Methods A controlled sublimation method was used for graphene growth on a 6H-SiC (0001) surface [16]. First, the SiC substrate was cleaned using a standard procedure for substrate cleaning [21]. Second, the optically polished Si-face surface was placed face-to-face with a polished graphite disk (FTG) and arranged such that uniform #Silmitasertib purchase randurls[1|1|,|CHEM1|]# Newton rings were observed in fluorescent light [21]. The optically finished substrate surfaces resulted in a higher rate of SiC decomposition compared to chemical–mechanical processed (CMP) surfaces and created multiple graphene layers. The epitaxial growth process was controlled by annealing

in a sequence of temperature ramp and dwell stages in

Ar background gas at a pressure slightly higher than 1 atm using a commercial furnace. The substrates were first dehydrated and cleaned in the furnace at 725°C for approximately 16 h. The temperature was ramped to 1,200°C for 30 min and then ramped at 100°C/min for graphene growth at a temperature (dwell time) of 1,850°C (45 min; samples 1 and 2) or 1,950°C (30 min; samples 3 and 4). The temperatures were measured and controlled using molybdenum-sheathed type ‘C’ thermocouples. When the samples were taken out of the furnace, they were imaged by tapping-mode HKI-272 nmr atomic force microscopy (AFM). They were then shipped from NIST to National Taiwan University, where they were patterning into Hall bars by standard photolithography using reactive ion etch in O2 plasma (see Figure 1 with size ratio L/W = 4). The pleats on the surface show that multilayer graphene was grown over most of the 6H-SiC (0001) surface [22]. Optically polished substrates produce much thicker graphene for the same processing conditions compared to that grown on CMP surfaces. The roughness of the optically polished surface provides much more off-axis surface area, relative to the (0001) atomic plane, and this accounts for the faster growth rate. The TEM images are taken from samples grown under the same conditions. Comparing the

AFM images with TEM imaging performed on other Carteolol HCl samples, we would estimate that the 1,850°C samples have four to five layers of graphene and the 1,950°C samples have five to six layers. All four-terminal electrical measurements were carried out using dc constant-current sources and multimeters. Figure 1 Optical microscopy image of Hall bar shows L = 100 and W = 25 μm. The green lines indicate the edges of the Hall bar. Results and discussion Figure 2 shows the magnetoresistivity measurements ρ xx (B) at various temperatures. Negative magnetoresistivity centered at B = 0 can be ascribed to suppression of weak localization by a magnetic field applied perpendicular to the graphene plane.