Process for coating a substrate with titanium dioxide

A process for coating a substrate surface with titanium dioxide, which process comprises the D.C. plasma sputtering and/or mid-frequency sputtering from a sputtering target which comprises sub-stoichiometric titanium dioxide, TiO x , where x is below 2.

The present invention will be further described with reference to the following Examples. 
 EXAMPLE 1 (comparative) A rotatable target comprising a tube of titanium metal of diameter 133 mm and length 800 mm was used to sputter titanium metal onto a glass plate placed at a distance of 18 cm from the target. The sputtering was carried out at a power level of 35 kW (80 A, 446 V) under a pressure of 5×10 −3 mBar of argon as the plasma gas. After 3½ minutes a layer of titanium metal 18000 Angstroms in thickness as measured by a profilometer had been deposited upon the glass plate. 
 EXAMPLE 2 (comparative) The procedure of Example 1 was repeated but substituting a mixture of 80% O 2 and 20% Ar as the primary plasma gas to replace the argon primary plasma gas of Example 1. The sputtering was carried out at a power level of 45 kW (97 A, 460 V) under a pressure of 4.5×10 −3 mBar. Using a titanium metal target as described in Example 1 a titanium dioxide layer of thickness 1500 Angstroms was deposited on a glass plate place above the target in 3½ minutes. 
 EXAMPLE 3 A rotatable target comprising a tube of stainless steel of diameter 133 mm and length 800 mm was coated with sub-stoichiometric titanium dioxide, TiO x , where x is below 2 as hereinbefore described by plasma spraying titanium dioxide onto the target using argon as the primary plasma gas and hydrogen as the secondary plasma gas. 72 liters (60% argon, 40% hydrogen) were used. The power level was 45 kW (455 A, 96 V). This target was then used as a sputtering target in the manner as described in Example 1. Using argon as the primary plasma gas the sputtering was carried out at a power level of 45 kW (97 A, 460 V) under a pressure of 5.4×10 −3 mBar Ar. A dark blue semi-transparent layer of sub-stoichiometric titanium dioxide, TiO x , of thickness 14000 Angstroms was deposited on a glass plate placed above the target in 3½ minutes. The sputtering proceeded smoothly without significant arcing. 
 EXAMPLE 4 A rotatable target prepared as described in Example 3 was used as a sputtering target in the manner as described in Example 3 using a mixture of 75% Ar and 25% O 2 as the plasma gas. The sputtering was carried out at a power of 45 kW (95 A, 473 V) under a pressure of 5×10 −3 mBar. A clear transparent coating of stoichiometric titanium dioxide of thickness 12500 Angstroms was deposited on a glass plate placed above the target in 3½ minutes. The sputtering proceeded smoothly without significant arcing. 
 EXAMPLE 5 (Comparative) A rotatable target was prepared as described in Example 3 by using pure argon (40 liters) at a power level of 34 kW (820 A, 42 V). The electrical conductivity of the target was ten times inferior to that of Example 3. Sputtering from the target was difficult due to arcing. The process was not stable enough to produce samples.