RBS investigations of buffer layers between YBa2Cu3O7−x and silicon

The deposition of high-quality high-T_c superconducting films on silicon wafers for future hybrid electronic devices is strongly hampered by the interdiffusion between films and substrate. This effect degrades the superconducting properties seriously and is a strong function of temperature. Since high processing temperatures are inevitable for good films, suitable buffer layers are needed to reduce the interdiffusion. We have investigated the combinations ZrO₂/Si(100), BaF₂/Si(100), and noble-metal/TiN/Si(100) at temperatures up to 780°C in oxidizing ambient. YBa₂Cu₃O_7−x films have been deposited onto the buffer layers by laser ablation. Thereafter the interfaces have been analyzed by Rutherford backscattering. So far only ZrO₂ has demonstrated sufficient stability to serve as a buffer layer for the laser-ablated YBa₂Cu₃O_7−x films. All other combinations suffer from interdiffusion or oxidation.     

Ion implantation doping and electrical conductivity enhancement of C60 films

Pristine C₆₀ films sublimed onto sheet mica were implanted with 20 keV K⁺ ions and I⁺ ions at doses of 1.0 × 10¹⁶/cm², 3.0 × 10¹⁶/cm² and 5.0 × 10¹⁶/cm², and with 20 keV Ar⁺ ions at a dose of 5.0 × 10¹⁶/cm². The distributions of dopants were studied using Rutherford backscattering spectrometry (RBS). The temperature dependence of sheet resistivity of the films was investigated applying a four-probe system. It was proposed that the conductivity enhancement of K⁺ implanted C₆₀ films was due to the implanted ions in the films, while for I⁺ implanted C₆₀ films, both implanted I⁺ ions and irradiation effects of the ions contributed to the enhancement of conductivity.     

Argon irradiation damage at a Cu/Al2O3 interface for different alumina structures

The evolution of damages at a Cu/Al₂O₃ device interface after Ar⁺ irradiation, depending on alumina structure, and the effect of surface roughness on sputtering have been studied. A polycrystalline Cu/Al₂O₃ bilayer and polycrystalline Cu on amorphous alumina were irradiated with 400 keV Ar⁺ ion beam at doses ranging from 5 × 10¹⁶ to 10¹⁷ Ar⁺/cm² at room temperature. The copper layer thicknesses were between 100 and 200 nm. RBS analysis was used to characterize the interface modification and to deduce the sputtering yield of copper. The SEM technique was used to control the surface topography. A RBS computer simulation program was used to reproduce experimental spectra and to follow the concentration profile evolutions of different elements before and after ion irradiation. A modified TRIM calculation program which takes into account the sputtering yield evolution as well as the concentration variation versus dose gives a satisfactory reproduction of the experimental argon distribution. The surface roughness effect on sputtering and the alumina structure influence at the interface on mixing mechanisms are discussed.     

Measurement of the H2-D mass difference with a nuclear microprobe

A 1.24 MeV deuteron (D) beam mixed with a H₂ molecular beam was separated with a microslit system of a nuclear microprobe consisting of a 100 μm diameter object and a 1 mm diameter aperture diaphragm. D was distinguished from H₂ by Rutherford backscattering (RBS) on a thin Au film. By slightly changing the magnetic field strength of the beam steerer installed in front of the object diaphragm, the maximum and the minimum RBS D/H₂ ratios were found to be 50.3 and 1.5, respectively. M/ΔM = 3.9 × 10³ was obtained as the mass resolution of the nuclear microprobe. The transmission of this system was 2 × 10⁻³.     

Micro-PIXE and channeling PIXE analysis of Ag-doped YBa2Cu3O7−δ thin films

Nuclear Microscopy, utilizing a 2 MeV He⁺ beam for channeling Rutherford Backscattering (RBS) and PIXE analysis, was used to characterise Ag-doped YBa₂Cu₃O_7−δ thin films and measure the lateral distribution of the Ag. The samples were prepared by in situ two-beam pulsed laser deposition in order to investigate the effects of such dopings on critical current densities [1 and 2]. Films deposited at temperatures above 650°C form needle-like surface structures with a length of up to 100 μm; these tend to align with in-plane a–b axis. Results for a sample prepared at a substrate temperature of 730°C and a maximum Ag concentration of 5 at.% are discussed. The needle-like structures were found to be rich in Ag and Cu, and the YBa₂Cu₃O_7−δ film contained 0.02 at.% Ag. Broad beam PIXE-channeling results indicate that 19% of the Ag is substitutional.     

Release of nitrogen from SiOxNy films during RBS measurement

We have found that nitrogen atoms are released very rapidly from ultrathin SiO_xN_y films (2.6 nm) during RBS measurement with 500 keV He⁺ ions. The release behavior strongly depends on the preparation technique of the SiO_xN_y films. There is no release from the film prepared by thermal nitridation of SiO₂, while 80% of the nitrogen atoms are released from the film prepared by plasma nitridation at a fluence of 1×10¹⁶ cm⁻². The release cross-section for plasma SiO_xN_y films is of the order of 10⁻¹⁶ cm². This large cross-section cannot be explained by a simple recoil mechanism. The nitrogen release is also observed under irradiation with 5–10 keV electrons though the cross-section is of the order of 10⁻¹⁹ cm². These findings suggest that the observed nitrogen release is an electronic excitation induced process.     

Structural and gasochromic properties of epitaxial WO3 films prepared by pulsed laser deposition

The structural and gasochromic properties of epitaxial tungsten trioxide (WO₃) thin films, prepared by ArF excimer pulsed laser deposition under the controlled oxygen atmosphere, have been investigated. The WO₃ films were grown on the α-Al₂O₃ substrates, as the oxygen pressure ranged from 0.57 to 1.20 Pa and the substrate temperature ranged from 432 to 538 °C. The deposited films were characterized by Rutherford backscattering spectroscopy (RBS)/channeling, X-ray diffraction, X-ray pole figures and Raman spectroscopy. RBS and XRD results demonstrated that monoclinic WO₃ (0 0 1) films were successfully grown on the α-Al₂O₃ substrates. The crystal quality was improved by increasing both the oxygen pressure and the substrate temperature. Gasochromic coloration in the WO₃ films by exposure to diluted hydrogen gas was found to correlate with the crystal quality of the films. The gasochromic coloration was suppressed by the epitaxial growth of the films.     

Room temperature ferromagnetism of Co doped TiO2 using ion implantation and defect engineering

Ferromagnetic (FM) semiconductors obtained by doping ferromagnetic elements into a nonmagnetic semiconductor matrix are essential for the second generation of spintronics devices. In this study, we investigate Co doping behavior and subsequent magnetic properties in Co implanted and thermally annealed TiO₂. In TiO₂ single crystals, a decrease in the oxygen partial pressure during thermal annealing is found to enhance the Co substitutional fraction by increasing the concentration of oxygen vacancies. Magnetic properties determined from superconducting quantum interference device magnetometer (SQUID) measurements show that TiO₂ crystals with a large fraction of substitutional Co are ferromagnetic at room temperature. In addition to single crystals, the feasibility of Co doping via ion implantation is studied in sol–gel synthesized TiO₂ thin films. Results from grazing incidence X-ray diffraction (GIXRD) show that the implantation can produce Co doped TiO₂ thin films and that the Co incorporation into Ti lattice site accompanies the transition from rutile to anatase phase. These results show that ion beam synthesis is a useful tool for producing ferromagnetic TiO₂ with a high Curie temperature (T_C).     

Modification of N-doped carbon induced by 30 MeV C60 ions

In the present work, 120 keV N-ion doped and 30 MeV C₆₀ ion irradiated graphite-like-carbon samples were characterized by RBS, micro-FTIR, micro-Raman, XPS spectroscopy and the variation of the properties of the samples with the N-dopant and/or C₆₀ irradiation fluence have been studied. The RBS spectra showed that C₆₀ irradiation can induce a partial diffusion of N atoms to the surface and the amount of the diffused N atoms increases slightly with increasing C₆₀ irradiation fluence. The FTIR and Raman spectra exhibit characteristic bands of carbon nitrogen bonds showing that the C and N atoms are chemically bonded. The amount of chemically bonded C and N atoms increases with increasing N-dopant. By deconvolution of the XPS spectra, the atomic concentration of N and C atoms were obtained and it was identified that the samples mainly consist of three phases, namely, C₃N₄, CN_x and tetrahedral amorphous carbon. The effect of N-dopant and C₆₀ irradiation fluence on the modification of the properties of the samples is also discussed.     

Carbon deposition from a γ-irradiated CO2/CO/CH4/C2H6 gas mixture on the manganese oxides MnO, Mn3O4 and Mn2O3

The composition of oxides formed on steel surfaces within power reactors may influence heat transfer efficiency. Previous studies have indicated that carbon is deposited on spinal-type oxides containing manganese, iron, cobalt, nickel and chromium. In this investigation, characterised manganese oxides have been subjected to γ-irradiation under conditions similar to those experienced in reactors in an effort to understand the catalytic processes involved in deposit initiation and growth. Mn₃O₄ and Mn₂O₃, under the conditions present in the γ-cell, were reduced to MnO during the time of exposure. Relative carbon deposition rates were observed to follow the trend MnO>Mn₃O₄≈Mn₂O₃.     

Compositional analysis of atom beam co-sputtered metal-silica nanocomposites by Rutherford backscattering spectrometry

Metal:SiO₂ (metal: Ni, Ag, Au) nanocomposite films of different compositions have been prepared by atom beam co-sputtering. The estimation of composition of films is done theoretically using sputtering yield and relative area of metal and SiO₂. The sputtering yields used for estimation of composition are calculated by three theoretical methods: Monte Carlo simulations (SRIM code), Sigmund’s theory and Sigmund’s theory modified by Anderson and Bay. Rutherford backscattering spectrometry (RBS) is also used to analyze the composition of the nanocomposite films. RUMP simulations of RBS data are performed. The errors in theoretical calculations and RBS results are estimated. It is found that SRIM is more appropriate for Ni:SiO₂ nanocomposite films, while modified Sigmund’s theory based method is better for Ag:SiO₂ and Au:SiO₂ nanocomposite films. The possible sources of errors in theoretical methods with respect to experimental (RBS) results are also discussed.     

Radiation damage induced by 5 keV Si ion implantation in strained-Si/Si0.8Ge0.2

The damage distributions induced by ultra low energy ion implantation (5 keV Si⁺) in both strained-Si/Si_0.8Ge_0.2 and normal Si are measured using high-resolution RBS/channeling with a depth resolution better than 1 nm. Ion implantation was performed at room temperature over the fluence range from 2 × 10¹³ to 1 × 10¹⁵ ions/cm². Our HRBS results show that the radiation damage induced in the strained Si is slightly larger than that in the normal Si at fluences from 1 × 10¹⁴ to 4 × 10¹⁴ ions/cm² while the amorphous width is almost the same in both strained and normal Si.     

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.     

Damage distributions in LiNbO3 crystal induced by MeV F tilted implantations

X-cut LiNbO₃ crystals have been implanted by 0.8, 1.0 and 1.2 MeV F⁺ tilted at angles of 15°, 45° and 60° with doses of 5 × 10¹⁴, 7 × 10¹⁴ and 5 × 10¹⁴ ions/cm², respectively. The Rutherford backscattering (RBS)/channeling technique was used to investigate the induced damage distributions. The damage profiles were deconvoluted from the measured spectra after considering the energy spread due to the different stopping power of channeled and nonchanneled ions. Good agreements were obtained between the measured damage profiles and the calculated defect profiles by TRIM'90 (transport of ions in matter, version 1990), except that the measured damage concentration was enhanced in the near-surface region. Information on the lateral and longitudinal damage spread in LiNbO₃ crystals was obtained from the damage profiles induced by tilted ion implantations and compared with TRIM'90 calculation.     

Ion beam enhanced etching of LiNbO3

Single crystals of z- and x-cut LiNbO₃ were irradiated at room temperature and 15 K using He⁺- and Ar⁺-ions with energies of 40 and 350 keV and ion fluences between 5 × 10¹² and 5 × 10¹⁶ cm⁻². The damage formation investigated with Rutherford backscattering spectrometry (RBS) channeling analysis depends on the irradiation temperature as well as the ion species. For instance, He⁺-irradiation of z-cut material at 300 K provokes complete amorphization at 2.0 dpa (displacements per target atom). In contrast, 0.4 dpa is sufficient to amorphize the LiNbO₃ in the case of Ar⁺-irradiation. Irradiation at 15 K reduces the number of displacements per atom necessary for amorphization. To study the etching behavior, 400 nm thick amorphous layers were generated via multiple irradiation with He⁺- and Ar⁺-ions of different energies and fluences. Etching was performed in a 3.6% hydrofluoric (HF) solution at 40 °C. Although the etching rate of the perfect crystal is negligible, that of the amorphized regions amounts to 80 nm min⁻¹. The influence of the ion species, the fluence, the irradiation temperature and subsequent thermal treatment on damage and etching of LiNbO₃ are discussed.     

Carbon clustering in Si1−xCx formed by ion implantation

Silicon-carbon alloys were formed by multiple energy implantation of C⁺ ions in silicon and in Silicon on Sapphire (SOS). The ion fluence ranged between 5 × 10¹⁶ − 3 × 10¹⁷ ions/cm² and the energy between 10–30 keV in order to obtain constant carbon concentration into a depth of 100 nm. The carbon atomic fraction (x) was in the range 0.22–0.59 as tested by Rutherford backscattering spectrometry (RBS). Thermal annealing of the implanted films induced a transition from amorphous to a polycrystalline structure at temperatures above 850°C as detected by Infrared spectrometry (IR) in the wavenumber range 600–900 cm⁻¹. The optical energy gap and the intensity of the infrared signal after annealing at 1000°C depended on the film composition: they both increased linearly with carbon concentration reaching a maximum at the stoichiometric composition (x = 0.5). At higher carbon concentration the IR intensity saturated and the optical energy gap decreased from the maximum value of 2.2 to 1.8 eV. The behaviour at the high carbon content has been related to the formation of graphitic clusters as detected by Raman spectroscopy.     

Pumping experiment of water on B and LaB6 films with an electron beam evaporator

The pumping characteristic of water vapor on boron and lanthanum hexaboride films formed with an electron beam evaporator have been investigated in high vacuum between 10⁻⁴ and 10⁻³ Pa. The measured initial maximum pumping speeds of water for the fresh B or LaB₆ films with a deposition amount from 2.3 × 10²¹ to 6.7× 10²¹ molecules/m² separately formed on a substrate are 3.2–4.9 m³/sm², and the saturation values of adsorbed water on these films are 2.1 ×10²⁰−1.3 × 10²¹ H₂O molecules/m².     

Microanalysis of a submicron patterned WSix structure using a nuclear microprobe

A metal-silicide wiring structure with submicron lateral feature size was analyzed successfully by a nuclear microprobe with a Liquid Metal Ion Source (LMIS). A minimum beam spot size of less than 80 nm at a current of 30 pA with a 300 keV Be²⁺ beam was used. The lateral distribution of WSi_x at submicron level was resolved using RBS mapping and tomographic imaging. The localized silicidation behavior between WSi_x on Si and on SiO₂ was compared by microbeam RBS measurement.     

Electrical and optical properties of Co ion implanted a-Si1 − xCx:H alloys

Low resistivity a-Si_1 − xC_x:H alloy films have been formed by high dose Co⁺ ion implantation. The influence of the carbon content of the films on the resistivity has been studied and the lowest values, of the order of 10 Ω/Sq, have been observed for the carbon free films. Even lower resistivities, a further reduction of up to 50%, have resulted from annealing at temperatures up to 500°C. Changes in the optical and structural properties of the implanted a-Si_1 − xC_x:H films have been studied by means of IR and Raman spectroscopy. Results show that the implantation produces considerable structural and chemical modifications. The formation of, and the transition to, a possible CoSi₂ phase has been observed by examining the IR and Raman spectra as a function of implant dose.     

Stopping cross sections of He+ ions in bismuth

The stopping cross sections, ?(E), of He⁺ ions in bismuth have been measured by Rutherford backscattering spectrometry (RBS) at incident energies ranging from E = 1.6–3.4 MeV. The energy loss of He⁺ ions and thicknesses of the bismuth films deposited on aluminium substrates were determined from the RBS spectra at each energy for scattering angles of 130° and 165°. The film thicknesses of some of the samples were also measured by weighing and the results compared with those from RBS. Parameters for energy dependence of stopping cross section in the Varelas-Biersack interpolation formula have been obtained for bismuth from a fit to all the available experimental data. Accuracy of our method based on RBS is demonstrated by measurements on copper, for which ?(E) is already well studied. It is also shown that reliable ?(E) values may be obtained even on samples with non-uniform film thickness.