The plasma characteristics of a new arc mode on carbon referred to as the ``stationary cathodic a... more The plasma characteristics of a new arc mode on carbon referred to as the ``stationary cathodic arc'' are reported. Particularly, optical emission spectroscopy, probe and ion energy distribution measurements are used to compare the properties of the stationary arc with the normal ``random cathodic arc'' on carbon. The measurements revealed that the plasma properties of both arc modes are similar. In addition, we have correlated the plasma characteristics to the film properties. Carbon films deposited using the stationary arc were found to have a surface particle density equivalent to those deposited using the filtered cathodic vacuum arc. The macro-particle free films were found to be highly tetrahedral and compressively stressed. Both the sp3 fraction and stress values were strongly dependent on the ion energy with maximum values of 85% and 9.4 GPa, respectively, occurring at ≊50 eV.
... Kimon C. Palinginis, Yoram Lubianiker, J. David Cohen, Adelina Ilie, Britta Kleinsorge, Willi... more ... Kimon C. Palinginis, Yoram Lubianiker, J. David Cohen, Adelina Ilie, Britta Kleinsorge, William I. Milne. ... PJ Fallon, VS Veerasamy, CA Davis, J. Robertson, GAJ Amaratunga, WI Milne, and J. Koskinen, Properties of filtered-ion-beam-deposited diamondlike carbon as a function ...
Vertically aligned carbon nanofibres were grown at temperatures as low as 120°C by plasma-enhance... more Vertically aligned carbon nanofibres were grown at temperatures as low as 120°C by plasma-enhanced chemical vapour deposition (PECVD). A systematic study of the temperature dependence of the growth rate found an activation energy of 0.23 eV, much less than that for thermal chemical vapour deposition (1.2 1.5 eV). This suggests that growth occurs by surface diffusion of carbon on nickel. Vertically aligned carbon nanofibres were grown by PECVD on to flexible plastic substrates. We show that individual lines and dots of free-standing 20 50 nm diameter nanotubes can be grown on to chromium-covered polyimide foil. The scalable deposition method allows large-area coverage without damaging or bending the sensitive substrate material. Field-emission cathodes were made for the purpose of demonstration.
Vertically aligned carbon nanotubes were grown at temperatures as low as 120 °C by plasma-enhance... more Vertically aligned carbon nanotubes were grown at temperatures as low as 120 °C by plasma-enhanced chemical vapor deposition. A systematic study of the temperature dependence of the growth rate and the structure of the as-grown nanotubes is presented using a C2H2/NH3 system and nickel as the catalyst. The activation energy for the growth rate was found to be 0.23 eV, much less than for thermal chemical vapor deposition (1.2-1.5 eV). This suggests growth occurs by surface diffusion of carbon on nickel. The result could allow direct growth of nanotubes onto low-temperature substrates like plastics, and facilitate the integration in sensitive nanoelectronic devices.
The carbon ion energy used during filtered cathodic vacuum arc deposition determines the bonding ... more The carbon ion energy used during filtered cathodic vacuum arc deposition determines the bonding topologies of amorphous-carbon (a-C) films. Regions of relatively low density occur near the substrate/film and film/surface interfaces; their thicknesses increase with deposition energy. The ion subplantation growth results in mass density gradients in the bulk portion of a-C in the growth direction; density decreases with distance from the substrate for films grown using ion energies <60 eV and increases for films grown using ion energies >160 eV. Films grown between these energies are the most diamondlike with relatively uniform bulk density and the highest optical transparencies. Bonding topologies evolve with increasing growth energy consistent with the propagation of subplanted carbon ions inducing a partial transformation of σ- to π-bonded carbon atoms.
A comprehensive study of the stress release and structural changes caused by postdeposition therm... more A comprehensive study of the stress release and structural changes caused by postdeposition thermal annealing of tetrahedral amorphous carbon (ta-C) on Si has been carried out. Complete stress relief occurs at 600-700 °C and is accompanied by minimal structural modifications, as indicated by electron energy loss spectroscopy, Raman spectroscopy, and optical gap measurements. Further annealing in vacuum converts sp3 sites to sp2 with a drastic change occurring after 1100 °C. The field emitting behavior is substantially retained up to the complete stress relief, confirming that ta-C is a robust emitting material.
The direct growth of vertically aligned carbon nanotubes onto flexible plastic substrates using p... more The direct growth of vertically aligned carbon nanotubes onto flexible plastic substrates using plasma-enhanced chemical vapor deposition is reported. We show that individual lines and dots of free-standing 20-50 nm diameter nanotubes can be grown onto chromium covered commercially available polyimide foil. The scalable deposition method allows large area coverage without degrading or bending the sensitive substrate material. Field emission measurements show a low turn-on field (3.2 V/μm) and a low threshold field (4.2 V/μm). The result establishes a method of flexible field emitter fabrication, which is well suited for display production and integration of nanotubes into plastic electronics.
It is shown that for a cathode consisting of compressed graphite powder, the cathodic arc dischar... more It is shown that for a cathode consisting of compressed graphite powder, the cathodic arc discharge is confined within deep erosion holes and the macroparticle emission is greatly reduced. Electron energy loss spectroscopy and scanning electron microscopy show that smooth tetrahedral amorphous carbon films with up to 85±10% sp3 bonding can be deposited without the use of magnetic filters. The new carbon arc discharge process holds potential for deposition of smooth tetrahedral amorphous carbon films on large area substrates due to the elimination of the magnetic filtering stage.
A systematic study is presented of the influence of catalyst film thickness on carbon nanostructu... more A systematic study is presented of the influence of catalyst film thickness on carbon nanostructures grown by plasma-enhanced chemical-vapor deposition from acetylene and ammonia mixtures. We show that reducing the Fe /Co catalyst film thickness below 3nm causes a transition from larger diameter (>40nm), bamboolike carbon nanofibers to small diameter (˜5nm) multiwalled nanotubes with two to five walls. This is accompanied by a more than 50 times faster growth rate and a faster catalyst poisoning. Thin Ni catalyst films only trigger such a growth transition when pretreated with an ammonia plasma. We observe a limited correlation between this growth transition and the coarsening of the catalyst film before deposition. For a growth temperature of ⩽550°C, all catalysts showed mainly a tip growth regime and a similar activity on untreated silicon, oxidized silicon, and silicon nitride support.
Scanning tunneling spectroscopy (STS) has been used to investigate the electronic structure of te... more Scanning tunneling spectroscopy (STS) has been used to investigate the electronic structure of tetrahedral amorphous carbon (ta-C) films. The density of states (DOS) was derived from the normalized conductivity spectra at fixed tip heights. Band edges were defined by extrapolating the generalized conductivity (dI/dV) within ±2 eV of the Fermi level. The resulting band gap was found to be similar to that measured optically for ta-C films of different sp3 content. The Fermi level of undoped ta-C was found to lie below midgap, confirming ta-C to be a weakly p-type semiconductor. The valence band tail is found to be steeper than the conduction band tail, the opposite of the situation in a-Si:H. With nitrogen addition, the Fermi level is found to move above midgap, confirming that n-type doping is occurring. The band gap is found to decline at higher N contents. The DOS at larger tip heights and as a function of surface etching shows evidence of a surface layer with a narrower band gap, which we identify as the sp2-rich surface layer seen previously by cross-sectional electron energy loss spectroscopy. The STS DOS shows peaks which we attribute to states of the surface layer having more graphitic bonds. The scanning tunneling microscopy images show that ta-C deposited on Si has a root mean square surface roughness of 1.7 Å and this increases to about 10 Å for films deposited on metals such as Ti.
The plasma characteristics of a new arc mode on carbon referred to as the ``stationary cathodic a... more The plasma characteristics of a new arc mode on carbon referred to as the ``stationary cathodic arc'' are reported. Particularly, optical emission spectroscopy, probe and ion energy distribution measurements are used to compare the properties of the stationary arc with the normal ``random cathodic arc'' on carbon. The measurements revealed that the plasma properties of both arc modes are similar. In addition, we have correlated the plasma characteristics to the film properties. Carbon films deposited using the stationary arc were found to have a surface particle density equivalent to those deposited using the filtered cathodic vacuum arc. The macro-particle free films were found to be highly tetrahedral and compressively stressed. Both the sp3 fraction and stress values were strongly dependent on the ion energy with maximum values of 85% and 9.4 GPa, respectively, occurring at ≊50 eV.
... Kimon C. Palinginis, Yoram Lubianiker, J. David Cohen, Adelina Ilie, Britta Kleinsorge, Willi... more ... Kimon C. Palinginis, Yoram Lubianiker, J. David Cohen, Adelina Ilie, Britta Kleinsorge, William I. Milne. ... PJ Fallon, VS Veerasamy, CA Davis, J. Robertson, GAJ Amaratunga, WI Milne, and J. Koskinen, Properties of filtered-ion-beam-deposited diamondlike carbon as a function ...
Vertically aligned carbon nanofibres were grown at temperatures as low as 120°C by plasma-enhance... more Vertically aligned carbon nanofibres were grown at temperatures as low as 120°C by plasma-enhanced chemical vapour deposition (PECVD). A systematic study of the temperature dependence of the growth rate found an activation energy of 0.23 eV, much less than that for thermal chemical vapour deposition (1.2 1.5 eV). This suggests that growth occurs by surface diffusion of carbon on nickel. Vertically aligned carbon nanofibres were grown by PECVD on to flexible plastic substrates. We show that individual lines and dots of free-standing 20 50 nm diameter nanotubes can be grown on to chromium-covered polyimide foil. The scalable deposition method allows large-area coverage without damaging or bending the sensitive substrate material. Field-emission cathodes were made for the purpose of demonstration.
Vertically aligned carbon nanotubes were grown at temperatures as low as 120 °C by plasma-enhance... more Vertically aligned carbon nanotubes were grown at temperatures as low as 120 °C by plasma-enhanced chemical vapor deposition. A systematic study of the temperature dependence of the growth rate and the structure of the as-grown nanotubes is presented using a C2H2/NH3 system and nickel as the catalyst. The activation energy for the growth rate was found to be 0.23 eV, much less than for thermal chemical vapor deposition (1.2-1.5 eV). This suggests growth occurs by surface diffusion of carbon on nickel. The result could allow direct growth of nanotubes onto low-temperature substrates like plastics, and facilitate the integration in sensitive nanoelectronic devices.
The carbon ion energy used during filtered cathodic vacuum arc deposition determines the bonding ... more The carbon ion energy used during filtered cathodic vacuum arc deposition determines the bonding topologies of amorphous-carbon (a-C) films. Regions of relatively low density occur near the substrate/film and film/surface interfaces; their thicknesses increase with deposition energy. The ion subplantation growth results in mass density gradients in the bulk portion of a-C in the growth direction; density decreases with distance from the substrate for films grown using ion energies <60 eV and increases for films grown using ion energies >160 eV. Films grown between these energies are the most diamondlike with relatively uniform bulk density and the highest optical transparencies. Bonding topologies evolve with increasing growth energy consistent with the propagation of subplanted carbon ions inducing a partial transformation of σ- to π-bonded carbon atoms.
A comprehensive study of the stress release and structural changes caused by postdeposition therm... more A comprehensive study of the stress release and structural changes caused by postdeposition thermal annealing of tetrahedral amorphous carbon (ta-C) on Si has been carried out. Complete stress relief occurs at 600-700 °C and is accompanied by minimal structural modifications, as indicated by electron energy loss spectroscopy, Raman spectroscopy, and optical gap measurements. Further annealing in vacuum converts sp3 sites to sp2 with a drastic change occurring after 1100 °C. The field emitting behavior is substantially retained up to the complete stress relief, confirming that ta-C is a robust emitting material.
The direct growth of vertically aligned carbon nanotubes onto flexible plastic substrates using p... more The direct growth of vertically aligned carbon nanotubes onto flexible plastic substrates using plasma-enhanced chemical vapor deposition is reported. We show that individual lines and dots of free-standing 20-50 nm diameter nanotubes can be grown onto chromium covered commercially available polyimide foil. The scalable deposition method allows large area coverage without degrading or bending the sensitive substrate material. Field emission measurements show a low turn-on field (3.2 V/μm) and a low threshold field (4.2 V/μm). The result establishes a method of flexible field emitter fabrication, which is well suited for display production and integration of nanotubes into plastic electronics.
It is shown that for a cathode consisting of compressed graphite powder, the cathodic arc dischar... more It is shown that for a cathode consisting of compressed graphite powder, the cathodic arc discharge is confined within deep erosion holes and the macroparticle emission is greatly reduced. Electron energy loss spectroscopy and scanning electron microscopy show that smooth tetrahedral amorphous carbon films with up to 85±10% sp3 bonding can be deposited without the use of magnetic filters. The new carbon arc discharge process holds potential for deposition of smooth tetrahedral amorphous carbon films on large area substrates due to the elimination of the magnetic filtering stage.
A systematic study is presented of the influence of catalyst film thickness on carbon nanostructu... more A systematic study is presented of the influence of catalyst film thickness on carbon nanostructures grown by plasma-enhanced chemical-vapor deposition from acetylene and ammonia mixtures. We show that reducing the Fe /Co catalyst film thickness below 3nm causes a transition from larger diameter (>40nm), bamboolike carbon nanofibers to small diameter (˜5nm) multiwalled nanotubes with two to five walls. This is accompanied by a more than 50 times faster growth rate and a faster catalyst poisoning. Thin Ni catalyst films only trigger such a growth transition when pretreated with an ammonia plasma. We observe a limited correlation between this growth transition and the coarsening of the catalyst film before deposition. For a growth temperature of ⩽550°C, all catalysts showed mainly a tip growth regime and a similar activity on untreated silicon, oxidized silicon, and silicon nitride support.
Scanning tunneling spectroscopy (STS) has been used to investigate the electronic structure of te... more Scanning tunneling spectroscopy (STS) has been used to investigate the electronic structure of tetrahedral amorphous carbon (ta-C) films. The density of states (DOS) was derived from the normalized conductivity spectra at fixed tip heights. Band edges were defined by extrapolating the generalized conductivity (dI/dV) within ±2 eV of the Fermi level. The resulting band gap was found to be similar to that measured optically for ta-C films of different sp3 content. The Fermi level of undoped ta-C was found to lie below midgap, confirming ta-C to be a weakly p-type semiconductor. The valence band tail is found to be steeper than the conduction band tail, the opposite of the situation in a-Si:H. With nitrogen addition, the Fermi level is found to move above midgap, confirming that n-type doping is occurring. The band gap is found to decline at higher N contents. The DOS at larger tip heights and as a function of surface etching shows evidence of a surface layer with a narrower band gap, which we identify as the sp2-rich surface layer seen previously by cross-sectional electron energy loss spectroscopy. The STS DOS shows peaks which we attribute to states of the surface layer having more graphitic bonds. The scanning tunneling microscopy images show that ta-C deposited on Si has a root mean square surface roughness of 1.7 Å and this increases to about 10 Å for films deposited on metals such as Ti.
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