tailieunhanh - Carbon Materials for Advanced Technologies Part 2

Tham khảo tài liệu 'carbon materials for advanced technologies part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 15 XANES and in a-C H films the sp2 sp3 ratio can be measured dứectly using nmr spectroscopy 71 . The classification of amorphous carbon films according to carbon bond type and hydrogen content can be represented in a triangular diagram Fig. 6 . 70 The comers at the base of the triangle correspond to graphite 100 sp2 carbon and diamond 100 sp3 carbon . The apex represents 100 H but the upper limit for formation of solid films is defined by the tie line between the compositions of polyethene - CH2 n- and polyethyne - CH n -. Fig. 6. Classification diagram for amorphous carbon films . 70 . The majority of a-C films contain mainly sp2 carbon but the sp3 carbon content can be varied over the range 5-55 the hardness of the films increase with sp3 content. The H content of a-C H films can be varied over a wide range and the hardness of a-C H films is inversely related to the hydrogen content. For both types of films a high sp3 content is produced by ion beam deposition. Films with a very high sp3 content -80-90 and a correspondingly high hardness have been called tetrahedrally-bonded amorphous carbon films ta-C films 70 . Hard a-C H films were called diamond-like carbon DLC and this term has been used as a generic name for all amorphous carbon films. Thus as a general rule hardness increases with sp3 carbon content as the proportion of diamondlike carbon increases. Conversely the films become softer as the sp2 carbon content and or the hydrogen content increases reflecting the increasing content 16 of graphite-like carbon or polymer-like carbon respectively. Clearly there is considerable scope for varying properties of the carbon films by careful control of processing parameters. There is evidence for segregation of sp2 and sp3 bonded carbon in a-C and a-C H films. The structure of a-C films with a high sp2 carbon content is envisaged as clusters of warped graphitic domains bounded by sp3 carbon 71 . In a-C H films the extent of segregation of sp2 and sp3 carbon .

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