Effect Of Ion Bombardment Research Articles

Electron and Ion Densities Measurement in Reactive Magnetron Zinc Sputtering Plasma

Abstract. Investigation on the plasma properties is an essential fundamental works in order to precisely control the growth of nanoscale thin film. In the present work, we produced and study the reactive magnetron sputtering plasma in Ar+O2 ambient using a solid Zn target as sputter source. We evaluate the electron temperature, electron density and ion density using Langmuir probe measurement as a function of O2 flow rate and working pressure. We found that the electron temperature increased spontaneously with the oxygen flow rate. The electron temperature was almost doubled when O2 flow rate increased from 0 sccm to 10 sccm. The electron and ion densities increased with the oxygen flow rate between 0 sccm and 5 sccm. However, after 5 sccm of O2 flow rate which is approximately 11% of O2/(O2+Ar) flow rate ratio the electron density decreased drastically. This is due to the electron attachment and the production of negative ion species in Ar+O2 plasma environment. In addition, we found that the ion flux increase monotonically with the O2 flow rate thus will increase the ion bombardment effect on the deposited thin film and eventually damage the thin film. Our experimental results suggest that the O2 flow rate and the working pressure would have a significant influence on ion bombardment effect on deposited thin film.

Nanostructured light-absorbing crystalline CuIn(1–x)GaxSe2 thin films grown through high flux, low energy ion irradiation

A hybrid effusion/sputtering vacuum system was modified with an inductively coupled plasma (ICP) coil enabling ion assisted physical vapor deposition of CuIn1−xGaxSe2 thin films on GaAs single crystals and stainless steel foils. With <80 W rf power to the ICP coil at 620–740 °C, film morphologies were unchanged compared to those grown without the ICP. At low temperature (600–670 °C) and high rf power (80–400 W), a light absorbing nanostructured highly anisotropic platelet morphology was produced with surface planes dominated by {112}T facets. At 80–400 W rf power and 640–740 °C, both interconnected void and small platelet morphologies were observed while at >270 W and above >715 °C nanostructured pillars with large inter-pillar voids were produced. The latter appeared black and exhibited a strong {112}T texture with interpillar twist angles of ±8°. Application of a negative dc bias of 0–50 V to the film during growth was not found to alter the film morphology or stoichiometry. The results are interpreted as resulting from the plasma causing strong etching favoring formation of {112}T planes and preferential nucleation of new grains, balanced against conventional thermal diffusion and normal growth mechanisms at higher temperatures. The absence of effects due to applied substrate bias suggests that physical sputtering or ion bombardment effects were minimal. The nanostructured platelet and pillar films were found to exhibit less than one percent reflectivity at angles up to 75° from the surface normal.

Nanostructures of mixed-phase boron nitride via biased microwave plasma-assisted CVD

Boron nitride films and nanostructures are deposited by the reaction of B2H6 and NH3 in H2 via biased microwave plasma-assisted chemical vapor deposition. One-dimensional boron nitride nanostructures (BNNSs) are observed on the BN layers by the processing of diamond/BN multilayer under ion-bombardment and plasma etching. At a substrate bias of −100 V, the morphologies of the BNNSs evolve from dense film to nanocorns to nanotips, when the number of the diamond/BN bi-layer increases. Various phases of boron nitride including amorphous-BN, hexagonal h-BN, turbostratic t-BN, rhombohedral r-BN, explosion E-BN, wurtzitic w-BN and cubic c-BN are detected in the BNNSs. The BN nanotips observed are considered to result from the tip structure growth from the combined effects of ion bombardment and plasma etching.

Diamond-like carbon sputtering by laser produced Xe plasma

The sputtering of diamond-like carbon (DLC) was investigated using Xe ion bombardment from the laser plasma X-ray source (LPX). The LPX we developed uses a solid Xe target and emits UV–X-rays and Xe ions. Using the LPX as an ion source, we measured etching depths of DLC, Ru, and Au films using a quartz crystal microbalance (QCM) to determine their ion sputtering rates at incident angles of 0° and 70°. The calculated results by the SRIM code were able to predict the measured results, except for the case of the DLC film at 0° incident. Our measured result indicated that the DLC sputtering at 0° was ten times larger than previously reported data, in which an ion gun was used. We consider that the difference was a characteristic effect of the laser plasma, and can be explained as a synergistic effect of ion bombardment and UV radiation from the Xe plasma.

Surface modification of Ti-6Al-4V alloy by cathode assiting discharge setup and conventional plasma nitriding methods

In order to improve the wear resistance of titanium alloys, the potential of the plasma nitriding process with a cathode assiting discharge setup was examined. Ti6Al4V alloy was nitrided by the cathode assiting discharge nitriding (CAN) and conventional DC plasma nitriding (CPN) methods, respectively. The micro-topography, phase composition and cross-sectional microhardness distribution of two nitriding layers were studied comparatively. The sliding wear resistance of the nitriding layers was examined by a ball-on-disk test against Si3N4 balls. The results indicated that the surface roughness Ra of the CAN layer was about 1 order less than that of the CPN layer. In addition, the CAN surfaces possessed significantly greater wear resistance than the CPN layer at higher loads, and increased the wear resistance of Ti6Al4V alloy by about 2 orders due to the higher loading bearing ability, higher rate of TiN phase, greater surface microhardness and bigger microhardness improving depth. This is because the double glow discharge effect in CAN strengthened the density of the active nitrogen atoms and the nitriding efficiency. Moreover, the ion bombardment effect on the surface of the nitriding titanium alloy was reduced obviously.

Effects of low energy ion bombardment on the formation of cubic iron mononitride thin films

The formation of cubic nitrides with stoichiometry close to FeN obtained by ion assisted sputter deposition has been studied as a function of deposition parameters. In particular, we have explored the influence of the energy deposited by the assistant beam per deposited Fe atom to understand changes in composition, phase formation and nanocrystallinity of the films. An optimum N2+ ion energy and a JN/JFe ratio (JN and JFe represent the current density of N2+ ions and Fe atoms respectively) have been determined in order to obtain only iron mononitride phases. X-ray diffraction and Mössbauer spectroscopy revealed a phase evolution from ε-Fex(x≈2)N to γ″ and γ‴-FeN as the N2+ ion energy and the JN/JFe flux ratio increase. Pure nanocrystalline iron mononitride, with nitrogen content close to 50%, is obtained when JN/JFe ratio reaches 5.9 and the N2+ ion energy is 63.4eV. Further increments of N2+ energies and JN/JFe values reverse this behavior and a phase evolution from γ″ and γ‴-FeN to ε-Fex(x≈2)N is found. This behavior is attributed to energy damage and resputtering phenomena. It has also been found that γ‴-FeN phase coexists with γ″-FeN phase when the deposition is performed at room temperature.

Vibronic fine structure in high-resolution x-ray absorption spectra from ion-bombarded boron nitride nanotubes

The authors have applied high-resolution near-edge x-ray absorption fine structure measurements around the nitrogen K-edge to study the effects of ion-bombardment on near-surface properties of boron nitride nanotubes. A notable difference has been observed between surface sensitive partial electron yield (PEY) and bulk sensitive total electron yield (TEY) fine-structure measurements. The authors assign the PEY fine structure to the coupling of excited molecular vibrational modes to electronic transitions in NO molecules trapped just below the surface. Oxidation resistance of the boron nitride nanotubes is significantly reduced by low energy ion bombardment, as broken B-N bonds are replaced by N-O bonds involving oxygen present in the surface region. In contrast to the PEY spectra, the bulk sensitive TEY measurements on as-grown samples do not exhibit any fine structure while the ion-bombarded samples show a clear vibronic signature of molecular nitrogen.

Bias deposition of nanoporous Cu thin films

Nanoporous Cu (NPC) thin films are deposited at room temperature using the bias RF-balanced magnetron sputtering technique. The morphologies of as-deposited NPC films are characterized by a field-emission scanning electron microscope. It is observed that a bicontinuous triangle-ligament/channel structure or a porous triangle-prism structure can be achieved depending on the substrate surface. Cu thin films are also deposited either without substrate bias or at an elevated substrate temperature, however, in which no nanoporosity is observed. Furthermore, a new surface selective charging effect rather than the traditional ion-bombardment and resputtering effects is proposed for a full explanation and thus the underlying growth mechanisms of as-deposited NPC films are revealed.

Effect of ion bombardment on the field emission of graphite materials

The field emission (FE) of surfaces of highly oriented pyrolytic graphite (HOPG) UPV-1T and glassy carbon SU-2000 after irradiation with 30-keV Ar+ ions at different temperatures and incidence angles has been investigated. It has been found that irradiation of the (001) basal plane of UPV-1T at temperatures of T = 250 and 400°C results in the emergence of low-voltage FE with threshold values of the electric-field strength from 3 to 17 V/μm depending on the temperature and irradiation geometry. The lowest field-emission threshold is observed following irradiation at T ≈ 250°C and normal ion incidence. It is shown that ion irradiation of glassy carbon can also result in the low-voltage FE of its surface.

Numerical Analysis of Thermal Stresses in Carbon Films Obtained by the Rf Pecvd Method on the Surface of a Cannulated Screw / Analiza Numeryczna Naprezen Cieplnych W Warstwie Weglowej Otrzymanej W Procesie Rf Pecvd Na Powierzchni Wkreta Kostnego

For many years, research on carbon films has been stimulated by the need to simultaneously optimize their biological and mechanical properties and by the challenges related to their deposition on medical implants. The residual mechanical stress occurring inside deposited films is the most important mechanical parameter which leads to the total destruction of these films by cracking and peeling. In the present work, we systematically studied the effect of ion bombardment during the process of radio frequency plasma enhanced chemical vapor deposition (RF PECVD) by monitoring the temperature distribution on a cannulated screw using the infrared technique. The obtained experimental and finite element modeling (FEM) results show that stresses in carbon films deposited on a cannulated screw are quite inhomogeneous and depend on the geometry of the sample and the relative position of the studied contact area between the substrate/film interface and the surface of the film.

Deposition of rutile (TiO2) with preferred orientation by assisted high power impulse magnetron sputtering

The effect of energetic ion bombardment on TiO2 crystallographic phase formation was studied. Films were deposited using high-power impulse magnetron sputtering (HiPIMS) assisted by an electron cyclotron wave resonance (ECWR) plasma. The ECWR assistance allows a significant reduction of pressure down to 0.075Pa during reactive HiPIMS deposition and subsequently enables control of the energy of the deposited species over a wide range. Films deposited at high ion energies and deposition rates form rutile with (101) a preferred orientation. With decreasing ion energy and deposition rates, rutile is formed with random crystallite orientation, and finally at low ion energies the anatase phase occurs. It is supposed that particles gain high energy during the HiPIMS pulse while the ECWR discharge is mostly responsible for substrate heating due to dissipated power. However, the energetic contribution of the ECWR discharge is not sufficient for annealing and phase transformation.

Comparative study on catalyst-free formation and electron field emission of carbon nanotips and nanotubes grown by chemical vapor deposition

The catalyst-free growth of carbon nanotips and nanotubes on silicon substrate pre-deposited with carbon film was realized under different temperatures in plasma-enhanced hot filament chemical vapor deposition system, in which methane, nitrogen and hydrogen were used as the reactive gases. The structure and composition of synthesized carbon nanotips and nanotubes were investigated using field emission scanning electron microscope, transmission electron microscope and micro-Raman spectroscopy, respectively. The results indicate that the carbon nanotips are formed at about 800°C while the carbon nanotubes are formed about 900°C. According to the ion bombardment effect and the diffusion at different temperatures, the catalyst-free formation of carbon nanotips and nanotubes was comparatively studied. The transformation from carbon film to spherical carbon particles at a high temperature results in the formation of carbon nanotubes depending on the diffusion of carbon. At a low temperature, the carbon film still locates at the substrate and leads to the formation of carbon nanotips relying on the sputtering-etching of etching ions and the deposition of carbonaceous ions. In addition, the electron field emission characteristics of carbon nanotips and nanotubes were investigated. The results indicate that there is much difference in the electron field emission properties for the carbon nanotips and nanotubes. According to the thermal effect produced by Joule heat during electron emission, the difference was interpreted.

Effect and mechanism of ion bombardment on coercive force of NdFeB magnet

Ion bombardment can apparently affect the coercive force of the NdFeB magnet. Compared with the dosage, the bombardment voltage has more obvious effect in change the coercive force of a magnet. When the voltage of ion is 1kV, the coercive force increases by 15% compared to untreated one. However, at a higher voltage of 50kV, ion bombardment induces a decrease of the coercive force by 18%. It is suggested that the irradiated defects play crucial roles in increasing the magnetic coercive force, and the defects were created by weakened lattice discrete breathers (DB) in the domain wall or grain boundary during ion bombardment.

Modelling the sputtering of Au surfaces using a multi time-scale technique

We present results from an atomistic computer simulation model of the sputtering of gold crystal surfaces under 500 eV ion bombardment by Au and Ar ions for doses up to 10 14 ions cm −2 . The multi time-scale technique uses molecular dynamics to calculate the fast ballistic collision processes in the early stages of the cascade, whereas an on-the fly kinetic Monte Carlo technique is used to model the relaxation and diffusion processes between successive ion impacts when the defect motion has begun to be dominated by rare events. The results indicate a large amount of crystalline recovery between impacts, some facetting of the crystal surfaces but no large sub-surface defect accumulation. Because of this recovery process, sputtering yields and energy distributions are in good agreement with those obtained assuming a perfect crystal surface and also with those experimentally measured.

Heavy-ion-induced modification of structural and mechanical properties of carbon-nanotube aerogels

We study the effect of 2MeV Xe ion bombardment at room temperature on the microstructure and mechanical properties of cross-linked carbon-nanotube-based nanoporous carbons. Irradiation causes a gradual densification and a decrease in the surface roughness of monoliths, an increase in Young’s modulus and failure stress, a decrease in the failure strain, and smoothening of nanoligament surfaces. Our results demonstrate a potential of heavy-ion bombardment for a controlled modification of nanoporous carbons.

An ion beam deceleration lens for ultra-low-energy ion bombardment of naked DNA

Study of low-energy ion bombardment effect on biological living materials is of significance. High-energy ion beam irradiation of biological materials such as organs and cells has no doubt biological effects. However, ion energy deposition in the ion-bombarded materials dominantly occurs in the low-energy range. To investigate effects from very-low-energy ion bombardment on biological materials, an ion beam deceleration lens is necessary for uniform ion energy lower than keV. A deceleration lens was designed and constructed based on study of the beam optics using the SIMION program. The lens consisted of six electrodes, able to focus and decelerate primary ion beam, with the last one being a long tube to obtain a parallel uniform exiting beam. The deceleration lens was installed to our 30-kV bioengineering-specialized ion beam line. The final decelerated-ion energy was measured using a simple electrostatic field to bend the beam to range from 10eV to 1keV controlled by the lens parameters and the primary beam condition. In a preliminary test, nitrogen ion beam at 60eV decelerated from a primary 20-keV beam bombarded naked plasmid DNA. The original DNA supercoiled form was found to change to relaxed and linear forms, indicating single or double strand breaks. The study demonstrated that the ion bombardment with energy as low as several-tens eV was possible to break DNA strands and thus potential to cause genetic modification of biological cells.

Raman spectra of heterogeneous nanostructures based on organosilicon films

We studied the effect of ion bombardment on the structure of SOG (spin-on-glass) films. We used IR and Raman spectroscopy and plan-view transmission electron microscopy to study the characteristic features of the structural transformation in organosilicon films when bombarded by nitrogen ions. We show that they are heterogeneous and we establish the presence of inclusions of nanocrystalline graphite.

Atom probe tomography of ion-irradiated ultra-thin Fe/Cr/Fe trilayers with sub-nm spatial resolution

Ion-bombardment effects in a magnetic trilayer Fe (10 nm)/Cr (0.7 nm)/Fe (10 nm) system have been studied by 3D atom probe tomography (APT). The films were bombarded by 30 keV Ga+ ions at low fluences. From APT, the positions of individual Cr and Fe atoms could be located with sub-nm spatial resolution, both before and after ion bombardment. In the pristine specimen the presence of the 0.7 nm Cr layer was verified and individual lattice planes with a spacing of ∼0.15 nm were identified which would correspond to the monolayer spacing of the Fe lattice, in agreement with the growth process. Upon irradiation, the Cr layer is broadened to ∼1.2 nm at a fluence of 3 × 1014 Ga+ cm−2 and to ∼3.4 nm at 3 × 1015 Ga+ cm−2. Computer simulations indicate that, at a fluence of 3 × 1014 Ga+ cm−2, each Cr atom in the intermediate layer is displaced on average once in the collision processes.

Ion-induced effects on grain boundaries and a-Si:H tissue quality in microcrystalline silicon films

Microcrystalline silicon films have been deposited by means of the remote expanding thermal plasma. The effect of ion bombardment on the microcrystalline silicon film properties has been investigated by applying an RF bias to the deposition substrate. The application of the RF substrate bias resulted in the formation of an additional plasma in front of the substrate holder. Neither the SiH4 depletion nor the growth flux was significantly enhanced upon substrate biasing, which suggests that (the composition of) the growth precursor flux is unaffected and that the ion-film interaction mechanisms were responsible for the observed material changes. Moderate bias conditions (i.e., dc bias voltages up to ∼70 V) led to an improved grain boundary passivation and densification of the amorphous silicon tissue, as concluded from the analysis of the infrared Si-Hx stretching modes. These improvements have been ascribed to ion-induced Si surface atom displacement, which enhances the surface diffusion length of the growth precursors. More-energetic ion bombardment (i.e., under applied dc bias voltages of ∼60 V and higher) resulted in enhanced (di)vacancy incorporation via ion-induced Si bulk atom displacement. The film crystallinity was found not to be affected by the ion bombardment, although a reduced crystallite size was observed under ion bombardment conditions where Si bulk displacement had been sufficiently activated. The extent of the ion-film interaction mechanism has been enhanced by increasing the ion-to-Si deposition flux ratio. Under specific ion bombardment conditions, i.e., dc bias voltage in the range of 40–70 V and ion/Si arrival rate ∼0.20, microcrystalline silicon films have been obtained which, on the basis of the Si-Hx stretching modes, are qualified as solar-grade, i.e., the intergranular space is filled with a dense amorphous silicon tissue which completely passivates the crystalline grain boundaries.

Effect of low energy ion bombardment on structure and photoluminescence characterization of Al-doped ZnO thin films

Al-doped zinc oxide (AZO) films are prepared by dual ion-beam assisted sputter deposition at room temperature. An assisting argon ion beam (ion energy Ei=0–300eV) directly bombards the substrate surface to modify the properties of the AZO films. The effects of assisting ion beam energy on the characteristics of AZO films were investigated based on transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and photoluminescence measurement. With increasing assisting ion beam bombardment, the crystalline quality of the AZO films was improved and the oxygen vacancies were increased observably. Two red emissions originating from the oxygen vacancies in the films appear at 1.71 and 1.64eV. This study suggests that wide-band-gap materials could act as effective visible light emitters and ion beam bombardment provides a simple route to synthesize such materials.