S.G. Ansari

Glucose sensor based on nano-baskets of tin oxide templated in porous alumina by plasma enhanced CVD.

A feasibility study of glucose oxidase (GOx) immobilized tin oxide thin films, consisting of nano-baskets, for glucose sensing is presented. The nano-baskets of SnO(2) were grown on in-house fabricated anodized aluminum oxide pores of approximately 80-nm diameter using plasma enhanced chemical vapor deposition (PECVD) at an RF power of 60W. Hydrated stannic chloride was used as a precursor and O(2) (20 sccm) as a reactant gas. The deposition was carried out from 350 to 450 degrees C at a pressure of 0.2 Torr for 15 min each. Deposition at 450 degrees C resulted in crystalline film with basket-like (nano-sized) structure. GOx was immobilized by physical adsorption (soaking films in GOx solution containing 1000 units for 3h). Increase in film conductivity was noticed after GOx immobilization. The immobilized films were found sensitive to glucose (C(2)H(12)O(6), dextrose) concentration from 10 to 360 mg/dl. Sensitivity increases linearly with glucose concentration. Nano-baskets resulted in higher sensitivity in comparison with other structures. From the elemental analyses of the films after GOx immobilization, GOx was found covalently attached with tin oxide, as evident by N 1s peak in the photoelectron spectra. A possible sensing mechanism is presented and discussed.

Effect of annealing temperature on structural and bonded states of titanate nanotube films

A conversion from commercial titania (TiO2) nanoparticles to nanotubes was achieved by a hydrothermal method. The titanate nanotube (titanate) film was then deposited on a Si (001) substrate using an electrophoretic deposition (EPD) technique. The post hydrothermal treatment was then carried out by annealing the films at 300–1000°C for 30min in the static air. A major amount of intercalated sodium (Na) in as-synthesized titanate nanotubes was removed during the electrodeposition process. The collapse of the tubular structure can be seen clearly when annealed above 500°C. X-ray diffraction data indicate a significant increase in the anatase phase peak intensity with annealing temperature. O 1s peak is found to be built up of subpeaks of H2O, −OH, and Ti–O. Annealing results in an increase of the Ti–O peak intensity while other peaks disappear. Clear changes in the O 1s peak positions, symmetry, and shift towards lower energy (0.8eV) are evident with the increasing annealing temperature. The doublet spectra...

Effect of substrate temperature on the bonded states of indium tin oxide thin films deposited by plasma enhanced chemical vapor deposition

Abstract Indium tin oxide (ITO) thin films were deposited on Si(100) substrates using plasma enhanced chemical vapor deposition technique. The metal-organic sources used in this study were Tris (2,2,6,6-tetramethyl-3,5-heptanedionato) indium(III) and tin(III) acetate of 99.9% purity, which are readily available. The deposition of ITO films was carried out for 1 h at different reaction temperatures (200, 250, 300 and 350 °C), with oxygen as reaction gas (20 sccm) and argon as carrier gas (200 sccm). The deposited films were analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The minimum sheet resistance, measured using a four-probe method, was 2500 Ω cm −2 at a deposition temperature of 300 °C. XRD analysis shows a structural change and a highly textured film with 〈100〉 preferred orientation with increasing deposition temperature. Growth rate, estimated from SEM images of the deposited film was ∼10 10 cm −2 h −1 . It was observed from XPS results that oxygen atoms were bonded to In and Sn atoms indicating formation of ITO compound (bonded states of In 2 O 3 ). It is also seen that all the examined ITO film contains amorphous and crystalline phases.

ITO thin films deposited at different oxygen flow rates on Si(100) using the PEMOCVD method

Abstract Indium tin oxide (ITO) thin films were deposited on Si(100) substrates using plasma enhanced metallorganic chemical vapor deposition (PEMOCVD). Precursors used in this study were tris (2,2,6,6-tetramethyl-3,5-heptanedionato) indium(III) and tin(III) acetate of 99.9% purity, which are readily available. The precursors decompose at very low temperatures, giving flexibility to use low temperature substrates. The deposition of ITO films was carried out at different oxygen flow rates (5–20 sccm) and Argon flow rate of 200 sccm. R.F. power and reaction temperature was fixed at 150 W and 300 °C, respectively. The deposited films were analyzed using X-ray diffraction, scanning electron microscopy, α-step profilometer and X-ray photoelectronic spectroscopy (XPS). Sheet resistance of ITO film was measured using four-probe method. XRD analysis shows that grains are aligned in (222) and (400) direction and changes from (222) to (400) direction with the increasing oxygen flow rate. SEM results shows that the size of grains decreases as the oxygen flow rate increases with a slight increase in size at 20 sccm. The thickness of the films is ∼7500 A in all the cases. Sheet resistance of ITO film decreases with increasing oxygen flow rate up to 15 sccm and a little increase in sheet resistance at 20 sccm. XPS results manifested that oxygen atoms are bonded to In and Sn atoms indicating the formation of ITO compound.

Synthesis of Magnesium Oxide Nanoparticles by Sol-Gel Process

Cubic shaped Magnesium oxide nanoparticles were successfully synthesized by sol-gel method using magnesium nitrate and sodium hydroxide at room temperature. Hydrated Magnesium oxide nanoparticles were annealed in air at 300 and 500°C. X-ray diffraction patterns indicate that the obtain nanoparticles are in good crystallinity, pure magnesium oxide periclase phase with (200) orientation. Morphological investigation by FESEM reveals that the typical sizes of the grown nanoparticles are in the range of 50-70nm. Powder composition was analyzed by the FTIR spectroscopy and the results confirms that the conversion of brucite phase magnesium hydroxide in to magnesium oxide periclase phase was achieved at 300°C.The Thermo-gravimetric analysis showed the phase transition of the synthesized magnesium oxide nanoparticles occurs at 280-300°C.

Electrochemically deposited ruthenium seed layer followed by copper electrochemical plating

Electrochemical deposition of ruthenium as a seed layer was investigated on Ti and TiN as barrier layers for Cu interconnects. The aqueous electrolyte, the N-bridged complex of ruthenium(IV) nitrosyl chloride (RuNC), for ruthenium electrochemical deposition was formed in situ. Electrochemical deposition of copper on the Ru seeded barrier layers was also demonstrated. The chemicals for the acid-bath ruthenium electrochemical deposition were ruthenium(III) chloride hydrate (RuCl 3 .3H 2 O), hydrochloric acid (HCI), sulfamic acid (NH 2 SO 3 H), and polyethylene glycol. The chemicals for the acid-bath copper electrochemical deposition were copper(II) sulfate hydrate (CuSO 4 .5H 2 O), sulfuric acid (H 2 SO 4 ), and polyethylene glycol. Results were analyzed by field-emission scanning electron microscopy, atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Ru-therford backscattering spectrometry. The Ru thin layer with equiaxial grains <10 nm on blanket Ti substrates were obtained by electrochemical deposition. Electrochemical Cu trench fill was successful on patterned TiN 130 nm 2.5 aspect ratio trenches with Ru as a seed layer.

A novel method for preparing stoichiometric SnO2 thin films at low temperature

Tin oxide is a well known nonstoichiometric material with dual valency. The invariance of stoichiometry is very intriguing. As of today no report is available for preparing perfect stoichiometric tin oxide. Here we report a novel method to prepare stoichiometric tin oxide by modifying the known plasma enhanced chemical vapor deposition technique using SnCl(4)-xH(2)O as precursor and O(2) as reactant gas at various temperatures from 300 to 800 degrees C. Tetragonal rutile structure of SnO(2) was found, grown along the [110] direction. X-ray photoelectron spectroscopic measurement showed constant Sn/O ratio. Sn 3d and O 1s were found composed of only Sn(4+) (487.2 eV) and O-Sn(4+) (531.2 eV) with equal peak widths. Raman band intensity ( approximately 633 cm(-1)) was found increasing with temperature, indicating the morphological changes. Sheet resistance of approximately 0.5 kOmega/at 300 degrees C was measured that reduces to approximately 0.1 kOmega/at 600 degrees C. It is found that film stoichiometry remains unaltered, while the structural morphology changes significantly.

Growth and morphological study of zinc oxide nanoneedles grown on the annealed titanate nanotubes using hydrothermal method

Hydrothermal growth of ZnO on the annealed titanate nanotube films results in the oriented hexagonal-needlelike structures. The size, shape, density, and alignment of ZnO film are significantly affected by annealing temperature and orientation of the beneath titanate layer. It is believed that oxygen and hydrogen vacancies, generated due to dehydration of interlayered OH groups while annealing of the titanate, are responsible for the changes in the morphology of the ZnO. Microscopic observations clearly resolved nanoneedles with the base diameter of ∼150nm and length of ∼5μm with lattice spacing of 0.52nm, indicating single crystalline ZnO and grown along the (0001) direction. A growth model is presented based on the layer-by-layer growth (three-step growth) as a function of growth time (2–6h). Thicknesses of these three steps were found increasing with growth time. The second step (II) of growth exhibits the same feature as that of the first step (I), i.e., bounded with six crystallographic, lower surfac...

Lonsdaleite diamond growth on reconstructed Si (100) by hot-filament chemical vapor deposition (HFCVD)

In this paper, the growth of Lonsdaleite diamond using hot-filament chemical vapor deposition (HFCVD) on flashed and reconstructed Si (100) is reported. Surface morphology studies using scanning electron microscopy (SEM) show that the film is composed of decahedron and icosahedron diamond particles. The X-ray diffraction (XRD) pattern has a strongest peak at 47° and a peak at 41°, which is indicative of Lonsdaleite nature of the grown diamond film. The Raman spectrum of the film shows a broadened diamond peak at wave number of 1,329 cm−1, which has shifted towards the peak position corresponding to Lonsdaleite nature of the diamond (1,326 cm−1).

Low temperature deposition and effect of plasma power on tin oxide thin films prepared by modified plasma enhanced chemical vapor deposition

This work presents low temperature (200 and 300°C) thin film deposition of tin oxide (SnO2) using modified plasma enhanced chemical vapor deposition as a function of radio frequency power (100–500W). Stannic chloride (SnCl4) was used as precursor and oxygen (O2, 300SCCM) as reactant gas. Fine granular morphology was observed with tetragonal rutile structure grown along the [110] direction, at all the deposition conditions. Higher plasma power resulted in smoother morphology, improved crystallinity, and enhanced conductivity. Electrical resistivity value of as low as ∼0.01Ωcm was obtained at the deposition temperature of 300°C and 250W of plasma power.