Damage recovery in ZnO by post-implantation annealing

ZnO bulk samples were implanted with 200 keV-Co ions at room temperature with two fluences, 1 × 10¹⁶ and 8 × 10¹⁶ cm^?2, and then annealed in air for 30 min at different temperatures up to 900 °C. After the implantation and each annealing step, the samples were analyzed by Rutherford backscattering spectrometry (RBS) in random and channeling directions to follow the evolution of the disorder profile. The RBS spectra reveal that disorder is created during implantation in proportion to the Co fluence. The thermal treatments induce a disorder recovery, which is however, not complete after annealing at 900 °C, where about 15% of the damage remains. To study the Co profile evolution during annealing, the samples were, in addition to RBS, characterized by secondary ion mass spectrometry (SIMS). The results show that Co diffusion starts at 800 °C, but also that a very different behavior is seen for Co concentrations below and above the solubility limit.     

High energy Si ions bombardment effects on the properties of nano-layers of SiO2/SiO2 + Ag

We grew 50 periodic SiO₂/SiO₂ + Ag multi-layers by electron beam deposition technique. The co-deposited SiO₂ + Ag layers are 7.26 nm, SiO₂ buffer layers are 4 nm, and total thickness of film was determined as 563 nm. We measured the thickness of the layers using in situ thickness monitoring during deposition, and optical interferometry afterwards. The concentration and distribution of Ag in SiO₂ were determined using Rutherford backscattering spectrometry (RBS). In order to calculate the dimensionless figure of merit, ZT, the electrical conductivity, thermal conductivity and the Seebeck coefficient of the layered structure were measured at room temperature before and after bombardment with 5 MeV Si ions. The energy of the Si ions was chosen such that the ions are stopped deep inside the silicon substrate and only electronic energy due to ionization is deposited in the layered structure. Optical absorption (OA) spectra were taken in the range 200–900 nm to monitor the Ag nanocluster formation in the thin layers.     

Er+ implantation in SnO2:SiO2 layers: Structure changes and light emission

Structure changes and light emission behavior in Er⁺ implanted SnO₂:SiO₂ layers are studied, using transmission electron microscopy (TEM), Rutherford backscattering (RBS) and cathodoluminescence (CL). SnO₂:SiO₂ layers of different composition deposited with RF magnetron sputtering on Si wafers were implanted with 200 keV Er⁺ to a fluence of 3 × 10¹⁵ cm^?2 at room temperature. The implanted structures were then annealed at 600–1000 °C for 30 min, resulting in the formation of crystalline SnO₂ nanoclusters. Cross-section TEM revealed a strong reduction of the SnO₂ crystallite size down to several nanometers in the implanted area of the SnO₂:SiO₂ layer as compared to the undoped layer. In addition, a very narrow layer of SnO₂ nanocrystals appears at the SiO₂/Si interface. Several narrow CL emission peaks and wide bands were found which could be related to the decay of SnO₂ free excitons, to oxygen deficiency centers in SiO₂ and to transitions between the energy levels in the Er ions, apparently located at nanoclusters. The mechanisms of nanostructuring as well as the emission process are discussed.     

High Resolution and Differential PIXE combined with RBS,EBS and AFM analysis of magnesium titanate (MgTiO3) multilayer structures

Thorough structural characterization of deep laying thin film, including the inference of interdiffusion profiles is frequently a complex problem. The use of RBS/PIXE holistic approaches, already shown to represent a powerful method, sometimes faces difficulties if standard experimental procedures are used. In this work, following a series of ⁴He Rutherford backscattering and ¹H elastic backscattering experiments, carried out to study the influence of SrTiO₃ as a possible cladding layer between Pt/TiO₂/SiO₂/(1 0 0)Si substrates and MgTiO₃ films, a simple holistic RBS-PIXE is shown to be not enough for the solution of such a problem. Establishing of the Sr depth profile, was only possible after AFM, High-Resolution EDS PIXE and differential PIXE analysis were carried out. Results, problems faced and conclusions obtained are presented.     

Er+ medium energy ion implantation into lithium niobate

Erbium-doped lithium niobate (Er:LiNbO₃) is a prospective photonics component, operating at 1.5 μm, which could find its use chiefly as an optical amplifier or waveguide laser. In this study, we have focused on the properties of the optically active Er:LiNbO₃ layers, which are fabricated by medium energy ion implantation under various experimental conditions. Erbium ions were implanted at energies of 330 and 500 keV with fluences of 1.0 × 10¹⁵, 2.5 × 10¹⁵ and 1.0 × 10¹⁶ cm^?2 into LiNbO₃ single-crystalline cuts of various orientations. The as-implanted samples were annealed in air at 350 °C for 5 h. The depth distribution and diffusion profiles of the implanted Er were measured by Rutherford Backscattering Spectroscopy (RBS) using 2 MeV He⁺ ions. The projected range R_P and projected range straggling ΔR_P were calculated employing the SRIM code. The damage distribution and structural changes were described using the RBS/channelling method. Changes of the lithium concentration depth distribution were studied by Neutron Depth Profiling (NDP). The photoluminescence spectra of the samples were measured to determine whether the emission was in the desired region of 1.5 μm. The obtained data made it possible to reveal the relations between the structural changes of erbium-implanted lithium niobate and its luminescence properties important for photonics applications.     

Erosion of tungsten-doped amorphous carbon films in oxygen plasma

Tungsten-doped amorphous carbon films with 0–9 at.% W concentration were produced by magnetron sputtering and eroded in oxygen plasmas applying different bias voltages and substrate temperatures. The partial C and W erosion rates were determined from the C and W areal density changes measured by Rutherford backscattering spectrometry (RBS). The initial C removal rate increases with increasing ion energy and temperature and decreases with increasing W concentration. For W-doped films the erosion rate decreases with increasing plasma exposure duration. At low bias voltages the erosion process stops after W accumulation at the surface, which protects the carbon underneath from further erosion. RBS and X-ray photoelectron spectroscopy suggest that the W-rich layer at the surface is carbon free and consists of porous WO₃. Biasing to 200 V leads to removal of W by physical sputtering and, therefore, inhibits the formation of the protecting W oxide layer and the C erosion proceeds.     

Lattice location and annealing studies of Hf implanted CaF2

Hafnium ions were implanted into calcium fluoride single crystals. The lattice damage introduced by the implantation was investigated with the Rutherford backscattering (RBS) channelling technique. The lattice location of the implanted ions was determined by performing channelling measurements for the 〈1 1 0〉 crystal direction. A comparison of the angular scan with Monte Carlo simulations leads to the conclusion that >90% of the Hf ions are on Ca sites directly after implantation. Subsequent annealing of the samples was performed in a rapid thermal annealing apparatus. Perturbed angular correlation (PAC) measurements with ¹⁸¹Hf(¹⁸¹Ta) show quadrupole interactions with ν_Q1 = 300(3) MHz (η = 0.00), ν_Q2 = 1285(13) MHz (η = 0.43) and ν_Q3 = 1035(10) MHz (η = 0.00) after annealing up to 1200 K.     

Homogeneously size distributed Ge nanoclusters embedded in SiO2 layers produced by ion beam synthesis

500 nm SiO₂ layers were implanted with 450 keV (F=3 × 10¹⁶ at./cm²) and 230 keV (F=1.8 × 10¹⁶ at./cm²) Ge ions at room temperature to obtain an almost constant Ge concentration of about 2.5 at.% in the insulating layer. Subsequently, the specimens were annealed at temperatures between 500°C and 1200°C for 30 min in a dry N₂ ambient atmosphere. Cross-sectional TEM analysis reveal homogeneously distributed Ge nanoclusters arranged in a broad band within the SiO₂ layer. Their mean cluster size varies between 2.0 and 6.5 nm depending on the annealing conditions. Cluster-free regions are always observed close to the surface of the specimens independent of the annealing process, whereas a narrow Ge nanocluster band appears at the SiO₂/Si interface at high annealing temperatures, e.g. ⩾1000°C. The atomic Ge redistribution due to the annealing treatment was investigated with a scanning TEM energy dispersive X-ray system and Rutherford back scattering (RBS).     

Heteroepitaxial Er0.49Gd0.51Si1.7 layers formed by channeled ion beam synthesis

Epitaxial ternary silicide Er_0.49Gd_0.51Si_1.7 layers with a good crystalline quality (χ_min of Er and Gd is 3.7%) have been formed by 60 keV Er and Gd ion implantation into Si(1 1 1) substrates to a total dose of 1.0 × 10¹⁷/cm² at 450°C using channeled ion beam synthesis (CIBS). The composition, the structure, the strain and the thermal stability of these layers have been studied using energy dispersive spectroscopy (EDS), Rutherford backscattering (RBS)/channeling and X-ray diffraction (XRD). It is shown that the perpendicular and parallel elastic strains of the Er_0.49Gd_0.51Si_1.7 epilayer are e^⊥=−0.46% ± 0.02% and e⁶=+0.73% ± 0.19%. The layer is stable up to 900°C. Annealing at 950°C results in a phase transformation.     

Stabilisation and phase transformation of hexagonal rare-earth silicides on Si(1 1 1)

Epitaxial, hexagonal rare-earth silicides, such as ErSi_1.7, can be formed using channeled ion beam synthesis. In the case of Gd-silicide, an orthorhombic GdSi₂ phase exists at high temperature; the transition temperature is related to the thickness and crystalline quality of the silicide. In the case of the lightest rare-earth metals, such as Nd, silicides only exist in a tetragonal or orthorhombic phase, which cannot grow epitaxially on Si(1 1 1). However, introduction of a fraction of yttrium (YSi_1.7 also possesses the aforementioned hexagonal lattice) drives the Nd–Si system into a hexagonal lattice structure. A combined backscattering and channeling spectrometry (RBS/C), X-ray diffraction (XRD) and transmission electron microscopy (TEM) study shows that an epitaxial, continuous ternary silicide is formed (and not a mixture of binaries) with a hexagonal structure, which is stable up to 950°C. Further annealing, however, results in a gradual transformation into polycrystalline phases. The experimental results are compared to total energy calculations of these (meta-)stable rare-earth silicides, using the density functional theory (DFT).     

SHI induced re-crystallization of Ge implanted SiO2 films

Ge nanocrystals embedded in SiO₂ matrix have been synthesized by swift heavy ion irradiation of Ge implanted SiO₂ films. In the present study, 400 keV Ge⁺ ions were implanted into SiO₂ films at dose of 3 × 10¹⁶ ions/cm² at room temperature. The as-implanted samples were irradiated with 150 MeV Ag¹²⁺ ions with various fluences. Similarly 400 keV Ge⁺ ions implanted into Silicon substrate at higher fluence at 573 K have been irradiated with 100 MeV Au⁸⁺ ions at room temperature (RT). These samples were subsequently characterized by XRD and Raman to understand the re-crystallization behavior. The XRD results confirm the presence of Ge crystallites in the irradiated samples. Rutherford backscattering spectrometry (RBS) was used to quantify the concentration of Ge in the SiO₂ matrix. Variation in the nanocrystal size as a function of ion fluence is presented. The basic mechanism of ion beam induced re-crystallization has been discussed.     

Boron lattice site location in (BGa)As and (BGa)P thin films studied using RBS and NRA with a channeled He+ ion beam

In this study the boron lattice site location in ternary B_xGa_1?xAs and B_xGa_1?xP thin films grown on (0 0 1) GaAs and (0 0 1) GaP, respectively, using low pressure metal-organic vapour-phase epitaxy (MOVPE) with boron concentrations between x = 0.8% and x = 3.2% was investigated with RBS and the ¹⁰B(α,p)¹³C nuclear reaction using a 2.3 MeV He⁺ ion beam. For this purpose, the ion beam was aligned with the [0 0 1], [0 1 1] and [1 1 1] axis and the RBS and proton yield from the nuclear reaction compared with random ion incidence. For comparison, theoretical proton yields which assume boron to be located on substitutional lattice sites only were calculated for each sample/axis combination and compared with the experimental yields. The RBS/channeling measurements show a very good crystal quality of the films with χ_min being in the range of 3–5% for the [0 1 1] axis. The best crystal qualities, i.e. the lowest χ_min values and dechanneling rates, are achieved for low boron concentrations. From NRA/channeling it can be deduced that in the B_xGa_1?xAs films the fraction of interstitial boron is approximately 5% for low boron concentrations of x = 1% and 6–10% for concentrations up to x = 3.2%, whereas the fraction of interstitial boron is less than 3% in the B_xGa_1?xP film studied despite a concentration of x = 2.0%. This indicates that antisite effects of the boron incorporation are more likely in GaAs compared to GaP.     

Nanohardness and structure of nitrogen implanted SixAly coatings post-implanted with oxygen

“Sialons” have several interesting mechanical, thermal and chemical properties which make them candidates for high temperature applications. Solid solutions in the Si–Al–O–N system were synthesised using nitrogen and oxygen implantation into Si₃₃Al₆₇, Si₄₅Al₅₅ and Si₆₇Al₃₃ thin films deposited by DC magnetron sputtering on glassy carbon substrates. Nitrogen has been implanted firstly at 50 and then at 20 keV, oxygen was post-implanted at 50 keV. The different implantation doses ranged from 1 to 10 × 10¹⁷ ions/cm². High depth resolution profiles were obtained using RBS and resonant nuclear reaction, the chemical bonds were investigated using LEEIXS and these results are correlated to the film structure measured by cross section TEM. The TEM micrographs show a columnar structure perpendicular to the substrate surface in unimplanted coatings. Nevertheless, when nitrogen is implanted grain formation is observed and after oxygen post-implantation gas bubbles appear at the film depth where the maximum oxygen concentration is observed. The correlation of these results with RBS and LEEIXS measurements indicates that nitrogen should be enclosed in these bubbles. Nanohardness was also measured. The highest values are observed in samples post-implanted with 1 × 10¹⁷ O/cm² where nanohardness increases from 3 to 10 Gpa.     

Modelling high-temperature co-implantation of N+ and Al+ ions in silicon carbide: the effect of stress on the implant and damage distributions

This work is an initial attempt to model the fundamental processes that occur when SiC is implanted at elevated substrate temperatures T_i (200°–800°) with high doses of N⁺ and Al⁺ ions to synthesise buried layers of (SiC)_1 − x(AlN)_x. The theoretical treatment has involved ballistic calculation of the implant and damage profiles by means of computer codes (TRIRS and DYTRIRS) specifically developed for modelling complex, multi-elemental targets. The influence of the mechanical stress induced the by implanted ions has been taken into account by adding a special term to the differential equations describing the evolution of the implant and damage distributions. Results from the simulations have been correlated with data obtained by Rutherford backscattering spectrometry/ion channelling (RBS/C). The theoretical approach described has enabled one to determine the interaction energies of the interstitials with the internal stress field as well as the role of stress on the defect distribution.     

Stopping cross-section and energy straggling of protons in SiC obtained by nuclear resonant reaction of protons with 12C and 28Si

In order to evaluate stopping cross-section and energy straggling of protons in compound material SiC and its constituents C and Si, resonant backscattering spectra have been measured using proton beams in an energy range 4.9–6.1 MeV per a 100 keV step. We have observed two sharp nuclear resonances at proton energies of 4.808 MeV by ¹²C and 4.879 MeV by ²⁸Si. By systematic analyses of the resonance peak profiles, i.e., energy shift of the peak position and broadening of the peak width, the values of the stopping cross-section and the energy straggling have been deduced to be compared with SRIM-2006 and Bohr’s prediction.     

Effect of ion-irradiation on the microstructure and microhardness of the W-2Y2O3 composite materials fabricated by sintering and hot forging

A W-2Y₂O₃ material was developed in collaboration with the Plansee Company (Austria). An ingot of the material having approximate dimension of 95 mm × 20 mm was fabricated by mixing the elemental powders followed by pressing, sintering and hot forging. The microstructure of the W-2Y₂O₃ composite was investigated using transmission electron microscopy (TEM). The microhardness was studied using nano-indentation technique. We observed that the W-grains having a mean size of about 1 μm already formed and these grains contain very low density of dislocations. The size of the yttria particles was between 300 nm and 1 μm and the Berkovich hardness was about 4.8 GPa. The specimens were irradiated/implanted with Fe and He ions at JANNuS facility located at Orsay/Saclay, France. The TEM disks kept were irradiated/implanted at 300 and 700 °C using Fe and He ions with an energy of 24 and 2 MeV, respectively. The calculated radiation dose was about 5 dpa produced by Fe ions and total He content is 75 appm at both 300 and 700 °C. From the TEM investigation of irradiated samples, few radiation loops are present on the W grains, whereas on yttria particles, the radiation induced damages appear as voids. Berkovich hardness of the irradiated sample is higher than that of the non-irradiated sample. Results on the microstructure and microhardness of the ion-irradiated W-2Y₂O₃ composites are presented in detail.     

Early stage of the crystallization in amorphous Fe–Si layers: Formation and growth of metastable α-FeSi2

Crystallization processes of amorphous Fe–Si layers have been investigated using transmission electron microscopy (TEM). Si(1 1 1) substrates were irradiated with 120 keV Fe ions at ?150 °C to a fluence of 1.0 × 10¹⁷ cm². An Fe-rich amorphous layer embedded in an amorphous Si was formed in the as-irradiated sample. Plan-view TEM observations revealed that a part of the amorphous Fe–Si layer crystallized to the metastable α-FeSi₂ after thermal annealing at 350 °C for 8 h. The lattice parameter of c-axis decreased with thermal annealing. It was considered that the change in the lattice parameter originates from the decrease of the Fe occupancy at (0, 0, 1/2) and its equivalent positions in the unit cell of the metastable α-FeSi₂.     

MeV Si ions bombardment effects on the thermoelectric properties of Co0.1SbxGey thin films

We have grown three different monolayer Co_0.1Sb_xGe_y (x = 2, 4, 11 and y = 15, 7, 15) thin films on silica substrates with varying thickness between 100 and 200 nm using electron beam deposition. The high-energy (in the order of 5 MeV) Si ion bombardments have been performed on samples with varying fluencies of 1 × 10¹², 1 × 10¹³, 1 × 10¹⁴ and 1 × 10¹⁵ ions/cm². The thermopower, electrical and thermal conductivity measurements were carried out before and after the bombardment on samples to calculate the figure of merit, ZT. The Si ions bombardment caused changes on the thermoelectric properties of films. The fluence and temperature dependence of cross plane thermoelectric parameters were also reported. Rutherford backscattering spectrometry (RBS) was used to analyze the elemental composition of the deposited materials and to determine the layer thickness of each film.     

RBS study of diffusion under strong centrifugal force in bimetallic Au/Cu thin films

The effect of the strong centrifugal force, mega-gravity (MG) on inter-diffusion between Au and Cu thin films was studied by using Au(60 nm)/Cu(500 nm)/α-Al₂O₃ (0 0 0 1) films. The Rutherford backscattering analysis of the Au and Cu depth profiles shows that Cu atoms diffuse through the Au layer, resulting in the formation of the Cu layer on the surface under both the thermal annealing at 220 °C and the application of 0.61 × 10⁶ G at 220 °C. The results indicate that the MG application enhances the layer thickness of the Cu layer on the surface.     

Thermal and irradiation induced interdiffusion in Fe3O4/MgO(0 0 1) thin film

The interface reactions in an epitaxial 10 nm-thick Fe₃O₄/MgO(0 0 1) film were investigated by using Rutherford Backscattering spectrometry (RBS), channeling (RBS-C) and X-ray reflectometry (XRR). The as-grown film had a good crystallinity indicated by the minimum yield and the half-angle value for Fe, respectively, χ_min(Fe) = 22% and ψ_1/2(Fe) = 0.62°. Annealing the films under partial argon pressure up to 600 °C led to a large enhancement of Mg out-diffusion into the film forming a wustite-type phase, but the total layer thickness did not change much. Ion irradiation of the film by 1 MeV Ar ion beam caused a strong Fe ion mixing resulting in a large interfacial zone with a thickness of 23 nm.