Search

Abstract: The wettability and surface energy of hydrogenated amorphous carbon films (a-C:H) elaborated by distributed electron cyclotron resonance plasma were studied by contact angle measurements in relation to composition, structure and topography. Tetrahedral a-C:H (ta-C:H) showed relatively high water contact angle (CA) up to 82.3°, and low surface energy (E s), down to 25.3 mJ/m2. Hydrophobicity was found to increase with the intensity of the ion bombardment and with the tetrahedral character. A decrease of the dispersive component is responsible of the decrease of surface energy with substrate bias. Low mass-density polymer-like a-C:H (PLC) presents also a relatively high hydrophobicity with high water CA, up to 76.7°, and low surface energy values, down to 32.1 mJ/m2. Hydrophobicity is interpreted as resulting from a surface layer rich in sp2-carbon for ta-C:H and rich in C–H bonds for PLC. [Copyright &y& Elsevier]

Abstract: Sulfur-assisted hot-filament chemical vapor deposition (HFCVD) was employed to grow nanocrystalline diamond at low substrate temperature, ∼300 °C, on molybdenum (Mo), and ∼250 °C, on polyimide film. The polyimide films remained flexible and strong after the deposition, clearly indicating that they did not experience temperatures near or above the glass transition temperature at ∼360 °C. The relative intensity of the diamond peak in the Raman spectra increases when the substrate temperature is decreased from ∼500 to ∼300 °C, a result that is inverted with respect to HFCVD without sulfur. This behavior was employed to obtain microcrystalline diamond on Mo at ∼270 °C. Profound changes induced to the gas phase chemistry and surface reactions when a trace amount of H2S is added to the HFCVD process seem to enable these results. [Copyright &y& Elsevier]

Abstract: Continuous nanocrystalline diamond (NCD) films were grown in an argon-rich gas atmosphere with relatively high growth rates by sustaining a low power (5 W) DC plasma in a hot filament chemical vapor deposition system (HFCVD). The parameter window for the synthesis of NCD films was studied as a function of argon, methane and hydrogen concentrations, as well as substrate temperature and DC bias. The results are consistent with reports indicating that the DC plasma induces re-nucleation by ion bombardment during the initial growth step and helps to maintain the atomic H and hydrocarbon species near the growing surface. It was found that DC plasma-assisted HFCVD enables high NCD growth rates and expands the parameter window, rendering it unnecessary to heat the filament above 2800 K. [Copyright &y& Elsevier]

Abstract: We have applied Density Functional Theory (DFT) within the Generalized Gradient Approximation to study the behavior of lithium impurities in the diamond lattice. It was found that, although isolated interstitial lithium atoms in tetrahedral sites have a donor state relatively close to the conduction band at 0.35 eV, their behavior is critically affected by adjacent interstitials. Lithium atoms that occupy adjacent interstitial tetrahedral sites cluster spontaneously and induce carbon–carbon bond breaking in their neighborhood. The corresponding charge distribution and electronic density of states analyses show that charge localization takes place at the carbon atoms around the lithium clusters and deeper mid-gap states are introduced in the diamond band gap. The formation energy was found to be 1.88 eV and 3.09 eV, for clusters of two and three lithium atoms, respectively, considered in this study. The calculations also indicate that Li clustering would not take place if Li ions instead of atoms were incorporated interstitially. [Copyright &y& Elsevier]

Results are reported on the electron field emission properties of microcrystalline and nanocrystalline carbon thin films grown on molybdenum substrates by S-assisted hot-filament chemical vapor deposition technique using methane (CH4), hydrogen sulfide (H2S), and hydrogen (H2) gas mixtures. Electron field emission measurements revealed that the S-assisted thin films have substantially lower turn-on fields and steep rising currents, for both microcrystalline and nanocrystalline carbon, as compared to those grown without sulfur. In order to study the property–structure correlations, we characterized the films’ microstructure with SEM, AFM and Raman spectroscopy (RS) techniques. It was found that sulfur addition causes significant microstructural changes in both micro- and nanocrystalline thin films. S-assisted films show smoother and finer-grained surfaces than those grown without it, and a higher content of non-diamond carbon (sp2-bonded C). Besides, although most of the S is expected to be electrically inactive, under the high doping conditions hereby employed, there may be a significant amount in donor states. The results are discussed in terms of the dual role of S by enhancing the creation of defects and the availability of conduction electrons. [Copyright &y& Elsevier]

We fabricated large area bilayer graphene by hot filament chemical vapor deposition (HFCVD) on Cu foil. The HFCVD technique can represent a significant advantage over other techniques for industrial scaling at low cost. We performed systematic experiments to determine the best parameters to obtain uniform graphene coverage over an area of ~ 16 cm 2 . The experimental growth parameters are grouped into two distinct regions according to the products obtained: (A) continuous bilayer graphene with low defect density and (B) continuous bilayer graphene with high defect density. The optimum graphene films obtained are uniform bilayer with low defect density, greater than 90% transmittance in the visible region, and no gaps. The high quality of the bilayer graphene was confirmed by Raman spectroscopy mapping. The results show that the ratio of 2D to G peak intensities ( I 2D / I G ) is in the 0.9–1.6 range over 90% of the area. Moreover, we employed the static cling property of polyethylene terephthalate (PET) to preserve the integrity of the as-grown graphene films in the transfer process, showing that the graphene films become well attached to the SiO 2 /Si substrates while the PET films were completely peeled off. [ABSTRACT FROM AUTHOR]

Abstract: Carbon nanotubes (CNTs) have been fabricated on free-standing microcrystalline diamond (FSD) films by hot filament chemical vapor deposition using Ni as catalyst. Micro Raman spectroscopy has been used as a primary technique to characterize the hybrid material, while electron microscopy and electron energy loss spectroscopy served as complementary characterization techniques. The fabricated material shows the presence of multiwall carbon nanotubes of diameters in the range of 10–15nm with a wall thickness of 5–6nm protruding from the free-standing microcrystalline diamond films of crystallite sizes ranging from 0.5 to 2.0μm. The CNT-FSD films show good field emission properties with low turn-on field, large field enhancement factor, and an excellent current stability over a period of 10days. [Copyright &y& Elsevier]

Abstract: We performed a systematic study of the bactericide and bacterial anti-adhesive properties of nanocrystalline diamond (NCD) and microcrystalline diamond (MCD) in comparison to other important industrial materials, such as copper, silver, polyethylene (Poly), and stainless steel (SS). The data show that NCD has better bactericide and bacterial anti-adhesive activity than Ag, but not as good as Cu. MCD, on the other hand, does not appear to have significant anti-bacterial activity. The superlative properties of NCD, such as mechanical hardness, resistance to oxidation and corrosion, and biological compatibility with blood and tissue, enable its use as antibacterial coating for medical implants. This is an application that cannot be achieved by Cu, which is known to be a highly effective antibacterial material but is not biocompatible. We also discuss possible underlying mechanisms to help understand the bactericide and bacterial anti-adhesive properties of the NCD surface. [Copyright &y& Elsevier]

Abstract: Spontaneously detaching self-standing diamond films were successfully fabricated using saturated hydrocarbon polymers as seeding source by hot filament chemical vapor deposition (HFCVD) technique. X-ray diffraction confirmed the crystal structure of diamond. The microcrystalline morphology of the diamond films was analyzed by atomic force microscopy (AFM) and scanning electron microscopy. Raman spectra from the front and back sides of the films show the characteristic diamond band at 1332cm−1 and no carbide layer. EELS spectra also show the signature features of diamond. The use of hydrocarbon polymers as seeding source will improve the cost-effectiveness of the fabrication of diamond wafers by simplifying the fabrication process. [Copyright &y& Elsevier]

Abstract: Sulfur-assisted hot-filament chemical vapor deposition (HFCVD) was recently employed to grow diamond nano-crystals on polyimide film [F. Piazza, G. Morell, Diamond and Related Materials, 16 (2007) 1950], unambiguously showing that the substrate temperature was below 360 °C, the polyimide glass transition temperature. This accomplishment has opened the door to employ diamond in a wide range of applications where it needs to be integrated with temperature sensitive materials. The result reported earlier relies on visible Raman spectroscopy analysis. We hereby report new additional evidences confirming the result from transmission electron microscopy (TEM), high-resolution TEM, energy dispersive X-ray analysis, electron energy loss spectroscopy and selected area electron diffraction. [Copyright &y& Elsevier]

Abstract: The activity of n-type sulfur-doped microcrystalline CVD diamond films for electrochemical hydrogen evolution is decreased reversibly by the presence of oxygen dissolved in acidic aqueous solution. The activity is measured as a current at a constant applied potential versus a reference electrode and provides the basis for an analytical method for measuring dissolved oxygen. It is proposed that the presence of oxygen may act to decrease the number of majority carrier electrons near the surface. A possible mechanism is proposed. [Copyright &y& Elsevier]

Abstract: Sulfur-assisted hot-filament chemical vapor deposition was successfully employed to synthesize diamond films at relatively low substrate temperatures, sub 500 °C, on Mo and glass substrates. This result is ascribed to sulfur-containing species that create an additional carbon transport channel to the substrate, which explicitly requires a large temperature gradient to effectively operate. The grain size and roughness were found to decrease when the Mo substrate temperature was decreased, while the quality factor only showed a slight decrease. Moreover, the diamond quality, grain size, and roughness were found to increase on glass substrates in comparison to those on Mo substrates. [Copyright &y& Elsevier]

Abstract: Boron carbonitride nanotubes (BCNNTs) were grown with high yield by DC arc discharge without catalyst particles or pre-grown template nanostructures. Two types of nanotubes (NTs) were formed: thin NTs with diameters of 10–15 nm and thick NTs with diameters of 25–50 nm. Transmission electron microscopy, electron energy loss spectroscopy, and Raman spectroscopy analyses indicate that the thin NTs are carbon NTs (CNTs) while the thick NTs are BCNNTs wrapped around CNTs. The growth kinetic appears to be faster for CNTs than for BCNNTs. Through the concerted substitution of B and N for C in the in situ grown CNTs, template growth of BCNNTs follows the CNTs growth without causing topological changes. [Copyright &y& Elsevier]

The effects of heavy-ion radiation over the electron field emission (EFE) properties of sulfur-doped nanocomposite carbon (n-C:S) films were investigated. Two identical sets of n-C:S films were prepared in a hot-filament chemical vapor deposition system using CH4, H2 and H2S. Films with various sp3 C and sp2 C fractions were present within each set. Raman spectroscopy revealed the composite nature of the films. One set of films was submitted to a 20 krad dose of energetic Si and Fe ions (GeV/amu) at Brookhaven National Laboratory''s alternating gradient synchrotron. Films originally having poor EFE properties showed a dramatic emission enhancement as a result of irradiation, while those having good EFE properties before irradiation showed a small emission improvement upon irradiation. This improved EFE behavior is explained as due to the formation of conductive trigonal carbon nano-channels within the tetragonally-bonded carbon matrix. The diameter of these trigonal carbon nano-channels is small enough to produce large local field enhancement, and large enough to withstand the relatively large emitted current densities. A mechanism is proposed for the creation of this graphitic carbon nano-wire network within the tetragonal carbon matrix upon energetic irradiation. The results suggest that radiation-hardened cold cathodes can be fabricated using nanocomposite carbon materials that would remain stable in their EFE properties while exposed to ionizing radiation. [Copyright &y& Elsevier]

We have investigated high sp2 content intrinsic and sulfur doped nanocrystalline diamond films to study field emission properties by electron emission microscopy operated in different modes. Electron emission microscopy enables real time imaging of the electron emission from a surface with a lateral resolution of ∼15 nm. The nanocrystalline intrinsic diamond films exhibit electron emission at room temperature from localized emission sites with weak temperature dependence, and a density of ∼103–104/cm2. In contrast, sulfur doped diamond films show similar emission characteristics at room temperature, but at elevated temperatures the emission significantly increases from the localized regions and a thermionic component is identified in the I/V dependence. We discuss the role of S-donor states to explain the enhanced emission of the S-doped nanocrystalline diamond. [Copyright &y& Elsevier]