| Atomic layer deposition（ALD）as a flexible surface-controlled fabrication technique has attracted widespread interest innumerous nanotechnology applications,which possesses the characteristics of precise thickness control,excellent uniformity,and conformality,relying on the self-limiting surface reaction,so that ALD can be used as an ideal tool for the production of ultrathin or two-dimensional molybdenum disulfide（Mo S2）films.However,there are still many defects in the preparation of Mo S2 films by ALD technique,which limits the practical applications in different fields for Mo S2 films deposited by ALD.Therefore,it is a challenging task to manufacture large-area,high-quality two-dimensional Mo S2 films,and it is very important for ALD to make in-depth research on Mo S2 films.In this paper,the precise manufacture of Mo S2 films by ALD,surface characteristics of the films and its application in the fields of microwave absorption have been studied,and the main results are as follows:（1）The research on the related mechanism of ALD deposition of Mo S2 films has been summarized.The surface reaction pathway for ALD to synthesize Mo S2 is described,the factors causing the saturated adsorption of precursor molecules are discussed,and two possible growth mechanisms are summarized and compared:one is based on the transformation of amorphous Mo S2,and the other is based on the extension of Mo S2 grains.For these two mechanisms,the deposition process of ALD-deposited Mo S2 can be divided into two stages:heterogeneous deposition stage and homogeneous deposition stage.And the mismatch between the deposited Mo S2 and the substrate surface lattice in the heterogeneous stage is the key factor leading to poor crystallinity of Mo S2 deposited by ALD.（2）A trickle flow aided ALD method is proposed to improve the quality of the deposited Mo S2 films.By placing the nickel foam on the top of the substrate surface to form trickle-fluidized precursor flow,the trickle-blended flow can effectively reduce the nucleation density of Mo S2 in the heterogeneous stage,and provide more space for the longitudinal expansion of crystal grains.As a result,the size of Mo S2 grains has been increased,and Mo S2 grains with a maximum size of 420 nm can be obtained in a single-layer sample by the trickle-assisted ALD method.The good thermal conductivity of the nickel foam can enhance the heat transfer around the substrate to achieve a more stable local temperature field to improve the crystallinity of Mo S2.In addition,the trickle-assisted ALD method can also be used to observe in detail the different changing processes of ALD deposited Mo S2 films in the heterogeneous stage and the homogeneous stage.（3）The surface characteristics of Mo S2 film deposited by ALD and its control strategy are studied.The controllability,hydrophilicity and hydrophobicity,surface morphology,and conformality of Mo S2 films deposited by ALD are discussed in detail.ALD is used to deposit Mo S2 films with controllable thickness on three different planar substrates（Si,Si O2 and Al2O3）to study the influence on the characteristics of Mo S2 films,including film thickness,substrate type,and substrate surface pretreatment.The influence of the surface morphology of ALD deposited Mo S2 films is explored and studied in the form of friction.The morphology and friction can be regulated by the film thickness,grain size,and substrate type.In addition,uniform Mo S2 films can be deposited on the complex surfaces on different micro-nano structures using the conformal properties of ALD.（4）The application and regulation strategy of ALD deposited Mo S2 films in microwave absorption are explored.Designing electromagnetic wave absorbing materials is a huge challenge to coordinately optimize the relationship between attenuation ability and impedance matching.A three-dimensional porous Mo S2/MXene composite aerogel structure with a conformal heterogeneous interface is proposed to optimize the wave absorption in this work.The Mo S2 is controllably deposited on the surface of Ti3C2Tx aerogel by ALD process to produce a conformal heterogeneous interface,therefore the impedance matching of the absorber is optimized and its microwave absorption performance is improved.During this process,the porous microstructure of the original Ti3C2Tx aerogel can be completely preserved to prolong the reflection and the scattering path of electromagnetic waves,which can improve the dielectric loss and enhance the attenuation ability.The interaction between attenuation ability and impedance matching can be adjusted by changing the number of ALD deposition Mo S2cycles.The sample obtained with 300 ALD cycles can show a minimum reflection loss of-61.65 d B at the thickness of 4.53 mm. |
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