The sputtering selective-coating surface has higher absorption (> 95 %) and lower emittance (< 5 %) than traditional selective coating surface. The sputtering selective-coating absorber is high resistance to long-term vapor condensation, high corrosive sulfur dioxide and high operating temperature. The effective resistance measured in the test is equivalent to a product life span exceeding 30 years. Good absorber material should have excellent heat transition, good resistance to corrosion and good welding ability.
The sputtering is a physical manufacturing process that involves coating a substratum with metal particles. The manufacturing process takes place in a high vacuum chamber and the coating process involves three stages, stabilizing layer coating, semi-conductor layer coating (radiation absorbent layer) and anti-refection layer coating, as shown in the following diagram.
In the vacuum chamber three target plates are installed above the copper fin. By creating a high-tension field between the targets and the copper fin and a magnetic field parallel to the target plates, positive helium ion release titanium atoms from the target plate. The atoms strike the copper fin and because of high kinetic energy of the atoms they attach themselves to the top of the copper fin. During the process this copper fin passes three targets plates.
First, a stabilizing layer of pure titanium is laid on the copper fin. This layer gives the surface of the copper fin long-term stability. Secondly, the titanium atoms react with oxygen to form an absorbent layer of titanium oxide (TINOx) on the first layer.
In this semi-conductor layer titanium atoms are orientated in such a way that 98% of incoming solar radiation can be absorbed. Finally, an anti-reflection layer is added on the absorbent layer. The anti-reflection layer has a very low reflection index and can let 98 to 99 % of incident solar radiation pass through the layer to be absorbed by the semi-conductor layer.