Rutherford Backscattering Channeling Research Articles

Damage creation threshold of Al2O3 under swift heavy ion irradiation

Among insulators, sapphire (Al2O3) is less sensitive than any amorphizable oxides regarding the irradiation with heavy ions in the electronic energy loss regime. Earlier experimental results indicated a critical energy loss for damage creation of around of 20keV/nm, while calculations based on the inelastic thermal spike model predict a value of ∼10keV/nm. In order to clarify this discrepancy, additional irradiation experiments were performed with different ions between Ni and U covering electronic energy losses between 10 and 43keV/nm and kinetic energies in the range from 1 to 11MeV/u. Irradiation effects were characterized by atomic force microscopy (hillock formation), profilometry (swelling), and channeling Rutherford backscattering (near-surface disorder). Combining the results from these measurements, an electronic energy loss threshold of 9.5±1.5keV/nm is extracted, indicating that the earlier threshold was overestimated and confirming the predictive power of the inelastic thermal spike model. Threshold predictions based on thermal spike model calculations are given for lower and higher beam energies.

Germanium strips for channeling: Study of the crystal quality after slicing and chemical etching

Abstract Aiming at the fabrication of germanium strips with lateral faces provided of excellent crystal quality for swift proton beams channeling, two different cutting techniques (diamond saw, DS, and wire electrical discharge machining, WEDM) were adopted to obtain germanium strips from Ga doped wafers (100 mm diameter, 500 μm thickness). After cutting, the damaged layer was removed by using two different chemical etching compositions, whose etch rate, anisotropy ratio and effects on morphology were investigated. The etch pits density of the as received material was evaluated through selective chemical etching and inspection with optical microscope, whereas the surface morphology of the as cut surface and after chemical treatment was investigated by scanning electron microscopy (SEM). The physical nature, amount and in-depth distribution of the cut induced lattice distortions were analyzed by low energy channeling Rutherford Backscattering Spectrometry (c-RBS), Raman spectroscopy and high resolution X-ray diffraction (HRXRD). The same set of techniques was also applied to monitor the structure evolution with increasing etching time. In the case of WEDM cut samples, though a remarkable recovery of the pristine crystal quality was achieved through removal of the sub-surface damage by prolonged wet etching as pointed out by c-RBS and HRXRD, the trend in crystal quality enhancement versus etching time is not as regular and reproducible as evidenced by the same techniques for DS samples.

Annealing of silver implanted 6H–SiC and the diffusion of the silver

Annealing and diffusion behavior of implanted silver in 6H–SiC has been investigated using Rutherford backscattering spectroscopy (RBS), channeling, Raman spectroscopy and scanning electron microscopy (SEM) techniques. Silver (109Ag+) ions with an energy of 360keV were implanted in SiC to a fluence of 2×1016cm−2 at room temperature (23°C), 350 and 600°C. After implantation the samples were annealed at temperatures up to 1400°C. The results revealed that implantation at room temperature created an amorphous layer of about 270nm from the surface while implantation at 350 and 600°C retained a crystalline structure with more damage created for 350°C implantation compared to 600°C. Diffusion of implanted Ag accompanied by loss from the surface started at 1300°C in the amorphous SiC with no diffusion observed in the crystalline SiC. A new model explaining this diffusion of silver accompanied silver loss is presented.

Investigation on the structural and magnetic properties of Co+ implanted rutile TiO2

Crystalline Co nanoparticles in rutile TiO2 were synthesized by 180keV Co+ ion implantation at 623K with the fluence of Φ=4×1016cm−2. The structural and magnetic properties of samples after thermal annealing at different temperatures were characterized by synchrotron radiation X-ray diffraction (SR-XRD), Rutherford backscattering/channeling (RBS/C) and superconducting quantum interference device (SQUID) magnetometer. The SR-XRD results reveal the formation of hcp Co nanoparticles in the as-implanted samples. With increasing annealing temperature, the transition of Co nanoparticles from hcp to fcc is observed. After annealing at 1073K, the lattice damage is significantly repaired compared with the as-implanted one. The Co nanoparticles forming inside TiO2 are the major contribution of the measured ferromagnetism.

Damage formation and recovery in Fe implanted 6H–SiC

Silicon carbide doped with magnetic ions such as Fe, Mn, Ni or Co could make this wide band gap semiconductor part of the diluted magnetic semiconductor family. In this study, we report the implantation of 6H–SiC single crystals with magnetic 56Fe+ ions with an energy of 150keV. The samples were implanted with 5×1014Fe+/cm2 and 1×1016Fe+/cm2 at different temperatures to study the damage formation and lattice site location. The samples were subsequently annealed up to 1500°C in vacuum in order to remove the implantation damage. The effect of the annealing was followed by Rutherford Backscattering/Channeling (RBS/C) measurements. The results show that samples implanted above the critical amorphization temperature reveal a high fraction of Fe incorporated into regular sites along the 〈0001〉 axis. After the annealing at 1000°C, a maximum fraction of 75%, corresponding to a total of 3.8×1014Fe+/cm2, was measured in regular sites along the 〈0001〉 axis.A comparison is made between the observed annealing behavior and the one measured in low fluence (2×1013cm−2) β emission channeling experiments using the radioactive isotope 59Fe (t1/2=45d), where the sample was implanted at room temperature and the β− emission channeling yield was measured by means of a position-sensitive detector.

Characterization of n-GaN dilute magnetic semiconductors by cobalt ions implantation at high-fluence

In this study, we present the structural and magnetic characteristics of cobalt ions implantation at a high-fluence (5×1016cm−2) into n-GaN epilayer of thickness about 1.6μm. The n-GaN was grown on sapphire by metal organic chemical vapor deposition (MOCVD). Rutherford backscattering channeling was used for the structural study. After implantation, samples were annealed at 700, 800 and 900°C by rapid thermal annealing in ambient N2. XRD measurements did not show any secondary phase or metal related-peaks. High resolution X-ray diffraction (HRXRD) was performed as well to characterize structures. Well-defined hysteresis loops were observed at 5K and room temperature using alternating gradient magnetometer AGM and Superconducting Quantum Interference Device (SQUID) magnetometer. Temperature-dependent magnetization indicated magnetic moment at the lowest temperatures and retained magnetization up to 380K for cobalt-ion-implanted samples.

Room Temperature Giant Hall Effect in (Ni61Fe39) x (Al2O3)1−x Percolating Nanogranular Films

A series of (Ni61Fe39) x (Al2O3)1−x films were prepared using the magnetron sputtering technique. The maximum of saturated Hall resistivity 4.06 μΩ⋅cm was observed in (Ni61Fe39)60(Al2O3)40 nanogranular film at room temperature, which was about two orders larger than that of pure ferromagnetic metallic films. For the first time, the composition in the atomic fraction at the quantum percolation threshold was accurately characterized by the Rutherford backscattering (RBS) channelling technique in order to substantiate the newly metal-insulator fraction of percolation threshold in the Giant Hall Effect. It also was identified from the TEM image of an as-deposited sample that this large enhancement of the Hall resistivity coefficient was interrelated with the percolation threshold. With a different annealing temperature (T A ) up to 300 °C , the saturated Hall resistivity of (Ni61Fe39)60(Al2O3)40 granular film decreased only a little, which showed its good thermal stability for potential application.

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).

Incorporation of hydrogen in CuInSe2: Improvements of the structure

CuInSe2 single crystals were ion implanted with a dose of 3 × 1016 cm−2 by 2.5 keV H+ at 150 and 250 °C. Before and after the implantation the crystals were analyzed by Rutherford backscattering/channeling (RBS/C) along the 〈112〉 axis using 2 MeV He+. The RBS/C spectra indicate that the implantation at 150 °C introduces a layer of radiation damage, whereas after the implantation at 250 °C no structural deterioration of the lattice can be seen. Quite the contrary, the RBS/C spectra reveal a considerable decrease in the dechanneling parameters suggesting improvements in the lattice structural quality attributed to the incorporation of hydrogen.

Lattice expansion and evolution of damage buildup in Be-implanted InAs

The lattice expansion in InAs single crystal, due to ion-implantation by 80 keV Be ions with the implantation fluencies ranging from 1 × 10 12 to 2 × 10 16 cm −2, has been investigated by using high resolution X-ray diffraction (HRXRD), transmission electron microscopy (TEM), and Rutherford backscattering spectrometry/channeling (RBS/C). In order to clarify the evolution of damage buildup, the nonlinear maximum perpendicular strain ε m as a function of the Be fluence was obtained and analyzed. The curve of ε m vs. Be fluence is subdivided into five regions, each having a different damage accumulation behavior. The involved probable mechanisms of microstructural variation in InAs due to Be implantation of different fluencies are analyzed in detail.

Structural Analysis of InxGa1−xN/GaN MQWs by Different Experimental Methods

Structural properties of InxGa1−xN/GaN multi-quantum wells (MQWs) grown on sapphire by metal organic chemical vapor deposition are investigated by synchrotron radiation x-ray diffraction (SRXRD), Rutherford backscattering/channelling (RBS/C) and high-resolution transmission electron microscopy. The sample consists of eight periods of InxGa1−xN/GaN wells of 2.1 nm thickness and 8.5 nm thickness of GaN barrier, and the results are very close, which verifies the accuracy of the three methods. The indium content in InxGa1−xN/GaN MQWs by SRXRD and RBS/C is estimated, and results are in general the same. By RBS/C random spectra, the indium atomic lattice substitution rate is 94.0%, indicating that almost all indium atoms in InxGa1−xN/GaN MQWs are at substitution, that the indium distribution of each layer in InxGa1−xN/GaN MQWs is very homogeneous and that the InxGa1−xN/GaN MQWs have a very good crystalline quality. It is not accurate to estimate indium content in InxGa1−xN/GaN MQWs by photoluminescence (PL) spectra, because the result from the PL experimental method is very different from the results by the SRXRD and RBS/C experimental methods.

Growth and characterization of epitaxial (La 2/3Sr 1/3)MnO 3 films by pulsed laser deposition

High quality epitaxial (La 2/3Sr 1/3)MnO 3 (0 0 1) thin films were grown by pulsed laser deposition on SrTiO 3 (0 0 1) substrate at optimized growth parameters. The films quality was confirmed by both structural and physical properties characterization. Channeling Rutherford Backscattering Spectrometry characterization showed the minimal channeling coefficient as low as 4%. The LSMO thin films growth on SrTiO 3 substrate follows the island growth model. The Curie temperature of LSMO films is around 360 K, which is the one of the highest reported in literature. The resistivity of LSMO films showed the metal–insulate transition temperature coincides with the Curie temperature. This high quality LSMO is suitable for room temperature magnetic devices application.

Surface damage on diamond membranes fabricated by ion implantation and lift-off

Thin membranes with excellent optical properties are essential elements in diamond based photonic systems. Due to the chemical inertness of diamond, ion beam processing must be employed to carve photonic structures. One method to realize such membranes is ion-implantation graphitization followed by chemical removal of the sacrificial graphite. The interface revealed when the sacrificial layer is removed has interesting properties. To investigate this interface, we employed the surface sensitive technique of grazing angle channeled Rutherford backscattering spectroscopy. Even after high temperature annealing and chemical etching a thin layer of damaged diamond remains, however, it is removed by hydrogen plasma exposure.

Micro-patterning of Si(100) surfaces by ethanol cluster ion beams

The irradiation of Si(100) surfaces by ethanol cluster ion beams exhibited high-rate sputtering and low-damage formation. The sputtered depth increased with increase of the acceleration voltage for ethanol cluster ions, and the sputtering yield was a few hundreds times larger than that by Ar monomer ion beams. Also, the RBS channeling measurement showed that the irradiation damage was much less than that by Ar monomer ion irradiation. Furthermore, the AFM image showed that the surface roughness of the irradiated Si(100) surface was less than 1 nm. As well as the Si(100) surface, the sputtered depth of the photo-resist surface increased with increase of the acceleration voltage for ethanol cluster ions. Based on these results, micro-patterning with various sizes in a range of 3 μm to 100 μm was performed on the Si(100) surfaces by the ethanol cluster ion irradiation. Various kinds of photo-resist mask patterns such as circle, square and line patterns were made on a Si(100) surface by photo-resist technique. The SEM observation showed that micro-patterns were prepared on the Si (100) surface by the ethanol cluster ion irradiation.

Strain in GaAsSb quantum well studied by X-ray diffraction and Rutherford backscattering/channeling

The strain state of a GaAs 1− x Sb x /GaAs single quantum well (SQW) was studied using high resolution X-ray diffraction (HR-XRD) and Rutherford backscattering/channeling (RBS/C). The results reveal that the GaAsSb quantum well has good crystalline quality and the Sb content x of the GaAsSb layer is 0.36. The 7.3 nm GaAs 0.64Sb 0.36 layer is highly strained with a perpendicular elastic strain of 2.0% and a degree of relaxation of 0.23. Photoluminescence (PL) measurement at room temperature presents a peak at 0.995 eV (1.224 μm) with a linewidth of 67 meV, revealing the optical properties of the GaAsSb SQW.

Epitaxial samarium disilicide films on silicon (0 0 1) substrates: growth, structural and electrical properties

In this paper the effect of the growth temperature on the structural and electrical properties of samarium silicide films is investigated. The growth of the epitaxial films is performed under ultrahigh vacuum by reactive-deposition epitaxy on silicon (0 0 1) substrates. The structural properties are assessed by reflection high-energy electron diffraction and x-ray diffractometry. Random and channelling Rutherford backscattering experiments show that the films have the correct stoichiometry, i.e. Sm/Si ratio = 1 : 2, with channelling yields as low as 20% for the best samples. The electrical properties of these films are studied by Hall effect and resistivity measurements. The films have a metallic character, with a high concentration of n-type charge carriers (>1022 cm−3) and a resistivity lower than 200 µΩ cm at room temperature. The metallic character is confirmed by the experimental optical conductivity deduced from ellipsometry experiments. Finally, evidence is presented showing the potential of SmSi2/n-type Si junctions for electronic application with a Schottky barrier height of about 0.32 eV.

Annealing behavior of LiNbO 3 planar waveguides formed by oxygen ion implantation

Single crystals of z-cut LiNbO 3 were implanted at room temperature using 3.0 MeV oxygen ions at a fluence of 5 × 10 14 ions/cm 2. The relative intensity of the light (TM polarized) reflected from a prism versus effective index profile for waveguides experiencing different annealing conditions (as-implanted, 200, 300, 400, and 500 °C for 30 min in air) were detected using the prism-coupling method. The refractive index profile in the implanted waveguide region was reconstructed using the SRIM (the stopping and ranges of ions in matter) and RCM (reflectivity calculation method) simulation packages. Damage formation was investigated by the Rutherford backscattering spectrometry/channeling (RBS/C) method. The results of RBS/C indicating that O + implantation did not cause detectable lattice damage in the near-surface region of the sample. Measured transmission spectra show that the implantation conditions we selected have little influence on the transmission ratio. The propagation losses and near-field profiles of the light in the planar waveguide were measured with an end-face coupling system. The propagation loss of the O +-implanted planar waveguide is reduced to 0.45 dB/cm after annealing at 300 °C for 30 min.

Ion-beam-induced damage formation in CdTe at a temperature of 15 K

Damage formation in 〈1 1 1〉-oriented CdTe single crystals irradiated with 270 keV Ar ions at fluences ranging from 1.0 × 10 11 to 6.0 × 10 16 cm −2 was investigated in-situ using Rutherford backscattering spectrometry (RBS) in channeling configuration. Irradiation and subsequent analysis were performed at 15 K without changing the target temperature. CdTe is not rendered amorphous even after irradiation with several 10 16 cm −2. Defect profiles calculated from the RBS channeling spectra using the computer code DICADA show the formation of a broad defect distribution which extends much deeper into the crystal than the projected range of the implanted ions. Energy-dependent RBS channeling analysis was used to identify the defects as predominantly uncorrelated displaced lattice atoms.

Computerized Control and Operation of Rutherford Backscattering/Channeling for an in situ Ion Beam System and Its Application for Measurement of Si(001) and ZnO(001)

A computer-automated Rutherford backscattering/channeling (RBS/C) system is developed to provide in situ ion beam analysis of the accelerator-TEM system in Wuhan University. The basic system components are a PC equipped with a multichannel analyzer data acquisition board, motion control hardware including the Panmure stepping motor controller and integrated circuit modules, and a Labview programmed operating system with associated electronics. Single crystalline Si(001) and ZnO(001) implanted with Mn ions were characterized with this computerized setup. The crystalline quality χmin and channeling half angle of Si(001) were measured to be 4.65% and 0.52°, respectively, which are comparable to theoretical values 4.2% and 0.32°. The ion implantation induced damage depth profile derived from channeling and random spectrum is in reasonable agreement with the result calculated by the SRIM Monte-Carlo simulation code.

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.