nan Govind

Photoconductivity and characterization of nitrogen incorporated hydrogenated amorphous carbon thin films

The observation and origin of photoconductivity in high base pressure (∼10−3 Torr) grown nitrogen incorporated hydrogenated amorphous carbon (a-C:H:N) thin films is reported. The magnitude of conductivity at room temperature was measured to increase by nearly two orders of magnitude and exhibits a maximum ratio of photoconductivity to dark conductivity of 1.5 as the nitrogen content increased to 15.1 at. %. X-ray photoelectron spectroscopy, micro-Raman spectroscopy, and Fourier transform infrared spectroscopy reveal enhanced sp2 bonding at higher nitrogen contents. Residual film stress, Tauc band gap, hardness, and elastic modulus are all found to decrease with addition of nitrogen. The electrical characteristics suggest the creation of a-C:H:N/p-Si heterojunction diodes having rectifying behavior. The conductivity and electrical characteristics are discussed in term of band model, and the results show that high quality a-C:H:N films can be grown at high base pressures with properties comparable to those grown at low base pressures.

Nanostructured porous silicon as functionalized material for biosensor application

In this work by means of PL, FTIR and XPS techniques, state-of-the-art porous silicon (PS) films with good mechanical and optical properties have been effectively utilized for the biofunctionalization purpose for its possible application in immunosensors. The functionalization of the PS surface has been achieved by silanization process using aminopropyltriethoxysilane (APTS) as a precursor. The presence of reactive amino groups on the PS surface along with glutaraldehyde as a linker aids in the covalent binding of the antibody (Human IgG) onto the PS surface. Different antigen concentrations can be detected with a good reproducibility with this technique which opens a huge possibility of using this biofunctionalized material for future biosensors.

Growth, differentiation, and migration of osteoblasts on transparent Ni doped TiO2 thin films deposited on borosilicate glass†

A simple and cost effective dip coating method was used to deposit thin films of amorphous (AM) or anatase (AN) titanium dioxide (TiO(2)) on borosilicate glass substrates, either with or without prior doping of TiO(2) with nickel (Ni) cations by a specially designed sol gel technique. The objective of the study was to compare the physicochemical and biological properties of these films and assess their use in orthopedic implants or for in vitro cell biological studies. Analytical techniques such as XRD and XPS, in combination with ATR-FTIR and SEM revealed that only AN films, prepared by controlled heating up to 450°C, irrespective of prior doping with Ni, contained significant crystalline structures of variable morphologies. This observation could be linked to the carbon and oxygen contents and the availability of functional groups in the films. Cell biological studies revealed that Ni doping of TiO(2) in both AM and AN films improved the adhesion, spreading, proliferation, differentiation, and migration of MC3T3 cells. Our studies provide a new approach to prepare optically transparent metal surfaces, with tunable physicochemical properties, which could be suitable for eliciting optimal osteoinductive cell responses and permit the detailed in vitro cell biological studies of osteoblasts.

Influence of temperature on the controlled growth kinetics and superstructural phase formation of indium on a reconstructed Si (113) 3???2 surface

The kinetics of growth, thermal stability and superstructural phase formation of the indium atom on a reconstructed Si (113) 3???2 surface at room temperature (RT), as well as at high substrate temperature (HT), is discussed. It was observed that at a very low flux rate of 0.08 ML min?1, In-adsorption at RT follows the Frank-van der Merwe (FM) growth mode, while for HT (>200 ?C), In-islands (the Volmer?Weber-growth mode) were formed. The residual thermal desorption (RTD) analysis revealed the anomalous behaviour of temperature-driven layering to the clustering rearrangement of In atoms on the Si (113) surface for RT- and 200 ?C-grown systems. The RTD study also demonstrates the effect of temperature on growth kinetics as well as on the multilayer/monolayer desorption pathway. The calculated bilayer desorption energy was found to be different for RT- (T B, 0.48 eV) and HT- (T B, 1.57 eV) grown In/Si(113) systems, while the monolayer desorption energy (T M, 2.56 eV) was the same in both the cases. Various coverage-dependent superstructural phases, such as Si(113) 3???2?+?3???1, 3???1, 3???2?+?1???3 and 1???1, have been observed during the RT- and HT-growth of In on the Si (113) surface. A complete phase diagram of In/Si(113) is deduced which depicts the evolution of novel phases as a function of substrate temperature and coverage.

Phase dependence of secondary electron emission at the Cs-Sb-Si (111) interface

The multi‐alkali antimonides adsorption on Si (111) surface has drawn much attention of several surface science studies due to its importance in both, fundamental and technological aspects of night vision devices & photocathodes. We report the formation of alkali metal antimonide ternary interface on Si(111)‐7×7 surface and in‐situ characterization by X‐ray Photoelectron Spectroscopy (XPS). The results show that Cs adsorption on clean Si(111) surface follows the layer‐by‐layer (Frank van der Merwe) growth mode at low flux rate, while Sb grows as islands (Volmer‐Weber) on Cs/Si surface. The changes in the Si (2p) and Cs (3d) core level spectra show the formation of a ternary interface (Sb/Cs/Si) at room temperature, which is further confirmed by changes in the density of states in the valence band spectra. The temperature controlled desorption of ternary interface, by monitoring the chemical species remnant on the surface after annealing at different temperatures, reveal that the Sb islands desorb at 750° C, which implies a stronger Cs‐Si bond to Cs‐Sb bond. The work function changes from 3.9 eV to 0.8 eV for Cs adsorption on Si, which further reduces to 0.65 eV after Sb adsorption on the Cs/Si interface. The changes in work function corresponds to the compositional and chemical nature of the interface and thus indicate that the secondary electron emission is an extremely phase dependent phenomena.The multi‐alkali antimonides adsorption on Si (111) surface has drawn much attention of several surface science studies due to its importance in both, fundamental and technological aspects of night vision devices & photocathodes. We report the formation of alkali metal antimonide ternary interface on Si(111)‐7×7 surface and in‐situ characterization by X‐ray Photoelectron Spectroscopy (XPS). The results show that Cs adsorption on clean Si(111) surface follows the layer‐by‐layer (Frank van der Merwe) growth mode at low flux rate, while Sb grows as islands (Volmer‐Weber) on Cs/Si surface. The changes in the Si (2p) and Cs (3d) core level spectra show the formation of a ternary interface (Sb/Cs/Si) at room temperature, which is further confirmed by changes in the density of states in the valence band spectra. The temperature controlled desorption of ternary interface, by monitoring the chemical spec...

Hydrosilylation of 1‐dodecene on Nanostructured Porous Silicon Surface: Role of Current Density and Stabilizing Agent

We report the formation of nanostructured PS on boron doped p‐type silicon wafer (100) by electrochemical anodization using aqueous hydrofluoric acid and isopropyl alcohol solution at different current densities 20 mAcm−2 and 50 mAcm−2 with pore size being 20–30 nm and 50–60 nm, respectively. For organic functionalization of PS surface 1‐Dodecene treatment under UV light was done. PL, FTIR and XPS studies have been carried out to characterize the PS after surface modification using dodecene. Stability studies were performed under normal ambience and humid condition for as‐anodized (Fresh PS) and dodecene‐treated samples. It is observed that the dodecene functionalized samples were more stable than as‐anodized porous silicon. The present study demonstrates that nanoporous silicon can provide chemically modified stable and high surface area for the sensing applications of PS.

Formation of Oxygen Induced Nanopyramids on Rh(210) Surface

Formation of oxygen induced nano pyramids on atomically rough and morphological unstable Rh (210) surface has been studied using Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and UHV‐scanning tunneling microscopy (STM). Nanometer sized pyramids can be formed upon annealing the oxygen‐covered Rh (2 1 0) surface at ⩾550 K in the presence of oxygen (10−8 Torr) and the facets of the pyramids are identified as two {731} face and a (1 1 0) face. The study suggests that the oxygen overlayer can be removed from the surface via catalytic reaction at low temperature using CO oxidation while preserving (“freezing”) the pyramidal facet structure. The resulting clean faceted surface remains stable for T∼600 K and for temperatures above this value, the surface irreversibly relaxes to the planar state. Atomically resolved STM measurements confirm the formation of nanopyramids with average pyramid size ∼18 nm. The nanopyramidal faceted Rh surface will be used as nanotemplates for growth of na...

Fabrication and chemical surface modification of nanoporous silicon for biosensing applications

In this work, porous silicon (PS) films with varied porosity (68–82%) were formed on the p-type, boron-doped silicon wafer (100) by the electrochemical anodisation in an aqueous hydrofluoric acid and isopropyl alcohol solution at different current densities (I d) ranging from 20–70 mA cm−2, respectively. Biofunctionalisation of the PS surface was carried out by chemically modifying the surface of PS by the deposition of 3-aminopropyltriethoxysilane thermally leading to high density of amine groups covering the PS surface. This further promotes the immobilisation of immunoglobulin (human IgG and goat anti-human IgG binding) on to the PS surface. Formation of nanostructured PS and the attachment of antibody–antigen to its surface were characterised using photoluminescence (PL), Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy techniques, respectively. The possibility of using these structures as biosensors has been explored based on the significant changes in the PL spectra before and after exposing the PS optical structures to biomolecules. These experimental results open the possibility of developing optical biosensors based on the variation of the PL position of the PL spectra of PS-based devices.

Optical and electron spectroscopy study of initial stages of room-temperature Mg film growth on Si (111)

The initial stages of room-temperature Mg film growth of Si (111) were studied using low-energy electron diffraction, electron energy-loss spectroscopy, and differential reflectance spectroscopy. In the studied range of magnesium film thickness (h = 0–0.2 nm), the formation of semiconductor magnesium silicide (Mg2Si), which is a promising material for silicon-silicide thermocouples, was detected. At small thicknesses of the deposited film, identical Mg2Si clusters are formed. An increase in the number of Mg atoms results in the formation of two-dimensional and then three-dimensional Mg2Si islands. Spectra of the optical response function δΛ″θ were measured for all structures; these spectra represent a characteristic of opticalproperties of these structures.