S. G. Ansari

Mass-Spectrometric Studies of Catalytic Chemical Vapor Deposition Processes of Organic Silicon Compounds Containing Nitrogen

The mechanism of catalytic chemical vapor deposition (Cat-CVD) processes for hexamethyldisilazane (HMDS) and trisdimethylaminosilane (TDMAS), which are used as source gases to prepare SiNx or SiCxNy films, was studied using three different mass spectrometric techniques: ionization by Li+ ion attachment, vacuum-ultraviolet radiation and electron impact. The results for HMDS show that Si–N bonds dissociate selectively, although Si–C bonds are weaker, and (CH3)3SiNH should be one of the main precursors of deposited films. This decomposition mechanism did not change when NH3 was introduced, but the decomposition efficiency was slightly increased. Similar results were obtained for TDMAS.

Rotational and vibrational state distributions of H2 activated on a heated tungsten filament

The rotational and vibrational state distributions of H2 activated on a heated tungsten filament were determined by employing a coherent anti-Stokes Raman scattering technique to examine the contribution to the catalytic chemical vapor deposition process. The rotational excitation could be confirmed and the distribution was Boltzmann-like. When the filament temperature was 2700 K and the H2 pressure was over 1.3 kPa, the rotational temperature monitored 5 cm under the filament was around 1200 K; it showed a sharp decrease below 670 Pa and it was 700 K at 67 Pa. This decrease in the rotational temperature suggests the importance of relaxation processes on the chamber walls. The first vibrationally excited H2 molecules could also be identified at pressures over 670 Pa and the vibrational temperature was not much different from the rotational one. This vibrational temperature is much lower than those in typical H2 plasma, showing that the direct vibrational excitation of H2 on hot filaments is inefficient co...

Application of pristine and doped SnO 2 nanoparticles as a matrix for agro-hazardous material (organophosphate) detection

With an increasing focus on applied research, series of single/composite materials are being investigated for device development to detect several hazardous, dangerous, and toxic molecules. Here, we report a preliminary attempt of an electrochemical sensor fabricated using pristine Ni and Cr–doped nano tin oxide material (SnO2) as a tool to detect agro-hazardous material, i.e. Organophosphate (OP, chlorpyrifos). The nanomaterial was synthesized using the solution method. Nickel and chromium were used as dopant during synthesis. The synthesized material was calcined at 1000 °C and characterized for morphological, structural, and elemental analysis that showed the formation of agglomerated nanosized particles of crystalline nature. Screen-printed films of powder obtained were used as a matrix for working electrodes in a cyclic voltammogram (CV) at various concentrations of organophosphates (0.01 to 100 ppm). The CV curves were obtained before and after the immobilization of acetylcholinesterase (AChE) on the nanomaterial matrix. An interference study was also conducted with hydroquinone to ascertain the selectivity. The preliminary study indicated that such material can be used as suitable matrix for a device that can easily detect OP to a level of 10 ppb and thus contributes to progress in terms of desired device technology for the food and agricultural-industries.

A Label-Free Photoluminescence Genosensor Using Nanostructured Magnesium Oxide for Cholera Detection.

Nanomaterial-based photoluminescence (PL) diagnostic devices offer fast and highly sensitive detection of pesticides, DNA, and toxic agents. Here we report a label-free PL genosensor for sensitive detection of Vibrio cholerae that is based on a DNA hybridization strategy utilizing nanostructured magnesium oxide (nMgO; size >30 nm) particles. The morphology and size of the synthesized nMgO were determined by transmission electron microscopic (TEM) studies. The probe DNA (pDNA) was conjugated with nMgO and characterized by X-ray photoelectron and Fourier transform infrared spectroscopic techniques. The target complementary genomic DNA (cDNA) isolated from clinical samples of V. cholerae was subjected to DNA hybridization studies using the pDNA-nMgO complex and detection of the cDNA was accomplished by measuring changes in PL intensity. The PL peak intensity measured at 700 nm (red emission) increases with the increase in cDNA concentration. A linear range of response in the developed PL genosensor was observed from 100 to 500 ng/μL with a sensitivity of 1.306 emi/ng, detection limit of 3.133 ng/μL and a regression coefficient (R2) of 0.987. These results show that this ultrasensitive PL genosensor has the potential for applications in the clinical diagnosis of cholera.

Nanostructured magnesium oxide biosensing platform for cholera detection

We report fabrication of highly crystalline nanostructured magnesium oxide (NanoMgO, size >30 nm) film electrophoretically deposited onto indium-tin-oxide (ITO) glass substrate for Vibrio cholerae detection. The single stranded deoxyribonucleic acid (ssDNA) probe, consisting of 23 bases (O1 gene sequence) immobilized onto NanoMgO/ITO electrode surface, has been characterized using electrochemical, Fourier Transform-Infra Red, and UltraViolet-visible spectroscopic techniques. The hybridization studies of ssDNA/NanoMgO/ITO bioelectrode with fragmented target DNA conducted using differential pulse voltammetry reveal sensitivity as 16.80 nA/ng/cm2, response time of 3 s, linearity as 100–500 ng/μL, and stability of about 120 days.

Thick film urea sensor based on nanostructured zinc oxide

Flower-like structures of ZnO was synthesised by solution method using zinc acetate dihydrate and sodium hydroxide. Hydroxylamine hydrochloride (0.4M and 0.8M) was used as a structure directing agent. Structural morphology significantly changed with precursor concentration from a flower-like structure to sea-urchin like structure. Thick films of this powder were prepared on Al-sheet, by conventional doctor blade method using organic additives and used for urea sensing. Urease was attached with zinc oxide (by soaking in urease solution containing 100 units for three hours). In general, film conductivity increases after urease immobilisation. Urease immobilised films were found sensitive to urea concentration from 1 mM to 100 mM. Flowery structure resulted in higher urea sensitivity. The sensor responses are reproducible, reliable, reversible and selective, with a response time of 6S.

Effect of H/sub 2/ dilution in the catalytic CVD processes of SiH/sub 4//NH/sub 3/ system

Catalytic chemical vapor deposition (Cat-CVD) is one of the most promising techniques for preparing thin SiN/sub x/ films at low substrate temperatures by using SiH/sub 4/ and NH/sub 3/ as material gases (Matsumura et al., 2001 and Osono et al., 2003). One of the problems in this technique has been the low decomposition efficiency of NH/sub 3/ in the presence of SiH/sub 4/. The decomposition efficiency decreases sharply by the introduction of a small amount of SiH/sub 4/ (Umemoto, 2003). Recently, it has been found that the addition of H/sub 2/ improves not only the decomposition efficiency of NH/sub 3/ in the presence of SiH/sub 4/ but also the SiN/sub x/ film quality (Mahan et al., 2003 and Wang et al., 2004). In the present work, the catalytic decomposition efficiency of NH/sub 3/ in the SiH/sub 4//NH/sub 3//H/sub 2/ system is determined. The absolute H-atom densities were also measured under several conditions.