Mahesh Kumar

Abstract: Abstract Amorphous carbon films have been deposited by filtered cathodic jet carbon arc technique under different gaseous environments. Scanning electron microscope and atomic force microscope studies have been performed on the deposited films for the surface morphological studies. The morphology of the deposited film changes with the change in gas environment. X-ray photoelectron spectroscopic (XPS) and Raman studies have been carried out on the deposited samples for the evaluation of the chemical bonding of carbon atoms with the ambient gas atoms. The sp3 and sp2 contents have been evaluated from the XPS studies and found to be dependent on the gaseous environment. The film deposited under hydrogen environment has the highest value of the sp3 content (54.6at.%) whereas the film deposited under helium environment has the lowest value of sp3 content (37at.%). For the evaluation of the electrical and mechanical properties of the deposited films, the electrical conductivity and nanoindentation measurements have been performed on the deposited films. It has been observed that the film deposited under helium environment has the highest electrical conductivity and the lowest hardness ( x223C;15GPa) value whereas film deposited under hydrogen environment has the highest hardness ( x223C;21GPa) and the lowest conductivity.

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Abstract: We report here the formation of single phase lead zirconate titanate (PZT) nanopowder with composition Pb(Zr(0.52)Ti(0.48))O(3) and average crystallite size 12-20 nm, synthesized by sol-gel process. The phase evolution of PZT gel powder, heat treated at temperatures 550, 650 and 800A degrees C was monitored by X-ray diffraction (XRD) and X-ray photo-electron spectroscopy (XPS). The high resolution XPS spectra of Pb4f, Zr3d, Ti2p and O1s show that PZT with pure perovskite structure is obtained at 800A degrees C while at lower temperatures pyrochlore phase co-exists with perovskite phase. The XRD results also support this analysis. We have also identified the pyrochlore phase using XPS by analyzing the corresponding variations in the FWHM values, peak positions and the separation between the spin doublets of Pb, Zr and Ti associated with it. The composition of the final powder obtained with pure perovskite structure is calculated and is close to the designed value.

Abstract: Motivated by the need to form 1D-nanostructured dopants on silicon surfaces, we have attempted to grow Ga on the high index Si(5 5 12) surface which has a highly trenched (1D) morphology. The evolution of the interface with Ga adsorption in the monolayer regime has been probed by in situ AES, LEED and EELS. Controlling the kinetics by changing the Ga flux rates shows an interesting difference in the 1.0 to 1.5 ML region. The low flux rate (0.03 ML/minute) results in a Frank van der Merwe (layer by layer) growth mode up to 2 ML while the higher flux rate (0.1 ML/minute) shows a transient island formation after the completion of 1 ML The low rate shows the formation of 2 x (3 3 7) and (2 2 5) superstructures, while only the 2 x (3 3 7) is observed in a wide coverage range for the higher rate. The results demonstrate the ability to kinetically control the surface phases with different electronic properties of this technologically important interface. (C) 2011 Elsevier B.V. All rights reserved.

Abstract: In this work, a colloidal suspension of trioctyl phosphine oxide/trioctyl phosphine (TOPO/TOP)-capped CdSe QD�s of size similar to 5 nm was prepared by chemical route and these QD�s were anchored on the surface of sol-gel prepared nanoporous TiO(2) layers in THF-ethanol solvent either by direct adsorption or with the aid of bi-functional linker molecule mercaptoacetic acid (MPA). The particle size estimation of both TiO2 and CdSe nanoparticles by X-ray diffraction (XRD) and transmission electron microscopic (TEM) measurements concur well with each other. Energy-dispersive X-ray spectroscopy (EDS) and Xray photoelectron spectroscopy (XPS) studies elucidate the signatures of TiO(2), CdSe nanoparticles and linker which is also supported by the presence of contrasting images in TEM studies respectively. XPS depth-profiling measurements have been used as a probe to determine the chemical composition and structure of CdSe nanocrystals and CdSe-TiO(2) nanocomposites respectively. The CdSe nanoparticles and CdSe-TiO(2) nanocomposites formed by different routes are modeled, based on the observations of several complimentary techniques. (C) 2011 Elsevier B.V. All rights reserved.

Abstract: Zinc-Tin-Oxide (ZTO) thin films were deposited on glass substrate with varying concentrations (ZnO:SnO(2); 100:0, 90:10, 70:30 and 50:50 wt.%) at room temperature by flash evaporation technique. These deposited ZTO films were annealed at 450 C in vacuum. These films were characterized to study the effect of annealing and addition of SnO(2) concentration on the structural, chemical and electrical properties. The XRD analysis indicates that crystallization of the ZTO films strongly depends on the concentration of SnO(2) and post annealing where annealed films showed polycrystalline nature. Atomic force microscopy (AFM) images manifest the surface morphology of these ZTO thin films. The XPS core level spectra of Zn(2p), O(1s) and Sn(3d) have been deconvoluted into their Gaussian component to evaluate the chemical changes, while valence band spectra reveal the electronic structures of these films. A small shift in Zn(2p) and Sn(3d) core level towards higher binding energy and O(1s) core level towards lower binding energy have been observed. The minimum electrical resistivity (rho approximate to 3.69 x 10(-2) Omega-cm), maximum carrier concentration (n approximate to 3.26 x 10(19)cm(-3)) and Hall mobility (mu approximate to 5.2 cm(2) v(-1) s(-1)) were obtained for as-prepared ZTO (50:50) film thereafter move towards lowest resistivity (rho approximate to 1.12 x 10(-3) Omega-cm), highest carrier concentration (n approximate to 2.96 x 10(20) cm(-3)) and mobility (mu approximate to 18.8 cm(2) v(-1) s(-1)) for annealed ZTO (50:50) thin film. (c) 2010 Elsevier B.V. All rights reserved.

Abstract: Abstract A structural model for two-dimensional silicide with structure (2/3 x221A;3 xD7;2/3 x221A;3)-R30 xB0;, consisting of five layers (three layers of Mg and two layers of Si) with all Mg x2013;Si fixed bonds, was proposed on the basis of EELS data. The observed redshift of EELS bulk plasmon on 0.8 eV is satisfactorily explained in the framework of the model by the reduction of carrier density and formation of fixed Mg x2013;Si bonds.

Abstract: Abstract During AES and EELS investigations of thermal stability of Mg and Mg2Si films it was found that metallic Mg desorbs from the surface at temperatures higher than 80 xA0; xB0;C, but the bulk-like Mg2Si film shows a thermal stability up to 180 xA0; xB0;C. The maximal thermal stability up to 230 xA0; xB0;C was observed for a two-dimensional magnesium silicide with structure (2/3 x221A;3 xD7;2/3 x221A;3)-R30 xB0;. A model of its thermal stability based on the peculiarities of the electronic structure of a two-dimensional magnesium silicide with structure (2/3 x221A;3 xD7;2/3 x221A;3)-R30 xB0; and on the continuity of 2D film was proposed.

Abstract: We report the change in electronic properties of the Ga/Si interface by monitoring the Ga(3d) core-level photoelectron spectra and electron diffraction induced by submonolayer Ga adsorption on Si(111)-7x7 surface. The spectra shows a flat band for submonolayer coverages, attributed to the metallic nature of the Si(111)-7x7 reconstruction and a premetallic band structure of two-dimensional Ga islands. At 1 ML, electron diffraction pattern shows metallic (7x7) to semiconducting (1x1) phase-transition and the spin-orbit split branching ratio of Ga(2p) core level attain the metallic bulk value, and the barrier assumes the Schottky-Mott value while full width half maxima and branching ratio attain bulk values. (C) 2010 American Institute of Physics. [doi:10.1063/1.3490250]

Abstract: The Cu(2)O nanoparticles having average crystallite diameters similar to 8-16 nm were synthesized by a simple solvothermal method. The Mn was doped in the Cu(2)O sample of crystallite size similar to 8 nm. The effects of the size and doping concentration on the crystal structures of the nanoparticles were investigated. The x-ray photoelectron spectroscopy studies clearly showed that the Mn was incorporated into the Cu(2)O lattice as Mn(2+) due to the substitution of the Cu(+) ions by Mn(2+) ions. The quantum confinement effects were observed in the nanoparticles. The multiple emissions from the Cu(2)O were quenched in the Mn doped nanoparticles and only blue light emitting Cu(2)O nanoparticles were obtained due to the transition (4)T(2)->(6)A(1) of Mn. The effects of the doping concentration and the particle size on the relaxations dynamics of the Cu(2)O nanoparticles were mainly investigated using photoluminescence decay.

Abstract: In this work, tri-octyl phosphine/tri-octyl phosphine oxide (TOPO)-capped cadmium selenide (CdSe) quantum dots (QDs) of varied sizes (5-9 nm), prepared by varying the input Cd:Se precursor ratio using chemical route, were dispersed in conducting polymer matrices viz. poly[2-methoxy, 5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and poly(3-hexylthiophene) (P3HT). By using a binary solvent mixture (pyridine-chloroform), homogeneous dispersion of CdSe nanocrystals in polymers (MEH-PPV, P3HT) could be realized. The properties of the resulting dispersions could be tailored by the composition and concentration of QDs in polymer. The emission and structural properties of polymer-CdSe nanocomposites are found to be dependent on the crystallite size and morphology of CdSe nanocrystallites. An effective quenching of photoluminescence emission in the polymer nanocomposite was observed for smaller CdSe quantum dots (size similar to 6 nm) as compared to larger CdSe quantum dots (size similar to 9 nm), thus ensuring efficient charge transfer process across the polymer-CdSe interface in the former case. The incomplete quenching, particularly for MEH-PPV:CdSe nanocomposites, could be as a result of insufficient coverage of polymers on the surface of CdSe nanocrystallites, mainly due to phase segregation for TOPO-stripped CdSe nanocrystallites. The superior morphology and optical properties of polymer nanocomposite (P3HT:CdSe QDs) could play a pivotal role for the realization of effective charge separation and transport in hybrid solar cells.

Abstract: Using the morphological differences of low and high index surfaces as templates for metal growth, several low dimensional overlayer structures with novel structural and electronic properties can be formed. We present here a first report on submonolayer adsorption and residual thermal desorption studies of In adatoms on reconstructed high index Si (5 5 12)-2 x 1 surface and compare it with the observations on planar Si (111)-7 x 7 surface. The study is done by using in-situ Ultra High Vacuum surface sensitive probes like Auger Electron Spectroscopy (AES) and Low Energy Electron Diffraction (LEED). These conventional wide area techniques provide an understanding of atomistic issues involved in the evolution of the interface. We have observed an anomalous growth mode during adsorption at room temperature (RT) above 2ML, which includes adatom layering and clustering on Si (111) surface. This is also manifested during the desorption experiments on both surfaces, and the subtle differences on the two surfaces are discussed. The observation of LEED pattern during the adsorption process shows formation of different superstructural phases on Si (111)-7 x 7 surface. On Si (5 5 12) 2 x 1 surface we observe the sequential 2 x (225), 2 x (337) and 2x (113) facet formation during adsorption/desorption, which include quasi 1D-nanowire/chain structures. A combination of lattice strain effects, presence of step-edge barrier and quantum size effects are employed to speculate the differences in adsorption and desorption. (C) 2010 Elsevier B.V. All rights reserved.

Abstract: Abstract The influence of substrate bias and hydrogen/nitrogen incorporation on the optical properties [studied by spectroscopic ellipsometry (SE)] and surface morphology [studied by atomic force microscopy] of tetrahedral amorphous carbon (ta-C) films, deposited by S bend filtered cathodic vacuum arc (FCVA) process, is reported. SE spectra of the imaginary part of the dielectric constant are used to estimate carbon bonding ratios. In ta-C films, optical constants increase with substrate bias and hydrogen/nitrogen incorporation. The optical band gap (Eg) and sp3 content increase up to 200V substrate bias and then decrease. Eg increases with hydrogen incorporation but is unchanged by nitrogen incorporation.

Abstract: Abstract Using the morphological differences of low and high index surfaces as templates for metal growth, several low dimensional overlayer structures with novel structural and electronic properties can be formed. We present here a first report on submonolayer adsorption and residual thermal desorption studies of In adatoms on reconstructed high index Si (5 5 12) 2��1 surface and compare it with the observations on planar Si (111) 7��7 surface. The study is done by using in-situ Ultra High Vacuum surface sensitive probes like Auger Electron Spectroscopy (AES) and Low Energy Electron Diffraction (LEED). These conventional wide area techniques provide an understanding of atomistic issues involved in the evolution of the interface. We have observed an anomalous growth mode during adsorption at room temperature (RT) above 2ML, which includes adatom layering and clustering on Si (111) surface. This is also manifested during the desorption experiments on both surfaces, and the subtle differences on the two surfaces are discussed. The observation of LEED pattern during the adsorption process shows formation of different superstructural phases on Si (111) 7��7 surface. On Si (5 5 12) 2��1 surface we observe the sequential 2�� (225), 2�� (337) and 2�� (113) facet formation during adsorption/desorption, which include quasi 1D-nanowire/chain structures. A combination of lattice strain effects, presence of step-edge barrier and quantum size effects are employed to speculate the differences in adsorption and desorption.

Abstract: The present study compares energetics of wetting behavior of crystalline and amorphous forms of a poorly water soluble drug, celecoxib (CLB) and attempts to correlate it to their surface molecular environment. Wettability and surface free energy were determined using sessile drop contact angle technique and water vapor sorption energetics was measured by adsorption calorimetry. The surface chemistry was elucidated by X-ray photoelectron spectroscopy (XPS) and crystallographic evaluation. The two solid forms displayed distinctly different wetting with various probe liquids and in vitro dissolution media. The crystalline form surface primarily exhibited dispersive surface energy (47.3 mJ/m(2)), while the amorphous form had a slightly reduced dispersive (45.2 mJ/m(2)) and a small additional polar (4.8 mJ/m(2)) surface energy. Calorimetric measurements, revealed the amorphous form to possess a noticeably high differential heat of absorption, suggesting hydrogen bond interactions between its polar energetic sites and water molecules. Conversely, the crystalline CLB form was found to be inert to water vapor sorption. The relatively higher surface polarity of the amorphous form could be linked to its greater oxygen-to-fluorine surface concentration ratio of 1.27 (cf. 0.62 for crystalline CLB), as determined by XPS. The crystallographic studies of the preferred cleavage plane (0 2 0) of crystalline CLB further supported its higher hydrophobicity. In conclusion, the crystalline and amorphous forms of CLB exhibited disparate surface milieu, which in turn can have implications on the surface mediated events. (C) 2010 Elsevier B.V. All rights reserved.

Abstract: Abstract The effect of substrate bias on X-ray photoelectron spectroscopy (XPS) study of nitrogen incorporated amorphous carbon (a-C:N) films embedded with nanoparticles deposited by filtered cathodic jet carbon arc technique is discussed. High resolution transmission electron microscope exhibited initially the amorphous structure but on closer examination the film was constituted of amorphous phase with the nanoparticle embedded in the amorphous matrix. X-ray diffraction study reveals dominantly an amorphous nature of the film. A straight forward method of deconvolution of XPS spectra has been used to evaluate the sp3 and sp2 contents present in these a-C:N films. The carbon (C 1s) peaks have been deconvoluted into four different peaks and nitrogen (N 1s) peaks have been deconvoluted into three different peaks which attribute to different bonding state between C, N and O. The full width at half maxima (FWHM) of C 1s peak, sp3 content and sp3/sp2 ratio of a-C:N films increase up to 150V substrate bias and beyond 150V substrate bias these parameters are found to decrease. Thus, the parameters evaluated are found to be dependent on the substrate bias which peaks at 150V substrate bias.

Abstract: Abstract Poly(dimethylsiloxane) (PDMS) has been used extensively for microfluidic components and as substrates for biological applications. Since the native nature of PDMS is hydrophobic it requires a functionalization step for use in conjunction with aqueous media. Commonly, oxygen plasma treatment is used for the formation of hydrophilic groups on the surface. However, the hydrophilic nature of these surfaces is short lived and the surfaces quickly revert back to their original hydrophobic state. In this work, branched-polyethylenimine (b-PEI) was used for long term modification of plasma treated PDMS surface. Contact angle, X-ray photoelectron spectroscopy (XPS) and Atomic force microscopy (AFM) were used for characterization of the modified surfaces and their stability with time was studied. The results obtained demonstrate that comparatively higher stability, hydrophilic, positively charged surfaces can be obtained after b-PEI treatment. These b-PEI treated PDMS surfaces can be used as fluidic channels for the separation of molecules as well as a substrate for the adherence of bio-molecules or biological cells.

Abstract: In this work, we have synthesized high quality TiO(2) nanocrystallites by sol-gel method (TiO(2) white (w)) and compared its properties with the ones synthesized by the simple hydrolysis method in aqueous solution (TiO2 transparent (t)). The TiO(2)/MEH-PPV nanocomposites are formed mainly by two ways: (i) Prepared in the form of the colloidal solution by adding the known concentration of the TiO(2) in MEH-PPV and then sonicate it well; (ii) In the thin film form by depositing the above solution over a glass substrate by spin coating. The properties of the resulting dispersions could be tailored by varying the composition and concentration of TiO(2) nanoparticles in CP�s. The TiO(2) nanoparticles prepared by both methods show anatase character of TiO(2) as elucidated by X-ray diffraction (XRD) studies. Transmission electron microscopic (TEM) studies reveal that the transparent colloidal suspension of TiO2 exhibits agglomeration of TiO(2) nanoparticles (size similar to 150-300 nm) and this trend is maintained in the MEH-PPV matrix for TiO(2)/MEH-PPV composites as well. However, the composite obtained by mixing MEH-PPV with sol-gel prepared TiO(2)(w) shows uniform nanoscale dispersion of TiO(2) (size similar to 20 nm) in MEH-PPV matrix. The UV-VIS absorption, photoluminescence (PL) and lifetime studies confirm the presence of dynamic quenching effect indicating efficient photoinduced charge transfer in TiO(2)/MEH-PPV hybrid composites particularly with white TiO(2). It is conjectured that the devices containing TiO(2)/MEH-PPV composites for TiO(2) prepared by the sol-gel method should lead to significant improvement in the photovoltaic performance of TiO(2)/MEH-PPV hybrid solar cells. (C) 2010 Elsevier BM. All rights reserved.

Abstract: Poly(dimethylsiloxane) (PDMS) has been used extensively for microfluidic components and as substrates for biological applications. Since the native nature of PDMS is hydrophobic it requires a functionalization step for use in conjunction with aqueous media. Commonly, oxygen plasma treatment is used for the formation of hydrophilic groups on the surface. However, the hydrophilic nature of these surfaces is short lived and the surfaces quickly revert back to their original hydrophobic state. In this work, branched-polyethylenimine (b-PEI) was used for long term modification of plasma treated PDMS surface. Contact angle, X-ray photoelectron spectroscopy (XPS) and Atomic force microscopy (AFM) were used for characterization of the modified surfaces and their stability with time was studied. The results obtained demonstrate that comparatively higher stability, hydrophilic, positively charged surfaces can be obtained after b-PEI treatment. These b-PEI treated PDMS surfaces can be used as fluidic channels for the separation of molecules as well as a substrate for the adherence of bio-molecules or biological cells. (C) 2010 Elsevier B.V. All rights reserved.

Abstract: ZnO nanorods are grown on seedless and ZnO seeded glass substrates using chemical solution method and their structural, morphological, optical and valence band studies have been carried out. On seedless substrate horizontal nanorods are observed whereas for the seeded substrates vertically aligned hollow and solid nanorods grows. X-ray diffraction analysis revealed the presence of tensile stress in the vertical nanorods. Blue shift has been observed in the band gap of the vertical nanorods as compared to the horizontal nanorods which is attributed to the presence of tensile stress in the vertically aligned nanorods. Photoluminescence spectra revealed the dominance of Zinc vacancies (V(Zn)) related. defects in the nanorods and oxygen defects are found to be higher in the vertically aligned nanorods as compared to the horizontal nanorods. The difference between the Fermi level and valence band maxima for horizontal, hollow vertical and solid vertical nanorods are found to be similar to 0.56 eV, similar to 0.70 eV and similar to 0.92 eV respectively indicating the possibility of p-type of conduction in the nanorods which has been attributed to presence of V(Zn) defects in the ZnO nanorods.

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Abstract: Monolayer Ga adsorption on Si surfaces has been studied with the aim of forming p-delta doped nanostructures. Ga surface phases on Si can be nitrided by N-2(+) ion bombardment to form GaN nanostructures with exotic electron confinement properties for novel optoelectronic devices. In this study, we report the adsorption of Gain the submonolayer regime on 7 x 7 reconstructed Si(1 1 1) surface at room temperature, under controlled ultrahigh vacuum conditions. We use in-situ Auger electron spectroscopy, electron energy loss spectroscopy and low energy electron diffraction to monitor the growth and determine the properties. We observe that Ga grows in the Stranski-Krastanov growth mode, where islands begin to form on two. at monolayers. The variation in the dangling bond density is observed during the interface evolution by monitoring the Si (LVV) line shape. The Ga adsorbed system is subjected to thermal annealing and the residual thermal desorption studied. The difference in the adsorption kinetics and desorption dynamics on the surface morphology is explained in terms of strain relaxation routes and bonding configurations. Due to the presence of an energetic hierarchy of residence sites of adatoms, site we also plot a 2D phase diagram consisting of several surface phases. Our EELS results show that the electronic properties of the surface phases are unique to their respective structural arrangement. (C) 2009 Elsevier B.V. All rights reserved.

Abstract: Adsorption of Group III metal In nanostructures on Si surfaces is an exciting field that integrates the exotic electronic properties of the nano-phase and the p-doping abilities of In. We present here the kinetics of growth of In on (7 x 7) reconstructed Si(l 11) surface by experiments done in ultra high vacuum in the submonolayer regime, probed in-situ by surface sensitive techniques. Indium is observed to grow in the layer by layer mode. The study reveals adsorption behavior dictated by layer-dependent mobilities of In atoms that causes initial island formation that later wet the surface. However the desorption studies manifest the initial agglormeration of top layer atoms, which at higher temperatures overcome step-edge barriers and consequently two-dimensional layering of three-dimensional islands before sublimation occurs. Thus the study reveals the kinetic details of the anamolour behavior of the In/Si interface formation and desorption that can enable the tailor making of several nano-phases and structures of characteristic properties.

Abstract: Lead (Pb) has been a prototypical system to study diffusion and reconstruction of silicon surfaces. However, there is a discrepancy in literature regarding the critical coverage at which island formation takes place in the Stranski-Krastanov (S-K) mode. We address this issue by studying the initial stages of evolution of the Pb/Si (1 1 1)7 x 7 system by careful experiments in ultra-high vacuum with in situ characterization by auger electron spectroscopy, electron energy loss spectroscopy and low-energy electron diffraction. We have adsorbed Pb onto clean Si(1 1 1) 7 x 7 surface with sub-monolayer control at different flux rates of 0.05 ML/min, 0.14 ML/min and 0.22 ML/min, at room temperature. The results clearly show that the coverage of the Pb adlayer before the onset of 3D Pb islands in the S-K mode depends on the flux rates. LEED results show the persistence of the (7 x 7) substrate reconstruction until the onset of the island formation, while EELS results do not show any intermixing at the interface. This suggests that the flux rates influence the kinetics of growth and the passivation of dangling bonds to result in the observed rate-dependent adlayer coverages. (C) 2009 Elsevier B.V. All rights reserved.

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Abstract: The surface topography of high index Si(5 5 12) presents a single-domain planar reconstruction that is composed of (225) and (337) regions with nanoscale widths and row like trenches and provides an unique template for the growth of nanostructures. In this study, Sb has been adsorbed on this Silicon surface to form various superstructural phases by steering the kinetic parameters and post growth annealing of the surface. Different pathways adopted have shown the formation of stabilized ordered superstructural phases corresponding to various coverages and substrate temperatures and are probed in-situ by complementary surface sensitive techniques such as Low Energy Electron Diffraction (LEED), Auger Electron Spectroscopy (AES), and Electron Energy Loss Spectroscopy (EELS). The growth of Sb at 300 degrees C substrate temperature and annealing the formed system to different temperatures upto 820 degrees C leads to the formation of low dimensional phases having anisotropicity along the (110) direction like atomic wires. The results also demonstrate the pathways in tailoring 1 D and 2D nanostructure formation, on this technologically and scientifically important interface.

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Abstract: Thin film electro-luminescent devices based on organic materials are very popular for organic light emitting diodes (OLEDs) fabrication. The authors have polymerized PPV precursor solution from p-Xylenebis (tetrahydrothiophenium chloride) salt. Thin films of PPV were prepared by spin-coating, the precursor onto ITO substrates and curing it at 220degreesC in the absence of oxygen. Organic light emitting diode structures were fabricated using ITO as the bottom electrode, PPV as an emitter layer as well as hole transport layer, US as an electron transport layer and aluminium as the cathode. In this configuration, US provides the advantage of excellent charge-transporting properties of an inorganic semiconductor. Electro-luminescence spectrum obtained from this hetero-junction device was similar to the emission spectrum of PPV. The devices give bright greenish-yellow electro-luminescence on application of about 10V under forward biased condition.

Abstract: The adsorption of Sb on the high index Si (5 5 12) has been studied at higher substrate temperature (HT) (800 degrees C), using in situ surface characterization techniques like Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED), and Electron Energy Loss Spectroscopy (EELS). The surface morphology of this high index Si (5 5 12) surface has row like trenches along (110) direction. The different pathways adopted during adsorption and desorption have suggested the dominant role of kinetics in forming various surface phases on the Si (5 5 12) substrate. The adsorption performed at the substrate temperature of 800 degrees C resulted in the formation of (113) like facets with anisotropic growth of Sb along one direction, at initial coverages and changed to the 2037 phase at the higher coverages. The annealing of the adsorbed surface to 800 degrees C, resulted in the formation of (2x113) phase. Annealing this 2x Si (337) phase to about 800 degrees C again resulted in the formation of anisotropic (337) phase. Thus, formation of interface by controlling the growth kinetics can result in the formation of various tailored structures with desired properties.

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