Surface Sputtering Research Articles

Mechanisms of nodule formation on Ni-Pt targets during sputtering

Ni-Pt alloys are employed in the formation of Ni-Pt silicide to facilitate contact and interconnection functions in semiconductor devices. However, the formation of nodules on the Ni-Pt target during sputtering results in a reduced deposition rate and abnormal discharge, significantly impacting the film quality. This study investigates the nodule formation mechanism on the surface of Ni-Pt targets during sputtering, utilizing field-emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD). The findings reveal that defects and inclusion areas in the target exhibit a slower sputtering rate compared to normal areas, ultimately leading to nodule formation. Notably, platinum-rich layers were observed on the surfaces of nodules, particularly those exceeding a height of 100 μm. The variations in target surface concentration, angular distribution, and sputter yield of Ni and Pt atoms, coupled with the blocking effect of the lateral areas of nodules, contribute to the formation and compositional variation of the Pt-rich layers on the nodule surfaces.

Polarity of homoepitaxial ZnO films grown by Nd:YAG pulsed laser deposition

We investigate the stability of the polar surface of ZnO films grown homoepitaxially on atomically flat ZnO (0001¯) O-face substrates by neodymium yttrium aluminum garnet (Nd:YAG) pulsed laser deposition (PLD). For films grown in the temperature range from 500 to 700 °C, ion scattering spectroscopy showed that the film surface termination was the same as the ZnO substrate. Even for a Mg0.2Zn0.8O/ZnO superlattice, no polarity reversal occurred, indicating that the ZnO (0001¯) O-face is highly stable, despite the film surface sputtering caused by the high kinetic energy of the PLD plume generated by the Nd:YAG laser.

Comprehensive study of Kinetic Trajectory Simulation method for multi-component magnetized plasma-wall interaction process

For a wide range of plasma applications across diverse fields, a comprehensive understanding of the plasma-wall interaction mechanism is indispensable due to its inherent connection with confined plasma. This work compilation delves into the Kinetic Trajectory Simulation (KTS) method for the interaction of multi-component magnetized plasma with wall, specifically focusing on its implications for the tungsten wall sputtering model. In the evolution of the 1d3v (one dimensional spatial coordinates and three dimensional velocity coordinates) KTS method, the coupled set of kinetic equations has been solved under specified boundary conditions which yields results of higher accuracy. At the particle injection boundary, we have assumed the velocity distribution function of particle species to be cut-off Maxwellians, meeting essential requirements for plasma-wall transition processes: quasineutrality, sheath edge singularity, continuity of macroscopic fluid variables, and the kinetic Bohm sheath condition. The kinetic Bohm sheath condition, a fundamental criterion for plasma sheath formation, is extended for multi-component plasmas, accounting for the cut-off Maxwellian distribution of negatively charged particles. A comparative study of the kinetic Bohm sheath condition for cut-off and Boltzmann distributions reveals a deviation of less than 2.0% in magnitude. The concentration ratio of positive or negative ion species and the presheath side electron temperature influence various plasma-wall transition characteristics, including wall potential, Debye sheath thickness, particle densities, potential distribution, particle fluxes towards the surface, particle drift velocity, phase-space trajectory evolution, and physical sputtering of the tungsten surface. Although lighter ions possess higher energy when striking the surface, the physical sputtering yield of the tungsten surface is greater for heavier ions due to their lower threshold energy and larger collision cross-section. Furthermore, a comparative study of plasma-wall transition properties using kinetic and fluid approaches demonstrates qualitative similarities, with a notable deviation of approximately 4.0% in the magnitude in the vicinity of the material surface.

Three‐Dimensional Electrostatic Hybrid Particle‐In‐Cell Simulations of the Plasma Mini‐Wake Near a Lunar Polar Crater

AbstractLunar polar region has become the focus of future explorations due to the possible ice reservoir in the permanently shadowed craters. However, the space environment near the polar crater is quite complicated, and a plasma mini‐wake can be caused by the topographic obstruction. So far, three‐dimensional (3D) numerical simulations of the mini‐wake around a crater far larger than the Debye length are still limited. Here we present a 3D electrostatic hybrid particle‐in‐cell model to study the plasma mini‐wake of a polar crater on scale of about 1 km. It is found that the mini‐wake can begin upstream from the crater with a cone angle of about 8.8°. There is a plasma void with extra electrons near the leeward crater wall, where the electric potential can be as low as −60 V. A part of solar wind ions can be diverted into the crater, and the ratio of the diverted flux is about 4% on the crater bottom and about 18% on the windward crater wall, which provide an important source for the surface sputtering. Further studies show that the mini‐wake can change with the solar wind parameters and the crater shapes. Our results are helpful to assess the space environment and the water loss rate of a polar crater, and have general implications in studying the plasma mini‐wake caused by a crater on the other airless bodies.

Remote plasma enhanced cyclic etching of a cyclosiloxane polymer thin film

The continuous evolution of chip manufacturing demands the development of materials with ultra-low dielectric constants. With advantageous dielectric and mechanical properties, initiated chemical vapor deposited (iCVD) poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane) (pV3D3) emerges as a promising candidate. However, previous works have not explored etching for this cyclosiloxane polymer thin film, which is indispensable for potential applications to the back-end-of-line fabrication. Here, we developed an etching process utilizing O2/Ar remote plasma for cyclic removal of iCVD pV3D3 thin film at sub-nanometer scale. We employed in-situ quartz crystal microbalance to investigate the process parameters including the plasma power, plasma duration and O2 flow rate. X-ray photoelectron spectroscopy and cross-sectional microscopy reveal the formation of an oxidized skin layer during the etching process. This skin layer further substantiates an etching mechanism driven by surface oxidation and sputtering. Additionally, this oxidized skin layer leads to improved elastic modulus and hardness and acts as a barrier layer for protecting the bottom cyclosiloxane polymer from further oxidation.

Synthesis of noble metal nanostructures by ion beam irradiation and their characterization

Platinum nanostructures (PtNSs) are versatile in catalysis, biotech, nanomedicine, and pharmacology. Their large surface area and self-humidifying properties benefit energy and the environment. This study investigates PtNSs synthesis and morphological changes on a ∼ 3 nm Pt film under 20 keV Ne+ ion irradiation (5 × 1014 to 5 × 1016 ions/cm2). Higher fluences (1 × 1015 ions/cm2) produce plateau-like structures, while additional irradiation (1 × 1016 ions/cm2) leads to fractal structures with increased roughness. Surface sputtering and agglomeration induced by ion irradiation drive the transformation from Pt nanoparticles to plateau to fractal structures. Understanding these relationships enhances PtNSs synthesis and paves the way for diverse applications.

Control of the preferential orientation and properties of HiPIMS and DCMS deposited chromium coating based on bias voltage

This study investigates the effects of varying bias voltages on the crystallographic orientation and properties of DCMS + HiPIMS-deposited chromium coatings. Under bias voltages varying from 100 to 500 V, dense Cr coatings were obtained, and the deposition rate decreased by 13 %. The bias voltage significantly impacts the hardness, crystallographic orientation, electrical conductivity, and bonding strength of the coating. As the bias voltage increases, the hardness of the Cr coating gradually increases. The crystallographic orientation of the coating is governed collectively by surface energy, strain energy, and sputtering effects. The preferential crystallographic orientation of the Cr coating transitions from (222) to (110), subsequently changing to a mixed preferential crystallographic orientation of (110), (211), and (222). Under the combined influence of thermal effects and ion bombardment, a (110) preferential crystallographic orientation was obtained at a bias voltage of 300 V, featuring moderate hardness and optimal wear resistance. This study establishes that the electrical characteristics of the coatings have a significant correlation with bias voltage levels.

A One‐Dimensional Model of Atmospheric Sputtering at Io Driven by S++ and O+

AbstractIo, the closest of Jupiter's four Galilean moons, suffers from intense ion bombardment from Jupiter's magnetosphere. The constant atmospheric erosion by energetic ion precipitation, referred to atmospheric sputtering, serves as an important mechanism of Io's atmospheric escape. This study is devoted to a state‐of‐the‐art study of atmospheric sputtering at Io, with the aid of constantly accumulated understandings of Io's space environment and atmospheric photochemistry, as well as the updated laboratory measurements. A Monte Carlo model is constructed to track the energy degradation of incident S++ and O+ and atmospheric recoils from which the sputtering yields of different atmospheric species are determined. Our calculations suggest a total escape rate of 3 × 1029 atom s−1 on Io, and SO2 is the dominant sputtered species. Further investigations reveal that S++ is the most efficient species for atmospheric sputtering on Io, and sputtering yields increase substantially with increasing incident ion mass, energy, and incidence angle. The model sensitivity to different influence factors is also discussed, including scattering angle distribution, atmospheric column density, proton precipitation, inelastic process, and surface sputtering, of which the former two dominate.

Formation of a periodic structure on the surface of InP crystal during irradiation with bismuth ions

This work is devoted to the study of the formation of periodic relief on the InP surface during ion sputtering by bismuth ions with an energy of 30 keV and an angle of incidence of 45° respect to normal incidence. We compared the reliefs formed by sputtering with atomic and cluster bismuth ions, as well as the relief appearing on the surface of the sample irradiated at elevated temperature (290 °C). Three different types of reliefs were found: surface waves with nanodots on the surface “waves”, nanodots with uniform distribution and relief in the form of columnar micro crystallites during sputtering of a heated target. With increasing irradiation dose, insignificant changes in characteristic surface dimensions were observed for all three reliefs. Based on the nonlinear character of surface sputtering (“thermal spot” sputtering mode), we described the formation of relief in the form of nano-dots and in the form of micro crystallites as a result of local melting areas formation and subsequent solidification (crystallization) on the target surface. Regarding wave relief, in our opinion, an adequate physical description is given by a model based on the stress driven dynamics of ion irradiated surface.

Sputtering from rough tungsten surfaces: Data-driven molecular dynamics simulations

The sputtering of tungsten surfaces caused by hot plasma particles is an important process in fusion reactors where divertors are typically made of tungsten sheets. In this study, we present a molecular dynamics simulation strategy to investigate the sputtering yields of tungsten surfaces with geometrical defects. This should serve as a model for non-monocrystalline surfaces in general and could also be a rough model for nanoscale “fuzzy” layers, which are known to be formed by surface bombardment with energetic particles. Using a non-cumulative approach, we simulate the irradiation of tungsten surfaces with cone-shaped, cylindrical, and spherical defects by argon atoms. We analyze the sputtering yields as functions of particle energy and defect sizes. As a result, we find that surfaces with distinctly shaped defects always exhibit reduced sputtering yields, compared to smooth ones. We also investigate the angular distributions of sputtered particles and find them mostly to be in accordance with prior experimental and computational results.

Investigation of surface orientation dependent sputtering of Ag

Sputtering of metal surfaces can be both a beneficial phenomenon, for instance in the coating industry, or an undesired side-effect, for instant materials subjected to irradiation. While the average sputtering yields are well known in common metals, recent studies have shown that the yields can depend on the crystallographic orientation of the surface much stronger than commonly appreciated. In this study, we investigate by computational means, molecular dynamics, the sputtering of single crystalline Ag surfaces under various incoming energies. The results at low and high energy are compared to experimental results for single crystalline Ag nanocubes of different orientations. We observe strong differences between the sputtering yields of different surface directions and ion energies. We analyze the results in terms of the atom cluster size of the sputtered materials, and show that the cluster size distribution is a key factor to understand the correspondence between simulations and experiments. At low energies mainly single atoms are sputtered, whereas at higher energies the sputtered material is mainly in atom clusters.

Transient to steady-state morphology evolution of carbon surfaces under ion bombardment: Monte Carlo simulations

Molecular dynamics (MD) simulations have established the sputtering yields of carbon under the low-energy bombardment of noble gas ions. Here, we upscale these MD results to account for the evolving surface morphology and sputtering yield with ion fluence using a Monte Carlo model, which considers the shadowing of the incident ion flux, redeposition of sputtered carbon material, and secondary sputtering induced by the surface impact of carbon sputterants. Results show that initially rough surface morphologies are consistently smoothened and flattened by a normal ion flux, resulting in sputtering yields that approach MD predictions. Under a highly oblique ion flux, however, the activation of multiple cooperative roughening and smoothening mechanisms at different scales lead to the formation of characteristic surface steps at the microscale, with steady-state sputtering yields that are up to an order-of-magnitude lower than MD predictions. While the observed surface features and the ensuing sputtering yield at steady-state are generally not sensitive to the initial surface morphology, the initial morphology controls the ion fluence to attain steady-state. We discuss surface design strategies to delay and abate sputtering.

Permeation of low-pressure deuterium through niobium under radio-frequency plasma condition

The behavior of permeation of deuterium through niobium under the condition of radio-frequency plasma has been investigated in this paper. The external solenoid coupled plasma was applied as plasma source. The dependences of stable permeation flux on mode of discharge, membrane temperature, input power, gas pressure, surface oxidation layer and impurity concentration have been studied. The bulk diffusion was one of the controlling steps with 0.5 mm membrane and the substantially increase was due to plasma assisted dissociation. The mixtures with large amount of argon or nitrogen had finite influence on stable permeation flux which was attributed to the ion energy driven dissociation at surface. These results imply the inductively coupled plasma driven permeation is beneficial to rapid separation and purification of hydrogen isotopes for low surface sputtering rate of membrane surface and gases with hydrogen-containing compounds.

Measurement and Simulation of Ultra-Low-Energy Ion-Solid Interaction Dynamics.

Ion implantation is a key capability for the semiconductor industry. As devices shrink, novel materials enter the manufacturing line, and quantum technologies transition to being more mainstream. Traditional implantation methods fall short in terms of energy, ion species, and positional precision. Here, we demonstrate 1 keV focused ion beam Au implantation into Si and validate the results via atom probe tomography. We show the Au implant depth at 1 keV is 0.8 nm and that identical results for low-energy ion implants can be achieved by either lowering the column voltage or decelerating ions using bias while maintaining a sub-micron beam focus. We compare our experimental results to static calculations using SRIM and dynamic calculations using binary collision approximation codes TRIDYN and IMSIL. A large discrepancy between the static and dynamic simulation is found, which is due to lattice enrichment with high-stopping-power Au and surface sputtering. Additionally, we demonstrate how model details are particularly important to the simulation of these low-energy heavy-ion implantations. Finally, we discuss how our results pave a way towards much lower implantation energies while maintaining high spatial resolution.

Sputtering and structural modifications induced in silicon dioxide (SiO2) thin films under (10–40 MeV) Auq+heavy ion irradiation

Surface sputtering and structural modifications induced in silicon dioxide thin films (SiO2/Si) deposited on silicon substrates and irradiated by swift (10–40 MeV) heavy Auq+(q = +4, +6, +7, and +9) ions were investigated by grazing‐incidence X‐ray diffraction (GIXRD) spectroscopy, Rutherford backscattering (RBS) spectrometry and time‐of‐flight elastic recoil detection (ToF‐ERDA) technique. The GIXRD analysis of the as‐deposited and irradiated samples revealed increasing structural modifications of the SiO2thin films under Auq+ion impacts with increasing ion‐beam energy. The changes consisted of decreased grain sizes with increased strain accompanied by a phase transformation from crystalline to amorphous films. RBS analysis showed a decrease in the mean stoichiometric (O/Si) ratio from (2.2 ± 0.1) to (1.7 ± 0.1), due to preferential sputtering of oxygen, as the incident ion energy increased. The obtained RBS‐results were then completed by those of ToF‐ERDA analysis technique using a 40 MeV Au9+heavy ion beam. The preferential sputtering yield ratios (YSi/YO) were determined experimentally both versus electronic stopping power and ion fluence. The obtained results were then compared to numerical values derived from the inelastic thermal spike (i‐TS) model, Sigmund's analytical formula and SRIM simulation code. A good agreement was observed between the measured preferential sputtering data and the i‐TS calculated values, when considering both nuclear elastic and electronic inelastic collision mechanisms. Besides, a close correlation is observed between the electronic stopping power dependent measured sputtering yields and the XRD peak intensity degradation per unit fluence. These observations suggest that the same mechanism of MeV heavy ion‐irradiation induced extended atomic disordering, occurs both in the case of structural modifications and surface sputtering. Finally, the obtained experimental results are discussed on the basis of the i‐TS model.

Influence of Surface Sputtering during High-Intensity, Hot Ion Implantation on Deep Alloying of Martensitic Stainless Steel

This article is devoted to the study of the effect of ion sputtering on the alloy surface, using the example of martensitic stainless steel AISI 420 with ultrahigh-dose, high-intensity nitrogen ion implantation on the efficiency of accumulation and transformation of the depth distribution of dopants. Some patterns of change in the depth of ion doping depending on the target temperature in the range from 400 to 650 °C, current density from 55 to 250 mA/cm2, and ion fluence up to 4.5 × 1021 ion/cm2 are studied. It has been experimentally established that a decrease in the ion sputtering coefficient of the surface due to a decrease in the energy of nitrogen ions from 1600 to 350 eV, while maintaining the ion current density, ion irradiation fluence and temperature mode of target irradiation increases the ion-doped layer depth by more than three times from 25 μm to 65 µm. The efficient diffusion coefficient at an ion doping depth of 65 μm is many times greater than the data obtained when stainless steel is nitrided with an ion flux with a current density of about 2 mA/cm2.

Detailed studies of the processes in low energy H irradiation of Li and Li-compound surfaces

We have used a combination of pico-to-nano temporal/spatial scale computational physics and chemistry modeling of plasma–material interfaces in the tokamak fusion plasma edges to unravel the evolving characteristics, not readily accessible by empirical means, of lithium-, oxygen-, and hydrogen-containing materials of plasma-facing components under irradiation by hydrogen and its isotopes. In the present calculation, amorphous lithium compound surfaces containing oxygen, Li2O, and LiOH were irradiated by 1–100 eV particles at incident angles on the surface ranging from perpendicular to almost grazing angles. Consequential surface processes, reflection, retention, and sputtering were studied at “the same footing” and compared to earlier results from amorphous Li and LiH surfaces. The critical role of charging dynamics of lithium, oxygen, and hydrogen atoms in the surface chemistry during hydrogen-fuel irradiation was found to drive the kinetics and dynamics of these surfaces in unexpected ways that ultimately could have profound effects on fusion plasma confinement behavior and surface erosion.

Molecular dynamics study of surface binding energy and sputtering in W-V alloys

This article used molecular dynamics to simulate the surface binding energy of W1-xVx (x = 0, 0.0625, 0.125, 0.25, 0.3125, 0.5) alloys along the (100) direction, considering the volume effect. The results showed that forming an alloy between W and V significantly improved the surface binding energy of W within the simulated proportion range, and the surface binding energy of W increased with increasing V proportion. However, when the simulated surface binding energy was input into the Monte Carlo program (SRIM-2013) to calculate the sputtering yield of W-V alloys, it was found that the alloy with V only greatly reduced the sputtering yield of W in the alloy, and the total sputtering yield of the alloy was higher than that of pure tungsten. Therefore, W still had the best anti-sputtering ability in the simulated material. The obtained results provided a reference for the selection of plasma-facing materials in future nuclear fusion.

Ion Beam as an External and Dynamic Metal Reservoir to Induce Nanoparticle Exsolution in Oxides

A central theme in solid oxide fuel cells (SOFC) and electrolyzers (SOEC) is to design stable and catalytically active solid/gas interfaces toward desired reactions. A recent advance in this regard is to synthesize nanoparticles decorated electrodes in a process termed “exsolution”. Exsolution generates stable and catalytically active metal nanoparticles via phase precipitation out of a host oxide. Unlike traditional nanoparticle infiltration techniques, the nanoparticle catalysts from exsolution are anchored in the parent oxide. This strong metal-oxide interaction makes the exsolved nanoparticles more resistant against particle agglomeration as compared to the infiltrated ones. In addition, the exsolved particles also open up the possibility of regeneration of catalysts. To date, the concept of exsolution has been successfully applied to a number of applications including SOFC/SOEC, ceramic membrane reactors, chemical looping combustion, and (electro)catalysis.As the exsolution process starts with a solid-solution that contains the to-be-exsolved transition metal ions, this method is often limited by the intrinsic solubility limit of the host oxide. Here, we propose that ion beam irradiation to be a unique tool to promote exsolution as it can introduce defects and dopants into the host oxides and at concentrations higher than thermodynamic limits. Moreover, due to the surface sputtering effect, ion beam irradiation can modulate the surface morphology, creating novel nanostructures.To demonstrate this approach, we chose thin-film perovskite SrTi0.65Fe0.35O3 (STF) and fluorite Ce0.5Zr0.5O2 (CZO) as model systems, both of which are promising materials in SOFC and SOEC. We modulated metal exsolution in both materials with in-situ 10-150 keV Ni irradiation at 800 °C in vacuum. Ni irradiation on STF controllably changed the exsolved particle composition from unitary Fe to bimetallic Fe-Ni. Moreover, it also reduced the particle size down to sub-2 nm, which outperforms other tuning methods thus far in the literature. As a result, the irradiation-modified STF demonstrated superior catalytic activity toward room-temperature oxygen evolution reactions (OER) than the conventional thermally exsolved STF. Regarding CZO, Ni irradiation also decorated the surface with well-dispersed nanoparticles, leading to enhanced high-temperature H2O splitting kinetics. The effective size and composition control over exsolution highlights the utility of metal ion beams in promoting and tailoring exsolved nanocatalysts for a broad range of applications in clean energy and fuel conversion. Figure 1

Nitriding in a cyclically switched glow discharge

The paper shows the prospects of nitriding in a cyclically switched discharge, the classification of nitriding processes in a glow discharge according to the criteria of the characteristics of the power source is given. A comparison of the advantages and disadvantages of nitriding processes with constant and cyclically switched discharge is given.From a theoretical point of view, the process of nitriding in a cyclically switched glow discharge is considered based on the concept of an energy model. In accordance with this model, tasks for further theoretical and experimental research are formulated. It is shown that the process of surface modification in a cyclically switched discharge opens up new possibilities associated with variants of the CSD itself, which is characterized by: frequency, period and pulse shape. The implementation of the process of adjusting the switching frequency, pitch - the ratio of the cycle period to the duration of the signal, and the shape of the signal itself opens up wide opportunities to significantly influence the results of surface treatment.
 The influence of the shape of the discharge power signal on the kinetics of the nitriding process and its results opens up wide opportunities for studying the process itself. The presence of surges at the beginning and at the end of the cycles can, in principle, significantly affect both the nature of the nitriding process itself and the structure and phase composition of the modified surface layer, since short-term and sufficiently powerful voltage surges should lead to intensive surface sputtering. The destruction of the monolayer of nitrides, which has just formed on the surface, will contribute to the increase of the depth of the nitrided layer due to the diffusion of nitrogen particles, as well as to a certain extent leveling off the blocking effect of the surface nitride layers.