keV Argon Ions Research Articles

Ion beam analysis of sputter-deposited gold films for quartz resonators

Sputter deposition using a focused ion beam has been investigated as an alternative to magnetron sputtering for the deposition of thin-film gold electrodes onto quartz resonators. One potential concern is the inclusion of argon in the growing film when argon ions are used for sputtering. Argon retention in sputter-deposited gold films using an 11.5 keV argon ion beam was investigated with Rutherford backscattering spectrometry and it was found that in layers deposited at close to normal ejection angles the argon trapping was at the level of ≤1 at.%, similar to magnetron-deposited layers, whereas argon incorporation increased with the ejection angle up to several per cent at large angles. Copyright © 2000 John Wiley & Sons, Ltd.

Side-wall damage in a transmission electron microscopy specimen of crystalline Si prepared by focused ion beam etching

In focused ion beam (FIB) fabrication of cross-sectional transmission electron microscopy (X-TEM) specimens, highly accelerated ion beams sometimes cause serious damage. The damage can be induced in both the specimen surface and the side walls. We used the X-TEM technique to investigate the sidewall damage in crystalline Si. The damaged layer was found to be about 20 nm thick in the case of 30-keV-FIB etching. We evaluated several techniques for reducing the damage, such as gas-assisted etching (GAE) with iodine, low-energy FIB etching, and cleaning by broad argon ion milling or by wet etching. The damage depth was 19 nm for GAE and 10 nm for 10 keV FIB etching, and was reduced to 7 nm by 3 keV argon ion milling with a beam current of 20 μA and a tilt angle between the beam and the specimen of 4°. Wet etching using a mixture of nitric and hydrofluoric acid removed most of the damaged layer. The effect of the damaged layer on TEM observation was also investigated, and it was shown that removal of the damaged layer results in a high-resolution TEM image.

Soft X-ray fluorescence measurements of irradiated polyimide and polycarbosilane films

Abstract Fluorescent soft X-ray carbon Kα and silicon L 2,3 emission spectra (XES) have been used to characterize the bonding of carbon atoms in polyimide (PI) and polycarbosilane (PCS) films. The PI films have been irradiated with either 40 keV nitrogen or argon ions, at concentrations ranging from 1×10 14 to 1×10 16 cm −2 . The PCS films have been irradiated with 5×10 15 carbon ions cm −2 of 500 keV and/or annealed at 1000°C. We find that the fine structure of the carbon XES of the PI films changes with implanted ion concentrations above 1×10 14 cm −2 which we believe is due to the degradation of the PI film into amorphous C:N:O. The bonding configuration of free carbon precipitates embedded in amorphous SiC which are formed in PCS films after irradiation with C ions or combined treatments (irradiation and subsequent annealing) is similar to that found in diamond-like films or in graphite-like films, respectively.

An X-ray photoelectron spectroscopy sputter profile study of the native air-formed oxide film on titanium

The incipient air-formed oxide film on titanium is approximately 80 Å in thickness and consists of TiO 2. Sputtering the oxide film in vacuum with 3 keV argon ions changes the composition of the oxide film. XPS depth profiles obtained by sputtering with 3 keV argon ions show that after sputtering, the outermost portion of the film consists of TiO 2 and that the inner portion consists of Ti 2O 3 and TiO. Mathematical analysis of the sputtered oxide film as a three-layer structure shows that with increased time of sputtering, the calculated thickness of TiO 2 and its mole fraction in the oxide film decreases faster than that due solely to thinning of the outermost layer. In addition, the mole fraction of the TiO layer increases, while that of the Ti 2O 3 remains relatively unchanged during sputtering. These observations suggest that the ion beam reduces part of the TiO 2 layer to Ti 2O 3, which in turn is then reduced to TiO.

The influence of ion bombardment intensity during deposition on nickel films microstructure

Nickel films were deposited from a vapour phase (e-gun source) onto amorphous glass substrates at room temperature during a simultaneous bombardment with nitrogen ions at low pressure (4 × 10 −2 Pa). Under a constant partial pressure of nitrogen and negative substrate bias voltages the effect of bombardment intensity on the texture and morphology of Ni films (about 1 μm) has been investigated by XRD and STM methods. The films under investigation exhibit a variable degree of (200) preferred orientation by changing the ion to atom flux ratio ( IAR) from 0.03 to 0.3. It was found that complete (200) texture was achieved for an IAR of about 0.1 and that further increase of IAR induces the decrease of preferred orientation. X-ray diffraction in combination with profiling by a 1 keV argon ion beam bombardment has been used for in. depth texture and grain size analysis. It has been shown that oriented growth, grain size and morphology correlate with changes of bombardment intensity during the deposition as well as with the substrate bias potential.

Ion-induced sputtering of a metal in the form of large clusters

A model is proposed for the ion-induced sputtering of a metal in the form of large clusters with a number of atoms N⩾5. The model is based on simple physical assumptions and is consistent with experiment. As an example, calculations are made of the relative cluster yield as a function of the number of atoms in the cluster as a result of the bombardment of various metals by singly charged 5 keV argon ions. A comparison is made with experimental data.

Irradiation effect on (Bi-Pb) 2223superconductor

The superconducting material with nominal composition Bi1.6Pb0.4Sr2Ca2Cu3Ox has been subjected to irradiation with 500 KeV argon ions at two doses 1 × 1017 and 2 × 1017 ions/cm2. X-ray diffraction, resistivity and magnetic susceptibility examined before and after irradiation. Tc decreased after irradiation. This decrease could be explained to displacement of Bi-Pb.

Study of argon-irradiation-induced defects and amorphization in silicon using a positron beam, Raman spectroscopy and ion channelling

Studies of irradiation-induced defects have been carried out on silicon single-crystal samples, irradiated with 140 keV argon ions to doses in the range 5 × 1014 to 5 × 1016 cm-2, using a variable-low-energy positron beam, Raman spectroscopy and ion channelling. The Doppler broadening lineshape S-parameter has been found to exhibit a peak as a function of the positron beam energy Ep and a subsequent saturation behaviour for all irradiated samples. The peak damage occurs at a depth of 100 nm, consistent with TRIM code calculations. The measured S-Ep curves are analysed using a positron diffusion model to obtain the depth profile of positron-trapping defects. The behaviour of the S-W correlation plots and the variation of the R-parameter indicate that the nature of the open-volume defects is independent of the dose and the dominant defects are vacancy clusters larger than divacancies. Raman spectroscopic studies indicate that all of the irradiated samples are amorphized, and the degree of residual crystallinity across the irradiated zone of the sample is obtained. Ion-channelling studies carried out on the samples have yielded thicknesses of the amorphized layer which are consistent with positron beam results. In contrast to the TRIM code calculations, the present results show the presence of defects at depths far beyond the Ar-ion range. The results of the positron beam, Raman and ion-channelling studies are discussed in the context of ion-induced defects and amorphization.

Soft X-ray fluorescence measurements of irradiated polymer films

Fluorescent soft X-ray carbon Kα emission spectra (XES) have been used to characterize the bonding of carbon atoms in polyimide (PI) and polycarbosilane (PCS) films. The PI films have been irradiated with 40 keV nitrogen or argon ions, at fluences ranging from 1 × 10 14 to 1 × 10 16 cm −2. The PCS films have been irradiated with 5 × 10 15 carbon ions cm −2 of 500 keV and/or annealed at 1000°C. We find that the fine structure of the carbon XES of the PI films changes with implanted ion fluence above 1 × 10 14 cm −2 which we believe is due to the degradation of the PI into amorphous C:N:O. The width of the forbidden band as determined from the high-energy cut-off of the C Kα X-ray excitation decreases with the ion fluence. The bonding configuration of free carbon precipitates embedded in amorphous SiC which are formed in PCS after irradiation with C ions or combined treatments (irradiation and subsequent annealing) is close to either to that in diamond-like films or in silicidated graphite, respectively.

Superficial defects induced by argon and oxygen bombardments on (110) TiO 2 surfaces

Compositional and chemical changes of titanium dioxide monocrystalline surfaces induced by bombardment with 4 keV argon and oxygen ions have been studied by AES, XPS and AFM. Argon ion bombardment induced strong changes in the composition and chemical state of the surface: loss of oxygen due to preferential sputtering occurred, and, related to this, Ti 4+ species were reduced to Ti 3+ and Ti 2+. During oxygen bombardment, competition between preferential sputtering of oxygen ions of the oxide surface and oxygen implantation was observed. This phenomenon was found to be strongly dependent upon the incidence angle of the oxygen ions. Moreover, an oxygen bombardment with normal incidence of the surface that had been previously submitted to an argon ion bombardment led to a restoichiometrization of the surface: no further Ti 3+ or Ti 2+ was found by XPS, only Ti 4+.

Long-range structural interaction effect in gallium arsenide during ion bombardment

Transmission electron microscopy is used to study changes in the structure of gallium arsenide samples after bombardment by high doses of 5 keV argon ions. A change in the structure of the samples is observed at depths exceeding the average penetration depth of the ions by an order of magnitude. A model is proposed to explain the long-range structural interaction effect in gallium arsenide in terms of a phase transition induced by elastic stresses in the sample.

Angular distributions of particles sputtered from polycrystalline platinum

The angular distributions of sputtered particles for 3–10 keV argon-ion bombardment of polycrystalline platinum at normal incidence have been investigated both experimentally and by computer simulation using the program TRIM.SP. Two types of targets were used. One is a fine-grained Pt polycrystal, the other is rolled sheet Pt. The angular distributions were measured applying RBS of the material deposited on a collector. For fine-grained platinum the angular distributions are cupola shaped and slightly overcosine. For rolled platinum the distributions are much more overcosine with a strong central Wehner spot due to the texture caused by rolling. Results from computer simulation show that the effect of the surface binding energy on the shape of the angular distribution is negligible. The dependence of the shape of the angular distribution on the ion energy interval from 3.5 to 10 keV was also found to be very weak. Good agreement has been found between the experimental and computed results for fine-grained platinum.

Growth kinetics of CoSi formed by ion beam irradiation at room temperature

Growth kinetics of cobalt silicide layers formed by ion beam irradiation was investigated at a temperature between room temperature and 100 °C. The CoSi phase was identified by x-ray diffraction of Co/Si samples irradiated with 25 keV argon ions to a dose of 2.0×1015 cm−2. The number of intermixed silicon atoms in the CoSi layers was evaluated as a function of dose, dose rate, and nuclear energy deposition rate at the Co/Si interface for samples irradiated with 40 keV focused silicon ion beams. The growth is shown to be diffusion-limited and attributed to radiation-enhanced diffusion with an activation energy of 0.16 eV. The number of intermixed silicon atoms is approximately proportional to the nuclear energy deposition rate at the initial Co/Si interface, while it is independent of dose rate, which shows that the CoSi phase is formed without contribution of the sample heating caused by irradiation.

Growth mechanism of cubic boron nitride thin films by ion beam assist sputter deposition

Cubic boron nitride (c-BN) thin films were successfully grown on Si(100) substrates by dual ion beam sputter deposition and the growth mechanism was studied with angle resolved in situ x-ray photoelectron spectroscopy (XPS) analysis. Boron was sputter deposited by 1 keV argon ions from a boron target and simultaneously bombarded with low energy nitrogen and argon ions mixture. Through Fourier transform infrared absorption spectroscopy (FTIR) and in situ XPS experiment, the optimum conditions for the c-BN growth such as the substrate temperature, the assist ion current density and the ion energy were determined to be 460 °C, 60 μA/cm2 and 350 eV, respectively. Angle resolved in situ XPS analysis showed that the 1.2±0.2 nm surface layer of the c-BN film is always in the hexagonal boron nitride (h-BN) phase, which clearly shows that c-BN phase grows by the transformation from the initially formed h-BN phase by low energy ion bombardment. Cross-sectional high resolution transmission electron microscopy (TEM) images show that the BN thin films on Si has a sequential layered structure which consists of an initial amorphous BN (a-BN) layer (∼4 nm), a transitional h-BN layer (∼5 nm), and a main c-BN layer. The transformation of the h-BN to the c-BN phase and the unusual sequential layered structure were discussed in view of the compressive stress model.

Ion beam induced surface modification of chemical vapor deposition diamond for x-ray beam position monitor applications

The Advanced Photon Source at Argonne National Laboratory is a third-generation synchrotron facility that generates powerful x-ray beams on its undulator beamlines for a variety of scientific and industrial user research programs. It is very important to know the position and the angle of the x-ray beam during experiments. Due to very high heat flux levels, several patented x-ray beam position monitors (XBPMs) exploiting beneficial characteristics of chemical vapor deposition (CVD) diamond have been developed. These XBPMs have a thin layer of low-atomic-mass metallic coating so that photoemission from the x rays generates a minute but measurable current for position determination. Another concept has been the graphitization of the CVD diamond surface to create a very thin, intrinsic conducting layer that can stand much higher temperatures and have minimal x-ray transmission losses compared to coated metallic layers. In the present study, a laboratory sputter ion source was used to transform selected surfaces of a CVD diamond substrate into graphite. The effect of 1–5 keV argon ion bombardment on CVD diamond surfaces at various target temperatures from 200 to 500 °C was studied using Auger electron spectroscopy and in situ electrical resistivity measurements. Graphitization after the ion bombardment was confirmed, and optimum conditions for graphitization were studied. Raman spectroscopy was applied to identify the overall diamond structure in the bulk of CVD diamond substrate after the ion bombardments. It was found that the target temperature plays an important role in the stability and electrical conductivity of the irradiated CVD diamonds.

Dose effects on amorphous silicon sputtering by argon ions: A molecular dynamics simulation

We have investigated, using molecular dynamics techniques, the sputtering yield enhancement of amorphous silicon produced by argon ion accumulation within the target. Several amorphous silicon samples, with different argon contents, were bombarded with 1 keV argon ions at normal incidence. To study the influence of the target structure, we considered samples with different argon arrangements, either uniformly distributed or within solid bubbles. We have observed that silicon sputtering yield increases linearly with dose until steady state conditions are reached. This enhancement is produced by the shallow argon atoms through the weakening of Si–Si bonds. We have also observed that argon release takes place even long after the end of the collisional phase, and it is produced by ion-induced desorption and bubble destabilization. This enhanced argon yield determines the dose where target saturation and steady state conditions are reached.

Multiply charged direct recoil spectra from Ar + and Kr + bombarded graphite

Measurements of the energy spectra of multiply charged positive and negative carbon ions (C n ± ) recoiling from graphite surface under 100 and 150 keV argon and krypton ion bombardment are presented. With the energy spectrometer set at recoil angle of 79.5°, direct recoil (DR) peaks have been observed with singly as well as multiply charged carbon ions C n ± , where n = 1 to 6. These C n ± ions have been seen recoiling with the characteristic recoil energy E DR = kE 0cos 2 θ DR, where θ DR is the direct recoil angle, k = 4m 1m 2 (m 1 + m 2) 2 , m 1 and E 0 are projectile mass and energy and m 2 is carbon mass. We have observed sharp DR peaks. A collimated projectile beam with divergence ∼ ±0.2° is supplemented with a similar collimation before the energy analyzer to reduce the background of sputtered ions due to scattered projectiles.

Ion bombardment of MoS 2 nanoplateletcoatings deposited by electrospraying

The present paper reports on a novel process for deposition ofMoS2 lubricating coatings by electrospraying aball-milled platelet suspension of stoichiometric MoS2particles. Ultralow friction coefficients in the range of0.010-0.020, in a dry-nitrogen atmosphere, were obtained with areciprocating ball-on-disk tribometer for a stainless-steel ballsliding on a MoS2-coated silicon substrate. Thesliding endurance for MoS2, as deposited, was measuredfor thicknesses ranging from 0.28 to 1.00 μm tobe between 0.6 and 44 m. The effect of a low-dose, high-energy,argon-ion bombardment was studied. Thus an ion bombardment with400 keV argon ions to a dose of 18 x 1015ions/cm2 increased the sliding endurance by a factorof about thirty, for a coating thickness of 0.3μm.

Damage ranges in metals after ion implantation

Mo〈110〉 single crystals were implanted with 150 keV argon ions at temperatures between 20 and 300 K and defect profiles were determined by α-particle channelling in a backscattering geometry. Analyses of the low temperature implants were performed in situ at various annealing steps up to room temperature. At all implantation and annealing temperatures, similar damage ranges were observed, which exceeded the trim estimate by more than a factor of two. Ranges did not change during warming up, but the defect density started to increase significantly above an annealing temperature of 77 K for implantation at a temperature below recovery stage I. The results are compared with previous studies on other metals. All available data on implantation damage in metals disagree with the assumption that defect structures beyond projected ion ranges are a result of point defect migration. It is proposed that the observed damage range enhancement in metals is due to a mechanism based on dislocation dynamics.

Study of implantation damage ranges in metals at temperatures ranging from 5 to 300 K

Cu〈111〉 single crystals were implanted with 150 keV argon ions at temperatures between 5 and 300 K and analysed in-situ by α-particle channeling in a backscattering geometry. At all temperatures similar damage ranges were observed, which exceed the TRIM-estimate approximately four times. Ranges did not change during warming up, but the defect density changed significantly in the case of the 5 K implantation. The observations are in disagreement with a simple point defect migration process as interstitial atoms become mobile only above 45 K. Possible mechanisms to explain these results are discussed. Furthermore some room temperature measurements of damage ranges in gold and silver single crystals are also given.