Nanofabrication on a hydrogen-terminated diamond surface is performed by controlling surface adsorbates, using a scanning probe microscope (SPM) technique. Insulated areas are successfully obtained by changing hydrogen termination to oxygen termination. The Auger electron spectrum (AES) indicated the presence of oxygen adsorbed on the modified surface area. A small isolated conductive area is fabricated. and using this structure, a metal-insulator-metal (MIM) diode-like I-V characteristic is observed. Anodic oxidation using the surface water is also suggested for our experimental results.