Incident angle dependence of electronic desorption and sputtering by energetic ions

It is shown that deviations of the dependence of sputtering yield on the incident angle, θ, from the standard (cos θ)⁻¹ dependence can be indicative of a depth dependence in the net energy deposition in the surface region. Information about the sputter ejection mechanism is shown to be obtained only secondarily. We give expressions that allow one to relate the measured dependence of the yields on angle of incidence to the dependence of energy deposition on depth. This is used to analyze results for condensed gas sputtering and heavy ion desorption of organic molecular ions. This analysis indicates that the spatial distribution of excitations produced by the secondary electrons is important in determining these yields. This is also confirmed by observed differences in the yields for transmission and back-sputtering which is a closely related effect.     

Temperature dependence of the sputtering yield of surface metal clusters

The method of molecular dynamics has been used to investigate the influence of thermal oscillations of atoms on the sputtering of surface metal nanoclusters. The sputtering of a copper cluster consisting of 75 atoms from the (100) surface of a copper substrate by 200-eV argon ions for the target being at an equilibrium temperature of 0 and 300 K has been simulated. For each temperature, the sputtering yields have been predicted for both the substrate and the cluster and the polar and azimuthal angular distributions of sputtered atoms have been obtained. The procedure of simulation of two-object cluster-substrate systems at equilibrium temperatures other than 0 K is discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 20–25, July, 2007.     

On the fluence dependence of the sputtering yield for low-energy noble gas ions

The fluence dependence of the sputtering yield has been studied on amorphous silicon under uhv conditions with 0.5 to 5keV Ar⁺ using the KARMA technique (Kombinierte Auger/Röntgen Mikro-Analyse). It allows to measure simultaneously the surface composition, the differential sputtering yield, and the total amount of implanted gas. For all energies, the yield increases initially and reaches saturation after the removal of a layer the thickness of which is closely correlated to the ion range. Gas implantation as a cause for these fluence effects can be ruled out by quantitative analysis. The relative yield increase is found to be larger for low energies than for higher ones. Both these findings can be qualitatively explained by a simple damage collection model.     

The dependence of sputtering efficiency on ion energy and angle of incidence

Abstract

Earlier measurements of sputtering efficiency of polycrystalline targets (fraction of impinging ion energy leaving the target through sputtering and backscattering) have been extended to higher energies. Lead and copper targets were bombarded with several different projectiles with energies between 80 and 1200 keV. The sputtering efficiency decreases with increasing energy. This decrease is ascribed to the combined influence of changes in the scattering cross section with energy, and to electronic stopping. The results may be described as a function of the mass ratio M ₂/M ₁ and the reduced energy ? only.

The sputtering efficiency was measured as a function of angle of incidence of the bombarding ions. To ensure complete collection of sputtered and backscattered particles, it was possible to cover only the region of incidence angle from 0° to 45°. Targets of copper, silver, and lead were investigated with 17 different ion-target combinations. The sputtering efficiency increased with angle of incidence. This increase is described well by a simple interpolation formula by Sigmund.     

Temperature dependence of angular characteristics of boron nitride sputtering

The angular dependence of the sputtering yield and the spatial distribution of particles ejecting from a boron nitride polycrystal with a wurtzite structure in the temperature range from 0 to 2800°C under bombardment with 300 eV xenon ions are calculated by the molecular dynamics method. A reduction of steepness of the curves of angular dependence of boron nitride sputtering with increasing temperature is revealed. Features of the obtained distributions are analyzed on the basis of mechanisms of interaction of slow heavy ions with surface target atoms.     

A measurement of the energy dependence of the inclusive yield of high-Pt events triggered by a large solid angle calorimeter

Large aperture calorimeter measurements of high transverse momentum events from 100, 200 and 340 GeV pp collisions are reported. Yields are higher by one to two orders of magnitude than the yield expected from uncorrelated statistical fluctuations in multiparticle events. The exponential slopes of the yields versus x_t exhibited a systematic change with $\text{s}\text{(x}{}_{\mathrm{<mtext>t</mtext>}}\text{= 2P}{}_{\mathrm{<mtext>t</mtext>}}\text{/}\text{s}\text{)}$. The events are shown to be more diffuse than pure jets as produced in e⁺e^? collisions. However, these events are consistent with a QCD-inspired 4-jet model.     

Determination of the mean energy of backscattered electrons in dependence on the exit angle

A semiconductor detector was used to measure the mean energy of backscattered electrons as a function of the exit angle. New regularities of electron backscattering were found. A nonmonotonic dependence of the mean energy of backscattered electrons on the exit angle and the primary electron energy for materials with different atomic numbers was revealed.     

The dose dependence of 45 keV V+ and Bi+Ion sputtering yield of copper

The sputtering yield of 45 keV V⁺ ions on copper is found to decrease with increasing dose even for very large doses, whilst the yield of 45 keV Bi⁺ ions on copper increases with increasing dose until approximately ten times the projected range of the Bi⁺ ions has been sputtered away. The fate of the incoming V⁺ and Bi⁺ ions was investigated. A radiotracer technique showed that vanadium accumulated on the target surface, whilst bismuth diffused into the target, as was seen by means of Rutherford-scattering of light ions.     

A general expression of the steady state composition for multicomponent system during ion sputtering

A general expression of the steady state composition during sputtering has been derived based on the preferential sputtering model. The resulting formula has been applied to calculate the steady state concentration in a AgAuPd ternary system and the calculated values are in agreement, at least qualitatively, with the experimental data.     

Correlation analysis of the beam angle dependence for elastography

Signal decorrelation is a major source of error in the displacements estimated using correlation techniques for elastographic imaging. Previous papers have addressed the variation in the correlation coefficient as a function of the applied compression for a finite window size and an insonification angle of zero degrees. The recent use of angular beam-steered radio-frequency echo signals for spatial angular compounding and shear strain estimation have demonstrated the need for understanding signal decorrelation artifacts for data acquired at different beam angles. In this paper, we provide both numerical and closed form theoretical solutions of the correlation between pre- and post-compression radio-frequency echo signals acquired at a specified beam angle. The expression for the correlation coefficient obtained is a function of the beam angle and the applied compression for a finite duration window. Accuracy of the theoretical results is verified using tissue-mimicking phantom experiments on a uniformly elastic phantom using beam-steered data acquisitions on a linear array transducer. The theory predicts a faster decorrelation with changes in the beam or insonification angle for longer radio-frequency echo signal segments and at deeper locations in the medium. Theoretical results provide useful information for improving angular compounding and shear strain estimation techniques for elastography.     

An analysis of the dependence of saccadic latency on target position and target characteristics in human subjects

Background  

Predictions from conduction velocity data for primate retinal ganglion cell axons indicate that the conduction time to the lateral geniculate nucleus for stimulation of peripheral retina should be no longer than for stimulation of central retina. On this basis, the latency of saccadic eye movements should not increase for more peripherally located targets. However, previous studies have reported relatively very large increases, which has the implication of a very considerable increase in central processing time for the saccade-generating system.     

转动传能中干涉相位角的时间特性

不同碰撞系统在碰撞过程中转动传能的量子干涉角度并不相同.而对干涉角的计算需采取最符合系统的相互作用势.从含时微扰的一级波恩近似出发,利用各向异性相互作用势,进一步研究了CO单三混合态在和He做碰撞伴时其跃迁振幅和干涉相位角的时间特性,计算显示跃迁振幅随时间显现衰减的震荡;对于给定的碰撞参数和碰撞速度,跃迁振幅变化非常明显并与跃迁前后的状态、能级差相关.     

转动传能中干涉相位角的时间特性

不同碰撞系统在碰撞过程中转动传能的量子干涉角度并不相同。而对干涉角的计算需采取最符合系统的相互作用势。从含时微扰的一级波恩近似出发,利用各向异性相互作用势,进一步研究了CO单三混合态在和He做碰撞伴时其跃迁振幅和干涉相位角的时间特性,计算显示跃迁振幅随时间显现衰减的震荡;对于给定的碰撞参数和碰撞速度,跃迁振幅变化非常明显并与跃迁前后的状态、能级差相关。     

Determination of time dependence of domain growth by direct observation of small metal clusters

The in situ growth of small gold clusters on amorphous carbon substrates has been measured by direct observation, utilizing high (single-atom) resolution scanning transmission electron microscopy. The time dependence of the width of the distribution of characteristic microscopic spatial frequencies in the samples was seen to obey a power-law behavior, HWHM = (t − t₀)^−a. The exponent measured, a = 0.15 ± 0.06, was in good agreement with scaling theories for domain growth. An excess of single atoms and small clusters was observed at all times, over that predicted by a uniform growth model of clusters. It is suggested that these support single-atom and few-atom cluster migration and activated accretion as important components of cluster growth at all times.     

Electrochromism in tungsten trioxide films obtained by reactive magnetron sputtering of a tungsten target

The results of structural investigations of electrochromic films of WO₃, obtained by reactive magnetron sputtering of a tungsten target, are presented. It is shown that at low temperatures an amorphous film of WO₃ is formed on the substrate. At a substrate temperature greater than 250°C the film that is formed is polycrystalline and has the structure of hydrotungstic bronze H_0.33WO₃. When annealed in air it transfers into the triclinic modification of WO₃. Spectral investigations showed that the electrochromic properties are most pronounced in amorphous films. Films of WO₃, having a polycrystalline structure after annealing in air, practically lose their ability for electrochromic coloration. Institute of High-Current Electronics, Sib. Otd., Russ. Akad. Nauk. Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 5, pp. 3–7, May, 1996.     

Structural and photoluminescence characteristics of ZnO films by room temperature sputtering and rapid thermal annealing process

ZnO thin films deposited on SiO₂/Si substrates at room temperature by sputtering technology were annealed with a rapid thermal annealing process at various temperatures from 200 °C to 900 °C. The physical and optical properties of the ZnO films were investigated by X-ray diffraction, scanning electron microscopy and room-temperature photoluminescence (PL). The surface structures of the thin films showed great variations with increased annealing temperature. The PL spectrum illustrated that a stronger UV emission intensity appeared at an annealing temperature of 500 °C. On the other hand, visible-light emission could be obtained when the ZnO films were annealed above 500 °C and reached a maximum intensity at 900 °C. The possible mechanisms for visible-light emission are discussed. PACS 81.15.Cd; 81.40.Ef; 78.55.-m; 78.55.Et