E. Rauhala

Interactive personal-computer data analysis of ion backscattering spectra

A new personal computer program package for ion backscattering data analysis with an interactive graphical interface has been developed. The assumed target composition is modified directly by pointing at the corresponding signals on the screen. Special attention has been paid to the physics details included. All projectile ions may be treated. A data base of non-Rutherford 1H and 4He scattering cross sections of several light elements, readily extendable by the user, is included. The most recent stopping power formulations are used. Contributions from electronic screening, corrected Bohr straggling and nonlinear detector response are taken into account. A procedure for subtracting the low energy tail background is provided. Smooth variations of elemental composition as a function of sample depth, as needed in diffusion or implantation profile analysis, as well as spectra taken in channeled sample orientations may be assumed. A short review of published computer methods for ion backscattering is included. Examples and applications of the present procedure to the analysis of 4He ion non-Rutherford and 12C ion RBS spectra are presented.

Atomic Layer Epitaxy Growth of TiN Thin Films

TiN thin films were grown on soda lime glass substrates by atomic layer epitaxy. Two different chemical schemes were studied: a direct reaction between the alternately supplied TiCl{sub 4} and NH{sub 3}, and a process employing a reducing zinc pulse given after the TiCl{sub 4} dose. The latter process was found to result in films with lower electrical resistivity. Resistivities as low as 50 {micro}{Omega} cm were measured for films grown with zinc at 500 C while those prepared without zinc had resistivities of about 250 {micro}{Omega} cm. In both cases the contents of chlorine residues were below the detection limit of Rutherford backscattering spectrometry (RBS), i.e., about 0.5 atom percent. In addition to RBS and electrical measurements, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, nuclear resonance broadening, and reflectance spectra measurements were employed for the film characterization. The possible reasons for the major drawback of the process, the low growth rate of only about 0.2 {angstrom}/cycle, are discussed.

Atomic Layer Epitaxy Growth of TiN Thin Films from Til4 and NH 3

TiN thin films were grown by atomic layer epitaxy using titanium tetraiodide (TiI 4 ) and ammonia (NH 3 ) as precursors. The films were characterized with Rutherford backscattering spectrometry, time-of-flight elastic recoil detection analysis, energy dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy, and resistivity measurements. Both the growth rate and film quality were markedly dependent on the growth temperature. As the temperature was increased from 400 to 500°C the growth rate increased from 0.12 to 0.30 A/cycle, and the resistivity decreased from 380 to 70 μΩ cm. Also, the oxygen content decreased with increasing temperature being about 10 atom % in the films grown at 475 to 500°C. The iodine contents were below 0.5 atom %.

Proton elastic scattering cross sections of carbon, nitrogen and silicon for backscattering analysis in the energy range 0.7—2.5 MeV

Differential elastic scattering cross sections of 0.7—2.5 MeV protons for carbon, nitrogen and silicon have been determined at a scattering angle θ = 170°. Results from previous measurements near θ = 170° show large variations, of the order of 10–30% in the nonresonant regions. The purpose of the present investigations is to tabulate cross section data for backscattering analysis at a single scattering angle for many elements. Proton backscattering in the non-Rutherford energy region is more sensitive in the detection of C, N and many other light elements than other ion beam methods when a high background from the matrix is absent. Proton backscattering by using the present scattering cross sections and computer data analysis are outlined. The possible interference from other nuclear reactions is considered.

Atomic Layer Deposition of SrTiO3 Thin Films from a Novel Strontium Precursor–Strontium-bis(tri-isopropyl cyclopentadienyl)

Strontium titanate thin films were grown by atomic layer deposition (ALD) at 250–325 °C from the novel strontium compound, strontium bis(tri-isopropyl cyclopentadienyl), titanium tetraisopropoxide, and water. Though completely self-limiting, deposition of strontium could not be achieved because of some minor decomposition of the strontium compound. This decomposition was slow enough to ensure that good control of film stoichiometry was obtained by controlling either the (Sr-O)/(Ti-O) pulsing ratio, or the strontium precursor exposure time. The films were polycrystalline and strongly oriented in the (100) direction. After annealing at 500 °C in air, the films with the optimal composition were found to have measured permittivity values of around 180.

NbCl5 as a precursor in atomic layer epitaxy

Abstract NbCl 5 was examined as a niobium source for ALE growth of NbN and Nb 2 O 5 films and for Nb doping of TiO 2 and SnO 2 films. The growth of NbN films was successfully accomplished both with and without reducing Zn pulses between the NbCl 5 and NH 3 pulses. The polycrystalline NbN films were nearly stoichiometric and free of chlorine residues. The main problem met was the low growth rate, only about 0.2 A/cycle. All attempts to employ NbCl 5 as a precursor in oxide processes failed which, with the aid of thermodynamic calculations, was ascribed to the stability of NbOCl 3 and NbO 2 Cl intermediate products.

Surface-controlled growth of LaAlO3 thin films by atomic layer epitaxy

LaAlO3 thin films were deposited by atomic layer epitaxy (ALE) from β-diketonate-type precursors La(thd)3 and Al(acac)3. Ozone was used as an oxygen source. Films were grown on soda lime glass, Si(100), MgO-buffered Si(100), sapphire and SrTiO3(100) substrates. The influence of the La∶Al precursor pulsing ratio on the film growth and quality in the temperature range of 325–400 °C was studied in detail. Stoichiometry and impurity levels were measured using RBS, TOF-ERDA and XPS while the chemical type of carbon impurity was identified by FTIR. XRD and AFM were used to determine crystallinity and surface morphology. The films were transparent and uniform and their thickness could be accurately controlled by the number of deposition cycles. The as-deposited films were amorphous but became crystalline upon annealing at 900 °C. The annealed films grown on Si(100) and MgO(111)-buffered Si(100) substrates had a preferred (110) orientation whereas those grown on MgO(100)-buffered Si(100) substrates showed a preferred (100) orientation. Epitaxial and smooth LaAlO3 thin films were obtained on SrTiO3(100) after annealing at 900 °C, verified by measurement of the X-ray rocking curve of the (200) reflection and the AFM surface roughness. Stoichiometric LaAlO3 films contained <1.9 atom% carbon and about 0.3 atom% hydrogen as impurities.

Oxygen detection by non-Rutherford proton backscattering below 2.5 MeV

Abstract Oxygen detection by proton backscattering has been investigated. The oxygen detection sensitivity of 2.5 MeV proton backscattering is shown to exceed that of 4He backscattering by even a factor of about 15 depending on the matrix. The needed proton elastic scattering cross sections of oxygen for θlab = 170° have been measured in the energy range Elab = 770–2480 keV relative to Ti and Sn elastic scattering cross sections using thin TiO2 and SnO2 samples. The angular dependence of the cross section was measured at energies Elab = 1790, 1990, 2191, and 2382 keV for backscattering angles. The experimental cross sections were found to be 1.1–5.7 times the pure Coulomb cross section. Theoretical calculations for the scattering cross sections were performed and their inapplicability to experimental purposes is demonstrated. Fits to experimental data are given.

Growth of ZnS, CdS and multilayer ZnS/CdS thin films by SILAR technique

Abstract Successive ionic layer adsorption and reaction (SILAR) technique was used to deposit cadmium sulfide (CdS) and zinc sulfide (ZnS) thin films on (100)GaAs. CdS thin films were also grown on ITO-covered glass substrates. Multilayer CdS/ZnS thin films were deposited on glass substrates. The crystallinity of the thin films was characterized by means of X-ray diffraction and they all turned out to be polycrystalline. The thin films looked relatively smooth and homogeneous in scanning electron microscopy (SEM) images. Energy dispersive X-ray analysis (EDX) and Rutherford backscattering spectroscopy (RBS) proved nearly 1 : 1 stoichiometry for the multilayer samples. Thickness of the thin films was measured by RBS and chemical analysis.

One‐Step Electrodeposition of Cu2 − x Se and CuInSe2 Thin Films by the Induced Co‐deposition Mechanism

The induced co-deposition mechanism in one-step electrodeposition of Cu 2-x Se and CuInSe 2 thin films was investigated. Cu 2-x Se and CuInSe 2 thin films were deposited potentiostatically on Mo substrates by a one-step process from an acidic electrolyte containing SCN - ions as complexing agents. The films were examined by scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, and ion beam analysis methods. Good control of stoichiometry was achieved over a wide potential range, thus indicating that the film composition may indeed be controlled by the induced co-deposition mechanism. The effects of the thiocyanate ions on the reduction potentials of Cu + , In 3+ , and Se 4+ ions were examined by cyclic voltammetry. In order to improve their crystallinity, the CuInSe 2 films were annealed under a N 2 atmosphere after deposition.