Using a variable-energy direct carbon ion beam deposition technique, thin amorphous carbon films were grown on a silicon substrate. Interface modification was performed using C− energies in the range of 300–500 eV prior to the growth of the film to enhance adhesion of the film. By lowering the energy of the C− beam to 150 eV, amorphous carbon film was continuously grown after the interface modification. High-resolution electron microscopy illustrated that the silicon surface was severely damaged by 500 eV C− beam and the thickness of damage layer was about 15 nm. The carbon concentration profile in silicon as determined by electron energy loss spectroscopy showed that 500 eV C− beam implanted carbon into silicon up to 30 nm in depth and carbon was mixed with silicon in this implanted region. Silicon L-edge study at the C/Si mixed region found C–Si bonding formation only at the surface of silicon over 2–3-nm-thick layers. The damage layer or C/Si mixing was not observed at 300 eV C− beam modification. Wear testing found that strong adhesion occurred in samples modified at 500 eV, which indicated complete mixing at the interface. At 300 eV, modified samples exhibited delamination failure, which indicated inferior adhesion of the films.

Very thin (<,100 nm) amorphous carbon films were grown on silicon substrates by unfiltered and filtered direct carbon ion beams. In situ surface modification was performed using C- energies in the range of 300–500 eV prior to the growth of the film. By lowering the energy of the C− beam to 150 eV, an amorphous carbon film was continuously grown after the surface modification. High-resolution electron microscopy showed that the film/substrate interface was damaged by 400 and 500 eV C− beams. The carbon composition profile at the interface investigated by electron energy-loss spectroscopy illustrated that the 500 eV C− beam generated a 30 nm thick carbon/silicon mixing layer at the interface. The damage and mixing layers were not observed at 300 eV modification. Wear testing found that strong adhesion occurred in samples modified at 400 and 500 eV. However, at 300 eV, modified samples exhibited delamination failure, which indicated inferior adhesion of the films. Surface roughness evolution of 30, 60, and 90 nm thick films was investigated by atomic force microscopy. The film surface roughness decrease as a function of film thickness was much faster when the films were grown by the filtered C− beam.

Using direct carbon ion beam deposition, in situ surface modification was performed by an energetic C − beam (400 and 500 eV) prior to amorphous carbon film growth to enhance adhesion of the film. It has been found from high-resolution electron microscopy that the C and Si mixing layer at the interface causes strong adhesion of the film. Electron energy loss spectroscopy was used to investigate chemical states of the C and Si mixing layer at the interface. The carbon composition profile in silicon showed that the thickness of the mixing layer was about 30 nm for 500 eV modification (at 200°C). Silicon L-edge study at the C/Si interface found C-Si bond formation only at the surface of silicon over 2-3-nm-thick layers. The C-Si bond formation is a function of C − ion impingement energy. The thickness of the bonding layer decreased to less than 1 nm for 400 eV surface modification. When the substrate was modified by a 500-eV C − beam at 800°C, the thickness of the SiC layer was about 10 nm. C-Si bond formation was enhanced by the supplemental thermal energy.

Hard carbon films can be prepared by the condensation of energetic carbon species at and below room temperature. These hydrogen-free films are primarily tetrahedrally coordinated and contain high fractions of sp3 bonding. Field emission from these and other forms of carbon has been considered previously, but it was generally unstable or based on surface treatments that limit their operating conditions. We report electron emission from amorphous carbon-cesium (a-C:Cs) thin films at applied fields as low as 7 V/μm. This emission characteristic is relatively insensitive to surface treatment; films left under ambient laboratory environment for more than six months show these favorable characteristics with no pretreatment. We describe the fabrication process and emission properties of these films.

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