Angular Dependence Of Sputtering Yield Research Articles

Model to estimate fractal dimension for ion-bombarded materials

Comprehensive fractal Monte Carlo model ITMC-F (Hu and Hassanein, 2012 [1]) is developed based on the Monte Carlo ion bombardment simulation code, i.e., Ion Transport in Materials and Compounds (ITMC) code (Hassanein, 1985 [2]). The ITMC-F studies the impact of surface roughness on the angular dependence of sputtering yield. Instead of assuming material surfaces to be flat or composed of exact self-similar fractals in simulation, we developed a new method to describe the surface shapes. Random fractal surfaces which are generated by midpoint displacement algorithm and support vector machine algorithm are combined with ITMC. With this new fractal version of ITMC-F, we successfully simulated the angular dependence of sputtering yield for various ion-target combinations, with the input surface roughness exponent directly depicted from experimental data (Hu and Hassanein, 2012 [1]). The ITMC-F code showed good agreement with the experimental data. In advanced, we compare other experimental sputtering yield with the results from ITMC-F to estimate the surface roughness exponent for ion-bombarded material in this research.

How surface roughness affects the angular dependence of the sputtering yield

Comprehensive model is developed to study the impact of surface roughness on the angular dependence of sputtering yield. Instead of assuming surfaces to be flat or composed of exact self-similar fractals, we developed a new method to describe the surfaces. Random fractal surfaces generated by midpoint displacement algorithm in computer graphics area and Support vector machine algorithm in pattern recognition area are combined with the Monte Carlo ion bombardment simulation code, i.e., Ion Transport in Materials and Compounds (ITMC) code [1]. With this new fractal version of ITMC-F, we successfully simulated the angular dependence of sputtering yield for various ion-target combinations. Examples are given for 5keV Ar ions bombarding iron, graphite, and silicon surfaces, with the input surface roughness exponent directly depicted from experimental data. Comparison is made with previous models to account for surface roughness and recent experimental data. The ITMC-F code showed good agreement with the experimental data.

Numerical Study of Hall Thruster Plume and Sputtering Erosion

Potential sputtering erosion caused by the interactions between spacecraft and plasma plume of Hall thrusters is a concern for electric propulsion. In this study, calculation model of Hall thruster’s plume and sputtering erosion is presented. The model is based on three dimensional hybrid particle-in-cell and direct simulation Monte Carlo method (PIC/DSMC method) which is integrated with plume-wall sputtering yield model. For low-energy heavy-ion sputtering in Hall thruster plume, the Matsunami formula for the normal incidence sputtering yield and the Yamamura angular dependence of sputtering yield are used. The validation of the simulation model is realized through comparing plume results with the measured data. Then, SPT-70’s sputtering erosion on satellite surfaces is assessed and effect of mass flow rate on sputtering erosion is analyzed.

An investigation of redeposition effect for deterministic fabrication of nanodots by focused ion beam

► A 3D surface topography model and simulation program was developed to imitate the focused ion beam machining process. ► The simulation program was a good tool to determine machining parameters for deterministic fabrication by focused ion beam. ► Redeposition effect reduced more than 1/3 of intended depth of the nanodots machined by focused ion beam. Focused ion beam machining is a powerful technique for micro/nanofabrication. However its machined surface form accuracy will be degrade due to atoms redeposition in the nanofabrication process. In this paper, a 3D surface topography model and associated simulation program are developed to study redeposition effect for precise and deterministic fabrication of nanodots by focused ion beam. The simulation is implemented by level set method. The angular dependence of sputtering yield is calculated by a Monte Carlo simulation program – TRIDYN. The simulation results have been evaluated by focused ion beam fabrication of nanodots experiment on a silicon substrate. It demonstrates that the simulation method can precisely describe the generation of 3D surface in focused ion beam machining process (with less than 10% simulation error). Redeposition has made significant contribution to the surface generation in nanoscale fabrication by reducing more than 1/3 of intended depth. The model and simulation program developed has approved to be a good tool to determine proper machining parameter to achieve deterministic nanofabrication by focused ion beam.

Dependence of the self-sputtering yield upon ion incidence angle

Solution of the problem of angular dependence of sputtering yield is divided into three parts: calculation of the number of cascade particles as a function of their path length, definition of the path length distribution of reflected particles, and convolution of the two results obtained. The theory is valid for the case of equal ion and target atom masses (self-sputtering) and contains two parameters: the ratio of the transport path length to the mean free path length and the parameter of inelastic energy losses.

Molecular dynamics simulation analyses on injection angle dependence of SiO 2 sputtering yields by fluorocarbon beams

Angular dependence of sputtering yields of SiO 2 substrates subject to CF 3 beam injections is evaluated with the use of molecular dynamics simulations. The obtained sputtering yield data are in reasonable agreement with experimental observations. Atomic compositions in the SiO 2-CF mixing layer as well as kinetic energies and atomic compositions of sputtered species also exhibit strong dependence of the injection angle.

The effect of microrelief evolution on the angular dependence of polycrystalline Cu sputtering yield

The dynamically steady-state surface relief of polycrystalline copper sputtered by high-dose (1018–1019ion/cm2) 30keV Ar+ ion bombardment at room temperature has been traced as a function of the ion incidence angle θi in a wide (0–80°) angular range. For each incidence angle the distribution of local slope angles of relief facets f(β) in ion incidence plane and the corresponding distribution of the local angles of incidence w(θ) have been measured using the laser goniophotometry (LGP) technique. It has been found that the distribution f(β) has a narrow peak at grazing ion incidence, two wide peaks at oblique, and three peaks at normal ion incidence. The obtained results are discussed in terms of the theory of surface erosion under ion bombardment. A correction to the angular dependence of the sputtering yield was produced using the OKSANA computer code simulation for a smooth copper surface and the measured distributions w(θ). The experimental data and the calculation results agree well in the angular range θi=0−60°. At θi>60° the experimental points are close to the simulated curve for a smooth surface.

A sputtering calculation: Angular dependence of sputtering yields

The material erosion induced by physical sputtering resulted from bombardments of hydrogen, helium and their isotopes is a critical problem for fusion technique. An important feature for such ion-induced sputtering is isotropic incidence condition. Therefore it is necessary to develop a sputtering theory which can be applied to the case of obliquely incident ion beams. The sputtering theory based on the bipartition model of ion transport has recently extended to treat the problem of sputtering calculation for the case of obliquely incident ion beam. In the present paper some calculation results have been given out. Comparison shows that the angular dependence of sputtering yields given by the bipartition model is in reasonable agreement with that given by TRIM-SP Monte Carlo code and experimental measurements.

On the Angular Dependence of Bombardment Induced Light Emission

Ion bombardment of solid targets leads to the emission of light either from sputtered or backscattered particles or from the solid materials [1]. Since a fraction of the sputtered particles leaves in some excited state and participates in the photon emission, it is of interest to compare the dependence of the sputtering yield on various parameters with the analogous dependence of light emission. Though the mechanisms of sputtered-atom excitation are not well understood, it is often assumed that the energy distributions of sputtered atoms in the excited state and in the ground state are identical. This implies that the light intensity from the sputtered atoms should be proportional to the total sputtering yield as it is evident from the energy dependence of light intensity measurements [2]. However, some recent experiments [3, 4] show that such a correspondence may not be always valid. In this communication, the angular dependence of excited atom yields is compared , to that of the total sputtering yield in order to test further the relation of atomic excitation with the sputtering process. Qualitatively, a typical angular dependence of photon yield curve is found to be similar to that of the neutral sputtering yield, i.e. the yield first rises monotonically with θ, the angle of ion incidence with respect to the surface normal, passes through a maximum at θ typically 60°-80° and then decreases sharply as θ approaches 900. For not-toooblique incidence, Sigmund [5] predicted a (cos θ) f dependence rather than the normally expected (cos θ) -1 trend, where 1 < f < 2. Quite recently, Yamamura [6] proposed an empirical formula containing two adjustable parameters for the angular dependence of sputtering yield covering the whole angular range. One of the parameters corresponds to Sigmund's f, while the other is related to O.

The angular dependence of sputtering yields of Ge and Ag

The angular dependence of physical sputtering yields of Ge and Ag was investigated for 30 keV Ar + and Kr + ion bombardment. It is found that Ag exhibits a weaker angular dependence, though its sputtering yield is higher than that of Ge. The results are compared to the existing theoretical and empirical formulas.

Angular dependence of sputtering yield of TiSi2 layers and analysis of titanium disilicide by SIMS and SCANIIR methods

AbstractThe values of sputtering yields of TiSi2, Ti and Si layers are determined for Ar+ (8 keV) bombardment at angles 0–80°. It is shown that the theoretical functions that we have suggested for TiSi2 sputtering yields from angular Ar+ bombardment, which are based on models of bicomponent compounds sputtering under normal ion bombardment, are in good agreement with the experimental curve for TiSi2.The calibration curves for the determination of TiSix layer compositions by SIMS and SCANIIR methods (in dynamic regime) are presented. It is shown with the help of the static SIMS method (E = 3 keV) that not only can the TiSix composition be determined but the TiSi2 crystal phase can also be identified.

The interdependence between the incidence angles associated with quasi-stable intersections during ion erosion

A general discussion, which is valid for any angular dependence of sputtering yieldS=S(θ), concerning the interdependence between the incidence anglesθe andθ0, associated with quasi-stable intersections during ion erosion, is given. The object was firstly to establish the location ofθe roots as a function ofθ0 and secondly to identify the stationary points and general trend for the complex dependenceθe=θe(θ0). The results obtained are applied to a quasi-stability analysis of some specific surface features during ion erosion. Various possible types of quasi-stable intersections (surface-surface, plane-surface, plane-plane) are reviewed from the point of view of their evolution caused by ion bombardment.

An empirical formula for angular dependence of sputtering yields

Abstract An analytic empirical formula for the angular dependence of light-ion sputtering and heavy-ion sputtering has been proposed. The present empirical formula has two adjustable parameters which are determined by the least-squares method. One of the two parameters corresponds to Sigmundf, and the other is the angle of incidence at the maximum yield. The present empirical formula is found to be very useful for preliminary descriptions of the angular dependence of sputtering yield. This work was carried out under the collaborating Research Program at the Institute of Plasma Physics, Nagoya University. Lindhard's theory of the nuclear stopping power is developed to take into account the binding force between the lattice atoms of solids. It is shown that the nuclear stopping power is proportional to the velocity (not the energy) of the moving atom at the low velocity limit. Debye temperature dependence of the nuclear stopping power is discussed.

Angular Dependence of Sputtering Yield of Au on Bombardment by 15 to 60 keV Ar+

The angular dependence of the sputtering yield of Au on bombardment by 15 to 60 keV Ar+ has been studied experimentally. The increase in the sputtering yield as the angle θ of the incident beam is tilted from the normal is proportional to (cos θ)-1. A critical angle at which the sputtering yield deviates from (cos θ)-1 dependence is derived, and its dependence on the ion energy is compared with the results calculated from a model of the reflection of ions at the vacuum/target interface.