Growth And Optoelectronic Properties Of Rhenium Disulfide Monolayers And Their Hybrids

Transition metal dichalcogenides?TMDCs?are highly attractive for fundamental research of novel physical phenomena and applications ranging from nanoscale electronics and optoelectronics to chemical catalysis and energy storage owing to their unique two-dimensional structures and excellent physical properties.The distorted octahedral?1T?phase renders rhenium disulfide?ReS₂?much weaker interlayer coupling.In addition,the presence of in-plane anisotropy gives rise to considerable anisotropy of electrical and optical properties.Therefore,ReS₂ holds potential applications in field effect transistors?FETs?,photodetectors and interband tunnel FETs etc.The main results in this thesis are listed as follows:First,monolayer ReS₂ flakes were grown on mica via a water-assisted chemical vapor deposition?CVD?.To control the nucleation,appropriate amount of water vapor was induced in the process,which is very important for reproducible growth of large size monolayer ReS₂ domains.The morphology,structure and composition of the as-prepared samples were characterized using optical microscope,transmissionelectronmicroscope?TEM?,X-rayphotoelectron spectroscopy?XPS?,atomic force microscope?AFM?.Most of the ReS₂monolayers with large lateral size about 30-50?m,high crystallinity and uniform distribution of thickness.In addition,back-gate FETs based on the as-grown ReS₂ monolayers were fabricated and exhibited carrier mobility of 0.99 cm²V^-1s^-11 and high on/off current ratio of 2×10⁶.Second,exfoliated monolayer ReS₂ and monolayer graphene van der Waals heterostructures were prepared and utilized for fabricating atomically thin field effect transistors.The G and 2D Raman peaks of the monolayer graphene interfaced with monolayer ReS₂ exhibit significant blue shift and the ratio of intensity between them dramatically increases compared with that of the bare graphene.The back gate transistor with monolayer ReS₂ as channel and monolayer graphene as electrodes exhibits on/off current ratio exceeding 10⁶,mobility of¹.1 cm²V^-1s^-11 and subthreshold swing⁷40 mV per decade.Finally,CdS-nanoparticles/ML-ReS₂ hybrids were synthesized on mica substrates via a two-step CVD process.The CdS nanoparticles preferentially grow on ReS₂ rather than mica with strong orientation alignment.The hybrids were used to fabricate high performance photodetector.The CdS/ReS₂ photodetectors are gate tunable,and exhibit high responsivity(>10⁴ A·W^-1),external quantum efficiency?>10⁴?.The responsivity is two orders of magnitude higher than that of the ML-ReS₂-based devices.We suggest that the high responsivity is attributed to the combination of strong light-matter interaction of CdS nanoparticles and excellent carrier transport property of the ML-ReS₂.We believe that the model presented here can be generalized to improve the optoelectronic performance of other 2D devices.