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In present work, wall-to-wall joining of two parallel multiwalled carbon nanotubes (MWCNTs) has been successfully demonstrated using electron beam inside high resolution transmission electron microscope. The used MWCNTs have been grown using cobaltocene and benzene as catalyst and carbon precursor, respectively via thermal CVD technique. We have proposed that in present case, irradiation induced joining is achieved if adequate balance between sputtered carbon atoms from the outer walls of MWCNTs and generation as well as migration of defects along the tube axis is obtained. Casimir effect is not found to play dominating role in the joining process. The proposed method can potentially be used for developing wall-to-wall interconnection between MWCNTs using electron beam. [ABSTRACT FROM AUTHOR]

Here we demonstrate that by using sugarcane bagasse as a carbon precursor, highly crystalline diamond films possessing H3 [N-V-N] and [Si-V] − optical centers can be grown on Si (100) substrates using a simple thermal chemical vapor deposition (thermal-CVD) system at atmospheric pressure and reduced temperature (~900 °C). In this process, the rich chemistry of effluent gas species produced during the pyrolysis of sugarcane bagasse is found to play a vital role. Diamond films have also been characterized by using X-ray diffraction (XRD), scanning electron microscope (SEM), micro-Raman, and photoluminescence (PL) spectrometer. Presence of nitrogen and silicon related defect was probed by PL and H3, i.e. [N-V-N] at 505 nm and [Si-V] − at 736 nm optical centers have been confirmed. The other observed peaks at 445.7 nm, 468 nm, and 884 nm are assigned to nitrogen-containing defects. [ABSTRACT FROM AUTHOR]

The localized effect of impurities in single GaN nanowires in the sub-diffraction limit is reported using the study of lattice vibrational modes in the evanescent field of Au nanoparticle assisted tip enhanced Raman spectroscopy (TERS). GaN nanowires with the O impurity and the Mg dopants were grown by the chemical vapor deposition technique in the catalyst assisted vapor-liquid-solid process. Symmetry allowed Raman modes of wurtzite GaN are observed for undoped and doped nanowires. Unusually very strong intensity of the non-zone center zone boundary mode is observed for the TERS studies of both the undoped and the Mg doped GaN single nanowires. Surface optical mode of A1 symmetry is also observed for both the undoped and the Mg doped GaN samples. A strong coupling of longitudinal optical (LO) phonons with free electrons, however, is reported only in the O rich single nanowires with the asymmetric A1(LO) mode. Study of the local vibration mode shows the presence of Mg as dopant in the single GaN nanowires. [ABSTRACT FROM AUTHOR]

Role of "O" defects in sensing pollutant with nanostructured SnO2 is not well understood, especially at low temperatures. SnO2 nanoparticles were grown by soft chemistry route followed by subsequent annealing treatment under specific conditions. Nanowires were grown by chemical vapor deposition technique. A systematic photoluminescence (PL) investigation of "O" defects in SnO2 nanostructures revealed a strong correlation between shallow donors created by the in-plane and the bridging "O" vacancies and gas sensing at low temperatures. These SnO2 nanostructures detected methane (CH4), a reducing and green house gas at a low temperature of 50 °C. Response of CH4 was found to be strongly dependent on surface defect in comparison to surface to volume ratio. Control over "O" vacancies during the synthesis of SnO2 nanomaterials, as supported by X-ray photoelectron spectroscopy and subsequent elucidation for low temperature sensing are demonstrated. [ABSTRACT FROM AUTHOR]

Friction behaviour of an ultrananocrystalline diamond film deposited by the microwave plasma-enhanced chemical vapour deposition technique is studied in a controlled humid atmosphere. The value of friction coefficient consistently decreases while increasing the humidity level during the tribology test. This value is 0.13 under 10% relative humidity conditions, which is significantly decreased to 0.004 under 80% relative humidity conditions. Such a reduction in friction coefficient is ascribed to passivation of dangling covalent bonds of carbon atoms, which occurs due to the formation of chemical species of hydroxyl and carboxylic groups such as C-COO, CH3COH and CH2-O bonding states. [ABSTRACT FROM AUTHOR]

ZnO nanorods prepared through chemical vapor deposition technique are characterized by microscopic and X-ray photoelectron spectroscopy (XPS) techniques to correlate the effects of size on the binding energy of Zn 2p3/2 photoelectrons. A positive shift in Zn 2p3/2-binding energy as compared to that in bulk ZnO is assumed to be the effect of size of ZnO tips. The shift in binding energy has been explained in terms of relaxation energy in the photoemission process. Simultaneously, Auger parameter of the nanorods is evaluated for stoichiometric composition. The extra peak in O1s spectrum of nanorods is explained as adsorbed O-bearing species or surface contaminants. [ABSTRACT FROM AUTHOR]

Diamond like carbon (DLC) films were deposited on Si (111) substrates by microwave electron cyclotron resonance (ECR) plasma chemical vapour deposition (CVD) process using plasma of argon and methane gases. During deposition, a d.c. self-bias was applied to the substrates by application of 13·56 MHz rf power. DLC films deposited at three different bias voltages (-60 V, -100 V and -150 V) were characterized by FTIR, Raman spectroscopy and spectroscopic ellipsometry to study the variation in the bonding and optical properties of the deposited coatings with process parameters. The mechanical properties such as hardness and elastic modulus were measured by load depth sensing indentation technique. The DLC film deposited at -100 V bias exhibit high hardness (~ 19 GPa), high elastic modulus (~ 160 GPa) and high refractive index (~ 2·16-2·26) as compared to films deposited at -60 V and -150 V substrate bias. This study clearly shows the significance of substrate bias in controlling the optical and mechanical properties of DLC films. [ABSTRACT FROM AUTHOR]

Abstract: Single crystal diamond films of varying quality are deposited using microwave plasma chemical vapor deposition (MPCVD) apparatus. Unpolished natural diamond seeds are used as substrates in the temperature (T s) range 850–1200 °C. The gas mixture of methane (CH4), hydrogen (H2) and oxygen (O2) is used for the deposition of diamond. The deposition pressure is varied in the range 90 to 150 Torr. The films are characterized using scanning electron microscopy (SEM), Atomic force microscopy (AFM) and Raman spectroscopy techniques. The growth morphology of the films is found to be a sensitive function of the deposition parameters. The crystalline nature of the films change from polycrystalline to single crystal as we increase T s and for a certain set of parameters the filamentary growth of the diamond crystals can be seen. The films are polycrystalline in the range of substrate temperatures 850–900 °C and oriented grains of diamond crystals are evident as the T s increases. The single crystal diamond growth is observed to proceed via the step growth mechanism with the evidence of bunching of the steps. Our study explores evolution of the growth of single crystal diamond in a wide range of parameters. [Copyright &y& Elsevier]

Polycrystalline diamond films with a predominant (100) texture were deposited onto silicon substrates using hot-filament chemical vapor deposition. During film deposition, different temperature gradients were created and imposed laterally across the substrate materials. Films grown under a gradient of 100 °C cm-1 displayed large (100) oriented grains. No crystallite (100) orientation was observed in the as-grown films prepared without a temperature gradient. It was observed that the diamond grain size varied as a /unction of the gradient. The lower gradient resulted in smaller grains and vice versa. Furthermore, the size of the grains was a function of the deposition time. The orientation of the diamond grains changed gradually across the substrate from (100) to (110) orientation as we scanned from the high-temperature to the low-temperature zone. The films were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectroscopy. XRD showed strong (400) reflections in the oriented samples. SEM results indicated the presence of smooth diamond surfaces consisting of predominantly (100) oriented platelets. As the (100) oriented diamond grains were grown on top of the (100) oriented silicon substrates, the faces were mostly aligned parallel to the substrate surface resulting in the deposition of a smooth diamond surface. AFM observations revealed the presence of steps located at the boundaries of the oriented grains. FTIR results showed the characteristic difference in hydrogen bonding in the oriented samples and gave useful information about mechanisms responsible for the orientation. Quantitative analysis was carried out to measure the H content in the films, and it was found that the oriented films contained less hydrogen. Our findings suggest that high saturation of carbon and a concentration gradient of sp³ CH2 species can be the key... [ABSTRACT FROM AUTHOR]

The structural properties of few-walled carbon nanotubes (FWCNTs) grown by thermal chemical vapor deposition are investigated using high resolution transmission electron microscopy and Raman spectroscopy. The temperature dependent conduction mechanism of FWCNT networks are studied in the temperature regime of 5-200 K, and found to follow a combination of two parallel conduction mechanisms, viz., variable range hopping and fluctuation induced tunneling. Further we elucidate with Raman spectra, that the conduction mechanism not only depends on wall number alone, but significantly influenced by structural defects. [ABSTRACT FROM AUTHOR]

To employ the multiwalled carbon nanotubes (MWCNTs) in electronic devices,  their growth on conductive substrates is a prerequisite. Since electronic properties of MWCNT might be influenced by catalyst and substrate, therefore, to understand their influence on the work function and electrical resistance, individual MWCNT needs to be studied. In this report, we have demonstrated the growth of MWCNTs on conducting substrates such as copper, stainless steel, and insulating SiO2 using thermal CVD technique. First, as-grown MWCNTs on different substrates have been characterized with scanning electron microscopy and Raman spectroscopy. Furthermore, electrical measurements on as-grown individual MWCNT has been performed using electrostatic force microscopy and conductive atomic force microscopy. Performed measurements reveal that work function and electrical resistance of MWCNT vary from 4.32 to 5.32 eV and 4-498 kΩ, respectively, depending on the nature of catalyst as well as substrates. We envision that performed study might boost the on-going research activity in the area of MWCNT-based nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Meso-crystalline alumina (Al2O3) coatings having a nano-platelet microstructure were synthesized using an indigenously designed combustion chemical vapor deposition facility. Aluminum acetylacetonate of 0.001 to 0.005 M concentrations dissolved in ethanol was used as the precursor. Ultrasonically atomized precursor aerosols were fed coaxially into a flame, where it underwent evaporation followed by decomposition on a substrate kept in the flame. The deposition was carried out at 1150 ± 15 °C. Microstructures consisting of vertically standing isolated and fused hexagonal alumina platelets were obtained using 0.003 M and 0.005 M precursor concentrations, respectively. At lower concentrations (0.001 M) platelets of irregular shapes were observed. The meso-crystalline platelets were of 1.0 to 1.5 µm length and 50 to 100 nm thickness. [ABSTRACT FROM AUTHOR]

Abstract: Diamond windows prepared using hot filament chemical vapor deposition (CVD) were irradiated with Au and Ag ions of energy 100 and 130 MeV, respectively with fluence in the range 1010 to 3×1013 ions/cm2. Scanning electron microscopy (SEM) images showed substantial damage at the surface of the windows irradiated with Au+ of energy 100 MeV and fluence of 3×1013 ions/cm2. At some locations on the diamond windows deposited at 16 kPa, the surface layer appeared to have melted and flowed like a liquid exposing small crystallites underneath. Raman spectra of windows after irradiation showed i) a decrease in the intensity of the one-phonon line at 1332 cm−1 along with an increase in its half width; ii) substantial reduction in the intensity of the graphite G band; and, iii) the appearance of a new band at 667 cm−1. The band at 667 cm−1 did not have a corresponding Stokes line and was therefore identified as a photoluminescence (PL) band. The ion induced damage and localized melting of CVD diamond windows are discussed in terms of the thermal spike model. [Copyright &y& Elsevier]

In this study, we report the differences in hydrogen (H 2 ) absorption properties of platinum (Pt) and palladium (Pd) functionalized gallium nitride (GaN) nanowires via gas sensing studies. GaN nanowires of ∼ 25 − 200 nm diameter and ∼ 50 − 75  μ m length are grown uniformly over large area (10 × 10 mm 2 ) using Au assisted chemical vapour deposition technique. The nanowires are grown at 900 for 2 h using gallium (Ga) as source material and ammonia (NH 3 ) as the reacting gas. The nanowires are functionalized with Pd and Pt nanoclusters using solution technique. H 2 absorption by these functionalized nanowires which is manifested as gas sensing response is compared in the temperature range of 50–200. The role of surface kinetics in Pd and Pt is shown to be responsible for the difference in the sensor response. [ABSTRACT FROM AUTHOR]

The present study aims to control the direction of magnetization in Fe 3 C, Co and Ni nanorods filled inside carbon nanotube (CNT). This control has been achieved during growth by modifying thermal chemical vapor deposition (CVD) system. As-grown in situ filled-CNTs were found to exhibit permanent magnetization. These CNTs have been characterized by using scanning electron microscopy (SEM), X-ray diffraction, Raman spectroscopy and transmission electron microscopy (TEM). Afterwards, direction of magnetization in Fe 3 C, Co or Ni nanorod filled inside CNT has been further probed by using magnetic force microscopy (MFM). MFM measurements reveal that nanorod exhibits single domain behavior and direction of magnetization, instead of being controlled either by shape or magneto crystalline anisotropy, has been found to be influenced by magnetic field gradient, produced in modified thermal CVD system. Direction of magnetization has been found either along tube axis in vertical grown CNTs or in radial direction i.e. perpendicular to the tube axis in randomly grown CNTs. Besides investigated structural and magnetic properties, plausible growth model of in situ filling as well as mechanism to understand unique magnetization behavior has been proposed. [ABSTRACT FROM AUTHOR]

Abstract: We report here, a detailed study of the parameter window of the deposition pressures to grow the diamond films on GaN coated quartz substrates using microwave plasma deposition technique. Hexagonal GaN films of 5 µm coated on quartz are used as substrates for diamond deposition in the pressure range of 80–140 Torr, using microwave plasma chemical vapor deposition (MPCVD) technique. The diamond films are characterized by scanning electron microscopy, XRD, photoluminescence and Raman spectroscopy. Scanning electron microscope image shows that the nucleation density of the films is high and we can deposit a continuous film for a deposition time ranging for 6–8 h. Oriented growth of diamond has been observed at higher pressure. [Copyright &y& Elsevier]