Effect Of Low-energy Ion Bombardment Research Articles

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

Effect of low-energy ion bombardment on structural and optical properties of gold functionalized hBN nanosheets

This work reports the effect of low-energy ion (30 KeV Si−1) bombardment on the structural and optical properties of gold-functionalized hexagonal boron nitride (Au-hBN) nanosheets. FE-SEM and XRD results indicate the successful synthesis of highly crystalline Au-hBN nanosheets. The grain size modulation and strain variation in Au-hBN nanosheets with increasing ion fluence clearly indicate defect-induced structural modifications. The optical properties of Au-hBN are investigated by Raman and UV–vis absorption spectroscopy. A systematic drop in the band gap and gradual rise in the Urbach energy of Au-hBN nanosheets with increasing fluence is observed. In addition, the FTIR results reveal the growth of cBN, eBN and wBN phases after irradiation. The theoretical simulations are done to study the defect formation and estimate the damage yields. The experimental and computational results establish the efficacy of the low-energy ion bombardment approach in systematically altering the structural and optical behavior of Au-hBN nanosheets.

The effect of low-energy ion bombardment on residual stress in thin metal films due to the generation of surface defects and their migration to the grain boundary

A kinetic model that describes the evolution of residual stress in thin polycrystalline films during bombardment by ions with energies below the sputtering threshold is presented. The mechanisms responsible for the change in stress are the generation of point defects on the surface and their redistribution over the film thickness along grain boundaries. The presented model was used to explain the experimental data on the change in stress in thin Cr films after treatment in Ar plasma of low-pressure RF induction discharge with ion energy of 15-30 eV.

(Invited) Photo- and Cathodo-Luminescence of InAsxP(1-x)/InP Quantum Well Structures Under the Effects of Low-Energy Ion Bombardment

We investigate photo-luminescence (PL) and cathodo-luminescence (CL) spectra of InAsP/InP quantum well (QW) structures under exposure to low energy ions, and more generally to the particles generated in a plasma reactor typically used for etching such materials. The samples contain QWs of constant thickness (7 to 8 nm) and graded As/P concentration such that each QW produces, at low temperature, a PL line at a well-defined and resolved energy. Adjusting the depth of the QWs below the sample surface, the PL/CL of these QWs is thus the signature of the depth-dependent interaction with the ions and particles from the plasma. We have exposed our QW structures to different kinds of plasmas, containing variable mixtures of halogen-based molecules / hydrocarbons / nitrogen and Ar. Previous studies [1], in particular based on a similar approach of using the QW as an internal probe of the ion – material interaction, have shown that atomic ions with energies in the range of 100 to a few 100’s eV penetrate III-V materials (like GaAs or InP) through a channeling process [2], even if their direction of impingement is not favorable for channeling. The angular dispersion is in general sufficient to produce channeling. The ions channel a certain distance into the crystal, and then stop due to de-channeling mechanisms. As a consequence, a quenching of the PL for the QWs in the region where the de-channeling occurred takes place. We extended the analysis looking not only at the intensity of the PL lines, but also at their spectral characteristics upon exposure to the ion fluxes. Fig. 1 illustrates a selection of the effects that we were able to identify and explain [3]. On fig. 1-a, a sample was exposed to the particles flux from a plasma discharge in SiCl4/H2/Ar. Under the conditions of this plasma discharge, etching actually occurs at a rate ≈ 250-300 nm/min., and we had to be careful not to etch the whole QW structure immediately. Fig. 1-a shows that: - the signal for the two QWs at the lower wavelength seems to disappear. These QWs are the ones closest to the sample surface - the emission bands from the other QWs exhibit energy shifts Transmission electron microscopy and secondary ion mass spectrometry (SIMS) show that actually the two QWs closest to the top surface have not been etched. SIMS shows the penetration of Cl-species below the surface, which probably play a role in the quenching of the PL for these QWs The sample on fig. 1-a was undoped. On fig. 1-b, the same experiment is conducted for a sample with the same QW sequence as that of fig. 1-a, but n-type doped such that a large built-in electric field is created across the QWs region. One can see that this changes completely the shape of the PL lines. The reason for this change can be attributed to the quantum confined Stark effect (QCSE), as shown in [4]. Interestingly, as seen on fig. 1-b, the effect of the interaction with the etching ions is significantly more pronounced than for the undoped sample. We have shown that this is caused by a specific channeling interaction involving ions (probably Cl- ions) which strongly screen the QCSE. Using plasmas containing N2 (which effect is to reduce the etch rate), very significant blue shifts of the PL lines are seen (up to more than 7 nm). These were associated with the incorporation of N deep in the sample, occupying interstitial positions, thus creating local compressive lattice deformation that leads to the blue shifts [3]. All these effects will be discussed in the context of a model that we established to describe the modifications of the luminescence properties of the QW structures under the effect of low-energy ion bombardment. We will also describe experiments on samples where we take benefit of the plasma etching to define nanoscale structures and examine the spatial variation of the PL/CL spectra after interaction with the ion beams. [1] D. L. Green, E. L. Hu, P. M. Petroff, V. Liberman, M. Nooney, and R. Martin, J. Vac. Sci. Technol., B 11, 2249 (1993). [2] R. Germann, A. Forchel, M. Bresch, and H. P. Meier, J. Vac. Sci. Technol., B 7, 1475 (1989). [3] J.P. Landesman, J. Jiménez, C. Levallois, F. Pommereau, C. Frigeri, A. Torres, Y. Léger, A. Beck, and A. Rhallabi, J. Vac. Sci. Technol., A 34, 041304-1 (2016). [4] L. Viña, E. E. Mendez, W. I. Wang, L. L. Chang and L. Esaki, J. Phys. C: Solid State 20, 2803 (1987). Figure 1

Luminescence effects of ion-beam bombardment of CdTe surfaces

In the present work, we report the effect of low-energy ion bombardment on CdTe surfaces. The effect is revealed by FESEM images and photoluminescence (PL) measurements carried out before and after irradiation of CdTe polycrystals by means of an ion-beam sputtering (IBS) system. An important improvement in the luminescence of CdTe was observed in the irradiated areas, related to defect-free surfaces.

Effect of low-energy ion bombardment on the crystal structure and superconductivity of niobium films

The effect of ion bombardment on the growth of Nb films and their crystal structure is investigated. Epitaxial niobium films with the (001) orientation are grown on (01i2) Al2O3 substrates heated to 600°C and biased at −20 V. Niobium films with pronounced axial texture in the [110] direction are grown on water-cooled Sitall (devitrified glass such as Pyroceram) substrates. In Nb films biased at −50 V, which are in the superconducting state, the motion of individual magnetic vortices is observed with a magnetooptic indicator.

The effect of low-energy ion bombardment on the density and crystal structure of thin films

The effect of low-energy ion bombardment on the growth and properties of thin films deposited by rf plasma sputtering at low substrate temperatures is studied. The dependences of the film thickness, density, crystal structure, and conductivity on the bias voltage applied to the substrate are obtained. At biases ranging from 0 to −30 V, nickel films are polycrystalline; at higher biases, they exhibit axial (111) texture. At the bias −60 V, the density of the Ni films is close to that of the bulk metal and the crystal structure of the films is the most ordered. With a further increase in the bias, the density of the films drops because of gas (argon and residual gases) atoms incorporated into the films. The same bias dependence of the density is observed for amorphous films of binary alloys of d and f metals. In this case, the films deposited at the substrate bias −40 V have the highest density.

Semiconductor surface diffusion: Effects of low-energy ion bombardment

We offer a revised mechanism to describe our previous measurements of surface diffusion under low-energy ion bombardment in the Ge/Si(111) system. We show that direct ion-induced motion of diffusing atoms (the effect commonly cited as important in ion beam assisted deposition) cannot account for these observations. Instead, we rationalize the results through processes in which ions create long-lived surface vacancies or spatially extended defects that heal continuously during bombardment. These ideas rationalize several important aspects of the experimental data that were previously unexplained, including the appearance of ion effects at very low ion fluxes, the simple Arrhenius behavior of the diffusivity, the rough magnitudes of the observed energy thresholds, and the ion-induced inhibition of diffusion at high temperatures.

Mechanistic study of ion-induced diamond nucleation

Abstract The effect of low-energy ion bombardment of silicon on diamond nucleation was investigated. By bombarding 100 eV ions of methane and hydrogen on a silicon substrate prior to diamond growth by chemical vapor deposition, diamond nucleation can be immensely enhanced. The ion beam treatment deposited a layer of nano-crystalline graphitic carbon embedded with amorphous SiC. Diamond then nucleated on the graphite overlayer; the nucleation density increased with increasing ion dose. At 1×1019 ions cm−2, a nuclei density of 4×108 cm−2 was obtained. These results show that ion bombardment of the substrate enhances diamond nucleation.

Microstructural Evolution of Ion Bombarded Copper Thin Films

AbstractThe effect of low-energy ion bombardment on the microstructure of copper films will be described. The copper films have been deposited on SiNx-coated, oxidized Si wafers by magnetron sputtering with a simultaneous bombardment of low-energy argon ions (60 eV). The films were annealed at 450°C in HV. The ion bombardment leads to a stronger and sharper {111} texture of the as-deposited films. After annealing, the ion-bombarded films had a significantly smaller grain size than films produced without ion bombardment. The experimental results will be discussed relating the textures of the as-deposited films with the grain sizes obtained after annealing. Details will be given describing how the microstructure of Cu films can be tailored using low-energy argon ion bombardment.

Smoothing During Ion-Assisted Growth by Transient Ion Beam-Induced Defects

AbstractSeveral studies have shown that the surface morphology can be smoother during simultaneous ion bombardment and growth than during growth alone, however, the atomistic mechanism responsible for the smoothing effect has been difficult to determine. We have developed Monte Carlo simulations of growth and defect diffusion to model the interaction between growth atoms and ion-induced defects and to present a simple atomistic mechanism that describes the effects of low-energy ion bombardment during ion-assisted growth of germanium. Measurements of ion-induced point defect production indicate that a large number of defects exist only temporarily on the surface at typical growth temperatures, because the defects have sufficient mobility to recombine and annihilate. We propose that this ion-induced transient defect population plays a significant role in modifying the dynamic surface morphology. the simulations support a surface smoothing mechanism that involves the destabilization of adatom islands by the transient ion-induced defects. the optimum simulated steady-state surface morphology can be achieved with ion-induced defect production rates less than or equal to 10 defects/ion. We find that low-energy ion bombardment during growth effectively lowers the temperature at which step-flow growth can be achieved.

Chemical routes to GaAs etching with low-energy ion beams

The interaction of halogens on GaAs surfaces lies at the heart of a whole host of dry-etching methods. This paper considers the adsorption characteristics of chlorine on GaAs(100)(4*1) and the effect of low-energy ion bombardment on the chemisorbed states formed. The results are discussed in relation to ultra-low damage and low contamination chemically assisted ion beam etching (CAIBE) processes.

Effects of low energy ion bombardment on GaAs molecular beam epitaxy

The effects of low-energy ion bombardment on molecular beam epitaxy (MBE) growth have been studied by low-energy ion scattering (LEIS). LEIS is a novel in situ MBE monitoring system which is highly sensitive to the atomic structure of topmost layers. Noble ion bombardments during the MBE growth of GaAs strongly affect the morphology and crystalline qualities of grown films. We have observed characteristic LEIS profiles, and surface structures such as diatomic steps and disordering by ion bombardment have been analysed. Although the effects of ion bombardment on electrical and optical properties of grown films have not been clarified yet, we have confirmed positive effects of the ion bombardment on the surface morphology. We discuss the mechanism of morphology improvements, and demonstrate the feasibility of ion bombardment during the MBE growth together with the usefulness of LEIS for structure analyses.

Modification Of Properties Of Ion-Beam-Sputtered Yttrium-Oxide Thin Films By Low-Energy Ion Bombardment

ABSTRACTThe effect of low-energy ion bombardment on ion-beam-sputtered yttrium-oxide films was studied. Yttria films were subjected to argon ions accelerated by a potential of up to 500 V with current densities of up to 8 μA/cm2 and were deposited at differing substrate temperatures. Yttria films bombarded during deposition were found to be amorphous, and trends observed with increased ion energy include reduced amount of residual compressive stress, increased argon content, and decreased refractive index, depending on deposited energy and substrate temperature.

Modification of zirconia film properties by low-energy ion bombardment during reactive ion-beam deposition

The effect of low-energy ion bombardment on the structure and properties of zirconia films deposited by reactive ion-beam process is investigated. Bombardment of 100-eV Ar+ during film growth is shown to induce a substantial relaxation of the residual stress as a result of structural modification by the increased mobility of adatoms. Concurrently, the oxygen gettering capability, or film stoichiometry, is improved by the enhanced diffusion of oxygen on substrate surface. The structural change by thermal annealing, up to 600 °C, demonstrates that fine-grained (200–400 Å) cubic zirconia can be stabilized down to room temperature without alloying stabilizers. The impingement of low-energy Ar+ during film growth results in an as-deposited film microstructure which promotes the growth of the cubic-phase crystallites upon post-deposition annealing as well as the texturing of film plane into (111) orientation. The refractive index and optical transmission of the zirconia films are shown to be dependent predominantly upon the oxygen content in the film and less sensitive to the improved atomic packing due to the low-energy Ar+ bombardment.

Etching of silicon and silicon dioxide by halofluorocarbon plasmas

The etching of silicon and silicon dioxide by halofluorocarbon (CF4, CF3Cl, CF3Br) discharges has been studied using discharge-sensitive techniques (actinometry, mass spectroscopy) and surface-sensitive techniques (in situ Auger electron spectroscopy, quartz crystal microbalances). The effect of low-energy ion bombardment has also been assessed by the application of bias voltages on samples used for surface analysis. The chemistry of the discharge has been shown to be affected by the etching reactions. Enrichments in chlorine- and bromine-containing species, due to the consumption of fluorine in etching, were observed. Plasma treatments induced the formation of a layer of silicon oxyfluoride with a stable composition on top of silicon dioxide, independent of the gas or the ion bombardment energy. Silicon halide layers were formed on the silicon surface. The increase in the energy of impinging ions led to thicker and more chlorine- and bromine-rich layers. In both cases low-energy ion bombardment induced steady increases in etch rate.

On the effect of low-energy ion bombardment on polystyrene and polymethylmethacrylate etch rates in rf plasmas

The effect of low-energy ion bombardment on CD4/O2 and CF3X (X=F, Cl, Br) plasma etching has been assessed by applying controlled rf bias voltages on polystyrene (PS) and polymethylmethacrylate (PMMA) samples. In both cases ion bombardment has been found to have a “chemical” effect. In the case of CF4/O2 discharges, ion bombardment has been found to change the relative etching efficiency of different mixtures. In the case of CF3X plasmas, ion bombardment has been found to alter PMMA and PS etch rates in a different way. In particular, the ratios between CF4 and CF3X (X=Cl, Br) etch rates of PS have been found to decrease with increasing bias voltage. This effect has been tentatively attributed to an ion bombardment-induced enhancement of the reaction between the aromatic ring and halogen molecules formed in CF3Cl and CF3Br discharges.

The role of ion/surface interactions and photo-induced reactions during film growth from the vapor phase

Recent progress in the understanding of mechanisms associated with low-energy (often < 100 eV) ion/surface interactions and photo-induced reactions during vapor-phase crystal growth are reviewed. Ion/surface interactions play an important role in a variety of deposition technologies including sputtering, plasma-assisted chemical vapor deposition, and, more recently, molecular beam epitaxy. Effects such as trapping, preferential sputtering, and collisional mixing are used to interpret and, in some cases, model experimental results concerning the effects of low-energy ion bombardment on nucleation and film growth kinetics, the evolution of film microstructure, elemental incorporation probabilities, surface segregation rates, and dopant depth distributions. The role of photo-stimulated gas-phase and surface reactions during laser-assisted chemical vapor deposition, including single, multiple, and multiphoton-initiated processes, radical production, and adlayer photochemistry, are also discussed together with newly developed laser-processing techniques during deposition. The focus of this review is on the development of an understanding of the controlling mechanisms in both ion/surface and photo-stimulated processes.

A review of the present understanding of the role of ion/surface interactions and photo-induced reactions during vapor-phase crystal growth

Recent progress in the use of low-energy (⪅200 eV) ion/surface interactions and photo-induced reactions during vapor-phase crystal growth in order to provide better control over film growth kinetics and hence the microstructure, microchemistry, and physical properties of as-deposited layers is reviewed. Ion/surface interaction effects such as trapping, preferential sputtering, and collisional mixing are used to interpret and, in some cases, model experimental results concerning the effects of low-energy ion bombardment on nucleation and film growth kinetics, elemental incorporation probabilities, surface segregation rates, dopant depth distributions, and film microstructure. The role of photo-stimulated gas-phase and surface reactions during laser-assisted chemical vapor deposition including single, multiple, and multi-photon-initiated-processes, radical production,and adlayer photochemistry are also discussed together with newly developed laser-processing techniques during deposition. The focus of this review is on the development of an understanding of the controlling mechanisms in both ion/surface and photo-stimulated processes in order to more fully utilize the advantages inherent in these techniques.

Diffusion enhancement due to low-energy ion bombardment during sputter etching and deposition

The effects of low-energy ion bombardment on enhancing elemental diffusion rates at both heterojunction interfaces during film deposition and over the compositionally altered layer created during sputter etching alloy targets have been considered. Depth dependent enhanced interdiffusion coefficients, expressed as D*(x)=D*(0) exp(−x/Ld), where D*(0) is more than five orders of magnitude greater than thermal diffusion values, were measured in InSb/GaSb multilayer structures deposited by multitarget bias sputering. D*(0) was determined from the amplitude u of the compositional modulation in the multilayered films (layer thicknesses between 20 and 45 Å) as measured by superlattice x-ray diffraction techniques. The value of D*(0) was found to increase from 3×10−17 to 1×10−16 cm2/sec as the applied substrate bias was increased from 0 to −75 V. However even at Va=0, the diffusion coefficient was enhanced owing to an induced substrate potential with respect to the positive space-charge region in the Ar discharge. The diffusion length of Ld of the ion bombardment created defects was ∼1000 Å. Enhanced diffusion also has a significiant effect on the altered layer thickness xe and the total sputtering time te (or ion dose) required to reach steady state during ion etching of multielement targets. The effects of using an exponentially depth dependent versus a constant value of the enhanced diffusion coefficient on calculated values of xe and te in single-phase binary alloys were considered. The results show that both xe and te are considerably larger using a depth dependent D*(x), when Ld&amp;lt;D*(0)/v, where v is the steady-state surface recession velocity during sputter etching. However, when Ld≳D*(0)/v, the usual case for most sputtering applications, the two solutions approach each other.