Rutherford Backscattering Data 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.

Differential evolution optimization of Rutherford backscattering spectra

We investigate differential evolution optimization to fit Rutherford backscattering data. The algorithm helps to find, with very high precision, the sample composition profile that best fits the experimental spectra. The capabilities of the algorithm are first demonstrated with the analysis of synthetic Rutherford backscattering spectra. The use of synthetic spectra highlights the achievable precision, through which it becomes possible to differentiate between the counting statistical uncertainty of the spectra and the fitting error. Finally, the capability of the algorithm to analyze large sets of experimental spectra is demonstrated with the analysis of the position-dependent composition of a SrxTiyOz layer on a 200 mm silicon wafer. It is shown that the counting statistical uncertainty as well as the fitting error can be determined, and the reported total analysis uncertainty must cover both.

Nondestructure diagnostics of surface layers elements content for cylindrical shape material objects

The methodics background for the nondestructive element concentration diagnostics of cylindric shape material objects surface layer is developed. The diagnostics is produced without objects form-factor distortion on base of ion beams and X-ray analytical methods. The depth element concentration distribution determination found on the ion beams Rutherford backscattering data and results of X-ray fluorescence testing in conditions of TXRF modified measurements. Possibilities of the elaborated analytical conception are illustrated by experimental data obtained at study of element content in surface layer of the nuclear heat release cell shell.

Modeling, analysis, and code/data validation of DIII-D tokamak divertor experiments on ELM and non-ELM plasma tungsten sputtering erosion

We analyzed recent DIII-D tokamak tungsten divertor probe experiments using advanced, coupled, sputter erosion/redeposition, plasma, and surface response code packages. Modeling is done for ELMing H-mode, and L-mode plasmas, impinging on various size tungsten deposits on Divertor Material Evaluation System (DiMES) carbon probes. The simulations compute 3D, full kinetic, sub-gyromotion, impurity sputtering and transport, including changes in tungsten surface composition and response due to mixed deuterium and carbon ions irradiation. Per our analysis, ELM (edge localized mode) plasma sputtering in DIII-D mostly involves free-streaming high energy (∼500–1000 eV) D+ and C+6 ions, with high near-surface plasma density. L-Mode sputtering is due to impurity sputtering (C, W) only, with lower density. All cases show complete redeposition of tungsten on the divertor, with significant redeposition on the tungsten spots themselves, and low self-sputtering. Comparison of ELM plasma gross tungsten erosion simulation results with in-situ spectroscopic data is good, as are code/data comparisons of net erosion using post-exposure Rutherford backscattering (RBS) data for the L-mode probes. The analysis, extrapolated to a full tungsten divertor, implies low net erosion and negligible plasma contamination from sputtering. These results support the use of high-Z plasma facing surfaces in ITER and beyond.

Memristor structure with the effect of switching resistance based on silicon nitride thin layers

The electrophysical properties and the resistive switching effect of the ITO/SiN x /Si memristor structure were studied. A silicon nitride film with a thickness of ~200 nm with an inhomogeneous element depth distribution was deposited by low-pressure chemical vapor deposition. Based on the Rutherford backscattering data, it was shown that the concentration of excess silicon atoms in the SiN x film increases from 9 to 44 % when approaching the Si substrate. The analysis of the current-voltage characteristics of ITO/SiN x /Si structures revealed that the conduction mechanism in the high-resistance state is determined by the nitride film properties and is described by the Poole-Frenkel model taking into account the hopping model of electron transport between traps. Switching to the low-resistance state is probably caused by the migration of indium or tin ions from the ITO contact to the SiN x layer. The conduction of the ITO/SiN x /Si structure in the low-resistance state is determined by both the mechanisms of charge-carrier injection from the contact and charge-carrier transport through the dielectric layer. Reverse polarity results in destructing the conductive channel and switching the structure to the high-resistance state. The photo-switching effect was found for the ITO/SiN x /Si structure, which opens up new possibilities of using memristors in silicon optoelectronic systems.

Structure of nanoporous VNx thin films obtained by ion-beam assisted deposition technology

Nanocrystalline porous VNx films obtained by ion-beam assisted deposition of vanadium on silicon substrates were investigated in this work. The influence of deposition time and film thickness on the regularities of the formation of nanoporosity was studied by means of high-resolution electron microscopy. It is shown that the combined effect of radiation defects and gas impurities leads to the formation of an open intergranular nanoporosity. VNx films comprise 150–250 nm-particles separated by porous boundaries 4–8 nm thick. The nanoparticles, in turn, are composed of 15–20 nm-grains. The structure, composition and formation mechanism of the mixing zones were also studied. It was revealed that these non-uniform zones contain areas of vanadium and silicon nitrides with different types of structure. According to the Rutherford backscattering data and profilometry measurements, VNx film porosity was 27%. Due to its structural features, the thin films obtained by ion-beam assisted deposition can be considered as a promising material for hydrogen storage.

Determining the potential based on Rutherford backscattering data and electron screening in nuclear fusion reactions

A technique for determining the interaction potentials of He+–W, Ta systems on the basis of experimental data on the Rutherford backscattering of accelerated particles at an angle of 165° is proposed. This method provides an opportunity to extend the range of short distances within which the experimentally determined potential is known to 0.005 au and calculate corrections for electron screening relevant to the measurement of cross sections of the d + d nuclear fusion reaction. These corrections agree closely with the experimental data.

Mediated Electrochemical Deposition of Copper and Silver Thin Films for Improved Resistivity, Grain Size and Intrinsic Stress

INTRODUCTION Copper interconnects are typically grown electrochemically as electrodeposition provides a means of depositing large amounts of material over complex geometries and is easily scalable. However, electrodeposition generally results in film microstructures that adversely affect resistivity and electromigration properties. Electromigration rates increase due to surfaces and grain boundaries, and this problem may worsen as smaller device scales lead to larger surface area to volume ratios. Chemical additives are typically used in electrolytes in order to mitigate these problems. Several additives often must be used to manufacture a high quality film, and the relative concentrations of additives can have significant impact on the microstructure of the film. Unfortunately these additives are poorly understood, and their effects are complex and empirically derived, which slows improvements in electrodeposition processes that rely on these additives. Mediating electrochemical deposition with under potentially deposited (UPD) monolayers of another elemental metal provides a controllable means of affecting the microstructure of the deposited film. The technique requires only one additive to the deposition solution, the mediating metal. This mediator must meet only a few characteristics. The mediating element must be less noble than, exhibit under potential deposition on, and not alloy with the deposited metal. The technique has been previously demonstrated for silver deposition on a single crystal gold substrate. [1,2] In this study, we extend the process to electrodeposition of silver and copper on industrially relevant polycrystalline substrates. RESULTS AND DISCUSSION We investigated UPD mediated electrodeposition of silver and copper films on polycrystalline substrates using lead as the mediating element. We varied the deposition potential to change the coverage of the UPD metal during electrodeposition, and this change in coverage caused a change in the growth mechanism of the depositing film. Silver films were deposited on polycrystalline gold films from 0.1M perchloric acid, 0.01M lead perchlorate and 0.5 mM silver perchlorate solutions. Copper films were deposited on Si substrates with polycrystalline copper seed films from 0.01M lead perchlorate and 0.01M copper perchlorate solutions. The copper films were deposited on silicon substrates as blanket films and patterned lines. We present resistivity data that demonstrate improvement over unmediated growth. In situ stress measurements of the growing films indicate UPD deposition significantly reduces the intrinsic stresses of deposited films. Atomic force microscopy images of the films are presented to show the effects of UPD on growth mechanism, surface roughness and grain sizes. We present Rutherford backscattering data to show the purity of the deposited films. Finally, we report the filling characteristics of UPD mediated deposition of Cu films on patterned Si substrates. Based on experimental results, we discuss how mediated deposition can be applied to improve the quality of electrodeposited copper for interconnect applications to improve electrical resistivity. We also discuss how this deposition technique might be applied to other film/substrate systems to tailor resistivities, intrinsic stresses, and microstructures of electrodeposited films. We also propose that the demonstrated correlation between intrinsic film stress, grain size and resistivities might be used for qualitative characterization of deposited films. The authors gratefully acknowledge materials support from Dr. Qiang Huang of IBM T. J. Watson Research Center. The authors gratefully acknowledge the support of NSF Award Number 1309849. 1. K. Sieradzki, S.R. Brankovic, and N. Dimitrov, Electrochemical Defect-Mediated Thin-Film Growth, Science, Vol. 284, pp. 138-141 (1999). 2. S.R. Brankovic, N. Dimitrov, K. Sieradzki, Surfactant Mediated Electrochemical Deposition of Ag on Au(111), J. Electrochem. Soc., Vol. 2, pp. 443-445 (1999). Figure 1

Electron screening of the Coulomb potential at small internuclear distances

Values of He+–Au potential at small internuclear distances (R=10−4 to 10−3nm) have been obtained from the Rutherford backscattering (RBS) data. The potential has been shown to be independent of the collision velocity and close to the potential approximation proposed in Zinoviev (2011) [1]. Experimental data on the electron screening of the Coulomb potential enabled calculation of corrections for the nuclear fusion cross-sections and improvement of the RBS data quantitative analysis.

The interaction potential of the He+-Au system determined from Rutherford backscattering data

The potential-internuclear-distance dependences for the He+-Au system are obtained by processing measurements of particle scattering cross sections at various collision energies. The potential is shown to be independent of the collision velocity. The values obtained made it possible to introduce a correction for the difference of the above potential from the Coulomb one involved in the Rutherford backscattering method, and thus to improve the measurement accuracy. The obtained data on the screening constants enable estimation of the screening effect on the increase in the nucleosynthesis cross sections.

Effect of Film Morphology on the Li Ion Intercalation Kinetics in Anodic Porous Manganese Dioxide Thin Films

Electrolytic manganese dioxide (EMD) films are electrodeposited from acid MnSO4 solution, targeting equivalent film thicknesses between 25 and 100 nm onto silicon substrates coated with Pt and TiN seed layers. The structure and morphology of the deposited EMD films are characterized and tied to the observed electrochemical performance. Deposition efficiencies as large as 80% are achieved, as determined from Rutherford back scattering (RBS). TEM and SEM show that our EMD films are highly porous. The degree of porosity is dependent on the deposition current density and also the deposition time. The electrochemical activity of the EMD films for lithium ion intercalation is investigated in propylene carbonate solvent with 1 M LiClO4. Reversible insertion and extraction of Li+ follows after removing water from the films by annealing and subsequent electrochemical cycling. The porous EMD thin films show a Li ion capacity up to 90% of the theoretical capacity at 0.8 C rate, based on the Mn content from RBS data ...

Band diagram of the Si-LiNbO3 heterostructures grown by radio-frequency magnetron sputtering

Highly c-axis-oriented polycrystalline LiNbO3 films on Si(001) substrates were prepared by the radio-frequency magnetron sputtering process. Measurements of the fundamental absorption edge indicated that the optical band gap corresponds to direct and indirect transitions with energies Egdir=4.2eV and Egind=2.2eV, respectively. Analysis of the Rutherford backscattering data suggested that Li atoms penetrate into silicon substrate forming inhomogeneous donor distribution. Based on the analysis of current–voltage and capacitance-voltage characteristics, the band diagram of the Si-LiNbO3 heterojunction was proposed. It was demonstrated that charge transport is affected by the barrier's properties at the heterojunction and it can be described in the framework of the Richardson–Schottky emission and Fowler–Nordheim tunneling.

Characterization and Processing of CdS/ZnS Thin Layer Films Deposited onto Quartz for Solar Cell Applications

In this work, synthesis and processing of CdS/ZnS multilayer thin film systems are studied; compositional changes within these thin films structures are investigated by the Rutherford backscattering (RBS) technique to determine the depth distributions of the mixed region and stoichiometry according to Rump simulation which is used to estimate layer thickness and compositions even for complex samples; depth profiling using this program is also determined. The RBS data reveal a more homogeneous film could be obtained after annealing in 400°C and stoichiometric film structures with composition Cd1–xZnxS, where x=0.6 are synthesized in ZnS/CdS bilayer

Formation mechanism, structure and adsorption characteristics of microporous nanocrystalline thin-film (V, Ti)-N-He composites

The main features of the formation of (V, Ti)-N-He thin films deposited under bombardment by mixed beams of high-energy N and He ions are studied. Their structural, phase, electrophysical, and adsorption characteristics are studied. The electron microscopy data proved that the structure of (V, Ti)-N-He compounds forms under the conditions of competition of several simultaneously occurring processes leading to the formation of a nanocrystalline structure that contains micropores with dimensions of 5 nm to 5 μm. The role of ion bombardment and gas adsorption from the residual atmosphere in forming porosity is discussed. The comparison of the Rutherford backscattering and profilometry data makes it possible to determine the value of the film porosity (27%). In the pressure range under study (up to 0.35 MPa), 600 cm3/g or more (7 wt %) of hydrogen was adsorbed. It is shown that pores accumulate the main portion of hydrogen; in this case, the amount of hydrogen depends not on the material composition, but on the microporous film structure and the composition of the gas medium in pores.

Ion beam analysis of a structural phase transition in porous TiO 2/V 2O 5 ceramics with rough surfaces

TiO 2/V 2O 5 based ceramic materials applied in catalysis were investigated. Structural properties like the grain diameter of these pressed ceramic powders were analysed by means of Rutherford backscattering (RBS) making use of an analytic model to describe the energy spectra of porous rough samples. Grain diameters of these samples were deduced as function of process temperature and chemical composition and related to a phase transition from the TiO 2-Anatase/V 2O 5-Shcherbinaite to Rutile solid solution (Rutile-ss) structure. RBS data were compared to results of scanning electron microscopy (SEM). The activation energy for the sintering at the phase transition was estimated to 5.4 eV.

Room temperature ferromagnetism in Ni-doped HfO2 thin films

In this paper detailed studies on modification of structural and magnetic properties of Ni-doped hafnium oxide (HfO2) thin films are reported. We used 200 keV Ni beam for doping of Ni. For homogeneous dispersion and activation of doped Ni ions, 120 MeV Ni swift heavy ions (SHI) irradiation was used. This unique combination of Ni doping by ion beam and dispersing and activating by Ni SHI irradiation of HfO2 films is reported for the first time. The origin of ferromagnetism in the Ni-doped HfO2 thin films is investigated. We demonstrate the cluster free nature of our film using cross-sectional high resolution transmission microscopy and magnetization versus temperature data. Rutherford backscattering data are used to establish that Ni ions are implanted in the HfO2 matrix at the predicted location. Dispersion of implanted Ni and lattice defects such as oxygen vacancies are attributed to be the main source of ferromagnetism. The observed magnetic moment is too large to be attributed to any secondary phase/magnetic clusters.

Intelligent methods for solving inverse problems of backscattering spectra with noise: a comparison between neural networks and simulated annealing

This paper investigates two different intelligent techniques—the neural network (NN) method and the simulated annealing (SA) algorithm for solving the inverse problem of Rutherford backscattering (RBS) with noisy data. The RBS inverse problem is to determine the sample structure information from measured spectra, which can be defined as either a function approximation or a non-linear optimization problem. Early studies emphasized on numerical methods and empirical fitting. In this work, we have applied intelligent techniques and compared their performance and effectiveness for spectral data analysis by solving the inverse problem. Since each RBS spectrum may contain up to 512 data points, principal component analysis is used to make the feature extraction so as to ease the complexity of constructing the network. The innovative aspects of our work include introducing dimensionality reduction and noise modeling. Experiments on RBS spectra from SiGe thin films on a silicon substrate show that the SA is more accurate but the NN is faster, though both methods produce satisfactory results. Both methods are resilient to 10% Poisson noise in the input. These new findings indicate that in RBS data analysis the NN approach should be preferred when fast processing is required; whereas the SA method becomes the first choice should the analysis accuracy be targeted.

GaN doped with neodymium by plasma-assisted molecular beam epitaxy

We report in situ doping of GaN with the rare earth element Nd by plasma-assisted molecular beam epitaxy. For the highest Nd effusion cell temperatures, Rutherford backscattering and secondary ion mass spectroscopy data indicate ∼5at.% Nd in epilayers grown on c-plane sapphire. X-ray diffraction found no evidence of phase segregation under nitrogen-rich conditions with up to ∼1at.% Nd, with the highest luminescence intensities corresponding to doping of ∼0.5at.%. Spectral correlation of the Nd emission multiplets for above (325nm) and below (836nm) GaN bandgap excitations implies enhanced substitutional doping at the Ga site.

GaN Doped with Neodymium by Plasma-Assisted Molecular Beam Epitaxy for Potential Lasing Applications

AbstractWe provide an investigation of in situ doping of GaN with the RE element Nd by plasma assisted-molecular beam epitaxy (PA-MBE). GaN epilayers are grown on c-plane sapphire and free standing GaN substrates and the Nd doping is controlled by an effusion cell. The ideal growth conditions for Nd incorporation maintaining crystal quality in GaN were investigated. The optical absorption characteristics indicate that the GaN:Nd epilayer remains transparent at the Nd emission wavelength of interest. For the highest Nd effusion cell temperatures, Rutherford backscattering and secondary ion mass spectrometry data indicate ˜5 at. % in epilayers grown on c-plane sapphire. X-ray diffraction found no evidence of phase segregation up to ˜1 at. % Nd. The highest luminescence intensities correspond to a doping range 0.05-1 at. %, with the strongest emission occurring at 1.12 eV (1107 nm). We also present the Stark energy sublevels of Nd3+ ions in GaN as determined by luminescence spectra. Photoluminescence excitation spectra reveal an optimal excitation energy of 1.48 eV (836 nm). We correlate the photoluminescence spectra with transitions from the 4F3/2 excited state to the 4I9/2, 4I11/2, and 4I13/2 multiplets of the Nd3+ ion for above (325nm) and below (836nm) bandgap excitation. Spectral correlation of the Nd emission multiplets in addition to site-selective spectroscopy studies using combined excitation-emission spectroscopy with confocal microscopy indicate enhanced substantial doping at the Ga site compared to other techniques (ion implantation and co-sputtering).

RBF neural networks for solving the inverse problem of backscattering spectra

This paper investigates a new method to solve the inverse problem of Rutherford backscattering (RBS) data. The inverse problem is to determine the sample structure information from measured spectra, which can be defined as a function approximation problem. We propose using radial basis function (RBF) neural networks to approximate an inverse function. Each RBS spectrum, which may contain up to 128 data points, is compressed by the principal component analysis, so that the dimensionality of input data and complexity of the network are reduced significantly. Our theoretical consideration is tested by numerical experiments with the example of the SiGe thin film sample and corresponding backscattering spectra. A comparison of the RBF method with multilayer perceptrons reveals that the former has better performance in extracting structural information from spectra. Furthermore, the proposed method can handle redundancies properly, which are caused by the constraint of output variables. This study is the first method based on RBF to deal with the inverse RBS data analysis problem.