Ultraviolet-visible-near Infrared Research Articles

Growth and characterization of molybdenum trioxide films

Thin films of molybdenum trioxide find wide applications in electronic display systems [1] and solid state microbatteries [2, 3]. The significance of the material arises rnainly due to its photochromism [4], electrochromic properties [5] and unique layered structure [6]. Various methods, such as vacuum evaporation [7, 8], reactive sputtering [9], d.c. magnetron sputtering [10] and rf sputtering [5], have been reported for the deposition of MoO 3 films. In the investigation reported here an attempt was made to prepare MoO 3 films by electron beam evaporation on well cleaned glass substrates, and to characterize them by smdying their structure, electrical and optical properties. The effect of heat treatment in air on the film properties was also studied. Thin films of MoO 3 were prepared by electron beam evaporation using a Balzers BA 510 E vacuum coating unit onto chemically and ultrasonically cleaned Corning 7059 glass substrates maintained in the temperature range 303-573 K, in a vacuum better than 5 x 10 .7 mbar (1 bar = 1 x 10 » Pa). The deposition rate, controlled by a quartz crystal thickness monitor, was 4 nms « . The thickness of the films under investigation was about 500 nm. The structure of the films was analysed by Philips X-ray diffractometer (XRD) with a scanning angle (20) range of 10-60 °. Copper K« ()~ = 0.1542 nm) target was used as the source of X-rays. The infrared (IR) transmittance was recorded using a Pye Unicam SP3-300 IR spectrophotometer in the range 200-1200cm -1. The optical transmittance was recorded using a Hitachi U-3400 ultraviolet-visiblenear infrared (UV-VIS-NIR) double-beam spectrophotometer in the wavelength region 300-1600 nm. The electrical conductivity was measured using the standard four-probe technique. The XRD spectra of the films deposited at different substrate temperatures are shown in Fig. 1. The films formed at 303 K exhibited amorphous nature. On increasing the substrate temperature (> 423 K), the films exhibited polycrystalline nature. The films showed (O k 0) and (0 k l) orientations indicative of MoO3 in c-/~ mixed phase. The films deposited at 523 K showed predominantly (0 k0) orientation. On thermal treatment in air (calcination) at about 653 K for 4 h the films exhibited only (0 k 0) orientation, representing the orthorhombic c-phase of MoO 3. The evaluation lattice parameters from the XRD profiles were a = 0.396 nm, b = 1.365 nm and c = 0.357 nm [11]. On transformation from c-/3 mixed phase to c-phase MoO3 displays a very strong (0 k 0) preferred orien¢'4

Sterilization of teeth by gamma radiation.

Clinical simulations and restorative materials research and development conducted in vitro require the use of large numbers of extracted teeth. The simultaneous need for infection control procedures and minimal alterations of structure and properties of the tissue prompted this study of gamma irradiation as a method to eliminate microbes associated with extracted teeth and their storage solutions. Evaluations of potential change in structure of dentin were conducted in terms of permeability, Fourier transform infrared spectroscopy (FTIR), and optical properties. The dose required for sterilization by gamma irradiation was established by means of a tooth model inoculated with Bacillus subtilis (10(8) organisms/mL). Sterilization occurred at a dose above 173 krad with use of a Cesium (Cs137) radiation source. Gamma irradiation did not affect permeability of crown segments of dentin. A comparative evaluation of the effects of four sterilization methods on dentin disks was based on FTIR and ultraviolet-visible-near infrared (UV/VIS/NIR) spectra before and after sterilization by (1) gamma irradiation; (2) ethylene oxide; (3) dry heat; and (4) autoclaving. No detectable changes were found with gamma irradiation, but all other methods introduced some detectable change in the spectra. This suggests that common methods of sterilization alter the structure of the dentin, but gamma irradiation shows promise as a method which both is effective and introduces no detectable changes as measured by FTIR, UV/VIS/NIR, or permeability.

Ferroelectric bismuth titanate films by hot wall metalorganic chemical vapor deposition

Ferroelectric bismuth titanate thin films were successfully deposited on Si, sapphire disks, and Pt/Ti/SiO2/Si substrates by hot wall metalorganic chemical vapor deposition. Triphenyl bismuth [Bi(C6H5)3] and titanium ethoxide [Ti(C2H5O)4] were used as the precursors. The deposition rates were in the range of 3.9–12.5 nm/min. The Bi/Ti ratio was easily controlled by precursor temperature, carrier gas flow rate, and deposition temperature. As-deposited films were pure Bi4Ti3O12 phase. The films were specular and showed uniform and fine grain size. Optical constants as a function of wavelength were calculated from the film transmission characteristics in the ultraviolet-visible-near infrared (UV-VIS-NIR) region. The 550 °C annealed film showed a spontaneous polarization of 26.5 μC/cm2 and a coercive field of 244.3 kV/cm.

Applications of Photoacoustic Spectroscopy to Speciation of Lanthanide Elements in Aqueous Solutions and of Solid Phase.

Actinide elements in near neutral aqueous solutions are involved in a variety of chemical reactions such as hydrolysis, complexation, redox reaction, sorption and precipitation. Study of these reactions necessitates identification of chemical and physical forms of actinide species (speciation). Photoacoustic spectroscopy (PAS) has been widely used for studying samples in the form of solids, liquids and gases. For actinide elements in solution, laser-induced PAS (LPAS) has been successfully applied in the past several years, and provided valuable information of the speciation and the microscopic chemical behavior(1)(3). However, little progress has been made for sorbed and precipitated actinide species. We have initiated applications of PAS techniques to speciate lathanide and actinide elements in aqueous phase/adsorbent/precipitate systems ; LPAS has been developed for aqueous species, and the ultraviolet-visible-near infrared (UV-VIS-NIR) PAS and Fourier transform infrared (FT-IR) PAS for adsorbed and precipitated species. These techniques all offer the advantages of PAS : a direct non-perturbing detection, minimal sample preparation, versatility in shape of sample, and high sensitivity. As the first step of the applications of PAS to the speciation, we carried out the measurement on photoacoustic spectra of lanthanide solutions and solids. This note focuses on some results of neodymium, intended to illustrate the efficacy of PAS as a versatile technique for lanthanide speciation. The PAS equipments and procedures we applied are briefly described.