Applications of ion-beam-assisted deposition

Modern applications of high energy ion beams: from “single-event burnout” to human eye cancer treatment

Liliaceous pollen cells were implanted by 4.0 MeV C2+ ion beam or by 25.0 keV N+ ion beam. Laser confocal scanning microscopy (LCSM) of the implanted intact samples showed that parts of the implanted pollen cells could be stained by propidium iodide (PI). This indicated that energetic ion beam could directly act on cells beneath the pollen coats and made channels for entry of the molecules from outside of the cells. LCSM analysis of green fluorescent protein (GFP) showed that energetic ion beam could mediate transient expression of gfp in treated pollen cells. Compared with 25.0 keV N+ ion beam, implantation of 4.0 MeV C2+ ion beam greatly improved gene transfer efficiency in pollen cells.

The thermal spike effect dominates rapid heating and quenching at the nanoscale in ion beam assisted materials surface phase engineering. This phenomenon often leads to the formation of metastable nanocrystalline phases in the resulting micro-/nanostructures. However, such a non-equilibrium process cannot be accurately described by the conventional Fourier thermal spike model. In this study, a non-Fourier model is proposed to elucidate the dynamics of heat diffusion in sub-keV Cu ion beam sputter deposition. The effects of beam density and energy on the non-equilibrium thermal and stress fields are quantitatively investigated. The influence of high stress field on nanocrystalline Cu phase content is also studied. It is found that the energetic Cu ion beams produce a rapidly oscillating stress field with a maximum of ∼ 10 GPa within 50 ps, which significantly constrains the growth of nanocrystalline Cu phase at a threshold of ∼ 4 GPa. This understanding provides new insights into the formation of metastable nanocrystalline phases in the fabrication and modification of surface micro-/nanostructures using ion beam assisted techniques.

The ion beam interaction with very thin films (0.5 μm thickness) of a fundamental polymer, polystyrene, was investigated by means of radiation chemistry. Radiation effects on solubility of spin-coated polystyrene films were measured for hydrogen, helium and nitrogen ion beams (0.4 - 3.3 MeV). Measurements were also carried out for 20 keV electrons. By using ion beam pulse radiolysis system, the transient phenomena excited by energetic ion beams were investigated. The time profiles of the excimer fluorescence from ion irradiated polystyrene thin film were measured for hydrogen, helium and nitrogen ions (0.6 - 2.8 MeV). The results for energetic ions were compared with those for low LET radiation, such as fast electron or gamma-ray. Very large differences in radiation effects on solubility and some differences in transient phenomena were found and discussed from the view point of high density electronic excitation.

The layered two-dimensional (2D) materials, e.g., the well-known graphene, transition metal dichalcogenides, and topological insulators, have attracted great interest of researchers from fundamental research as well as industries owing to their intriguing properties in a number of aspects. In practical applications, the efficient modification of the features of 2D materials is compelling and essential to achieve desired functionalities. Ion implantation has been successfully applied to synthesize graphene. The most exotic advantage of ion beam technology is that it offers distinct options of energetic beams, which has recently shown the unique capability to modify and tailor the properties of versatile 2D materials. To name a few, the energetic ion beams could implement the surface morphology or layer-to-layer structural engineering of 2D materials. At the microcosmic level, the introduction of ion beam induced defects and intentional doping of specific ions are the basis of tailoring properties of 2D materials. By manipulating the parameters of ion beams (energies, species, fluences, incident angles, etc.), the modified 2D materials may possess novel properties, which are unprecedented in pristine ones. Promising applications based on these 2D materials with ion beam tailored features have been realized in a broad range of fields. In this work, we systematically review the latest research progress on the deployed techniques and property modifications of graphene and other 2D materials under the treatment of various ion beams. A few selected applications are presented to indicate the practical potentials of ion beam modified 2D materials in distinct areas. Perspectives on future developments are also provided by focusing on several promising topics.

The exceptional performance of nanomaterials, as a result of their size and unique morphology, has attracted a lot of researchers. The structure and constituents of materials have been modified using a variety of techniques. The ion beam techniques have so far been widely employed to modify the performance of different nanomaterials. The surface configuration and chemical composition of nanomaterials can be altered by energetic ion beams. The ion beam techniques approach is purely physical in comparison to conventional methods. These techniques exhibit outstanding control and reproducibility without adding any impurities to the target materials. Here, current developments in surface modification of nanomaterials employing ion beam methods are thoroughly reviewed.

Turbulent Alfvén waves exist ubiquitously in space and astrophysical plasmas. They may be generated by many different source mechanisms. Among them, ion beam instability is well known. Almost all instability theories are interested in the discussion whether a perturbation will grow or be damped in a given unperturbed state. Few papers elaborate the meaning of growth or amplification in terms of the initial condition. This brief communication complements the existing discussions by considering the effect of spontaneous generation of the waves. In the present study, we estimate the level of spectral energy of Alfvénic turbulence due to the presence of a beam of energetic ions. It is found that the spectral energy may be much higher than the average kinetic energy of the background plasma particles.

Interaction processes of heavy ions and ionized matter have been investigated experimentally. A Monte‐Carlo code to simulate charge exchange and energy loss processes in a plasma environment has been developed to plan the experiments, to analyze the results, and to investigate the influence of magnetic fields on the particle trajectories inside the plasma target. The first results of the beam plasma interaction experiments are:•The stopping power of ionized matter is increased compared to that of cold, non‐ionized matter. This effect is especially pronounced at low ion energies (E<100 keV/u) where an enhancement factor of up to 40 has been observed. At higher energies (E≳1 MeV/u) this effect is less dramatic, but is still on the order of 2−3, depending on the ion species.•The charge state of ions traversing a fully ionized plasma is increased due to reduced capture cross sections of free plasma electrons.•It is possible to focus intense heavy ion beams of high magnetic rigidity using a plasma lens. This ideal focusing device achieves a high focusing power for ion beams almost comparable to optical systems for intense beams from high power lasers.•Energetic ion beams are very well suited to heat cylindrical target volumes and to create a dense plasma. The characteristic inner‐shell target and projectile x rays provide a tool to analyze the hydrodynamic behavior of beam heated targets with space and time resolution.

Two processes have been undertaken using Partially ionized cluster deposition (PICBD) and energetic ion bombardment beams deposition (IBD) respectively. C60 films deposited by PICBD at V=0 and 65 V, which result in highly textured close-packed structure in orientation (110) and being more polycrystalline respectively, the resistance of C60 films to oxygen diffusion contamination will be improved. In the case of PICBD, the ionized C60 soccer-balls molecules in the evaporation beams will be fragmented in collision with the substrate under the elevated accelerating fields Va. As a new synthetic IBD processing, two low energy (400 and 1000 eV) nitrogen ion beams have been used to bombard C60 films to synthesize the carbon nitride films.

O2 gas cluster ion beam (O2-GCIB) assisted depositions were employed to deposit high quality dielectric films (Ta2O5, Nb2O5 and SiO2). The optimum irradiation energy and ion current density for Ta2O5 and Nb2O5 film were 5 to 9 keV and 0.5 mA/cm2, respectively. The Nb2O5/SiO2 films deposited with O2-GCIB irradiation showed very uniform and dense structures without columnar or porous structures. Due to the significant surface roughness improvement effect of GCIB, the interface and top surface of Nb2O5/SiO2 multi-layer were quite flat. The interference filter deposited with O2-GCIB assist deposition was very stable and there was no shift of wavelength before and after environmental tests. As O2-GCIB is equivalently very low-energy ion beam and is able to deposit flat and dense amorphous films at low substrate temperature, it suitable for deposition of multi-layered films where low-energy assisting ions are required.

The review is devoted to the use of powerful submicrosecond ion beams for the synthesis and modification of material properties. Powerful ion beams, originally developed for the problems of inertial thermonuclear fusion, have been increasingly used over the past 30 years as a powerful pulsed heating source providing ample opportunities for modifying the surface layer of materials. By varying the key parameters of the beams, such as the composition (type of ions), the duration of the accelerating pulse (10 ns – 1 μs), the kinetic energy of the ions (0.1 – 1 MeV), the energy density transmitted by the beam to the target surface per pulse (0.1 – 50 J/cm2), the main areas of application of high-power ion beams in materials science were determined: modification of the surface layer by ultrafast quenching, melting and ultrafast recrystallization with the formation of micro- and nanostructures, pulsed implantation of ions accompanied by energetic action, deposition of thin films and synthesis of nanosized powders from ablative plasma.

Film growth and relationship between microstructure and mechanical properties of a-C:H:F films deposited by PECVD

The superconducting properties of thin films made by mixing alternating layers of Au and Si using ion-beam bombardment correlate with the formation of metastable metallic phases in what is otherwise a simple eutectic system. Transmission-electron-microscopy measurements reveal the superconducting phases to be amorphous. Compound formation and the nature of Au-Si bonding in these metastable phases are demonstrated from x-ray photoelectron spectroscopy and from a previous study of x-ray-absorption spectroscopy. After mixing with a beam of Xe ions, multilayered films with an average nominal composition ${\mathrm{Au}}_{\mathit{x}}$${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$, where x=0.2, 0.4, 0.5, 0.72, and 0.8, exhibited superconducting transition temperatures in the range 0.2--1.2 K. A double transition feature in the magnetic field dependence of the resistivity is attributed to the formation of more than one metastable metallic phase in the same sample as the ion dose increases.

We have studied the influence of substrate surface roughness on the growth of Ge on self-affine fractal Si surfaces. Self-affine fractal surfaces can be prepared by irradiating surfaces of solid materials with an energetic ion beam, which modifies the surface morphology predominantly via an erosion process. By tuning the ion beam energy, surface parameters such as surface roughness (σ0) and correlation length (ξ), can be controlled. Values of σ0 and σ0/ξ affect the effective free energy of the surface. When materials are grown on surfaces with different values of surface roughness parameters, the morphology of the deposited layer is expected to be influenced. In comparison with an earlier study where 2 MeV Si ion irradiation was used, we have produced surfaces with larger values of σ0 and σ0/ξ by irradiating the surfaces with 45 keV Si ions. We have made a comparison for Ge growth on Si surfaces irradiated with 2 MeV and 45 keV Si ions and have observed remarkably different growth behaviour. Upon Ge deposition, in the former case, the surface roughness decreases at smaller length scales and remains practically unchanged at larger length scales. This indicates that Ge has grown preferentially within the valleys of the rough surface. In the latter case, where σ0 is large and ξ is small on the substrate surface, the roughness increases at all length scales by almost a factor of 2, upon Ge deposition, indicating the lack of preferential growth within the surface valleys. Following Ge deposition, in the former case the roughness exponent increases from 0.82 to 0.99, while in the latter case it remains practically unchanged (∼0.83). Roughness parameters of the substrate surface are found to have a significant influence on the morphology of the overlayers.

We have developed a unique technology for mutation induction of plants using energetic ion beams at the RI Beam Factory (RIBF) of Rikagaku Kenkyūjo (RIKEN) (Institute of Physical and Chemical Research). Ion beams effectively induce mutations at relatively low doses without severely inhibiting growth. The irradiation treatment can be given to various plant materials and mutation can be induced in a short time, between seconds and a few minutes. The linear energy transfer (LET) of ions depends on the nuclide and velocity. Since LET value affects the mutation frequency, it is an important parameter to determine the most effective irradiation condition in mutagenesis. We determined the most effective dose in each LET for mutation induction in imbibed rice seeds. Subsequently, we analysed the mutated DNA responsible for the phenotype in morphological mutants. Most of the mutations were small deletions of less than 100 bp. Irradiations of C-ions and Ne-ions are effective for plant breeding because of the very high mutation rate and sufficient energy to disrupt a single gene. On the other hand, all mutations induced by Ar-ion (290 keV/μm) irradiation were large deletions ranging from 176 bp to approximately 620 kb. The average number of mutations in the target exon regions was 7.3, 8.5 and 4.3 per M3 mutant plant in C-ions, Ne-ions and Ar-ions, respectively. The number of mutations induced by heavy-ion irradiation was relatively small. We could identify six responsible genes for eight mutants induced by C-ion and Ne-ion irradiations and two responsible genes for four mutants induced by Ar-ion irradiation. Three of these were genes not previously described.