Fabrication of diamond (including diamond like carbon: DLC) films as electronic materials, for example, to be used as electron-emitter, requires several following conditions. They are: (1) low-temperature fabrication (or deposition on several substrates and sometimes ones with low melting point, like glasses) below 400 degreesC; (2) wide area film deposition onto wide substrates of several square inches, like Si wafer and glass substrate; (3) reproducible deposition of well-defined film quality and (4) others. In these respects, we have initiated, in the author's laboratories at Osaka University and Kochi University of Technology, a quite new approach to satisfy the above requirements by using microwave plasma CVD under a magnetic field to be called as "magnetoactive plasma CVD". The films fabricated by the magnets-active plasma CVD and also recently by cathodic arc methods combined with our special nano-seeding method, have been utilized for electron-emitter to exhibit very high efficiency.