Basic Study On Spraying Method To Fabricate Films Of Two-dimensional Materials

Since the first preparation of graphene,the two-dimensional material field has become the focus of scientific and industrial research.Unlike bulk materials,two-dimensional materials exhibit superior performance in many aspects such as electrical,mechanical,and optical field.In addition to graphene,two-dimensional materials based on transition metals,carbon group elements,and chalcogens have also been successively developed and exhibit excellent performance.Among these,transition metal chalcogenides?TMDs?have attracted wide attention in recent years due to their superior performance.Unlike the zero bandgap structure of graphene,the TMDs material has indirect bandgap.However,when the material is single-layer,the indirect bandgap in bulk turns direct.WS₂ is a member of TMDs family.It is used to fabricate high performance transistors,performs as a catalyst for the hydrogen evolution reaction and forms a heterostructure with MoS₂ in researches on account of its good electrical properties.Recently,there have been numerous researches on the preparation methods of two-dimensional WS₂,such as mechanical exfoliation.Each method has their advantages and disadvantages.Although mechanical exfoliation and liquid exfoliation are relatively inexpensive,the size and thickness of the resulting sample are not controllable,and the choice of substrates is limited.Thus,it usually requires a transfer step for further study.Samples obtained by chemical vapor deposition are of good quality,while it requires a high temperature and a vacuum environment.Therefore,how to obtain the large-area two-dimensional material in a simple and low-cost way is always a hotspot.In this study,we used spray-casting method to prepare the two-dimensional material.The solution is atomized into small mist-like particles by an atomizer,and then forms a liquid film on the substrate.Under the circumstance of suitable temperature and humidity,a two-dimensional film remained on the substrate.We studied the influencing factors such as substrate pre-treatment,solution concentration,spraying duration and interval time,and we achieved the thickness control by controlling the number of spraying cycles.In the spraying process of WS₂,we used Piranha solution and oxygen plasma bombardment for pre-hydrophilic treatment.The concentration of the selected solution is 2mg/ml,the duration of the spraying is set to 5s,and the interval time is 5 minutes.The homogeneity and smoothness of the samples are good,and the thickness of the film is within 20 nanometers.The samples obtained by spray-casting method have large sizes and are thickness-controllable.A large range of substrate selection is allowed.This method is both cost and time-efficient.In this study,we studied the process of solution spray deposition and applied the obtained thin film samples for preliminary device preparation and electrical performance testing.