2b ws2'in cvd yöntemi ile büyütülmesi ve karakterizasyonu

TMDC monolayers such as MoS2, WS2, and MoSe2 possess a direct bandgap, which allows them to be utilized as detectors in optics, as transistors and sensors in electronics. Among these TMDCs, atomically thin, large area WS2 has great interest due to its unique properties such as direct bandgap, large bandgap energy, high photoluminescence intensity and low response time. Despite the promising results which have been reported by different research groups for the last few years, still a general insight towards the basic understanding of the CVD process is missing and the aim of realizing large-scale, low- cost monolayer growth is not fully accomplished. In this work, we present a controlled growth of monolayer tungsten disulfide (WS2) via chemical vapor deposition (CVD) technique in a systematic sequence. We have gained knowledge about two-dimensional (2D) WS2 synthesis with a comprehensive investigation of process parameters such as H2 gas inclusion into the main carrier gas, growth duration and temperature. Moreover, by changing the radical vapor density associated with WO3, we realized seed formations control inside the monolayer structures. We confirm that, via its reductive reagent nature, H2 gas inclusion into the carrier gas is directly involved in WO3 reduction. So that requirement of more effective sulfurization consequently monolayer formation process is achieved. In addition, by developing the growth configuration and restricting the reactant radicals, we obtained increased tungsten vapor density ambient. Therefore, we succeed in obtaining larger WS2 monolayer flakes and films, which is still a technological challenge in order to utilize these structures for practical applications. Further optimization of the growth process is presented by modifying the growth duration to avoid the undesired seed formations and additional layers which will conceivably limit the device performance of the monolayer flakes or films when applied.