A few-layered molybdenum disulfide (MoS2) thin film grown by plasma enhanced chemical vapor deposition was etched using a CF4 inductively coupled plasma, and the possibility of controlling the MoS2 layer thickness to a monolayer of MoS2 over a large area substrate was investigated. In addition, damage and contamination of the remaining MoS2 layer surface after etching and a possible method for film recovery was also investigated. The results from Raman spectroscopy and atomic force microscopy showed that one monolayer of MoS2 was etched by exposure to a CF4 plasma for 20 s after an initial incubation time of 20 s, i.e., the number of MoS2 layers could be controlled by exposure to the CF4 plasma for a certain processing time. However, XPS data showed that exposure to CF4 plasma induced a certain amount of damage and contamination by fluorine of the remaining MoS2 surface. After exposure to a H2S plasma for more than 10 min, the damage and fluorine contamination of the etched MoS2 surface could be effectively removed.

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Using an RF-compensated Langmuir probe, plasma parameters have been investigated in a discharge produced by a dual frequency-dual antenna: the next generation of large-area inductively coupled plasma (ICP) sources. The ICP source was made of two concentric spiral copper coils embedded into each other. The inner and outer coils were energized by RF frequencies of 2 and 13.56 MHz, respectively. The discharge was operated at an average pressure of 10 mTorr in an argon gas environment. The probe was positioned at a fixed location of 70 mm from the source and 160 mm from the centre of the ICP source to measure the plasma parameters. However, for discharge uniformity measurements, the probe position was varied from the centre of the discharge to 200 mm towards the edge. It was found that the ion density distribution over the wafer varies with RF power ratio (P 2 MHz /P 13.56 MHz). For a fixed power at 13.56 MHz (P 13.56 MHz), the plasma density increases very slowly with P 2 MHz , when P 2 MHz < 400 W; however, the plasma density increases rapidly when P 2 MHz > 400 W. The electron temperature and plasma potential measurements show decreasing trends with increasing P 2 MHz at constant P 13.56 MHz. The ion density measurements over the substrate show that good discharge uniformity (∼4%) can be achieved by adjusting the RF power ratio (P 2 MHz /P 13.56 MHz).

We propose a novel doping method of graphene using the cyclic trap-doping method with low energy chlorine adsorption. Low energy chlorine adsorption for graphene chlorination avoided defect (D-band) formation during the doping by maintaining the π-bonding of the graphene, which affects conductivity. In addition, by trapping chlorine dopants between the graphene layers, the sheet resistance could be decreased by ∼ 88% under optimized conditions. Among the reported doping methods, including chemical, plasma, and photochemical methods, the proposed doping method is believed to be the most promising for producing graphene with extremely high transmittance, low sheet resistance, high thermal stability, and high flexibility for use in various flexible electronic devices. The results of Raman spectroscopy and sheet resistance showed that this method is also non-destructive and controllable. The sheet resistance of the doped tri-layer graphene was 70 Ω per sq. at transmittance of 94%, and which was maintained for more than 100 h in a vacuum at 230 °C. Moreover, the defect intensity of graphene was not increased during the cyclic trap-doping.