Hall effect measurements on PPy-diamond heterojunctions. (a) Schematic top view of the diamond in-plane mesa structure for Hall effect measurements showing a bare H-terminated mesa structure and its transformation into PPy-diamond mesa structure. Mesa surroundings are electrically insulated by oxidation of diamond surface. The resin encapsulation is used to confine PPy growth to the mesa area. (b) Hall voltage on the PPy-diamond mesa structure measured under +0.3 T (triangles) and - 0.3 T (squares) as a function of time. (c) The same Hall voltage plotted as a function of magnetic field. All measurements were done under the cold light illumination.