectric PLZT thin film and their optical properties

Abstract: A series of experiments for growing epitaxial PLZT thin films has been made with rf sputtering. X-ray and electron diffraction analyses confirm that the fabricated films grow epitaxially on SrTiO3 and MgO crystals. A good transparency in the region above 0.4 μm to infrared with good ferroelectric properties is obtained. Propagation loss of He−Ne laser light is less than 6 dB/cm, and the PLZT thin film is a promising candidate for the optical modulator and other functional elements for integrated optics.

Coherence time measurement of picosecond pulses by a light-induced grating method

Abstract: The temporal coherence function |Γ(τ)| of picosecond pulses from a Nd: YAG laser has been measured by diffraction at a transient grating. The coherence timetc=7 ps is small compared to the pulse widthtp=22 ps but is in correspondence with the spectral bandwidth Δv=12·1010 Hz. The new method for measuring the coherence function |Γ(τ)| is discussed and compared with a previous experiment.

Time bunching of slow positrons for annihilation lifetime and pulsed laser photon absorption experiments

Abstract: Methods are described for gathering positrons from an extended region and causing them to impact upon a target surface within a small time interval. The most optimistic of these proposed schemes suggests that one should be able to produce ∼10−9s positron pulses with peak intensities of ∼1011s−1 starting with a ∼200 m Ci58Co β+ source. These pulses should be useful for studying time-dependent interactions of positrons at surfaces.

Electrostatic and Optical Resonances of Arrays of Cylinders

Abstract: The solutions of the electrostatic potential problem for the square and hexagonal arrays of circular cylinders with zero applied field (homogeneous or resonant solutions) are studied. We show that for non-touching cylinders, the set of resonances is discrete except in the neighbourhood of one point, at which the dielectric constant of the array has an essential singularity. For arrays of touching cylinders, the set is well represented by a continuous distribution. This representation enables the derivation of the asymptotic form of the expansion for the dielectric constant of the array when the dielectric constant of the cylinders is large. The known value of the first term in the expansion enables us to derive the second term. The physical characteristics of the resonant solutions are studied. Metals achieve values of dielectric constant which are close to the resonant values (real and negative) for certain wavelengths. Curves are given which enable the prediction of those wavelengths at which the optical resonances of both arrays occur, for any area fraction and composition of a columnar cerment film.

High concentration effects of ion implanted boron in silicon

Abstract: The diffusion behaviour of implanted boron in silicon was investigated using the10B(n,α)7 Li nuclear reaction. An anomalous behavior with a strong reduction of the diffusivity above an effective solubility limit at 1.5×1019, 6×1019, and 1.1×1020 cm−3 was found for annealing temperatures of 800, 900, and 1,000°C, respectively.

Imaging properties and applications of scanning optical microscopes

Abstract: This review paper is concerned with the imaging properties and major uses of scanning optical microscopes. It is shown that the confocal scanning microscope exhibits a form of super-resolution and that the instrument in general has great application in nonlinear microscopy and the inspection of electronic devices.

State selective step-wise photoionization of NO with mass spectroscopic ion detection

Abstract: State and isotope selective two-step photoionization of NO with mass spectroscopic ion detection has been demonstrated and investigated. Using saturation condition the photoionization cross section for a single rotational level of the intermediate state, No(A 2Σ+, ν′=0), has been measured: σi=(7.0±0.9) X 10−19 cm2. The charge transfer15NO++14NO→15NO+14NO+ has been observed and investigated, yielding a cross section of the order of 13×10−16 cm2, consistent with recent measurements at about 1 eV.

Photo-intercalation: Possible application in solar energy devices

Abstract: Theoretical considerations and preliminary photo-electrochemical experiments with ZrSe2 indicate the possibility of converting and simultaneously storing solar energy by means of light driven electrochemical reactions producing intercalation compounds of layer-type semiconducting material. A precondition is that the intercalated compound maintains a semiconducting behaviour and that its ionic properties complement in a favourable way. Promising substrates were identified inp-type zirconium-and hafniumdichalcogenides, but also TiS2 would be useful if it could be madep-conducting. Solar cells based on photo-intercalation — if they could be developed for practical use — would not only be simple [sandwich ofp-conducting layer-type semiconductor (e.g. ZrS2)/ionic conductor (wet or solid)/metal of intercalating species (e.g. Cu)], but also more convenient to use in irregular sunlight than conventional devices. Some thermodynamic properties and attainable efficiencies of this new type of solar cell are discussed as well as difficulties which would have to be surmounted.

Brewster window and windowless resonant spectrophones for intracavity operation

Abstract: We report a new design for an acoustically resonant spectrophone well suited for intracavity operation with widely tunable lasers. Operation with Brewster angle windows or in a windowless mode is possible, and high quality factors (560 and 509, respectively) are achieved. Windowless operation permits continuous monitoring of ambient air. We discuss factors limiting the sensitivity, ∼10−7 cm−1, and present a double chopping scheme capable of significantly reducing the acoustical background encountered in windowless operation. The sensitivity of the spectrophone's performance to misalignment is also examined.

Excimers and excimer lasers

Abstract: The development of excimers and excimer lasers are reviewed The excimers of the noble gases (Xe 2 * , Kr 2 * , Ar 2 * ) and of the noble gas halides (eg KrF, XeCl) which, respectively, radiate in the vacuum ultra-violet and ultra-violet regions of the spectrum are described in terms of their structure, spectroscopy and formation kinetics and the methods of pumping, operational characteristics and applications of the lasers are discussed

Angular Distribution and Differential Sputtering Yields for Low-Energy Light-Ion Irradiation of Polycrystalline Nickel and Tungsten

Abstract: Angular differential and total sputtering yields of polycrystalline nickel and tungsten have been measured for 1 and 4 keV H+ and 4 keV He+ ion bombardment at incidence angles between 0° and 80°. The differential sputtering yields (dY/dΩ) were determined with the aid of the collector technique, whereas the total yieldY was determined from the weight loss of the target during irradiation. Asymmetric angular distributions are observed at oblique angles of incidence, the emission maximum being shifted in forward direction (with respect to the incident ions). Even more pronounced than the change in shape of the emission distribution is an increase in the differential yield:dY/dΩ rises with increasing incidence angle over the whole range of ejection angles, the increase being most prominent in the direction of primary recoil emission. This effect is therefore ascribed to emission of surface atoms in direct projectile-surface atom collisions.

The measurement of energy spectra of neutral particles in low energy ion scattering: Apparatus and experiments

Abstract: An apparatus is described for low energy (0.1–10 keV) ion scattering (LEIS) experiments. A time of flight (TOF) spectrometer is incorporated in the system to be able to measure the energy of particles in the neutral state after scattering. The energy resolution ΔE/E of the TOF spectrometer is discussed and found to be 0.5% (FWHM). This is sufficient for our scattering experiments. An electrostatic analyzer (ESA) is used to measure the energy of scattered ions [ΔE/E=0.5% (FWHM)]. Experiments show that in general the ion dose needed to obtain a TOF spectrum (2×1010 ions/cm2) is much smaller than the dose needed for an ESA-spectrum (6×1013 ions/cm2). The ion spectra measured with the TOF spectrometer, by subtracting the neutral yield from the total yield, as well as with the ESA are found to agree quite well. This provides a way to calibrate the TOF spectrometer. The determination of the ion fraction of scattered particles is discussed [10 keV40Ar+ on Cu(100), scattering angle 30°]. It is shown that the TOF spectrometer is able to measure light recoil particles (e.g. hydrogen) from a heavy substrate. In the analysing system is, in addition to the TOF spectrometer, also incorporated a stripping cell to measure the energy of neutral scattered particles. An energy spectrum of neutral scattered particles measured with both methods is shown.

Photoelectron-spectroscopy investigation and electronic properties of LiNbO 3 crystal surfaces

Abstract: The electronic properties of Ar-ion and electron bombarded single-crystal surfaces of LiNbO3 have been investigated at room temperature by ultraviolet photoelectron spectroscopy (UPS) and x-ray excited photoelectron spectroscopy (XPS). In crystals reduced in this way, the loss of oxygen is accompanied with a loss of lithium and the creation of Nb4+ and Nb3+ ions. The relative concentrations of the various defects have been determined from their corresponding XPS core line spectra. When surface defects are produced an emission in the region of the bulk band gap appears. This gap emission is identified as arising from Nb 4d electrons due to the reduction of Nb5+ ions to Nb4+ and Nb3+ ions. The different behaviour of the gap emission upon surface treatment in the UPS and the XPS spectra is discussed.

Broad band resonant light pressure

Abstract: This paper treats the mechanical pressure of resonant light acting on a two-level system, where the degenerate magnetic sublevels are taken into account. The theory is developed with arbitrary relations between the quantization axis and the propagation and polarization of the light. Rate terms are obtained both for spontaneous and induced transitions; the requirements of incoherence put restrictions on the possible geometries of the experiment. The rate equations are restricted to motion along a light beam only; this one-dimensional case is simpler to handle. For small recoil velocities a Fokker-Planck equation is derived, and an adiabatic elimination procedure enables us to derive an equation for the velocity distribution of the total population. The assumptions and approximations are formulated and discussed.

A high power N 2 -laser of long pulse duration

Abstract: An N2-laser of 19 ns pulse-duration and an energy of 30 mJ has been developed and examined. A dc preionization, a grooved electrode and a partial electrical screening of the discharge tube permit reproducible single-shot operation and yield a homogeneous beam.

Generation of tunable picosecond light pulses covering the frequency range between 2700 and 32,000 cm−1

Abstract: The travelling-wave parametric process allows the generation of intense picosecond pulses tunable between 2700 and 17,000 cm−1. Angle- and temperature tuning was investigated using LiNbO3 crystals of different cuts. Various factors determining the bandwidth of the new pulses are evaluated and experimental spectra are presented. Frequency doubling readily leads to light pulses up to 32,000 cm−1. The jitter of two parametric systems operating in parallel is less than 1 ps for pump pulses of 7 ps.

Light-pressure cooling of trapped ions in three dimensions

Abstract: We formulate a Fokker-Planck theory for the three-dimensional cooling of a trapped ion by means of a single laser beam. Both the steady state and the dynamics of the cooling are discussed, and the correlations between the vibrational modes due to the light pressure are elucidated. A few comments on the actual experiments are presented.

Laser cooling of trapped particles I: The heavy particle limit

Abstract: We discuss laser cooling of a trapped ion. The problem is formulated for a harmonic trapping well and one-dimensional cooling. We carry out an adiabatic elimination and a Fokker-Planck expansion in the limit of a slowly oscillating particle. The ensuing Fokker-Planck equation is discussed and solved in certain limits. Especially the final cooling stages and ultimate width are of interest. The approach is related to earlier work and its validity is discussed.

Mössbauer surface studies on Tife hydrogen storage material

Abstract: By means of Conversion Electron Mossbauer Spectroscopy (CEMS) Fe clusters have been found on the surface of activated TiFe specimens. The magnetic moments of the Fe precipitates order ferromagnetically with a field of 328 KOe and are aligned parallel to the surface. The Fe precipitates are produced by the thermal treatment under hydrogen atmosphere and can be regarded as catalysts for the dissociation of the H2 molecules.

Investigation of viscosity dependent fluorescence lifetime using a synchronously operated picosecond streak camera

Abstract: Exciting with picosecond pulses from a mode locked cw dye laser and using the Synchroscan continuously operating streak camera, the variation in the fluorescence lifetime with viscosity over the range 0.5 cp–250 cp of some mode locking and potential mode locking polymethine dyes of the cyanine family were investigated. The measured lifetimes were found to follow a ∼2/3 or 1/3 power dependence of the viscosity η.

Double-core single-mode optical fiber as directional coupler

Abstract: This work describes the preparation and testing of a double-core single-mode optical fiber intended for use as a directional coupler A short survey of optical directional coupler theory is followed by a description of the preparation of the double-core preform The drawn fibers have a core diameter of 5μm with a spacing between core centers of 13μm Sections of the double-core fiber were tested at λ=633 nm and 876 nm The coupling factor measured for straight fiber sections of different length was found to be considerably lower than that calculated assuming equal phase velocities for both waveguides This was concluded to be due to a difference between phase velocities caused mainly by a 4 to 5% difference between core diameters At 876 nm a maximum coupling ratio of 13% was observed Bending the fiber section was found to influence the coupling factor due to a change in the phase velocity difference This effect can be utilized for tuning couplers A double-core fiber section may be applied as a sensor for measuring the bending angle

A study of deformation-produced deep levels in n-GaAs using deep level transient capacitance spectroscopy

Abstract: Deformation-produced deep levels, both of electron and hole traps, have been studied using deep level transient capacitance spectroscopy (DLTS) for an undopedn-type GaAs (HB grown) compressed at 440°C. Concentrations of two grown-in electron trap levels (E c −0.65eV andE c −0.74eV) and one grown-in hole trap level (E v +∼0.4eV) increase with plastic deformation, while that of a grown-in electron trap level (E c −∼0.3eV) decreases in an early stage of deformation. While no new peak appeared in the electron trap DLTS spectrum after plastic deformation, in the hole trap DLTS spectrum a broad spectrum, seemingly composed of many peaks, newly appeared in a middle temperature range, which may be attributed to electronic energy levels of dislocations with various characters.

Two-photon resonant four-wave mixing processes in atomic barium

Abstract: By means of a N2-laser pumped dye-laser (PL≈20kW, ΔvL < 10 GHZ) different two-photon resonant four-wave coupling processes in Ba vapour (nBa≈1016 cm−3) using the Ba states 6s8s1So and 7s5d1D2 were investigated. Coherent line radiation with conversion rates up to 10−3 was generated within the range of λ=190–200 nm by sumfrequency mixingvUV=2v1+v2 of 3 laser photons and within the range of λ=250–380 nm by couplingvUV=2v1±vIR of 2 laser photons with one photonvIR stimulated emitted in laser-induced Ba transitions. For the second coupling type the various nonlinear processes contributing to the formation of the coupling components are discussed. The power of the UV-component as function of inensity and resonance detuning of the laser as well as on the phase-mismatch was calculated on the basis of the small signal theory and compared to the experimental data.

Electron-hole pair production and the structure of ultraviolet isochromats

Abstract: Isochromat spectra are generally considered to reflect the density of empty one-electron states in the anode material of the x-ray tube employed. Comparison of various measurements with theoretically determined density-of-states functions indicate that such a first-order picture applies only immediately above threshold. In this paper, we show that electron-hole pair production contributes considerably at higher energies above threshold. Taking this effect into account removes most of the existing discrepancy between theory and experiment in this region. Results are presented for the 5d transition metals hafnium, tantalum, and tungsten.

Wide-range line-tunable oscillation of an optically pumped NH3 laser

Abstract: Selective single-line oscillation has been obtained from an NH3 laser in the range from 11 to 13 μm. Pumping of high pressure NH3−He mixture with theR(30) line of a TEA-CO2 laser made it possible to tune on more than 30 lines with the aid of a grating. However, such line tunable oscillation was not observed when theR(16) line was used for pumping. Reasons for this difference are discussed.

Influence of the Solvent Matrix on the Overlapping of the Absorption and Emission Bands of Solute Fluorescent Dyes

Abstract: It has been observed that the separation between the absorption and the emission bands of a fluorescent dye is smaller in a rigid polymer matrix than in the liquid monomer. Low temperature measurements have been carried out in order to understand this phenomena. It has been found, that the molecular mobility of the matrix, in which the dye is dissolved, plays an important role. By doping the rigid matrix with molecules of high mobility, the separation between the absorption and emission bands can be increased. A nearly complete separation can be achieved by this doping method if the difference of the dipole moments in the ground and excited states of the dye molecules is very large. This allows, for example, to increase the brightness of the fluorescence-activated liquid-crystal display (FLAD) and the efficiency of solar collectors based on fluorescent dyes.

The characteristics of high current amorphous silicon diodes

Abstract: Amorphous siliconp−n junctions with various doping profiles have been prepared by the glow discharge technique and the effect of the barrier profile on electrical properties investigated. Current densities of up to 40 A cm−2 with rectification ratios of 104–105 were obtained withn +−ν−p + structures. The diode quality factor has also been investigated, both in the dark and under illumination.