Bioceramic Coating on Titanium by Physical and Chemical Vapor Deposition - Biological and Biomedical Coatings: Processing and Characterization - page 313

(a) (b)

Source gas

Source gas

Optical lens

Quartz window

Quartz window

Laser beam

Laser beam

Quartz window

Substrate Substrate Exhaust

Exhaust

FIGURE 7.19
Schematic diagrams of (a) pyrolytic laser CVD and (b) photolytic laser CVD.

precursor gases react to form a film by a high-energy laser. In conventional pyrolytic and
photolytic laser CVD, however, deposits are limited to nanosized or thin-film forms. For
thick and wide-area coatings for engineering applications such as thermal barriers, antiabra-
sive and bioceramic coatings by laser CVD have been thought to be impossible.
The present authors have developed a large spot size (~20 mm) laser CVD enabling a high
deposition rate of several hundreds µm/h to several tens mm/h for various ceramic coat-
ings. This laser CVD is different from the conventional pyrolytic or photolytic laser CVD; a
laser can ionize precursor gases forming plasma (plasma laser CVD), where the precursor
gases can be highly activated as illustrated in Figure 7.20, enabling significant high-speed
and low-temperature deposition of films. YSZ and SiO 2 coatings several hundreds µm in
thickness have been prepared by this laser CVD at 660 (55) and 27.5 mm/h (56) , respectively.

Thermal CVD

PVD, mainly plasma spray, and sol-gel have been widely applied for bioceramic coat-
ings. CVD has not been applied for such applications, the lack of appropriate precursors
being one of the reasons. CaTiO 3 bioceramic coating by thermal CVD was first prepared
by the present authors at 950 to 1050 K using Ca(dpm) (dpm: dipivaloylmethanate) and
Ti(OiPr) 2 dpm 2 (OiPr: orso-iso-propoxide). (25) CaTiO 3 coating with a well-developed columnar
microstructure exhibited good adherence and compatibility with a Ti substrate. Although
CaTiO 3 coating is bioactive and well compatible with a Ti substrate, the osteoconductivity

Adsorbed
species

Coating

Plasma

Laser light

e -

e -

e -

e -

e -

e -

Substrate

e -

e -

e -
e -

e -

e -

e -

e -

Source
gas

Contact front

Desorption

FIGURE 7.20
Schematic diagram of plasma laser CVD.