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Publications in 2017 

ABSTRACT: Hybrid nanostructures composed of layered materials have recently attracted a lot of attention due to their promising electronic and catalytic properties. In this study, we describe a novel synthesis strategy of ZnO/ZnS/MoS2 core-shell nanowire growth using a three-step route. First, ZnO nanowire array was grown on a silicon wafer. Second, the sample was immersed in ammonium molybdate solution and dried. At the third step, the sample was annealed in a sulfur atmosphere at 700 °C. Two solid state chemical reactions occur simultaneously during the annealing and result in a formation of ZnS and MoS2 phases. Produced ZnO/ZnS/MoS2 core-shell nanowires were characterized by scanning and transmission electron microscopy, whereas their chemical composition was confirmed by selected area electron diffraction and micro-Raman spectroscopy.

Journal of Crystal Growth, Volume 459, 1 February 2017, Pages 100-104.
DOI: 10.1016/j.jcrysgro.2016.11.106
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ABSTRACT: Uranium L3-edge X-ray absorption spectroscopy was used to study the atomic structure of uranium dioxide (UO2). The extended X-ray absorption fine structure (EXAFS) was interpreted within the ab initio multiple-scattering approach combined with classical molecular dynamics to account for thermal disorder effects. Nine force-field models were validated, and the role of multiple-scattering contributions was evaluated.

Progress in Nuclear Energy, Volume 94, January 2017, Pages 187-193.
DOI: 10.1016/j.pnucene.2016.07.017
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ABSTRACT: Zn-Ir-O (Zn/Ir ≈ 1/1) thin films have been reported to be a potential p-type TCO material. It is, however, unknown whether it is possible to achieve p-type conductivity at low Ir content, and how the type and the magnitude of conductivity are affected by the film structure. To investigate the changes in properties taking place at low and moderate Ir content, this study focuses on the structure, electrical and optical properties of ZnO:Ir films with iridium concentration varying between 0.0 and 16.4 at.%.
ZnO:Ir thin films were deposited on glass, Si, and Ti substrates by DC reactive magnetron co-sputtering at room temperature. Low Ir content (up to 5.1 at.%) films contain both a nano-crystalline wurtzite-type ZnO phase and an X-ray amorphous phase. The size of the crystallites is below 10 nm and the lattice parameters a and c are larger than those of pure ZnO crystal. Structural investigation showed that the film's crystallinity declines with the iridium concentration and films become completely amorphous at iridium concentrations between 7.0 and 16.0 at.%. An intense Raman band at approximately 720 cm−1 appears upon Ir incorporation and can be ascribed to peroxide O2−1 ions. Measurable electrical conductivity appears together with a complete disappearance of the wurtzite-type ZnO phase. The conduction type undergoes a transition from n- to p-type in the Ir concentration range between 12.4 and 16.4 at.%. Absorption in the visible range increases linearly with the iridium concentration.

Thin Solid Films, Volume 636, 31 August 2017, Pages 694-701.
DOI: 10.1016/j.tsf.2017.05.049
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ABSTRACT: A comparative study of heterostructured CuO/CuWO4 core/shell nanowires and double-layer thin films was performed through X-ray diffraction, confocal micro-Raman spectroscopy and electron (SEM and TEM) microscopies. The heterostructures were produced using a two-step process, starting from a deposition of amorphous WO3 layer on top of CuO nanowires and thin films by reactive DC magnetron sputtering and followed by annealing at 650 °C in air. The second step induced a solid-state reaction between CuO and WO3 oxides through a thermal diffusion process, revealed by SEM-EDX analysis. Morphology evolution of core/shell nanowires and double-layer thin films upon heating was studied by electron (SEM and TEM) microscopies. A formation of CuWO4 phase was confirmed by X-ray diffraction and confocal micro-Raman spectroscopy.

Journal of Crystal Growth, Volume 480, 15 December 2017, Pages 78-84.
DOI: 10.1016/j.jcrysgro.2017.10.011
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ABSTRACT: X-ray diffraction, micro-Raman and the Fourier transform infrared spectroscopies as well as magnetometry measurements were performed on nanosized manganese oxides to probe their phase composition and magnetic properties. It was shown that the XRD method is less sensitive to phase composition of manganese oxide samples than spectroscopic methods. While in some samples the XRD method recognised only the manganosite MnO phase, the Raman and FT-IR methods revealed additionally the presence of the hausmannite Mn3O4 phase.

Acta Phys. Pol. A (2017) 1013-1016.
DOI: 10.12693/APhysPolA.133.1013
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ABSTRACT: Single-phased La0.95Ln0.05InO3 (Ln – Dy, Ho), La0.90Dy0.05Ho0.05InO3, LaInO3 ceramic samples as well as the La0.95Ln0.05In0.98Sb0.02O3 (Ln – Dy, Ho), La0.90Dy0.05Ho0.05In0.98Sb0.02O3, LaIn0.98Sb0.02O3 samples with additional impurity LaSbO3 phase were prepared by solid-state reactions method. Their excitation and photoluminescence (PL) spectra were measured at room temperature. It was established that PL bands intensity of spectra obtained for samples of nominal composition La0.95Dy0.05In0.98Sb0.02O3, La0.95Ho0.05In0.98Sb0.02O3, La0.90Dy0.05Ho0.05In0.98Sb0.02O3 is much higher than that of single-phase La0.95Dy0.05InO3, La0.95Ho0.05InO3, La0.90Dy0.05Ho0.05InO3 solid solutions. It may be probably explained by sensitizing effect of Sb3+ ions on Dy3+, Ho3+ ions photoluminescence. Although it can’t be excluded that the reason could be higher PL of Dy3+ and Ho3+ ions in impurity matrix than in LaInO3-based matrix. It was observed in the PL spectrum of La0.90Dy0.05Ho0.05In0.98Sb0.02O3 sample that under the excitation by λex = 320 nm an intense simultaneous emission of blue, green and yellow light took place.

Journal of Luminescence, Volume 190, October 2017, Pages 298-308.
DOI: 10.1016/j.jlumin.2017.05.064
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ABSTRACT: The proper choice of coating materials and methods in core–shell nanowire (NW) engineering is crucial to assuring improved characteristics or even new functionalities of the resulting composite structures. In this paper, we have reported electron-beam-induced reversible elastic-to-plastic transition in Ag/Al2O3 and Au/Al2O3 NWs prepared by the coating of Ag and Au NWs with Al2O3 by low-temperature atomic layer deposition. The observed phenomenon enabled freezing the bent core–shell NW at any arbitrary curvature below the yield strength of the materials and later restoring its initially straight profile by irradiating the NW with electrons. In addition, we demonstrated that the coating efficiently protects the core material from fracture and plastic yield, allowing it to withstand significantly higher deformations and stresses in comparison to uncoated NW.

Nanotechnology, Volume 28, Number 50 (2017).
DOI: 10.1088/1361-6528/aa973c

ABSTRACT: Development of methods for direct delivery of different bioactive substances into the cell is a promising and intensively approached area of research. It has become a subject of serious research for multidisciplinary team of scientists working in such areas as physics, biology, and biotechnology. Plant calluses were grown on medium supplemented with different nanoparticles to be used as a model for biotechnological research. Gold nanoparticles with mesoporous silica coating were used as hormone carriers, since they possess many of critical properties required for cellular transportation instrument. Some of those properties are great biocompatibility and controlled release of carried molecules. Significant changes in hormones common impact were detected. The great increase in ploidy numbers, embryogenesis, induction, and methylation level was observed when compared to the “conventional” methods of targeted hormones delivery that embrace usage of Au nanoparticles as a main hormone carrier. The authors suppose the research under consideration can provide a new pathway to the design of a novel targeted plant hormone and bioactive substances carrier.

Journal of Nanomaterials, January 2017, 2017(2):1-9.
DOI: 10.1155/2017/7143269
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Institute of Solid State Physics, University of Latvia, Thin Films Laboratory