| AVS 60th International Symposium and Exhibition | |
| Thin Film | Friday Sessions |
| Session TF+EM+NS+SS-FrM |
| Session: | Thin Film: Growth and Characterization III |
| Presenter: | K. Yu, Case Western Reserve University |
| Authors: | K. Yu, Case Western Reserve University C. Hayman, Case Western Reserve University W. Fan, Momentive Performance Materials, Inc. I.T. Martin, Case Western Reserve University H. Martin, Case Western Reserve University R.M. Sankaran, Case Western Reserve University |
| Correspondent: | Click to Email |
Pyrolytic graphite (PG) is a semi-crystalline form of carbon with wide-ranging electronic and thermal applications.1,2 The unique anisotropic and unparalleled electronic and thermal properties of PG stem from the alignment of its planar graphite sheets. A variety of structural forms of PG are currently commercially produced by high temperature (>1500 ◦C) hot-wall chemical vapor deposition (CVD). The degree of alignment (i.e. crystallinity) of the graphite in three dimensions and the growth rate, both of which affect the material properties and cost, depend discretely on process conditions, including growth temperature, gas chemistry, flow geometry, and pressure.
We have recently built a laboratory-scale, high-temperature vacuum reactor to study PG growth. Mixtures of methane and hydrogen gas are reacted to deposit as a carbon film on a heated substrate (1100-2000 ◦C). Solid carbon deposition under different conditions has been examined to understand the interplay of gas-phase chemistry and substrate nucleation. As-deposited materials are characterized by a suite of analytical techniques. Cross-sectional SEM provides visualization of the interaction of the carbon film with the substrate. The degree of alignment is assessed by micro Raman spectroscopy and X-ray diffraction (XRD). The Raman intensity ratio of the disordered carbon (D) to graphitic carbon (G) bands, an indicator of defects, decreases with increasing deposition temperature, consistent with commercial samples. Perfect Bernal stacking is only found for PG deposited at >2000 ◦C, as revealed by the 2D band. XRD also reveals the crystallite size through a Scherrer analysis of the peak widths. Smaller crystallite size and larger d-spacing are observed for PG samples deposited at lower temperature. In this talk, we will use discussion of these results to provide a picture of the mechanisms behind graphite nucleation and the PG growth during thermal CVD.
1. Materials for Aircraft, Missiles and Space Vehicles; Symposium on Materials for Aircraft, Missiles, and Space Vehicles; the 4th Pacific Area National Meeting: Los Angeles, 1962.
2. Flynn, S. B. Using Annealed Pyrolytic Graphite in Conduction Cooled Electronics Cooling Applications; Carleton University: Canada, 2006.