Rutherford Backscattering Channeling Research Articles

Surface Processing by Polyatomic Cluster Ion Beams

We produced polyatomic clusters such as ethanol and water clusters by an adiabatic expansion phenomenon of vaporized material. The cluster ions were irradiated by changing the incident energy on various kinds of substrates such as mica, Si(100), SiO2 and photo-resist substrates. AFM observation showed that irradiation trace with the diameter of approximately 20 nm was formed on mica substrates by ethanol cluster ion irradiation. Also, it showed that surface roughness of Si(100) substrates irradiated was less than 1 nm, even though the surface was sputtered by ethanol and water cluster ion irradiation. Furthermore, RBS channeling measurement showed that the irradiation damage of Si(100) surfaces sputtered by ethanol and water cluster ions was smaller than that by the Ar monomer ion irradiation. With regards to sputtering and patterning, the sputtered depth of Si(100), SiO2 and photo-resist surfaces by ethanol cluster ion irradiation increased with increase of the acceleration voltage. The sputtering yield of the Si(100) surface was a few hundreds times higher than that by Ar monomer ion irradiation at the same acceleration voltage. In addition, micro-patterning was performed on the Si(100) surface, and sharp-edged patterns with a line-width of 0.5 μm to 3 μm were achieved by ethanol cluster ion irradiation. [DOI: 10.1380/ejssnt.2011.168]

Structural change of micropipes in Al-implanted SiC crystals by post-implantation annealing

We have studied the structural change of defects caused by annealing Al-implanted SiC crystals at 1600 °C using channeling Rutherford backscattering spectrometry (RBS) and synchrotron white beam x-ray topography. Comparison of the RBS spectra before and after annealing showed damage recovery, i.e. a drastic decrease in interstitial atoms. X-ray topography revealed that the size of the white elliptical contrast in micropipe images was decreased by annealing. This result suggested that excess interstitial atoms near the micropipes flowed into their internal walls, and consequently, shrinkage of their hollow cores occurred during annealing.

Lattice location of nickel in diamond by RBS channelling and PIXE

AbstractColour centres in diamond are important for potential applications in quantum information technology. Centres based on Ni have attractive properties but the structures are still not fully understood. One interesting colour centre is NIRIM‐2 which emits around 884 nm and is based on Ni preferentially incorporated into the <111> growth sector during high‐pressure high‐temperature diamond growth in the presence of a Ni catalyst. To help understand the structure of this colour centre a combination of Rutherford backscattering spectrometry (RBS) with ion channelling and particle induced X‐ray emission (PIXE) with 2 MeV H and He ions has been used to study the location of the Ni atoms in the diamond lattice. The Ni concentration, typically below 25 ppm, is well below the detection threshold for RBS, but the yield of characteristic Ni Kα X‐rays shows a decrease when the ion beam is channelled into the <111> growth sector of the diamond. This suggests a significant fraction of Ni is incorporated substitutionally in the diamond lattice. Correlation of Ni location in the diamond host with optical properties of Ni‐related centres in the same growth sector of the diamond offers the possibility of advancing our understanding of the structure of these important optical centres.

Structural and optical properties of Er implanted AlN thin films: Green and infrared photoluminescence at room temperature

In this work erbium ions were implanted into AlN films grown on sapphire with fluence range: (0.5–2) × 10 15 at/cm −2, ion energy range: 150–350 keV and tilt angle: 0°, 10°, 20°, 30°. The optical and structural properties of the films are studied by means of photoluminescence and Raman spectroscopy in combination with Rutherford backscattering/channeling (RBS/C) measurements. The photoluminescence spectra of the Er 3+ were recorded in the visible and infrared region between 9 and 300 K after thermal annealing treatments of the samples. The emission spectrum of the AlN:Er films consists of two series of green lines centered at 538 and 558 nm with typical Er 3+ emission in the infrared at 1.54 μm. The green lines have been identified as Er 3+ transitions from the 2H 11/2 and 4S 3/2 levels to the 4I 15/2 ground state. Different erbium centers in the matrix are suggested by the change of infrared photoluminescence relative intensity of some of the emission lines when different excitation wavelengths are used. The relative abundances of these centers can be varied by using different implantation parameters. The Raman and RBS/C measurements show good crystalline quality for all the studied films.

Interface Properties of Single and Bi-Layer Fe3O4Films Grown on MgO(001) Studied by RBS and Channeling Experiments

Series of Fe3O4/MgO(001) and Fe3O4/Fe/MgO(001) films (single- and bi-layer films, respectively) with a total layer thickness in the range of 20¥150 nm were investigated by the Rutherford backscattering spectrometry (2 MeV He+ ion beam), by the Rutherford backscattering spectrometry channeling experiments (1.5 MeV He+ ion beam). Depending on the layer thickness of each layer and the film geometry, a single Fe peak and/or a double-anomaly feature was revealed in the Rutherford backscattering spectra. For all films no magnesium presence in the surface layer was observed. For both single- and bi-layer films with a total layer thickness less than 60 nm only one minimum was observed in the channeling curves, while a double minimum was revealed for the bi-layer films with a larger thickness. X-ray reflectometry measurements have revealed that the film density is the same as that of the bulk one.

Effect of annealing on AlN/GaN quantum dot heterostructures: advanced ion beam characterization and X‐ray study of low‐dimensional structures

AbstractMultilayers consisting of six GaN quantum dot (QD) layers separated by AlN spacer layers were grown by molecular beam epitaxy. Structural properties and the effects of thermal annealing were analyzed using X‐ray diffraction (XRD), X‐ray reflection (XRR) and Rutherford backscattering spectrometry/Channeling (RBS/C). Annealing was performed in nitrogen atmosphere for 20 min at temperatures between 1000 and 1200 °C.The GaN QDs on the surface were destroyed at temperatures ≥ 1100 °C while the AlN spacer layers protected the deeper lying QD layers. The multilayer structure was well preserved for all studied temperatures. Indications of interdiffusion in the interfaces were found. Thickness fluctuations were evidenced by XRR. Copyright © 2010 John Wiley & Sons, Ltd.

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 × 10 15–1 × 10 16 cm −2) of europium ions. Rutherford backscattering channelling shows that for fluences above 5 × 10 15 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 Eu 2O 3 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 Al 2O 3 lattice the highest intensity line of the Eu 3+ ions corresponds to the forced electric dipole 5D 0 → 7F 2 transition that occurs ∼616 nm. For the MgO samples the Eu 3+ optical activation was also achieved after implantation with different fluences. Here, the lanthanide recombination is dominated by the magnetic dipole 5D 0 → 7F 1 transition near by 590 nm commonly observed for samples were Eu 3+ 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.

Ion irradiation induced bubble relaxation in SiC

He ion irradiation at 140 keV and subsequent annealing at 1200 K were used to introduce voids in 4H-SiC. Then, 1 MeV Si ion irradiation at room temperature was used to study irradiation-induced athermal annealing. Transmission electron microscopy and channeling Rutherford backscattering spectrum analysis were used to characterize samples. Platelet-like voids were formed at the boundary of heavily damaged layer with Si ions implanted to a fluence of 1×1015 cm−2. When Si fluence was increased to 1×1016 cm−2, transition of platelet-like voids into large voids was observed. The study provides evidence of ion irradiation induced athermal annealing. Monte Carlo simulation of atomic displacement on the internal surface of the He bubble suggests that ballistic collision from damage cascades plays an important role in bubble relaxation.

Fe-implanted SiC as a potential DMS: X-ray diffraction and rutherford backscattering and channelling study

Single crystalline (0 0 0 1)-oriented 6H-SiC samples were implanted at 380 °C with low-energy Fe ions (in the 100 keV range) with the aim of synthesizing so-called diluted magnetic semiconductors. X-ray diffraction and Rutherford backscattering spectrometry and channeling are used to study the microstructural changes in these Fe-implanted SiC crystals submitted to furnace annealing and laser processing, both treatments being performed in order to eliminate the implantation-induced defects.

Structural and magnetic properties of Co+ implanted n-GaN dilute magnetic semiconductors

The n-type GaN epilayer was grown on sapphire prepared by metal organic chemical vapour deposition and subsequently Co+ ions implanted. The properties of Co+ ions implanted GaN epilayer were investigated by structural and magnetic measurements. The results of Rutherford backscattering spectrometry and channeling illustrate that an excellent crystalline quality (χmin=1.3%) of as-grown GaN. After the implantation of 150 keV Co+ ions with dose 3×1016 cm−2 into GaN and subsequently annealed at 700, 800 and 900 °C, no secondary phase or metal related-peaks were detected by typical XRD. In addition high-resolution X-ray diffraction (HRXRD) was performed to study structural related properties. The magnetization curves were obtained by SQUID and AGM measurements, a well-defined hysteresis loop was observed even at 300 K. The temperature dependence of magnetization was taken in FC and ZFC conditions showed the highest Curie temperature (TC) ∼370 K recorded for Co+ implanted GaN.

Determination of tetragonal distortion of Al0.69In0.09Ga0.22N/GaN heterostructure by RBS/C and HRXRD

Abstract Rutherford backscattering/channeling spectrometry (RBS/C) was used to characterize the composition and structure of an Al0.69In0.09Ga0.22N/GaN crystalline film (κmin = 3.075%). The elastic strain induced tetragonal distortion value, e T , was determined by RBS/C and high resolution X-ray diffraction (HRXRD). Within the error range, the two methods gave fair agreement on the degree of strain. Comparing the two results, a possible correction due to a deviation for Vegard’s law when large strain exists is discussed.

Defect studies in ion irradiated AlGaN

Abstract Defects created in Al 0.4 Ga 0.6 N crystals by 320 keV Ar ion irradiation were studied using Rutherford Backscattering Spectroscopy/Channeling (RBS/C) and Transmission Electron Microscopy (TEM) techniques. One of the main aims of the work was to use a revised version of McChasy, a Monte-Carlo simulation code of backscattering spectra, for the analysis of experimental results obtained for a dislocation-containing crystal. TEM was used to get a better insight into dislocation and dislocation loop geometries in order to restrict the range of parameters used in simulations. RBS/C analysis was performed in a 1.5–3 MeV energy range to check if MC simulations correctly reproduce backscattering spectra at different energies.

Fabrication and sub-band-gap absorption of single-crystal Si supersaturated with Se by pulsed laser mixing

Selenium supersaturated silicon layers were fabricated by pulsed excimer laser induced liquid-phase mixing of thin Se films on Si(001) wafers. Sufficiently low Se coverage avoids destabilization of rapid epitaxial solidification, resulting in supersaturated solid solutions free of extended defects, as shown by transmission electron microscopy. The amount of retained Se depends on the original film thickness, the laser fluence, and the number of laser pulses irradiating the same spot on the surface. Using this method, Se has incorporated into the topmost 300 nm of the silicon with a concentration of 0.1 at.%. Channeling Rutherford backscattering spectrometry measurements show that the substitutional fraction can be as high as 75% of the total retained Se. These alloys exhibit strong sub-band-gap absorption with optical absorption coefficient ranging up to about 104 cm−1, thus making them potential candidates for applications in Si-based optoelectronic devices.

Multistep damage evolution process in cubic zirconia irradiated with MeV ions

This work reports the study, via the combination of Rutherford backscattering spectrometry and channeling, x-ray diffraction, and transmission electron microscopy experiments, of the damage formation in cubic yttria-stabilized zirconia single crystals irradiated with medium-energy (4 MeV) heavy (Au) ions. The damage buildup, which is accounted for in the framework of the multistep damage accumulation model, occurs in three steps. The first step at low fluences (up to 1015 cm−2), characterized by a regular increase in both the damage yield and the elastic strain, is related to the formation of small defect clusters. The second step in the intermediate fluence range (from 1015 to 5×1015 cm−2) leads to a sharp increase in the damage yield and to a large drop of the strain due to the formation of dislocation loops which collapse into a network of tangled dislocations. The third step at high fluences (above 5×1015 cm−2) exhibits a surprising decrease in the damage yield, which may be attributed to the reorganization of the dislocation network that leads to the formation of weakly damaged regions with a size of the order of 100 nm.

Azimuthal dependence and accurate determination of the half-angle in RBS channeling

Rutherford Backscattering Channeling (RBSC) is often used in the studies of single crystalline materials with regard to issues hinging upon the location of specific atomic species within the crystal lattice. Results are deduced from the characteristics of an angular scan curve representing the yield of close collision events from the constant scattering of the probing projectiles from the crystalline sample in a sequence of directions lying in a plane perpendicular to one particular crystal lattice direction. Such angular scans exhibit dips near major channels, and their angular widths are of concern. On a fundamental level, accurate determination of these angular widths in the case of axial channeling and their interpretation come up against uncertainties arising out of the absence of a preferred choice for the plane of scan. Here, we shall illustrate these uncertainties in a representative case, channeling of 2 MeV He + ions in the 〈1 0 0〉 direction of Si.

Structural and optical characterization of Eu-implanted GaN

GaN was implanted with 300 keV Eu ions over a wide fluence range from 1 × 1013 to 1 × 1016 Eu cm−2 at room temperature (RT) or 500 °C. Detailed structural and optical characterizations of the samples were performed using Rutherford backscattering spectrometry and channelling, transmission and scanning electron microscopy, wavelength dispersive x-ray emission and RT cathodoluminescence (CL) spectroscopy. RT implantation results in a sigmoidal-shaped damage build-up curve with four regimes that were correlated with the formation of specific kinds of defects. After annealing at 1000 °C only samples implanted to fluences below 0.8 × 1015 Eu cm−2 showed near complete recovery of the crystal. Implantation at elevated temperature significantly decreases the implantation damage and increases the fraction of Eu incorporated on substitutional Ga-sites. The improved structural properties of samples implanted at elevated temperature are reflected in a higher intensity of Eu-related red light emission after annealing at 1000 °C. The RT CL intensity is correlated with the number of Eu ions on substitutional Ga-sites after annealing. Furthermore, a detailed study of optical activation shows that the optimum annealing temperature depends on the implantation fluence due to the sensitive balance of defects removed and created during high temperature annealing.

A geometric procedure for improved Rutherford backscattering channeling analysis of materials

Solving geometric and sample alignment issues is a major part of multi-axial Rutherford backscattering channeling (RBS-C) analysis of materials, especially involving complicated samples. However, a geometric standard does not exist for RBS-C, which complicates experimental procedures and makes experimental methods and data presentation inconsistent among different experiments. Our approach to solving RBS-C geometric issues, discussed here, is to introduce a geometric adjustment and sample manipulation procedure which defines the orientation and rotation of the sample with respect to a fixed coordinate system. This method makes rotational, alignment and sample manipulation operations involved in RBS-C more flexible and simpler. As a test case, we present multi-axial RBS-C maps of Si obtained via this methodology. Distortions arising in such RBS-C maps due to geometric effects, how they can affect alignment procedure and data extraction, and how our approach treats these issues are discussed.

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.

Thermal and irradiation induced interdiffusion in magnetite thin films grown on magnesium oxide (0 0 1) substrates

Epitaxial Fe 3O 4(0 0 1) thin films (with a thickness in the range of 10–20 nm) grown on MgO substrates were characterized using low-energy electron diffraction (LEED), conversion electron Mössbauer spectroscopy (CEMS) and investigated using Rutherford backscattering spectrometry (RBS), channeling (RBS-C) experiments and X-ray reflectometry (XRR). The Mg out-diffusion from the MgO substrate into the film was observed for the directly-deposited Fe 3O 4/MgO(0 0 1) films. For the Fe 3O 4/Fe/MgO(0 0 1) films, the Mg diffusion was prevented by the Fe layer and the surface layer is always a pure Fe 3O 4 layer. Annealing and ion beam mixing induced a very large interface zone having a spinel and/or wustite formula in the Fe 3O 4-on-Fe film system.

Blistering kinetics of GaN by hydrogen implantation at high temperature

The hydrogen ion implantation condition for the ion-cut process in wurtzite-phase GaN and the associated mechanisms of surface blistering of GaN films were investigated. The hydrogen ions were implanted at 40 keV with fluences in the range of (1.5–5) × 10 17 H +/cm 2 over a wide temperature range (RT-450 °C), and at 60 keV at room temperature with fluences in the range of (3–5) × 10 17 H +/cm 2. The influences of the ion fluence, implant temperature and the post-implantation annealing conditions on blistering process were studied. Optical microscopy, field emission scanning electron microscopy (FE-SEM), high resolution X-ray diffraction (HRXRD), Rutherford backscattering spectrometry/channeling (RBS/C), and cross-sectional transmission electron microscopy (XTEM) were used to investigate splitting kinetics, and the optimum conditions for achieving blistering only after post-implantation annealing were determined for the GaN ion-cut process. The optimum fluence for the GaN blistering by hydrogen implantation and subsequent low temperature annealing (250–350 °C) was in the (2–3) × 10 17 H +/cm 2 range within the implantation temperature window of 150–300 °C with activation energies in the range of 1.0–1.6 eV depending on the implanted ion fluence and implant temperature.