Sputtering and surface state evolution of Bi under oblique incidence of 120 keV Ar ions

The sputtering and surface state evolution of Bi/Si targets under oblique incidence of 120 keV Ar⁺ ions have been investigated over the range of incidence angles 0° ? θ_i ? 60°. Increasing erosion of irradiated samples (whose surface thickness reduced by ∼3% at normal incidence up to ∼8% at θ = 60°) and their surface smoothing with reducing grain sizing were pointed out using Rutherford backscattering (RBS), atomic force (AFM) and X-ray diffraction (XRD) techniques. Measured sputtering yield data versus θ_i with fixed ion fluence to ∼1.5 × 10¹⁵ cm⁻² are well described by Yamamura et al. semi-empirical formula and Monte Carlo (MC) simulation using the SRIM-2008 computer code. The observed increase in sputter yield versus incidence angle is closely correlated to Bi surface topography and crystalline structure changes under ion irradiation.     

Structural studies of silicon oxynitride layers formed by low energy ion implantation

Silicon oxynitride (Si_xO_yN_z) layers were synthesized by implanting ¹⁶O₂⁺ and ¹⁴N₂⁺ 30 keV ions in 1:1 ratio with fluences ranging from 5 × 10¹⁶ to 1 × 10¹⁸ ions cm⁻² into single crystal silicon at room temperature. Rapid thermal annealing (RTA) of the samples was carried out at different temperatures in nitrogen ambient for 5 min. The FTIR studies show that the structures of ion-beam synthesized oxynitride layers are strongly dependent on total ion-fluence and annealing temperature. It is found that the structures formed at lower ion fluences (∼1 × 10¹⁷ ions cm⁻²) are homogenous oxygen-rich silicon oxynitride. However, at higher fluence levels (∼1 × 10¹⁸ ions cm⁻²) formation of homogenous nitrogen rich silicon oxynitride is observed due to ion-beam induced surface sputtering effects. The Micro-Raman studies on 1173 K annealed samples show formation of partially amorphous oxygen and nitrogen rich silicon oxynitride structures with crystalline silicon beneath it for lower and higher ion fluences, respectively. The Ellipsometry studies on 1173 K annealed samples show an increase in the thickness of silicon oxynitride layer with increasing ion fluence. The refractive index of the ion-beam synthesized layers is found to be in the range 1.54-1.96.     

Raman investigation of incident N-, Xe-ions induced effects in ZnO thin films

Highly c-axis orientation ZnO thin films with hundreds nanometers in thickness have been deposited on (1 0 0) Si substrate by RF magnetron sputtering. These films are implanted at room temperature by 80 keV N-ions with fluences from 5.0 × 10¹⁴ to 1.0 × 10¹⁷ ions/cm², implanted by 400 keV Xe-ions with 2.0 × 10¹⁴ to 2.0 × 10¹⁶ ions/cm², irradiated by 3.64 MeV Xe-ions with 1.0 × 10¹² to 1.0 × 10¹⁵ ions/cm², or irradiated by 308 MeV Xe-ions with 1.0 × 10¹² to 5.0 × 10¹⁴ ions/cm², respectively. Then the ZnO films are investigated using a Raman spectroscopy. The obtained Raman spectra show that a new Raman peak located at about 578 cm⁻¹ relating to simple defects or disorder phase appears in all ZnO films after ion implantation/irradiation, a new Raman peak at about 275 cm^-1 owing to N-activated zinc-like vibrations is observed in the N-implanted samples. Moreover, a new Raman peak at about 475 cm⁻¹ is only seen in the samples after 400 keV and 3.64 MeV Xe-ions bombardment. The area intensity of these peaks increases with increasing ion fluence. The effects of ion fluence, element chemical activity, atom displacements induced by nuclear collisions as well as energy deposition on the damage process of ZnO films under ion implantation/irradiation are discussed briefly.     

Silkworm eggs: An ideal model for studying the biological effects of low energy Ar ion interaction in animals

The object of the current work was to study low energy Ar⁺ ion beam interactions with silkworm eggs and thus provide further understanding of the mechanisms involved in ion bombardment-induced direct gene transfer into silkworm eggs. In this paper, using low-energy Ar⁺ ion beam bombardment combined with piggyBac transposon, we developed a novel method to induce gene transfer in silkworm. Using bombardment conditions optimized for egg-incubation (25 keV with ion fluences of 800 × 2.6 × 10¹⁵ ions/cm² in dry state under vacuum), vector pBac{3 × P3-EGFPaf} and helper plasmid pHA3pig were successfully transferred into the silkworm eggs. Our results obtained from by PCR assay and genomic Southern blotting analysis of the G1 generations provide evidence that low-energy ion beam can generate some craters that play a role in acting as pathways of exogenous DNA molecules into silkworm eggs.     

Ion bombardment induced changes in the optical and electrical properties of polycarbonate

The changes in the optical and electrical properties of polycarbonate (PC) films, bombarded with He and Ar ion beams, have been studied. The PC films were divided into two groups where the first group was bombarded with 130 keV He ions of fluences ranged from 1 × 10¹⁴ cm⁻² to 2 × 10¹⁶ cm⁻², while the second one was bombarded with 320 keV Ar of fluences (1 × 10¹³ cm⁻² and 1 × 10¹⁵ cm⁻²). The surface morphology of the unirradiated and irradiated PC films was studied using scanning electron microscopy (SEM) technique. The optical properties of the two groups have been carried out using UV-Vis spectrophotometer and the direct current (DC) electrical conductivity was also performed. The obtained results showed a decrease in the optical energy gap, the optical activation energy and the electrical activation energy with increasing the fluence of both He and Ar ions. Meanwhile, an increase in the DC conductivity was obtained with increasing the fluence of the ions. The bombardment of the PC films with He and Ar ion beams induced formation of carbon clusters near the polymer surface and, also, resulted in scission in the polymer chains.     

Bulk-compositional changes of Ni2Al3 and NiAl3 during ion etching

Bulk-compositional changes of Ni₂Al₃ and NiAl₃ in a Ni-50 wt% Al alloy during ion etching have been investigated by transmission electron microscopy and energy dispersive X-ray spectroscopic analyses. After etching with 7, 5 and 3 keV Ar⁺ ions for 15, 24 and 100 h nickel contents in both Ni₂Al₃ and NiAl₃ exceeded greatly those in the initial compounds and increased with the decrement of the sputtering energy. After 100 h etching with 3 keV Ar⁺ ions the compositions of these two compounds reached a similar value, about Ni_80-83Al_12-15Fe_3-4Cr_1-2 (at%). A synergistic action of preferential sputtering, radiation-induced segregation and radiation-enhanced diffusion enables the altered-layers at the top and bottom of the film extend through the whole film. The bulk-compositional changes are proposed to occur in the unsteady-state sputtering regime of ion etching and caused by an insufficient supply of matter in a thin film.     

A systematic study on analysis-induced radiation damage in silicon during channeling Rutherford backscattering spectrometry analysis

Channeling Rutherford backscattering spectrometry (RBS) is an essential analysis technique in materials science. However, the accuracy of RBS can be significantly affected by disorders in materials induced by the analyzing ion beam even under channeling mode. We have studied RBS analysis-induced radiation damage in silicon. A 140-keV H⁺ ion beam was incident along 〈1 0 0〉 Si axis at room temperature to a fluence ranging from 1.6 × 10¹⁶ cm⁻² to 7.0 × 10¹⁶ cm⁻². The evolution of the aligned yields versus fluences has been examined and found to agree well with a model proposed by us.     

Fabrication of hollow Ag nanoclusters in silica by irradiation with Ar ions

Ion irradiation is an effective method to control the morphology, size and distribution of metal nanoclusters in substrates. In this work, Ag nanoclusters embedded in silica by 200 keV Ag⁺ ion implantation were irradiated at room temperature with Ar⁺ ions at 200 keV and 500 keV to different fluences. After irradiation, a transmission electron microscopy (TEM) study revealed that nanovoids are formed in the larger Ag nanoclusters. With the increase of fluence and energy of the Ar⁺ ions, the number and average size of the nanovoids grow combining with increases in the average size of the larger Ag nanoclusters within a projected range. During the ion irradiation process, the electronic energy and nuclear energy loss of the Ar⁺ ions determine the size of the hollow Ag nanoclusters and the change of the size and distribution of Ag nanoclusters in silica, leading to changes in the optical absorption spectra.     

Structural characterization of buried nitride layers formed by nitrogen ion implantation in silicon

The synthesis of buried silicon nitride insulating layers was carried out by SIMNI (separation by implanted nitrogen) process using implantation of 140 keV nitrogen (¹⁴N⁺) ions at fluence of 1.0 × 10¹⁷, 2.5 × 10¹⁷ and 5.0 × 10¹⁷ cm⁻² into 〈1 1 1〉 single crystal silicon substrates held at elevated temperature (410 °C). The structures of ion-beam synthesized buried silicon nitride layers were studied by X-ray diffraction (XRD) technique. The XRD studies reveal the formation of hexagonal silicon nitride (Si₃N₄) structure at all fluences. The concentration of the silicon nitride phase was found to be dependent on the ion fluence. The intensity and full width at half maximum (FWHM) of XRD peak were found to increase with increase in ion fluence. The Raman spectra for samples implanted with different ion fluences show crystalline silicon (c-Si) substrate peak at wavenumber 520 cm⁻¹. The intensity of the silicon peak was found to decrease with increase in ion fluence.     

Erosion of carbon fiber composites under high-fluence heavy ion irradiation

The ion-induced erosion, determining by sputtering yield Y and surface evolution including structure and morphology changes of the modified surface layers, of two commercial carbon fiber composites (CFC) with different reinforcement - KUP-VM (1D) and Desna 4 (4D) have been studied under 30 keV Ar⁺ high fluence (φt ∼ 10¹⁸-10²⁰ ion/cm²) irradiation in the temperature range from room temperature to 400 °C. Ion-induced erosion results in the changes of carbon fiber structure which depend on temperature and ion fluence. Monitoring of ion-induced structural changes using the temperature dependence of ion-induced electron emission yield has shown that for Desna 4 and KUP-VM at dynamic annealing temperature Т_а ≈ 170 °С the transition takes place from disordering at T < T_a to recrystallization at T > T_a. The annealing temperature Т_а is close to the one for polycrystalline graphites. Microscopy analysis has shown that at temperatures Т < T_a the etching of the fibers results in a formation of trough-like longitudinal cavities and hillocks. Irradiation at temperatures T > T_a leads to a crimped structure with the ribs perpendicular to fiber axis. After further sputtering of the crimps the fiber morphology is transformed to an isotropic globular structure. As a result the sputtering yield decreases for Desna 4 more than twice. This value is almost equal to that for KUP-VM, Desna 4, polycrystalline graphites and glassy carbons at room temperature.     

Proton beam induced luminescence of silicon dioxide implanted with silicon

Light emission from a silicon dioxide layer enriched with silicon has been studied. Samples used had structures made on thermally oxidized silicon substrate wafers. Excess silicon atoms were introduced into a 250-nm-thick silicon dioxide layer via implantation of 60 keV Si⁺ ions up to a fluence of 2 × 10¹⁷ cm⁻². A 15-nm-thick Au layer was used as a top semitransparent electrode. Continuous blue light emission was observed under DC polarization of the structure at 8-12 MV/cm. The blue light emission from the structures was also observed in an ionoluminescence experiment, in which the light emission was caused by irradiation with a H₂⁺ ion beam of energy between 22 and 100 keV. In the case of H₂⁺, on entering the material the ions dissociated into two protons, each carrying on average half of the incident ion energy. The spectra of the emitted light and the dependence of ionoluminescence on proton energy were analyzed and the results were correlated with the concentration profile of implanted silicon atoms.     

Destruction of CO ice and formation of new molecules by irradiation with 28 keV O ions

The effect of solar wind on cometary ice was studied by using oxygen ions with energy near to that corresponding to their maximum abundance in space for bombarding CO ice. This gas was condensed on a CsI substrate at 14 K and irradiated by 28 keV ¹⁸O⁶⁺ ions up to a final fluence of 1.3 × 10¹⁶ cm⁻². We have used a methodology in which the sputtering yields, the destruction rate of CO, and the rate of formation of new molecular species are determined by Fourier transform infrared spectroscopy (FTIR). In the current experiment, the condensation of a thin water ice film has prevented the CO sputtering. Quantities such as the dissociation yield, Y_d (the number of ice molecules destroyed or dissociated per projectile impact), and the formation yield, Y_f (the number of daughter molecules of a given species formed per projectile) are found to be more appropriate and useful than using an integrated or average cross section, since the projectiles are slowing down in the ice from their initial energy until zero velocity (implantation).     

FTIR and RBS study of ion-beam synthesized buried silicon oxide layers

Single crystal silicon samples were implanted at 140 keV by oxygen (¹⁶O⁺) ion beam to fluence levels of 1.0 × 10¹⁷, 2.5 × 10¹⁷ and 5.0 × 10¹⁷ cm⁻² to synthesize buried silicon oxide insulating layers by SIMOX (separation by implanted oxygen) process at room temperature and at high temperature (325 °C). The structure and composition of the ion-beam synthesized buried silicon oxide layers were investigated by Fourier transform infrared (FTIR) and Rutherford backscattering spectroscopy (RBS) techniques. The FTIR spectra of implanted samples reveal absorption in the wavenumber range 1250-750 cm⁻¹ corresponding to the stretching vibration of Si-O bonds indicating the formation of silicon oxide. The integrated absorption band intensity is found to increase with increase in the ion fluence. The absorption peak was rather board for 325 °C implanted sample. The FTIR studies show that the structures of ion-beam synthesized buried oxide layers are strongly dependent on total ion fluence. The RBS measurements show that the thickness of the buried oxide layer increases with increase in the oxygen fluence. However, the thickness of the top silicon layer was found to decrease with increase in the ion fluence. The total oxygen fluence estimated from the RBS data is found to be in good agreement with the implanted oxygen fluence. The high temperature implantation leads to increase in the concentration of the oxide formation compared to room temperature implantation.     

Mixing of Cr and Si atoms induced by noble gas ions irradiation of Cr/Si bilayers

Cr/Si bilayers were irradiated at room temperature with 120 keV Ar, 140 keV Kr and 350 keV Xe ions to fluences ranging from 10¹⁵ to 2 × 10¹⁶ ions/cm². The thickness of Cr layer evaporated on Si substrate was about 400 Å. Rutherford backscattering spectrometry (RBS) was used to investigate the atomic mixing induced at the Cr-Si interface as function of the incident ion mass and fluence. We observed that for the samples irradiated with Ar ions, RBS yields from both Cr layer and Si substrate are the same as before the irradiation. There is no mixing of Cr and Si atoms, even at the fluence of 2 × 10¹⁶ ions/cm². For the samples irradiated with Kr ions, a slight broadening of the Cr and Si interfacial edges was produced from the fluence of 5 × 10¹⁵ ions/cm². The broadening of the Cr and Si interfacial edges is more pronounced with Xe ions particularly to the fluence of 10¹⁶ ions/cm². The interface broadening was found to depend linearly on the ion fluence and suggests that the mixing is like a diffusion controlled process. The experimental mixing rates were determined and compared with values predicted by ballistic and thermal spike models. Our experimental data were well reproduced by the thermal spikes model.     

Ion-induced electron emission monitoring of the structure and morphology evolution in HOPG

The temperature dependences of the ion-induced electron emission yield γ of highly-oriented pyrolytic graphite (HOPG) under high-fluence (10¹⁸-10¹⁹ ions/cm²) 30 keV Ar⁺ ion irradiation at ion incidence angles from θ = 0^o (normal incidence) to 80^o have been measured to trace both the structure and morphology changes in the basal oriented samples. The target temperature has been varied during continuous irradiation from T = −180 to 400 ^oC. The surface analysis has been performed by the RHEED and SEM techniques. The surface microgeometry was studied using laser goniophotometry (LGF). The dependences of γ(T) were found to be strongly non-monotonic and essentially different from the ones for Ar⁺ and N₂⁺ ion irradiation of the polygranular graphites. A sharp peak at irradiation temperature T_p ≈ 150 ^oC was found. A strong influence of electron transport anisotropy has been observed, and ion-induced microgeometry is discussed.     

Stoichiometry evolution of polyethylene terephtalate under 3.7 MeV He irradiation

A 3.7 MeV He⁺ ion beam was simultaneously used for Polyethylene Terephtalate (PET) film degradation and characterization. To enhance the potentialities of the characterization method, a multi-detector Ion Beam Analysis (IBA) technique was used. The stoichiometry change of the PET target following the irradiation is quantified at a beam fluence varying between 7 × 10¹³ and 1.8 × 10¹⁶ He⁺ cm⁻². The damage induced in PET films by He⁺ bombarding was analyzed in-situ simultaneously through Rutherford Backscattering Spectrometry (RBS), Particle Elastic scattering Spectrometry (PES) and Hydrogen Elastic Recoil Detection (ERD).Appropriate experimental conditions for the observation of absolute changes in composition and thickness during irradiation were determined. The oxygen and carbon content evolution as a function of the ion fluence was monitored by He⁺ backscattering whereas the hydrogen content was measured by H(α, H)α collisions in which both the scattered He⁺ ions and the recoiling H could be observed. The present study reveals that, at the highest fluence 1.8 × 10¹⁶ He⁺ cm⁻², the PET films have lost approximately 15% of the carbon, more than 45% of the hydrogen and 85% of the oxygen of the amount contained in the pristine sample. The energy shift of recoiling H⁺ ions at a forward angle 45° was followed in order to study the mass loss effect.The experimental results are consistent with the bulk molecular recombination model. Based on the results, hydrogen, oxygen and carbon release cross sections are determined. For hydrogen, comparison with deuteron irradiation indicates a cross section linear dependence on the stopping power.     

Effect of swift heavy ion irradiation on structural, optical and electrical properties of Cd2SnO4 thin films

Transparent conducting cadmium stannate thin films were prepared by spray pyrolysis method on Corning substrate at a temperature of 525 °C. The prepared films are irradiated using 120 MeV swift Ag⁹⁺ ions for the fluence in the range 1 × 10¹² to 1 × 10¹³ ions cm⁻² and the structural, optical and electrical properties were studied. The intensity of the film decreases with increasing ion fluence and amorphization takes place at higher fluence (1 × 10¹³ ions cm⁻²). The transmittance of the films decreases with increasing ion fluence and also the band gap value decreases with increasing ion fluence. The resistivity of the film increased from 2.66 × 10⁻³ Ω cm (pristine) to 5.57 × 10⁻³ Ω cm for the film irradiated with 1 × 10¹³ ions cm⁻². The mobility of the film decreased from 31 to 12 cm²/V s for the film irradiated with the fluence of 1 × 10¹³ ions cm⁻².     

Optical properties of InxGa1−xP/InP grown at high fluence Ga implantation on InP using focused ion beam

Single-crystalline InP(1 0 0) substrate was implanted by 30 keV Ga⁺ ions with fluences of 1 × 10¹⁶-1.5 × 10¹⁷ cm⁻² followed by post-annealing treatment at 750 °C to recover implantation-induced structural defects and activate dopants into the lattices. The optical property, composition, and microstructure of the Ga⁺-implanted InP were studied by Raman spectroscopy and transmission electron microscopy (TEM). Raman spectra show that the In_xGa_1−xP phase is formed at a critical fluence of 7 × 10¹⁶ cm⁻². The newly grown phase was identified with the appearance of Ga rich TO_InP and In rich TO_GaP modes of a random alloy in the 1 bond-2 phonon mode configuration along with TEM structural identification.     

Ion-irradiation-induced athermal annealing of helium bubbles in SiC

We have compared the microstructural evolution of helium bubbles under ion irradiation and high temperature annealing. 4H-SiC was irradiated first by 140 keV He ions to a fluence of 1.0 × 10¹⁷ cm⁻² and then annealed at 1200 K for 30 min. Then, the samples were either irradiated by 2 MeV He ions to a fluence of 3.0 × 10¹⁶ cm⁻² at room temperature or annealed additionally at 1200 K for 30 min. Before and after 2 MeV He ion irradiation, significant microstructural changes were observed, similar to effects of high temperature annealing. Thus, the study provides evidence of ion-irradiation-induced athermal annealing on defect Ostwald ripening process and bubble evolution. Possible mechanisms are discussed.     

Relationship between radiation damage anisotropy in MgO and YSZ single crystals and the Ion/Atom ratio deposition parameter in biaxially-textured MgO and YSZ thin films fabricated by ion beam assisted deposition

To elucidate the underlying physics of ion beam assisted deposition (IBAD), irradiation damage effects in magnesia (MgO) and yttria-stabilized zirconia (YSZ) were investigated. Ion irradiations were performed on MgO and YSZ single crystals of three low-index crystallographic orientations using 100 and 150 keV Ar⁺ ions over a fluence range from 1 × 10¹⁴ to 5 × 10¹⁶ Ar/cm². Damage accumulation was analyzed using Rutherford backscattering spectrometry combined with ion channeling. Damage evolution with increasing ion fluence proceeded via several characteristic stages and the total damage exhibited a strong dependence on crystallographic orientation. For both MgO and YSZ, damage anisotropy was maximal at a stage when the damage saturated, with the (1 1 0) crystallographic orientation being the most radiation damage resistant. The Ion/Atom ratio deposition parameter reported for IBAD of MgO and YSZ films was found to correlate with the damage plateau stage described above. Finally, the role of the Ion/Atom ratio is discussed in terms of radiation damage anisotropy mechanism.