Preparation And Properties Of Transition Metal Carbides By Thermal Atomic Layer Deposition

Transition metal carbides（TMCs）have received extensive attention due to their unique electronic structures,excellent chemical stability,and corrosion resistance.Among them,TMCs exhibit excellent catalytic properties due to the hybridization between metal element and carbon element orbitals（similar to the electron orbitals of noble metals）.It can be used as alternative materials for noble metal catalysts.Researchers’continuous exploration has spawned a variety of methods for preparing nanostructured TMCs materials.However,different preparation methods have different properties.In recent years,atomic layer deposition（ALD）has become a cutting-edge technology for the preparation of nanostructured materials.Owing to its unique self-limiting growth mechanism,ALD has excellent reproducibility.ALD can precisely tune the thickness of thin films,nanomaterials’composition,and the distribution of active atomic sites.Materials prepared by ALD have a variety of excellent,predictable properties and are expected to play an essential role in nanomaterials preparation.However,there are few reports on preparing transition metal carbides from ALD.Furthermore,the types,growth mechanisms,and properties of transition metal carbides remain to be studied.Therefore,it is vital to develop the ALD process to prepare transition metal carbide nanomaterials for application in catalysis.In conclusion,in this study,nanomaterials of transition metal Co-and Ni-based carbides were prepared by thermal atomic layer deposition（T-ALD）,and their catalytic properties were explored.The specific research is as follows:（1）The Co（acac）₂·TMEDA complex was synthesized,and its thermochemical properties were studied by thermal weight loss analysis.The results show that it has good volatility and stability that meets the requirements of ALD for precursors.Then,experiment of ALD thin film deposition with Co（acac）₂·TMEDA and HCCOH as precursors,and optimization of ALD related processes.Through the study of film growth characteristics,when the pulse time of cobalt precursor is 2 s,the pulse time of formic acid is 2 s.When the deposition temperature is260-280°C,the growth rate of the film is constant,reaching 0.46?/cycle.SEM,XPS,and XRD characterized the prepared films.The composition of the films was determined to be Co₃C_x.The surface of the films was composed of particles with good continuity and uniform film thickness.Based on the experiment of depositing thin films,when the deposition temperature was 280℃,the Co₃C_x thin film was deposited on the foamed nickel substrate to obtain the composite electrode material and the electrocatalytic performance was studied.（2）The Ni（acac）₂·TMEDA complex with good volatility and stability was selected as the nickel precursor,and film deposition experiments were carried out through ALD technology.The ALD process was also explored.It is found that the characteristics of the film are different in different deposition temperature ranges through studying the influence of growth temperature on the deposited film.The films（deposited at 120-200℃）are completely dissolved in water,while films（deposited at 250-300°C）are insoluble.The films were characterized by SEM,XPS,XRD,FT-IR,and Mass,the former is nickel carboxylate[（Ni COO-）_x],and the saturation growth rate reaches 1.21?/cycle.The latter is Ni₃C_x film,and the saturation growth rate reaches0.81?/cycle.Then,the growth mechanism of the film was studied through different solution-phase reactions.Finally,under the optimal process conditions for ALD-Ni₃C_x film deposition,Ni₃C_x/Ti O₂ composite catalysts were prepared with Ti O₂ as a carrier,and the catalysts were tested and analyzed by SEM,TEM,XRD,UV-Vis DRS and PL.The morphology,chemical composition and optical properties of Ni₃C_x/Ti O₂ were tested.The photocatalytic performance of Ni₃C_x/Ti O₂ was tested by using the blue light catalytic degradation of methylene as a probe reaction.