Dependence Of Sputtering Yield Research Articles

Study of the dependence of light ion sputtering yields of carbon-modified surface titanium layers on their thickness

A theoretical sputtering model based on two mechanisms is used in this work to investigate the dependence of light ion sputtering yields of carbon-modified surface titanium layers on their thickness. The model used allows not only to correctly describe the nonlinear dependence of the sputtering yields on the layer thickness, but also to analyze the resulting dependencies. Calculations of the total sputtering yields of helium and hydrogen ions of surface layers of titanium modified with carbon are given in comparison with the results of computer simulations.

Total and Differential Sputtering Yields Explored by SRIM Simulations

Total sputtering yield and spatial distributions of sputtered atoms are important for numerous deposition techniques. We performed SRIM (Stopping and Range of Ions in Matter) simulations to analyze the total sputtering yield and angular distribution of sputtered atoms for a range of single-element target materials. The simulations were conducted for normal argon ion incidence in the 300–1200 eV range and at an oblique angle for selected ion energies. We examined the total and differential sputtering yields for the transition metals in the periods 4–6 and groups 4–6 (Ti, V, Cr; Zr, Nb, Mo; Hf, Ta, and W) and group 11 (Cu, Ag, and Au) of the periodic table, and other materials that are relevant to sputtering (B and C; Al and Si). For the transition metals, the total sputtering yield increases with the group of the periodic table. The elements in group 4 (i.e., Ti, Zr, and Hf) have the lowest sputtering yield, while the elements in group 11 (i.e., Cu, Ag, and Au) exhibit the highest sputtering yield. The angular distribution of the sputtered atoms shows a cosine distribution for the transition metal atoms. The angular distribution of the sputtered atoms for the oblique ion incidence is more asymmetric for the lower ion energies, while for the higher ion energies, the atoms are sputtered more symmetrically. The symmetry also depends on the group of the periodic table and the atomic mass of the target material. The elements in group 11 show the most symmetric distribution, while the elements in group 4 experience the most asymmetric distribution. Furthermore, in an individual group, the distribution becomes more symmetric with heavier target elements. We also examined in detail the influence of the surface binding energy, atomic mass, and ion energy on the total sputtering yield. These parameters were analyzed with regard to the simplified analytical formula for the total sputtering yield, which was derived by Sigmund. This formula was modified by introducing a power fitting parameter, which accounts for the non-linear sputtering yield dependence on the ion energy. The equation provided good estimates for the total sputtering yield of the transition metals that were sputtered by argon ions with energies up to 1200 eV.

Study of surface evolution via Modified Ion Beam Sputtering Semi-Empirical Model (MIBSEM)

An Ion Beam Sputtering Monte Carlo Model (IBSM) was modified to study the effect of different surface diffusion mechanics on the surface height and surface roughness of materials when bombarded with energetic ions. The extension was done by incorporating Seahet al.’s semi-empirical ion sputtering equations into the sputter erosion algorithm of the MC model and by enforcing curvature dependence of sputter yield. Also, TRansport of Ions in Matter (TRIM) software, was used to calculate the sputter yield and the values obtained were compared with those obtained from Seahet al.’s semi-empirical model and the sputter yield obtained from sputtering experiments. Our studies show that the surface diffusion mechanics that occurs during a sputtering process controls the substrate surface height and its roughness while curvature dependence of sputter yield has little or no contribution to the target surface height and its roughness. Our comparison of the calculated sputter yield values of TRIM and Seahet al.’s model with experimental sputter yield values show that Seahet al.’s model gives sputter yield values closer to experimental values than TRIM at a normal angle of incidence while TRIM gives sputter yield values closer to experimental values at 60°angle of incidence.

Molecular Dynamics Simulations and Ion Beam Treatment of Polyethylene

A polymer like polyethylene (PE) has attracted intense research exploits in recent years due to their inherent versatile properties like high optical clarity, mechanical properties, light weight and high packing density. PE is the simplest of all commercial polymers used for making catheters, meshes, artificial joint, drug delivery packages (biomedical applications), light emitting diode, electrical bio-sensing, solid state battery, and plastic containers. Over the years, several techniques have been employed to enhance the properties of the polymer surface which include surface etching, laser deposition, plasma deposition, ion implantation technologies and doping. However, this study is concerned with ion-beam sputtering of PE to investigate its sputtering yield dependence. Moreover, molecular dynamics simulations of a PE system were performed to deduce the thermodynamics properties of the system at relatively high temperature (700 K). The results show that the sputtering yield of PE system is dependent on the incident angles and the ion energies. Additionally, the peak of the sputtering yield was found to be around 83° incident angle. Also, the temperature of the PE system varies with the time steps imposed on it. Finally, the structural and dynamical properties of the PE show minimal fluctuations as the density of the polymer linearly increases across the duration.

Effect of surface diffusion algorithm on nanostructure formation in a semi-empirical Monte Carlo model of sputter erosion of materials

A semi-empirical ion sputtering model (SEISM) was extended for clearer ripple profiles on material surfaces on which atoms self-organise into rippled topography. The improvement was by way of modifying the sputter erosion algorithm with implementation of the curvature dependence of sputter yield and the avoidance of shadowing effect. And by way of modifying surface relaxation through adaptation of a surface diffusion algorithm that is popular in Monte Carlo simulations of material growth by particle deposition (growth of thin films) as a replacement for the surface reorganisation algorithm of the SEISM. Prior to these extensions, the SEISM model exhibited some characteristic properties of sputtered surfaces but gave indistinct ripples. With the extensions, the model gives a clearer indication of distinct ripple topographies. Specifically, surface stability was improved when the original surface reorganisation algorithm of the SEISM was replaced.

Correlation between Magnetron Discharge and Characteristics of Alloy (Ti,Cu)N Nano-Structure Thin Films

Reactive magnetron sputtering using an alloy TiCu target and nitrogen as working gas was utilized to deposit ternary (Ti,Cu)N thin films. The aim of present work is to provide insight into the significance of nitrogen pressure, Ti addition, reflected neutral particles and energy flux on the characteristic of (Ti,Cu)N films.The ion induced secondary electron emission and surface poisoning of TiCu target were studied using I- V characteristic of magnetron discharge. The dependence of sputtering yield of Cu, Ti and TiCu target on incident angle of ions was simulated. Elemental titanium to copper (Ti:Cu) ratio in (Ti,Cu)N films was estimated using a model based on sputtering and mass transport. An estimation of energy flux due to reflected N neutrals toward substrate was presented. The structural analysis was identified using X- ray diffraction (XRD) technique. Phase identity is strongly depending on nitrogen pressure. Ti accommodation to Cu3N structure results in lattice constant expansion and (100) preferential orientation (texture growth). The Bonding environment of pure and Ti inserted Cu3N thin films were obtained from Raman spectroscopy. The Surface morphology and chemical composition of the films were studied by scanning electron microscope/energy dispersive X-ray spectroscopy (SEM/EDX), respectively. Ti addition deforms pyramidal- like grains to spherical ones. The optical study was performed by UV- Vis- near IR transmittance spectroscopy. Ti addition to Cu3N structure kills indirect semiconducting transition and governs the direct bandgap around 2.75 eV. Ti entrance results in interstitial N excess (N-richness) which acts as acceptor centers cause to hole injection to valence band (excited semiconductor) and bandgap widening. Electrical resistance of (Ti,Cu)N thin films shows quasi-metallic behavior. Grain boundary sliding causes to decrease in hardness of (Ti,Cu)N thin films.

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.

Depth Resolution, Angle Dependence, and the Sputtering Yield of Irganox 1010 by Coronene Primary Ions

A study is reported of the depth resolution and angle dependence of sputtering yields using the reference organic material, Irganox 1010, for a new coronene(+) depth profiling ion source at 8 and 16 keV beam energies. This source provides excellent depth profiles as shown by 8.5 nm marker layers of Irganox 3114. Damage occurs but may be ignored for angles of incidence above 70° from the surface normal, as shown by X-ray photoelectron spectroscopy (XPS) of the C 1s peak structure. Above 70°, XPS profiles of excellent depth resolution are obtained. The depth resolution, after removal of the thickness of the delta layers, shows a basic contribution of 5.7 nm together with a contribution of 0.043 times the depth sputtered. This is lower than generally reported for cluster sources. The coronene(+) source is thus found to be a useful and practical source for depth profiling organic materials. The angle dependencies of both the undamaged and damaged materials are described by a simple equation. The sputtering yields for the undamaged material are described by a universal equation and are consistent with those obtained for C60(+) sputtering. Comparison with the sputtering yields using an argon gas cluster ion source shows great similarities, but the yields for both the coronene(+) and C60(+) primary ion sources are slightly lower.

Sputtering of a coarse‐grained benzene and Ag(111) crystals by large Ar clusters – effect of impact angle and cohesive energy

Molecular dynamics computer simulations are employed to investigate the role of the substrate cohesive energy on the impact angle dependence of the sputtering yield for Ar60 and Ar2953 projectiles bombarding a benzene molecular solid and a Ag(111) atomistic sample. A different dependence of the total sputtering yield on the impact angle is observed for small and large projectiles for benzene, while a similar dependence is observed for Ag(111). It is demonstrated that the increase of the cohesive energy leads to a significant decrease of the total ejection signal for both Ar60 and Ar2953 projectiles. The shape of the impact angle dependence, however, is much less sensitive to this parameter. The ‘washing out’ mechanism and the structural differences of the irradiated samples are proposed to be responsible for the different shapes of the impact angle dependence. Copyright © 2012 John Wiley & Sons, Ltd.

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.

Deterministic fabrication of nanostructures for plasmonic lens by focused ion beam

Plasmonic lens is a key component in the development of sub-wavelength resolution optical system for bio-imaging and nanolithography applications. In order to develop a deterministic fabrication capability for nanostructures on plasmonic lens by using focused ion beam, this paper presents a highly robust and accurate surface topography model based on level set method. Sputtered atom distribution and angular dependence of sputter yield are calculated by Monte Carlo simulation programs SRIM/TRIM and TRIDYN, respectively. Redeposition effect is included in the physical model and successfully embedded into a topography simulation program by applying the level set method. The proposed model is validated and evaluated in the focused ion beam fabrication experiments. Simulation error of less than 7% is obtained. Two types of nanostructures for plasmonic lens were fabricated using the machining parameters approved by this simulation model. Simulation errors of 7 and 2 nm were found in a nanodots array and a spiral Bragg grating, respectively. The results clearly demonstrate the effectiveness of the modelling approach developed for deterministic fabrication of nanostructures.

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 of low-energy sputtering of Pt (111) surface by oblique Ni atom bombardment

The low-energy sputtering on Pt (111) surface by Ni atom at incident angle in a range of 0 80 (with respect to the direction normal to the surface) is studied by molecular dynamics simulations. The atomic interaction potential obtained with embedded atom method is used in the simulation. The dependence of sputtering yield, energy and angular distribution of sputtered particles as well as sticking probability of Ni atom on incident angle are discussed. The dependence of sputtering yield on incident angle can be divided into three different regions in , i.e., 20, 20 60, and 60. Based on sticking probability and movement of incident atom, physical mechanism of low-energy sputtering at oblique particle bombardment is suggested. When the incident angle is smaller than 20, the reflection of incident atom by target atom dominates the sputtering process of surface atom, which is similar to the sputtering mechanism for the case of = 0. While for 20 60, the reflection of incident atom is no longer important for the low-energy sputtering. For the case of 60, there occurs no sputtering.

Effect of impact angle and projectile size on sputtering efficiency of solid benzene investigated by molecular dynamics simulations

Molecular dynamics computer simulations have been used to investigate the effect of the cluster size on the sputtering yield dependence on the impact angle. Ar366 and Ar2953 cluster projectiles with 14.75keV of incident energy are directed at the surface of a solid benzene crystal described by a coarse-grained representation at angles between 0° and 70°. It is observed that the shape of the angular dependence of sputtering efficiency is strongly affected by the cluster size. For the Ar366 cluster, the sputtering yield only slightly increases with the impact angle, has a broad maximum around 40°, and decreases at larger angles. For the Ar2953 cluster, the yield strongly increases with the impact angle, has a maximum around 45° followed by a steep decrease at larger angles. For both investigated cluster projectiles the primary energy is deposited so close to the surface so that the sputtering efficiency only weekly benefits from the shift of the deposited energy profile toward the surface which occurs at larger impact angles. In this study, molecular dynamics computer simulations are used to probe the effect of the impact angle on the efficiency of ejection molecules emitted from solid benzene by 14.75keV Ar366 and Ar2953 clusters.

Erosion of Ag surface by continuous irradiation with slow, large Ar clusters

Molecular dynamics computer simulations are employed to probe processes taking place during continuous irradiation of Ag(111) surface by keV Ar872 projectiles. Surface modification, the total sputtering yield, and the angular distributions of ejected species are calculated at fluences ranging from 0 up to ∼6×1013impacts/cm2. It has been shown that two trends can be identified in the development of surface roughness. At the beginning surface roughness increases fast. This fast increase terminates around 1×1013impacts/cm2 and is followed by a slow increase that finally saturates. The effect of the surface roughness on the sputtering yield depends on the impact angle. At normal incidence the sputtering yield is rather insensitive to the development of the surface topography. Modification of the surface morphology has, however, a significant influence on the total sputtering yield at large impact angles. Both the shape of the sputtering yield dependence on the impact angle and the angular spectra of ejected particles are sensitive to the surface roughness.

Dwell time dependent morphological transition and sputtering yield of ion sputtered Sn

Self-organized nano-scale patterns may appear on a wide variety of materials irradiated with an ion beam. Good manipulation of these structures is important for application in nanostructure fabrication. In this paper, dwell time has been demonstrated to be able to control the ripple formation and sputtering yield on Sn surface. Ripples with a wavelength of 1.7 µm were observed for a dwell time in the range 3–20 µs, whereas much finer ripples with a wavelength of 540 nm and a different orientation were observed for a shorter dwell time in the range 0.1–2 µs. The sputtering yield increases with dwell time significantly. The results provide a new basis for further steps in the theoretical description of morphology evolution during ion beam sputtering.

Sputtering effects during plasma immersion ion implantation of metals

Changes in the surface topography during ion bombardment are a ubiquitous effect, which is nevertheless sparsely understood, especially for polycrystalline metals. Beside nucleation and grain growth processes, sputtering of individual atoms is the dominant factor. Here, the development of the surface topography is investigated for austenitic stainless steel and CoCr alloy using oxygen, nitrogen or argon ion bombardment. For a better quantification with 3D optical profilometry, a time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used for the experiments. Beside an orientation dependent sputter yield, inversely correlated with the positive secondary ion yield for the present fcc metals, an increase in the nanoroughness with increasing fluence was observed, with the effect much more pronounced for CoCr than for stainless steel. No significant influence of the ion species was observed. In addition, an increased roughness is observed during PIII nitriding, depending on the incident ion flux. Here, the combined roughness from nitriding and SIMS depth profiling leads to a broadening of the nitrogen profile edge, which has to be corrected for.

Determination of angle dependence of sputtering yield for a multicomponent target by the time characteristics of the sputtering process

A method for determining the variations of sputtering yield of multicomponent target based on studies of time characteristics of the sputtered particles flux has been proposed and tested on an example of the angle dependence of sputtering yield. Time dependences of variation in the fluxes of the sputtered atoms of multicomponent oxides at different incidence angles of Ar ions were studied. Angular dependences of the sputtering yield for these compounds were obtained by direct measurements and computations. It has been shown that the angular dependence of the sputtering yield in a stationary mode can be obtained from the time dependences of the fluxes of the sputtered particles.