T. Kho et al., DEVELOPMENT, PRELIMINARY TESTING AND FUTURE APPLICATIONS OF A RATIONAL CORRELATION FOR THE GRAIN DENSITIES OF VAPOR-DEPOSITED MATERIALS, Journal of Materials Science, 30(13), 1995, pp. 3440-3448
It is conjectured and found in this work that the grain densities (sui
tably normalized) of vapour-deposited solid materials depend principal
ly on competition between the successful arrival rate of their reagent
molecules and the surface diffusion rate of admolecules on their grow
ing surfaces. The ratio of these two rates defines an important dimens
ionless Damkohler number, called here the ''burial'' parameter, beta.
Available grain density data for seven vapour deposited materials [sil
icon (Si), gallium arsenide (GaAs), silicon carbide (SiC), silicon nit
ride (Si3N4), titanium oxide (TiO2), boron nitride (BN) and graphite (
C)] are used to establish and test the ''universality'' of the propose
d normalized grain density versus burial parameter correlation. As ant
icipated, these data show that the normalized grain densities of these
materials increase with their corresponding burial parameters. Moreov
er, for estimated burial parameters much less than unity, the deposits
formed are indeed reported to be amorphous, while the deposits are ob
served to be crystalline under conditions for which beta much greater
than 1 is estimated. As the burial parameter decreases, the reported g
rain densities of turbostratic, ''layered'', materials are found to de
crease more gradually than for materials with no turbostratic structur
e. While the present implementation of this basic hypothesis cannot be
regarded as ''complete'', it is argued that a rationally-based, reaso
nably ''universal'' vapour deposit density correlation of this general
form can be quite useful in making rational predictions of deposit qu
ality. Moreover, it appears that this path to such mechanistically pla
usible correlations, which, using available experimental data, can be
implemented/tested even in the absence of a ''complete'' theory, can b
e broadened to include other important deposit characteristics via the
introduced of additional characteristic time ratios.