User:Aaronujl/sandbox

Graphene
Many variations of CVD can be utilized to synthesize graphene. The most popular carbon source used to produce graphene is methane gas. Less popular choices include petroleum asphalt, notable for being inexpensive but more difficult to work with. The use of catalyst is viable in changing the physical process of graphene production. Notable examples include iron nanoparticles, nickel foam, and gallium vapor. These catalysts can either be used in situ during graphene buildup, or situated at some distance away at the deposition area. Some catalysts require another step to remove them from the sample material. Physical conditions such as surrounding pressure, temperature, carrier gas, and chamber material play a big role in production of graphene.
 * Carbon source
 * Use of catalyst
 * Physical conditions

Most systems use LPCVD with pressures ranging from 1 to 1500 Pa. However, some still use APCVD. Low pressures are used more commonly as they help prevent unwanted reactions and produce more uniform thickness of deposition on the substrate.

On the other hand, temperatures used range from 800-1050°C. High temperatures translate to an increase of the rate of reaction. Caution has to be exercised as high temperatures do pose higher danger levels in addition to greater energy costs. Hydrogen gas and inert gases such as argon are flowed into the system. These gases act as a carrier, enhancing surface reaction and improving reaction rate, thereby increasing deposition of graphene onto the substrate. Standard quartz tubing and chambers are used in CVD of graphene. Quartz is chosen because it has a very high melting point and is chemically inert. In order words, quartz does not interfere with any physical or chemical reactions regardless of the conditions. Raman spectroscopy, X-ray spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) are used to examine and characterize the graphene samples.
 * Carrier gas
 * Chamber material
 * Methods of analysis of results

Raman spectroscopy is used to characterize and identify the graphene particles; X-ray spectroscopy is used to characterize chemical states; TEM is used to provide fine details regarding the internal composition of graphene; SEM is used to examine the surface and topography.

Sometimes, atomic force microscopy (AFM) is used to measure local properties such as friction and magnetism.