Rutherford Backscattering Channeling Research Articles

An approach to tune the amplitude of surface ripple patterns

An approach is presented to tune the amplitude of ripple patterns using ion beam. By varying the depth location of amorphous/crystalline interface, ripple patterns of different amplitude with similar wavelength were grown on the surface of Si (100) using 50 keV Ar+ beam irradiation. Atomic force microscopy study demonstrates the tuning of amplitude of ripples patterns for wide range. Rutherford backscattering channeling measurement was performed to measure the depth location of amorphous/crystalline interface. It is postulated that the ion beam stimulated solid flow inside the amorphous layer controls the wavelength, whereas mass rearrangement at amorphous/crystalline interface controls the amplitude.

Radiation damage study of MeV ions-implanted Nd:YVO4 crystal

• Damage formation mechanism in MeV ion-implanted Nd:YVO 4 is studied. • 3 MeV Si + implantation results in substantial surface damage in Nd:YVO 4 . • Electronic energy loss plays a key role in surface damage formation. • The contributions of nuclear and electronic energy loss to damage are analyzed. • Threshold of electronic stopping power for damage formation is about 1.7 keV/nm. Damage formation mechanism of Nd:YVO 4 implanted with MeV ions is investigated. MeV Si + ions were implanted into Nd:YVO 4 crystal, and the lattice damage was measured using Rutherford backscattering spectroscopy/channeling (RBS/C) method. The damage creation kinetic indicates a significant contribution from electronic energy loss to the surface damage. A detailed analysis allows us to deduce the different contributions from electronic and nuclear stopping powers to the lattice damage production. An obvious difference in extent of damage from 1 MeV and 3 MeV Si + implantations also implies that there exists a threshold value of the electronic energy deposition for damage formation. The exact value of threshold is obtained by comparison with the experimental data obtained from 3 MeV O + , F + and Si + implantation results, which turns out to be (1.7 ± 0.1) keV/nm.

Lattice constant and substitutional composition of GeSn alloys grown by molecular beam epitaxy

Single crystal epitaxial Ge1−xSnx alloys with atomic fractions of tin up to x = 0.145 were grown by solid source molecular beam epitaxy on Ge (001) substrates. The Ge1−xSnx alloys formed high quality, coherent, strained layers at growth temperatures below 250 °C, as shown by high resolution X-ray diffraction. The amount of Sn that was on lattice sites, as determined by Rutherford backscattering spectrometry channeling, was found to be above 90% substitutional in all alloys. The degree of strain and the dependence of the effective unstrained bulk lattice constant of Ge1−xSnx alloys versus the composition of Sn have been determined.

RBS/C, HRTEM and HRXRD study of damage accumulation in irradiated SrTiO3

Damage accumulation in argon-irradiated SrTiO3 single crystals has been studied using a combination of Rutherford backscattering/channeling (RBS/C), high-resolution transmission electron microscopy (HRTEM) and high-resolution X-ray diffraction (HRXRD) techniques. The RBS/C spectra were fitted using McChasy, a Monte Carlo simulation code that allows for a quantitative analysis of amorphous-like and dislocation-like types of defects. The results were interpreted by using a multi-step damage accumulation model under the assumption that the damage accumulation occurs in a series of structural transformations that are triggered by lattice stress caused by formation of a free volume in the irradiated crystal. This assumption has been confirmed by HRTEM and HRXRD.

Fabrication of Si1-xGexAlloy on Silicon by Ge-Ion-Implantation and Short-Time-Annealing

In our contribution we present the fabrication of Si1−xGex alloy by ion-implantation and millisecond ash lamp annealing. The 100 keV Ge ions at the uence of 10 × 10, 5 × 10, and 3 × 10 cm−2 were implanted into monocrystalline (100)-oriented Si wafers covered by 50 nm thermal oxide. In the consequence, the 50 nm amorphous Ge rich Si layers were obtained. The recrystallization of the implanted layers and the Si1−xGex alloying were accomplished by ash lamp annealing with the pulse duration of 20 ms. Flash lamp treatment at high energy densities leads to local melting of the Ge-rich silicon layer. Then the recrystallization takes place due to the millisecond range liquid phase epitaxy. Formation of the high quality monocrystalline Si1−xGex layer was con rmed by the μ-Raman spectroscopy, the Rutherford backscattering channeling and cross-sectional transmission electron microscopy investigation. The μ-Raman spectra reveal three phonon modes located at around 293, 404, and 432 cm−1 corresponding to the Ge Ge, Si Ge and Si Si in the Si1−xGex alloy vibrational modes, respectively. Due to much higher carrier mobility in the Si1−xGex layers than in silicon such system can be used for the fabrication of advanced microelectronic devices.

Study of radiation damage in InGaN and AlGaN films induced by 8.9 MeV Bi33+ ions

Homogeneous radiation damage was induced in ∼250-nm-thick In0.18Ga0.82N and Al0.2Ga0.8N films by irradiation with 8.9MeV Bi33+ ions at room temperature. The ion fluence was in the range from 5×1011 to 5×1013cm−2. From the Rutherford backscattering/channeling (RBS/C) measurements, it is shown that Al0.2Ga0.8N had a radiation resistance at least one order of magnitude higher than In0.18Ga0.82N. When the ion fluence was increased from 1×1013 to 5×1013cm−2, enhanced surface peaks were observed in the RBS/C spectra for both the In0.18Ga0.82N and Al0.2Ga0.8N films, which may be attributed to the high charge state of the incident ions. Moreover, from the Raman spectra measurements, the evolution of the disorder-related B1 bands and TO-like peaks with the fluence was observed for the In0.18Ga0.82N and Al0.2Ga0.8N films, respectively.

Towards semi-insulating InGaAsP/InP layers by post-growth processing using Fe ion implantation and rapid thermal annealing

In this paper, we report on an effective post-growth processing technique for developing semi-insulating (SI) photonic thin films absorbing in 1.3 µm. For that purpose, we examined a 1 µm thick unintentionally n-doped In0.72Ga0.28As0.61P0.39 epilayer (0.95 eV bandgap) modified by multiple-energy MeV Fe ion implantation. Fe was chosen as a deep-level impurity. The ion beam processing was performed at room temperature, followed by rapid thermal annealing (RTA) at 800 °C for 15 s. We investigated the impact of ion fluence on electrical properties by Hall effect measurements. Channelling Rutherford backscattering spectrometry, x-ray diffraction and photoluminescence measurements were carried out to evaluate crystal quality after each fabrication step. Beyond the onset of amorphization, when the total Fe fluence was more than 4.8 × 1013 cm−2, the implanted InGaAsP layer showed evidence of a poor recrystallization after RTA, and its isolation was impaired. Maximum resistivity values were achieved below the onset of amorphization where annealing reduced ion de-channelling and recovered damage-induced strain. With a total Fe fluence of 1.6 × 1013 cm−2, the electrical resistivity and Hall mobility reached values of 1.4 × 104 Ω cm and 4 × 102 cm2 V−1 s−1. These results add important insights on the optimization of this process for the development of InP-based SI photoconductive films.

GaNAsP: An intermediate band semiconductor grown by gas-source molecular beam epitaxy

Dilute nitride GaNAsP thin films were grown via a GaAsP metamorphic buffer on GaP(100) substrate with gas-source molecular beam epitaxy. The compositions of this III-V-V-V compound were determined by channeling Rutherford backscattering spectroscopy and nuclear reaction analysis. Photoreflectance shows two distinctive transitions from the valence band to the split conduction bands due to N incorporation. Photoluminescence and optical absorption show the fundamental bandgap of Ga(N)AsP is largely tailored by the small amount of N. The observed multiband characteristics and the bandgap tunability of GaNAsP are two merits that fit into the intermediate-band solar cell roadmap, and GaNAsP of high crystal quality provides a strong candidate for intermediate band solar cell materials.

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.

Lithium implantation at low temperature in silicon for sharp buried amorphous layer formation and defect engineering

The crystalline-to-amorphous transformation induced by lithium ion implantation at low temperature has been investigated. The resulting damage structure and its thermal evolution have been studied by a combination of Rutherford backscattering spectroscopy channelling (RBS/C) and cross sectional transmission electron microscopy (XTEM). Lithium low-fluence implantation at liquid nitrogen temperature is shown to produce a three layers structure: an amorphous layer surrounded by two highly damaged layers. A thermal treatment at 400 °C leads to the formation of a sharp amorphous/crystalline interfacial transition and defect annihilation of the front heavily damaged layer. After 600 °C annealing, complete recrystallization takes place and no extended defects are left. Anomalous recrystallization rate is observed with different motion velocities of the a/c interfaces and is ascribed to lithium acting as a surfactant. Moreover, the sharp buried amorphous layer is shown to be an efficient sink for interstitials impeding interstitial supersaturation and {311} defect formation in case of subsequent neon implantation. This study shows that lithium implantation at liquid nitrogen temperature can be suitable to form a sharp buried amorphous layer with a well-defined crystalline front layer, thus having potential applications for defects engineering in the improvement of post-implantation layers quality and for shallow junction formation.

The energy loss effects on the absorption edge of LiTaO3 irradiated by energetic heavy ions

The z-cut LiTaO3 single crystals were irradiated by 6MeV Xe-ion at the fluences in the range from 1.0×1012 to 1.0×1015ions/cm2, or 30, 375, 1980MeV Kr ions at the fluences in the range from 1.0×1011 to 1.0×1013ions/cm2. The irradiated samples were analyzed by optical spectrometer and Rutherford backscattering-channeling spectroscopy. It was found that the UV absorption edge of LiTaO3 shifts toward to longer wavelength (red-shift) as a result of heavy-ion irradiation. In 6MeV Xe-ion irradiated samples, the red-shifts are weak even at a high fluence of 1.0×1015ions/cm2 when the irradiated layer becomes amorphous. However, in 30, 375, 1980MeV Kr-ion irradiated samples, significant red-shifts were observed even at low fluences. The effects of nuclear energy loss and electronic energy loss on the red-shift of absorption edge in LiTaO3 are discussed.

Radiation effects in nuclear materials: Role of nuclear and electronic energy losses and their synergy

Ceramic oxides and carbides are promising matrices for the immobilization and/or transmutation of nuclear wastes, cladding materials for gas-cooled fission reactors and structural components for fusion reactors. For these applications there is a need of fundamental data concerning the behavior of nuclear ceramics upon irradiation. This article is focused on the presentation of a few remarkable examples regarding ion-beam modifications of nuclear ceramics with an emphasis on the mechanisms leading to damage creation and phase transformations. Results obtained by combining advanced techniques (Rutherford backscattering spectrometry and channeling, X-ray diffraction, transmission electron microscopy, Raman spectroscopy) concern irradiations in a broad energy range (from keV to GeV) with the aim of exploring both nuclear collision (Sn) and electronic excitation (Se) regimes. Finally, the daunting challenge of the demonstration of the existence of synergistic effects between Sn and Se is tackled by discussing the healing due to intense electronic energy deposition (SHIBIEC) and by reporting results recently obtained in dual-beam irradiation (DBI) experiments.

Interstitial Ti for intermediate band formation in Ti-supersaturated silicon

We have analyzed by means of Rutherford backscattering spectrometry (RBS) the Ti lattice location and the degree of crystalline lattice recovery in heavily Ti implanted silicon layers subsequently pulsed laser melted (PLM). Theoretical studies have predicted that Ti should occupy interstitial sites in silicon for a metallic-intermediate band (IB) formation. The analysis of Ti lattice location after PLM processes is a crucial point to evaluate the IB formation that can be clarifyied by means of RBS measurements. After PLM, time-of-flight secondary ion mass spectrometry measurements show that the Ti concentration in the layers is well above the theoretical limit for IB formation. RBS measurements have shown a significant improvement of the lattice quality at the highest PLM energy density studied. The RBS channeling spectra reveals clearly that after PLM processes Ti impurities are mostly occupying interstitial lattice sites.

Cluster-ion bombardment studies to reveal the amorphization mode in strained Si0.8Ge0.2

Radiation damage caused by cluster ions of different sizes is predicted to be distinctly different if materials follow disparate phenomenological models of amorphization, namely overlap and direct amorphization methods. Determination of an amorphization model for a crystalline solid can be accomplished based on its radiation response to cluster sizes of bombarding ions. In the present study, we use this approach and apply it to study radiation damage in Si0.8Ge0.2 caused by Ag n clusters with the number of atoms in a cluster, n, taking values from 1 to 4. The displacements measured by using channeling Rutherford backscattering spectrometry show size-enhanced damage accumulation, which is in good agreement with the atomistic detail obtained by molecular dynamics simulations. Our studies suggest that strained SiGe, a material known to have poor radiation tolerance, follows the overlap model rather than the direct amorphization model.

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 induced changes in small angle grain boundaries in mosaic Cu thin films

We studied the effect of irradiation on small angle grain boundaries in mosaic structured Cu thin films. The films showed a decrease in mosaic spread via a narrowing of the full width at half maximum in XRD rocking curves and a smaller minimum yield of RBS channeling after irradiation. These data indicate the irradiation decreased the misorientation angles between mosaic blocks separated by small angle grain boundaries. Mechanisms involving interactions between grain boundary dislocations and irradiation induced defects are discussed.

Dense and nanometric electronic excitations induced by swift heavy ions in an ionic CaF2crystal: Evidence for two thresholds of damage creation

CaF${}_{2}$ crystals as representatives of the class of ionic nonamorphizable insulators were irradiated with many different swift heavy ions of energy above 0.5 MeV/u providing a broad range of electronic energy losses (${S}_{e}$). Beam-induced modifications were characterized by Channeling Rutherford Backscattering Spectrometry (C-RBS) and x-ray diffraction (XRD), complemented by transmission electron microscopy (TEM). Results from C-RBS give evidence of significant damage appearing above a ${S}_{e}$ threshold of 5 $\ifmmode\pm\else\textpm\fi{}$ 2 keV/nm. A second critical ${S}_{e}$ appears around 18 $\ifmmode\pm\else\textpm\fi{}$ 3 keV/nm; below this value the damage as function of ion fluence saturates at 20$%$, while above this the damage saturation level increases with ${S}_{e}$, reaching $\ensuremath{\sim}$60$%$ for ions of ${S}_{e}$ $=$ 30 keV/nm. XRD measurements also show effects indicating two threshold values. Above 5 keV/nm, the widths of the XRD reflection peaks increase due to the formation of nanograins, as seen by TEM, while a significant decrease of the peak areas only occurs above 18 keV/nm. The track radii deduced from C-RBS measurements are in agreement with those extracted from the fluence evolution of the widths of the XRD peaks. Moreover, track radii deduced from the peak area analysis are slightly smaller but in agreement with previous track observations by high resolution electron microscopy. Calculations based on the inelastic thermal spike model suggest that the lower threshold at 5 keV/nm is linked to the quenching of the molten phase, whereas the threshold at 18 keV/nm can be interpreted as quenching of the boiling phase. The results of CaF${}_{2}$ are compared with other nonamorphizable materials such as LiF and UO${}_{2}$.

Ion implantation of Cd and Ag into AlN and GaN

AbstractGaN and AlN thin films were implanted with cadmium (Cd) or silver (Ag), to fluences ranging from 1×1013 to 1.7 × 1015 at/cm2. The implanted samples were annealed at 950 °C under flowing nitrogen. While implantation damage could be fully removed for the lowest fluences, for higher fluences the crystal quality was only partially recovered. For the high fluence samples the lattice site location of the ions was studied by Rutherford Backscattering/channelling (RBS/C). Cd ions are found to be incorporated in substitutional cation sites (Al or Ga) while Ag is slightly displaced from this position. To further investigate the incorporation sites, Perturbed Angular Correlation (PAC) measurements were performed and the electric field gradients at the site of the probe nuclei were determined (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dislocation and Elastic Strain in an InN Film Characterized by Synchrotron Radiation X-Ray Diffraction and Rutherford Backscattering/Channeling

Dislocation information and strain-related tetragonal distortion as well as crystalline qualities of a 2-μm-thick InN film grown by molecular beam epitaxy (MBE) are characterized by Rutherford backscattering/channeling (RBS/C) and synchrotron radiation x-ray diffraction (SR-XRD). The minimum yield χmin = 2.5% deduced from the RBS/C results indicates a fairly good crystalline quality. From the SR-XRD results, we obtain the values of the screw and edge densities to be ρscrew = 7.0027 × 109 and ρedge = 8.6115 × 109 cm−2, respectively. The tetragonal distortion of the sample is found to be −0.27% by angular scans, which is close to the −0.28% derived by SR-XRD. The value of |e⊥/e∥| = 0.6742 implies that the InN layer is much stiffer along the a axis than that along the c axis, where e∥ is the parallel elastic strain, and e⊥ is the perpendicular elastic strain. Photoluminescence results reveal a main peak of 0.653 eV with the linewidth of 60 meV, additional shoulder band could be due to impurities and related defects.

Synthesis of embedded Si nano-particles using swift heavy ions and its optical properties

ABSTRACTEmbedded Si nano-particles of average size around 5nm were synthesized in an amorphous Si matrix by two stage ion implantation processes. It has been observed that amorphous Si (a-Si) layers were recrystallized using 50 MeV Au ions with enhanced regrowth rate with activation energy in the range of 0.29 eV. During the crystallization process Si nanocrystals were formed in the a-Si layers due to sudden quenching of the molten tracks created by MeV Au ions. The recrystalizations were confirmed by Rutherford backscattering spectrometry-Channeling (RBSC) technique. The structural modification and nanocluster creation that emerged during recrystallization process was observed in high-resolution transmission electron microscopy and photoluminescence (PL) spectroscopy. The PL emission was observed over a broad band of 2.8 – 3.4 eV and centered at 3.25 eV. The Si nano-crystal formation can be explain by a mechanism combining the melting within the ion tracks by thermal spike process and the subsequent recrystallization nucleated from the crystalline sides at the interface.