Comparison of the damage in sapphire due to implantation of boron, nitrogen, and iron

The damage microstructure and optical properties of sapphire implanted with boron, nitrogen and iron were examined by RBS-C, TEM, and optical absorption. Implantations were conducted at RT and 1000 °C at 150 keV and fluences of 3 × 10¹⁶-1 × 10¹⁷ ions/cm². Optical absorption measurements indicate that the boron-implanted samples contained the highest number of F-type centers and the nitrogen-implanted samples the fewest. The microstructure of the boron-implanted samples shows only ‘black-spot’ defect clusters, as did the iron-implanted samples at the lower fluences. At higher fluences, the iron implanted samples revealed the presence of nanometer-sized precipitates of single crystal bcc iron that contributed to additional optical scattering. Bubbles formed in samples implanted with low fluences of nitrogen. A second damage region is apparent in the RBS-C patterns for higher fluences of nitrogen.     

Damage creation in α-Al2O3 by MeV fullerene impacts

Single crystals of α-Al₂O₃ were irradiated at room temperature with C₆₀ clusters at normal and grazing incidences. The extent of the induced damage was determined using Rutherford backscattering spectrometry in channeling geometry (RBS-C). A damage cross-section of 3.1 × 10⁻¹² cm² was obtained for the highest electronic stopping power (76.2 keV nm⁻¹). From electron microscopy observations continuous amorphous tracks were evidenced around the projectile trajectory and an electronic stopping power threshold for damage creation of 18 keV nm⁻¹ was also determined. The spatial correlation in depth of the cluster components were deduced from both direct track length measurements and the damage profiles extracted from RBS-C analysis. The maximal correlation length represents about one-third of the projected range (R_p) of a free carbon. Using atomic force microscopy (AFM), conically shaped hillocks corresponding to the out of plane expansion of the latent tracks were observed. These structures characterize nanometric changes of the plastic properties of sapphire induced by high electronic excitations.     

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.     

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.     

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).     

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.     

Controlling the microstructure of ZnO nanoparticles embedded in Sapphire by Zn ion implantation and subsequent annealing

(0 0 0 1) α-Al₂O₃ single crystals (sapphire) were implanted with Zn ions of 60 keV at a fluence of 1 × 10¹⁷ ions/cm². Transmission electron microscopy and optical absorption spectroscopy studies show the formation of ZnO nanoparticles in the sapphire substrate after the implanted sample was annealed at 700 °C in oxygen ambient. The photoluminescence spectrum of the annealed sample indicates the formation of ZnO nanoparticles with perfect lattice structure. The selected-area electron diffraction pattern proves that the ZnO nanoparticles have the (0 0 0 2) orientation which follows the orientation of Al₂O₃ substrate. The result shows that the crystallographic orientation of nanoparticles obtained through ion implantation is defined by the substrate.     

Optical and electrical characterizations of Mn doped p-type β-FeSi2

β-FeSi₂ has attracted increasing attention as a promising material for optoelectronic and thermoelectronic devices due to a high optical absorption coefficient (α) of about 10⁵ cm⁻¹ near 1.0 eV and its chemical stability at higher temperatures. For the future practical use of this material in devices, the control of each electrical conductivity type and the improvement of the material quality are highly required. Although unintentionally doped β-FeSi₂ layers formed on n-type Si(1 0 0) by the conventional electron-beam deposition (EBD) have typically shown n-type conductivity, the p-type β-FeSi₂ layers were formed by the introduction of Mn impurity using ion-implantation at room temperature (RT) and subsequent annealing procedures. In this study, we aimed to make p-type β-FeSi₂ by implantation of ⁵⁵Mn⁺ ions into EBD-grown n-type β-FeSi₂ layers/n-Si, where ⁵⁵Mn⁺ ions were implanted at two different temperatures (T_sub) of RT and 250°C using an energy and a dose of 300 keV and 2.68 × 10¹⁵ cm⁻², respectively. Their optical and electrical properties, which ought to be affected by implantation and annealing temperatures (T_a2), were investigated by Raman scattering, optical transmittance, reflectance and van der Pauw measurements. The results showed that the ⁵⁵Mn⁺ doping with T_sub=RT and higher thermal annealing at T_a2=900°C produced p-type layers of good quality with maximum hole mobility of 454.5 cm²/Vs at about 65 K.     

Matrix effects in SIMS analysis of high-dose boron implanted silicon wafers

Secondary ion emission from ¹¹B⁺ implanted silicon wafers with dose of 1 × 10¹²−5 × 10¹⁶ cm⁻² has been investigated. Experiments were performed using O₂⁺ primary ions with an impact energy of 8.0 keV and an incident angle of 39° from the surface normal. The emission of ¹¹B⁺ is enhanced and ²⁸Si⁺ is suppressed at the peak region of boron profile for the high-dose sample, such as at doses ⩾ 5 × 10¹⁵ cm⁻² (peak concentration ∼5 × 10²⁰ cm⁻³). The secondary ion energy distribution of ¹¹B⁺ is broadened and ²⁸Si⁺ is sharpened with increasing the boron concentration. The mechanisms of these phenomena are also considered.     

Damage recovery and optical activity in europium implanted wide gap oxides

In this study we compare and discuss the defects and optical behaviour of sapphire and magnesium oxide single crystals implanted at room temperature with different fluences (1 × 10¹⁵-1 × 10¹⁶ cm⁻²) of europium ions.Rutherford backscattering channelling shows that for fluences above 5 × 10¹⁵ cm⁻² the surface disorder level in the Al-sublattice reaches the random level. Implantation damage recovers fast for annealing in oxidizing atmosphere but even for the highest fluence we recover almost completely all the damage after annealing at 1300 °C, independently of the annealing environment (reducing or oxidizing). Annealing above 1000 °C promotes the formation of Eu₂O₃ in the samples with higher concentration of Eu. The optical activation of the rare earth ions at room temperature was observed after annealing at 800 °C by photoluminescence and ionoluminescence. In Al₂O₃ lattice the highest intensity line of the Eu³⁺ ions corresponds to the forced electric dipole ⁵D₀ → ⁷F₂ transition that occurs ∼616 nm. For the MgO samples the Eu³⁺ optical activation was also achieved after implantation with different fluences. Here, the lanthanide recombination is dominated by the magnetic dipole ⁵D₀ → ⁷F₁ transition near by 590 nm commonly observed for samples were Eu³⁺ is placed in a high symmetry local site. The results clearly demonstrate the possibility to get Eu incorporated in optical active regular lattice sites in wide gap oxides.     

Thermal annealing behavior of hydrogen and surface topography of H2+ ion implanted tungsten

Tungsten (W) has been proposed as a plasma-facing material in fusion reactors due to its outstanding properties. Degradation of the material properties is expected to occur as a result of hydrogen (H) isotope permeation and trapping in W. In this study, two polycrystalline W plates were implanted with 80 keV H₂⁺ ions to a fluence of 2 × 10²¹ H⁺/m² at room temperature (RT). Time-of-flight secondary ion mass spectrometry (ToF-SIMS), focused ion beam (FIB), and scanning electron microscopy (SEM) were used for sample characterization. The SIMS data shows that H atoms are distributed well beyond the ion projected range. Isochronal annealing appears to suggest two H release stages that might be associated with the reported activation energies. H release at RT was observed between days 10 and 70 following ion implantation, and the level was maintained over the next 60 days. In addition, FIB/SEM results exhibit H₂ blister formation near the surface of the as-implanted W. The blister distribution remains unchanged after thermal annealing up to 600 ?C.     

Nuclear tracks in garnets studied by means of Rutherford backscattering and X-ray diffraction

(Y, La)₃(Fe, Ga)₅O₁₂ epitaxial garnet films on (111) Gd₃Ga₅O₁₂ substrates irradiated with ²³⁸U ions of 1.4 MeV/u specific energy in the dose range 10¹⁰ cm^?2 to 3 × 10¹¹ cm^?2 were measured by means of Rutherford backscattering and double-crystal X-ray diffraction before and after thermal annealing in oxygen. The nuclear track diameter of 10 nm confining a cylindrical volume of highly disordered material caused by each ion impact has been deduced from the comparison of the backscattering spectra of the irradiated and unirradiated film areas. The fraction of randomly backscattered ions due to the irradiation-induced damage as well as the lattice expansion perpendicular to the crystal surface caused by irradiation-induced lateral compressive stress are proportional to the ion dose. After thermal annealing the comparison of the almost identical backscattering yield of the irradiated areas and the unirradiated film regions demonstrates a nearly perfect recrystallization of the damaged track volumes.     

Aggregation of ion-implanted silver in magnesium oxide single crystals

Ag precipitates are obtained by thermal annealing between 25°C and 1500°C of MgO single crystals implanted at room temperature with Ag⁺ ions (180 keV, 5 × 10¹⁶−10¹⁷ ions cm⁻²). These results are analysed in the light of MIE theory which has bee justified by TEM observations.The TEM enabled us to clarify the nature of the precipitates (metallic silver), their shape, their size and their orientation in relation to the matrix.This relationship was defined as: [100]_Ag∥[100]_MgO and (001)_Ag∥(001)_MgO.     

Structure and optical properties of sapphire implanted with boron at room temperature and 1000 °C

Many previous studies of ion-implanted sapphire have used gas-forming light ions or heavier metallic cations. In this study, boron (10¹⁷ cm⁻², 150 keV) was implanted in c-axis crystals at room temperature, 500 and 1000 °C as part of a continuing study of cascade density and “chemical” effects on the structure of sapphire. Rutherford backscattering-ion channeling (RBS-C) of the RT samples indicated little residual disorder in the Al-sublattice to a depth of 50–75 nm but almost random scattering at the depth of peak damage energy deposition. The transmission electron micrographs contain “black-spot” damage features. The residual disorder is much less at all depths for samples implanted at 1000 °C. The TEM photographs show a coarse “black-spot damage” microstructure. The optical absorption at 205 nm is much greater than for samples implanted with C, N, or Fe under similar conditions.     

Microstructure and Surface Properties of Silver after High Dose Nitrogen Ion Implantation

In this paper the effect of nitrogen ion implantation at the energy of 50 keV and doses in the range between 10¹⁷ and 2 × 10¹⁸ ions/cm² on silver surface has been discussed. X-ray diffraction (XRD) analysis was used to characterize microstructure of implanted layer. The XRD results confirmed that by such implantation AgN₃ has been produced. Silver trinitride with orthorhombic structure was formed on cubic structure of silver surface. RMS roughness of implanted samples have been obtained using atomic force microscopy (AFM) analysis and compared with un-implanted sample. Microhardness properties of implanted samples measured by Vickers test. The results show that by increasing the ion dose up to 1 × 10¹⁸ ions/cm² hardness enhances. Finally, reflection changes at the UV–Vis-NIR region measured by diffuse reflectance accessory of a spectrophotometer. The results of spectrophotometry analysis show reduction in diffused reflection spectrum of nitrogen implanted samples.     

A study of the irradiation behaviour of Zr3Al

Zr₃Al is an ordered f.c.c. alloy of the L1₂ type. In this investigation, the stability of the ordered phase when subjected to Ar⁺ ion bombardment was explored using transmission electron microscopy. At low ion fluences (up to 10¹² ions/cm²) individual damaged regions were observed. Imaging with fundamental reflections revealed those regions having a spherically symmetrical strain field whereas imaging with superlattice reflections also revealed disordered regions. At ion fluences above 10¹² ions/cm² overlap of the damage regions occurred thus resulting in a complex damage configuration. In the fluence regime 5 × 10¹⁴ to 1 × 10¹⁶ ions/cm², complete disordering of Zr₃Al initially occurred and this was followed by complete transformation to the amorphous state. The fluence required to reach a particular disordered state and degree of amorphicity was dependent upon the amount of annealing which occurred within the defect cascade at the temperature of the bombardment.     

Effects of Mg-ion implantation in α-Al2O3 and α-Al2O3:Mg crystals: Electrical conductivity and electronic structure changes

Undoped and Mg-doped α-Al₂O₃ single crystals were implanted with Mg ions, with an energy of 90 keV and a fluence of 10¹⁷ ions/cm². DC electrical measurements using the four-point probe method, between 295 and 428 K, were used to characterize the electrical conductivity of the implanted area. Measurements in this temperature range indicate that the electrical conductivity after implantation is thermally activated with an activation energy of about 0.03 eV both in undoped and in reduced Mg-doped α-Al₂O₃ crystals, whereas the activation energy in oxidized Mg-doped α-Al₂O₃ crystals remains close to that before implantation. The I-V characteristics of the latter samples reveal a blocking behavior of the electrical contacts on the implanted area in contrast to the ohmic contacts observed in α-Al₂O₃ single crystals with the c-axis perpendicular to the broad face, where the Mg ions were implanted. We conclude that the enhancement in conductivity observed in the implanted regions is related to the intrinsic defects created by the implantation, rather than to the implanted Mg ions. The relationship between the oxygen vacancy concentrations at different stages of etching and the changes in the electronic structure, the chemical bonding, and the Al³⁺(2p)/O²⁻(1s) and Mg²⁺(1s)/O²⁻(1s) relative intensities was studied by X-ray Photoemission Spectroscopy.     

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.     

Post-annealing effects on the shallow-junction characteristics caused by high-fluence 77 keV BSi molecular ion implantations at room and liquid nitrogen temperatures

In this study, n-type <1 0 0> silicon specimens were liquid nitrogen temperature (LT) and room temperature (RT) implanted with 2 × 10¹⁵ cm⁻² 77 keV BSi molecular ions to produce shallow junctions. Post-annealing methods under investigation included furnace annealing (FA) at 550 °C for 0.5, 1, 2, 3 and 5 h and rapid thermal annealing (RTA) at 1050 °C for 25 s. Post-annealing effects on the shallow-junction characteristics were examined using one-step (FA) and two-step (FA + RTA) post-annealing treatments. Secondary ion mass spectrometry (SIMS), cross-sectional transmission electron microscopy (XTEM), a four-point probe and Raman scattering spectroscopy (RSS) were employed to analyze junction depths (x_j), damage microstructures, sheet resistance (R_s) and damage characteristics, respectively. The results revealed that the shallow-junction characteristics of the LT implant are better than those of the RT one when post-annealing time in FA exceeds 1 h. A post-annealing time of 3 h in FA is needed in order to obtain the optimal one- or two-step post-annealing effects on the shallow-junction characteristics in both the LT and RT implants.