Síntese e caracterização de material de carbono sp2 sem uso de catalisador

Abstract

This work aims to study graphene synthesis via Chemical Vapor Deposition (CVD) without the use of metallic catalysts. We grew films directly on SiO₂/Si substrates. We demonstrated that catalyst-free graphene growth is not self-limiting; in other words, the film thickness strongly depends on the growth time. We investigated synthesis durations of 3 hours, 2 hours, 1 hour, and 30 minutes, and observed significant differences in film thicknesses and surface coverage. No carbon-based material growth was observed at 30 minutes, and films grown for longer periods tended to be less crystalline compared to those grown for shorter times. In order to obtain more crystalline films with full substrate coverage, we developed a method we named “pulsed gas flow.” This method is innovative, as we are unaware of similar approaches reported in the literature. The pulsed gas flow technique involves growth with curing intervals during deposition, in which the introduction of the carbon precursor gas (CH₄) is periodically interrupted. This approach is intended to promote greater ordering of carbon-carbon bonds, enabling the formation of crystalline films without the presence of disordered carbon atoms. We performed 3-hour syntheses using pulsed flow and tested three different curing times: 1 minute, 3 minutes, and 5 minutes. For the shortest curing time, the resulting films were similar to those grown under continuous flow, while for the longest curing time, no carbon material growth was observed. The characterization of our films was carried out using scanning electron microscopy (SEM), Raman spectroscopy, and electrical characterization via the Hall effect. The synthesized material was found to be p-type doped, in agreement with previous reports in the literature. To demonstrate the practical relevance of this type of synthesis, we fabricated a field-effect transistor (FET) using samples grown under both continuous and pulsed gas flows. We swept the gate voltage from (−30.0±0.1) V to (30.0±0.1) V and observed a shift in the Fermi level, along with an increase in current and conductivity of the synthesized material.