Described is a method for producing high purity tantalum, the high purity tantalum so produced and sputtering targets of high purity tantalum. However the graphics processing unit has a mode of operation in which a private bus is formed with a second graphics processing unit. The present invention encompasses a restrained surface wave resonator device and a restrained surface wave resonator system. The iron oxide-based layer is usually an applied coating or an oxidised surface of a substrate, the surface of which contains iron.