The temperature (T ) dependence of electrical resistivity in graphene has been experimentally investigated between 10 and 400 K for samples prepared on various substrates; HfO2, SiO2 and h-BN. The resistivity of graphene shows a linear T -dependence at low T and becomes superlinear above a substrate-dependent transition temperature. The results are explained by remote interfacial phonon scattering by surface optical phonons at the substrates. The use of an appropriate substrate can lead to a significant improvement in the charge transport of graphene.

The electrical performance of suspended few-layer MoTe2 field-effect-transistors with ionic liquid gating has been investigated. The suspended structure not only enhances the mobility of MoTe2 by removing the influence of the substrate but also allows ions to accumulate on both the top and the bottom surface of MoTe2. The consequent increase of the gate capacitance resulted in an improved subthreshold swing (~73 mV/dec) and on-off ratio (10 6 ) at room temperature for suspended MoTe2 compared to substrate-supported devices. Suspended transistors with ionic liquid gating enable larger charge density compared to ionic liquid gated supported devices, and may provide a useful platform to study screening physics in 2D materials. Two-dimensional transition metal dichalcogenide compound (TMDC) materials have a variety of properties depending on the crystal structure and constituent elements and attract broad interests for applications in nanoelectronics and optics. 1,2 Among them, MoTe2 has received increasing attention owing to its low phase transition barrier 3,4 and its sizeable bandgap close to that of Si. [5][6][7] MoTe2 has an indirect electronic bandgap of 0.88 increasing to 1.0 eV going from bulk to few-layer, with a direct bandgap of about 1.1 eV for the monolayer. [7][8][9][10][11] Field-effect-transistors (FETs) based on α-MoTe2 have been reported 8,12-20 and applied to logic circuits 21 and sensors. 19,22 However, much lower mobilities have been reported than the theoretically predicted phonon-limited mobility at room temperature of ~240 cm 2 V -1 s -1 for bulk, 23 and ~100-2500 cm 2 V -1 s -1 for monolayer, 10,24 mainly due to charged traps at the MoTe2/substrate interface and Schottky barriers at the MoTe2/metal contacts. 13 High-κ screening can reduce the influence of the charged traps, and an enhanced electron mobility (80 cm 2 V -1 s -1 at room temperature) has been reported for a MoTe2 device capped with Al2O3. 15 On the other hand, ionic liquid (IL) gating is an attractive doping method for TMDC because of the high gate capacitance of the electric double layer (EDL) formed on the sample surface. Heavy doping of the semiconductor can result in the reduction of the effective Schottky barrier, and in addition the high dielectric constant of ionic liquids can improve the performance of MoTe2 FETs as shown by previous studies on substrate-supported multilayer devices. 8,25

Boron-doped graphene (B-doped graphene) films with large area, high quality, and good uniformity are successfully prepared by chemical vapor deposition using ethylboronic acid (C2H7BO2) as the sole precursor. The pre-treatment of the copper foil and post-annealing are introduced to the growth process and proved to be greatly influential to the quality of B-doped graphene. The films prepared are mainly monolayer with the transmittance of about 97.1%, the B/C ratio of about 2.3%, the sheet resistance of 1.5–3 kΩ/◻, and the carrier density of 1.13 × 1013 cm−2 at room temperature.

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