Formation of Iron Oxides by Surface Oxidation of Iron Plate

Oxidation of iron plates (α-phase) at high temperatures and in atmospheric conditions was monitored. The composition of oxidation products was analyzed with XRD, Raman and Mössbauer spectros-copies, whereas the morphologies of oxidation products were inspected by FE-SEM. The oxidation products formed at 300 and 400 °C consisted dominantly of magnetite and small fractions of hematite, whereas at 500 and 600 °C hematite was the dominant phase, as shown by XRD. In all these samples Raman spectra showed the presence of hematite in the outer oxidation layer. FE-SEM analysis showed the formation of nanowires at 500 °C and vertically grown hematite spikes against the lower oxidation layers at 600 °C. Oxidation products formed at 800 °C consisted of wüstite (Fe1–xO) as the dominant phase, nonstoichiometric magnetite (Fe3–xO4) and hematite (α-Fe2O3) in small fractions. The surface of these oxidation layers showed a hierarchical microstructure, as well as the hexagonal hematite rods vertically grown against the lower oxidation layers. The formation of the oxidation products can be considered a process which includes the oxidation of α-Fe to Fe1–xO and its transformation to Fe3–xO4 that further transforms to α-Fe2O3, probably via a short-lived γ-Fe2O3 (maghemite) phase. (doi: 10.5562/cca1943

Grain growth from amorphous phase

Time dependence of the grain growth in phosphorus doped silicon thin films deposited in situ at 530 ◦C was investigated. The samples were annealed at 950 ◦C in different time intervals. The theories, which give the tn time dependent increase of grain size, cannot fit the observed data. We derived a differential equation which describes the grain growth from amorphous phase. Our experimental results and the solution of the differential equation show the effect of grain growth stagnation and even grain growth stop. The solution also comprises all the features of the result of the Monte Carlo simulation of the grain growth of purematerials

Surface Enhanced Raman Spectroscopy for Molecular Identification- a Review on Surface Plasmon Resonance (SPR) and Localised Surface Plasmon Resonance (LSPR) in Optical Nanobiosensing

Surface plasmon resonance (SPR) allows for real-time, label-free optical detection of many chemical and biological substances. Having emerged in the last two decades, it is a widely used technique due to its non-invasive nature, allowing for the ultra-sensitive detection of a number of analytes. This review article discusses the principles, providing examples and illustrating the utility of SPR within the frame of plasmonic nanobiosensing, while making comparisons with its successor, namely localized surface plasmon resonance (LSPR). In particular LSPR utilizes both metal nanoparticle arrays and single nanoparticles, as compared to a continuous film of gold as used in traditional SPR. LSPR, utilizes metal nanoparticle arrays or single nanoparticles that have smaller sizes than the wavelength of the incident light, measuring small changes in the wavelength of the absorbance position, rather than the angle as in SPR. We introduce LSPR nanobiosensing by describing the initial experiments performed, shift-enhancement methods, exploitation of the short electromagnetic field decay length, and single nanoparticle sensors are as pathways to further exploit the strengths of LSPR nanobiosensing. Coupling molecular identification to LSPR spectroscopy is also explored and thus examples from surface-enhanced Raman spectroscopy are provided. The unique characteristics of LSPR nanobiosensing are emphasized and the challenges using LSPR nanobiosensors for detection of biomolecules as a biomarker are discussed. This work is licensed under a Creative Commons Attribution 4.0 International License

Raman and Photoluminescence Spectroscopy with a Variable Spectral Resolution

Raman and photoluminescence (PL) spectroscopy are important analytic tools in materials science that yield information on molecules’ and crystals’ vibrational and electronic properties. Here, we show results of a novel approach for Raman and PL spectroscopy to exploit variable spec- tral resolution by using zoom optics in a monochromator in the front of the detector. Our results show that the spectral intervals of interest can be recorded with different zoom factors, significantly reducing the acquisition time and changing the spectral resolution for different zoom factors. The smallest spectral intervals recorded at the maximum zoom factor yield higher spectral resolution suitable for Raman spectra. In contrast, larger spectral intervals recorded at the minimum zoom factor yield the lowest spectral resolution suitable for luminescence spectra. We have demonstrated the change in spectral resolution by zoom objective with a zoom factor of 6, but the perspective of such an approach is up to a zoom factor of 20. We have compared such an approach on the prototype Raman spectrometer with the high quality commercial one. The comparison was made on ZrO2 and TiO2 nanocrystals for Raman scattering and Al2O3 for PL emission recording. Beside demonstrating that Raman spectrometer can be used for PL and Raman spectroscopy without changing of grating, our results show that such a spectrometer could be an efficient and fast tool in searching for Raman and PL bands of unknown materials and, thereafter, spectral recording of the spectral interval of interest at an appropriate spectral resolution

Transmission electron microscopy, x-ray diffraction and Raman scattering studies of nanophase TiO_2

Dye-sensitized solar cells differ from conventional semiconductor devices in that they separate the function of light absorption from charge-carrier transport. The device is based on a 10-µm-thick optically transparent film of titanium dioxide (TiO_2) particles of a few nanometers in size, coated with a monolayer of charge-transfer dye to sensitize the film for light harvesting. In the present authors' review, the principal role of the TiO_2 photoanode is emphasized by a detailed presentation of its characterization by different experimental methods, while the photoelectric responses of the cells, a work which is still in progress, are indicated in the references cited. Hydrolysis of Ti(IV)-isopropoxide in isopropanol by the addition of water is a suitable chemical reaction for the production of nanosized TiO_2. The properties of nanosized TiO_2 can be modified by the hydrolysis catalyst, pH of the solution, temperature, presence of complexing ligand and the colloidal state of TiO_2 precursor. In the present work, the microstructural properties of nanosized TiO_2 were studied by HREM, ED, XRD, SAXS and Raman spectroscopy. HREM was used to determine both grain and pore sizes. Electron diffraction and X-ray diffraction provided evidence of nanocrystalline anatase and brookite phases. The grain sizes of the anatase and brookite phases changed from (5±1) to (12±3) nm with an increase of the treating temperature up to 773 K, as shown by XRD. An method of determining nanosized TiO_2 grain size based on low-frequency Raman scattering, is presented

Studij nanofaznog TiO2 elektronskom mikroskopijom, difrakcijom x-zračenja i Ramanovim raspršenjem

Dye-sensitized solar cells differ from conventional semiconductor devices in that they separate the function of light absorption from charge-carrier transport. The device is based on a 10-mm-thick optically transparent film of titanium dioxide (TiO2) particles of a few nanometers in size, coated with a monolayer of charge-transfer dye to sensitize the film for light harvesting. In the present authors\u27 review, the principal role of the TiO2 photoanode is emphasized by a detailed presentation of its characterization by different experimental methods, while the photoelectric responses of the cells, a work which is still in progress, are indicated in the references cited. Hydrolysis of Ti(IV)-isopropoxide in isopropanol by the addition of water is a suitable chemical reaction for the production of nanosized TiO2. The properties of nanosized TiO2 can be modified by the hydrolysis catalyst, pH of the solution, temperature, presence of complexing ligand and the colloidal state of TiO2 precursor. In the present work, the microstructural properties of nanosized TiO2 were studied by HREM, ED, XRD, SAXS and Raman spectroscopy. HREM was used to determine both grain and pore sizes. Electron diffraction and X-ray diffraction provided evidence of nanocrystalline anatase and brookite phases. The grain sizes of the anatase and brookite phases changed from (5±1) to (12±3) nm with an increase of the treating temperature up to 773 K, as shown by XRD. An method of determining nanosized TiO2 grain size based on low-frequency Raman scattering, is presented.Solarne ćelije senzitizirane bojom razlikuju se od klasičnih poluvodičkih uređaja u tome da imaju odvojenu funkciju apsorpcije svjetla od transporta nositelja naboja. Nov tip solarne ćelije osniva se na 10-µm-debelom, optički prozirnom filmu titanovog dioksida (TiO2) čija su zrna veličine nekoliko nm. Oksidni film je prekriven monoslojem boje za prenošenje naboja kojom se izvodi senzitacija filma za sakupljanje svjetla. U ovom se radu istražuju mikrostrukturna svojstva TiO2 nanoveličine primjenom visokorezolucijske elektronske mikroskopije, elektroske difrakcije, difrakcije X-zracenja, raspršenjem rentgenskog zračenja pod malim kutom i Ramanovog raspršenja. U zrnima TiO2 detektirani su anatas i brukit primjenom elektronske difrakcije i difrakcije X zračenja. Veličina zrna anatasa i brukita su bile od (5 $1) do (12$ 3) nm s odgovarajućim povećanjem temperature do 773 K, što je određeno difrakcijom X-zračenja. Prikazana je nova metoda određivanja veličine zrna TiO2 nanoveličine primjenom niskofrekvencijskog Ramanovog raspršenja. Postignuto je dobro slaganje rezultata pri određivanju nanoveličine zrna TiO2 navedenim instrumentalnim tehnikama

Silicon Nanowires Substrates Fabrication for Ultra-Sensitive Surface Enhanced Raman Spectroscopy Sensors

The silicon based substrates for surface enhanced Raman spectroscopy (SERS) have been synthesized and tested. The silver-assisted electroless wet chemical etching method has been utilized for silicon nanowires production which has been proved as the promising SERS substrate. The morphology of the silicon nanowires coated with silver nanoparticles has been examined by scanning electron microscopy. The SERS measurements tested on rhodamine 6G molecules indicated the optimal silicon nanowire substrate production obtained for 5 M hydrofluoric acid and 30 mM silver nitrate etching solution. The results show SERS detection limit of 10–8 M rhodamine in aqueous solution. This work is licensed under a Creative Commons Attribution 4.0 International License