The electron mobility and conductivity initially linearly increase and then gradually reach saturation with thickness. The results are consistent with the I-V behaviors. For a low thickness value, the graphene does not form a continuous film but many islands, check details which collect and fuse each other with deposition time, leading to the mobility and conductivity increasing linearly and then up to their ultimate values. The conductivity of the graphene film with a 7-nm thickness is about 1,240 S/cm, superior to that of Levendorf et al. [24] who reported 102 S/cm for the same thickness. The sheet resistance R s in Figure 6c has a reversed tendency with thickness, i.e., initially significantly

drops and slowly decreases. Especially, R s drops from 105 to 103 Ω/sq as the thickness

increases from 2 to 7 nm. The typical R s of the ITO film is 103 ~ 106 Ω/sq. Hence, the R s of about 103 Ω/sq shows that the deposited graphene has very low resistivity, satisfying the need for transparent conducting films. This value is about two times smaller than that of Wang et al. [27] who reported 2 kΩ/sq and very close to 350 Ω/sq of graphene deposited on copper then transferred on SiO2[22]. Wu et al. [11] reported that a graphene film with a thickness of 7 nm and a sheet resistance of 800 Ω/sq was used as a good transparent conductor of an OLED. Figure 6 Relation of thickness and deposition selleck time, electron mobility, conductivity, and sheet resistance. (a) The relation of thickness of the graphene films with deposition time. (b) The dependences of electron mobility and conductivity on graphene thickness. (c) The sheet resistance R s changing with the thickness. The graphene sample deposited for 5 min has a high transparency of over 85% in the visible wavelength range of 400 to 800 nm and a sheet resistance of 103 Ω/sq. These properties are much superior to those of GO films as transparent conductors. The high performance is attributed to the CVD technique that produced compact, large-area,

uniform, and high-purity graphene films. Conclusions The transparent conducting properties of graphene films with different thicknesses were investigated. Ultrathin graphene films were deposited on quartz substrates Calpain by controlling a very low reactive flow rate and pressure of CH4 in the CVD technique. The transmission rate of the graphene films decreases with the thickness of the film, which is over 85% for the film of about 5 to 7 nm. The mobility and conductivity were found to rapidly increase up to their saturation values with the thickness of the film. The sheet resistance rapidly drops from 105 to 103 Ω/sq as the film thickness increases from 2 to 7 nm. The largest conductivity is up to 1,240 S/cm and the minimum sheet resistance is about 103 Ω/sq, showing that the graphene films have very low resistivity and completely satisfy the need for transparent conducting films.