National Institute Of Materials Physics - Romania

The charge storage properties of Ge nanocrystals-based MOS-like capacitors with tunnel and gate HfO2 are studied. HfO2/Ge/HfO2/Si trilayer structures were prepared by magnetron sputtering (in Ar) and subsequent rapid thermal annealing (650 degrees C). HfO2/Si structures were also prepared, some under similar conditions, while others were deposited in Ar:O-2. TEM investigations and C-V measurements were performed. TEM on annealed trilayers evidences the formation of ordered and precisely positioned array of Ge nanocrystals embedded in crystalline HfO2. The annealed Al/HfO2/Ge/HfO2/p-Si/Al capacitors present counterclockwise C-V hysteresis (0.8 V memory window) mainly given by Ge nanocrystals, with negligible contribution from crystallized-HfO2 traps.

One of the most fundamental aspects of the heterogeneous catalysis field is the manipulation of the catalysts' activity. In photocatalysis this is carried out by maximizing the right crystal plane of a semiconductor oxide. Until now, most of the papers have achieved this by a combination of different oxides, with noble metals and sometimes with carbon nanomaterials. In this work MWCNTs (multiwalled carbon nanotubes) were applied as "crystallization promoters" in a very simple, safe, one-step hydrothermal method. By this method TiO2 nano/micro crystals with exposed {001} facets were obtained in the first step. The next episode in the crystal manipulation "saga" was the modification of the (001) crystallographic plane's structure by creating ordered/own faceted "crystallographic holes". These elements are capable of further enhancing the obtained activity of titania microcrystals to a higher extent, as shown by the UV driven photocatalytic phenol degradation experiments. The appearance of the holes was "provoked" by simple calcination and their presence and influence were demonstrated by XPS and HRTEM.

Ge and Si nanocrystals (NCs), quantum dots (QDs), and amorphous nanoparticles (NPs) have a significant role in the developement of micro- and nanoelectronic devices due to capability to tune their electrical and photoconductive properties by tailoring the morphology and structure parameters. Ge and Si NCs/QDs/NPs are zero-dimensional (0D) systems and the SiO2 films containing them are percolative systems. In this review, the role of deposition and annealing conditions in the morphology and structure of Ge and Si NCs/QDs/NPs embedded in amorphous SiO2 matrix is discussed for a wide variety of films and multilayered structures. The electrical and photoconductive properties of nanostructures deposited by different techniques as magnetron sputtering, ion implantation, chemical vapour deposition, sol-gel and molecular beam epitaxy, and subsequently annealed in conventional furnace or by rapid thermal annealing under different conditions are analised. We demonstrate how the electrical and photoconductive properties of nanostructures can be tuned by varying the deposition and annealing parameters. The role of Si-rich oxide and defects in the formation of Ge and Si NCs is shown and the role of defects in improving electrical properties and enhancing the photoconductivity of films and multilayered structures is highlighted. We evidence the contribution of quantum confinement effect and show that the most probable transport mechanisms in these percolative systems are tunnelling and hopping.

The most widely occurring collagen in the extracellular matrix of the mammalian tissues - type I collagen has attracted huge interest from both theoretical and practical points of view. The results presented herein are mainly confined to a study of the thermal stability of type I collagen (CI) extracted from calfskin in acidic solutions (10(-2) M HCl). A two-step process associated with the heat-induced denaturation of CI was revealed by using ultra sensitive differential scanning calorimetry. The minor endothermic transition (peak temperatures of about 30.5-30.8 degrees C) has been assigned to the defibrillation of small supramolecular CI assemblies (occurring in solution) while the major endothermic transition (about 34.8-35.0 degrees C) has been ascribed to denaturation of CI, consisting of a complete unfolding of the native triple-helical conformation of the collagen molecule. The calorimetric data were supported by information obtained from capillary viscometry performed on the same solutions. The native state of CI (molecular integrity and triple-helical conformation) for all the systems studied in this paper was confirmed by transmission electron microscopy, ultraviolet circular dichroism and capillary viscometry. At the same time, based on the sodium dodecyl sulphate-polyacrylamide gel electrophoresis and an appropriate image processing of the corresponding electropherogram, a certain degree of intramolecular crosslinking of CI was detected, mainly between alpha 1 and alpha 2 chains of the collagen triple-helix. Such a feature seems to be caused by both the nature of the extraction procedure and the storage conditions.

We analyse the influence of the strain field on the parameters of trapping centres. The system under study is high resistivity Si implanted with Bi6+ and I6+ ions respectively, of 28 MeV kinetic energy, 3(O) off <100> axis orientation and 5x10(11) ions/cm(2) fluence. The strain field is the consequence of size and mass difference of the irradiation ions in respect to the atoms of the lattice, and the defects are produced during the slowing-down of ions, as a result of the energy transfer from the ion to Si atoms. These results are of interest for the design and manufacturing of microelectronic devices incorporating strain, particularly for quantum computers with qubits based on the interaction of electronic and nuclear spins of group-V donors in Si.

Water splitting by means of semiconducting photoelectrodes and solar light represents a promising alternative to conventional fossil fuel economy. In this process the photoactive electrode absorb sunlight directly thus initiating the photochemical reaction which create excess electrons in the conduction band of the semiconducting electrode. Titanium doped iron oxide seems to be a promising semiconducting material for photoelectrodes. Consequently, we investigated the effect of Ti doping on the structure, electrical and photoelectrochemical properties alpha-Fe2O3. The Ti doped alpha-Fe2O3 were prepared by a slightly modified mixed oxide route, consisting in a prolonged mixing of the raw materials in a high energy planetary ball mill until the particles decreased to the nanometric sizes. Optimum results were obtained for samples doped with 5 at. % titanium and sintered at 1200 degrees C. Photocurrents as high as 8.4 mA/cm(2), for illumination from a 300 W xenon lamp, were recorded for such samples. It is hoped that such photoelectrodes show promise for water splitting.

Silver azide is a primary high explosive that can be initiated by different means. In this work, silver azide nanoparticles were obtained, embedded into silica, and further derivatized with biotin. TEM, DLS, and IR measurements were used to characterize the hybrid energetic nanoparticles. The hybrid nanoparticles are made from an explosive core (silver azide) and a shell (silica), to which has been attached through an organic linker a biological target vectot (biotin). These hybrid nanoparticles can be used as models to study smart energetic nano-materials

Heterostructures with layers from small molecules organic compounds were deposited on ITO/glass substrate by thermal vacuum evaporation (TVE) technique. Structural, optical and morphological investigations were carried out on the realised layers (zinc phthalocyanine-ZnPc, fullerene-C60 and 1,4,5,8-naphthalene-tetracarboxylic dianhydride-NTCDA). The films are polycrystalline keeping the morphological features characteristic to these materials. The prepared heterostructures reveal a large absorption domain in the visible domain. The current-voltage (I-V) characteristics of the investigated structures, recorded in dark, present an improvement in the current value (similar to one order of magnitude) for the standard structure (ITO/PEDOT: PSS/ZnPc/C60/NTCDA/Al) with a supplimentary layer of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). For the inverted structure (Al/NTCDA/C60/ZnPc/ITO) was also noticed an increased curent value in comparasion with that observed for the standard structure.

A family of mesoporous, self-aggregated zinc oxide materials with spherical morphologies of high crystalline quality, is obtained through a facile, additive-free polyol procedure. The forced hydrolysis of zinc acetylacetonate in 1,4-butanediol (BD), in various reaction conditions, affords ZnO materials with versatile morphologies and optical properties. The reaction parameters (temperature, time and zinc source concentration) modulate the ZnO nanocrystallites size (from 8.1 to 13.2 nm), the spheres diameter (ranging from 50 up to 250 nm), the internal structure of the spherical aggregates (hollow or solid) and their specific surface area (from 31 to 92 m(2) g(-1)). Polycrystalline spheres with hollow cores are obtained at the lowest temperature (90 degrees C) and zinc cation concentration (0.1 M), while at higher reaction temperatures (140-180 degrees C), solid spherical aggregates are developed. A reaction mechanism for ZnO formation via zinc layered hydroxide (LDH-Zn) is proposed based on nuclear magnetic resonance (H-1 NMR and C-13 NMR) and powder X-ray diffraction (XRD) studies. The obtained ZnO materials have a functionalized surface, derived from the polyol and act as a nitrogen selective photocatalyst in the reduction reaction of NO3-. The organic residual attached on the ZnO surface plays a crucial role in the denitrification reaction, since the photo-cleaned sample showed negligible photocatalytic activity. The ZnO materials also exhibited microbicidal and anti-biofilm activity against reference and clinical strains, highlighting their potential for the development of novel antimicrobial formulations.

The effects of strain field are studied in Si wafers implanted with heavy iodine and bismuth ions and in multi-quantum well structures. The experimental method of thermally stimulated currents without applied bias is used, and the trapping centres parameters are determined by modelling the discharge curves. In both cases, the strain field produces temperature-dependent parameters of trapping levels. So, due to the high strain field in the neighbourhood of implanted ions, energy levels broaden and cross sections become temperature dependent. In multilayer structures, for the trapping centres corresponding to strain-induced defects both concentrations and capture cross sections are temperature dependent.