Bioceramic Coating on Titanium by Physical and Chemical Vapor Deposition - Biological and Biomedical Coatings: Processing and Characterization - page 312

20 µm

FIGURE 7.17
Cross-sectional microstructure of yttria-stabilized zirconia (YSZ) thermal barrier coating (TBC).

Auxiliary energy such as plasma and light (or laser) has been employed to enhance
chemical reactions in CVD, enabling further lower deposition temperature. They are
termed plasma CVD and light (or laser) CVD, respectively. Although there has been no
report so far on bioceramic coatings by plasma CVD, laser CVD has been applied to pre-
pare Ca-P-O coatings by the present authors.
Laser CVD can be categorized into two types: pyrolytic laser CVD and photolytic laser
CVD, with the laser being used to activate thermal reactions as a heat source in the first
type and for photochemical reactions as a light source in the latter. (54) Schematic diagrams
of pyrolytic and photolytic laser CVD are illustrated in Figure 7.19a and b, respectively. In
pyrolytic laser CVD, a laser is focused on the substrate surface, where the spot size may be
commonly less than several tens of micrometers. Nanodots/nanowires and patterned depos-
its have been prepared without etching by pyrolytic laser CVD. In photolytic laser CVD, a
laser passes through source gas often parallel to the substrate. Without heating the substrate,

Main gas stream

Reactants

Homogeneous
gas reaction

Formation of
intermediate
compounds

Diffusion of
by-products

Diffusion to
substrate surface

Heterogeneous
interface reaction

Adsorption of
reactants

Desorption of
by-products

Surface diffusion

Substrate

FIGURE 7.18
Schematic representation of various chemical reactions and mass-transfer steps in CVD.