Rutherford Backscattering Channeling Research Articles

Crystal Lattice Recovery and Optical Activation of Yb Implanted into β-Ga2O3.

β-Ga2O3 is an ultra-wide bandgap semiconductor (Eg~4.8 eV) of interest for many applications, including optoelectronics. Undoped Ga2O3 emits light in the UV range that can be tuned to the visible region of the spectrum by rare earth dopants. In this work, we investigate the crystal lattice recovery of (2¯01)-oriented β-Ga2O3 crystals implanted with Yb ions to the fluence of 1 ×1014 at/cm2. Post-implantation annealing at a range of temperature and different atmospheres was used to investigate the β-Ga2O3 crystal structure recovery and optical activation of Yb ions. Ion implantation is a renowned technique used for material doping, but in spite of its many advantages such as the controlled introduction of dopants in concentrations exceeding the solubility limits, it also causes damage to the crystal lattice, which strongly influences the optical response from the material. In this work, post-implantation defects in β-Ga2O3:Yb crystals, their transformation, and the recovery of the crystal lattice after thermal treatment have been investigated by channeling Rutherford backscattering spectrometry (RBS/c) supported by McChasy simulations, and the optical response was tested. It has been shown that post-implantation annealing at temperatures of 700-900 °C results in partial crystal lattice recovery, but it is accompanied by the out-diffusion of Yb ions toward the surface if the annealing temperature and time exceed 800 °C and 10 min, respectively. High-temperature implantation at 500-900 °C strongly limits post-implantation damage to the crystal lattice, but it does not cause the intense luminescence of Yb ions. This suggests that the recovery of the crystal lattice is not a sufficient condition for strong rare-earth photoluminescence at room temperature and that oxygen annealing is beneficial for intense infrared luminescence compared to other tested environments.

Temperature Effects of Nuclear and Electronic Stopping Power on Si and C Radiation Damage in 3C-SiC.

Silicon carbide has been considered a material for use in the construction of advanced high-temperature nuclear reactors. However, one of the most important design issues for future reactors is the development of structural defects in SiC under a strong irradiation field at high temperatures. To understand how high temperatures affect radiation damage, SiC single crystals were irradiated at room temperature and after being heated to 800 °C with carbon and silicon ions of energies ranging between 0.5 and 21 MeV. The number of displaced atoms and the disorder parameters have been estimated by using the channeling Rutherford backscattering spectrometry. The experimentally determined depth profiles of induced defects at room temperature agree very well with theoretical calculations assuming its proportionality to the electronic and nuclear-stopping power values. On the other hand, a significant reduction in the number of crystal defects was observed for irradiations performed at high temperatures or for samples annealed after irradiation. Additionally, indications of saturation of the crystal defect concentration were observed for higher fluences and the irradiation of previously defected samples.

Defect accumulation in β-Ga2O3 implanted with Yb

Radiation-induced crystal lattice damage and its recovery in wide bandgap oxides, in particular beta-gallium oxide (β-Ga2O3), is a complex process. This paper presents the detailed study of defect accumulation in the β-Ga2O3 single crystal implanted with Ytterbium (Yb) ions and the impact of Rapid Thermal Annealing (RTA) on the defects formed. The (2¯01)oriented β-Ga2O3 single crystals were implanted with eleven fluences of Yb ions ranging from 1 × 1012 to 5 × 1015 at/cm2. Channeling Rutherford Backscattering Spectrometry (RBS/c) was used to study the crystal lattice damage induced by ion implantation and the level of structure recovery after annealing. The quantitative and qualitative analyses of collected spectra were performed by computer simulations. As a result, we present the first defect accumulation curve of β-Ga2O3 implanted with rare earth ion that reveals a two-step damage process. In the first stage, the damage of the β-Ga2O3 is inconspicuous, but begins to grow rapidly from the fluence of 1 × 1013 at/cm2, reaching the saturation at the random level for the Yb ion fluence of 1 × 1014 at/cm2. Further irradiation causes the damage peak to become bimodal, indicating that at least two new defect forms develop for the higher ion fluence. These two damage zones differently react to annealing, suggesting that they could origin from two phases, the amorphization phase and the new crystalline phase of Ga2O3. High-resolution x-ray diffraction (HRXRD) demonstrates the presence of strain and the γ phase of Ga2O3 after implantation, which disappear after annealing.

Atomic structure and annealing-induced reordering of ε-Ga2O3: A Rutherford backscattering/channeling and spectroscopic ellipsometry study

The crystallographic structure of thin Ga2O3 layers grown by metal–organic vapour phase epitaxy on Al2O3 substrate was analyzed by Rutherford Backscattering Spectrometry/Channeling (RBS/C) angular yield scans performed around the c-axis of as-grown Ga2O3. The measured widths and minimum yields of the scan curves for the Ga and O component were compared to calculations based on the continuum steering potential model. The results obtained are consistent with a crystal structure containing oxygen atoms arranged in a 4H hexagonal closely packed lattice and Ga atoms preferentially occupying octahedral interstitial sites in the 4H cells - a structure closely related to the ε-Ga2O3 polymorph. After high-temperature annealing remarkable structural transformation is detected via significant changes in the RBS/C spectra. This effect is related to the hexagonal-monoclinic, i.e., ε-β phase transformation of Ga2O3. Spectroscopic ellipsometry spectra of as-grown and annealed samples can be best fitted using a vertically graded single-layer B-spline model. Significant differences in the dielectric functions were found, showing bandgap reduction for long term annealing. These features are related to the ε-β polymorphic transformation, variation of the preferred crystallographic orientation upon annealing, and differences in residual strain and defect structure determined by the annealing conditions.

Electrostatic accelerator facilities and their applications at Peking University

<p indent="0mm">Electrostatic accelerators are powerful tools in many research fields, such as nuclear physics, materials science, and archaeology. Three electrostatic accelerators, the 1.7 MV tandem, the single stage Van de Graaff with a terminal voltage of 4.5 MV, and the EN tandem with a terminal voltage of 6 MV, were installed in 1980s and have been put into operation since the early 1990s at Peking University. The 1.7 MV tandem accelerator is equipped with a radio frequency charge exchange negative ion source and a cesium sputtering negative ion source, which can produce most of the ions from H to Au. It accelerates the ions to energies from several hundreds of keV to several MeV. The accelerator is used for ion irradiation, ion beam modification of materials, as well as ion beam analysis (IBA), such as Rutherford backscattering spectroscopy (RBS) and channeling. Many significant achievements have been made by using the ion irradiation beamline, especially in the research of nuclear materials. The superlattice steel containing a high density of B2-ordered Ni(Al, Fe) superlattice nanoprecipitates (NPs) was irradiated with <sc>6 MeV</sc> Au ions at different high temperatures. The superlattice steel exhibits extraordinary radiation tolerance, namely, zero void swelling at 400–600°C under an average radiation damage of up to <sc>2350 dpa,</sc> outperforming most of the other steels studied to date. This paper demonstrates a counterintuitive strategy to enhance the radiation resistance of metallic materials by simply ordered superlattice NPs. For the 4.5 MV electrostatic accelerator, the isotope ions of hydrogen or helium can be produced in the energy range of <sc>0.7–3.8 MeV,</sc> and continuous or pulsed quasi-monoenergetic neutron fields <sc>(0.03–7 MeV,</sc> <sc>14–19 MeV)</sc> can be generated by ion beam bombarding targets. The neutron fields have applied it to measure (n, α) reaction cross section. Based on the 4.5 MV electrostatic accelerator, a total-IBA system has been established. Total-IBA can obtain self-consistency results through analyzing spectra of different emission particles, without massive modification of equipment. RBS-nuclear reaction analysis (NRA)-particle-induced X-ray emission analysis (PIXE) integrated IBA experiment was carried out to study a Fe-based alloy. The incident particle is ³He⁺ under <sc>3.0 MeV.</sc> The integrated charge is obtained by fitting the RBS spectrum. The content and depth distribution of C element can be determined by analyzing the NRA spectrum. The signal of O element can also be observed in the NRA spectrum, and its depth distribution can be obtained by fitting RBS. More than ten trace elements are analyzed by PIXE, and P has the lowest content, which is <sc>158.2 ppm.</sc> The 6 MV EN tandem accelerator, which has supported much basic and application research at Peking University, was transferred from Oxford University, UK. It is suitable for accelerator mass spectrometry (AMS), ion irradiation and ion beam analysis. The accelerator can also be applied for detector calibration. CR-39 nuclear track detectors were irradiated by <sc>3–8 MeV</sc> mono-energetic protons and <sc>6–30 MeV</sc> mono-energetic carbon ions, which were produced by the 6 MV tandem accelerator. The relationships between particle energy and orbital diameter in CR-39 detectors are established. These data on CR-39 detectors will be useful for identifying reaction products in laser-plasma experiments with complex conditions. With the technique development such as modern ion beam analysis technology and multi-beam to one target, more attractive applications are expected.

1 MeV Au+ ion modification of Fe3O4-based epitaxial films

The effect of 1 MeV Au+ ion irradiations on the layer stability of the Fe3O4-based films grown epitaxially on MgO(001) substrates was investigated by Rutherford backscattering spectroscopy (RBS) and RBS-Channelling (RBS-C). The ion mixing effect leads to an appearance of the additional FeO x layer and a large enlargement of the thickness of the mixed (Fe,Mg,O) layer in the interfaces. Au+ ions were found to be implanted deeply in the MgO substrate. RBS-C experiments have confirmed that the heavy metallic ion irradiations induce a disorder in the crystalline lattice.

A method to predict texture effect on ion beam channeling analysis of polycrystals and the application to study the mosaic spreading effect in highly oriented pyrolytic graphite

We propose a method to convert the channeling Rutherford backscattering spectrum yield map of a single crystal to a polycrystal through a matrix rotation technique. The rotation matrix is determined by the deviation of the crystal axial direction from the original z axis. The final yield map is created after averaging the rotated yields using the texture function as the weight factor. For highly oriented pyrolytic graphite (HOPG) exhibiting mosaic spread, the method leads to a Gaussian kernel averaging of the map obtained from a single crystal. The yield map of a single crystal is obtained by a simulation of ion trajectories in a potential field described by Moliere screened Coulomb potentials. Yield maps are calculated under variousσ values (standard deviations of mosaic spread). The simulated results are compared with experimental results obtained using 1.2 MeV alpha particle. σ is extracted through the best fitting, demonstrating that the method can be used to obtain texture details. The effects of mosaic spread on minimum yield χmin and the half-width at half maximum of angular scans ψ1/2 are systematically modeled and compared with previous theoretical equations. The study also shows that previous theoretical equations are valid only at small σ values. The proposed method can be applied to any type of polycrystal and is not limited to HOPG. It provides near-surface mosaic spread and crystallography information with a longitudinal depth resolution of tens of nanometers and is not influenced by grain shapes.

The study of channeling parameters of protons along axial and planar directions of Si

In this work, the channeling parameters, the ratio of channeling to random stopping power, and the mean channeling distance, of protons along the 〈100〉, 〈110〉, {100} and {110} directions of Si were studied in terms of the atomic potential of channels. The channeling parameters were deduced using the simulation of the channeling Rutherford backscattering spectra based on the exponential dechanneling function. The best simulation parameters were set using the Levenberg- Marquardt algorithm. The RBS/C spectra were taken in energy interval 1400–2200 keV, using a Si wafer. Considering the deduced parameters along the 〈100〉, 〈110〉, {100} and {110} directions in terms of the atomic potential of channels and using the data along the 〈111〉 and {111} channels reported in the literature, the channeling behavior of protons along the 〈111〉 and {111} direction was explained concerning the shallow and deep potentials. Finally, the mean channeling distance along the {111} channel was estimated.

Surface Integrity of Diamond Turned (100)Ge

The resulting surface integrity of (100)Ge subjected to off-axis single point diamond turning was investigated. Feedrate was varied using 9 and 20 μm/rev at 10 μm nominal depth of cut. Surface topography was measured with coherence scanning interferometry and atomic force microscopy. The resulting near surface lattice disorder was investigated with channeling Rutherford Backscattering Spectrometry and Raman Spectroscopy. Measured near surface lattice disorder was quantified in terms of equivalent amorphous layer thickness and minimum channeling yield. A comparison of the resulting surface integrity was made with surfaces created by chemomechanical polishing and magnetorheological finishing.

Electrical properties of ZnO films implanted with rare earth and their relationship with structural and optical parameters

ZnO implanted with Rare Earth (RE) ions has a potential application as phosphor or in white light sources. The paper discusses the structural, optical and electrical changes caused by Yb, Dy and Pr ions implanted into thin ZnO films grown by Atomic Layer Deposition (ALD). Using channeling Rutherford Backscattering Spectrometry (RBS/c), room temperature photoluminescence (RT PL) technique and Hall effect measurements, it has been shown that the initial damages of the ZnO crystal lattice caused by the rare earth (RE) ion implantation can to a certain extent be removed via post-implantation thermal treatment, provided the fluence is lower than 1.5 × 1015 at.cm−2.A comparison of the structural optical and electrical properties of annealed ALD–ZnO:RE layers with the results of analogous studies performed on thermally untreated RE-implanted films allows us to conclude that properly selected annealing steps allow for a substantial improvement in the conductivity of the layers as well as the intensity of luminescence, which can be attributed to the appearing recrystallization phenomena in the ZnO lattice.

Swift heavy ion beam stimulated epitaxial recrystallization of Si/SiO2 heterostructure

Ion beam induced epitaxial crystallization of Si/SiO2 heterostructure has attracted significant interest in device fabrication because of its low-temperature processing. In this report, we have used 200 keV Kr+ ions to amorphize the Si/SiO2 layer at room temperature and 100 MeV Ni7+ swift heavy ions to recrystallize at elevated substrate temperature range of 100–300 °C. The regrowth of amorphous layers and out-diffusion of Kr+ ions confirmed by Rutherford backscattering spectrometry channeling (RBS-C) measurement. The layer-by-layer growth of epitaxial recrystallization during high energetic ion irradiation is elucidated by the thermal spike-induced vacancy migration mechanism near the amorphous/crystalline (a/c) interface.

Effects of helium implantation fluence on the crystal-ion-slicing fabrication of Y-cut lithium niobate film

In the present work, the contribution of Helium implantation fluence on the Crystal-Ion-Slicing fabrication (CIS) of Y-cut LiNbO3 film were systematically investigated. Y-cut Lithium niobate (LN) thin films with a submicron thickness on the Y-cut LN substrates were successfully fabricated by CIS technique by employing He implantation. By varying the implantation fluence, the structure evolution of the LN exfoliation layer was systematically investigated by Rutherford backscattering/channeling (RBS/C), X-ray Diffraction (XRD), Raman spectroscopy, as well as Atomic Force Microscopy (AFM). Upon gradually increasing the implantation fluence from 1.0 x 1016 to 4.0 x 1016 cm-2, the lattice damage together with the tensile strain in the as-implanted LN becomes intensive according to the Raman spectroscopy investigations. In addition to the crystalline quality, the root mean square roughness becomes 1.4 nm upon increasing fluence till 4.0 x 1016 cm-2. The blistering threshold fluence for Y-cut LN is found to be between 1.0 x 1016 and 2.0 x 1016 cm-2, and the Arrhenius plot of the blistering time as a function of reciprocal temperature shows that the activation of blistering is 2.14 eV, 1.77 eV and 1.44 eV for samples under fluence of 2.0 x 1016, 3.0x 1016 and 4.0 x 1016 cm-2, respectively. Our experimental results unambiguously contribute to exploring the avenue of achieving high-quality layer, particularly highly anisotropic ones, by CIS techniques.

Post-implantation defects in heavy ion implanted monocrystalline ZnO

Monocrystalline ZnO samples were implanted with Co (transition metal) and with Ar and Kr noble gas ions, with energies and doses leading to comparable damage in the host lattice as regards its extension and magnitude. Structural properties of the implanted ZnO were investigated by channeled Rutherford Backscattering Spectrometry (cRBS), aided with calculations using McChasy code. It was shown that the damage produced by implantation does not reach an amorphization level in all cases and is produced deeper in the crystal in comparison with theoretical predictions. The range and magnitude of damaged region are comparable in all cases of ion implantation.

Structure and luminescence of a-plane GaN on r-plane sapphire substrate modified by Si implantation* *Project supported by the Key-Area Research and Development Program of Guangdong Province, China (Grant Nos. 2019B010132001, 2020B010174003, and 2019B121204004), the Basic and Application Basic Research Foundation of Guangdong Province, China (Grant Nos. 2020A1515110891 and 2019A1515111053), and the Fund from the Ion Beam Center (IBC) at HZDR.

We show the structural and optical properties of non-polar a-plane GaN epitaxial films modified by Si ion implantation. Upon gradually raising Si fluences from 5 × 1013 cm−2 to 5 × 1015 cm−2, the n-type dopant concentration gradually increases from 4.6 × 1018 cm−2 to 4.5 × 1020 cm−2, while the generated vacancy density accordingly raises from 3.7 × 1013 cm−2 to 3.8 × 1015 cm−2. Moreover, despite that the implantation enhances structural disorder, the epitaxial structure of the implanted region is still well preserved which is confirmed by Rutherford backscattering channeling spectrometry measurements. The monotonical uniaxial lattice expansion along the a direction (out-of-plane direction) is observed as a function of fluences till 1 × 1015 cm−2, which ceases at the overdose of 5 × 1015 cm−2 due to the partial amorphization in the surface region. Upon raising irradiation dose, a yellow emission in the as-grown sample is gradually quenched, probably due to the irradiation-induced generation of non-radiative recombination centers.

The damage investigations of 4H–SiC after P-ion irradiation

In this work, a single crystal of 4H–SiC was subjected to phosphorus irradiation at 100 keV with four different fluences at room temperature (RT) and post-irradiation annealing treatments at temperature range from 200 to 600 °C. The measured effective refractive index reflected that the disorder increased with the increasing fluences and partially recovered after our annealing treatments. Rutherford backscattering /channeling (RBS/C) experiments displayed that above the fluence of 5.0 × 1014 ions/cm2, severe damage caused in the surface of 4H-SiC crystal. The amorphous layer about 136 nm induced when the fluence is up to 1.0 × 1015 ions/cm2 according to the transmission electron microscopy (TEM) results. The amorphous phenomenon was explained by lattice swelling. We obtained the damage threshold value for the formation of amorphous in 4H–SiC crystal is about 0.3 dpa. Phosphor is one of the important semiconductor dopant elements. This work provides reference data on selective doping of SiC-based electronic devices.

Optical Response of Epitaxial ZnO Films Grown by Atomic Layer Deposition and Coimplanted with Dy and Yb

In this study, structural and optical properties of ZnO:Dy, ZnO:Yb, and ZnO:(Dy,Yb) films are investigated. Epitaxial ZnO films are grown by atomic layer deposition at 300 °C and implanted with Yb and Dy ions to the fluence of 5 × 1014 cm−2. The effects of Dy and Yb implantation, Dy/Yb coimplantation, and postgrowth annealing are studied by channeling Rutherford backscattering spectrometry (RBS/c) and room‐temperature photoluminescence (RT PL). The damage built up after implantation is found to be similar for Dy and Yb ions, but crystal structure recovery after annealing is more efficient for ZnO:Yb than for ZnO:Dy, when similar annealing conditions are applied. Colorimetric analysis of the RT PL spectra shows that (Dy,Yb) coimplantation allows shifting the optical response of ZnO:Dy films toward white color light. The correlated color temperature can be tuned in this way from 2500 to 3200 K, which makes these films attractive for indoor applications.

Erbium-ion implantation of single- and nano-crystalline ZnO

This paper reports on the results of Er+ ion implantation into various ZnO structures – standard single crystal c-plane (0001) ZnO, nanostructured thin films and nanorods. Er+ ions were implanted using an ion implantation energy of 400 keV and implantation fluences in the range of 5 × 1014 to 5 × 1015ions/cm2. Er concentration depth profiles and the degree of crystal damage were measured using Rutherford backscattering spectrometry (RBS) and RBS/channelling (RBS/C). Additionally, Raman spectroscopy was used to analyse structural modifications of the prepared samples. The main focus was placed on the luminescence properties of various ZnO structures. The results showed that the characteristic bands of ZnO, i.e. near-band-edge (NBE) luminescence and deep-level emission (DLE) – that can be influenced by the excitation wavelength – appeared in the spectra of single crystals and nanorods. The characteristic luminescence bands of erbium ions in the NIR region appeared in non-annealed ZnO single-crystal samples and nano-crystalline films.

A comparative study of epitaxial InGaAsBi/InP structures using Rutherford backscattering spectrometry, X-ray diffraction and photoluminescence techniques

In this work, we used a combination of photoluminescence (PL), high resolution X-ray diffraction (XRD), and Rutherford backscattering spectrometry (RBS) techniques to investigate material quality and structural properties of MBE-grown InGaAsBi samples (with and without an InGaAs cap layer) with targeted bismuth composition in the 3%–4% range. XRD data showed that the InGaAsBi layers are more homogeneous in the uncapped samples. For the capped samples, the growth of the InGaAs capped layer at higher temperature affects the quality of the InGaAsBi layer and bismuth distribution in the growth direction. Low-temperature PL exhibited multiple emission peaks; the peak energies, widths, and relative intensities were used for comparative analysis of the data in line with the XRD and RBS results. RBS data at a random orientation together with channeled measurements allowed both an estimation of the bismuth composition and analysis of the structural properties. The RBS channeling showed evidence of higher strain due to possible antisite defects in the capped samples grown at a higher temperature. It is also suggested that the growth of the capped layer at high temperature causes deterioration of the bismuth-layer quality. The RBS analysis demonstrated evidence of a reduction of homogeneity of uncapped InGaAsBi layers with increasing bismuth concentration. The uncapped higher bismuth concentration sample showed less defined channeling dips suggesting poorer crystal quality and clustering of bismuth on the sample surface.

Microstructural evolution of helium-irradiated 6H–SiC subjected to different irradiation conditions and annealing temperatures: A multiple characterization study

The microstructural phenomena occurring in 6H–SiC subjected to different irradiation conditions and annealing temperatures were investigated to assess the suitability of 6H–SiC as a structural material for nuclear applications. To this aim, a single crystal of 6H–SiC was subjected to He+ irradiation at 300 keV with different fluences and at temperatures ranging from 25 to 750 °C. Rutherford backscattering/channeling (RBS/C), X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses were combined to shed light on the microstructural changes induced by irradiation and subsequent annealing (750 to 1500 °C). At room temperature, amorphization starts to occur at a fluence of 2.5 × 1016 cm−2 (0.66 dpa). On the contrary, amorphization was prevented at high irradiation temperatures and fluences. Furthermore, a thin and highly strained region located around the maximum He concentration (Rp) formed. This region results from the accumulation of interstitial atoms which are driven toward the highly damaged region under the actions of a strain gradient and high temperature. Regardless of the fluence and irradiation temperature, the material stores elastic energy, which leads to the trapping of He in dissimilar defect geometries. For irradiation temperatures below 750 °C, helium was accumulated in bubbles which coarsened after annealing. On the other hand, for an irradiation temperature of 750 °C, helium was trapped in platelets (even for medium fluence), which evolved into a homogeneous dense array of cavities during annealing. DFT calculations show that the bubbles are under high pressure and contribute to developing the overall tensile strain in the single crystal 6H–SiC.

P -type codoping effect in (Ga,Mn)As: Mn lattice location versus magnetic properties

In the present work, we perform a systematic investigation on p-type codoping in (Ga,Mn)As. Through gradually increasing Zn doping concentration, the hole concentration increases, which should theoretically lead to an increase of the Curie temperature (TC) according to the p-d Zener model. Unexpectedly, although the film keeps its epitaxial structure, both TC and the magnetization decrease. The samples present a phase transition from ferromagnetism to paramagnetism upon increasing hole concentration. In the intermediate regime, we observe a signature of antiferromagnetism. By using channeling Rutherford backscattering spectrometry and particle-induced x-ray emission, the substitutional Mn atoms are observed to shift to interstitial sites, while more Zn atoms occupy Ga sites, which explains the observed behavior. This is also consistent with first-principles calculations, showing that the complex of substitutional Zn and interstitial Mn has the lowest formation energy.