Papers by Keyword: Raman Spectroscopy

Abstract: We tested stability of 43 selective sorbents, covering the widest range of functional groups, efficiency of sorption, method of production, and which are theoretically useful for sorption of cesium, strontium, cobalt, arsenic and actinoids. We present 3 of them: A = TiO₂, B = Al₂O₃ and C = MxH(TiO)₄(SiO4)₃ . z H₂O. In first testing, sorbents were exposed to the model solution of boric acid for 168 hours, in which they were mixed in a closed container with a rotator. After the exposure, sorbent solutions were filtered and analysed by spectroscopic techniques (Infrared Spectroscopy (IR), Raman Spectroscopy (RS) and newly by Scanning Electron Microscopy (SEM), combined with Energy Dispersive Spectroscopy (EDS)). Exposed spectra were compared with spectra of new, non-exposed sorbents. In second testing, sorbents were exposed to gamma radiation for 12 days with total dose 666 ± 43 kGy, produced by cobalt bomb and analysed by same techniques. The aim of our testing was to find out how sorbents behave in model boric acid solution and what effect has the gamma radiation on sorbent spectra and to analyse sorbents by SEM with EDX.

Abstract: A novel two-stage technique to fabricate silicon nanoparticles is reported. At the first stage, silicon nanowire arrays are formed by metal-assisted chemical etching. At the second stage, the nanoparticles are produced by pulsed laser ablation of the silicon nanowire targets in water and ethanol. The fabricated particles have relatively small mean size in the range of 24 – 45 nm depending on the used buffer liquid. The ablation threshold of the silicon nanowire arrays is 2 – 11 times smaller than that for crystalline silicon targets. Owing to the achieved parameters, the proposed technique is more efficient in comparison with traditional approaches of mechanical milling of silicon nanowires and laser ablation of crystalline silicon. Raman spectroscopy study revealed crystalline structure of the fabricated silicon nanoparticles. The properties of the produced nanoparticles indicate their high potential in biophotonics.

Abstract: We demonstrated efficient crystallization of amorphous Si films induced by their direct irradiation with near-IR femtosecond laser pulses coming at sub-MHz repetition rate. Comprehensive analysis of morphology and composition of the laser-annealed film by atomic-force microscopy, Fourier-transform IR, Raman and energy dispersive X-ray spectroscopy as well as numerical modeling of optical spectra confirmed efficient crystallization of amorphous Si and high-quality of the obtained films opening pathway for applications in thin-film solar cells, transistors and displays.

Abstract: In the present work, the self-healing process in concrete was evaluated using analytical techniques. For this purpose, two concrete mixes of different composition (one used as control) were prepared with a water-to-binder ratio of 0.45. The self-healing process was triggered by the introduction in the concrete mix of a commercial expansive admixture (calcium sulfo-aluminate), two dicarboxylic acids, and sodium carbonate salt. After 28 days curing in water, the specimens were artificially cracked (crack width ≤ 900 μm) and then again water-cured for further 60 days until self-healing occurred. The progress of self-healing was investigated with a stereomicroscope at 40, 50, and 60 days, after cracking, to identify the quality and the degree of the healing. The efficiency of the self-healing process was also evaluated using micro-Raman spectroscopy and X-ray micro-computed tomography. Significant reduction in the crack width was observed as a result of a calcite filling, generated during the self-healing process. In some cases (crack width < 400 μm), the crack was completely healed. The experimental methodology used provided new insights into the evolution of the self-healing phenomenon in concrete.

Abstract: The scratch damage that caused the generation of double Shockley stacking faults (DSFs) in heavily nitrogen doped 4H-SiC crystal was investigated quantitatively. Scratch tests were carried out on 4H-SiC substrates with a nitrogen concentration of 2.6 × 10¹⁹ cm^-3. A residual tensile stress of 40 MPa was detected around the scratch loaded at 30 mN with a diamond tip. DSFs were generated from this scratch by annealing at 1100°C for 2 h in Ar atmosphere. After annealing, the residual stress around the scratch was reduced to a tensile stress of 10 MPa. This result suggests that the reduction of residual stress around the scratch coincided with the formation of DSFs.

Abstract: A complex ZnO/ZnAl₂O₄ heterostructures thin films on glass and Si (111) substrates have been successively obtained by a soft ultrasonic spray pyrolysis (USP) method deposition using the Zn/Al molar ratios concentrations of 0.07/0.13 and 0.1/0.1, respectively. According to (XRD) an ordered zinc oxide (ZnO) and zinc aluminate (ZnAl₂O₄) structures deposited onto glass from the air annealing at 500 °C during 2 hours was observed and confirmed by the (EDX), (FTIR) and Raman spectroscopy techniques. The estimated crystallites size and stress values of ZnO and ZnAl₂O₄ in the ZnO/ZnAl₂O₄/glass film were 19 nm/0.469 GPa and 11 nm/-0.292 GPa, respectively. The lower Zn/Al molar ratio around 0.035/0.06 produced only ZnO as a single phase, suggesting the Al insufficient quantity. The Si (100) substrate with 0.07 Zn molarity conducted to the Zn₂SiO₄/ZnO/ZnAl₂O₄ composite. The Raman integrated intensity bands of ZnO and ZnAl₂O₄ increases with increasing Zn to Al molar ratio (0.1/0.1 comparatively to 0.07/0.13). The ZnO&ZnAl₂O₄ crystallinity enhances as Zn molarity increases. The ZnO films in the composites grow with (002) texture. The TC(hkl) value indicated that ZnAl₂O₄ in the ZnO/ZnAl₂O₄/glass layer is polycrystalline preferentially oriented along the (311) plane. Spinel ZnAl₂O₄ oxide onto Si (111) substrate grown according to the (220) orientation. Crystallites are larger in ZnO/ZnAl₂O₄/Si than in ZnO/ZnAl₂O₄/glass. The ZnO/ZnAl₂O₄ film onto glass substrate is transparent in the visible and near infrared regions and sensitive to UV absorption, as characterized by UV-Vis spectroscopy. The ZnO and ZnAl₂O₄ E_g values in the ZnO/ZnAl₂O₄/glass composite were 3.25 and 3.88 eV, respectively.

Abstract: Porous silicon has generated interest in scientific community after its photoluminescence discovery and thereafter, research was focused on to the chemical functionalization of silicon and subsequent anchoring of nanoparticles onto silicon surface. In the present work, the porous silicon has been effectively modified with magnetic nanoparticles which were prepared through metallorganic approach. The as-fabricated magnetic-porous silicon composites were characterised using FTIR and Raman spectroscopies, Scanning Electron Microscopy (SEM) as well as magnetic measurements.

Abstract: The authors studied the volume distribution of particles from ultrafine powders of natural diamond, used as a hardener for a post of diamond tools made on a metal basis by powder metallurgy methods. In [15-17], the authors determined that the addition of ultrafine natural diamond powders to the melt of tin bronze in an amount of 2-3% by weight has a positive effect on the physicomechanical and operational properties of the metal post. It was also determined that the hardening mechanism of the materials under study depends on the nature of the distribution of the hardener particles in the bulk of the matrix. In accordance with previous studies, the authors set the aim - to determine the distribution nature of reinforcing phase particles in the volume of the metal matrix. The studies were carried out using optical metallography, SEM microscopy and Raman spectroscopy. It was established that the particles of the hardener in the volume of the matrix are distributed evenly along the phase boundaries and in the body of the grains and reduce the number of pores formed during sintering compared with the original samples. With the established nature of the distribution of particles, a grain-boundary hardening mechanism is realized, in which dislocations are inhibited by grain boundaries, which are an insurmountable obstacle for them. It is also established that a part of the particles settle directly inside the grains of the material and is distributed throughout the volume uniformly contributing to the dispersion hardening mechanism.

Abstract: Stainless steel is widely utilized due to its higher corrosion resistance and gloss than ordinary steels. However, the applications of stainless steel are still limited because of its low surface hardness. Graphene is a superb material, which has an intrinsic strength of 130 GPa. In this report, the growth of high quality graphene on S304 stainless steel by chemical vapor deposition using acetylene gas as a carbon source is demonstrated. The surface hardness of stainless steel after growing high quality graphene is investigated by nanoindentation technique. High quality graphene can increase the surface hardness of stainless steel from 1.54 GPa to 10.08 GPa. Moreover, the effect of graphene quality on the surface hardness of S304 stainless steel is studied. High quality graphene grown by CVD using acetylene gas as a carbon source can increase the surface hardness of stainless steel about two times more than low quality graphene grown by using methane gas.

Abstract: This chapter aims at reviewing the characterisation techniques that are commonly used for high temperature oxidation study, especially on stainless steels. In addition, the experimental studies about the high temperature oxidation i.e. thermogravimetric method and chromium volatilisation measurement are explained. The various kinds of characterisation techniques for physico-chemical and electronic properties of thermal oxide scales are reviewed, starting from optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), focused ion beam coupled with scanning electron microscope (FIB/SEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), and photoelectrochemical characterisation (PEC). The review focuses on the basic concepts and shows how the characterising tools can be applied to thermal oxide characterisation.