Low Energy Ar Ion 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.

Effective Removal Method for Layer of FIB-Induced Surface Damage in Austenitic Stainless Steel

There is substantial concern about the phase change to artificial ferrite or martensite in commercial austenitic stainless steels during intense focused-ion-beam milling. In this work, severe Ga ion milling to prepare microscale samples was found to produce thin transformed layers on the surface of austenitic stainless steel. The surface BCC phase transformation layer was clearly distinguished on the specimen processed with the focused ion beam using cross-sectional analysis. It was determined that Ga ions had accumulated in the surface BCC layer. However, it was also confirmed that the Ga ion accumulation was localized at the top of the surface. This is expected to be caused by the decrease in the formation energy of the body-centered crystalline phase, which may result from the considerable changes in chemical composition and stress state by the accumulation of implanted Ga atoms. We propose an effective method to overcome the phase change problem caused by FIB, by using low-energy Ar ion milling. It was determined that low-energy FIB milling was insufficient by itself to clear the phase transformation layer. High quality micro-scale experimental samples of austenitic stainless steels can be achieved by additional low-energy Ar ion milling at an energy of 1 keV or less after high-energy FIB milling.

Site-selective low-temperature growth of Au nanowires on Si substrates irradiated with low-energy Ar ions

We demonstrated the site-selective growth of freestanding single-crystalline Au NWs at a low temperature (approximately 573 K) by pretreating a silicon substrate with low-energy ion beams, followed by thermal evaporation of Au. Using this method, Au NWs with aspect ratios up to 1000 or more, that is, 50–200 nm in diameter and lengths ranging from several hundred nanometers to approximately 100 μm, were fabricated. Au NWs could only be grown at the boundary between the ion-irradiated and unirradiated regions on the Si substrates during the deposition of Au. Furthermore, patterning the Si substrate by masking it with a fine mesh during ion irradiation creates more boundaries between the irradiated and unirradiated regions, increasing the number of Au NWs. Transmission electron microscopy and selected-area electron diffraction revealed that the NWs were single crystals and grew along the [110] direction.

Site-specific preparation of plan-view samples with large field of view for atomic resolution STEM and TEM studies of rapidly solidified multi-phase Al Cu thin films

The present work describes application of a method for site-specific plan-view sample preparation for atomic column resolution scanning transmission and transmission electron microscopy (STEM and TEM) from free-standing thin films of multi-phase Al-alloys after laser irradiation induced rapid solidification (RS). The electron-transparent multilayer thin film samples (amorphous Si3N4 substrate plus metal alloy layer) had a total initial thickness of ≈ 130–200 nm. At such large total sample thickness frequently multiple grains of the same or different phases overlap along the electron beam path in the RS microstructures of the alloys. Consequently, accurate atomic resolution images in TEM and STEM mode, and composition sensitive analytical data of the metastable microstructural features presenting in the RS microstructures cannot be obtained with confidence. Using low-energy concentrated Ar ion beam milling, locally thinned regions with thickness of 20–30 nm with large fields of view ≥ (30 μm)2 suitable for high-resolution TEM/STEM studies have been created with micron-scale site-specificity. As example application, atomic scale resolution TEM/STEM imaging has been performed of the banded grain regions of the RS microstructure established in multi-phase AlCu alloy thin films. The sample preparation strategy described here appears to be readily applicable to freestanding thin film specimens in general.

Functionalization of low-k surfaces with low-energy Ar ions

In this work low-energy Ar impacts on low- k surfaces were simulated with ab initio density functional theory method. The obtained results reveal the mechanism of CH3-group removal under Ar atom/ion irradiation; the threshold energy of this process was estimated. Keywords: low-k dielectrics, functionalization, simulation, diffusion barriers, methyl groups.

Effect of irradiation with Ar ions on properties of proton conductors on the base of LaScO3

The effect of irradiation with low-energy Ar ions on the structure and conducting properties of lanthanum scandate synthesized by acceptor doping and creation of a lanthanum deficit has been studied.

Site-Selective Low-Temperature Growth of AU Nanowires on Si Substrates Irradiated with Low-Energy Ar Ions

Site-Selective Low-Temperature Growth of AU Nanowires on Si Substrates Irradiated with Low-Energy Ar Ions

Toward a systematic discovery of artificial functional magnetic materials

Although ferromagnets are found in all kinds of technological applications, only few substances are known to be intrinsically ferromagnetic at room temperature. In the past twenty years, a plethora of new artificial ferromagnetic materials have been found by introducing defects into non-magnetic host materials. In contrast to the intrinsic ferromagnetic materials, they offer an outstanding degree of material engineering freedom, provided one finds a type of defect to functionalize every possible host material to add magnetism to its intrinsic properties. Still, one controversial question remains: Are these materials really technologically relevant ferromagnets? To answer this question, in this work the emergence of a ferromagnetic phase upon ion irradiation is systematically investigated both theoretically and experimentally. Quantitative predictions are validated against experimental data from the literature of SiC hosts irradiated with high energy Ne ions and own experiments on low energy Ar ion irradiation of TiO$_2$ hosts. In the high energy regime, a bulk magnetic phase emerges, which is limited by host lattice amorphization, whereas at low ion energies an ultrathin magnetic layer forms at the surface and evolves into full magnetic percolation. Lowering the ion energy, the magnetic layer thickness reduces down to a bilayer, where a perpendicular magnetic anisotropy appears due to magnetic surface states.

Extraction and transport of low-energy Ar ion beams with a broad cross-section

Low-energy argon (Ar) ion beams were accelerated from a quiescent discharge in a custom-designed ion reservoir. Around 100 eV Ar ion beams were extracted from an ion source with different multi-cusp magnetic field configurations through a 4-cm diameter two-electrode extraction system. Langmuir probe measurements correlated the source plasma characteristics to the extracted ion beam properties that were determined using a retarding potential analyzer and a moving Faraday cup. The ion extractor configuration allowed primary electrons from the ion reservoir to seep downstream to neutralize the space-charge of the Ar ions. The broad cross-section ion beam system is designed for material synthesis and surface modification.

Influence of Surface Curvature on Silicon Sputtering by Low-Energy Ar Ions

Molecular dynamics (MD) method was used to study 200 eV Ar ion impact on silicon nanoparticles of various sizes . Based on the MD simulations, the analysis of sputtering mechanisms and differences in the ion energy deposition which are determined by the curvature of the target surface, is performed in the paper.

Measurements of the energy distribution of W atoms sputtered by low energy Ar ions using high-resolution Doppler spectroscopy

Emission spectra of neural tungsten (W) sputtered by impact of argon (Ar) ions in a weakly magnetized (<0.1 T) Ar plasma were measured using a high resolution spectrometer at normal incidence angle to the surface. The measurements were performed for the mono-energetic impact energies between 70 and 150 eV using the neutral tungsten (W I) line at 4982.593 Å. The line shape of this line was simulated using a Doppler-shifted emission model to determine the energy distribution. Additional broadening mechanisms were taken into account: instrumental broadening, Zeeman effect and finally the photon or light reflectance at the W surface.The obtained energy distribution was found in a very good agreement with the Thompson distribution, even though deviations for lower impact energies are observed, e.g. the high-energy tail of sputtered particles demonstrates a faster drop compared to 1/E 2 at energies below 100 eV. Moreover, the standard cosine (Knudsen cosine law) distribution provides a rather good description of emission spectra in the energy range of study. Finally, the energy distribution was also compared with simulations carried out with the binary collision approximation (BCA) based Monte-Carlo code SDTrimSP. It shows a marginally worse description at low energies and better description of the high energy tail compared to the Thompson one. Furthermore, the model was used to determine in-situ the degree of light reflection at the W surface. The results are in excellent agreement with the literature data.

Efficacy of ion irradiation in strengthening the surface plasmon resonance effect of Au nanoparticles

Au-Fullerene nanocomposite thin films synthesized by thermal co-evaporation method are irradiated by low energy (2.6 MeV) Ar ions at fluence ranging from 1 × 1014 ions-cm−2 to 3 × 1016 ions-cm−2. To avoid the retrogression of attributes of fullerene subjected to presence of Au, selected concentration and thickness of gold film is kept very small. UV–visible spectroscopy demonstrates the surface plasmon resonance (SPR) peak at 677 nm for the pristine film and at 590 nm after irradiation at fluence of 1 × 1014 ions-cm−2, displaying a shift of 87 nm towards lower side. This confirms that the refractive index of fullerene decreases as an influence of exposure to Ar beam irradiation. Shift in refractive index is explained on the basis of Mie theory which is established by the existence of D and G band after irradiation as displayed in the results of Raman Spectroscopy. A slight increase in the size of Au nanoparticles in irradiated films is observed which is illustrated by TEM images. Atomic Force Microscopy (AFM) images indicate the varying roughness of thin films after irradiation and morphology is determined by SEM images. I-V characterization shows the conductive behavior of Au-fullerene nanocomposite film before and after irradiation at different fluence. There are two phenomena occurring simultaneously with the increase in ion irradiation fluence; one is increase in the size of metal nanoparticle and another is transformation of fullerene in amorphous carbon. This leads to the change in the SPR position of metal fullerene nanocomposite thin film, making ion irradiation as an effective tool to enhance and optimize the optical properties of metal fullerene nanocomposite thin film.

Features of Low-Energy He and Ar Ion Irradiation of Nanoporous Si/SiO2-Based Materials

Low-energy (50–200 eV) He and Ar ion irradiation of on Si/SiO2-based nanoporous materials is modeled with the use of the molecular dynamics method. The obtained results corroborate the experimentally observed effect of densification of near-surface layers of materials with small-size pores and low porosity due to the ion-induced pore collapse process. The differences in the He and Ar ion irradiation of nanoporous materials and the influence of ion energy on the intensity of structural changes are studied.

Влияние кривизны поверхности на процессы физического распыления кремния ионами Ar низкой энергии

In this paper molecular dynamics simulations of the irradiation of silicon nanoparticles with 200 eV Ar ions were performed. The detailed analysis of the results obtained demonstrates special features of the interaction between incident low-energy Ar ions and silicon targets with different surface curvature.

Analysis of the Results of Silicon Sputtering Simulation as Functions of Different Ar–Si Potentials

The influence of the form of the Ar–Si interatomic potential on the results of simulating the physical sputtering of amorphous Si by low-energy Ar ions is analyzed. The yields of Si sputtering by Ar ions with an energy of 50–300 eV at normal incidence are calculated using the molecular dynamics (LAMMPS software) and the Monte Carlo methods by means of the MOTREV program developed at the Skobeltsyn Institute of Nuclear Physics, the Moscow State University, and used quantum-mechanical elastic-scattering cross sections. The semiempirical Moliere and ZBL pair potentials and a potential developed on the basis of density functional theory calculations are applied to describe Ar–Si interaction. The energy dependences of the sputtering yields obtained using different potentials are analyzed in this paper. Conclusions concerning the applicability of the considered Ar—Si interaction potentials to simulation of the physical sputtering of amorphous Si in the indicated range of projectile energies are drawn.

X-ray scattering by the fused silica surface etched by low-energy Ar ions.

Anomalously high x-ray scattering at a wavelength of 0.154 nm by super-polished substrates of fused silica, which were etched by the argon ions with the energy of 300 eV, is detected. The scattering intensity increases monotonically with increasing of the etching depth. The effect is explained by the scattering on the volume inhomogeneities with the lateral size greater than 0.5 μm of the subsurface "damaged" layer. The concentration of volume inhomogeneities increases with the increase of the fluence of argon ions, but the concentration of implanted argon atoms in the layer quickly reaches the maximum value and then begins a trend of going down. The thickness of the "damaged" layer is approximately equal to the penetration depth of the Ar atoms and can be directly determined from the x-ray specular reflection. It is shown that the presence of volume inhomogeneities of the subsurface "damaged" layer does not affect the geometric roughness of the surface. The observed effect imposes limitations on the usage of grazing incidence x-ray optics without reflective coatings and of the diffuse x-ray scattering (DXRS) method for studying the substrate roughness. A new method that potentially enables to evaluate the applicability of the DXRS method in practice is proposed.

Ion Beam Induced Artifacts in Lead-Based Chalcogenides.

Metal chalcogenides have attracted great attention because of their broad applications. It has been well acknowledged that microstructure can alter the intrinsic properties and performance of metal chalcogenides. The structure-property-performance relationships can be investigated at atomic scale with scanning transmission and transmission electron microscopy (STEM and TEM). Nevertheless, careful specimen preparation is paramount for accurate analyses and interpretations. In this work, we compare the effects of a variety of well-established TEM specimen preparation methods on the observed microstructure of an ingot stoichiometric lead telluride (PbTe). Most importantly, from aberration corrected STEM and first principles calculations, we discovered that argon (Ar) ion milling can lead to surface irradiation damage in the form of Pb vacancy clusters and self-interstitial atom (SIA) clusters. The SIA clusters appear as orthogonal nanoscale features when characterized along the crystal orientation of the rock salt structured PbTe. This obfuscates the interpretation of the intrinsic microstructure of metal chalcogenides, especially lead chalcogenides. We demonstrate that with sufficiently low energy (300 eV) Ar ion cleaning or appropriate high-temperature annealing, the surface damage layer can be properly cleaned and the orthogonal nanoscale features are significantly reduced. This reveals the materials' intrinsic structure and can be used as the standard protocol for future TEM specimen preparation of lead-based chalcogenide materials.

Influence of porosity and pore size on sputtering of nanoporous structures by low-energy Ar ions: Molecular dynamics study

In this paper we have carried out molecular dynamics simulation of the low-energy Ar ion irradiation of nanoporous homogeneous material with different porosity and pore sizes. Our results demonstrate that in a model with small pores (Rpore = 0.8 nm) and relatively low (22%) porosity, the pores at near-surface layers collapsed due to the ion bombardment, whereas in a model with larger pores (Rpore = 2.8 nm) and higher (44%) porosity no significant structural changes occurred under the same irradiation conditions. To study thermal stability of porous structures and to reveal the effects of both the pore radius and the porosity on pore collapsing, our nanoporous structures were subjected to gradual heating. The simulation results demonstrate distinct mechanisms of structural changes in the nanoporous materials depending on the value of the excess surface energy per unit volume.

Argon clustering in silicon under low-energy irradiation: Molecular dynamics simulation with different Ar–Si potentials

In this paper, the authors carried out a molecular dynamics simulation of crystal and amorphous silicon sputtering by low-energy (200 eV) Ar ions at normal incidence. The gradual damage of silicon caused by the ion bombardment was taken into account in order to study the dynamics of argon accumulation and clustering. For describing interatomic Ar–Si interaction, they used three different potentials: two binary screened Coulomb potentials (Molière and Ziegler–Biersack–Littmark) and the potential developed on the basis of density functional theory. The obtained results demonstrated the substantial influence of the chosen Ar–Si potential on calculated sputtering yields and on the processes of argon accumulation and clustering.

Temporal evolution on SiO2 surface under low energy Ar+-ion bombardment: roles of sputtering, mass redistribution, and shadowing

Self-organized pattern evolution on SiO2 surface under low energy Ar-ion irradiation has been investigated extensively at varied ion energies, angles of ion incidence, and ion flux. Our investigations reveal an instability on SiO2 surface in an angular window of 40° ̶ 70° and for a comprehensive range of Ar-ion energies (200–1000 eV). Different topographical features, viz. ripples, mounds, and elongated nanostructures evolve on the surface, depending upon the angle of incidence and ion fluence. The results are compiled in the form of a parametric phase diagram (ion energy versus angle of incidence) which summarizes the pattern formation on SiO2 surface. To understand the evolution of observed patterns, we have carried out theoretical estimation, taking into account the synergetic roles of ion induced curvature-dependent sputter erosion and prompt atomic redistribution. It is shown that irradiation-induced mass redistribution of target atoms plays a crucial role in determining the critical angle of ion incidence for pattern formation on SiO2 under the present experimental conditions, whereas the contribution of curvature-dependent sputtering needs to be considered to understand the existence of the angular window of pattern formation. In addition, ion-beam shadowing by surface features are shown to play a dominant role in the formation of mounds and elongated structures at higher ion fluences.