Surface Sputtering Research Articles

Surface modification by metal ion implantation forming metallic nanoparticles in an insulating matrix

There is special interest in the incorporation of metallic nanoparticles in a surrounding dielectric matrix for obtaining composites with desirable characteristics such as for surface plasmon resonance, which can be used in photonics and sensing, and controlled surface electrical conductivity. We have investigated nanocomposites produced by metal ion implantation into insulating substrates, where the implanted metal self-assembles into nanoparticles. The nanoparticles nucleate near the maximum of the implantation depth profile (projected range), which can be estimated by computer simulation using the TRIDYN code. TRIDYN is a Monte Carlo simulation program based on the TRIM (Transport and Range of Ions in Matter) code that takes into account compositional changes in the substrate due to two factors: previously implanted dopant atoms, and sputtering of the substrate surface. Our study show that the nanoparticles form a bidimentional array buried a few nanometers below the substrate surface. We have studied Au/PMMA (polymethylmethacrylate), Pt/PMMA, Ti/alumina and Au/alumina systems. Transmission electron microscopy of the implanted samples show that metallic nanoparticles form in the insulating matrix. These nanocomposites have been characterized by measuring the resistivity of the composite layer as a function of the implantation dose. The experimental results are compared with a model based on percolation theory, in which electron transport through the composite is explained by conduction through a random resistor network formed by the metallic nanoparticles. Excellent agreement is found between the experimental results and the predictions of the theory. We conclude in that the conductivity process is due only to percolation (when the conducting elements are in geometric contact) and that the contribution from tunneling conduction is negligible.

Molecular dynamics simulations of ion irradiation of a surface under an electric field

The presence of high electric fields may affect significantly the process of sputtering of metal surfaces by energetic ions, especially in the vicinity of rough surface features. The effect can be significant if the energy of ions is fairly low. Moreover, the nanosized rough surface features – invisible to a naked eye, both intrinsic ones due to technological processing of surfaces and those forming because of sputtering – may affect the topology of surface erosion under ion bombardment. In this work we study by means of concurrent electrodynamics–molecular dynamics the sputtering yield of Cu+ ions hitting a flat Cu surface or a nanosized Cu protrusion as a function of both ion energy and electric field strength. The results show that the sputtering yield is significantly enhanced in the presence of an electric field in both cases.

Ethanol photoreactions over Au–Pd/TiO2

A prototype Au–Pd/TiO2 catalyst was prepared, characterized and tested for the photoreaction of ethanol. XPS Au4f and Pd3d indicated that the as-prepared material is composed of metallic Au, metallic Pd as well oxidized Pd (Pd2+). Ar ion sputtering (5 min) of the catalyst surface resulted in almost total reduction of Pd2+ to metallic Pd in addition to considerable reduction of surface Ti cations to Ti3+ and Ti2+ cations; XPS Au4f lines were not affected. Transmission electron microscopic studies indicated that Au particles have a mean particle size of about 3.5 nm while Pd particles are smaller 1–1.5 nm in size. UV excitation of the catalyst in ultrahigh vacuum (UHV) conditions resulted in the formation of acetaldehyde and hydrogen in addition to photodesorption of the reactant ethanol. Hydrogen production, representing ca. 30 % of the desorbing products, was delayed compared to acetaldehyde desorption. This was interpreted as due to kinetic effect whereby initially most electrons transferred to the conduction band are trapped by surface hydroxyls as well inevitable presence of oxygen in the powder accelerating acetaldehyde formation (dehydrogenation). Only once most oxygen-containing species have reacted and molecular hydrogen was formed. To our knowledge, this is the first UHV in situ study of hydrogen production from ethanol photocatalytically over M/TiO2 system.

Changes in the surface morphology induced by 1.0‐MeV Au ion bombardment of Ti and Ti‐6Al‐4V

The effects of surface sputtering by 1.0‐MeV Au ion implantation in commercially pure Ti and its alloy Ti‐6Al‐4V have been studied. These materials are associated with applications in orthopaedic implants. There are few studies that try to explain the ion implantation process of Au in these materials when considering the effects generated on the surface by sputtering, especially at energies of the order of MeV. Discs of these materials were mirror polished and then implanted with 1.0‐MeV Au ions for 4.7 × 1017 ions/cm2 at 45° incident angle with respect to the surface. Part of the eroded material was deposited simultaneously on glass slides to determine their spatial distribution. These discs and the slides were analysed by Rutherford backscattering spectroscopy (RBS), scanning electron microscopy (SEM), optical microscopy and atomic force microscopy. The implanted materials show the initial production of surface ripples that evolve into banded structures. Copyright © 2014 John Wiley & Sons, Ltd.

Sputtering of Lunar Regolith by Solar Wind Protons and Heavy Ions, and General Aspects of Potential Sputtering

New simulation results for the sputtering of lunar soil surface by solar-wind protons and heavy ions will be presented. Previous simulation results showed that the sputtering process has significant effects and plays an important role in changing the surface chemical composition, setting the erosion rate and the sputtering process timescale. In this new work and in light of recent data, we briefly present some theoretical models which have been developed to describe the sputtering process and compare their results with recent calculation to investigate and differentiate the roles and the contributions of potential (or electrodynamic) sputtering from the standard (or kinetic) sputtering.

Fragmentation processes of vanadium and niobium oxide clusters sputtered by ion bombardment

The mass distribution of emitted VnOm− and NbnOm− clusters and their unimolecular decay by all stoichiometrically possible fragmentation channels, which takes place under the sputtering of niobium and vanadium surfaces and blowing by oxygen, are studied. It is shown that the formation, excitation, and unimolecular fragmentation of VnOm− and NbnOm− clusters can be described by a statistical recombination mechanism. Clusters are formed over the target surfaces as a result of binary collisions of independently sputtered ions, atoms, and molecules.

An experiment on the dynamics of ion implantation and sputtering of surfaces

A major impediment towards a better understanding of the complex plasma-surface interaction is the limited diagnostic access to the material surface while it is undergoing plasma exposure. The Dynamics of ION Implantation and Sputtering Of Surfaces (DIONISOS) experiment overcomes this limitation by uniquely combining powerful, non-perturbing ion beam analysis techniques with a steady-state helicon plasma exposure chamber, allowing for real-time, depth-resolved in situ measurements of material compositions during plasma exposure. Design solutions are described that provide compatibility between the ion beam analysis requirements in the presence of a high-intensity helicon plasma. The three primary ion beam analysis techniques, Rutherford backscattering spectroscopy, elastic recoil detection, and nuclear reaction analysis, are successfully implemented on targets during plasma exposure in DIONISOS. These techniques measure parameters of interest for plasma-material interactions such as erosion/deposition rates of materials and the concentration of plasma fuel species in the material surface.

Irradiation effect of gas-hydrate cluster ions on solid surfaces

In our newly developed gas-hydrate cluster ion source, a vapor of water bubbling with carbon dioxide (CO2) gas was ejected through a nozzle into a vacuum region, and mixed beams of water clusters and carbon dioxide-hydrate clusters were produced by adiabatic expansion. According to time-of-flight measurements, the largest water clusters consisted of approximately 2800 molecules at a vapor pressure of 0.3MPa. Also, the largest mixed clusters contained approximately 2000 molecules. Copper and silicon substrates were irradiated by the water cluster ions as well as carbon dioxide-hydrate cluster ions. X-ray photoelectron spectroscopy measurements showed that carbon was included in the Cu and Si substrates irradiated by the carbon dioxide-hydrate cluster ions, and a chemical shift owing to the formation of carboxyl radicals occurred on the Cu surface. Furthermore, the Cu surface was sputtered, and the sputtering depth was larger than the distance penetrated by the water cluster ion irradiation. Therefore, the formation of carboxyl radicals played an important role in the sputtering of the Cu surface, which occurred effectively in carbon dioxide-hydrate cluster ion irradiation.

TRI3DYN – Collisional computer simulation of the dynamic evolution of 3-dimensional nanostructures under ion irradiation

A computer program is described which allows fully three-dimensional dynamic collisional simulations of ion irradiation effects in particular in nanosystems. The program is based on the well-known TRIDYN code which describes dynamic modifications along one dimension. In a computational volume composed of fixed and equisized voxels, local atomic density changes due to ion implantation or recoil relocation are relaxed to constant predefined atomic volumes. This is accomplished by interaction with neighboring voxels and by material transport towards and away from the surface. Arbitrary initial system shapes and elemental distributions can be defined as well as a wide range of irradiation conditions including non-uniform beam profiles. The paper addresses details of the involved algorithms and discusses potential artifacts with respect to surface sputtering, broadening of compositional profiles, and surface contours. It demonstrates the capabilities of the program by examples of focused ion beam erosion, self-organized surface pattering, and ion implantation and sputter-shaping of nanostructures.

Synthesis of Porous Silicon with Silver Nanoparticles by Low–Energy Ion Implantation

In this paper a new technique for synthesis of porous silicon layers with silver nanoparticles based on the method of low − energy and high − dose metal ion implantation into Si is proposed. For demonstration of this technique, room temperature Ag + ion implantation of polished Si wafer with ion energy of 30 keV, ion dose of 1.5 ⋅ 10 17 ion/cm 2 and ion current density of 8 μA/cm 2 was carried out. By high resolution scanning electron and atomic − force microscopy, electron probe microanalysis and Raman scattering we have shown that as a result of ion implantation a thin amorphous layer of porous Si is formed on the surface of irradiated Si with average pore sizes of 150—180 nm, pore depth of about 100 nm and wall thickness between pores of about 30—60 nm. Moreover, porous Si contains Ag nanoparticles with sizes of 5—15 nm. We established that during ion implantation the sputtering of Si surface by Ag + ions occurs which was not observed before. On the basis of these data we concluded that the proposed physical technique for porous Si formation compared to chemical techniques could be integrated into an advanced process of fabrication and improvement of electronic circuits based on industrial ion implantation.

Development of protective metal coatings on aluminum by magnetron sputtering

Depositions of copper and titanium coatings on aluminum foils and polished aluminum plates for thier protection against corrosion in alkaline media were performed. The coatings were deposited in three different types of magnetron sputtering systems: a direct current (DC) magnetron discharge, a high current impulse magnetron discharge, and a DC magnetron discharge with melted cathode. Only aluminum foils coated with copper films obtained by combined ion-plasma technology, which included preliminarily sputtering of the aluminum surface with an ion beam, deposition of a dense interlayer in the DC magnetron discharge with ion assistance of initial stage of deposition, and deposition of additional layer in the magnetron discharge with melted cathode, were resistant against 30 wt % NaOH solution.

Influence of Temperature and Stress on Near-Surface Cascades in Alpha-Zirconium Revealed by Molecular Dynamics Simulation

Molecular dynamics simulations are used to study cascades near the surface in hcp Zr. The influences of several factors, namely the primary knock-on atom (PKA) in different layers, angle of incidence, temperature and stress, on the number and type of defects are considered. Compared to bulk cascades, near-surface cascades show different characteristics in defect type and quantity when the PKA is in different layers. Low angle incidences create surface sputtering while the effects of high angle incidences are similar to those of bulk cascades. The effect of temperature is mainly focused on the number of sputtered atoms, with little influence on the total number of surviving defects. Stress helps to create more defects and the influence of compressive stress is more prominent than tensile stress.

Formation of Au–Ge nanodots by Au− ion sputtering of Ge

Energetic Au ion sputtering of crystalline Ge surface at normal incidence and room temperature can produce nanodot morphology, which has been studied by atomic force microscopy. The cross-sectional transmission electron microscopy of the dot structure reveals that the implanted Au does not form solid solution with Ge, but preferentially segregates at the top edges of the dots as well as near the amorphous/crystalline interface. The mechanism of dot formation is discussed in the light of local transient melting of the surface due to a high rate of energy deposition by the Au ions and the subsequent cooling.

Surface reaction between water cluster ion and silicon substrate

The surface reaction between water cluster ions and Si substrates was investigated. The incident angle dependence of the sputtering yield of Si induced by the irradiation of a water cluster ion beam was measured at the acceleration voltage of 6kV. The mean cluster size was 6.3×103 molecules. The sputtering yield of Si relative to that of normal incidence had a broad peak around the incident angle of 50°. The Si surface irradiated with a water cluster ion beam at the incident angle of 0° was more strongly oxidized than that irradiated at the incident angle of 50°. The contact angle of the Si surface irradiated with a water cluster ion beam decreased when the water cluster ion beam was irradiated at 0°, but increased at larger angles. The substrate temperature dependences of the sputter depth and numbers of disordered atoms in Si substrates indicated the limited contribution of water molecules that adsorbed on the Si surfaces to the sputtering and oxidation of the Si surfaces.

Sputtering of the target surface by Cs+ ions: Steady-state concentration of implanted cesium and emission of CsM+ cluster ions

Experimental data for the variation of the work function on the Si and GaAs semiconductor surfaces irradiated by cesium ions are presented. The formation mechanism of CsM+ cluster ions (M is the analyte) is considered. Ionization potentials for some CsM molecules are calculated, and a simple experimental technique to determine the concentration of cesium penetrating into the subsurface region of various materials during cesium ion sputtering is suggested. This technique uses a preimplanted potassium as an “internal standard.”

Surface morphology and sputtering yield of SiO2 with oblique-incidence gas cluster ion beam

The dependence of surface morphology and sputtering yield of SiO2 thin films on the incident angle of gas cluster ion beams (GCIBs) was studied. When the incident angles (θ) were either 0° or 30° ripples did not form on the surface of SiO2, and the sputtering depth increased linearly with increasing ion fluence. When θ=45°, ripples formed in the direction perpendicular to that of the incident beam. The ripple pattern became shaper and wider with increasing θ–60°. When θ=60°, the ripple wavelength and amplitude increased linearly with increasing ion fluence. However when θ=80°, ripples formed in the direction parallel to that of the GCIB. When θ=60°, the etching depth decreased with increasing ion fluence. This change in the sputtering rate can be associated with the change in the structure of the ripples.

Ionization probability of sputtered indium atoms: Dependence on projectile impact angle

Motivated by recent model calculations describing secondary ion formation during sputtering of a metallic surface, we have investigated the dependence of the ionization probability of atoms sputtered from clean indium surfaces on the projectile impact angle. For that purpose, the secondary ions and their neutral counterparts were detected under otherwise identical experimental conditions using time-of-flight mass spectroscopy in combination with VUV laser post-ionization. It is found that the average ionization probability depends on the impact angle of the projectile ion beam in such a way that more oblique incidence leads to a larger ion fraction. These preliminary results, which corroborate a corresponding prediction from the model calculation, are interpreted in terms of the kinetic substrate excitation induced by the impinging projectile.

Modelling the sputtering of Au surfaces using a multi time-scale technique

We present results from an atomistic computer simulation model of the sputtering of gold crystal surfaces under 500 eV ion bombardment by Au and Ar ions for doses up to 10 14 ions cm −2 . The multi time-scale technique uses molecular dynamics to calculate the fast ballistic collision processes in the early stages of the cascade, whereas an on-the fly kinetic Monte Carlo technique is used to model the relaxation and diffusion processes between successive ion impacts when the defect motion has begun to be dominated by rare events. The results indicate a large amount of crystalline recovery between impacts, some facetting of the crystal surfaces but no large sub-surface defect accumulation. Because of this recovery process, sputtering yields and energy distributions are in good agreement with those obtained assuming a perfect crystal surface and also with those experimentally measured.

Properties of aluminium oxide thin films deposited in high effective reactive pulsed magnetron sputtering process

Pulsed magnetron sputtering of metal targets in the presence of reactive gas is widely used to deposit compound materials. This method is very popular but still the aim of research is to obtain more stable and efficient processes. The standard procedure of compound thin film deposition is sputtering in so called reactive mode of magnetron work — sputtering of the target surface covered with the formed compound. The authors postulate that the problem of low deposition rate of reactive compounds can be solved if the magnetron source operates in the metallic mode or near the border of metallic and transient mode. Aluminium oxide thin films were deposited using high effective reactive pulsed magnetron sputtering. The main purpose of the research was electrical characterization of metal-compound-metal structures in the wide range of frequencies and determination of deposition technique influence on the thin film properties.

Sputtering of Au surfaces at realistic dose rates using molecular dynamics and on-the-fly kinetic Monte Carlo

We present results from computer simulation of the sputtering of an Au(010) crystal surface under 500eV ion bombardment at realistic dose rates for doses up to 1014ionscm−2. Molecular dynamics is used to calculate the fast ballistic collision processes while an on-the fly kinetic Monte Carlo technique is used to model the relaxation and diffusion processes between successive ion impacts. The results indicate a remarkable degree of crystalline recovery between impacts, no large sub-surface defect accumulation and a saturation of the surface roughness.