Rutherford Backscattering Spectrometry Data Research Articles

Correlation of compositional and structural changes during pulsed laser deposition of tantalum oxide films

Tantalum oxide films have been grown by KrF excimer laser ablation of a tantalum target in oxygen atmosphere. The ambient pressure was varied from 1.5 to 50 Pa to investigate the structural and compositional changes during the transition from non-stoichiometric to Ta2O5 films. The growth rate was determined not only as the rate of thickness increase, but also as elemental deposition rates, i.e. the quantity of Ta and O atoms sticking to the substrate surface. On the basis of compositional, structural and roughness information, derived from the analysis of Rutherford backscattering spectra, three domains have been identified. Below 10–12 Pa sub-oxides are obtained in form of dense, compact films. Nearly stoichiometric films can be deposited in the pressure window between approximately 12 and 25 Pa with slightly increasing porosity. Exceeding 25 Pa the films become very porous, ready to trap oxygen-containing molecules from the surrounding atmosphere. Both ellipsometric and Rutherford backscattering spectrometry data confirm that the films grown at 400 °C substrate temperature are denser than those deposited at RT.

Chemical composition and local structure of plasma enhanced chemical vapor-deposited Si nanodots and their embedding silica matrix

X-ray absorption measurements in total electron yield mode have been carried out on Si nanodots embedded in amorphous silica produced by plasma enhanced chemical vapor deposition (PECVD). The amount of Si atoms composing the Si nanodots and the chemical composition of the amorphous host matrix has been determined thanks to the comparison with Rutherford backscattering spectrometry data. The influence of nitrogen, incorporated during the PECVD procedure, on the structure of the host silica matrix has been discussed.

High Pressure Deposition of Epitaxial PZT Thin Films on Sr(Nb)TiO3

ABSTRACTEpitaxial thin ferroelectric films of Pb(Zr0.53Ti0.47) (PZT) were successfully grown on Sr(Nb)TiO3(SNTO) single crystal substrates by high-pressure rf sputtering. Pure O2was used as working gas at a pressure above 1 Torr. Deposition temperature was varied from 550°C to 600°C. Under these conditions we were able to deposit films at a rate of 2.7 Å/min. Their crystalline properties, evaluated by Θ/2Θ, ω and φ scans, showed both in-plane and out of plane orientation. Film composition and film-substrate interface characteristics were studied by Rutherford Backscattering Spectroscopy (RBS). For RBS data the composition ratios for the films were calculated having obtained the expected values for a stoichiometric composition. A very thin diffusion layer of Pb at the film-substrate interface was also introduced. However, the deficiency in Pb, which is correlated to the presence of oxygen vacancies, is lower in our films produced at high O2 pressure than those reported for films produced by sputtering at lower pressures. The ferroelectric hysteresis loops measured in the Pt/PZT/SNTO heterostructures show good ferroelectric behavior with remanent polarizations of 12μ Ccm-2and coercive field of 50kVcm-1at 5V. The high-pressured technique representing a useful and capable method capable of obtainingin situepitaxial, fully oxygenated, pyrochlore-free ferroelectric thin film with high quality structural, compositional and dielectric properties, without post deposit treatment.

Interdiffusion and phase behavior at homopolymer/random copolymer interfaces

Interdiffusion in polymer bilayers of polystyrene (PS) and the statistically random copolymer poly(styrene- r-4-bromostyrene) (PBS), (C 8H (8− x) Br x ) N , where x is the mole fraction of brominated repeat units in the copolymer and N the degree of polymerization, was studied using Rutherford backscattering spectroscopy (RBS). PS/PBS bilayers with 0.04< x<0.63 and the ratio N PS/ N PBS varied from 0.06< N PS/ N PBS<18.1 were examined. PBS volume fraction versus depth profiles were obtained from the evolution of the bromine peak in the RBS spectra. It is shown that as the phase boundary is approached, interdiffusion occurs until layer compositions indicative of binodal conditions are reached. These observations are in very good agreement with phase diagrams obtained using Flory–Huggins theory and a PS/PBS interaction parameter measured using small angle X-ray scattering. For N PS/ N PBS≠1, the mobility is dictated by the faster diffusing (lower N) component, resulting in an interface which moves toward the faster diffusing component. This result is consistent with fast mode theory; equilibrium conditions correspond to the asymmetry of the phase diagrams. Mutual diffusion coefficients were determined by comparison of the RBS data to a mean-field interdiffusion model using the fast mode expression for mobility. The mutual diffusion coefficient is shown to decrease with increasing N and x and increase with temperature. The implications of this miscibility dependence of the interdiffusion behavior, based on both composition of the copolymer and degree of polymerization, are discussed in the context of strengthening homopolymer/random copolymer interfaces.

Effects of impurities on the optical properties of poly-3-hexylthiophene thin films

Commercial poly-3-hexylthiophene was used to create thin films, which were analyzed to determine density, the dependence of the optical absorption on film thickness and the effects of impurities on the optical properties of the polymer. Rutherford backscattering spectroscopy (RBS) demonstrated Zn and Br impurities in the films, which could be removed with methanol extraction. These impurities affect the optical properties of the polymer. Film thicknesses were measured using atomic force microscopy, and in combination with the RBS data, the density of the polymer film was ascertained to be 1.33±0.07 g/cm 3. The dependence of the polymer absorbance on the film thickness is well modeled by the linear function T= 136.8±2.4 A λ max + 6.9±2.0 , where T is the film thickness and A (λmax) is the absorbance maximum.

The distribution of InCl x compounds in model polymeric LEDs: A combined low and high-energy ion beam analysis study

A combination of low- and high-energy ion beam analysis techniques was used to determine the distribution of indium chloride compounds in model polymeric light-emitting diodes (p-LEDs). Parts of polymeric LEDs (polydialkoxyphenylenevinylene (OC 1C 10-PPV) on indium-tin-oxide (ITO) substrates) were exposed to a HCl/Ar flow to simulate the processes occurring during conversion of precursor PPVs and acid treatment of polymers. Samples with variable exposure times as well as pristine samples were studied with Rutherford backscattering spectrometry (RBS), low energy ion scattering (LEIS), X-ray photoelectron spectroscopy (XPS) and particle induced X-ray emission (PIXE). The RBS measurements show that after HCl exposure indium is distributed throughout the OC 1C 10-PPV layer. LEIS and XPS measurements indicate that the indium and chlorine are present at the outermost surface of the OC 1C 10-PPV layer. PIXE measurements in combination with the RBS data demonstrate that the indium chloride in the OC 1C 10-PPV layer is distributed in blisters (∅=50 μm) which are orientated perpendicular to the sample surface. To study the OC 1C 10-PPV/ITO interface, samples were delaminated by peeling the polymeric layer of the ITO using Scotch tape. LEIS measurements on the fracture planes demonstrate the formation of an interfacial layer between the ITO and the PPV. The implications for p-LEDs are discussed.

A Study of the Decomposition of GaN during Annealing over a Wide Range of Temperatures

ABSTRACTAnnealing experiments were carried out on gallium nitride layers, which were grown on sapphire through Metal Organic Chemical Vapor Deposition (MOCVD). Rutherford Backscattering Spectrometry (RBS) was performed on as-grown and annealed GaN samples using a 2 MeV proton beam to study the stoichiometric changes in the near-surface region (750 nm) with depth resolution better than 50 nm. No decomposition was measured for temperatures o up to 800 °C. Decomposition in the near-surface region increased rapidly with a further increase o of temperature, resulting in a near-amorphous surface-region for annealing at 1100 °C. The depth profiles of nitrogen and incorporated oxygen in the decomposed GaN are extracted from the nanoscale RBS data for different annealing temperatures. The surface roughness of the GaN layers observed by atomic force microscopy (AFM) is consistent with RBS decomposition measurements. We describe the range of annealing conditions under which negligible decomposition of GaN is observed, which is important in assessing optimal thermal processing conditions of GaN for both conventional and nanoscale optoelectronic devices.

Artificial neural network analysis of RBS data of Er-implanted sapphire

Rutherford backscattering spectrometry (RBS) is a well-established technique for the elemental depth profile of the surface layers of samples, including the determination of the dose and depth of implanted elements. We have developed a code based on artificial neural networks (ANN) to analyse RBS data. The ANN was trained using the traditional backpropagation algorithm, which is designed to minimise the average error on a training set of generated data. The algorithm was applied to one important particular case, namely the determination of the amount of Er implanted in sapphire samples, and the depth at which the Er is located. The Er fluence was between 8×10 13 Er +/cm 2 and 2×10 16 Er +/cm 2, for implant energies of 200 and 800 keV. The analysis is instantaneous, automated, and requires absolutely no knowledge from the user aside the experimental conditions. The results obtained are hence well-suited for on-line data analysis.

Preparation of TiO2-anatase film on Si(001) substrate with TiNand SrTiO3 as buffer layers

An epitaxial TiO2-anatase thin film was grown on the Si(001) substratewith SrTiO3/TiN as the buffer layers by the pulsed laser depositiontechnique under an oxygen gas supply. The typical thicknesses ofTiO2-anatase, SrTiO3 and TiN layers were 760 nm, 450 nm and 230 nm,respectively. The characterization of the epitaxial TiO2-anatase film wasperformed using the x-ray diffraction method. The crystallographicrelationships between the TiO2-anatase film and SrTiO3/TiN buffer layerswere analysed by the θ-2θ scan and pole figure measurement. Thegrowth direction of the films was determined asTiO2⟨001⟩/SrTiO3⟨001⟩/TiN⟨001⟩/Si⟨001⟩and their in-plane relationshipTiO2{110}||SrTiO3{100}||TiN{100}||Si{100}. The crystallinequality of TiO2-anatase was examined by the rocking curve analysis. Thecomposition of the thin film packaging was characterized by Rutherfordbackscattering spectrometry (RBS) using a 2.0 MeV 4He beam. The simulationof the RBS data points to the possible intermixing of Ti (from TiN) and Si.

Quench properties of Y-Ba-Cu-O films after overpowering quenches [superconducting fault current limiters

The authors present the property degradation and quench behavior of a current limiting element under repeated quenches. The current limiting element was meander type YBa/sub 2/Cu/sub 3/O/sub 7/ stripes deposited on Al/sub 2/O/sub 3/ substrates and coated with a Au shunt. The films showed reproducible quench properties under repeated quenches when the gold layer was coated in-situ on the YBCO film. The films, however, revealed apparent degradation in properties even after the second quench when the gold layer was coated ex-situ on the YBCO film. The authors speculate that incomplete contact between the YBCO and the gold layer produced negative effect on the limiter property. The quench current density J/sub q/ was improved at source voltages up to 300 V/sub rms/ and saturated afterwards when the voltage was increased stepwise by 10 V/sub rms/ from 100 V/sub rms/ to 350 V/sub rms/. It is believed that the thermal shock in a rapid superconducting-normal transition gives the annealing effects to the sample. X-ray diffraction and Rutherford backscattering spectroscopy data did not change considerably after repeated quenches but some minor change appeared. This change might be related to the improvements in the quench current density.

Irradiation-induced amorphization ofCd2Nb2O7pyrochlore

Several investigations have recently been undertaken in order to achieve a more complete understanding of the radiation-damage mechanisms in ${\mathrm{A}}_{2}{\mathrm{B}}_{2}{\mathrm{O}}_{7}$ pyrochlore-structure compounds. The present work represents the first systematic study of the irradiation-induced amorphization of a pyrochlore with A- and B-site cation valences of +2 and +5, respectively. Relatively large single crystals of ${\mathrm{Cd}}_{2}{\mathrm{Nb}}_{2}{\mathrm{O}}_{7}$ were grown for these experiments. In situ ion-irradiation experiments were carried out in a transmission electron microscope in conjunction with ex situ Rutherford backscattering measurements of ion-irradiated ${\mathrm{Cd}}_{2}{\mathrm{Nb}}_{2}{\mathrm{O}}_{7}$ single crystals. ${\mathrm{Cd}}_{2}{\mathrm{Nb}}_{2}{\mathrm{O}}_{7}$ can be amorphized in situ by Ne or Xe ions at temperatures up to 480 and 620 K, respectively. At room temperature, the amorphization fluence was 36 times higher for 280 keV ${\mathrm{Ne}}^{+}$ than for 1200 keV ${\mathrm{Xe}}^{2+},$ corresponding to a displacement dose that was higher by a factor of 3. Disordering of Cd and Nb over the available cation sites occurs at intermediate ion doses prior to amorphization. The temperature dependence of the amorphization dose is modeled, and the results are compared to those of a previous model. The bulk-sample Rutherford backscattering spectroscopy (RBS) results were generally consistent with the in situ TEM measurements. Effects of crystallographic orientation and ion charge state had relatively little effect on the damage accumulation in bulk crystals. The RBS data are consistent with a defect-accumulation, cascade-overlap model of amorphization of ${\mathrm{Cd}}_{2}{\mathrm{Nb}}_{2}{\mathrm{O}}_{7},$ as are the in situ TEM observations.

Amorphous carbon nitride films irradiated with argon ions

Hard, electrical-conductive and corrosion-resistant coatings can be obtained by energetic ion irradiation of amorphous carbonaceous materials such as organic polymers and hydrogenated amorphous carbon films. In this work, amorphous carbon nitride films (a-C:N) containing hydrogen and oxygen were deposited in glow discharges of C2H2, N2 and O2 mixtures and then irradiated with 150 keV Ar+ ions at fluences ranging from 1018 to 1020 m−2. The molecular structure and elemental composition of the as-deposited and irradiated films were studied using infrared reflectance spectrophotometry (IRS) and Rutherford backscattering spectroscopy (RBS). A significant change in the composition and structure of the films, produced by ion irradiation, was revealed by the IRS spectra. Increasing the ion fluence, Φ, the concentration of unsaturated CC bonds increased while that of N–H, C–H and CO bonds decreased. From the RBS data it was concluded that the O/C and N/C atomic ratios decreased with ion irradiation. Modifications of the electronic structure were manifested by changes in the optical gap, EG, and in the electrical conductivity, σ. Ultraviolet-visible spectroscopy was used to determine EG while σ was obtained using a two-point probe. While EG decreased, σ increased with increasing Φ. The dependence of EG and σ on the structural modifications is discussed. Comparison of the electrical conductivity measurements of this work with those reported for irradiated amorphous diamond like carbon (DLC) films revealed that even at high fluences – when the content of both the a-C:N and the DLC films are nearly 100% carbon – the electronic structures of these materials are different.

Concentration profiles and structural changes of silver intercalated titanium disulfide

For the purpose of studying the concentration profile of partially intercalated silver in the layered crystal TiS 2, X-ray photoelectron spectroscopy (XPS) was combined with Rutherford backscattering spectrometry (RBS) using the Nuclear Microprobe at the MicroAnalytical Research Centre, University of Melbourne. The XPS measurements show 4–5 atomic layers of silver on the surface of the Ag x TiS 2 compound. The RBS data exhibit a sharp intercalation front. Silver was found to be present over the whole investigated area of the crystal but to a depth of 100 nm only. In deeper layers the intercalation was restricted to the border zone close to the prism edge. The width of this zone increased with intercalation time. In addition, channeling measurements demonstrate that the intercalation of silver into the TiS 2 crystals results in a deterioration of the crystal quality.

Accuracy of energy dispersive x-ray composition analysis of YBCO films on yttrium-containing substrates as compared to Rutherford backscattering spectroscopy

We address the accuracy of Energy Dispersive X-ray Spectroscopy (EDS) composition analysis of YBa2Cu3O\(_{7 - x} \) (YBCO) thin films. YBCO films deposited on yttrium stabilized zirconia (YSZ) and strontium titanate (STO) substrates were analyzed by EDS and Rutherford Backscattering Spectrometry (RBS) to determine their compositions. The YSZ substrates used in this work contained a common element, yttrium; therefore, EDS intensities of yttrium signals resulting from the film alone were calculated using EDS results of blank YSZ substrates. The EDS compositions of all the elements were obtained using the proportionality factor, k calculated from RBS data from a standard film deposited on silicon and the intensity ratios of the respective standard obtained from EDS. The film thickness was found to be an important factor to consider when choosing the optimum accelerating voltage for the EDS analysis. For films having comparable thickness to that of the standard (∼0.8 μm), we found 25 kV was the optimum accelerating voltage for the EDS analysis that obtained compositions in good agreement with the RBS data. For films having half the thickness of the standard film, EDS composition analyses were unreliable quantitatively and were best qualitatively at 15 kV.

Strain and Compositional Analysis of InGaN/GaN Layers

ABSTRACTWe investigate strain and composition of epitaxial single layers of wurtzite InxGa1−xN (0&lt;x&lt;0.25) grown by MOCVD on top of GaN/Al203 substrates. It is shown that significant inaccuracies may arise in composition assessments if strain in InxGa1−xN/GaN heterostructures is not properly taken into account. Rutherford backscattering spectrometry (RBS) measures composition, free from the effects of strain and with depth resolution. Using X-ray diffraction (XRD) we measure both a- and c- parameters of the strained wurtzite films. By measuring both lattice parameters and solving Hooke's equation, a good estimation for composition can be obtained from XRD data. The agreement between RBS and XRD data for composition allows reliable values for perpendicular (εzz) and parallel strain components ( (εxx) to be determined. RBS and depth resolved cathodoluminescence (CL) measurements further indicate that the indium content is not uniform over depth in some samples. This effect occurs for the most strained layers, suggesting that strain is the driving force for compositional pulling.

Use of Rutherford Backscattering Spectrometry for studying the passivation of materials of rechargeable batteries: application to petroleum coke in LiCF3SO3/carbonates mixture electrolyte

The evolution of the passivating layer (during the first reduction/reoxidation cycle, in function of the number of reduction/reoxidation cycles and with the storage of the electrode in the electrolyte) formed at the surface of a lithiated carbon electrode in LiCF 3 SO 3 /carbonates mixture electrolyte has been followed by using 1 MeV 4 He + induced Rutherford Backscattering Spectrometry (RBS). Two RBS simulation codes RUMP and PERM , whose approaches are different, have been applied to the treatment of the RBS data and have allowed to obtain informations about the structure (thickness and atomic elemental composition) of the passivating layer. These two codes provide similar results. The passivating layer has a thickness in the range 20-30 nm. Its structure appears to be complex with the presence of two different sublayers respectively composed of the reduction products of the salt in the inner sublayer (with the main presence of fluorine and sulphur indicating the possible existence of LiF and Li 2 S) and reduction products of the solvents in the outer sublayer (with a high concentration in oxygen indicating the presence of Li 2 CO 3 and RCO 3 Li where R is an alkyl radical).

High-temperature oxidation behaviour of EN-1.4301 stainless-steel after surface Ce deposition by a modified CVD method

The oxidation of EN-1.4301 (18Cr–8Ni) stainless-steel specimens after Ce deposition at 1173 K under synthetic air is studied. Cerium deposition was carried out by pyrolysis of Ce(NO3) aerosols. Thermogravimetric results show that total mass gain after 22 h of oxidation is one order of magnitude smaller than for the untreated specimen, indicating that the deposition treatment is very effective in increasing the oxidation resistance of EN-1.4301 stainless steel. After oxidation the scale is composed mainly of Cr2O3 and Cr–Mn spinels. Preoxidation in air of the stainless steel prior to Ce deposition does not alter significantly the composition of the oxide scale except for a slight increase in iron content and a reduction in mass gain and thickness of the oxide layer. Rutherford backscattering spectrometry data confirm these results and show a homogeneous in-depth distribution of Ce along the oxide scale. The presence of cerium oxide particles in the scale, in contrast to the presence of perovskite phases on depositing lanthanum, suggests that the silica layer found at the alloy/scale interface could be responsible for the reactive element effect. Copyright © 2000 John Wiley & Sons, Ltd.

Depth distribution of luminescent Si nanocrystals in Si implanted SiO2 films on Si

Depth-resolved measurements of the photoluminescence of Si implanted and annealed SiO2 films on Si have been performed to determine the depth distribution of luminescent Si nanocrystals. Si nanocrystals with diameters ranging from ∼2 to 5 nm were formed by implantation of 35 keV Si ions into a 110-nm-thick thermally grown SiO2 film on Si(100) at a fluence of 6×1016 Si/cm2, followed by a thermal anneal at 1100 °C for 10 min. The photoluminescence spectrum is broad, peaks at λ=790 nm, and contains contributions from both recombination of quantum confined excitons in the nanocrystals and ion-implantation-induced defects. By chemical etching through the SiO2 film in steps and analyzing the changes in the photoluminescence spectrum after each etch step, the depth from which each of the two luminescence features originate is determined. The etch rate of the oxide, as derived from Rutherford backscattering spectrometry data, varies from 1.3 nm/s in the regions of small excess Si to 0.6 nm/s at the peak of the concentration profile (15 at. % excess Si). It is found that the defect luminescence originates from an ∼15-nm-thick near-surface region. Large nanocrystals luminescing at long wavelengths (λ=900 nm) are mainly located in the center of the film, where the Si concentration is highest (48 at. %). This is corroborated by transmission electron microscopy that shows a high density of Si nanocrystals in the size range of 2–5 nm in the center of the film. The largest density of small luminescent nanocrystals (λ=700 nm), not detectable by electron microscopy is found near the SiO2 surface and the SiO2/Si interface. This is attributed to either the fact that the surface and the SiO2/Si interface affect the Si nanocrystal nucleation kinetics in such a way that small nanocrystals are preferentially formed in these regions, or an optical interaction between nanocrystals of different sizes that quenches the luminescence of small nanocrystals in the center of the film.

Depth profile determination with confidence intervals from Rutherford backscattering data

A new simulation program for Rutherford backscattering spectroscopy (RBS) together with an adaptive kernel method in the Bayesian probability theory framework was applied to the analysis of RBS data. Reconstructed depth profiles are free from noise-induced ringing, even for strongly overlapping RBS peaks. This has been achieved by the use of the adaptive kernel method, which generates the least informative depth profile according to the data and in addition allows one to calculate the uncertainty of the obtained depth profiles. The method is applied to erosion measurements of carbon samples.

High dose rate effects in silicon by plasma source ion implantation

An investigation of high dose rate effects in silicon subsurface morphology has been performed. The unique capability of plasma source ion implantation to operate in the high current/low energy regime, where the near-surface structure can be effectively controlled, has been studied. At an ion energy of ∼40 keV and an estimated dose of 1×1015 cm−2 Ar ions were implanted at various instantaneous dose rates (0.75–8.3 mA/cm2) and two different pulse widths (25–50 μs) into 2 in. diam silicon wafers at a constant repetition rate of 10 Hz. The irradiation damage to the wafers’ structures was characterized by Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). A visual observation indicated amorphization of the silicon at 0.75 mA/cm2, but not at 8.3 mA/cm2. The transition from the crystalline-to-amorphous phase was confirmed by TEM electron diffraction studies. RBS data, however, indicated there was a large discrepancy in the total dose retained between the high dose rate (8.3 mA/cm2) and the low dose rate (0.75 mA/cm2). Two simulation methods for the substrate temperature profile have been compared to predict the profile. A comparison of the fraction of irradiation damage from the RBS data indicated that the substrate heating effects are more dominant then the dose rate effects. Improved methods of cooling the wafer are presently being investigated.