CERCETĂRI XRD ȘI XPS ALE STRATURILOR DE AlN, AlGaN, GaN DEPUSE PE SILICIU PRIN METODA HVPE

Prin metoda reacțiilor chimice de transport HVPE (Hydride Vapor Phase Epitaxy) in sistemul (H2-NH3-HCl-Al-Ga-Si) au fost sintetizate straturi subțiri de AlN, AlGaN, GaN pe substraturi de siliciu, Si(111). Morfologia suprafeței, precum și a secțiunilor transversale ale structurilor a fost cercetată prin metoda SEM (Scanning Electron Microscopy) de rezoluție înaltă. Compoziția în secțiune transversală a structurilor a fost studiată prin metoda XRD (X-Ray Diffraction method), iar de suprafață – prin metoda XPS (X-Ray Photoelectronic Spectroscopy). Afară de aluminiu, galiu și azot în straturi au fost depistate oxigen și carbon. S-a stabilit că concentrația oxigenului pe suprafața straturilor de GaN, depuse la temperaturi relativ mai joase, este mai mică. Se presupune că concentrația ridicată a oxigenului în straturi are loc în urma descompunerii cuarțului, din care este confecționat reactorul, la temperaturi ridicate. S-a constatat că încorporarea galiului în straturile de AlGaN este diminuată de fluxul precursorilor aluminiului. Prin aceasta se demonstrează că viteza reacțiilor chimice ale precursorilor azotului cu ale aluminiului este semnificativ mai mare decât cu ale galiului, ultimele fiind înlăturate din zona de depunere de fluxul gazului de transport.XRD AND XPS INVESTIGATIONS OF THE AlN, AlGaN, GaN LAYERS DEPOSITED ON SILICON BY THE HVPE METHODUsing the HVPE (Hydride Vapor Phase Epitaxy) transport method, in system (H2-NH3-HCl-Al-Ga-Si), thin layers of AlN, AlGaN, GaN on silicon substrates were synthesized. Surface morphology as well as transverse sections of structures was investigated by the high resolution SEM (Scanning Electron Microscopy) method. The cross-sectional composition of the structures was studied by the X-Ray Diffraction Method (XRD) and Surface X-Ray (X-Ray Photoelectronic Spectroscopy). Outside of aluminum, gallium and nitrogen in the layers were detected oxygen and carbon. It has been established that the concentration of oxygen on the surface of the GaN layers deposited at relatively lower temperatures is lower. It is assumed that the high concentration of oxygen in the layers takes place after the decomposition of the quartz, from which the reactor is made, at high temperatures. It has been found that the incorporation of gallium into the AlGaN layers is diminished by the flux of aluminum precursors. This demonstrates that the rate of chemical reactions of the nitrogen precursors with the aluminum is significantly higher than with the latter being removed from the deposition area by the transport gas stream.</p

Aqueous medium-induced micropore formation in plasma polymerized polystyrene: an effective route to inhibit bacteria adhesion

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Surface Wettability of ZnO-Loaded TiO2 Nanotube Array Layers

Herein we report on the synthesis and the effects of gradual loading of TiO2 nanotube array layers with ZnO upon surface wettability. Two-step preparation was chosen, where TiO2 nanotube layers, grown in a first instance by anodization of a Ti foil, were gradually loaded with controlled amounts of ZnO using the reactive RF magnetron sputtering. After crystallization annealing, the formerly amorphous TiO2 nanotubes were converted to predominantly anatase crystalline phase, as detected by XRD measurements. The as-prepared nanotubes exhibited a well-aligned columnar structure, 1.6 μm long and 88 nm in diameter, and a small concentration of oxygen vacancies. Ti2+ and Ti3+ occur along with the Ti4+ state upon sputter-cleaning the layer surfaces from contaminants. The Ti2+ and Ti3+ signals diminish with gradual ZnO loading. As demonstrated by the VB-XPS data, the ZnO loading is accompanied by a slight narrowing of the band gap of the materials. A combined effect of material modification and surface roughness was taken into consideration to explain the evolution of surface super-hydrophilicity of the materials under UV irradiation. The loading process resulted in increasing surface wettability with approx. 33%, and in a drastic extension of activation decay, which clearly points out to the effect of ZnO-TiO2 heterojunctions

On the Electrical and Optical Properties Stability of P3HT Thin Films Sensitized with Nitromethane Ferric Chloride Solutions

The electrical and optical properties stability of poly(3-hexylthiophene) (P3HT) thin films sensitized with nitromethane ferric chloride (FeCl3) solution was investigated. The optical properties modifications were studied by spectrophotometry and ellipsometry. For electrical characterizations, electrical resistivity measurements were performed. In agreement with the observations of other authors, an important decrease in the electrical resistivity by six orders of magnitude was noticed. In addition, the repeatability and stability of this phenomenon were investigated over a few weeks after sensitization and during different cycles of heating and cooling, both in the dark and under illumination

Porous-Wall Titania Nanotube Array Layers: Preparation and Photocatalytic Response

Electrochemical anodization is already a well-established process, owing to its multiple benefits for creating high-grade titanium dioxide nanotubes with suitable characteristics and tunable shapes. Nevertheless, more research is necessary to fully comprehend the basic phenomena at the anode-electrolyte interface during anodization. In a recent paper, we proposed the use of sawtooth-shaped voltage pulses for Ti anodization, which controls the pivoting point of the balance between the two processes that compete to create nanotubes during a self-organization process: oxide etching and oxidation. Under these conditions, pulsed anodization clearly reveals the history of nanotube growth as recorded in the nanotube morphology. We show that by selecting the suitable electrolyte and electrical discharge settings, a nanoporous structure may be generated as a repeating pattern along the nanotube wall axis. We report the findings in terms of nanotube morphology, crystallinity, surface chemistry, photocatalytic activity, and surface hydrophilicity as they relate to the electrical parameters of electrochemical anodization. Aside from their fundamental relevance, our findings could lead to the development of a novel form of TiO2 nanotube array layer

Revealing the Effect of Synthesis Conditions on the Structural, Optical, and Antibacterial Properties of Cerium Oxide Nanoparticles

Cerium oxide nanoparticles were prepared by a precipitation method using Ce(IV) sulphate as precursor dispersed in glycerol with varying synthesis parameters such as temperature or precipitating agent. The structural and morphological characteristics of the obtained nanoparticles were investigated by X-ray diffraction, transmission electron microscopy, and diffuse reflectance spectroscopy. The crystallite size of the nanoparticles varied between 13 and 17 nm. The presence of Ce3+ and Ce4+ was proved by XPS data in the CeO2 samples and the conservation of the fluorite structure was evinced by X-ray diffractograms with a contraction of the lattice parameter, regardless of the size of the nanoparticle. From diffuse reflectance spectra, two band gap energy values for the direct transition were observed. Depending on the synthesis condition, the red shift of gap energy and the blue shift of Urbach energy with increasing content of Ce3+ were ascertained. The antibacterial tests revealed that the cerium oxide nanoparticles show good antimicrobial activity towards the common pathogens Escherichia coli and Staphylococcus aureus

Surface wettability of titania thin films with increasing Nb content Surface wettability of titania thin films with increasing Nb content

Multi-scale order in amorphous transparent oxide thin films J. Appl. Phys. 112, 054907 (2012) Growth of continuous and ultrathin platinum films on tungsten adhesion layers using atomic layer deposition techniques Appl. Phys. Lett. 101, 111601 (2012) Effect of tip polarity on Kelvin probe force microscopy images of thin insulator CaF2 films on Si(111) Appl. Phys. Lett. 101, 083119 (2012) Epitaxial growth and metal-insulator transition of vanadium oxide thin films with controllable phases Appl. Phys. Lett. 101, 071902 (2012) Additional information on J. Appl. Phys. TiO 2 and TiO 2 /Nb amorphous thin films were grown on glass substrates by a sol-gel technique (spin coating). Films&apos; surface composition, structure, and morphology were derived from x-ray photoelectron spectroscopy, x-ray diffraction, and atomic force microscopy data. The investigated films showed a smooth surface (roughness values below 5 nm). A separate surface wettability investigation showed that by increasing the Nb amount in pristine titania films results in a decrease of contact angle (CA) values from 40 to nearly 0 , thus, indicating a super-hydrophilic conversion under UV illumination. This conversion rate is greatly enhanced by increasing the Nb content, the surface super-hydrophilic behavior occurring after a couple of minutes in the TiO 2 /Nb samples, but after 4 h in the pristine titania specimen. The current results are discussed in terms of the optical band gap shift towards higher energies, by increasing the Nb content in the films, a process explained based on small polaron hopping model. V C 2012 American Institute of Physics

Matching the Cellulose/Silica Films Surface Properties for Design of Biomaterials That Modulate Extracellular Matrix

The surface properties of composite films are important to know for many applications from the industrial domain to the medical domain. The physical and chemical characteristics of film/membrane surfaces are totally different from those of the bulk due to the surface segregation of the low surface energy components. Thus, the surfaces of cellulose acetate/silica composite films are analyzed in order to obtain information on the morphology, topography and wettability through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle investigations. The studied composite films present different surface properties depending on the tetraethyl orthosilicate (TEOS) content from the casting solutions. Up to a content of 1.5 wt.% TEOS, the surface roughness and hydrophobicity increase, after which there is a decrease in these parameters. This behavior suggests that up to a critical amount of TEOS, the results are influenced by the morphology and topographical features, after which a major role seems to be played by surface chemistry&mdash;increasing the oxygenation surfaces. The morphological and chemical details and also the hydrophobicity/hydrophilicity characteristics are discussed in the attempt to design biological surfaces with optimal wettability properties and possibility of application in tissue engineering

Matching the Cellulose/Silica Films Surface Properties for Design of Biomaterials That Modulate Extracellular Matrix

The surface properties of composite films are important to know for many applications from the industrial domain to the medical domain. The physical and chemical characteristics of film/membrane surfaces are totally different from those of the bulk due to the surface segregation of the low surface energy components. Thus, the surfaces of cellulose acetate/silica composite films are analyzed in order to obtain information on the morphology, topography and wettability through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle investigations. The studied composite films present different surface properties depending on the tetraethyl orthosilicate (TEOS) content from the casting solutions. Up to a content of 1.5 wt.% TEOS, the surface roughness and hydrophobicity increase, after which there is a decrease in these parameters. This behavior suggests that up to a critical amount of TEOS, the results are influenced by the morphology and topographical features, after which a major role seems to be played by surface chemistry—increasing the oxygenation surfaces. The morphological and chemical details and also the hydrophobicity/hydrophilicity characteristics are discussed in the attempt to design biological surfaces with optimal wettability properties and possibility of application in tissue engineering