Scanning tunneling electron microscopy (STM) has recently shown great promise for surface modification in the nanometer regime. As is well known, the normal STM tips are easily damaged by mechanical contact with the sample surface in most cases. In this paper we describe a new type of diamond STM tip prepared by the microwave plasma chemical vapor deposition technique. The reactant is a gas mixture of methane and hydrogen. Diamond crystals are grown on a tungsten tip. The diamond tips are very hard and always have enough electrical conductivity for STM experiments. They can be used as a machining tool to scratch the metal surfaces.