In situscanning tunneling microscopic and spectroscopic investigation of magnetron-sputtered C and CN thin films

Abstract

Carbon and carbon nitride films, grown in argon or nitrogen discharges by reactive dc magnetron sputtering of a graphite target, were characterized by in situ scanning tunneling microscopy. When the growth temperature increased from ambient to 800°C, we observed a topographic evolution of the carbon films from an amorphous to a graphitelike structure, and further to a distorted-graphitic phase with curved and intersecting basal planes, and finally to a surface containing nanotubes and nanodomes. When nitrogen was incorporated into the films, distortion of the graphitic basal planes occurred at a lower temperature compared to the pure carbon case. At temperatures of ϳ200°C and above, regions of a nongraphitic phase, containing a high degree of carbon sp 3 bonds were observed. Spatially resolved tunneling spectroscopic measurements indicated that the band gaps were 0, ϳ0-0.6 eV, and ϳ0.4-2.0 eV for graphitelike structures, the distorted-graphitic phase, and the nongraphitic phase, respectively. Together with ex situ x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy measurements, the results suggest that the incorporation of nitrogen promotes bending of the graphitic basal planes and thereby facilitates the formation of three-dimensional covalently bonded networks with a high degree of sp 3 -coordinated carbon atoms.

Quantitative REELS of amorphous carbon and carbon nitride films

“…Our results indicate rather clearly an increase of sp 3 hybridization in the CN x films with respect to a-C films in agreement with the results reported by Lin et al 16 for CN x films grown by magnetron sputtering. All this suggests that the content of sp 2 bonds in a determined CN x film does not only depend on the composition but also on the deposition method.…”

“…All this suggests that the content of sp 2 bonds in a determined CN x film does not only depend on the composition but also on the deposition method. While CN x films grown by electroncyclotron resonance 16 or ablation laser 5 seem to increase the graphite-like character of the material when nitrogen is incorporated, those CN x films grown by sputtering methods show the opposite behaviour.…”

Fullerene-like Carbon Nitride: A Resilient Coating Material

“…Only a few groups have reported NMR studies of CN x materials, [48][49][50][51][52][53] and most seem to indicate a predominant sp 2 character of the films.…”

Fullerenelike arrangements in carbon nitride thin films grown by direct ion beam sputtering

“…5 As compared with pure C materials, the introduction of N reduces the energy barrier to induce curvature in the basal planes. 6,7 So far, the production of well-structured FL-CN x thin films has been only reported by reactive dc magnetron sputtering ͑dc-MS͒ while, recently, pulsed laser deposition ͑PLD͒ resulted also in partially structured films. 8 Low-energy ͑Ͻ100 eV͒ ion bombardment and moderate substrate temperatures ͑400-800 K͒ have been shown to be essential for the synthesis of FL-CN x thin films by dc-MS. 9 The required growth conditions are necessary to promote threefold N bonding environments over N atoms in low-coordination sites ͑i.e., pyridine-and cyanogenlike environments͒.…”