Xe-implanted zirconium oxycarbide studied by variable energy positron beam

The effect of annealing on defects and the formation of Xe bubbles were investigated in zirconium oxycarbide implanted with 800-keV¹³⁶Xe²⁺ ions at two fluences 1 × 10¹⁵ and 1 × 10¹⁶ Xe/cm². Doppler broadening technique combined with slow positron beam was used. The analysis of the S depth profiles and S-W maps revealed that in the as-implanted samples at both fluences Xe bubbles are not formed. The post-implantation annealing of the samples implanted at 1 × 10¹⁶ Xe/cm² caused formation of Xe bubbles. The response of the lower implantation dose samples to this post implantation annealing was found rather complicated and is discussed.     

Study of Er+ ion-implanted lithium niobate structure after an annealing procedure by RBS and RBS/channelling

Erbium-doped lithium niobate (Er:LiNbO₃) is a prospective photonics component, operating at λ = 1.5 μm, which could be used as an optical amplifier or waveguide laser. We have focused on the structure of Er:LiNbO₃ layers created by 330 keV erbium ion implantation (fluences 1.0 × 10¹⁵, 2.5 × 10¹⁵ and 1.0 × 10¹⁶ cm^?2 1) in the X, Z and two various Y crystallographic cuts of LiNbO₃. Five hours annealing at 350 °C was applied to recrystallize the as-implanted layer and to avoid clustering of Er. Depth distribution of implanted Er has been measured by Rutherford Backscattering Spectroscopy (RBS) using 2 MeV He⁺ ions. Defects distribution and structural changes have been described using the RBS/channelling method. Data obtained made it possible to reveal the relations between the crystallographic orientation of the implanted crystal and the behaviour during the restoration process. The deepest modified layer has been observed in the perpendicular Y cut, which also exhibits the lowest reconstruction after annealing. The shallowest depth of modification and good recovery after annealing were observed in the Z cut of LiNbO₃. Since Er-depth profiles changed significantly in the perpendicular Y cut, we suppose that the crystal structure recovery inhibits Er mobility in the crystalline structure.     

Damage evolution of yttria-stabilized zirconia induced by He irradiation

The study presents an investigation of damage evolution of yttria-stabilized zirconia (YSZ) induced by irradiation of 100 keV He ions at room temperature as a function of fluence. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and atomic force microscopy (AFM) were used in order to study the nature and evolution of structural damage at different levels. Our study shows that various kinds of defects are formed with the increasing fluence. Firstly, at low fluences, from 1 × 10¹⁶ to 4 × 10¹⁶ cm^?2, of which maximum values of displacement per atom (dpa) range from 0.29 to 1.17, an elastic strain which is attributed to the accumulation of irradiation-induced discrete point defects, is presented. Secondly, in the intermediate fluences ranging from 8 × 10¹⁶ to 1 × 10¹⁷ cm^?2 with corresponding dpa varying from 2.33 to 2.91, a large drop of elastic strain occurs accompanied by presence of an intensive damage region, which is comprised by large and interacted defect clusters. Thirdly, at the two high fluences of 2 × 10¹⁷ and 4 × 10¹⁷ cm^?2, of which dpa are 5.83 and 11.65 respectively, a great amount of ribbon-like He bubbles with granular structure and cracks are presented at the depth of maximum concentration of deposited He atoms. The structural damage evolution and the mechanism of formation of He bubbles are discussed.     

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.     

Low temperature formation of luminescent Si nanocrystals with combined process of excimer UV-light irradiation and RTA

Si ion implantation was widely used to synthesize specimens of SiO₂ containing supersaturated Si and subsequent high temperature annealing induces the formation of embedded luminescent Si nanocrystals. In this work, the potentialities of excimer UV-light (172 nm, 7.2 eV) irradiation and rapid thermal annealing (RTA) to achieve low temperature (below 1000 °C) formation of luminescent Si nanocrystals in SiO₂ have been investigated. The Si ions were introduced at acceleration energy of 180 keV to fluences of 7.5 × 10¹⁶ and 1.5 × 10¹⁷ ions/cm². The implanted samples were subsequently irradiated with an excimer-UV lamp for 2 h. After the process, the samples were rapidly thermal annealed at 1050 °C for 5 min before furnace annealing (FA) at 900 °C. Photoluminescence spectra were measured at various stages at the process. Effective visible photoluminescence is found to be observed even after FA at 900 °C, only for specimens treated with excimer-UV lamp and RTA, prior to a low temperature FA process. Based on our experimental results, we discuss the mechanism for the initial formation process of the luminescent Si nanocrystals in SiO₂, together with the effects with excimer lamp irradiation and RTA process on the luminescence.     

Depth-profiling of implanted 28Si by (α,α) and (α,p0) reactions

Silicon nanocrystals enclosed in thin films (Si quantum dots or Si QDs) are regarded to be the cornerstone of future developments in new memory, photovoltaic and optoelectronic products. One way to synthesize these Si QDs is ion implantation in SiO₂ layers followed by thermal annealing post-treatment.Depth-profiling of these implanted Si ions can be performed by reactions induced by α-particles on ²⁸Si. Indeed, for high incident energy, nuclear levels of ³²S and ³¹P can be reached, and cross-sections for (α,α) and (α,p₀) reactions are more intense. This can help to increase the signal for surface silicon, and therefore make distinguishing more easy between implanted Si and Si coming from the SiO₂, even for low fluences.In this work, (α,α) and (α,p₀) reactions are applied to study depth distributions of 70 keV ²⁸Si⁺ ions implanted in 200 nm SiO₂ layers with fluences of 1 × 10¹⁷ and 2 × 10¹⁷ cm^?2. Analysis is performed above E_R = 3864 keV to take advantage of resonances in both (α,α) and (α,p₀) cross-sections. We show how (α,p₀) reactions can complement results provided by resonant backscattering measurements in this complex case.     

AFM surface investigation of polyethylene modified by ion bombardment

Polyethylene (PE) was irradiated with 63 keV Ar⁺ and 155 keV Xe⁺ ions to fluences of 1 × 10¹³ to 3 × 10¹⁵ cm⁻² with ion energies being chosen in order to achieve approximately the same penetration depth for both species. The PE surface morphology was examined by means of atomic force microscopy (AFM), whereas the concentration of free radicals and conjugated double bonds, both created by the ion irradiation, were determined using electron paramagnetic resonance (EPR) and UV–VIS spectroscopy, respectively. As expected, the degradation of PE was higher after irradiation with heavier Xe⁺ ions but the changes in the PE surface morphology were more pronounced for Ar⁺ ions. This newly observed effect can be explained by stronger compaction of the PE surface layer in the case of the Xe⁺ irradiation, connected with a reduction of free volume available.     

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.     

Doping of 6H–SiC pn structures by proton irradiation

The influence of proton irradiation on current–voltage characteristics, N_d − N_a values and parameters of deep centres in 6H–SiC pn structures grown by sublimation epitaxy has been studied. The irradiation was carried out with 8 MeV protons in the range of doses from 10¹⁴ to 10¹⁶ cm⁻². Irradiation with a dose of 3.6 × 10¹⁴ cm⁻² leaves the voltage drop at high forward currents (10 A/cm²) practically unchanged. For higher irradiation dose of 1.8 × 10¹⁵ cm⁻², the forward voltage drop and the degree of compensation in the samples increased ; partial annealing of the radiation defects and partial recovery of the electrical parameters occurred after annealing at T∼400–800 K. Irradiation with a dose of 5.4 × 10¹⁵ cm⁻² resulted in very high resistance in forward biased pn structures which remained high even after heating to 500°C. It is suggested that proton irradiation causes decreasing of the lifetime and formation of an i- or an additional p-layer.     

Lattice location and annealing behaviour of Pt and W implanted sapphire

Sapphire (α-Al₂O₃) single crystals were implanted with different doses of Pt and W ions in the range of 1 × 10¹⁴ at/cm² to 5 × 10¹⁶ at/cm² at room temperature. Detailed angular scans through the main axial directions show that up to 10¹⁵ at/cm² fluences about 80% of the W and Pt ions are incorporated into substitutional or near substitutional lattice sites. Below the amorphization threshold implantation damage show a double peak structure which anneals out partially at low temperature (800^oC). Amorphization of the implanted region starts for doses of the order of 1 × 10¹⁶ at/cm². The amorphous layer regrowths epitaxially in vacuum at 1100^oC, with a velocity of 3 Å/min and stops when the crystalline/amorphous interface reaches the region of maximum Pt concentration. When the annealing is done at ambient atmosphere the damage recovers completely at 1100^oC even for doses of the order of 5 × 10¹⁶ Pt⁺/cm² leading to the formation of Pt precipitates.     

Effects of BF2+ implantation on the strain-relaxation of pseudomorphic metastable Ge0.06Si0.94 alloy layers

Metastable pseudomorphic Ge_0.06Si_0.94 alloy layers grown by molecular beam epitaxy (MBE) on Si (1 0 0) substrates were implanted at room temperature by 70 keV BF₂⁺ ions with three different doses of 3 × 10¹³, 1 × 10¹⁴, and 2.5 × 10¹⁴ cm⁻². The implanted samples were subsequently annealed at 800°C and 900°C for 30 min in a vacuum tube furnace. Observed by MeV ⁴He channeling spectrometry, the sample implanted at a dose of 2.5 × 10¹⁴ BF₂⁺ cm⁻² is amorphized from surface to a depth of about 90 nm among all as-implanted samples. Crystalline degradation and strain-relaxation of post-annealed Ge_0.06Si_0.94 samples become pronounced as the dose increases. Only the samples implanted at 3 × 10¹³ cm⁻² do not visibly degrade nor relax during anneal at 800°C . In the leakage current measurements, no serious leakage is found in most of the samples except for one which is annealed at 800°C for 30 min after implantation to a dose of 2.5 × 10¹⁴ cm⁻². It is concluded that such a low dose of 3 × 10¹³ BF₂⁺ cm⁻² can be doped by implantation to conserve intrinsic strain of the pseudomorphic GeSi, while for high dose regime to meet the strain-relaxation, annealing at high temperatures over 900°C is necessary to prevent serious leakages from occuring near relaxed GeSi/Si interfaces.     

Au implantation into various types of silicate glasses

The implantation of gold ions into three types of silicate glass was studied. The energies of the implanted Au⁺ ions were 1701 keV, and the fluences of the ions were 1 × 10¹⁴, 1 × 10¹⁵, 3 × 10¹⁵ and 1 × 10¹⁶ cm^?2. The as-implanted samples were annealed in air at two temperatures (400 and 600 °C). The Au concentration depth profiles were investigated using Rutherford Backscattering Spectrometry (RBS) and compared to simulated profiles from the SRIM. The structural changes were studied by UV–vis absorption spectroscopy. The obtained mono-mode waveguides were characterised using Dark Mode Spectroscopy at 671 nm to yield information on the refractive index changes. The results showed interesting differences depending on the type of glass and the post-implantation treatment. The obtained data were evaluated on the basis of the structure of the glass matrix, and the relations between the structural changes, waveguide properties and absorption, which are important for photonics applications, were formulated.     

Investigation of hydrogen concentration and hardness of ion irradiated organically modified silicate thin films

A study of the effects of ion irradiation of organically modified silicate thin films on the loss of hydrogen and increase in hardness is presented. NaOH catalyzed SiNa_wO_xC_yH_z thin films were synthesized by sol–gel processing from tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) precursors and spin-coated onto Si substrates. After drying at 300 °C, the films were irradiated with 125 keV H⁺ or 250 keV N²⁺ at fluences ranging from 1 × 10¹⁴ to 2.5 × 10¹⁶ ions/cm². Elastic Recoil Detection (ERD) was used to investigate resulting hydrogen concentration as a function of ion fluence and irradiating species. Nanoindentation was used to measure the hardness of the irradiated films. FT-IR spectroscopy was also used to examine resulting changes in chemical bonding. The resulting hydrogen loss and increase in hardness are compared to similarly processed acid catalyzed silicate thin films.     

Annealing of ion implanted 4H–SiC in the temperature range of 100–800 °C analysed by ion beam techniques

Ion implantation induced damage formation and subsequent annealing in 4H–SiC in the temperature range of 100–800 °C has been investigated. Silicon Carbide was implanted at room temperature with 200 keV ⁴⁰Ar ions with two implantation fluences of 4 × 10¹⁴ and 2 × 10¹⁵ ions/cm². The samples were characterized by Rutherford backscattering and nuclear reaction analysis techniques in channeling mode using 2.00 and 4.30 MeV ⁴He ion beams for damage buildup and recovery in the Si and C sublattices, respectively. At low ion fluence, the restoration of the Si sublattice is evident already at 200 °C and a considerable annealing step occurs between 300 and 400 °C. Similar results have been obtained for the C sublattice using the nuclear resonance reaction for carbon, ¹²C(α,α)¹²C at 4.26 MeV. For samples implanted with the higher ion fluence, no significant recovery is observed at these temperatures.     

X-ray diffraction analysis of titanium tritide film during 1600 days

The generation and accumulation of ³He by tritium decay modified the physical and chemical properties of tritides. Here the evolution of lattice defects in long-aged titanium tritide films is investigated by X-ray diffraction and changes in the positions, intensities and line shapes of diffraction peaks have been determined over a period of about 1600 days (>4 years). Texture effects are also observed by biased intensities in standard θ–2θ scans. The results show that the TiT_1.5 film keeps an fcc structure during 1600 days and reveals an hkl-dependent unit-cell expansion and line width broadening which are interpreted in terms of isolated tetrahedral interstitial ³He atoms and isolated bubble growth models by dislocation loop-punching or dislocation dipole expansion combined with Krivoglaz theory. In the first 12 days of aging, isolated tetrahedral interstitial ³He atoms or ³He clusters are formed, then interstitial ³He atoms diffuse into (1 1 1) planes and precipitate into clusters. The spontaneous formation of Frenkel pairs, the self-interstitial atoms produced are built into dislocations resulting in formation platelet bubbles and dislocation dipoles between 12 and 27 days. Above 27 days, multiple stages of ³He bubbles growth appear: (1) between 27 and 85 days platelet helium bubbles growth by dislocation dipoles expansion, (2) between 85 and 231 days the transition from platelet bubbles to sphere bubbles by loop emission, (3) after 231 days sphere bubbles growth by dislocation loop-punching and probably formation of sub-grain boundaries by dislocation rearrangement.     

Investigation of efficient 131I production from natural uranium at Tehran research reactor

Iodine-131, which has a half-life of 8.05 days, is the one of the most widely used radionuclides in medical diagnosis and treats some diseases of thyroid gland. Optimization of ¹³¹I production in Tehran research reactor (TRR) was studied by two different methods. Primarily, standard nuclear codes such as ORIGEN, WIMS and CITATION were applied and then analytical solutions technique was followed.Calculated results and experimental works in the bench scale indicate that, by irradiation of 100 g natural Uranium (UO₂) for 100 h at 3.5 × 10¹³ (n’s/cm² s) thermal neutron flux in the TRR, one can produce about 5 Ci of ¹³¹I for medical purposes, on the other hand can produce very useful radionuclides like ⁹⁹Mo and ¹³³Xe in one batch irradiation in the unique production line.     

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).     

Damage accumulation and annealing in 6H–SiC irradiated with Si+

Damage accumulation and annealing in 6H-silicon carbide (α-SiC) single crystals have been studied in situ using 2.0 MeV He⁺ RBS in a 〈0 0 0 1〉-axial channeling geometry (RBS/C). The damage was induced by 550 keV Si⁺ ion implantation (30° off normal) at a temperature of −110°C, and the damage recovery was investigated by subsequent isochronal annealing (20 min) over the temperature range from −110°C to 900°C. At ion fluences below 7.5 × 10¹³ Si⁺/cm² (0.04 dpa in the damage peak), only point defects appear to be created. Furthermore, the defects on the Si sublattice can be completely recovered by thermal annealing at room temperature (RT), and recovery of defects on the C sublattice is suggested. At higher fluences, amorphization occurs; however, partial damage recovery at RT is still observed, even at a fluence of 6.6 × 10¹⁴ Si⁺/cm² (0.35 dpa in the damage peak) where a buried amorphous layer is produced. At an ion fluence of 6.0 × 10¹⁵ Si⁺/cm² (−90°C), an amorphous layer is created from the surface to a depth of 0.6 μm. Because of recovery processes at the buried crystalline–amorphous interface, the apparent thickness of this amorphous layer decreases slightly (<10%) with increasing temperature over the range from −90°C to 600°C.     

Temperature behavior of damage in sapphire implanted with light ions

In this study, we compare and discuss the defect behavior of sapphire single crystals implanted with different fluences (1 × 10¹⁶–1 × 10¹⁷ cm^?2) of carbon and nitrogen with 150 keV. The implantation temperatures were RT, 500 °C and 1000 °C to study the influence of temperature on the defect structures. For all the ions the Rutherford backscattering-channeling (RBS-C) results indicate a surface region with low residual disorder in the Al-sublattice. Near the end of range the channeled spectrum almost reaches the random indicating a high damage level for fluences of 1 × 10¹⁷ cm^?2. The transmission electron microscopy (TEM) photographs show a layered contrast feature for the C implanted sample where a buried amorphous region is present. For the N implanted sample the Electron Energy Loss Spectroscopy (EELS) elemental mapping give evidence for the presence of a buried damage layer decorated with bubbles. Samples implanted at high temperatures (500 °C and 1000 °C) show a strong contrast fluctuation indicating a defective crystalline structure of sapphire.     

Ion beam shaping of Au nanoparticles prepared by micellar technique

Irradiation-induced burrowing and ion-induced shaping effects of Au nanoparticles are investigated. Hexagonally arranged Au nanoparticles prepared by micellar technique with diameter ～10 nm and inter-particle distance of about 80 nm were sequentially irradiated with 200 keV Ar⁺ ions to fluences of 5×10¹⁵ ions/cm². Irradiation with Argon ions causes sinking of the Au nanoparticles into the subjacent SiO₂ layer due to capillary driving forces related to specific wetting conditions while the spherical shape is conserved. Subsequent irradiation with 54 MeV Ag⁸⁺ swift heavy ions of these spherical Au nanoparticles confined within a silica matrix shapes them into prolate nanorods and nanowires whose principal axes are aligned along the beam direction. Above a threshold fluence two deformation regimes have been observed. For relatively low fluences Au nanoparticles elongate into nanorods depending on their volume. For high fluences, the formation of nanowires is observed provided that the inter-particle distance is short enough to allow for an efficient mass transport through the silica matrix.