Tapio Kanniainen

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.

Electrodeposition of PbTe thin films

Abstract Lead telluride (PbTe) thin films were electrodeposited potentiostatically on SnO 2 and Cu substrates from aqueous alkaline solutions of Pb(CH 3 COO) 2 , disodium salt of ethylendiaminetetraacetic acid (EDTA) and TeO 2 . Film deposition reactions were studied with cyclic voltammetry. The films were characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA), deuteron induced reactions and profilometry. Potential ranges where PbTe films with constant composition were achieved were −0.70 to −0.90 V versus SCE on SnO 2 substrates and −0.80 to −0.95 V versus SCE on Cu substrates when the concentration of PbEDTA 2− was 0.1 M. The corresponding potential ranges were −0.75 to −0.95 and −0.85 to −0.95 V versus SCE when the PbEDTA 2− concentration was 0.05 M. The concentration of TeO 3 2− was 0.001 M in both cases. The films were smooth, dense and crystalline having the cubic PbTe structure but they contained an excess of tellurium.

Electrodeposition of lead selenide thin films

PbSe thin films have been electrodeposited potentiostatically from aqueous solutions containing lead complexed with EDTA (ethylenediaminetetraacetic acid) and SeO2 . The effects of deposition parameters such as deposition potential, concentrations of source materials and current density were studied. Cyclic voltammetry was used for studying the film deposition reactions and for finding the appropriate deposition potential range. The films were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA), deuteron induced reactions and profilometry. Nearly stoichiometric, smooth, mirror-like PbSe films were obtained at deposition potentials between –0.6 and –0.8 V vs. saturated calomel electrode (SCE) when the concentration of lead was ten times higher than the concentration of selenium, and between –0.4 and –0.75 V vs. SCE when the lead excess was a hundred-fold.

Growth of strongly orientated lead sulfide thin films by successive ionic layer adsorption and reaction (SILAR) technique

Lead sulfide thin films were grown at room temperature by the successive ionic layer adsorption and reaction (SILAR) technique on soda lime glass, ITO and Al2O3 covered glass, SiO2, (100)Si and (111)Si substrates. SILAR utilises sequential treatment of the substrate with aqueous precursor solutions. Dilute solutions of lead acetate and thioacetamide were used as precursors for Pb2+ and S2–, respectively. The lead precursor solution also contained triethanolamine (tea) as a complexing agent, with a Pb: tea mole ratio of 1 : 2. On glass the growth rate was 0.12 nm per cycle with 0.2 mol dm–3 lead and 0.4 mol dm–3 thioacetamide solution. The appearance of the films was metallic. X-Ray diffraction studies revealed a strong [200] orientation of the films. According to the Rutherford back-scattering (RBS) and nuclear reaction analysis (NRA) results the films were stoichiometric PbS and contained small amounts of some lighter impurities, possibly O and H. Scanning electron microscope (SEM) images revealed that the films were rather rough and consisted of grains with a diameter approximately corresponding to the thickness of the film.

Growth of ZnS thin films by liquid-phase atomic layer epitaxy (LPALE)

Abstract ZnS thin films were grown by the LPALE method on soda lime glass, ITO- and Al2O3-covered glass and Si substrates. 0.05–0.2M ZnCl2 and Na2S solutions were used as immersion solutions. Immersion time was 20 s. Depending on the concentrations the rinsing time was 100–200 s and the flow rate of water 600–800 ml/min. The growth rate was 0.7–0.8 A/ cycle with concentrations ZnCl2 0.1M and Na2S 0.05M, and 1.7–2.0 A/ cycle with doubled concentrations. The appearance of the films was smooth and no cracks could be detected. The films were polycrystalline with presumably cubic structure and showed slight (111) preferential orientation. The S/Zn ratio was approximately 0.8 and the films contain uniformly distributed oxygen.

Thin multilayer CdS/ZnS films grown by SILAR technique

Abstract Multilayer ZnS/CdS thin films were grown on glass, ITO-covered glass and (100)GaAs substrates by successive ionic layer adsorption and reaction (SILAR) technique at room temperature and ambient pressure. The layers in multilayer thin film structures were nominally 1–6 nm thick and the amount of layers varied so that the total thickness of 100–120 nm was achieved. The films were polycrystalline according to X-ray diffraction analysis and scanning electron microscopy. The interfaces between the separate cadmium sulfide (CdS) and zinc sulfide (ZnS) layers were not sharp, but contained thin Cd x Zn 1− x S solid solution layers. Annealing enhanced the mixing of the different layers and after 50 h at 300°C no separate CdS and ZnS X-ray reflections could be detected. About 20 nm thick layers could be detected as separate fields by scanning electron microscopy.

Lateral force microscopy and force modulation microscopy on SILAR-grown lead sulfide samples

In this study lateral force microscopy (LFM) and force modulation (FM) microscopy have been used for investigations on PbS thin films deposited on glass substrates with the successive ionic layer adsorption and reaction method (SILAR). Information of friction and surface elasticity obtained by scanning force microscopy revealed local surface properties of the thin films, which have been used to distinguish thin film constituents from environmental contamination and/or contamination due to the preparation process. Furthermore, these scanning force microscopy (SFM) applications yielded information about the surface coverage which is particularly important in the early stages of film deposition.

Growth of lead selenide thin films by the successive ionic layer adsorption and reaction (SILAR) technique

This paper describes the growth of lead selenide (PbSe) thin films on glass and on ITO-covered glass substrates at room temperature under normal pressure utilising the successive ionic layer adsorption and reaction (SILAR) technique. Aqueous precursor solutions, lead acetate complexed with triethanolamine and sodium selenosulfate, were used for lead and selenide, respectively. The films were found to be metallic and adherent. The properties of the films were characterised by means of X-ray diffraction (XRD), Rutherford back-scattering spectrometry (RBS), nuclear reaction analysis (NRA) and scanning electron microscopy (SEM).

Growth of zinc sulfide thin films by the successive ionic layer adsorption and reaction (Silar) method on polyester substrates

Abstract Polyester foils were used as substrate material for zinc sulfide thin films grown by the successive ionic layer adsorption and reaction method. The polyester substrates were pretreated with 0.1 M SnCl 2 to attain a good adhesion between zinc sulfide and the substrate surface. The growth rate of the ZnS thin film was 0.16 nm/cycle when precursor solutions of 0.1 M ZnCl 2 and 0.05 M Na 2 S were used, and 0.22 nm/cycle when the concentrations of the precursor solutions were doubled. Thin ZnS films grown on polyester were amorphous, but when the film thickness exceeded 250 nm, the films showed crystallinity on X-ray diffraction. The films were slightly zinc rich and contained some oxygen, possibly as zinc oxide and water. The band gap of the ZnS thin films was 3.44 eV. The films appeared to be smooth and homogenous and the attachment of the ZnS thin film to the polyester substrate was good.

Deposition of manganese-doped zinc sulfide thin films by the successive ionic layer adsorption and reaction (SILAR) method

Abstract Manganese-doped zinc sulfide, ZnS:Mn, thin films were grown by the successive ionic layer adsorption and reaction method on glass, on ITO- and Al2O3-covered glass, and on quartz and CaF2 using 0.1 M ZnCl2, 0.05 M Na2S and 0.01 M MnCl2 as precursor solutions. The immersion time was 20 s and the rinsing time 100 s. The manganese was doped into the film by using separate ZnS and MnS deposition cycles. The desired Mn level (0.3–0.8 wt.%) in the ZnS film was achieved using a MnS ZnS cycle ratio of 1:100. The growth rate of the ZnS:Mn film was 0.09 nm cycle−1. The films were polycrystalline and presumably cubic. The appearance of the ZnS:Mn films, studied by scanning electron microscopy, was rougher than pure ZnS films but annealing for 3 h at 500 °C in a nitrogen atmosphere flattened the films. The refractive indices varied from 2.04 to 2.22 in films grown on glass and from 2.13 to 2.32 in those grown on ITO-covered glass. According to the Rutherford backscattering spectrometry and nuclear reaction analyses the ZnS:Mn films contained approx. 20 at.% oxygen and 3–15 at.% hydrogen, but their content was significantly reduced after annealing.