Rutherford Backscattering Spectrometry And Channeling Research Articles

Mechanical properties and structure evolution of single-crystalline silicon irradiated by 1 MeV Au+ and Cu+ ions

Abstract Mechanical and structural evolutions of single-crystalline silicon irradiated by a series of doses 1 MeV Au+ ions and Cu+ ions are characterized by Surface laser-acoustic wave spectroscopy by (LA wave), Rutherford backscattering spectrometry and channeling (RBS/C) and transmission electron microscopy (TEM). The behavior of implanted Au+ and Cu+ ions was also simulated by using Stopping and range of ions in matter (SRIM) software package, respectively. It is demonstrated that LA wave and RBS could be applied for accurate evaluation of the TEM observed amorphous layer’s thickness. The modified mechanical properties depend on the species and the dose of implantation. For 1 MeV Au+ ions, the threshold dose of completely amorphous is 5 × 1014 atoms/cm2, while the one for Cu+ ions is 5 × 1015 atoms/cm2. Upon completely amorphous, the young’s modulus and layer density decreased significantly while saturated with the dose increasing sequentially.

Low energy cathodoluminescence analysis of damage build-up in ion irradiated spinel mono- and polycrystals

Abstract In contrast to single crystalline materials a quantitative determination of defect formation in polycrystals is challenging. Here we use low-energy (3 keV) cathodoluminescence (CL) for structural characterization of single and polycrystalline magnesium aluminate spinel (MgAl2O4) exposed to irradiation with 300 keV Ar+ ions at room temperature in a wide fluence range of 1 × 1012–2 × 1016 cm−2. The results for single crystalline materials are also compared with conventional Rutherford Backscattering and Channeling spectrometry (RBS/C). It is demonstrated that damage formation in both single and polycrystalline spinels exhibits a multi-step character where polycrystalline material is more susceptible to ion irradiation. The results also imply that the low-energy CL is more sensitive to low damage levels as compared to RBS/C and it can be efficiently used as a complementary tool showing new perspectives in the damage accumulation studies in single- and polycrystalline materials.

Influence of annealing temperature on the magnetic properties of Cr+ implanted AlN thin films

Abstract Diluted magnetic semiconductor (DMS) AlN:Cr films were produced by implanting various doses Cr + ions into AlN thin films at room temperature followed by a thermal annealing process. The structural and magnetic characteristics of the samples were investigated as a function of annealing temperature by means of Rutherford backscattering and channeling spectrometry (RBS/C), X-ray diffraction (XRD), Raman spectroscopy, vibrating sample magnetometer (VSM) and SQUID. Structural analyzes demonstrate that implantation damages gradually decrease with the increasing of annealing temperature. Moreover, better recrystallization in the implanted part of the samples was observed for the sample annealed at 950 °C. Both XRD and Raman pattern illustrate that no secondary phase or metal related-peaks were appear in all the samples. Magnetic analysis reveals that annealed Cr + -implanted samples exhibit ferromagnetism at room temperature, however, the sample annealed at 950 °C shows improved magnetic characteristics. The saturation magnetization is estimated to be 9.0×10 −5 emu/g and the coercive field ( H c ) is approximately 200 Oe for the samples annealed 950 °C. In SQUID analysis, FC/ZFC measurements indicate that the Curie temperature ( T C ) is well above room temperature.

Copper ion implanted aluminum nitride dilute magnetic semiconductors (DMS) prepared by molecular beam epitaxy

Diluted magnetic semiconductor (DMS) AlN:Cu films were fabricated by implanting Cu+ ions into AlN thin films at various ion fluxes. AlN films were deposited on c-plane sapphire by molecular beam epitaxy followed by Cu+ ion implantation. The structural and magnetic characterization of the samples was performed through Rutherford backscattering and channeling spectrometry (RBS/C), X-ray diffraction (XRD), Raman spectroscopy, vibrating sample magnetometer (VSM) and SQUID. Incorporation of copper into the AlN lattice was confirmed by RBS, while XRD revealed that no new phase was formed as a result of ion implantation. RBS also indicated formation of defects as a result of implantation process and the depth and degree of damage increased with an increase in ion fluence. Raman spectra showed only E2 (high) and A1 (LO) modes of wurtzite AlN crystal structure and confirmed that no secondary phases were formed. It was found that both Raman modes shift with Cu+ fluences, indicating that Cu ion may go to interstitial or substitutional sites resulting in distortion or damage of lattice. Although as implanted samples showed no magnetization, annealing of the samples resulted in appearance of room temperature ferromagnetism. The saturation magnetization increased with both the annealing temperature as well as with ion fluence. FC/ZFC measurements indicated that the ferromagnetic effect was not related with superparamagnetic phase formation. In spite, it was due to the formation of AlN based DMS material. The Curie temperature (TC) of the sample prepared at an ion fluence of 5×1015cm−2 and an annealing temperature of 950°C was found to lie above 340K.

Dislocation density and tetragonal distortion of a GaN epilayer on Si (1 1 1): A comparative RBS/C and TEM study

Rutherford backscattering and channeling spectrometry (RBS/C) as well as transmission electron microscopy (TEM) are used to characterize the crystalline structure of a GaN layer grown on a Si (111) substrate. The channeling measurements are performed along the off-normal 〈12¯13〉 axis in the {101¯0} plane of the GaN layer. The threading edge dislocation defect density obtained from RBS/C is quantitatively compared to the results obtained from TEM. The strain is found not to be completely relaxed, eT≠0, in spite of the large thickness of the GaN layer (3.0μm), and in spite of the incorporation of various buffer layers.

Cu IONS IRRADIATION IMPACT ON STRUCTURAL AND OPTICAL PROPERTIES OF GaN THIN FILM

Epitaxial grown Gallium nitride ( GaN ) thin film on sapphire was irradiated with Cu ions at various fluences (5×1014, 1 ×1015 and 5×1015 cm -2). The level of lattice disorder, as measured by Rutherford backscattering spectrometry and channeling (RBS/C), gradually increases with the increasing of ions fluence. Lattice amorphization is observed for the sample irradiated with fluence of 5×1015 cm -2 which is also confirmed by X-ray diffractometer (XRD) analysis. It was found that both Raman modes of GaN layer clearly shifted with Cu + fluences. Both Raman and X-ray analyses explore that Cu atom substituted into Ga sites. Atomic force microscopy (AFM) images show the irradiated GaN surface roughness increases with the increasing ions fluence. The UV-visible transmittance spectrum and ellipsometric measurements show a decrease in the band gap value after irradiation of Cu ions in the GaN film. Moreover, the optical constants (n and k) of the films vary with the increasing of Cu ion fluences.

Ion-beam modifications of mechanical and dimensional properties of silicon carbide

3C-SiC single crystal epitaxial layers, 6H-SiC single crystal plates and α-SiC Hexoloy sinters were irradiated with 4.0 MeV Xe or 4.0 MeV Au ions at room temperature. Mechanical and dimensional evolutions of silicon carbide are studied by means of nano-indentation and step-height measurements which are correlated with Rutherford backscattering spectrometry and channelling (RBS/C) data in single crystals. Irradiation with Xe ions induces a total lattice disorder related to amorphization for a fluence of 1 × 1015 cm−2 in both polytypes. When complete amorphization is reached, around the same values of Young's modulus (∼350 GPa) and Berkovich hardness (∼27 GPa) are found in both polytypes. The out-of-plane expansion increases with irradiation dose and the saturation value measured in the amorphous layer (normalized to the projected range of the ions) is close to 20–25%. Modifications of macroscopic properties are mainly governed by the disordered fraction of the material in a two-step damage process. A similar behaviour of material evolution is found for the cubic and hexagonal polytypes, either in single crystals or sintered polycrystalline samples. Calculations of Young's modulus and volume swelling are carried out using the analytical (Reuss and Voigt) models of homogenization.

Irradiation damage in Gd2Ti2O7single crystals: Ballistic versus ionization processes

The structural transformations induced in Gd${}_{2}$Ti${}_{2}$O${}_{7}$ single crystals irradiated at high energies (870-MeV Xe), where ionization processes (electronic stopping) dominate, and at low energies (4-MeV Au), where ballistic processes (nuclear stopping) dominate, have been studied via the combination of Rutherford backscattering spectrometry and channeling (RBS/C), Raman spectroscopy, and transmission electron microscopy (TEM) experiments. At high energy, amorphization occurs directly in individual ion tracks from the extreme electronic-energy deposition, and full amorphization results from the overlapping of these tracks as described by a direct impact model. The track diameters lie in the range 6--9 nm. At low energy, amorphization occurs via indirect processes, driven by ballistic nuclear energy deposition from the ions, that is accounted for in the framework of both direct-impact/defect-stimulated and multi-step damage accumulation models. The ion fluence for total amorphization of the irradiated layer is much higher at low energy (0.5 ion nm${}^{\ensuremath{-}2}$) than at high energy (0.05 ion nm${}^{\ensuremath{-}2}$), consistent with the nuclear stopping at low energy (5.2 keV/nm) compared to the electronic stopping at high energy (29 keV/nm).

Superparamagnetic nanoparticles formed in Fe-implanted ZnO

Due to its potential application to diluted magnetic oxides, transition metal doped ZnO has been under intensive investigation. We present a correlation between the structural and the magnetic properties of Fe implanted ZnO bulk crystals. Crystalline damage recovery, structural and magnetic properties are studied by Rutherford backscattering spectrometry and channelling (RBS/C), synchrotron radiation X-ray diffraction (SR-XRD), and superconducting quantum interference device magnetometer (SQUID), respectively. The 623 K Fe ion implantation and the high vacuum annealing at 823 K lead to the formation of secondary phase -Fe and -Fe nanoparticles. The discrepancy between the zero-field cooling and the field cooling curves further indicates that Fe-implanted ZnO is superparamagnetic and the observed ferromagnetism originates from the Fe nanoparticles.

Tetragonal Distortion of InN Thin Films by RBS/Channeling

Rutherford backscattering and channeling spectrometry (RBS/C) are used to identify the crystalline quality (χ min = 4.87%) of an InN thin film as a function of depth, and make a non-destructive quantitative analysis of the structure, in order to analyze the tetragonal distortion of the InN thin film at the depth determined.

Fabrication of GaAs on Si Heterostuctures by Helium Implantation and Direct Wafer Bonding

Transfer of GaAs layers onto Si by helium ion implantation at room temperature and direct wafer bonding was investigated. The in uence of the ion energy (100 keV and 500 keV), the ion uence and the subsequent annealing condition on exfoliation and/or blistering was studied by using optical microscopy, Rutherford backscattering and channeling spectrometry (RBS/C), X-ray di raction (XRD) and cross-sectional transmission electron microscopy (XTEM) analysis and the optimum conditions for achieving thin layer exfoliation only after post-implantation annealing were experimentally determined. Our results suggest that the optimum uence for the GaAs ion-cut is in the range of (2 { 5) 1017 He+/cm2. Thin 400 GaAs layers were successfully transferred onto silicon after bonding of helium-implanted GaAs and Si wafers via a silicon-oxide intermediate layer and subsequent low-temperature splitting annealing at less than 220 C. Field emission scanning electron microscopy (FE-SEM) showed that a uniform transfer of the GaAs layer onto Si was obtained with no detectable defects at the GaAs/SiO2/Si bonding interfaces. XTEM observations of the as-split GaAs layers revealed that the relatively undamaged layer close to the intermediate layer could be extended by appropriate choices of the bonding process and/or implanted ion energy.

Amorphization and dynamic annealing of hexagonal SiC upon heavy-ion irradiation: Effects on swelling and mechanical properties

Structural, mechanical, and dimensional evolutions of silicon carbide (SiC) induced by heavy-ion irradiations are studied by means of Rutherford backscattering spectrometry and channeling (RBS/C), nanoindentation, and surface profilometry measurements. 4H- and 6H-SiC single crystals were irradiated with 4 MeV Au2+ and 4 MeV Xe+ ions at room temperature (RT) or 400 °C. Using a Monte Carlo program to simulate the RBS/C spectra (MCCHASY code), we find that Au ion irradiation at RT induces a total silicon sublattice disorder related to full amorphization at a dose of about 0.4 displacement per atom (dpa). A two-step damage process is found on the basis of the disordered fractions deduced from RBS/C data. Complete amorphization cannot be reached upon both Au and Xe ion irradiations at 400 °C up to about 26 dpa because of the dynamic annealing of defects. When complete amorphization is reached at RT, the Young’s modulus and Berkovich hardness of irradiated 6H-SiC samples are lower by, respectively, 40% and 45% than those of the virgin crystals. The out-of-plane expansion measured by surface profilometry increases versus irradiation dose and the saturation value measured in the completely amorphous layer (normalized to the ion projected range) is close to 25%. We show that the modifications of the macroscopic properties are mainly due to the amorphization of the material. The macroscopic elasticity constants and dimensional properties are predicted for a composite material made of crystalline matrix containing dispersed amorphous inclusions using simple analytical homogenization models. Voigt’s model seems to give the best approximation for disordered fractions larger than 20% in the second step of the damage process.

Radiation effects in yttria-stabilized zirconia: Comparison between nuclear and electronic processes

Yttria-stabilized zirconia (YSZ) single crystals were irradiated with heavy ions at energies ranging from a few MeV to a few GeV in order to compare the effects of nuclear collisions and electronic excitations. The amount of damage created by irradiation was measured as a function of the ion fluence by Rutherford backscattering and channeling spectrometry (RBS/C). Monte-Carlo simulations of RBS/C data show that both the depth distributions of radiation damage and the damage build-up strongly depend on the type of irradiation. At low energy (4MeV Au ions) the damage exhibits a peak around the ion projected range (∼500nm) and it accumulates with a double-step process; at high energy (940MeV Pb ions) the damage profiles are rather flat up to several micrometers and the damage accumulation is monotonous (one-step). RBS/C and X-ray diffraction results show that the various irradiations never lead to total disordering of irradiated layers (amorphization), even at the highest fluences used in the experiments.

Electrical and structural characterization of as-grown and annealed hydrothermal bulk ZnO

Hall effect measurements in the range 20–370 K on as-grown and annealed hydrothermal bulk ZnO have been performed. The bulk conductivity in the highly resistive as-grown sample was found to decrease and then increase after annealing at 550 °C and 930 °C, respectively. The conduction in the as-grown material is attributed to a deep donor which is replaced by a much shallower donor after annealing at 930 °C. Annealing at both temperatures also produced strong surface conduction effects. Nondegenerate low-mobility surface conduction dominated the electrical properties of the sample annealed at 550 °C, while a degenerate surface channel was formed after annealing at 930 °C. In addition, Rutherford backscattering and channeling spectrometry (RBS/C) was used to assess the effect of annealing on the crystalline quality of the samples. RBS/C measurements reveal that annealing at 930 °C leads to significant improvement of the crystalline quality of the material, while annealing at 550 °C results in the segregation of a nonchanneling impurity at the surface.

Substitution and diffusion behaviour of MeV implanted Sb in Si(1 0 0) after carbon irradiation

We investigate the effect of high-energy ion irradiation (HEII) on the dopant behaviour for a 1.5 MeV Sb implantation in Si(1 0 0). For HEII, 8 MeV carbon ions were utilized. In addition to exploring the Sb substitution, distribution and diffusion, after HEII, Si lattice damage has also been studied. Effects of annealing, both prior to and after HEII, have also been investigated. Techniques of Rutherford backscattering spectrometry and channeling (RBS/C) have been applied to understand the dopant behaviour as well as the damage and crystallization of Si lattice. The results show that the vacancy (V) supersaturation created during HEII promotes a high (93%) Sb substitution and a low Si damage after a 400 °C anneal. This is an anomalous result as the SPEG of Si is expected at 600 °C. Enormous redistribution of Sb is observed indicating that the dopant defect interactions become crucial after HEII. In-diffusion of Sb is noticed at higher temperatures. Sb diffusion or redistribution is not observed in the absence of HEII. Results indicate that the excess V after HEII can control the dopant behaviour as well as the Si lattice damage.

Formation and Microstructure of Cubic Metastable Iron Silicides Synthesized during Pulsed Laser Annealing

The phase formation and crystallization processes of metastable [CsCl]Fe1−x Si phases were investigated by irradiatingɛ-FeSi/Si(111) thin films with a pulsed excimer laser in the energy density range 300–900 mJ/cm2. The samples were analysed by Rutherford backscattering and channeling spectrometry (RBS/C), cross-sectional transmission electron microscopy (TEM) and conversion electron Mossbauer spectroscopy (CEMS). Laser irradiation results in mixing of the FeSi with the Si substrate, with the final concentration depending on the laser energy density. Due to the extremely rapid quench of the melt, a non-uniform Fe concentration is obtained. Analysis by cross-sectional transmission electron microscopy confirmed that this phase, which exhibits epitaxial ordering, corresponds to the metastable [CsCl]Fe1−x Si phase, which converts into the semiconductingβ-FeSi2 upon annealing at 600°C. CEMS indicates that no stable Fe-silicide phase nor a combination of stable phases have been formed. The CEM spectra consist of a distribution of quadrupole doublets and isomer shifts, in agreement with a [CsCl]Fe1−x Si phase that exhibits a (i) composition gradient and (ii) a random number of Fe vacancies in the neighbouring shells. These distributions make the CEM spectra hard to interpret. Full-Potential Linearized Augmented Plane Wave (FLAPW) calculations were performed to gain more insight in the hyperfine interaction parameters of the metastable [CsCl]Fe1−x Si phase and their dependence on a concentration variation. These calculations confirm the decreasing trend of the isomer shift with increasing number of laser pulses.

Clustering in Pb thin films on Si(1 1 1) and Pb-induced Si surface ordering

Pb thin films (10 nm) were deposited from a Knudsen cell on sputter-cleaned Si(1 1 1) substrates under ultrahigh vacuum conditions. Films were deposited at room temperature and subsequently annealed at 300 °C for 30 min. Rutherford backscattering spectrometry and channeling (RBS/C) measurements did not show any channeling in the as-deposited as well as annealed Pb layer. For the annealed sample the spectral broadening in RBS/C spectra occurred due to clustering of Pb, with a simultaneous reduction in the minimum yield from the Si substrate. Prior to Pb deposition the sputter-cleaned Si substrate was annealed at 500 °C, which was insufficient to remove all the damages introduced by Ar + sputtering. Thus the reduction of minimum yield in the substrate for the annealed Pb/Si(1 1 1) system compared to unannealed Pb/Si(1 1 1) may be interpreted as Pb-induced ordering of the Si surface. From the analysis of the step structure observed near the Si edge of the RBS/C spectrum for the annealed sample, it was found that Pb islands (average height ∼35 nm) have been formed on a uniform Pb layer of ∼1 nm thickness. The island formation has been confirmed by atomic force microscopy measurements.

Damage profiles and damage annealing behavior in Al 0.168Ga 0.348In 0.484P/GaAs implanted with 200 keV Zn + ions

Damage profiles and the associated annealing behavior in Al 0.168Ga 0.348In 0.484P/GaAs samples implanted with 200 keV Zn + ions were investigated by using Rutherford backscattering spectrometry and channeling (RBS/C) technique. A computer code was used to extract quantitative damage profiles from the RBS/C spectra. The measured damage profiles are compared with those obtained from TRIM98 computer simulation code, and a good agreement between the measurements and the TRIM98 simulations was observed. The annealing behavior of the damage induced in the AlGaInP/GaAs samples was studied and compared with that induced in GaP bulk crystal substrates under the same implantation and annealing conditions. The result shows that the structure of the radiation damage induced in the quaternary III–V compound, AlGaInP, is more complicated than that in the binary III–V compound, GaP.

Silicon-on-Insulator Structure Fabricated by Electron Beam Evaporation of Si on Porous Si and Epitaxial Layer Transfer

Epitaxial monocrystalline Si was grown on porous silicon by ultra-highvacuum electron beam evaporation. Results of reflection high-energyelectron diffraction, atomic force microscopy, cross-sectiontransmission electron microscopy and Rutherford backscatteringspectrometry and channelling (RBS/C) show that the epitaxial layeris of a good quality. Furthermore, silicon-on-insulator materials weresuccessfully produced by bond and etch back of porous silicon. Thequality of the silicon-on-insulator samples was investigated by RBS/Cand spreading resistance profiling. Experimental results show that boththe crystalline quality and electrical quality are good. In addition,the interface between the top Si layer and SiO2 buried layer is verysharp.

Defect formation and annealing behavior of Si implanted by high-energy 166Er ions

Si crystals were implanted at room temperature with 2.0 MeV 166 Er + ion doses of 5×10 12, 1×10 14, 5×10 14, 1×10 15 and 2.5×10 15 ions/ cm 2 . Conventional furnace thermal annealings were carried out in the temperature range from 600°C to 1150°C. The radiation damage and annealing behavior were investigated using the Rutherford backscattering spectrometry and channeling (RBS/C) technique. Doses above 5×10 14 ions/ cm 2 were found to produce amorphous layers. The experimental results show that the annealing behavior of 2.0 MeV Er + implanted into silicon is strongly influenced by the implantation dose and annealing temperature. For the samples with dose of 5×10 14 ions/ cm 2 and more, an abnormal annealing behavior was found and a qualitative explanation has been given. For the sample implanted with dose of 2.5×10 15 ions/ cm 2 , a substantial Er outdiffusion has been investigated. Er outdiffusion increases with annealing temperature, Er depth distribution changes from an initially unimodal Gaussian form to a bimodal distribution with a build up of Er concentration near the surface.