HRBS/channeling studies of ultra-thin ITO films on Si

High-resolution Rutherford backscattering spectroscopy (HRBS)/channeling techniques have been utilized for a detailed characterization of ultra-thin indium tin oxide (ITO) films and to probe the nature of the interface between the ITO film and the Si(0 0 1) substrate. Channeling studies provide a direct measure of the lattice strain distribution in the crystalline Si substrate in the case of amorphous over layers. The measurements on DC magnetron sputtered ITO films have been carried out using the recently installed HRBS facility at the Centre for Ion Beam Applications (CIBA). The thickness of the ultra-thin (∼9.8 nm) ITO films was calculated from the HRBS spectra having an energy resolution of about 1.4 keV at the superimposed leading (In + Sn) edge of the ITO film. The films were near stoichiometric and the interface between ITO film and Si was found to include a thin SiO_x transition layer. The backscattering yields from (In + Sn) of ITO were equal in random and channeling directions, thereby revealing the non-crystalline nature of the film. Angular scans of HRBS spectra around the off-normal [1 1 1] axis clearly showed a shift in the channeling minimum indicative of compressive strain of the Si lattice at the SiO_x/Si interface. The observed strain was about 0.8% near the interface and decreased to values below our detection limits at a depth of ∼3 nm from the SiO_x/Si interface.     

Swift iodine ion modification of the structural and magnetotransport properties of Fe/Cr systems

Fe/Cr/Fe trilayers and (Fe/Cr)₂₀ multilayers prepared under ultrahigh vacuum conditions by thermal evaporation were irradiated with 200 MeV I¹³⁺ ions in the fluence range between 1 × 10¹¹ and 8 × 10¹² I/cm². The structural properties of the Fe/Cr/Fe trilayers and (Fe/Cr)₂₀ multilayers were measured by X-ray reflectivity (XRR) and conversion electron Mössbauer spectroscopy (CEMS). Magnetic exchange coupling between the Fe layers through the Cr spacer layer was observed by SQUID magnetization measurements. Magnetoresistance effect was measured using four probe method at room temperature. The XRR spectra showed an increase of the interface roughness versus increasing irradiation fluence in the multilayers, while in the trilayers smoothening of the interfaces in the sample irradiated with fluence equal to 4 × 10¹¹ I/cm² and very slight change for other fluences were observed. Improving of the interface structure in the trilayers at this fluence was observed also by CEMS. Moreover the Mössbauer spectra also confirm roughening of the interfaces as a function of fluence for multilayers. Before irradiation an antiferromagnetic coupling fraction dominated in all samples. After irradiation the changes of magnetic coupling were different in both types of samples. The trilayers were less sensitive to the irradiation fluence than multilayers and an increase of the antiferromagnetic fraction at small fluences was observed. In the multilayers a continuous decrease of the antiferromagnetic fraction as a function of fluence was evidenced. Vanishing of the antiferromagnetic coupling, observed for the largest fluence, resulted in the decrease of magnetoresistance effect in the Fe/Cr multilayers.     

Properties of FINEMET with Fe partially replaced by Mn

Thin films and foils of Fe_73.5−xSi_13.5B₉Cu₁Nb₃Mn_x, the FINEMET based amorphous and nanocrytalline alloys with high Mn doping (x = 9, 11, 13, 15 at%), were studied by means of transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and with Mössbauer spectroscopy (MS), as-quenched (a-q) and after annealing (a). Mn, partially replacing Fe, causes common crystallisation temperature T_cr for the identified crystal structures, decrease of the lattice constants a₀, c₀, decrease of hyperfine parameters: magnetic field H_hf and isomer shift IS for amorphous phases and in consequence the Curie temperature T_Cu.     

On the emission of MoCs molecular ions from Cs irradiated molybdenum surface

The present paper deals with the emission of atomic and molecular ions from elemental molybdenum surface under Cs⁺ bombardment to explore the MCs⁺ formation mechanism with changing Cs surface coverage. Integrated count of MoCs⁺ shows a monotonic increase with increasing primary ion energy (1-5 keV). Change in MoCs⁺ intensity is attributed to the variation of surface work function ? and cesium surface concentration c_Cs due to varying impact energies. Variation of c_Cs has been obtained from the expression, c_Cs ∝ 1/(1 + Y) where Y is the elemental sputtering yield estimated from TRIM calculations. Systematic study of the energy distributions of all species emerging from Mo target has been done to measure the changes in surface work function. Changing slopes of the leading parts of Cs⁺ energy distributions suggest a substantial depletion in surface work function ? with decreasing primary ion energies. Δ? shows a linear dependence on c_Cs. The maximum reduction in surface work function Δ?_max = 0.69 eV corresponds to the highest value of c_Cs = 0.5. A phenomenological model, based on the linear dependence of ? on c_Cs, has been employed to explain the MoCs⁺ data.     

Effect of 200 MeV Ag ion irradiation on structural and electrical transport properties of Fe3O4 thin films

Thin films of Fe₃O₄ have been deposited on single crystal MgO(1 0 0) and Si(1 0 0) substrates using pulsed laser deposition. Films grown on MgO substrate are epitaxial with c-axis orientation whereas, films on Si substrate are highly 〈1 1 1〉 oriented. Film thicknesses are 150 nm. These films have been irradiated with 200 MeV Ag ions. We study the effect of the irradiation on structural and electrical transport properties of these films. The fluence value of irradiation has been varied in the range of 5 × 10¹⁰ ions/cm² to 1 × 10¹² ions/cm². We compare the irradiation induced modifications on various physical properties between the c-axis oriented epitaxial film and non epitaxial but 〈1 1 1〉 oriented film. The pristine film on Si substrate shows Verwey transition (T_V) close to 125 K, which is higher than generally observed in single crystals (121 K). After the irradiation with the 5 × 10¹⁰ ions/cm² fluence value, T_V shifts to 122 K, closer to the single crystal value. However, with the higher fluence (1 × 10¹² ions/cm²) irradiation, T_V again shifts to 125 K.     

Interface strain study of thin Lu2O3/Si using HRBS

The interface of thin Lu₂O₃ on silicon has been studied using high-resolution RBS (HRBS) for samples annealed at different temperatures. Thin rare earth metal oxides are of interest as candidates for next generation transistor gate dielectrics, due to their high-k values allowing for equivalent oxide thickness (EOT) of less than 1 nm. Among them, Lu₂O₃ has been found to have the highest lattice energy and largest band gap, making it a good candidate for an alternative high-k gate dielectric. HRBS depth profiling results have shown the existence of a thin (∼2 nm) transitional silicate layer beneath the Lu₂O₃ films. The thicknesses of the Lu₂O₃ films were found to be ∼8 nm and the films were determined to be non-crystalline. Angular scans were performed across the [1 1 0] and [1 1 1] axis along planar channels, and clear shifts in the channeling minimum indicate the presence of Si lattice strain at the silicate/Si interface.     

Thickness and MeV Si ions bombardment effects on the thermoelectric properties of Ce3Sb10 thin films

The three single layer Ce₃Sb₁₀ thin films were grown on silicon dioxide and quartz (suprasil) substrates with thicknesses of 297, 269 and 70 nm using ion beam assisted deposition (IBAD) technique. The high-energy cross plane Si ion bombardments with constant energy of 5 MeV have been performed with varying fluence from 1 × 10¹², 1 × 10¹³, 1 × 10¹⁴, 1 × 10¹⁵ ions/cm². The Si ions bombardment modified the thermoelectric properties of films as expected. The fluence and temperature dependence of cross plane thermoelectric parameters that are Seebeck coefficient, electrical and thermal conductivities were determined to evaluate the dimensionless figure of merit, ZT. Rutherford backscattering spectrometry (RBS) enabled us to determine the elemental composition of the deposited materials and layer thickness of each film.     

Separation of potential and kinetic electron emission from Si and W induced by multiply charged neon and argon ions

The total secondary electron emission yields, γ_T, induced by impact of the fast ions Ne^q+ (q = 2-8) and Ar^q+ (q = 3-12) on Si and Ne^q+ (q = 2-8) on W targets have been measured. It was observed that for a given impact energy, γ_T increases with the charge of projectile ion. By plotting γ_T as a function of the total potential energy of the respective ion, true kinetic and potential electron yields have been obtained. Potential electron yield was proportional to the total potential energy of the projectile ion. However, decrease in potential electron yield with increasing kinetic energy of Ne^q+ impact on Si and W was observed. This decrease in potential electron yield with kinetic energy of the ion was more pronounced for the projectile ions having higher charge states. Moreover, kinetic electron yield to energy-loss ratio for various ion-target combinations was calculated and results were in good agreement with semi-empirical model for kinetic electron emission.     

Xenon-ion irradiation of Co/Si bilayers: Effects of interface structure and ion energy

Heavy-ion irradiation of ferromagnetic thin layers changes their micromagnetic and microstructural properties, due to the production of defects, relaxation or build-up of stress, or changes of grain size. When the ion range exceeds the layer thickness, ion mixing processes take place, leading to the formation of silicide phases. The present study deals with Co(30 or 55 nm)/Si bilayers irradiated at room temperature with 100- or 200 keV Xe ions to fluences of up to 15 × 10¹⁵/cm². The Si(1 0 0) wafers were either crystalline or pre-amorphized by 1 keV Ar⁺ implantation. Rutherford backscattering spectroscopy, in-plane magneto-optical Kerr effect, and X-ray diffraction served to analyse the samples before and after irradiation. The results will be compared with those obtained for other heavy-ions for Co/Si bilayers and in similar studies on Fe/Si bilayers.     

K-shell X-ray fluorescence cross-sections and intensity ratios for some pure metals at 59.5 and 123.6 keV

K-shell X-ray fluorescence cross-sections for some pure metals such as Cr, Fe, Co, Cu, Zn, Ga, Se, Y, Mo, Cd, In, Sn, Te, Ba, Ta, W and Bi have been theoretically and experimentally determined. The Cr, Fe, Co, Cu, Zn, Ga, Se, Y, Mo, Cd, In, Sn, Te and Ba metals were excited by 59.5 keV γ-ray from 50 mCi ²⁴¹Am radioactive source and the Ta, W and Bi targets were excited by 123.6 keV γ-ray from 25 mCi ⁵⁷Co radioactive source. The characteristic K X-rays emitted by samples were detected by using a super Si(Li) detector having a resolution of 150 eV at 5.9 keV. In addition, the I_Kβ/I_Kα intensity ratios for these metals were studied. The obtained experimental values of the K-shell X-ray fluorescence cross-sections and the I_Kβ/I_Kα intensity ratios have been compared with theoretical values. The measured values were in good agreement with theoretical values.     

Positron annihilation on the surfaces of SiO2 films thermally grown on single crystal of Cz-Si

Two-detector coincidence system and mono-energetic slow positron beam has been applied to measure the Doppler broadening spectra for single crystals of SiO₂, SiO₂ films with different thickness thermally grown on single crystal of Cz-Si, and single crystal of Si without oxide film. Oxygen is recognized as a peak at about 11.85 × 10⁻³m₀c on the ratio curves. The S parameters decrease with the increase of positron implantation energy for the single crystal of SiO₂ and Si without oxide film. However, for the thermally grown SiO₂-Si sample, the S parameters in near surface of the sample increase with positron implantation energy. It is due to the formation of silicon oxide at the surface, which lead to lower S value. S and W parameters vary with positron implantation depth indicate that the SiO₂-Si system consist of a surface layer, a SiO₂ layer, a SiO₂-Si interface layer and a semi-infinite Si substrate.     

Differential cross-sections for nuclear reactions on Al and Si induced by deuterons at low energy (1-2 MeV)

Recent progress in thin film techniques has made possible the fabrication of stable and pollution-free reference standards. Thin Si₃N₄ film (thickness 70 nm) and thin Al foil (150 nm) were selected to measure the differential cross-sections of nuclear reactions induced by deuterons, from 1 to 2 MeV. The absence of oxygen and carbon in the standard, as well as the stoichiometry, were checked prior to measurement by RBS. The differential cross-sections of the ²⁷Al(d,p₀p₁)²⁸Al, ²⁷Al(d,p₂p₃)²⁸Al, ²⁷Al(d,p₅p₆)²⁸Al, ²⁷Al(d,p₉)²⁸Al, ²⁷Al(d,p₁₀)²⁸Al, ²⁷Al(d,p₁₁)²⁸Al, ²⁷Al(d,p₁₂)²⁸Al, ²⁷Al(d,α₀)²⁵Mg and ²⁷Al(d,α₂)²⁵Mg reactions for aluminium and ²⁸Si(d,p₀)²⁹Si- ²⁹Si(d,p₁)³⁰Si, ²⁸Si(d,p₁)²⁹Si- ²⁹Si(d,p₂)³⁰Si, ²⁸Si(d,p₂)²⁹Si, ²⁸Si(d,p₃)²⁹Si, ²⁸Si(d,p₉p₁₀)²⁹Si reactions for silicon were determined for a detector angle of 150°.     

Structural characterization of Fe/Ag bilayers by RBS and AFM

Fe/Ag thin films are intensively investigated due to their special magnetic properties. Recently a deposition-order dependent asymmetric interface has been found. When iron is grown on silver, the interface is sharp, while the growth of Ag on Fe results in a long, low-energy tail of the Ag peak in the Rutherford backscattering spectrometry (RBS) spectra. The main purpose of this paper is to show that the low-energy Ag tail is caused by grain boundary diffusion, and that, when elevating the growing temperature of the Ag layer this effect becomes more significant. Two sets of polycrystalline and epitaxial Fe/Ag bilayers were prepared simultaneously onto Si(1 1 1) and MgO(1 0 0), respectively. The iron layers were grown at 250 °C and annealed at 450 °C in both sets, while the Ag layer was grown in the first set at room temperature (RT) and in the second set at 250 °C (HT). The sample composition, the interface sharpness and the quality of the epitaxy were studied by Rutherford backscattering spectrometry (RBS) combined with channeling effect. The surface morphology was determined by atomic force microscopy (AFM). RBS spectra show that in the case of RT samples the epitaxial MgO/Fe/Ag bilayer has sharp, well-defined interface, while for the polycrystalline Si/Fe/Ag sample the silver peak has a low-energy tail. Both the Fe and Ag peaks smeared out in the case of HT samples. AFM-images show that the RT samples have a continuous Ag layer, while the HT samples have fragmented surfaces. The RBS spectra taken on the HT samples were successfully simulated by the RBS-MAST code taking into account their fragmented structures.     

Photoconduction investigations in 75 MeV oxygen ion irradiated kapton-H polyimide

Photoconduction behaviour of 75 MeV oxygen ion irradiated (Fluences: 1.8 × 10¹¹, 1.8 × 10¹² and 1.8 × 10¹³ ions/cm²) kapton-H polyimide film in the visible region has been investigated at different temperatures ranging 400-2500 °C and at various electric fields ranging 40-600 kV/cm. A photoinduced exciton formation is the major source for providing charge carriers through thermolization and field-assisted dissociation processes. An attempt has been made to fit the field dependence of the steady state photocurrent to one of the several possible conduction mechanisms. In the high and low fluence (1.8 × 10¹³ and 1.8 × 10¹¹ ions/cm²) irradiated samples there exists a possibility of Poole-Frankel type of photoconduction mechanism, whereas at intermediate fluence (1.8 × 10¹² ions/cm²) a Schottky type photoconduction mechanism may be operative. The log I_ps versus 1/T plots consist of two straight lines with a knee point around 800-1000 °C. The activation energy estimated from the slope of these lines is field dependent varying from 0.40 to 0.73 eV and 0.18 to 0.23 eV above and below the knee point, respectively. This indicates the presence of more than one type of trapping levels in irradiated kapton-H polyimide.     

Thermal conductivities of hypostoichiometric (U, Pu, Am)O2−x oxide

The thermal conductivities of (U_0.68Pu_0.30Am_0.02)O_2.00−x solid solutions (x = 0.00-0.08) were studied at temperatures from 900 to 1773 K. The thermal conductivities were obtained from the thermal diffusivities measured by the laser flash method. The thermal conductivities obtained experimentally up to about 1400 K could be expressed by a classical phonon transport model, λ = (A + BT)⁻¹, A(x) = 3.31 × x + 9.92 × 10⁻³ (mK/W) and B(x) = (−6.68 × x + 2.46) × 10⁻⁴ (m/W). The experimental A values showed a good agreement with theoretical predictions, but the experimental B values showed not so good agreement with the theoretical ones in the low O/M ratio region. From the comparison of A and B values obtained in this study with the ones of (U,Pu)O_2−x obtained by Duriez et al. [C. Duriez, J.P. Alessandri, T. Gervais, Y. Philipponneau, J. Nucl. Mater. 277 (2000) 143], the addition of Am into (U, Pu)O_2−x gave no significant effect on the O/M dependency of A and B values.     

Crystal structure and physical properties of PuPd5Al2

We report on the crystallographic aspects and the basic properties of the plutonium based compound PuPd₅Al₂. This material is antiferromagnetic at T_N = 5.6 K and does not present any hint of superconductivity down to 2 K. This material crystallizes in the ZrNi₂Al₅-type of structure with lattice parameters: a = 4.1302 Å and c = 14.8428 Å. The magnetization, heat capacity and electrical resistivity measurements indicate clearly antiferromagnetic order at T_N = 5.6 K. This material is compared to the structurally related cerium based material CePd₅Al₂ presenting superconductivity induced by pressure.     

Determination of mass attenuation coefficients, effective atomic and electron numbers for Cr, Fe and Ni alloys at different energies

The total mass attenuation coefficients (μ_m), for Cr, Fe, Ni and Fe_xNi_1−x (x = 0.8, 0.7, 0.6, 0.5, 0.4, 0.3 and 0.2), Fe_xCr_yNi_1−(x+y) (x = 0.7, y = 0.1; x = 0.5, y = 0.2; x = 0.4, y = 0.3; x = 0.3, y = 0.3; x = 0.2, y = 0.2 and x = 0.1, y = 0.2) and Ni_xCr_1−x (x = 0.8, 0.6, 0.5, 0.4 and 0.2) alloys were measured at 22.1, 25.0, 59.5 and 88.0 keV photon energies. The samples were irradiated with 10 mCi Cd-109 and 100 mCi Am-241 radioactive point source using transmission arrangement. The γ- and X-rays were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. Total atomic and electronic cross-sections (σ_t and σ_e), effective atomic and electron numbers (Z_eff and N_eff) were determined experimentally and theoretically using the obtained mass attenuation coefficients for investigated 3d alloys. The theoretical mass attenuation coefficients of each alloy were estimated using mixture rule. The experimental values were compared with the calculated values for all samples.     

Synchrotron X-ray induced damage in polymer (PS) thin films

Thin polystyrene (PS) films (M_w = 234,000) are spin coated on silicon substrates with a Chromium (Cr) layer as a sandwiched metallic layer that produces photoelectrons (by synchrotron X-rays). Earlier studies on synchrotron radiation damage in PS films, without metallic layer, have shown a decrease in interfacial roughness and a slight increase in thickness, at temperatures below T_g [A.G. Richter, R. Guico, K. Shull, J. Wang, Macromolecules 39 (2006) 1545]. Similar trend is observed in the presence of a thin layer of Cr film (∼2.5 nm). For the sample with a thick Cr layer the opposite effect was observed for X-ray radiation damage. For the 50 nm thick Cr film system thickness of the polystyrene film decreased by ≈4.4% which amount to a loss of about 0.021 nm³ per incident photon in the fluence range studied (6.8 × 10⁹ photons mm⁻² to 1 × 10¹⁴ photons mm⁻²). Interfacial roughness also increased from about 1.0 nm to 2.1 nm in the process. These effects are explained by invoking the presence of more number of X-ray induced photoelectrons and secondary electrons for 50 nm thick Cr film case compared to 2.5 nm thin film case.     

Change in magnetic properties of MgB2 thin films after irradiation by 200 MeV Au ion beam

The SHI irradiation induced effects on magnetic properties of MgB₂ thin films are reported. The films having thickness 300-400 nm, prepared by hybrid physical chemical vapor deposition (HPCVD) were irradiated by 200 MeV Au ion beam (S_e ∼ 23 keV/nm) at the fluence 1 × 10¹² ion/cm². Interestingly, increase in the transition temperature T_c from 35.1 K to 36 K resulted after irradiation. Substantial enhancement of critical current density after irradiation was also observed because of the pinning provided by the defects created due to irradiation. The change in surface morphology due to irradiation is also studied.     

Structural study of the oxidation process and stability of NbOxNy coatings

In the present work, we study the oxidation behaviour of NbON multilayer films. The films were deposited by DC magnetron sputtering with a reactive gas pulsing process. The nitrogen flow was kept constant and the oxygen flow was pulsed. Pulse durations of 10 s produced multilayered coatings with a period of λ = 10 nm. Three different films with increasing duty cycles have been deposited.Rutherford backscattering spectroscopy (RBS) was used to study the chemical composition variations at different annealing temperatures (as-deposited, 400 °C, 500 °C and 600 °C) combined with X-ray diffraction (XRD) to identify the crystalline phases formed. At 400 °C, for all films a very thin layer starts to form at the surface with enhanced O concentration. The composition of the deeper part of the samples remains unchanged. At 500 °C, the oxide scale grows, encompassing about half the film thickness. At 600 °C, the process is finished and a single layer is formed with reduced Nb and increased O concentration. Fourier-transformation infrared spectroscopy (FTIR) results confirmed the increase of this surface oxidation, while XRD revealed that crystallization of Nb₂O₅ occurs at 600 °C.