SCANNING TUNNELING MICROSCOPY AND ATOMIC FORCE MICROSCOPY OF CARBON-DIAMOND FILMS

We have used both scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) to image and measure electrical properties of diamond films. The carbon-diamond films were deposited on {100}, 1-5 W cm, n-type Si substrates from a 13.56 MHz, capacitively coupled CH4 Ar rf plasma. Film thicknesses ranged from 10 nm to 150 nm and were transferred immediately into UHV for measurement. In the case of the 10 nm films, images were obtained in the STM revealing three types of morphology: (i) large atomically-flat regions with an unpinned Fermi level exhibiting semiconductor-like behaviour with a band gap of ∼4 eV as determined by taking current-voltage (1 V) characteristics at selected sites. Such characteristics also showed a reverse bias stability with no evidence of breakdown up to 8 eV. (ii) Three-dimensional crystalline regions with crystal sizes up to 200 nm. (iii) Amorphous regions occupying spaces between grains and often decorating the surfaces of crystalline regions. The electrical characteristic of these regions showed an essentially metallic-like behaviour with no obvious band structure, indicating that they were probably amorphous carbon. Thicker carbon-diamond films became increasingly difficult to image in the STM indicating that most of the voltage was being dropped within the film, preventing electrons being injected into the conduction band of the silicon substrate for detection. In these cases samples were imaged in the AFM which indicated that the films were essentially flat with a roughness of ∼5 nm. Friction measurements carried out with the AFM gave a value of 0.03 which agrees favourably with previous measurements on pure diamond in air. © 1992.