Rutherford Backscattering Studies Research Articles

APPLICATION OF RUTHERFORD BACKSCATTERING METHOD FOR STUDYING RADIATION-INDUCED SEGREGATION OF HIGH-ENTROPY NICKEL-BASED ALLOYS

In this study, radiation-induced segregation was studied in high-entropy alloys (HEA) CoCrFeNi, CoCrFeMnNi, irradiated with helium ions He2+ with an energy of 40 keV at room temperature. Changes in the concentrations of HEAs and their depth distributions were studied by Rutherford Backscattering (RBS) and energy dispersive x-ray spectroscopy (EDS) methods. Measurements using the RBS and EDS methods showed that non-irradiated HEAs have a composition close to equiatomic, where the average concentration for CoCrFeNi is 24.8 atomic percents (at.%), and for CoCrFeMnNi – 20 at.%. The EDS results were significantly different from the RBS in Ni/Co concentrations, and indicated no significant changes in element distribution in both HEAs after irradiation. According to the RBS data, the largest changes in concentrations during irradiation in both HEAs relate to the enrichment of Ni atoms. In CoCrFeNi, upon irradiation, Ni/Co atoms undergo the greatest segregation, and in CoCrFeMnNi, the Ni/Co/Fe concentrations change significantly. In CoCrFeMnNi, the change in element concentrations with increasing irradiation fluence was more pronounced than in CoCrFeNi. In CoCrFeMnNi, changes in concentrations of all elements at both fluences reached 0.5–17% (0.1–3.1 at.%) and exceeded changes in CoCrFeNi, which reached 2–11% (0.5–1.9 at.%). It was found that the resistance to segregation when irradiated with helium ions under these conditions was lower for CoCrFeMnNi than for CoCrFeNi. In CoCrFeNi and CoCrFeMnNi, changes in the concentrations of Co, Fe, Cr, and Mn were significantly less than changes near sinks and defect clusters when irradiated with nickel ions with similar doses in other studies at temperatures close to the halfmelting temperature of nickel HEAs. The RBS study showed a uniform distribution of atoms in depth and resistance to segregation in CoCrFeNi, CoCrFeMnNi when irradiated with helium ions.

Effect of evaporation behavior of zinc tin phosphide alloys on the composition, structure, and photoconductive properties of their thin films

The evaporation behavior of zinc tin phosphide (ZTP) alloys and its effect on the composition, structure, and photoconductive properties of the deposited films were investigated. ZTP alloys were prepared, and they were found to be of ZnSn-phosphide composition and chalcopyrite structure as obtained by thermogravimetric and x-ray diffraction analysis. The evaporation of the alloys produced random and inhomogeneous deposition with unevaporated residues due to the large difference in vapor pressure, particularly, between Zn and Sn. A closed spaced vapor deposition type setup favored uniform deposition of the films, however, with a dramatic deviation of composition and structure from that of the alloys. Rutherford backscattering, x-ray photoelectron, and energy dispersive spectroscopic studies revealed that the composition of the films is close to ZnP2 stoichiometry with less than 2% of Sn content. Raman spectroscopy and transmission electron microscopy studies showed that the films are of polycrystalline tetragonal ZnP2 structure and evolve to monocrystalline on electron irradiation. The films exhibited a broad band photoresponse in the visible wavelength region with high responsivity to the red light. The study establishes the effect of evaporation behavior of materials with large difference in vapor pressure on the properties and activity of the deposited films thereof.

Low-Temperature Phase-Controlled Synthesis of Titanium Di- and Tri-sulfide by Atomic Layer Deposition.

Phase-controlled synthesis of two-dimensional (2D) transition-metal chalcogenides (TMCs) at low temperatures with a precise thickness control has to date been rarely reported. Here, we report on a process for the phase-controlled synthesis of TiS2 (metallic) and TiS3 (semiconducting) nanolayers by atomic layer deposition (ALD) with precise thickness control. The phase control has been obtained by carefully tuning the deposition temperature and coreactant composition during ALD. In all cases, characteristic self-limiting ALD growth behavior with a growth per cycle (GPC) of ∼0.16 nm per cycle was observed. TiS2 was prepared at 100 °C using H2S gas as coreactant and was also observed using H2S plasma as a coreactant at growth temperatures between 150 and 200 °C. TiS3 was synthesized only at 100 °C using H2S plasma as the coreactant. The S2 species in the H2S plasma, as observed by optical emission spectroscopy, has been speculated to lead to the formation of the TiS3 phase at low temperatures. The control between the synthesis of TiS2 and TiS3 was elucidated by Raman spectroscopy, X-ray photoelectron spectroscopy, high-resolution electron microscopy, and Rutherford backscattering study. Electrical transport measurements showed the low resistive nature of ALD grown 2D-TiS2 (1T-phase). Postdeposition annealing of the TiS3 layers at 400 °C in a sulfur-rich atmosphere improved the crystallinity of the film and yielded photoluminescence at ∼0.9 eV, indicating the semiconducting (direct band gap) nature of TiS3. The current study opens up a new ALD-based synthesis route for controlled, scalable growth of transition-metal di- and tri-chalcogenides at low temperatures.

Backscattering analysis of short period ZnO/MgO superlattices

In this work, Rutherford Backscattering and Channeling (RBS/C) studies and Transmission Electron Microscope (TEM) characterization of ZnO/MgO short period superlattices (SLs) grown on crystalline a- and c-plane ZnO substrates are presented. All structures were obtained using Molecular Beam Epitaxy. ZnO and MgO layers were deposited sequentially and their thicknesses were controlled by the growth time. The structures were composed of 30–80 pairs of thin, 1–3 nm, layers of ZnO and MgO. High-resolution TEM was used to control the quality of the SLs. The angular dependence of the backscattering yield was measured across off-normal channels to determine the strain in the structures and lattice constants in relaxed, thick MgZnO layers. Channeling measurement revealed that the growth of ZnO/MgO SLs was nearly perfect, as the χmin value in the backscattering yield for the SLs is almost the same as for the ZnO substrate. TEM imaging showed that the growth of the SLs was coherent and the MgO layers retained the wurtzite structure. These results allow to conclude that the in-plane lattice constants of the wurtzite MgO layers in the SLs are like in bulk ZnO. No traces of foreign phase precipitates were found.

Enhancement of ferromagnetism in C ion implanted CeO2 thin films

This investigation reports on room temperature ferromagnetism in pristine and C ion implanted CeO2 thin films deposited on Si (111) substrates by the radio frequency (RF)-sputtering method. X-ray diffraction analysis shows that the face-centered cubic (FCC) structure corresponds to CeO2. The Raman spectra further confirm the formation of phase and also indicate the presence of defects, mainly oxygen vacancies, in these films. The presence of C is evident from Rutherford backscattering studies. Atomic force microscopy images indicate that the surface roughness values of the films reduce after C ion implantation. It is observed that the magnetic properties in CeO2 thin films are enhanced by C ion implantation. The saturation magnetization of the pristine film increases from ∼7 emu cm−3 to ∼27 emu cm−3 for a fluence of 6 × 1016 ions cm−2. It is also observed that the coercivity values change after C ion implantation and reduce for a film with an ion fluence of 6 × 1016 ions cm−2 compared with other films. Mechanisms such as the F-center exchange (FCE) model are considered when attempting to understand the enhanced ferromagnetism of C ion implanted CeO2 thin films.

Atomic diffusion processes in MgO/Fe/MgO multilayer

In present work, atomic diffusion processes in MgO/Fe/MgO structure is investigated. This structure is deposited by using e-beam evaporation method in ultra-high vacuum (10−7 Torr). X-ray diffraction pattern exhibits amorphous nature of MgO layer, however, Au and Fe layers are polycrystalline in nature. Structural quality investigated using transmission electron microscopy shows the presence of short-ranged crystalline ordering in MgO layer. Oxygen atoms of this layer exhibit its interaction with Mg to form MgO, however, Fe layer exists in metal form with onset of oxidation at interface. Rutherford backscattering study shows the diffusion of atoms from upper layers to the layers underneath and to the substrate. Au atoms exhibit exponential diffusion profile in the structure, however, the compositional variation of Fe atoms is described using the combination of exponential decay and exponential growth functions.

Rutherford Backscattering Spectrometry Analysis and Structural Properties of ZnxPb1-xS Thin Films Deposited by Chemical Spray Pyrolysis

Zinc lead sulphide ternary thin films were prepared by chemical spray pyrolysis on soda lime glass substrates using zinc acetate, lead acetate, and thiourea sources precursor. The films were characterized using Rutherford backscattering (RBS) spectrometry, energy dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM), and X-ray diffractometry (XRD). RBS studies revealed variation in thickness and stoichiometry of the films with respect to compositional substitution between Zn and Pb, thereby giving effective composition ZnxPb1-xS, where x=0, 0.035, 0.069, 0.109, 0.176, and 0.217. Film thickness obtained by length conversion ranged from 81.02 nm to 90.03 nm. Microstructural analyses also indicated that the growth and particle distribution of the films were uniform across substrate’s surface. Diffraction studies showed that the films possess FCC crystalline structure. Crystallite size reduced from 14.28 to 9.8 nm with increase in Zn2+ in the ZnxPb1-xS samples.

Rutherford backscattering spectroscopy and structural analysis of DC reactive magnetron sputtered titanium nitride thin films on glass substrates

Titanium nitride thin films were deposited on sodalime glass substrate using DC reactive magnetron sputtering technique with 99.99 % pure titanium target. High purity nitrogen and argon gases were used as the reactive and sputtering gases respectively. The sputtering deposition time was fixed at 10 min for all samples, while the chamber sputtering pressure was varied from 0.80 to 11.33 Pa with corresponding change in the nitrogen partial pressure. The films were characterized using Rutherford backscattering (RBS) spectroscopy, UV–visible spectrophotometry, scanning electron microscopy and optical microscopy. The RBS studies revealed disparity in film thicknesses and stoichiometry with respect to the deposition sputtering pressure. Up to 10 % oxygen concentration was observed in films deposited at relatively low sputtering pressures of 0.80 and 1.07 Pa, while no oxygen was detected in the films deposited at higher sputtering pressure. High pressure sputtered TiNx films showed distinct optical properties reminiscent of indium tin oxide with high transmission of 86.74 % maximum in the visible range and wide band gap energy of 3.78 eV.

Influence of ion-irradiation parameters on defect formation in silicon films

It is shown that unlike bulk silicon, for which amorphization is observed at an irradiation dose of 5 × 1016 ion/cm2, thin silicon films on sapphire are amorphized at lower critical doses (1015 ion/cm2). An undamaged surface layer remains when the silicon films are irradiated with Si+ ion beams. Its thickness depends on the current density of the incident beam. Rutherford backscattering studies show that annealing at 950°C improves the crystallinity of the irradiated silicon film. Annealing of the films at 1100°C leads to mixing of the silicon-sapphire interface.

RBS/Channeling Analysis of Zinc Oxide Films Grown at Low Temperature by Atomic Layer Deposition

The results of the Rutherford backscattering/channeling study of ZnO layers are presented. ZnO layers were deposited on the silicon single crystals and GaN epitaxial layers at low temperature by atomic layer deposition. Deposition temperature varied between 100 and 300 ◦C. A random spectra analysis was performed to determine layer thickness and composition. In turn, analysis of the aligned spectra allows us to study evolution of ingrown defects. The Rutherford backscattering study supports the results of X-ray photoelectron spectroscopy measurements, performed separately, that the ZnO-ALD layers deposited at low temperature contain a higher oxygen content. Composition measurements, performed as a function of growth temperature, show that oxygen content decreases with the increasing temperature of the atomic layer deposition growth process.

Structural and optical studies of nanostructured TiO2–Ge multi-layer thin films

This paper reports the effects of annealing on structural and optical properties of nanostructured multi-layer TiO2–Ge thin films. These films were characterized using different techniques such as X-ray diffraction, X-ray reflectivity, Rutherford backscattering (RBS), and Fourier Transform Infrared spectroscopy. Annealing was responsible for pronounced changes in structural and optical properties of these films, as associated with changes in their structures, stoichiometry and stress-state.Three sets of TiO2–Ge multi-layer films were deposited by electron beam evaporation and resistive heating with different Ge layer thickness (5, 10 and 15nm), and TiO2 layer thickness was fixed to 20nm. The films were annealed in air up to 500°C for 2h. RBS studies showed that the layer structure of TiO2–Ge multi-layer films had been formed. The absorption spectra and band gap energy showed a blue shift with decrease in Ge layer thickness. The absorption spectra of these films suggest quantum confinement that increases with annealing temperature before the complete oxidation of Ge. Apparently complete oxidation results in sudden or sharp rise in band gap energy that matches with that of TiO2. RBS study reveals that layered structure of TiO2–Ge multi-layer films is not destroyed by annealing, which may be due to non-wetting behavior of Ge and its oxide with TiO2. These results imply that nanostructured TiO2–Ge multi-layer thin films may be employed as heterojunctions (with tunable band gap energy) based on quantum confinement effects for use in photovoltaics.

Rutherford backscattering studies of strain-relaxed SiGe films grown on Si substrate with compositionally graded buffer layers

We investigated the structural properties of 2-μm thick Si0.58Ge0.42 thin films grown on a combined set of Si1−xGex stepwise buffer layers and a Si0.51Ge0.49 strain-inverted layer on Si substrates. Raman spectroscopy and Rutherford backscattering measurements showed smaller residual strain and superior crystalline lattice ordering compared to a sample without any buffer layer. Furthermore, a Si0.58Ge0.42 thin film with a low dislocation density of less than 105cm−2 and a smooth surface roughness of 0.903nm can be achieved by using a combined set of Si1−xGex stepwise buffer layers and a Si0.51Ge0.49 strain-inverted layer, because most dislocations can be confined within each Si1−xGex buffer layer.

Raman scattering and Rutherford backscattering studies on InN films grown by plasma-assisted molecular beam epitaxy

A series of InN thin films was grown on sapphire substrates via plasma-assisted molecular beam epitaxy (PA-MBE) with different nitrogen plasma power. Various characterization techniques, including Hall, photoluminescence, Raman scattering and Rutherford backscattering, have been employed to study these InN films. Good crystalline wurtzite structures have been identified for all PA-MBE grown InN films on sapphire substrate, which have narrower XRD wurtzite (0002) peaks, showed c-axis Raman scattering allowed longitudinal optical (LO) modes of A 1 and E 1 plus E 2 symmetry, and very weak backscattering forbidden transverse optical (TO) modes. The lower plasma power can lead to the lower carrier concentration, to have the InN film close to intrinsic material with the PL emission below 0.70 eV. With increasing the plasma power, high carrier concentration beyond 1 × 10 20 cm − 3 can be obtained, keeping good crystalline perfection. Rutherford backscattering confirmed most of InN films keeping stoichiometrical In/N ratios and only with higher plasma power of 400 W leaded to obvious surface effect and interdiffusion between the substrate and InN film.

Enhancement of photoluminescence in Er-doped Ag–SiO 2 nanocomposite thin films: A post annealing study

Silver–silica (with Ag 2.8 at.% and 8.7 at.%) nanocomposite (NC) thin films doped with Er +3 (0.1–0.9 at.%) were synthesized by atom beam co-sputtering using 1.5 keV Ar atoms. Optical absorption and photoluminescence (PL) studies of pristine and annealed films were performed, together with Rutherford backscattering and secondary ion mass spectroscopy studies for elemental characterization of the NC films. Optical absorption results of pristine and annealed NC film (with Ag ∼8.7 at.%) confirmed the formation of Ag nanoparticles evidenced by the appearance of characteristic surface plasmon resonance absorption features. Photoluminescence (PL) studies, carried out using Ar Laser pumping at 0.488 μm, the wavelength that the Er ions can absorb resonantly, indicated the presence of PL emission around 1.54 μm in the case of all the as-synthesized samples. The observed PL peak corresponds to the atomic transitions of Er as reported in literature. A relative enhancement in the intensity of PL peak has been observed after annealing the NC films. In the case of NC film with 0.9 at.% Er and 8.7 at.% Ag, the enhancement in PL intensity is almost twice, with respect to the as-deposited sample, for a heat treatment of about 1 h at 600 °C in a nitrogen atmosphere. However for a NC film with Er 0.1 at.% + Ag 2.8 at.%, the PL intensity is enhanced by approximately 3.7 times after annealing at 400 °C for 1 h in nitrogen atmosphere. Since the samples with surface plasmon resonance (SPR) did not show the PL enhancement, the role of SPR in the enhancement of the PL is ruled out. The enhanced PL emission from Er and Ag codoped silica indicates that the Er photo-stimulation is mediated by the energy transfer from Ag nanostructures or ions to Er. Lifetimes of PL peaks for the pristine and annealed samples were also studied. The observed lifetime ∼10 ms is a good indication of excellent PL efficiency.

Preparation of zinc tin oxide films by reactive magnetron sputtering of Zn on liquid Sn

Zn is sputter-deposited on melted Sn films by radio-frequency magnetron sputtering in oxidizing plasma. The samples present an absorption cut-off wavelength close to the one of ZnO, and an optical transparency higher than 50% in the visible range. Ex-situ thermal annealing improves visible transparency and produces a slight blue-shift in the optical bandgap. X-ray diffraction patterns show typical spectra due to polycrystalline ZnO with evidence of the presence of crystalline SnO, before annealing, and Zn 2SnO 4, after annealing. Rutherford Backscattering studies reveal the existence of a ZnO layer on top of an O-rich (Zn, Sn)O thin film. After optimal thermal treatment, electrical characterization exhibits carrier concentrations of 10 16–10 17 cm − 3 and mobilities of 20–80 cm 2 V − 1 s − 1 for the resulting (Zn, Sn)O n-type films.

Evaluation of zinc interstitial in Si-ion implanted ZnO bulk single crystals by a Rutherford backscattering study: An origin of low resistivity

The relation between low resistivity and Zn interstitial in ZnO single crystals implanted with the peak Si atomic concentration of 2.62 × 1020 cm−3 is studied by combining Rutherford backscattering spectroscopy/channeling, photoluminescence, and Van der Pauw methods. The variation in resistivity from ∼104 Ω cm for un-implanted ZnO to ∼10−3 Ω cm for as-implanted ones is observed. The lattice displacement of Zn atoms of ∼0.10 Å from the 〈0 0 0 1〉 row is estimated from the normalized angular yield profiles, preserving the single crystallinity in as-implanted ZnO with a minimum yield (χmin) of ∼11%. The low resistance is maintained by the 1000 °C annealing, accompanied with the lattice displacement of Zn atoms of ∼0.07 Å. These results suggest the existence of the shallow donor consisting of Zn interstitial and/or Zn interstitial-related complex corresponding to a newly appeared 3.33 eV-emission located at ∼40 meV from the bottom of the conduction band.

SiO xN y thin films with variable refraction index: Microstructural, chemical and mechanical properties

In this work amorphous silicon oxynitride films with similar composition (ca. Si 0.40N 0.45O 0.10) were deposited by reactive magnetron sputtering from a pure Si target under different N 2–Ar mixtures. Rutherford backscattering (RBS) studies revealed that the coatings presented similar composition but different density. The mechanical properties evaluated by nanoindentation show also a dependence on the deposition conditions that does not correlate with a change in composition. An increase in nitrogen content in the gas phase results in a decrease of hardness and Young's modulus. The microstructural study by high resolution scanning electron microscopy (SEM-FEG) on non-metalized samples allowed the detection of a close porosity in the form of nano-voids (3–15 nm in size), particularly in the coatings prepared under pure N 2 gas. It has been shown how the presence of the close porosity allows tuning the refraction index of the films in a wide range of values without modifying significantly the chemical, thermal and mechanical stability of the film.

RBS and TEM studies of indium phosphide irradiated with 100 keV Au ions

Transmission Electron Microscopy (TEM) and Rutherford Backscattering (RBS) have been used to observe the spatially isolated disordered zones in InP resulting from 100 keV Au ion irradiation at room temperature. Studies were carried out in interval of irradiation fluences less than lower value of full amorphization fluence. Such a value of fluence, as was established in the studies, can be estimated of order ∼2.5 × 1013cm−2. The accumulation of damage due to the 100 keV Au ion irradiation was described in this material using a composite theoretical model accounting for both homogeneous and heterogeneous amorphization processes.

Electrical and photoluminescence properties of carbon implanted ZnO bulk single crystals

Carbon-ions, which are expected as an amphoteric impurity, are implanted into ZnO bulk single crystals with a fluence of 1.5×1015cm−2. The carbon-ion implanted ZnO shows the n-type conductivity and the resistivity varies from 6×104Ωcm (for unimplanted samples) to 3×10−2Ωcm (for 800°C-annealed ones). The Rutherford backscattering (RBS) studies show the existence of the displaced zinc atoms. In photoluminescence (PL) measurements, the broad emission at 2.34eV observed in un-implanted and as-implanted samples is related to oxygen vacancy and zinc interstitial. After annealing, the weak PL-emission related to carbon donor is observed at 3.06eV, indicating that the donor level lies at ∼310meV below the conduction band. The carbon-ion implanted ZnO layer with the low resistivity achieved in the present study suggests the possibility of transparent conductive oxide.

Studies on transparent spinel magnesium indium oxide thin films prepared by chemical spray pyrolysis

Ternary semiconducting oxide compound magnesium indium oxide films (MgIn 2O 4), manifesting high transparency were prepared by metal organic chemical spray pyrolysis technique. Precursors prepared for various cationic ratios of Mg/In = 0.35, 0.40, 0.45 and 0.50 were thermally sprayed onto quartz substrates, decomposed at 450 °C and the spinel phase evolution was studied. X-ray diffraction, Rutherford backscattering and X-ray photoelectron spectroscopy studies have been conducted to confirm the formation of single-phase MgIn 2O 4 films with Mg/In ratio 0.50. From optical transmission studies, the observed optical band gaps varied from 3.18 to 3.86 eV (0.35 < Mg/In < 0.5). The electrical conductivity variations of these films were measured in the temperature range between 30 and 150 °C by four-probe technique (34.07–1.44 × 10 − 5 S cm − 1 ) and the Hall coefficient showed n-type electrical conduction and high carrier concentration (0.16 × 10 20–0.89 × 17 cm − 3 ).