These include flame pyrolysis, electro-explosion, laser ablation, high-temperature evaporation, and plasma synthesis techniques. Flame pyrolysis has been used for many years in the fabrication of simple materials such as carbon black and fumed silica, and is being used in the fabrication of many more compounds. Laser ablation is capable of making almost any nanomaterial, since it utilizes a mix of physical erosion and evaporation. However, the production rates are extremely slow and most suited to research uses. Both RF and DC plasmas are being used successfully to make a wide range of materials. The heat source is very clean and controllable and the temperatures in the plasmas can reach in excess of 9000°C, which means that even highly refractory materials can be processed. However, this also means that the technique is unsuitable for processing organic materials.The production of fullerenes and carbon nanotubes is a specific subset of gas-phase synthesis techniques. All the techniques essentially involve the controlled growth of a nanotube on a catalyst particle through the cracking of carbon-rich gases such as methane. It is possible to make low-purity nanotubes using electric discharge techniques, but this results in wide variations in materials within a batch. Most techniques are increasingly focused on the production of either single- or multi-walled nanotubes, with significant efforts going into increasing the purity and yields.