Growth of SrS thin films by pulsed-laser deposition

High-quality luminescent thin films of strontium sulphide (SrS) with excellent stoichiometry have been grown by pulsed-laser deposition. The crystallinity, stoichiometry and cathodoluminescence (CL) have been investigated for the films deposited onto two differently coated glass substrates. Furthermore the importance of post-deposition annealing has been studied. SrS thin films grown at 450 degrees C onto glass substrates coated with tin-doped indium oxide show good crystallinity, with a preferred orientation along the (200) axis. Cerium-doped SrS (SrS:Ce) gives a strong blue CL output at 400 nm. Energy-dispersive X-ray spectroscopy shows that the films are stoichiometric and that the stoichiometry is controllable by varying deposition parameters.

SUPERCONDUCTING YBA2CU3O7 THIN-FILMS ON MGO BY KRF LASER ABLATION - OPTIMIZATION OF DEPOSITION PARAMETERS

The optimization of interrelated deposition parameters during deposition of in situ YBa2Cu3O7 thin films on MgO substrates by KrF laser ablation was systematically studied in a single experimental chamber. The optimum condition was found to be a substrate temperature of 720-degrees-C and a target-substrate distance of 5 cm in an oxygen partial pressure of 100 mTorr. These conditions produced films with T(c) = 87 K. The presence of YO in the plasma plume was found to be important in producing good quality films. The films were characterized by resistance-temperature measurements, energy dispersive x-ray analyses, scanning electron microscopy, and x-ray-diffraction measurements, and the physical reasons underlying film quality degradation at parameter values away from optimal are discussed.

Inorganic species of arsenic in soil solution determined by microcartridges and ferrihydrite-based diffusive gradient in thin films

The bioavailability of soil arsenic (As) is determined by its speciation in soil solution, i.e., arsenite [As(III)] or arsenate [As(V)]. Soil bioavailability studies require suitable methods to cope with small volumes of soil solution that can be speciated directly after sampling, and thereby minimise any As speciation change during sample collection. In this study, we tested a self-made microcartridge to separate both As species and compared it to a commercially available cartridge. In addition, the diffusive gradient in thin films technique (DGT), in combination with the microcartridges, was applied to synthetic solutions and to a soil spiked with As. This combination was used to improve the assessment of available inorganic As species with ferrihydrite(FH)-DGT, in order to validate the technique for environmental analysis, mainly in soils. The self-made microcartridge was effective in separating As(III) from As(V) in solution with detection by inductively coupled plasma optical emission spectrometry (ICP-OES) in volumes of only 3 ml. The DGT study also showed that the FH-based binding gels are effective for As(III) and As(V) assessment, in solutions with As and P concentrations and ionic strength commonly found in soils. The FH-DGT was tested on flooded and unflooded As spiked soils and recoveries of As(III) and As(V) were 85–104% of the total dissolved As. This study shows that the DGT with FH-based binding gel is robust for assessing inorganic species of As in soils.

Strain dependent microstructural modifications of BiCrO3 epitaxial thin films

Strain-dependent microstructural modifications were observed in epitaxial BiCrO3 (BCO) thin films fabricated on single crystalline substrates, utilizing pulsed laser deposition. The following conditions were employed to modify the epitaxial-strain: (i) in-plane tensile strain, BCOSTO [BCO grown on buffered SrTiO3 (001)] and in-plane compressive strain, BCONGO [BCO grown on buffered NdGaO3 (110)] and (ii) varying BCO film thickness. A combination of techniques like X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (TEM) was used to analyse the epitaxial growth quality and the microstructure of BCO. Our studies revealed that in the case of BCOSTO, a coherent interface with homogeneous orthorhombic phase is obtained only for BCO film with thicknesses, d < 50 nm. All the BCOSTO films with d = 50 nm were found to be strain-relaxed with an orthorhombic phase showing 1/2 <100> and 1/4 <101> satellite reflections, the latter oriented at 45° from orthorhombic diffraction spots. High angle annular dark field scanning TEM of these films strongly suggested that the satellite reflections, 1/2 <100> and 1/4 <101>, originate from the atomic stacking sequence changes (or “modulated structure”) as reported for polytypes, without altering the chemical composition. The unaltered stoichiometry was confirmed by estimating both valency of Bi and Cr cations by surface and in-depth XPS analysis as well as the stoichiometric ratio (1 Bi:1 Cr) using scanning TEM–energy dispersive X-ray analysis. In contrast, compressively strained BCONGO films exhibited monoclinic symmetry without any structural modulations or interfacial defects, up to d ~ 200 nm. Our results indicate that both the substrate-induced in-plane epitaxial strain and the BCO film thickness are the crucial parameters to stabilise a homogeneous BCO phase in an epitaxially grown film.

Monodomain strained ferroelectric PbTiO(3) thin films: Phase transition and critical thickness study

This work demonstrates that instead of paraelectric PbTiO(3), completely c-oriented ferroelectric PbTiO(3) thin films were directly grown on (001)-SrTiO(3) substrates by pulsed-laser deposition with thickness up to 340 nm at a temperature well above the Curie temperature of bulk PbTiO(3). The influence of laser-pulse frequency, substrate-surface termination on growth, and functional properties were studied using x-ray diffraction, transmission electron microscopy, and piezoresponse force microscopy. At low growth rates (frequency 8 Hz) a domains were formed for film thickness above 20-100 nm. Due to coherency strains the Curie temperature (T(c)) of the monodomain films was increased approximately by 350 degrees C with respect to the T(c) of bulk PbTiO(3) even for 280-nm-thick films. Nonetheless, up to now this type of growth mode has been considered unlikely to occur since the Matthews-Blakeslee (MB) model already predicts strain relaxation for films having a thickness of only similar to 10 nm. However, the present work disputes the applicability of the MB model. It clarifies the physical reasons for the large increase in T(c) for thick films, and it is shown that the experimental results are in good agreement with the predictions based on the monodomain model of Pertsev et al. [Phys. Rev. Lett. 80, 1988 (1998)].

Piezoresponse force microscopy of ferroelectric thin films: Frequency dependence of phase imaging

The objective of this work is an evaluation of quantitative measurements of piezoresponse force microscopy for nanoscale characterization of ferroelectric films. To this end, we investigate how the piezoresponse phase difference Delta Phi between c domains depends on the frequency omega of the applied ac field much lower than the cantilever first resonance frequency. The main specimen under study was a 102 nm thick film of Pb(Zr(0.2)Ti(0.8))O(3). For the sake of comparison, a 100 nm thick PbTiO(3) film was also used. From our measurements, we conclude a frequency dependent behavior Delta Phi similar to omega(-1), which can only be partially explained by the presence of adsorbates on the surface. (C) 2008 American Institute of Physics.

Photobactericidal effects of TiO 2 thin films at low temperatures - A preliminary study

The efficacy of TiO ₂ photocatalysis for the destruction of pathogenic bacteria has been demonstrated by a number of groups over the past two decades. Pathogenic bacteria represent a significant hazard for the food and drink industry. Current practices in this industry dictate that rigorous sanitizing regimes must be regularly implemented resulting in lost production time. The incorporation of a TiO ₂ antibacterial surface coating in this setting would be highly desirable. In this paper we report a preliminary study of the efficacy of a TiO ₂ coating, doped with the lanthanide, neodymium, at low temperature conditions such as those utilised in the food and drink sector. The rapid destruction of Staphylococcus aureus, a common foodborne pathogen, was observed using TiO ₂ films coated to glass and steel substrates.