National Institute Of Materials Physics - Romania

Iron and nitrogen doped TiO2 nanoparticles were synthesized and investigated with the aim to obtain photocatalytic systems with enhanced visible light efficiency. In a first step, commercially available Degussa P25 was impregnated with iron (0.3, 0.5, and 1 at. %) and nitrogen under hydrothermal conditions. In the second step, Fe-N doped TiO2 was synthesized by a hydrothermal route starting with TiCl3, FeCl3 center dot 6H(2)O and Urea, at 200 degrees C for 2 h. All samples were post annealed at 400 degrees C for 2h. The X-ray diffraction (XRD) revealed a two phase nanoscaled composition (Anatase and Rutile) of Degussa P25 and a single phase-nanoscaled Anatase content of the hydrothermally synthesized (1at.%) Fe-N doped TiO2 sample. The presence of Fe and nitrogen in samples was confirmed by Mossbauer and X-ray photoelectron spectroscopy measurements (XPS). Transmission electron microscopy (TEM) revealed the structure, particle dimension and morphology. The photocatalytic measurements (based on degradation of Methylene Blue) evidenced the most efficient composition in TiO2 Degussa P25 series as corresponding to 1 at.% Fe, in both UV and visible spectrum. At the same time, the hydrothermal synthesized sample (1at.%) Fe-N doped TiO2 exhibits the best activity in visible spectral region. The nanoscaled systems were synthesized in view of tests on textile materials.

NiO/mesoporous SnO2 was deposited by incipient wetness impregnation of the SnO2 powder prepared by hydrothermal synthesis route templated by Brij (R) 35. The sensing properties were acquired and the dependence on the operating temperature of the sensitive material was pointed out. Sensitive selectivity towards H2S detection was highlighted at 350 degrees C.

The influence of light illumination on the programming of a capacitor floating gate memory based on Ge nanocrystals in HfO2 was studied. The capacitor was fabricated on a c-Si substrate by magnetron sputtering deposition of a layer sequence of HfO2/Ge-HfO2/HfO2 and post-growth rapid thermal annealing for nanocrystals formation at 600 degrees C. The illumination of the structure was performed through a semi-transparent Au contact (20% transparency). A maximum value of the light- induced change of 90% in C-V curve was obtained for 5 mW/cm(2) illumination during +5 V writing programming. The effect of the light exposure on the relative change of the C-V curve can be increased by reducing the writing time at 1 min.

The electrical and photosensing properties correlated with structure and morphology of TiO2/(GeSi/TiO2)(2) multilayers are investigated. The multilayers are prepared by magnetron sputtering followed by rapid thermal annealing. Studies of Raman spectroscopy, transmission electron microscopy and X-ray diffraction are carried out. Measurements of dark current versus voltage and temperature are done. The photosensing properties are studied by measuring photocurrent spectra at different temperatures. We obtain multilayers with 10 - 15 nm Ge0.6Si0.4 nanocrystals (NCs) by annealing at 800 degrees C. We evidence the tunneling mechanism between neighbor NCs (T-1/2 law) in the dark current-temperature dependence. The photocurrent spectrum has a maximum with position shifting from 940 to 980 nm when the measurement temperature increases from 150 to 300 K, being due to the GeSi NCs.

The specific morphology and magnetic properties of magnetite-based glass-ceramics obtained by crystallization of Fe-containing borosilicate glassmelts in the presence of P2O5 as nucleating agent are investigated. We found that the distribution of the tiny nanoparticles of magnetite determines the low temperature response to magnetic field. The observed effects are discussed with respect to the following factors: (1) the existence of a multimodal size distribution of the tiny grains as revealed by Mossbauer spectroscopy, magnetometry, and high-resolution electron microscopy; (2) the existence of a disordered layer at the grain surface which is driven by field in a magnetically ordered state; and (3) the interplay between the relaxation mechanisms in different temperature ranges.

Single ZnO nanowires prepared by wet and dry methods are used as channels in high performance back-gated field effect transistors working in low power operation mode, with on-off ratios up to 10(5) and mobilities up to 167 cm(2) V-1 s(-1). The nanowires' properties, generated by the growth techniques, influence the parameters of the transistors, therefore a throughout comparison is made.

Thermal behavior of repa-germanium (C6H10Ge2O7, Ge-132) during heating in air or in argon is investigated using DSC-TGA, XRD, SEM,TEM, and FT-IR measurements. Nine domains of thermal transformations were identified from room temperature to 1200 degrees C, in air or argon. The first reversible transformation is below 220 degrees C and it was assigned to an isomerization process, based on DSC, XRD and IR measurements. The next five transformation domains (220-910 degrees C) are decompositions accompanied by weight loss. The main product of thermal decomposition is Ge. The next transformation domain (910-970 degrees C) corresponds to melting of Ge, both in argon and air. In the air, this step is followed by oxidation of Ge (970-1100 degrees C) and, finally, by melting of GeO2. Amorphous phases formed between 220 and 720 degrees C. Observed processes are discussed based on crystal chemistry and bonds dynamics considerations. (C) 2016 Elsevier B.V. All rights reserved.

Vapor transport growth of atomically thin MoS2 layers on patterned substrates is investigated, as it is a step towards the self-aligned growth and formation of heterojunctions, which could be useful in future applications. Enhanced formation of MoS2 flakes at the pattern edges is observed on both the substrates examined, namely, patterned thermal SiO2 on Si(100) and graphene flakes on SiO2. The diffusion driven growth leads to the formation of MoS2 monolayers (MLs) with sizes of tens of micrometers around the edges of SiO2 patterns. The growth mode and the optical quality of the MoS2 flakes can be controlled by varying the substrate temperature. Besides the lateral growth, 3R-type pyramids are obtained on prolonging the growth. Lateral MoS2-graphene heterostructures are obtained by using graphene flakes on SiO2 as a substrate.

The development of innovative technologies to modify natural textiles holds an important impact for medical applications, including the prevention of contamination with microorganisms, particularly in the hospital environment. In our study, Fe and N co-doped TiO2 nanoparticles have been obtained via the hydrothermal route, at moderate temperature, followed by short thermal annealing at 400 degrees C. These particles were used to impregnate polyester (PES) materials which have been evaluated for their morphology, photocatalytic performance, antimicrobial activity against bacterial reference strains, and in vitro biocompatibility on human skin fibroblasts. Microscopic examination and quantitative assays have been used to evaluate the cellular morphology and viability, cell membrane integrity, and inflammatory response. All treated PES materials specifically inhibited the growth of Gram-negative bacilli strains after 15 min of contact, being particularly active against Pseudomonas aeruginosa. PES fabrics treated with photocatalysts did not affect cell membrane integrity nor induce inflammatory processes, proving good biocompatibility. These results demonstrate that the treatment of PES materials with TiO2-1% Fe-N particles could provide novel biocompatible fabrics with short term protection against microbial colonization, demonstrating their potential for the development of innovative textiles that could be used in biomedical applications for preventing patients' accidental contamination with microorganisms from the hospital environment.

Disordered Sm3+ doped Y3ScxAl5-xO12 (Sm:YS(x)AG) polycrystalline ceramics with compositional parameter x = (0.05, 0.5, 1, 2) and different Sm3+ ions concentrations were obtained by solid state reaction method. XRD investigations show the linear increase of the lattice constant with compositional parameters x. New spectroscopic data obtained from high resolution optical absorption and emission spectra of Sm3+ doped YS(x)AG ceramics reveal composition effects on Sm3+ optical spectra: modification of the shapes and shifts of the lines, presence of the additional satellites and unresolved multicenter structure, etc. The analysis of these data allowed us to establish a partial structure of Sm3+ energy levels in Sm:YS(x)AG (x = 2) ceramics. The emission kinetics of the (4)G(5/2) level for different Sm3+ concentrations and Sc content in Sm:YS(x)AG were measured and analyzed. (C) 2016 Elsevier B.V. All rights reserved.