Electrical transport properties of CdTe:Sb films

Hall coefficient and dc conductivity measurements are made on p-type CdTe:Sb films grown by vacuum evaporation technique on glass substrate. The grain boundary potential barrier, which is found mainly to limit the mobility of carriers is calculated as a function of film thickness. The n-type conduction is found to dominate over p-type conduction above about 330 K. The ratio of electron to hole mobility is also calculated.     

Role of Impurity Precipitates on Microhardness of KBr:Ba2+ Crystals

Microhardness of KBr crystals doped with various concentration of Ba²⁺ have been investigated in the asgrown state and after quenching from various elevated temperatures. It is observed that hardness increases with increase in impurity concentration and at high concentration the hardness starts decreasing. Microstructural investigations have showed the formation of visible precipitates at high concentrations. The heat treatment studies showed that in crystals quenched from elevated temperatures the visible precipitates dissociate and hardness increases.     

Microhardness studies on some compound semiconductors

Vickers microhardness studies on some III–V and II–VI compound semiconductors have been made. The results showed that ZnS has the highest microhardness value. These results are compared with other properties of the crystals such as melting point, ionicity etc. Variation of microhardness with load was also studied on all the crystals. The results indicated that the hardness value increases at low loads. These results have been analysed by using resistance pressure model and interpreted.     

Dielectric and electrical studies on as-grown CeO2 films

Thin film capacitors of CeO₂ were fabricated by thermal evaporation. The dielectric properties of these films were studied in the frequency range 0.05–16 KHz at various temperatures, starting from liquid nitrogen temperature to 390 K. The effect of annealing on capacitance and tan δ were studied for different frequencies. The behaviour was explained on the basis of relief in strain energy. The plot between current density and temperature was drawn, and from the slope of the plot the activation energy was calculated and found to be 0.52 ev. The results were discussed.     

Electrical properties of Al-CeO2-Al thin film capacitor structures

Cerium Oxide films were prepared by vacuum thermal evaporation from tantalum boat in a conventional vacuum coating unit. Current-voltage characteristics were studied for different film thicknesses. The breakdown voltage (V_B) and dielectric field strength (E_B) were calculated. It is found that the breakdown voltage increases and dielectric field strength decreases as the thickness of the film increases. The applicability of Forlani-Minnaja relation is discussed. Current-voltage characteristics were also drawn at different temperatures and breakdown voltages were calculated. The breakdown voltage decreases as the temperature of the structure increases but the variation is nonlinear. The variation of current density with temperature was studied and the activation energy for the migration of charge carriers was calculated and it is about 0.52 ev. The results were discussed.     

5-(Perfluorooctylthio)acetamidofluorescein (5-FOAF) as a convenient tag for inspecting the surface coverage of fluorinated coatings

Fluorinated compounds are commonly used for anti-stick coating but it is difficult to inspect the coverage of the coating without expensive instruments. Herein, we demonstrated that the 5-(perfluorooctylthio)acetamidofluorescein (5-FOAF) probe can be synthesized in one step and used as a testing reagent to inspect the fluorinated coating on silica- or metal-based surfaces. 5-FOAF is composed of a perfluoroalkyl domain, which has high specific affinity towards fluorinated compounds, and a fluorophore domain, which exhibits fluorescence emission visible by naked eyes. Thus, 5-FOAF will retain on the surface coated with fluorinated compounds but not on the un-coated surface and the emitted fluorescence from the retained tags serves as a semi-quantitative measure of the fluorine coverage across the surface. For this study, silica-based or metal-based surfaces were activated by silane chemistry and then coated with fluorinated compounds. The coating procedure was judiciously optimized to achieve a homogeneous coating. 5-FOAF probe was synthesized in-house and shown to retain on the fluorinated surface 2-5 times stronger than the bare surface. Moreover, by studying the retention on a non-fluoro hydrophobic substrate made of polydimethylsiloxane, the affinity of 5-FOAF with the fluorinated coating was confirmed to be specific and distinguishable from nonspecific hydrophobic interaction. In conclusion, we synthesized a novel chemical, 5-FOAF, and demonstrated its usefulness as a simple testing reagent for fluorinated coatings.     

Enantioselective synthesis of oseltamivir phosphate

The key steps in the enantioselective synthesis of Tamiflu include an asymmetric Diels-Alder reaction, Mitsunobu inversion using Fukuyama modified Weinreb reagent, carbamate directed epoxidation. Epoxide opening with trimethylsilyl azide furnished a 3:1 mixture of regioisomers that converged to afford the same aziridine. Attempted preparation of the unsaturated ester regioselectively using 2-iodoxybenzoic acid (IBX) following Nicolaou’s protocol failed. The unsaturated ester was prepared by phenylselenylation followed by selenoxide elimination.     

Influence of pH and microwave calcination on the morphology of KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> particles derived by Pechini Sol–Gel method

KGd(WO₄)₂ (KGW) particles were synthesized at 3.5, 5.5 and 7.5 pH values by Pechini polymeric complex sol–gel method using potassium nitrate, gadolinium nitrate, ammonium paratungstate, citric acid and ethylene glycol as starting materials. Deionized water was used as solvent. Polymeric precursor gel was formed with citric acid as complexing agent and ethylene glycol as binder. Synthesized gel was analyzed by FT-IR spectroscopy. Prepared precursor gels were further annealed using resistive and microwave processes at 550 and 700 °C, respectively. The properties of heat treated samples were characterized by powder XRD, FT-IR, Raman and SEM analysis to understand the crystallinity, organic liberation, tungstate ribbon formation and surface morphology, respectively. The phase formation and different phases of intermediate oxides in pre-fired samples were investigated by powder XRD. Organic liberation in the samples in relation to temperature, and the carbon content in the pre-fired powder was analyzed using FT-IR spectrum. Raman spectrum reveals the formation of tungsten ribbons as well as the quality of the samples. The morphological changes at different synthesis conditions were observed with SEM micrographs.     

Asymmetric synthesis of (4S,5S)-2-oxo-4-phenyloxazolidine-5-carboxylic acid using a 1,2-addition of PhMgBr to an N-sulfinimine derived from (R)-glyceraldehyde acetonide and (S)-t-BSA

We report an asymmetric synthesis of (4S,5S)-2-oxo-4-phenyloxazolidine-5-carboxylic acid via stereoselective addition of phenylmagnesium bromide (PhMgBr) to an N-sulfinimine derived from (R)-glyceraldehyde acetonide. (S)- and (R)-Glyceraldehyde acetonides, important chiral synthons in synthetic organic chemistry, are prepared from the corresponding epichlorohydrin using an identical synthetic methodology.