The Fraunhofer Institute for Mechanics of Materials, Germany, together with colleagues from the Commonwealth Scientific and Industrial Research Organization (CSIRO), Australia, have developed a saw wire that can reduce kerf loss when cutting silicon wafers. In place of diamond-impregnated steel wires, the researchers use ultra-thin and extremely stable threads made of carbon nanotubes coated with diamond.
The potential of coated carbon nanotubes has long been understood: Possible applications include its use as a hard and tough composite material or as a component of highly sensitive sensors and thermoelectric generators. However, the new material is extremely difficult to synthesize. Diamonds grow at temperatures of around 900°C in an atmosphere containing hydrocarbons. In order to catalyze the formation of the diamond phase, it is necessary to use reactive hydrogen to prevent the deposition of graphite. However, this process also damages the carbon nanotubes.
IWM scientist Manuel Mee found a solution for protecting the fine carbon nanotubes, which grow like forests on a substrate. “During our first experiments, fused silica from the reaction chamber accidentally came into contact with the coating plasma,” he said. “It settled on the substrate and protected it against the aggressive hydrogen. Diamonds were able to grow on this layer. We had to study the silicon oxide layer, which was deposited in an undefined manner, and find a method of controlling the deposition and optimizing the process.” Tests with a transmission electron microscope at CSIRO’s lab in Australia revealed that the nanotubes actually survived under their protective layer.
