Ion Bombardment Research Articles

Evolution of microstructure and properties of TiNbCrAlHfN films grown by unipolar and bipolar high-power impulse magnetron co-sputtering: The role of growth temperature and ion bombardment

Growth temperature (Ts) and ion irradiation energy (Ei) are important factors that influence film growth as well as their properties. In this study, we investigate the evolution of crystal structure and residual stress of TiNbCrAlHfN films under various Ts and Ei conditions, where the latter is mainly controlled by tuning the flux of sputtered Hf ions using bipolar high-power impulse magnetron (BP-HiPIMS). The results show that TiNbCrAlHfN films exhibit the typical FCC NaCl-type structure. By increasing Ts from room temperature to 600 °C, the film texture changes from high-surface-energy (111) to low-surface-energy (100) accompanied by a higher crystallinity in the out-of-plane direction and a more disordered growth tilt angle to the surface plane. In addition, compressive stress decreases with increasing Ts, which is ascribed to changes in the film growth both in the early and post-coalescence stages and more tensile thermal stress at elevated Ts. In contrast, a clear texture transition window is seen under various Ei of Hf+ ions, i.e., high-surface-energy planes change to low-surface-energy planes as Ei exceeds ∼110 eV, while low-surface-energy planes gradually transform back to high-surface-energy planes when Ei increases from 210 to 260 eV, indicating renucleation events for Ei > 210 eV. Compressive stress increases with increasing Ei but is still lower than that of a reference series with DC substrate bias UDC = −100 V. The study shows that it is possible to tailor properties of FCC-structured high-entropy nitrides by varying Ts and Ei in a similar fashion to conventional transition metal nitrides using the approach of unipolar and bipolar HiPIMS co-sputtering.

Structural Properties of He-Irradiated Zr/Nb Multilayer Investigated by Grazing Incidence X-ray Diffraction

Zr/Nb nanoscale multilayers are regarded as one of the important candidate materials used in next-generation reactors. Understanding structural evolution induced by ion bombardment is crucial for the evaluation of lifetime performance. Magnetron sputter-deposited Zr/Nb multilayers with a periodicity of 7 nm were subjected to 300 keV He ion irradiation with three different fluences at room temperature. The depth-resolved strain and damage profiles in the Zr/Nb multilayers were investigated by grazing incidence X-ray diffraction. The tensile strain was found in the deposited Zr/Nb films. After He ion irradiation, the intensity of diffraction peaks increased. The change in diffraction peaks depends on He fluence and incident angle. Irradiation-induced pre-existing defect annealing was observed and the ability to recover the microstructure was more significant in the Zr films compared to the Nb films. Furthermore, the efficiency of defect annealing depends on the concentration of pre-existing defects and He fluence. When the He fluence exceeds the one for pre-existing defect annealing, residual defects will be formed, such as 1/3<12¯10> and 1/3<11¯00> dislocation loops in the Zr films and 1/2<111> dislocation loops in the Nb films. Finally, introducing deposited defects and interfaces can improve the radiation resistance of Zr/Nb nanoscale multilayers. These findings can be extended to other multilayers in order to develop candidate materials for fusion and fission systems with high radiation resistance.

Plasma Parameters and Kinetics of Reactive Ion Etching of SiO2 and Si3N4 in an HBr/Cl2/Ar Mixture

The parameters of the gas phase and the kinetics of reactive ion etching of SiO2 and Si3N4 under conditions of an induction RF (13.56 MHz) discharge with a varying HBr/Cl2 ratio is studied. The study includes plasma diagnostics using Langmuir probes, plasma modeling to find stationary concentrations of active particles, measuring velocities, and analyzing etching mechanisms in the effective interaction prob-ability approximation. It is found that the substitution of HBr by Cl2 at a constant argon content (a) is accompanied by a noticeable change in the electrical parameters of the plasma; (b) leads to a weak increase in the intensity of ion bombardment of the treated surface; and (c) causes a significant increase in the total concentration and flux density of reactive particles. It is shown that the etching rates of SiO2 and Si3N4 increase monotonically as the proportion of Cl2 increases in a mixture, while the main etching mechanism is an ion-stimulated chemical reaction. The model description of the kinetics of such a reaction in the first approximation assumes (a) the additive contribution of bromine and chlorine atoms and (b) the direct pro-portional dependence of their effective interaction probabilities on the intensity of ion bombardment. The existence of an additional channel of heterogeneous interaction with the participation of HCl molecules is proposed.

Magnetron deposition of copper oxide coatings in a metallic mode enhanced by RF-ICP source: A role of substrate biasing

The article describes deposition of copper oxide coatings using magnetron sputtering in a metallic mode enhanced by a radio-frequency inductively coupled plasma (RF-ICP) source. The role of substrate biasing (floating potential, −70 and −140 V) on structural properties and elemental composition of copper oxide coatings is determined using SEM with EDS, XRD and TEM. This study shows the change of coating microstructure from columnar to dense/compact and the increase in crystallinity degree of coatings, when the substrate is biased. EDS analysis reveals the presence of Ar and the increase in O content in the coating due to intensive ion bombardment. Deposition conditions are changed using substrate biasing, which suggests the contribution of ion bombardment to the coating deposition in the case of magnetron sputtering of copper oxide in the metallic mode.

Ion Irradiation Effects on Two-Dimensional MXene Ti2C for Applications in Extreme Conditions: Combined Ab Initio and Monte Carlo Simulations

As an emerging category of two-dimensional (2D) materials, transition metal carbides and/or nitrides (MXenes) have attracted considerable interest for various disciplines. They exhibit unique properties typical of both metals and ceramics, rendering significant potential for harsh conditions such as in outer space and nuclear systems. In this work, using Ti2C as a prototype probe, we investigate the ion irradiation effects by combining ab initio and Monte Carlo simulations. We first consider the structures and energetics of various atomic vacancies in Ti2C. Based on binary collision approximation, a Monte Carlo approach is developed to explore the defects induced by ion bombardment. Systematic Monte Carlo (MC) simulations of different incident ions (i.e., H, He, Li, Be, B, C, N, O, F, and Ne) and selected isotopes reveal that defects are formed via primary collision and in-plane recoils, and the number of displaced atoms decreases with incident energy and increases with the atomic number of incident ions. Interestingly, Ti atoms are much easier to be knocked out than C atoms, beneficial for selective etching for nanoelectronics. We show that Ti2C remains metallic with vacancies of large size, indicating the high irradiation tolerance of electrical conductivity. This work not only provides fundamental insights into the irradiation response of MXenes but also paves the way for future exploration and implementation of 2D nanostructures in extreme conditions, e.g., as coatings or structural materials for nuclear reactors.

MODELING AND SIMULATION OF MAGNETRON-SPUTTERRED NiTi THIN FILM DEPOSITION BY SRIM/TRIM

Nickel-Titanium (Ni-Ti) thin films have gained a lot of attention due to their unique features, such as the shape memory effect. Micro-actuators, micro-valve, micro-fluid pumps, bio-medical applications, and electronic applications have a lot of interest in these smart thin films. Sputter-deposited NiTi thin films have shown the potential to be very useful as a powerful actuator in micro-electro-mechanical systems (MEMS) because of their large recovery forces and high recoverable strains. Despite the advancement of improved deposition methods for the NiTi thin films, there are still certain unsolved challenges that impede accurate composition control throughout the deposition process. Many applications, spanning from the aerospace industries to a range of nanotechnologies, require knowledge of the sputtering characteristics of the materials that are subjected to bombardment, ejection, and deposition of ions. In recent decades, atomic scale modeling has been given a high emphasis in ion sputtering research, providing an adequate and precise description of collision cascades in solids using the Stopping and Range of Ions in Matter (SRIM) and Transport of Ions in Matter (TRIM). In this paper, SRIM is used to address how the heavy ions interact with the target materials. A variety of ion-solid interaction characteristics, including the sputter yield, have been determined by simulating collision cascades in the solids. On the other hand, TRIM was used to describe the range of ions that enter into the matter and cause damage to the target throughout the process. The simulation was carried out to compare the sputtering yield of Ni and Ti by varying the energy input (from 300[Formula: see text]V to 1300[Formula: see text]V). SRIM simulation was conducted by varying the thickness of the film, the angle of incidence of ions, and the energy involved in the sputtering process. The characterization of the films has been carried out using Field Emission Scanning Electron Microscopy (FESEM) to comprehend the surface and interface morphologies of the films and to validate the simulated results. With an increase in energy input (target voltage), the sputtering yield increased. The sputtering yield of the Ni target was higher than the Ti target indicating that Ni can be removed relatively easier than Ti.

Toward Perfect Surfaces of Transition Metal Dichalcogenides with Ion Bombardment and Annealing Treatment.

Layered transition metal dichalcogenides (TMDs) are two-dimensional materials exhibiting a variety of unique features with great potential for electronic and optoelectronic applications. The performance of devices fabricated with mono or few-layer TMD materials, nevertheless, is significantly affected by surface defects in the TMD materials. Recent efforts have been focused on delicate control of growth conditions to reduce the defect density, whereas the preparation of a defect-free surface remains challenging. Here, we show a counterintuitive approach to decrease surface defects on layered TMDs: a two-step process including Ar ion bombardment and subsequent annealing. With this approach, the defects, mainly Te vacancies, on the as-cleaved PtTe2 and PdTe2 surfaces were decreased by more than 99%, giving a defect density <1.0 × 1010 cm-2, which cannot be achieved solely with annealing. We also attempt to propose a mechanism behind the processes.

Radial microstructural nonuniformity of boron nitride films deposited on a wafer scale substrate by unbalanced magnetron sputtering

The nonuniform deposition behavior of boron nitride (BN) films, which is governed by the natural gradient of plasma density, was examined by investigating their microstructure and phase formation. The BN films were deposited on a 10 cm diameter, negatively self-biased Si wafer via unbalanced magnetron sputtering. At a bias voltage of −160 V, where only a turbostratic BN (tBN) film formed, the (0002) hexagonal BN laminates composing the film were aligned normal to the substrate. However, their degree of alignment tended to decrease as their distance from the substrate center increased. At a bias voltage of −220 V, a cubic BN film formed at the center of the substrate, while a tBN film formed on the periphery. These two deposition behaviors were attributed to the bombarding ion flux gradient inherent in the plasma used in sputtering.

Cerium-Doped Indium Oxide as a Top Electrode of Semitransparent Perovskite Solar Cells

Semitransparent perovskite solar cells (ST-PSCs) play a very important role in high-efficiency tandem solar cells and building integrated photovoltaics (BIPV). One of the main challenges for high-performance ST-PSCs is to obtain suitable top-transparent electrodes by appropriate methods. Transparent conductive oxide (TCO) films, as the most widely used transparent electrodes, are also adopted in ST-PSCs. However, the possible ion bombardment damage during the TCO deposition and the relatively high postannealing temperature usually required for high-quality TCO films is not conducive to improving the performance of the perovskite solar cells with low ion bombardment and temperature tolerances. Herein, cerium-doped indium oxide (ICO) thin films are prepared by reactive plasma deposition (RPD) at substrate temperatures below 60 °C. A high carrier mobility of 50.26 cm2 V-1 s-1, a low resistivity of 7.18 × 10-4 Ω·cm, and an average transmittance of 86.53% in the wavelength range of 400-800 nm and 87.37% in the wavelength range of 800-1200 nm are achieved. The RPD-prepared ICO film is used as a transparent electrode on top of the ST-PSCs (band gap ∼1.68 eV), and photovoltaic conversion efficiency (PCE) of 18.96% is achieved on the champion device.

Improvement of the uniformity of structural and electrical properties of transparent conductive Al-doped ZnO thin films by inductively coupled plasma-assisted radio frequency magnetron sputtering

Transparent conductive Al-doped Zinc oxide thin films were deposited on glass substrates by conventional radio frequency magnetron sputtering (C-RFMS) and inductively coupled plasma-assisted radio frequency magnetron sputtering (ICP-RFMS) methods. The structural and electrical properties of films were studied as a function of the radial position (r) of the substrate in both methods. A good thickness uniformity was obtained in ICP-RFMS, while a significant decrease in film thickness was observed at r=30mm (erosion zone) in C-RFMS. The c-axis orientation was achieved in all positions in ICP-RFMS, while crystallinity was degraded at r≥25mm in C-RFMS. Low resistivity ρ of the order of 10−4Ωcm was obtained at all positions in ICP-RFMS, while ρ was rapidly increased at r≥30mm in C-RFMS. In ICP-RFMS, high-energy ion bombardment is suppressed due to the modified plasma density profile and lower space potential. As for transparency, the sample prepared at r=0mm in ICP-RFMS showed an average visible transmittance of 81%, higher than that in C-RFMS. Throughout the study, it was demonstrated that ICP-RFMS method was promising to improve the radial distribution of structural, electrical, and optical properties of Al-doped ZnO thin films.

Chemical Reactivity of Strongly Interacting, Hydrogen-Bond-Forming Molecules Following 193 nm Photon Irradiation: Methanol in Amorphous Solid Water at Low Temperatures.

Mixtures of methanol and amorphous solid water (ASW) ices are observed in the interstellar medium (ISM), where they are subject to irradiation by UV photons and bombardment by charged particles. The charged particles, if at high enough density, induce a local electric field in the ice film that potentially affects the photochemistry of these ices. When CD3OD@ASW ices grown at 38 K on a Ru(0001) substrate are irradiated by 193 nm (6.4 eV) photons, products such as HD, D2, CO, and CO2 are formed in large abundances relative to the initial amount of CD3OD. Other molecules such as D2O, CD4, acetaldehyde, and ethanol and/or dimethyl ether are also observed, but in smaller relative abundances. The reactivity cross sections range from (2.6 ± 0.3) × 10-21 to (3.8 ± 0.3) × 10-25 cm2/photon. The main products are formed through two competing mechanisms: direct photodissociation of methanol and water and dissociative electron attachment (DEA) by photoelectrons ejected from the Ru(0001) substrate. An electric field of 2 × 108 V/m generated within the ASW film during Ne+ ions bombardment is apparently not strong enough to affect the relative abundances (selectivity) of the photochemical products observed in this study.

Effect of Low-Energy Ion Bombardment on the Texture and Microstructure of Platinum Films

Effect of Low-Energy Ion Bombardment on the Texture and Microstructure of Platinum Films

Influence of Low-Energy Ion Bombardment on the Texture and Microstructure of Pt Films

Influence of Low-Energy Ion Bombardment on the Texture and Microstructure of Pt Films

Electron-assisted PR etching in oxygen inductively coupled plasma via a low-energy electron beam

In this study, electron-assisted photoresist (PR) etching is conducted using oxygen inductively coupled plasma at a pressure of 3 mTorr. During the PR etching, a low-energy electron beam is generated and is controlled by varying the acceleration voltage (0–40 V) on the grid to assist with the PR etching. When a low acceleration voltage (&amp;lt;20 V) is applied, no electron beam is generated, and PR etching is assisted by the accelerated ions. However, the acceleration voltage is increased (about 20–25 V), an electron beam is generated, and PR etching is assisted by the electron beam. At high acceleration voltages (&amp;gt;25 V), the etch rate increases, and the ion bombardment energy decreases with increasing electron beam energy. The electron energy probability function is measured to verify the relation between the etch rate and acceleration voltage with respect to the sheath thickness on the grid. Furthermore, low contribution of the O radical to the etch rate increment is observed via optical emission spectroscopy measurements.

Pulsed chemical vapor deposition for crystalline aluminum nitride thin films and buffer layers on silicon and silicon carbide

Low temperature aluminum nitride (AlN) deposition has applications ranging from serving as a heat spreading material to serving as a buffer layer for III-V semiconductors on silicon or silicon carbide (SiC) for radio frequency, power, and microLED devices. While crystalline AlN is traditionally deposited at high temperature (>800 °C), in the present study AlN is deposited on Si(100), Si(111), and 4H-SiC substrates by two modest temperature processes using a metal precursor with high thermal stability, tris(dimethylamido) aluminum (III), and a highly reactive nitrogen source, anhydrous hydrazine. A 580 °C pulsed chemical vapor deposition (CVD) process is compared to a more complex 400 °C atomic layer annealing process, in which the same precursors are utilized with periodic ion bombardment to induce film crystallinity. Films deposited by both processes template preferential c-axis orientation in subsequently sputtered AlN on unheated substrates. Both templating techniques demonstrate equivalent enhancements in crystallinity of the sputtered AlN relative to a non-templated sputtered film by x-ray diffraction and transmission electron microscopy studies. On 4H-SiC substrates, a comparison of sputtering directly and templating with the 580 °C pulsed CVD process reveals epitaxial deposition by the 580 °C pulsed CVD process which extends into the low temperature sputtered AlN.

Insights on film growth conditions on a floating substrate during reactive Ar/O2 bipolar high power impulse magnetron sputter deposition

We report several effects found in reactive bipolar high-power impulse magnetron sputtering (abbreviated as bipolar HiPIMS or BPH) discharges at the substrate level. The role of the negative peak current and the positive pulse voltage, U, on the deposition flux at the electrically insulating substrate is discussed and the results are compared to conventional DC discharges. In particular, the normalized energy flux, ϕ n , delivered to the substrate is found higher under BPH conditions at U = +300 V ( eV·nm−3) as compared to the HiPIMS ( eV·nm−3) and DCMS ( eV·nm−3) regimes which is assumed to be provoked by an intensification of the positive ion bombardment. Accordingly, the mean energy and the count of positively charged metal and gaseous ions increase in line with U as measured by energy-resolved mass spectrometry. Contrariwise, our analysis has shown a significant decrease (≈20 %) of negative oxygen ion count under BPH conditions.

The effect of the surface patterning by ion beam irradiation on the Ag directional outflow in Ag/AlN nano-multilayers

Surface templating of nano-multilayers is a promising step for the advanced industrial application of these nanomaterials. In the present work, the effect of focused ion beam modification of Ag/AlN nano-multilayer near-surface region on the Ag surface outflow is revealed. Surface patterning by ion beam irradiation leads to the formation of a higher amount of Ag crystals in relation to the intact surface region. Heat treatment initiates grooving of Ag grain boundaries, resulting in the formation of channels in the nano-multilayer volume. These channels act as pathways for mass transport of Ag to the film surface. Ion bombardment creates regions of high concentration of non-equilibrium defects, which locally increase the driving force for grooving and channeling, thereby promoting creation of more pathways for Ag surface migration. The obtained experimental results indicate that surface modification by focused ion beam can be used for production of nano-multilayers with designed templates of surface outflow.

Nanoscale pattern formation produced by ion bombardment of a rotating target: The decisive role of the ion energy.

We study the nanoscale patterns that form on the surface of a rotating sample of an elemental material that is bombarded with a broad noble gas ion beam for angles of incidence θ just above the critical angle for pattern formation θ_{c}. The pattern formation depends crucially on the ion energy E. In simulations carried out in the low-energy regime in which sputtering is negligible, we find disordered arrays of nanoscale mounds (nanodots) that coarsen in time. Disordered arrays of nanodots also form in the high-energy regime in which there is substantial sputtering, but no coarsening occurs close to the threshold angle. Finally, for values of E just above the sputter yield threshold, nanodot arrays with an extraordinary degree of hexagonal order emerge for a range of parameter values, even though there is a broad band of linearly unstable wavelengths. This finding might prove to be useful in applications in which highly ordered nanoscale patterns are needed.

Can One Series of Self-Organized Nanoripples Guide Another Series of Self-Organized Nanoripples during Ion Bombardment: From the Perspective of Power Spectral Density Entropy?

Ion bombardment (IB) is a promising nanofabrication tool for self-organized nanostructures. When ions bombard a nominally flat solid surface, self-organized nanoripples can be induced on the irradiated target surface, which are called intrinsic nanoripples of the target material. The degree of ordering of nanoripples is an outstanding issue to be overcome, similar to other self-organization methods. In this study, the IB-induced nanoripples on bilayer systems with enhanced quality are revisited from the perspective of guided self-organization. First, power spectral density (PSD) entropy is introduced to evaluate the degree of ordering of the irradiated nanoripples, which is calculated based on the PSD curve of an atomic force microscopy image (i.e., the Fourier transform of the surface height. The PSD entropy can characterize the degree of ordering of nanoripples). The lower the PSD entropy of the nanoripples is, the higher the degree of ordering of the nanoripples. Second, to deepen the understanding of the enhanced quality of nanoripples on bilayer systems, the temporal evolution of the nanoripples on the photoresist (PR)/antireflection coating (ARC) and Au/ARC bilayer systems are compared with those of single PR and ARC layers. Finally, we demonstrate that a series of intrinsic IB-induced nanoripples on the top layer may act as a kind of self-organized template to guide the development of another series of latent IB-induced nanoripples on the underlying layer, aiming at improving the ripple ordering. The template with a self-organized nanostructure may alleviate the critical requirement for periodic templates with a small period of ~100 nm. The work may also provide inspiration for guided self-organization in other fields.

Damage Effects of Heavy Ion Irradiation on MOST/C Multilayer Films

In this study, the nano-multilayer film was prepared by alternating deposition of MoS2/Ti composite layer and amorphous C layer, and the irradiation damage effect was studied by the heavy ion bombardment experiment of 2 MeV Au2+. The results show that the irradiation region of the film is about 500 nm deep. The MoS2 crystal inside the MoS2/Ti composite layer in the irradiation-affected area is destroyed by incident Au2+ ions and turns into a disordered state. With the increase of irradiation dose, the hardness of the film increases from 1.58 to 3.28 GPa, and the wear life of the film decreases sharply from 3 × 104 to 5 × 103 r due to the destruction of the internal crystal and the embrittlement of the structure. In addition, with the increase of irradiation dose, the interlayer interface is gradually blurred and the interlayer diffusion is gradually aggravated.