The thickness of the mica of the GFETs (named as T1-T5) was 24, 29, 35, 40, and 47 nm respectively. The optical images of the topography of T3 and T5 are shown in Figure 2a, 1b, respectively. Figure 3a shows the R�CVGS characteristics of the GFETs T1-T5. The carrier mobility of the GFETs was calculated by:[31, 32] (1) It can be observed in Figure 3b that with the increase of the thickness of mica gate dielectric, the transconductance decreases, as a result of the decrease in gate capacitance. No significant change in the effective carrier mobility as a function of the thickness of mica gate dielectric Biperiden HCl from 24 nm to 47 nm was observed. This is in consistent with other groups' results, that is, the dielectric thickness dependence of carrier mobility is only significant selleck screening library when L < 10 nm.[33, 34] It has also been reported that, for the channel length up to several micrometers, the carrier mobility saturates to a constant value. [31] Based on Equation 1, the calculated carrier mobility of T1�CT5 falls in the range of 2000�C2700 cm2/Vs. The variation of the calculated carrier mobility of the devices could be attributed to the slight difference in the channel dimensions of each fabricated devices (L = 6�C8 ��m and W = 1�C1.5 ��m). The mobility improvement of the mica-based GFET as compared to silicon oxide-based GFET could be attributed to the high surface smoothness of mica. As reported, free-standing graphene consists of microscopic corrugations due to thermal fluctuation,[35] whereas the supported graphene conforms and follows the morphology of the underlying substrates with the presence of ripples of different origins.[5] The substrate effect and the thermally created ripples result in the long-range scattering potential that contributes dominantly to the resistivity of the graphene.[36] Therefore, the surface morphology of the substrate plays a significant role in limiting the carrier transport of the graphene. Mica is well-known of its atomically flat surface on which ultra-flat graphene with height variation of <25 pm could be achieved.[19] Theoretical analysis by Rudenko et al. has predicted that ultra-flat graphene on mica interacts with K+ ions between mica surface and graphene, resulting in good conformation of graphene on mica.[22] The reduced in the surface <a href="http://www.selleckchem.com/products/Rapamycin.html">Sirolimus roughness and the ripples of graphene on mica are believed to be the main factor for the mobility improvement of the mica-based GFET. It has been noted that surface roughness scattering is especially critical for low dimensional materials,[37] such as 2D graphene and 1D CNTs. Our result of mobility improvement of graphene on mica is consistent with the mobility improvement of CNTFETs on mica.[18] Charged impurity scattering was widely accepted to be the source of scattering in graphene. However, Ponomarenko et al.
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