Threshold Energy For Sputtering Research Articles

Simulation of ranges and sputtering of low energy Helium and Argon ions irradiation on Tungsten surface

The interactions of low energy He and Ar ions with pure W target were simulated by a new Monte-Carlo (MC) based computer code which was designed to insure maximum accuracy. For these irradiation systems, incident ions projected ranges in the target material, sputtering yield, and the percentage of backscattered ions at various incident energies were studied. furthermore, the effect of the angle of incidence on sputtering yield and the percentage of backscattered ions were also simulated. Our simulation results were compared with experimental data and those calculated by the TRIM simulation program. Our code is based on an algorithm that uses detailed numerical solutions for the classical scattering integral for evaluating the binary collision process. This approach has provided sputtering yield data with a higher level of accuracy compared to TRIM's simulation results. Also, a new approach of using a reduced atomic displacement threshold in the top surface monolayer enhances the simulation results in the near sputtering threshold energy range and eliminates its dependence on the selected value of the displacement energy threshold Ed. Nonetheless, both simulation programs produced less contrasting results in terms of incident ions mean projected ranges. Furthermore, fundamental discrepancies in the percentage of backscattered ions between the results of both simulation programs were found.

Molecular dynamics simulations of Ar[formula omitted] bombardment of Fe(0,0,1), (1,0,1), and (1,1,1) surfaces: Study of threshold energy and angular characteristics of sputtering

The surface-sputtering or ion bombardment processes of solid materials have attracted considerable attention due to their applications in materials science and technology. Here, using the classical molecular dynamics simulations, we investigate the low-energy sputtering process of iron in the argon plasma by taking into account the primary knock-on atom (PKA) and secondary knock-on atom (SKA) for different crystal plane orientations. Moreover, the effect of projectile energy on the sputtering yields and the influence of the incident angle of Ar+ ions on these yields, the threshold energy, and the surface binding energy is analyzed. It is shown that the maximum sputtering yields due to the PKA and SKA processes are in the range of 5 to 15 degrees and 15 to 25 degrees, respectively. It is also indicated that the lowest binding and threshold energies of iron are related to the incident angle of 37 degrees and Fe(1,1,1) where the atoms have a lot of space to move and collide with other Iron atoms. Finally, we examine the azimuthal and polar angle distributions of the sputtered atoms to obtain the optimal angle in order to the deposition of sputtered atoms.

Plasma Atomic Layer Etching of SiO2 and Si3N4 with Low Global Warming C4H3F7O Isomers

In this study, plasma atomic layer etching (ALE) of C4H3F7O isomers heptafluoropropyl methyl ether (HFE-347mcc3), heptafluoroisopropyl methyl ether (HFE-347mmy), and perfluoro propyl carbinol (PPC) having low global warming potential were investigated and developed for SiO2 and Si3N4 films. Fluorocarbons generated from C4H3F7O isomer plasmas were used to fluorinate the SiO2 and Si3N4 surfaces, and the fluorinated surface was etched using Ar plasmas in the following step. The HFE-347mmy produces the lowest F 1s/C 1s ratio or carbon-rich fluorocarbon. The chemical sputtering threshold energy of Si3N4 was found to be 5–10 V lower than that of SiO2. The ALE window was observed in the range of 50–60 V for all isomers, and the EPC of SiO2 was determined to be 2.1, 1.8, and 5.2 Å/cycle for HFE-347mcc3, HFE-347mmy, and PPC, respectively. The EPC of Si3N4 is higher than that of SiO2 in all precursors. The highest etch selectivity of SiO2 and Si3N4 over poly-Si was achieved with HFE-347mmy as high as 103 for SiO2 to poly-Si and 189 for Si3N4 to poly-Si. This study demonstrates that C4H3F7O isomers can help reduce global warming by replacing the conventional perfluorocarbons and achieving high selectivity of SiO2 to poly-Si and Si3N4 to poly-Si.

Microstructural evolution of Ti2ZrHfV0.5Mo0.2 refractory multi-principal alloy under low-energy, high-flux He ion irradiation

The irradiation response of refractory multi-principal element alloys (RMPEAs) has gained increasing attention for the potential applications in future fusion devices. In controlled fusion reactors, plasma-facing materials have to suffer continuous low-energy high flux helium (He) ion irradiations. During high flux He irradiation, vacancy-interstitial pairs can be generated through trap mutation mechanism even without cascade collision. To simplify the model, Ti2ZrHfV0.5Mo0.2 RMPEA was irradiated with 50 eV He+ (less than the minimum He displacement energy of the alloy EdTi = 67 eV) under 1200 K to various fluences of 5 × 1024 - 1 × 1026 ions/m2, and the microstructural evolution was investigated. In the irradiated RMPEA, the intense sputtering of Ti, the growth and degradation of fuzz mainly composed of Zr, Hf elements on the surface, as well as the formation of V, Mo enriched band and high density large He cavities in the subsurface layer were observed. Although the sputtering threshold energy for He of V is similar to that of Ti (ETi = 24 eV, EV = 29 eV), V showed anomalous enrichment in the subsurface layer. Moreover, unlike the W fuzz growth process, the adatoms used to form fuzz in Ti2ZrHfV0.5Mo0.2 were derived from the Zr, Hf atoms diffusing through the vacancy-solute exchange mechanism, rather than from the atoms formed by the loop-punching mechanism. The anomalous enrichment of V atoms and the different fuzz growth mechanism were attributed to (i) different migration rates for different species of atoms in the alloy under vacancy diffusion mechanism and (ii) the formation of AB2 (A = Ti, Zr, Hf; B = V, Mo) phase blocking the continued formation of prismatic dislocation loops mainly composed of V and Mo.

The influence of impurities on the erosion of tungsten by low energy high flux deuterium plasma irradiation

The erosion behavior of tungsten (W) exposed to low-energy, high flux deuterium (D) plasma has been investigated. The samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and ion beam analysis (IBA). The eroded thicknesses increase with increasing irradiation fluence from 4.8 × 10 25 to 1.64 × 10 26 m −2 for 100 eV D plasma bombardment at a temperature of approximately 600 K, however, the corresponding sputtering yields gradually decrease as a function of fluence. A number of possible erosion mechanisms for enhanced sputtering of W by D near the energy threshold which include impurities in the plasma and sample, retained D, surface roughness and morphology, were analyzed. As the sputtering threshold energy predicted by theory and simulation for deuterium on pure W is ~216 eV and for W with carbon contamination is ~85 eV, a sputtering yield of 2.32 × 10 −6 which was measured for W with only C impurity exposed to a 60 eV deuterium fluence of 1.08 × 10 26 m −2 indicates that there were a little amount of impurities such as carbon or oxygen in the D plasma but they show an important contribution to the sputtering yield of the W under 100 eV D plasma erosion. The C impurity in the sample can significantly enhance the sputtering yield of W through increasing energy transfer efficiency in a triple collision cascade system, and the change of C concentration from 14 at.% at the surface to 5.6 at.% in the deeper region of the sample dominates the change of erosion rate under 100 eV plasma bombardment. It is recommended to reducing the impurity concentration to very low levels, whether from background D plasma or contaminants in the near-surface of W wall, will be very beneficial for decreasing W erosion in Tokamak operation.

Numerical Study of the Thresholds of Sputtering of Metals during Bombardment with Low-Energy Ions

The transfer of energy from bombarding $${{{\text{K}}}^{ + }}$$ and $${\text{A}}{{{\text{r}}}^{ + }}$$ ions ( = 10–100 eV) to vanadium atoms is studied via molecular dynamics using the Vs potential. The threshold energy of vanadium sputtering is determined, and a numerical way of determining the thresholds of sputtering for solids is proposed.

Effect of heat treatment on physical properties of tungsten coating obtained by pulse electrodeposition

Tungsten coated CuCrZr alloy with high thermal and electrical conductivity is a candidate for plasma facing components due to its high threshold energy for physical sputtering and favourable thermo-mechanical properties. The properties of over-aged CuCrZr alloy could be improved by annealing treatment. It is essential to investigate the effects of heat treatment on the properties of the tungsten coating. After annealed at 703 K for 12 h, and then air cooled out of the furnace, there is no significant changes on the preferred orientation and microstructure of the tungsten coating. Although the heat treated tungsten coating exhibited a tensile surface stress, the bonding strength between W coating and CuCrZr substrate was also near 60 MPa. Compared to the coatings prepared by plasma spraying, the heat-treated tungsten coating maintained a high the thermal conductivity which was measured to be about 149 W m−1 K−1.

Additive manufacturing of pure tungsten by means of selective laser beam melting with substrate preheating temperatures up to 1000 ∘C

Abstract The preferred plasma-facing material in present-day and future magnetic confinement thermonuclear fusion devices is tungsten. This material is mainly chosen because of its high threshold energy for sputtering by hydrogen isotopes as well as its low retention of tritium within the material. From an engineering point of view, however, tungsten is a challenging material to work with as it is an inherently hard and brittle metal. In this respect, established fabrication technologies for tungsten and tungsten based materials are a limiting factor directly affecting the design of plasma-facing components. Against this background, additive manufacturing technologies could prove very beneficial with regard to plasma-facing component applications as they offer flexibilities beyond the possibilities that conventional manufacturing methods offer. Within the present contribution, we report on recent results regarding the additive manufacturing of tungsten by means of powder-bed based selective laser beam melting. In more detail, investigations on pure tungsten manufactured by using elevated substrate preheating temperatures up to 1000 ∘C are described.

Chemically assisted physical sputtering of Tungsten: Identification via the [formula omitted] transition of WD in TEXTOR and ASDEX Upgrade plasmas

Tungsten (W) is a preferred plasma-facing material for areas of high particle and power impact in present day and future fusion devices. The lifetime of W plasma-facing components (PFCs) under steady-state conditions is limited by erosion processes induced by energetic impinging particles such as impurities (carbon C, oxygen O, nitrogen N, etc.) and hydrogen isotopes above the threshold energy for Physical Sputtering (PS). We discovered for the first time, in addition to the bare physical sputtering process of W, a second W erosion mechanism at PFCs in TEXTOR (limiter surfaces) and ASDEX Upgrade (divertor target plates) during deuterium plasma bombardment. The tungsten deuteride molecule WD has been identified spectroscopically via the 6Π→6Σ+ transition in parallel to ordinary neutral W line emission of the WI transition (5d5(6S)6s 7S3 → 5d5(6S)6p 7P4) at λ=400.9nm used as measure to quantify the bare PS process or, more precisely, the gross erosion of W. We identified the underlying process for the molecular release as Chemically Assisted Physical Sputtering (CAPS) as observed also in the case of beryllium or lanthanum. Measurements in TEXTOR and ASDEX Upgrade showed a dependence of the WD band emission on the surface temperature - connected to the deuterium content in the near W surface - as well as on the flux and energy of impinging energetic particles. A quantification of the released WD is not yet possible due to lack of appropriate molecular data for the conversion of photons into particles, but the spatially resolved ratio of atomic (WI) and molecular photon flux (WD) indicates that the release takes place at the same time, but differently distributed along the target plates and limiters reflecting the variation in the described critical parameters (impinging ion flux, ion impact energy, and material temperature) along the surface. The plasma conditions in front of the interaction zone are in both cases fully ionising with an electron temperature Te > 10eV, thus, recombination into WD can be excluded.

The Formation of Hollow Lead Structures on the Surface of PbSe Films Treated in Argon Plasma

Conditions for ion sputtering of a PbSe/CaF2/Si(111) epitaxial system in high-density inductively coupled plasma of high-frequency low-pressure discharge in argon have been established that ensure the formation of submicron-sized hollow lead structures on a lead-selenide surface. The surface was plasma-treated for time periods within 60–240 s at low energy (20–30 eV) of Ar+ ions, which is close to their sputtering threshold energy. The properties of the obtained material were studied by the techniques of scanning electron microscopy and energy-dispersive X-ray microanalysis. It is shown that the characteristic size, shape, and density of surface structures can be varied within broad limits depending on the time of plasma treatment and temperature of the material surface. Physical processes responsible for the formation of hollow lead structures under the proposed conditions of plasma sputtering are considered.

Формирование полых свинцовых структур на поверхности пленок PbSe при обработке в аргоновой плазме

AbstractConditions for ion sputtering of a PbSe/CaF_2/Si(111) epitaxial system in high-density inductively coupled plasma of high-frequency low-pressure discharge in argon have been established that ensure the formation of submicron-sized hollow lead structures on a lead-selenide surface. The surface was plasma-treated for time periods within 60–240 s at low energy (20–30 eV) of Ar^+ ions, which is close to their sputtering threshold energy. The properties of the obtained material were studied by the techniques of scanning electron microscopy and energy-dispersive X-ray microanalysis. It is shown that the characteristic size, shape, and density of surface structures can be varied within broad limits depending on the time of plasma treatment and temperature of the material surface. Physical processes responsible for the formation of hollow lead structures under the proposed conditions of plasma sputtering are considered.

Molecular dynamics investigation of hexagonal boron nitride sputtering and sputtered particle characteristics

The sputtering of hexagonal boron nitride (h-BN) by impacts of energetic xenon ions is investigated using a molecular dynamics (MD) model. The model is implemented within an open-source MD framework that utilizes graphics processing units to accelerate its calculations, allowing the sputtering process to be studied in much greater detail than has been feasible in the past. Integrated sputter yields are computed over a range of ion energies from 20 eV to 300 eV, and incidence angles from 0° to 75°. Sputtering of boron is shown to occur at energies as low as 40 eV at normal incidence, and sputtering of nitrogen at as low as 30 eV at normal incidence, suggesting a threshold energy between 20 eV and 40 eV. The sputter yields at 0° incidence are compared to existing experimental data and are shown to agree well over the range of ion energies investigated. The semi-empirical Bohdansky curve and an empirical exponential function are fit to the data at normal incidence, and the threshold energy for sputtering is calculated from the Bohdansky curve fit as 35 ± 2 eV. These results are shown to compare well with experimental observations that the threshold energy lies between 20 eV and 40 eV. It is demonstrated that h-BN sputters predominantly as atomic boron and diatomic nitrogen, and the velocity distribution function (VDF) of sputtered boron atoms is investigated. The calculated VDFs are found to reproduce the Sigmund-Thompson distribution predicted by Sigmund's linear cascade theory of sputtering. The average surface binding energy computed from Sigmund-Thompson curve fits is found to be 4.5 eV for ion energies of 100 eV and greater. This compares well to the value of 4.8 eV determined from independent experiments.

Morphology and composition of Fe–W coatings after deuterium plasma exposure as a model system for RAFM steels

A model system representing the RAFM steel EUROFER-97 is produced by magnetron sputter deposition of iron and 1.5 at% tungsten and investigated in order to study the consequences of plasma exposures. The alloy is deposited as coatings with a thickness of 400 nm on polycrystalline, high purity iron substrates. To understand the erosion mechanisms and morphology changes the coatings were exposed to a linear plasma device with an ion flux of 3×1021 D+ m−2 s−1 and an electron temperature of 13 eV. Samples were exposed at sample temperatures of about 420 and 770 K at incident ion energy of 30 eV (floating potential), 70 and 190 eV. Additionally, the effect of ion fluence was investigated. The coatings before and after plasma exposure were investigated by electron microscopy and glow discharge optical emission spectroscopy (GD-OES). Microstructure observation revealed a complex morphology with distinct sharp spikes formed under the plasma exposure at incident ion energies of 70 and 190 eV. The tungsten enrichment by a factor of 3 in the spikes was visualized by backscatter electron observation and confirmed by both energy-dispersive x-ray spectroscopy and GD-OES. No visible erosion and, by that, tungsten enrichment was observed after the plasma exposure at an incident ion energy of 30 eV, as expected since it is below the threshold energy for sputtering of iron.

Sputtering and reflection of self-bombardment of tungsten material

In present research, the sputtering and reflection yield of self-bombardment of tungsten are investigated with the aid of molecular dynamics simulations. The source of sputtered and reflected atoms is detected by traced the original locations of sputtered and reflected atoms. Results show that for the reflected atoms no specific region exists which means cluster atoms are randomly reflected. But almost all of sputtered atoms are from a conical region under the landing point of cluster. So we can determine the sputtering yield by study the dimension of the sputtering region. Molecular dynamics shows the depth and radius of the conical are power functions of impacting energy. The effects of cluster size and temperature of target on sputtering and reflection rate are also preformed in present study. Both sputtering and reflection yield are proportion to cluster size in present cluster size, i.e. 66–2647 atoms. Higher target temperature can increase sputtering yield and deduce sputtering threshold energy, but little effect on reflection rate.

Simulation of erosion of the tungsten wall by impurities in the divertor plasma

Divertor is a component that directly contacts the plasma in tokamak. To ensure the lifetime of the device, it is necessary to reduce the erosion of the divertor wall by plasma. In this work, a particle-in-cell model is used to study the influences of plasma temperature and impurity concentration on the erosion of tungsten divertor wall by carbon and beryllium ions. The steady-state sheath, particle and energy fluxes to the wall, and the energies and angle of the incident ions can be obtained. Then, these data can be used as the input parameters for the plasma-surface interaction model, to evaluate the erosion rate of the plate based on the empirical formulas for physical sputtering. It is found that the erosion by heating plays a negligible role under the plasma condition of this work. Due to the low physical sputtering threshold energy of tungsten by impurities and the impurity ions accelerated by sheath, the physical sputtering of the tungsten by the impurities plays an dominant role in the total erosion. In addition, the erosion rate increases with the increase of plasma temperature and impurity concentration.

Investigation of ion beam induced nanopattern formation near the threshold energy

The nanoscale ripple formation on mica surface is studied at off-normal ion incidence angles θ under Ar+ bombardment at energies E close to or below the threshold energy for physical sputtering. A phase diagram for domains of pattern formation is presented as a function of θ and E, which shows the stability/instability bifurcation angle close to 40°. The instability grows as ripple-like structures at lower angles, while at grazing angles the pattern emerges as dense array of needles. The results support the pure mass redistribution based paradigm for surface patterning as the erosion due to sputtering essentially tends to zero.

Study on low-energy sputtering near the threshold energy by molecular dynamics simulations

Using molecular dynamics simulation, we have studied the low-energy sputtering at the energies near the sputtering threshold. Different projectile-target combinations of noble metal atoms (Cu, Ag, Au, Ni, Pd, and Pt) are simulated in the range of incident energy from 0.1 to 200 eV. It is found that the threshold energies for sputtering are different for the cases of M1 < M2 and M1 ≥ M2, where M1 and M2 are atomic mass of projectile and target atoms, respectively. The sputtering yields are found to have a linear dependence on the reduced incident energy, but the dependence behaviors are different for the both cases. The two new formulas are suggested to describe the energy dependences of the both cases by fitting the simulation results with the determined threshold energies. With the study on the energy dependences of sticking probabilities and traces of the projectiles and recoils, we propose two different mechanisms to describe the sputtering behavior of low-energy atoms near the threshold energy for the cases of M1 < M2 and M1 ≥ M2, respectively.

A study of suppression effect of oxygen contamination by bias voltage in reactively sputtered ZrN films

A scrupulous cleaning and degreasing of the deposition chamber allows to make a ZrN film with stoichiometry of 1.3 and to achieve a level of oxygen contamination equal to 5%. This film exhibits a low number of carriers estimated at N*=3×1021cm−3 and with a very high electrical resistivity value of about 105μΩ·m. This result points the way for further improvements in the quality of the material.This amount of oxygen contamination may be reduced in conditions in which only the oxygen will be removed without disturbing the zirconium presence in the film. A bias voltage value between 8eV and 20eV reduces the oxygen contamination.The ionic assistance is often proposed as a mean to minimize the oxygen contamination. However, one must consider the negative phenomena as re-sputtering, ion implantation, atom displacement and stress generation that introduce defects in the film and affect its properties. This work proposes a very low bias voltage value to control oxygen contamination. The bias voltage value is chosen higher than the nitrogen sputtering threshold energy and lower than the argon sputtering threshold energy. The re-sputtering phenomenon, far from being a problem, can be used to achieve the stoichiometry if one starts from a nitrogen-rich compound. In this way, ZrNx is grown with x about 1, with an effective free electron concentration N*=8.9×1021cm−3. Furthermore its resistivity value is about 2μΩ·m and the oxygen Secondary Ion Mass Spectrometry (SIMS) signal is similar to the noise signal.

Net sputtering rate due to hot ions in a Ne-Xe discharge gas bombarding an MgO layer

An analytical method is developed for determining net sputtering rate for an MgO layer under hot ions with low energy (<100 eV) in a neon-xenon discharge gas at near-atmospheric pressure. The primary sputtering rate is analyzed according to spatial and energy distributions of the hot ions with average energy, Ehi, above a threshold energy of sputtering, Eth,i, multiplied by a yield coefficient. The threshold energy of sputtering is determined from dissociation energy required to remove an atom from MgO surface multiplied by an energy-transfer coefficient. The re-deposition rate of the sputtered atoms is calculated by a diffusion simulation using a hybridized probabilistic and analytical method. These calculation methods are combined to analyze the net sputtering rate. Maximum net sputtering rate due to the hot neon ions increases above the partial pressure of 4% xenon as EhNe becomes higher and decreases near the partial pressure of 20% xenon as ion flux of neon decreases. The dependence due to the hot neon ions on partial pressure and applied voltage agrees well with experimental results, but the dependence due to the hot xenon ions deviates considerably. This result shows that the net sputtering rate is dominated by the hot neon ions. Maximum EhNe (EhNe,max = 5.3 − 10.3 eV) is lower than Eth,Ne (19.5 eV) for the MgO layer; therefore, weak sputtering due to the hot neon ions takes place. One hot neon ion sputters each magnesium and each oxygen atom on the surface and distorts around a vacancy. The ratio of the maximum net sputtering rate is approximately determined by number of the ions at Ehi,max multiplied by an exponential factor of –Eth,i/Ehi,max.

Molecular dynamics and dynamic Monte Carlo studies of mixed materials and their impact on plasma wall interactions

A molecular dynamics technique was used to study the sputtering characteristics of co-deposited carbon (C) and to investigate subsequent effects of introducing beryllium (Be) impurities. Amorphous C layers containing hydrogen (H) with atomic ratios of H/(C + H) < 0.3 together with a small amount of Be with ratios of Be/(C + H + Be) < 0.06 are produced on top of a tungsten (W). Noncumulative bombardment of the amorphous C layer without H ( i.e., H/(C + H) = 0) by H atoms, produces no atomic C sputtering at energies less than the threshold energy for physical sputtering, as calculated by a dynamic Monte Carlo code, EDDY. By examining the H uptake in the layer, it was observed that hydrocarbon sputtering occurs when the dominant emitted species are small radicals e.g. CH and at low H/(C + H) ratios (<0.1). When the ratio was increased, larger radicals (CH 2 and CH 3) were emitted. In the eV energy range, the larger molecules were the dominant emitted species, whilst C atoms were emitted even at very low energies. A small percentage of Be was implanted in the C layer, and was found to reduce sputtering of the large molecules, whereas the emission of the small molecules and the C atoms was slightly reduced or remained unchanged.