Nanostructured titanium-dioxide thin films for environmental applications

Titanium-dioxide nanostructures and thin films are interesting for application in environmental protection, for water and air purification from toxic compounds, and photocatalytic degradation of water, where separation of H2 is important for the development of new energy sources. Furthermore, they are interesting for fabrication of solar cells, various sensor applications, transparent conducting oxides (TCO), etc [1-3]. Stoichiometric TiO2 phase has a wide optoelectronic band gap of ~3.2 eV, which makes it a dielectric at lower temperatures and a semiconductor at higher temperatures. It has a high absorption coefficient in the range of UV radiation, but low in the visible light region, and this makes significant constrains for its usage as a photocatalyst. For reducing energy gap, better absorption in visible light region and more efficient application it is necessary to add doping material species, which can be metal or non-metal ions.When used as a photocatalyst in form of a powder, TiO2 nanoparticles are embedded in photosensitizing dyes which absorb visible light, or they are partly covered with nanoparticles of some transition metal to enhance injection of charge carriers. Recent developments involve the use of physical vapor deposition (vacuum evaporation or ion sputtering) to synthesize TiO2 thin film structures, and ion implantation for their doping. The advantage of using physical vapor deposition is that the Ti:O ratio can be varied, and the films can be deposited on any supporting or large area substrates. On the other hand, ion implantation is a proven technique for introducing dopant atomic species into the crystal lattice of semiconductor materials. In these experiments TiO2 thin films were synthesized by physical vapor deposition (PVD) method, using three different procedures: (i) reactive d.c. ion sputtering of pure Ti target, using Ar ions and introducing O2 in the deposition chamber; (ii) r.f. sputtering of TiO2 target, using Ar + O2 gas mixture; and (iii) reactive e-beam evaporation of pure Ti in the presence of introduced O2 . In case of reactive d.c. ion sputtering additional experiments involved a controlled introduction of nitrogen in the interaction chamber, which yielded doping of the deposited TiO2 thin films, in reducing their band gap and enhancing absorption of visible light. The films were deposited to a thickness of a few hundred nm on silicon wafers and glass slide substrates. Structural and compositional characterization of samples included X-ray diffraction analysis (XRD), transmission electron microscopy (TEM, HRTEM), Rutherford backscattering spectrometry (RBS), and X-ray photoelectron spectroscopy (XPS). Optical characterizations were done by measuringthe transmission and diffuse reflection UV/VIS spectra. Photocatalytic activity was measured by determining the photodegradation rate of organic solutions Structural characterization revealed that as-deposited samples grow in form of a mixture of very fine nanocrystalline grains of rutile and anatase TiO2 phases and TiO. Hence, in order to homogenize the TiO2 stoichiometry andinduce the growth of larger grains it was necessary to anneal the samples in air, at temperatures of 400 and 600 o C [4]. This procedure was performed on all samples after deposition. Bright-field cross-sectional images taken from two different TiO2 films deposited on Si wafers are shown in Fig. 1. Sharp contrast regions within the films indicate their polycrystalline structure. The results of investigations showed that it is possible to tailor the structure and properties of the obtained TiO2 thin films by adjusting the processing parameters.8th Symposium Chemistry and Environmental Protection : May 30 - June 1, Kruševac, 2018

Comparative Analysis of Different Methods for Graphene Nanoribbon Synthesis

Graphene nanoribbons (GNRs) are thin strips of graphene that have captured the interest of scientists due to their unique structure and promising applications in electronics. This paper presents the results of a comparative analysis of morphological properties of graphene nanoribbons synthesized by different methods. Various methods have been reported for graphene nanoribons synthesis. Lithography methods usually include electron-beam (e-beam) lithography, atomic force microscopy (AFM) lithography, and scanning tunnelling microscopy (STM) lithography. Sonochemical and chemical methods exist as well, namely chemical vapour deposition (CVD) and anisotropic etching. Graphene nanoribbons can also be fabricated from unzipping carbon nanotubes (CNTs). We propose a new highly efficient method for graphene nanoribbons production by gamma irradiation of graphene dispersed in cyclopentanone (CPO). Surface morphology of graphene nanoribbons was visualized with atomic force and transmission electron microscopy. It was determined that dimensions of graphene nanoribbons are inversely proportional to applied gamma irradiation dose. It was established that the narrowest nanoribbons were 10-20 nm wide and 1 nm high with regular and smooth edges. In comparison to other synthesis methods, dimensions of graphene nanoribbons synthesized by gamma irradiation are slightly larger, but the yield of nanoribbons is much higher. Fourier transform infrared spectroscopy was used for structural analysis of graphene nanoribbons. Results of photoluminescence spectroscopy revealed for the first time that synthesized nanoribbons showed photoluminescence in the blue region of visible light in contrast to graphene nanoribbons synthesized by other methods. Based on disclosed facts, we believe that our synthesis method has good prospects for potential future mass production of graphene nanoribbons with uniform size, as well as for future investigations of carbon nanomaterials for applications in optoelectronics and biological labeling

Effects of the Ar ions pre-amorphization of Si substrateon interface mixing of Fe/Si bilayers

Ion beam mixing of Fe/Si bilayers, induced by 100 keV (40)Arions at room temperature was investigated. Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied for structural characterization. The main focus of this study was on the influence of the substrate structure on interface mixing. The influence of the substrate structure is due to the two classes of irradiated bilayers, Fe thin films deposited on crystalline or pre-amorphized Si substrates. An about 76% higher efficiency of atomic transport across the pre-amorphized Fe/a-Si interface as compared to that of Fe/c-Si bilayers was observed

Prophylactic anti-heparanase activity by PG545 is anti-viraland protects against Ross River virus disease in mice

Recently we reported on the efficacy of pentosan polysulfate (PPS), a heparan sulfate mimetic, to reduce the recruitment of inflammatory infiltrates and protect the cartilage matrix from degradation in Ross River virus (RRV) infected PPS--treated mice. Herein, we describe both prophylactic and therapeutic treatment with PG545, a low molecular weight heparan sulfate mimetic, for arthritogenic alphaviral infection. We first assessed anti-viral activity, through a 50% plaque reduction (IC) assay. Increasing concentrations of PG545, inhibited plaque formation prior to viral adsorption in viral strains; RRV T48, Barmah forest virus 2193 (BFV 2193), chikungunya East/Central/South African virus (CHIKV ESCA) and CHIKV Asian strain, suggesting a strong anti-viral mode of action. The viral particle--compound dissociation constant (K) was then evaluated through isothermal titration calorimetry (ITC). Furthermore, prophylactic RRV-infected PG545-treated mice had reduced viral titres in target organs corresponding to lower clinical scores of limb weakness and immune infiltrate recruitment. At peak disease, PG545-treated RRV-infected mice had lower concentrations of the matrix degrading enzyme heparanase (HPSE) in conjunction with a protective effect on tissue morphology as seen in the histopathology of skeletal muscle. ELISA quantification of cartilage oligomeric matrix protein (COMP) and crosslinked C-telopeptides of type II collagen (CTX-II) and knee histopathology showed increased matrix protein degradation and cartilage erosion in RRV-infected PBS-treated mice in comparison to their PG545-treated RRV infected counterparts. Taken together these findings suggest that PG545 may have a both a direct anti-viral effect on arthritogenic alphaviral infection, as well curtailing RRV-induced inflammatory disease when administered as a prophylaxis

Facile synthesis of water-soluble curcumin nanocrystals

In this paper, a facile synthesis of water-soluble curcumin nanocrystals is reported. Solvent exchange method was applied to synthesize curcumin nanocrystals. Different techniques were used to characterize the structural and photophysical properties of the curcumin nanocrystals. It was found that the nanocurcumin prepared by this method had good chemical and physical stability, could be stored in the powder form at room temperature, and was freely dispersible in water. It was established that the size of curcumin nanocrystals varied in the range of 20-500 nm. Fourier transform infrared spectroscopy and UV-Vis analyses showed the presence of tetrahydrofuran inside the curcumin nanocrystals. Furthermore, it was found that the nanocurcumin emitted photoluminescence with a yellow green color

hiResilient response and performance of bitumen stabilized materials with foam incorporating reclaimed asphalt

Thesis (PhD)--Stellenbosch University, 2014.ENGLISH ABSTRACT: The increased use of reclaimed asphalt (RA) in Bitumen Stabilised Materials (BSMs), shortcomings in the existing design guidelines and manuals and ongoing developments in the concepts and understanding of these materials require further research into the fundamental properties and behaviour of BSMs. The state-of-the-art of foamed bitumen techniques is reviewed in the literature study. Current best practices in the design of BSMs and pavements incorporating such materials are also included in this literature study. Shortcomings and areas for further improvement of the design practice have been identified. With new environmental legislation, the importance of BSM technology including RA as an environmentally-friendlier and more sustainable construction technique is set to increase in the coming years. Changes in the behaviour of materials and failure mechanisms of BSM mixes are long-term phenomena. This implies that the study of the physico-chemical and mechanical properties of the mixes with increasing amount of RA is vital. Therefore, fundamental understandings of moisture damage and thermo-physical characteristics, which are related to material properties, are required. The main objective of this study is to advance BSM technology by assessing the influence of the selected materials on durability behaviour, temperature distribution and long-term performance in all phases of application (i.e. mix design, construction, and in-service condition). This study begins with a comprehensive literature review of research dealing with the interactions between RA and mineral aggregates. The properties of RA and mineral aggregates were reviewed. This was followed by a review into the mechanical properties of BSM-foam mixes with high percentage of RA and its durability performance. Factors influencing the temperature gradient of BSMs were then identified. Achieving a better understanding of the fundamental performance properties and temperature influence on the behaviour of BSMs with high percentage of RA is one of the key factors of this research, with a view to using the extended knowledge for improvements to current mix design and structural design practices. Finally, the fundamental theories on thermo-conductivity and the mechanical properties of the BSM were used to create a relationship between temperature and mechanical properties in a pavement section. A laboratory testing programme was set up to study the properties and behaviour of BSMs and to establish links with the compositional factors, i.e. the type of binder used, the percentage of RA in the mix and the addition of a small amount of cement as active filler. BSMs were blended in three different proportions of RA and good quality crushed stone materials: 100% RA (with 2 % bitumen content), 50% RA and 50% G2 Hornfels crushed stone (with 2.1% bitumen content) and 100% G2 (with 2.3 % bitumen content). Tri-axial testing was carried out to determine shear parameters, resilient modulus and permanent deformation behaviour, while brushing testing was carried out to determine the possible durability performance of the BSMs. The mixture durability in terms of moisture damage was investigated. Temperature data were collected and a model to accurately simulate the temperature distribution in the BSMs was identified and proposed for further investigation and validation. It was found from the laboratory temperature data collected in this study that the temperature gradient varied according to the depth of the BSMs. A considerable part of the efforts of this study were dedicated to characterise and model the temperature distribution in a pavement section, taking into account the mechanical properties and performance of the BSMs at different temperature layers. The study provides an insight into fundamental mechanical performance, material durability properties, and the thermal capacity and conductivity of the BSM-foam mixes with high percentage of RA. This will assist in improving the current procedure for selection, combining and formulation of the mix matrices for BSMs. In addition, the study provides guidelines that will enable practitioners to confidently understand the relationship between temperature gradient and mechanical behaviours of BSM-foam pavement section. The specific durability-related issues addressed in this study are substance for future research.AFRIKAANSE OPSOMMING: Die toenemende gebruik van herwonne asfalt (Engels: reclaimed asphalt (RA)) in bitumen gestabiliseerde materiaal (Engels: Bitumen Stabilised Materials (BSMs)), tekortkominge in die bestaande ontwerpriglyne- en handleidings en deurlopende verbeteringe in die konsepte en begrip van hierdie material vereis verdere navorsing oor die fundamentele eienskappe en gedrag van BSM. In die literatuurstudie word die huidige stand van kennis van die ontwerp van skuimbitumentegnieke ondersoek. Die literatuurstudie dek ook die huidige beste praktyke in die ontwerp van BSM en plaveisels wat hierdie materiale insluit. Tekortkominge en areas van verdere verbetering in die ontwerppraktyke is geïdentifiseer. Onlangse omgewingswetgewing verhoog die belangrikheid van BSM tegnologie, insluitend RA, as ‘n meer omgewingsvriendelike en volhoubare konstruksie-tegniek. Hierdie faktor sal in die toekoms al hoe belangriker word. Die verandering in die gedrag van materiaal en die falingsmeganismes van BSM mengsels is langtermynverskynsels. Dit impliseer dat die studie van die fisio-chemiese en meganiese eienskappe van mengsels met toenemende verhoudings van RA van kardinale belang is’n Fundamentele begrip van die vogskade en temo-fisiese eienskappe, wat verwant is aan die materiale se eienskappe, word vereis. Die primêre doelwit van die studie is die bevordering van BSM tegnologie deur die invloed van die geselekteerde materiale op duursaamheid, temperatuurverspreiding en langtermyn gedrag in al die fases van toepassing (mengselontwerp, konstruksie en in-dienstoestand) te bepaal. Die verhandeling begin met ‘n omvattende literatuuroorsig van navorsing oor die interaksie tussen RA en mineraalaggregate. Die eienskappe van RA en die mineraalaggregate word bespreek. Dit word gevolg deur ‘n oorsig van die meganiese eienskappe van die BSM-skuimbitumenmengsels met ‘n hoë persentasie RA en die duursaamheidgedrag daarvan. Faktore wat die temperatuurgradient van BSM beïnvloed word dan aangetoon. ‘n Beter begrip van die fundamentele gedragseienskappe en die invloed van temperatuur op die gedrag van BSM met ‘n hoë persentasie RA is een van die sleutelfaktore van hierdie navorsing. Dit het ten doel om die uitgebreide kennis te gebruik om huidige mengselontwerp en strukturele ontwerppraktyke te verbeter. Laastens is die fundamentele teorie van termogeleiding en die meganiese eienskappe van BSM gebruik om ‘n verhouding tussen temperature en meganiese eienskappe in ‘n plaveiselsnit te ontwikkel. ‘n Laboratoriumtoetsprogram is opgestel om die eienskappe en gedrag van BSM te bestudeer en om verwantskappe tussen samestellende faktore soos die tipe bindmiddel gebruik, die persentasie RA in die mengsel en die toediening van klein hoeveelhede sement as aktiewe vuller te bepaal. BSM is in drie verskillende verhoudings van RA en goeie gehalte gebreekte klipmateriaal vermeng: 100% RA met 2 % bitumen, 50% RA en 50 % G2 Hornfels gebreekte klip met 2.1 % bitumen en 100% G2 met 2.3 % bitumen. Drie-assige druktoetse is gebruik om skuifsterkteparameters, elastiese modulus en permanente vervormingsgedrag te bepaal. Borseltoetse is gebruik om die duursaamheidgedrag van BSM te bepaal. Die mengsels se duursaamheid is ook in terme van vogskade ondersoek

Characterization of as implanted silicides by frequency noise level measurements

Silicides belong to a very promising group of materials which are of great interest both in the physics of thin films and in microelectronics. Their low resistivity and expected good temperature stability make them desirable for fabrication of reliable and reproducible electrical contacts. Investigations of this type of contacts include both their experimental development and the development of methods for their characterization such as noise level measurement and RES analysis. The noise level measurements enable the control of the noise, which is important characteristic of metal-semiconductor (M/S) electrical contacts (especially 1/f noise). In our work we compare the RES spectra and low frequency noise spectra of As+ implanted layers of TiN-Ti-Si structures, obtained in different conditions. Low frequency noise spectra are also obtained at different sample temperatures. Results of our measurements and analysis are of interest for solving the problems related to the application of ion implantation of As+ ions for the formation of silicides on p-Si, that are discussed by many authors in their investigations recently.Advanced Materials and Processes, 2nd Yugoslav Conference on Advanced Materials (YUGOMAT II), Sep 15-19, 1997, Herceg Novi, Yugoslavi

Crystallographic characteristics and fine structures of semiconducting transition metal silicides

Silicide-based photonic materials have attracted a great deal of research interest due to their compatibility with the well-developed silicon technology. Extensive efforts have been made for the synthesis and characterisation of these materials. This paper covers some aspects of the microstructural and crystallographic characteristics of ion beam synthesised silicides such as the semiconducting iron and ruthenium silicides, using transmission electron microscopy. A previously predicted new orientation relationship has been found to exist between the Si substrate and ion beam synthesised beta FeSi2 nanocrystals, which are free of 90 degrees rotational order domain boundaries. (C) 2011 Elsevier B. V. All rights reserved

Mixing and silicide formation during Xe-ion beam irradiations of Ta/Si bilayers

Thin Ta layers deposited on Si (100) substrates were irradiated with 475 keV Xe+ ions to fluences of (0.5-2) x 10(16) ions/cm(2) at temperatures between room temperature and 400 degreesC. By means of Rutherford Backscattering Spectrometry, the interface mixing and tantalum silicide formation were monitored as function of the ion fluence. TaSi2 phase formation was verified using X-ray diffraction. The interface broadening variance was found to depend linearly on the ion fluence and was explained with the help of a compound formation model involving global thermal spikes