Characteristics of a copper bromide laser with flowing Ne-HBr buffer gas

The operating characteristics of a small self-heated copper halide laser (=510.6 and 578.2 nm) are described, where the copper lasant atoms are produced by electric-discharge dissociation of copper bromide that is generatedin situ by flowing Ne-HBr gas mixture over copper pieces in the laser tube. The excitation technique permits fast startup (<1 min to laser oscillation from cold), and rapid and simple control of the CuBr vapour pressure, simultaneously introducing H₂ to increase the efficiency. Specific laser output energies and average powers of 12J cm^–3 and 195 mW cm^–3, respectively, are almost a factor of 2 higher than those previously reported in the literature for multi-kilohertz copper bromide lasers. A maximum power of 7.8 W was obtained from the 40 cm³ active region. At its highest efficiency (0.8%) the laser produced 6.1 W.     

Surface phonon dispersion of Cu(100)c(2×2)N

The Cu(100) surface covered with atomic nitrogen has been studied with low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and inelastic electron scattering (EELS). Atomic nitrogen, formed by thermal dissociation of NH₃ adsorbed at 100 K, forms a c(2×2) overlayer on the Cu(100) surface. The dispersion of adsorbate and substrate associated modes of the Cu(100) surface covered with a c(2×2) nitrogen overlayer has been measured along the two dimensional Brillouin zone in the - by inelastic electron scattering. The experimental data are compared to a lattice dynamical slab calculation. The Rayleigh-mode (S₄-phonon) is only slightly changed by the N-overlayer. An optimum fit for the perpendicular and parallel nitrogen modes (=320 cm^–1 and =740 cm^–1 at =0.1) is obtained when the nitrogen atom is placed 0.6 Å above the first copper layer.     

The behavior of copper impurity in CdSnAs2

Single crystals of n-type CdSnAs₂ with a carrier concentration of 2 ·10¹⁷–4 ·10¹⁸ cm^–3 and mobility (3 to 6) · 10³ cm²/V ·sec were copper doped by diffusion saturation at temperatures from 400 to 570C. As a result of the study of the electrical properties of the doped crystals it was established that the copper in CdSnAs₂ is a fast-diffusing acceptor impurity. The solubility of Cu depends primarily on the donor-center concentration and has clearly a retrograde character. Low-temperature heat treatment (over the 200–400C range) of the Cu-doped specimens results in an increase in the acceptor concentration. The form of the log R(10³/T) curve indicates the existence of acceptor centers with an ionization energy of 0.05 eV in the Cu-doped CdSnAs₂ specimens.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 7, pp. 39–44, July, 1973.     

Surface modification by intense proton irradiation

In the present paper the mixing of thin metal layers on silicon or copper substrates induced by HIPIB (High Intensituy Pulsed Ion Beams) was investigated using a device which delivers mainly protons with a maximum ion energy of E ₀=250 keV, a pulse length of =50 ns, and an energy density per pulse of 3 J/cm². The temperature distribution in the samples which was evaluated by solving the one-dimensional heat-flow equation indicates that 1 m layers are heated well above the melting point. The samples were analysed by RBS (Rutherford Backscattering Spectrometry), SNMS (Sputtered Neutral Mass Spectrometry), X-ray diffraction and a microprobe. If the surface tension of the molten layer is larger than the one of the substrate, the layer material is splashed off. Chromium layers on copper are completely mixed after irradiation by a few shots and a considerable hardening of the surface is observed.     

Laser ablation of copper and aluminium in air

The ablation behavior of copper alloy and aluminium irradiated in air by 1.06 m, 10 ns pulsed laser with power density of 6.4×10⁹W/cm² was studied using scanning electron microscopy (SEM), MCS-RBS and X-ray microanalysis. Evidence of bulk vaporization via bubble formation was observed for the copper alloy under the laser irradiation. Silver-enrichment microregions were found in the ablation crater created by the laser shots on the copper alloy sample. Material removal rates of these materials were determined by crater shape-profile measurement. Using self-similar solutions of the gas-dynamic equations, gas-dynamic parameters of the vaporization waves are obtained. These parameters are used to calculate material removal rates and impulse coupling coefficients of these materials under the pulsed laser irradiation. The calculated mass removal rates and the coupling coefficients are compared with the corresponding experimentally determined values. The surface kinetic energy of the irradiated area on the Al sample is estimated. Possible mechanisms for laser ablation of the materials under study are discussed.     

The Migdal-Kadanoff renormalization group scheme for the Ising model with a free surface

The Migdal-Kadanoff scheme is applied to the Ising model with a free surface. The resulting renormalization group transformation and the duality transformation commute in any dimension. Two simple recursion relations are obtained which reproduce the global phase diagram for the semi-infinite Ising model. The surface critical exponents space methods. In dimensiond=2+, we find the exponentsy t ₁ ^(SB)= andy h ₁ ^(SB)=1+ for the multicritical surface-bulk transition. We also derive and discuss approximate differential recursion relations for the bulk and the surface free energies.     

On the geometric origin of the equation ϕ,11 — ϕ,22 = eϕ — e-2ϕ

It is shown that the equation ,11 — ,22 = e — e^-2 determines the intrinsic geometry of the two-dimensional affine sphere in the three-dimensional unimodular affine space like the sine-Gordon equation describes the metric on the surface of a constant negative curvature in the three-dimensional Euclidean space. The linear equations that determine the moving frame on the affine sphere are the Lax operators to the equation ,11 — ,22 = e — e^-2.     

Muon diffusion in copper bolow 2K

Transverse field SR experiments were performed on several different samples of copper in the temperature range below 2K, including isotope separated copper, Fe and Si doped polycrystalline copper and monocrystalline copper. No strong isotope dependent effect was observed. A⁶³Cu and a natural copper sample of identical purity both yield 0.16 s^–1 for the low-temperature plateau, while an increased linewidth inthe⁶⁵Cu case may be related to the strong effects of Fe impurities. Careful transverse field measurements on large single crystals at 0.08K reveal non-Gaussian lineshapes in accordance with the picture of diffusing muons at this temperature. This allows us to reject several of the existing models for muon behaviour in copper below 2K.     

Ions trapped near the free surface of superfluid helium: A review

Suitable ions or other charged particles can be trapped electrostatically just below the free surface of superfluid⁴He. Examples of such particles are the socalled negative ion, which is an electron in a bubble, and the so-called positive ion, which is a⁴He⁺ ion surrounded by a small region (snowball) of solid helium. The trapping mechanism can be used to create two-dimensional pools of ions. Three types of experiment can be carried out with such pools: those that relate to the ionic structure; those in which the ions are used as probes of the properties of the superfluid helium; and those in which the pools are studied as examples of simple two-dimensional fluids or solids. Experiments that have been carried out so far are reviewed, and prospects for the future are assessed.     

Search for superconducting effect on the decay of99m Tc

An experimental investigation of the influence of superconductivity on the decay rate of^99m Tc, _T, has been performed by means of a differential method. The^99m Tc samples containing⁹⁹Tc as a carrier were prepared by electrodeposition on a copper plated tungsten wire. For production of metallic technetium the samples were reduced in pure hydrogen gas at 800~1000°C. X-ray analysis of the samples showed they were surely metallic with anhcp structure. The lattice constants observed area=2.741 Å andc=4.398 Å. The transition temperature was found to be 7.5±0.2K. Comparison of two sources, normal (room temperature) and superconducting (4.2 K), did not show an appreciable effect of superconductivity on the decay rate of^99m Tc exceeding the limit of uncertainty of our experiment:/ _T=(1.1±2.7) × 10^–4.     

Exploration of the ultimate patterning potential achievable with high resolution focused ion beams

Controlled and reproducible fabrication of nano-structured materials will be one of the main industrial challenges in the next few years. We have recently proposed exploitation of the nano-structuring potential of a high resolution Focused Ion Beam Tool, to overcome basic limitations of current nano-fabrication techniques. The aim of this article is to present some new routes for material patterning, which benefit from ion-induced local property modifications or damage. In the experiments we describe hereafter an ultra-sharp pencil of 30 keV gallium ions is used to tailor the characteristics of several materials at a scale of a few nanometres. The experimental results are then compared to simulations. First, we simulate the control of collisional defects generated in a thin magnetic layer under FIB irradiation. The results explain the stable magnetic structures we have obtained experimentally. This was achieved with a low surface ion dose (10¹² to 10¹⁴ ions/cm²). In addition we have explored the promising direction of Bottom-up or self-organization processes using a FIB instrument. We have defined artificial surface defects. These defects created by the impact of an 8-nm FWHM probe were used to pin the diffusion and to organize nanometre-sized gold clusters on a graphite surface. PACS 79.20.Rf; 81.07.-b     

Femtosecond time-resolved reflection second-harmonic generation on polycrystalline copper

Optical Second-Harmonic Generation (SHG) in reflection from a polycrystalline copper surface in air was studied using femtosecond time-resolved pump and probe measurements at =625 nm. The observed time dependence of second-harmonic yield from the probe beam demonstrates, that SHG is a very sensitive technique for measuring transient electron temperatures of metals even when these are covered by an oxide layer. For polycrystalline copper, an electron-phonon energy transfer time of 2 ps was observed, corresponding to a coupling constant of 3.75×10¹⁷ W/m³ K at average lattice temperatures of about 500 K. The analysis of experimental data indicates that the time dependence of SHG is governed by the linear dielectric function which, in turn, is affected by the electron temperature. There is no evidence for a temperature dependence of the nonlinear susceptibility ⁽²⁾.Paper presented at the 129th WE-Heraeus-Seminar on Surface Studies by Nonlinear Laser Spectroscopies, Kassel, Germany, May 30 to June 1, 1994     

Nucleation of He clusters at111In in metals

Helium has been implanted in copper. Its interaction with¹¹¹In atoms during isochronal annealing is observed by the perturbed angular correlation (PAC) technique. The results reveal that the nucleation of He-clusters at the¹¹¹In site is accompanied by reactions of intrinsic defects. Therefore, in the case of Cu, where the knowledge of intrinsic defects is nearly complete, the successive building-up of He-clusters can be pursued.This work was supported by the Bundesminister für Forschung und Technologie.     

Surface tension in Ising systems with Kac potentials

We consider an Ising spin system with Kac potentials in a torus of ^d,d>-2, and fix the temperature below its Lebowitz-Penrose critical value. We prove that when the Kac scaling parameter vanishes, the log of the probability of an interface becomes proportional to its area and the surface tension, related to the proportionality constant, converges to the van der Waals surface tension. The results are based on the analysis of the rate functionals for Gibbsian large deviations and on the proof that they -converge to the perimeter functional of geometric measure theory (which extends the notion of area). Our considerations include nonsmooth interfaces, proving that the Gibbsian probability of an interface depends only on its area and not on its regularity.     

Determination of dislocation damping in copper single crystals with stress pulse method

Dislocation damping in copper single crystals was determined by the stress pulse method. For this purpose very short stress pulses were used, maximum length 30 s, by which loading conditions of a metallic matrix in the frontal region of a propagating brittle crack were simulated. At loading by these very short stress waves, strain rates above 10⁴ s^–1 are achieved, however, the strain rate during loading is not constant. Therefore a technique was elaborated that enables to compare the measured results of mechanical characteristics with very short stress pulses ( const.) with results obtained on a device with a constant strain rate of the specimen. With the use of the dependence = ( ) the existence of damping mechanisms of a viscous character was proved and the damping coefficientB determined. These results agree with theoretical assumptions in [10,20] about the probable mechanical behaviour in the region of the propagating brittle crack.ikova 22, Brno, Czechoslovakia.     

Surface diffusion of copper on tantalum substrates by Ostwald ripening

In this work, we report on the determination of surface diffusion coefficient of copper on tantalum substrates by Ostwald ripening. It is shown that impurities, such as oxygen, strongly influence the kinetics of dewetting of copper films on tantalum substrates. Two technologically important interfaces with copper were investigated: Cu/β-Ta and Cu/α-Ta. For copper surface diffusion on β-Ta surface, a surface diffusion coefficient of was measured at 550 °C. The temperature dependence of surface diffusion was investigated between 400 °C and 550 °C. Using an Arrhenius relationship, an activation energy of 0.83 ± 0.1 eV and a pre-exponential factor of were calculated. For copper surface diffusion on α-Ta surface, a diffusion coefficient of was measured at 550 °C. We discuss the diffusion mechanism involved during the cluster growth and the origin of the faster surface diffusion of copper on the β-Ta substrate as compared to the α-Ta phase.     

The hole concentration on oxygen sites in the highT c superconductor Y1−Ba2−Cu3−O7−x

From XPS core level spectroscopy the average copper charge on the Cu sites in the high temperature superconductor Y₁Ba₂Cu₃O_7–x is determined as function of the oxygen vacancy concentrationx. Analysis of these data leads to the suggestion that there are holes on the oxygen sites in the basal plane of the crystal structure. The probability for holes on these oxygen ions is rather constant for 0x0.3 with a value of 0.64 and decreases to zero forx=0.5. The dependence of the superconducting transition temperature on the hole concentration is discussed. An energy level diagram for Cu²⁺ and Cu³⁺ in YBa₂Cu₃O_7–x is constructed.     

A new model for ZnO:Cu undergoing dynamic Jahn-Teller coupling

In the paper we present a unifying model for the dominant copper impurity in ZnO: Neutral copper atoms at interstitial sites with octahedral symmetry have the electron configuration 3d² 4s ¹ 4p ². They undergo a weak dynamic Jahn-Teller coupling. The vibronic states are² P,⁴ P and⁶ P. Electric dipole transitions coupled to vibration modes give rise to IR and visible absorption bands, showing vibrational progressions. The splitting factors of the various states are calculated by means of the Landé rule which is slightly modified by a reduction of the orbital momentum. The experimental findings concerning IR stimulated fluorescence and electrical conductivity can also be understood within the frame of this model.     

Translation of J. D. van der Waals' “The thermodynamik theory of capillarity under the hypothesis of a continuous variation of density”

Van der Waals justifies the choice of minimization of the (Helmholtz) free energy as the criterion of equilibrium in a liquid-gas system (Sections 1–4). If density is a function of heighth then the local free energy density differs from that of a homogeneous fluid by a term proportional to (d ² /dh ²); the extra term arises from the energy not from the entropy (Section 5). He uses this result to show how varies withh (Section 6), how this variation leads to a stable minimum free energy (Section 7), and to calculate the capillary energy or surface tension (Section 9). Near the critical point varies as ( _k -)^3/2, where _k is the critical temperature (Section 11). The paper closes with short discussions of the thickness of the surface layer (Section 12), of the difficulty of assuming that varies discontinuously with height (Section 14), and of the possible effect of derivatives of higher order than (d ² /dh ²) on the free energy and surface tension (Section 15).Originally published (in Dutch) inVerhandel. Konink. Akad. Weten. Amsterdam (Sect. 1), Vol. 1, No. 8 (1893).     

Hyperthermal surface-collisions of water cluster cations

Size-selected, protonated water cluster cations (H₂O)_nH⁺, 4 n 32, are scattered at normal incidence from the surface of a diamond-coated silicon wafer at collision energies 0 E _coll 500 eV. The size distribution of collision-induced fragment-ions and the ion yield of scattered particles are analyzed, using a secondary time-of-flight mass spectrometer, as a function of the cluster size, n, and the collision energy, E _coll. Even at low impact energies only very small fragment-ions can be detected, with a maximum fragment size of 35% of the colliding parent cluster ions. For clusters consisting of more than 10 molecules, the protonated water dimer (H₂O)₂H⁺ becomes the predominant fragment-ion. The total charge survival yield obeys a nonlinear increase with cluster size; for the largest clusters investigated, more than 35% of the impacting ions survive the surface collision in the cationic charge state.