Sputtering Yield Research Articles

Spatially varying chemical phase formation on silicon nano ripple by low energy mixed ions bombardment

We report mixed (CO+ and N2 +) ion beam induced spatially varying chemical phases formation on Si (100) surface in nanometer length scale. Simultaneous bombardment of carbon, oxygen and nitrogen like three reactive ions leads to well-defined ripple development and spatially varying periodic chemical phases formation. Post bombardment chemical changes of Si surface are investigated by x-ray photoelectron spectroscopy, and spatially resolved periodic variation of chemical phases are confirmed by electron energy loss spectroscopy. The thickness of ion modified amorphous layer, estimated by Monte Carlo simulation (SRIM), is in excellent agreement with the cross-sectional transmission electron microscopy measurements. The formation of such periodic nanoscale ripple having multiple chemical phases at different parts is explained in terms of chemical instability, local ion flux variation and difference in sputtering yield. Potential applications of such newly developed nano material are also addressed.

Experimental investigation on divertor tungsten sputtering with neon seeding in ELMy H-mode plasma in EAST tokamak

Neon (Ne) seeding is used to cool the edge plasma by radiation to protect the divertor tungsten (W) target in the Experimental Advanced Superconducting Tokamak (EAST). The W sputtering in the outer divertor target with Ne seeding is assessed by the divertor visible spectroscopy system. It is observed that the W sputtering flux initially increases with Ne concentration in the divertor despite the decreasing plasma temperature. After reaching a maximum around 25 eV, the W sputtering rate starts to decrease, presenting a suppression effect. The effect on the divertor W sputtering flux and yield due to the competition between the increase of the Ne concentration and the decrease of the plasma temperature is discussed. The results show that enough Ne seeding is essential to effectively reduce the electron temperature and thus to suppress W sputtering. Moreover, ELM suppression is observed when Ne and W impurities enter the core plasma, which could be correlated to the enhanced turbulence transport in the pedestal.

Chemical reactions in H2O:CO interstellar ice analogues promoted by energetic heavy-ion irradiation

ABSTRACT H2O:CO, at concentrations of (3:2) and (10:1), was condensed on CsI substrate at 15 K and irradiated with 46-MeV 58Ni11 + ion beam. Radiolysis induced by fast heavy ions was analyzed by infrared spectroscopy (FTIR). The formation of nine molecular species: CO2, H2O2, HCOOH, HCO, H2CO, 13CO2, CH3OH, O3, and C3O2 was observed. For both concentrations, carbon dioxide (CO2), formaldehyde (H2CO), formic acid (HCOOH), and hydrogen peroxide (H2O2) are the most abundant products species, and tricarbon dioxide (C3O2) is much less abundant. Precursor destruction cross-sections and formation cross-sections of products are determined. The CO destruction cross-section for the (3:2) concentration is almost five times higher than that of water, while those for the (10:1) concentration are practically the same. Atomic sputtering yields are estimated for the two ice films, the total mass sputtered is approximately 2.5 × 106 u per impact. These results contribute to figure out the chemical pathways of compounds synthesized from the two most abundant organic species (H2O and CO) observed in the ices of grain mantles of the circumstellar envelopes and interstellar medium. In additional, the finding results reveal that molecular astronomical percentages are comparable to those obtained after 15 eV molec−1 of deposited dose in current experiments compared with the relative concentration of molecules in solid phase observed in MYSO, LYSO, BG Stars, and Comets.

Irradiation damage of reduced activation ferritic/martensitic steel CLAM exposed to low-energy high-flux D + He mixture plasma

Irradiation damage behavior of reduced activation ferritic/martensitic steel CLAM exposed to D + He mixture plasma was extensively investigated using the linear plasma facility PSIEC at a sample temperature of ∼800 K with an ion flux of ∼4.0 × 1021 m−2 s−1, an ion fluence of ∼7.0 × 1024 m−2 and an incident ion energy of ∼89 eV. Fiber-like nanostructure fuzz was formed on the irradiated CLAM steel surface. D and He bubbles were observed both inside and under the fuzz structure from cross-sectional TEM characterization. Damage level of the steel surface has been found to gradually increase as increasing He concentration in the mixed plasma. The growth process of fuzz can be described as pinholes (which originated from nano-bubbles) to nano-sphere structures, wavy erosion layers, rods, and eventually develops to nano-fuzz. Tungsten enrichment in the near-surface has been determined after plasma exposure due to preferential sputtering of middle-Z elements of iron and chromium. The measured surface tungsten concentration varied from 1.9 to 4.0 wt.%, depending on He concentration in the plasma. Obtained sputtering yield increased as well with increasing He concentration in the mixed plasma.

Sputtering yield and nanopattern formation study of BNSiO2 (Borosil) at elevated temperature relevance to Hall Effect Thruster

Lower sputtering yield of the discharge wall material is a crucial parameter for the performance of Hall Effect Thruster (HET). In this article, we report the sputtering yield of HET wall material BNSiO2 (borosil) at elevated temperature ∼ 600 °C using quartz crystal microbalance (QCM). We observe a linear increase in the sputtering yield with temperature and it remains stable during long duration experiments using Xe ions. Two different crystallographic orientations of borosil give a slight variation in the yield. The higher yields for higher operating temperatures is proposed to be due to the thermal spike nature. Microscopic surface morphology shows only different grains of BNSiO2, however high resolution nanoscopic view reveals the formation of nanoripple like structures over different grains. The periodicity of such features increases with ion dose (sputtering time) and temperature in the range of 70–190 nm. Local curvature dependent erosion plays crucial role in such pattern formation.

Comparison experiment on the sputtering of EUROFER, RUSFER and CLAM steels by deuterium ions

In this work, the RAFM steels EUROFER, RUSFER and CLAM, along with a reference pure Fe sample, were all exposed to the same source of deuterium and analyzed using the same techniques, allowing a direct comparison of the experimental results. A 200 eV/D mass-selected deuterium ion beam at the SIESTA facility was used to bombard the samples to a fluence of 5 × 1024 Dm−2 at 450 K. The surface morphology of the samples was investigated with Scanning Electron Microscopy. The sputter yield of the samples was determined by weight-loss measurements and confirmed by measurements of the eroded depth. The near-surface enrichment of W and Ta was investigated via Energy-dispersive X-ray spectroscopy, X-ray Photoelectron Spectroscopy and Rutherford Backscattering Spectrometry. Grain-orientation-dependent sputtering was studied with Confocal Laser Scanning Microscopy and Electron Backscatter Diffraction. Lastly, Nuclear Reaction Analysis and Thermal Desorption Spectrometry were employed to analyze deuterium retention in all the samples. The erosion behavior of all three steels under deuterium bombardment was confirmed to be similar. The measured sputter yield was comparable for all three steels, and significantly lower than that of pure Fe. Likewise, all steels develop a needle-like surface morphology under the given exposure conditions and a W- and Ta-enriched layer in the range of few nanometers, while the Fe sample remained smooth. Retained deuterium amounts were also comparable among the steel samples, and were overall larger than the retention measured for the pure Fe sample.

Re-deposition of ITER-grade Be on plasma gun facility QSPA-Be: Characterization & plasma cleaning

Studies of contaminants obtained by spraying ITER-grade Be on a quasi-stationary plasma gun facility QSPA-Be are presented. Contaminating films, consisting mainly of Be and O in approximately equal proportions, were deposited on substrates of quartz, sapphire, single crystalline silicon (SC-Si) and NaCl crystal. Characterization of the deposits was performed using SEM, XPS, EBS, AFM, SE, TEM&SAED and micro-interferometry showing polycrystalline BeO films similar as found in JET-ILW. Films on SC-Si and NaCl were used to characterize their composition and morphology. The cleaning rates in the 81.36 MHz RF discharges in He or D2 at 2 Pa were measured on the SC-Si target. The measured etching rate of the deposited films was several times higher than the rate calculated from the theoretical value of beryllium oxide sputtering yield. Test cleaning of these contaminants was carried out in a capacitively coupled RF discharge (CCRF) from the surface of sapphire and quartz plates, which were considered as a mock-ups of the protective window of the first mirror unit (FMU) designed for ITER divertor Thomson scattering diagnostic system (DTS).

Effect of low energy proton and He particle irradiation on CsPbBr3 material

In this paper, the effect of proton and He particle bombardment in CsPbBr3 material was investigated by the Monte Carlo simulation including ion range, backscattering, vacancies and sputtering yield. The energies of proton and He particle varied from 50 keV to 180 keV and the particle incidence angles increased from 0o to 89.9o . The calculated results showed that with the increase of incidence energies, the range and vacancies increased, and the backscattering ions and sputtering yield reduced for proton and He particle. Meanwhile, the vacancies, backscattering ions and sputtering yield induced by He particle were much more proton at the same energy. With the increase of incidence angles, the range and vacancies were reduced, and the sputtering yield increased for proton and He particle. Also, it is obvious that the effects of He particle on CsPbBr3 material were much more serious than proton.

Study of the influence of the energy of argon ions on the surface roughness of the main sections of single-crystal silicon

The paper presents the results of studying the energy dependences of the sputtering yields and the value of the effective surface roughness of single-crystal silicon upon irradiation with argon ions with an energy of 200-1000 eV. As a result of the work, the parameters of ion-beam etching with accelerated Ar ions were determined, providing a high sputtering yield (etching rate) and an effective roughness value in the spatial frequency range 4.9·10-2-6.3·101 μm-1 less than 0.3 nm for the main cuts monocrystalline silicon <100>, <110> and <111>. Keywords: sputtering yield, roughness, single-crystalline, monocrystalline, accelerated ions.

Sputtering of carbide films from the surface of the metal by helium ions bombardment

The paper investigates the dependence of the sputtering yields by light ions bombardment of the surface layers of titanium and tungsten, modified with carbon, on the thickness of the layer. The theoretical study was conducted on the basis of a sputtering model (previously adapted to describe the sputtering of two-component targets and layered-inhomogeneous surfaces), based on two sputtering mechanisms, which allows to analyze the obtained dependencies. Theoretical calculations of the total yields sputtering by helium ions bombardment of the surface layers of titanium and tungsten modified with carbon are given in comparison with the results of computer simulation obtained using the SRIM-2013pro program. Keywords: modified surface, ion bombardment, sputtering, light ions, layered surface, metal carbide, sputtering yield, partial sputtering yield.

Simulation of ion irradiation of crystalline and amorphous targets tokamak-reactor first wall materials

An overview of results concerning simulation of various processes which occur due to atomic bombardment of crystalline and amorphous solids is presented. With the use of original computational codes, the following data were obtained: reflection coefficients, projected energy losses and ranges of ions in solids, channeling data as well as sputtering yield and its dependence on incident angle of bombarding particles for Be-W and Ne-W combinations. Be, C and W targets were studied as these are among the plasma-facing materials in tokamaks, including ITER. The emphasis was made on atom-target combinations which lack reliable experimental data. Experimental data on other materials were used to verify calculations. A significant influence of the interaction potential used on the simulation results is shown. The reviewed results are tied by a common subject a study of interaction of plasma ions and first-wall materials of a tokamak-reactor and also by a common method of study the use of an original computational code. Keywords: scattering, ion sputtering, interaction potential, energy release.

Accurate Thickness Measurements in Thin Films with Surface Analysis

Quantification in surface analysis using Auger electron spectroscopy and X-ray photoelectron spectroscopy has been the topic of significant work at NPL. A new approach to the quantification of materials that are homogeneous over the analysis volume has been developed using new average matrix relative sensitivity factors. These show agreement between theory and experiment at ~10% for all peaks and elements analysed. For samples that are not homogeneous, layer thicknesses are often required. For ultra-thin gate oxides, the International Technology Roadmap for Semiconductors requires 1.3% accuracy. For this purpose, angle-resolved XPS is a good candidate. In a wide study under the auspices of the Consultative Committee for Amount of Substance (CCQM), the accuracy of measurements of the thicknesses of SiO2 layers <8 nm thick on Si have been assessed. This study involved 45 sets of measurements in laboratories using MEIS, NRA, RBS, EBS, XPS, SIMS, ellipsometry, GIXRR, NR and TEM. The relative strengths and weaknesses become clear. These show that if XPS is used under reference conditions it can be reliable and fast with an accuracy, based on a calibration from the study, ~ 1%. Inter-method correlations as good as 0.05 nm are achieved over the 8 nm range. Furthermore, certain methods, thought to be accurate, suffer from incompleteness of the measurement method. For thicker layers, sputtering is generally used. Here a new method has been tested to generate a sputter yield database, for argon ions, of 26 critical elements. This database has been used to help evaluate a new semi-empirical theory of sputtering yields that includes terms missing from the current semi-empirical theories and removes errors that are up to, and may exceed, a factor of 5. The new theory agrees with published data at ~ 10% and shows why certain elements have anomalously high yields.

Нелинейные эффекты при распылении арсенида галлия и кремния кластерными ионами висмута

An experimental study on the influence of the energy and the number of atoms in the bombarding ions Bin+ (n = 1-4) on the sputter yield of GaAs was carried out. It was shown that the specific sputter yield Ysp nonadditively increase with an increasing of n and specific kinetic energy Esp per an atom in the bombarding ion, and the efficiency of energy transfer from bombarding ions to target atoms also increases with an increasing of n. A comparison was made with the previously obtained results for Si targets.

Nonlinear effects in the sputtering of gallium arsenide and silicon by bismuth cluster ions

An experimental study on the influence of the energy and the number of atoms in the bombarding ions Bin+ (n=1-4) on the sputter yield of GaAs was carried out. It was shown that the specific sputter yield Ysp non-additively increases with increasing n and specific kinetic energy Esp per an atom in the bombarding ion, and the efficiency of energy transfer from bombarding ions to target atoms also increases with increasing n. A comparison was made with the previously obtained results for Si targets. Keywords: ion sputtering, non-additivity factor, cluster ions, bismuth.

Angular distribution of particles sputtered from the vanadium target by 5 keV Kr ions: simulation study

The sputtering of vanadium particles at normal incidence was simulated. The SRIM-code combined to a new ANGULAIR and SDTrimSP simulation was employed to obtain the sputtering yields and the angular distribution of the atoms. The simulation was made for a large number of incident Kr+ ions with 5 keV energy, letting the computer count the number of emitted particles in the solid angle. The angular distribution of differential sputtering yields of vanadium shows an over-cosine tendency.

Изучение влияния энергии ионов аргона на шероховатость поверхности основных срезов монокристаллического кремния

The paper presents the results of studying the energy dependences of the sputtering yields and the value of the effective surface roughness of single-crystal silicon upon irradiation with argon ions with an energy of 200-1000 eV. As a result of the work, the parameters of ion-beam etching with accelerated Ar ions were determined, providing a high sputtering yield (etching rate) and an effective roughness value in the spatial frequency range 4.9*10-2-6.3*101 μm-1 less than 0.3 nm for the main cuts monocrystalline silicon &lt;1 0 0&gt;, &lt;1 1 0&gt; and &lt;1 1 1&gt;.

Dependence of the Sputtering Yield on the Angle of Ion Incidence on the Target Surface

We investigated the behavior of sputtering yield for oblique angles of ion incidence on the target surface. The range of incidence angles varied from 0o (normal incidence) to almost 90o (limiting grazing incidence). Computer simulation was performed by the program PAOLA. Theoretical analysis included numerical solution of the Chandrasekhar integral equation. The results obtained are compared with the results of other authors Keywords: sputtering under ion bombardment, oblique ion incidence, sputtering yield, computer simulation, theoretical analysis.

The influence of target film material and coating on neutron yield and sputtering yield

The long-life, high yield deuterium-deuterium (D-D) neutron tube has become one of the research hotspots. Here, deuterated polyethylene target, heavy water target and titanium target were investigated by Stopping and Range of Ions in Matter (SRIM). The calculation showed that the deuterated polyethylene target, which was a potential target material, had the highest yield at an incident energy of 120 keV. Further, considering the unfavorable factors such as impurity ions and high temperature, the coating was used to protect the target material. Diamond, boron carbide, boron nitride, silicon carbide, and aluminum carbide were selected. The simulation results showed that the diamond composite deuterated polyethylene film had the best sputtering resistance, and the aluminum nitride composite heavy water target film had the lowest sputtering yield. The two coating materials shield the target, reduced the energy loss of incident ions, and provided a new method for the research of high yield and long life neutron tube.

Sputtering, Cluster Primary Ions and Static SIMS

Sputtering using cluster primary ion beams is very important for the future development of static SIMS and the SIMS depth profiling of organic layers. However, different results from different laboratories may be confusing. Analytical models have an important function for enabling the prediction of behaviour for practical analysis. Sigmund's model for sputtering, often used in surface analysis, is helpful and accurate in the linear cascade regime. However, for cluster sputtering this is no longer the case and spike effects need evaluation. Evidence will be presented of the spike model validity for clusters of up to more than 10 atoms over 3 orders of magnitude in sputtering yield. Using data from one primary ion, extremely good descriptions of measurements reported with other primary ions can then be achieved. This theory is then used to evaluate the molecular ion yield behaviour of interest in the static SIMS of organics. This leads to universal dependencies for the de-protonated molecular ion yields, relating all primary ions, both single atom and cluster, which are illustrated by experimental data over 5 decades of emission intensity. This formulation permits the prediction of the (M-H)- secondary ion yield for different, or new, primary ion sources. It is shown how further gains are predicted. For analysing materials, raising the molecular secondary ion yield is extremely helpful but it is the ratio of this yield to the disappearance cross-section (the efficiency) that is critical. The relation of the damage and disappearance cross sections is formulated. Data are evaluated and a description is given to show how these cross sections are related and to provide a further universal relation for the efficiency/yield dependence of all cluster ions.

Преимущественное распыление при облучении сплавов газовыми кластерными ионами

Topography and composition of the surface of nickel-based alloys under irradiation with Ar2500+ cluster ions with the energy of 20 keV, and atomic Ar+ ions with the energy of 3 keV have been studied. It has been experimentally found that the surface of the alloys is depleted by a component with a lower binding energy. It is shown that the change in the surface concentrations of the alloy components upon irradiation with cluster ions is an order of magnitude greater than upon sputtering with atomic ions. The degree of change in the surface composition is determined by the ratio of the sputtering yields of the alloy components.