Study Of Pt Based Area Selective Atomic Layer Deposition With High Precision And Its Application On Catalysis

Atomic layer deposition（ALD）is a bottom-up chemical vapor deposition method with high precision based on the surface self-limited reaction.Compared with other thin film deposition technique,ALD possesses unique self-limited saturated chemisorption reaction mechanism.As a result,ALD shows advantages like the accurate control of thin film thickness in sub-nanometer level,uniformity in large area and conformality in the complex structure with high aspect ratio.Recently,it has seized researchers’eyes in catalysis,energe source,microelectronics,photics et.al.With the development of ALD,the selective ALD method which enables selective deposition on specific area is attached importance.This thesis develops a series of selective deposition methods based on the ALD process parameters control and reaction barrier control of precursors on the substrate,which realizes the directional deposition with high precision.And this method is utilized in the controlled synthesis of catalysts with high performance.Firstly,a selective atomic-layer-deposition method is developed to decorate Pt nanoparticles with Ni O_x,resulting in greatly improved catalytic performance.During the initial growth stage,Ni O_x can be selectively deposited on the low coordinated sites of Pt NPs.The Ni O_x/Pt/Al₂O₃ catalysts show enhanced activity toward CO oxidation.More importantly,the sintering resistance of the composite Ni O_x/Pt/Al₂O₃ catalysts has been improved significantly,which can be attributed to the stabilization of volatile atoms at low coordinated sites and the strong metal oxide interaction that anchors Pt NPs.Pt can keep stable after 750℃calcination.In the following research first-principles calculations combined with microkinetic methods are employed to shed light on the edge-selective growth mechanism of 3d-transition metal oxide on Pt nanoparticles in ALD from the metal M（Cp）₂（M=Fe,Co,and Ni）.The M（Cp）₂ decomposition on the surface of Pt nanoparticles exhibits robust preferential growth,following the order of edge>（100）>（111）,which indicates that edges are naturally selected to be covered and the（111）facets could survive toward the M（Cp）₂precursors.Moreover,the reaction rate analysis indicates that the edge selectivity of M（Cp）₂on Pt nanoparticles is temperature dependent,and a high temperature will suppress the selectivity between different sites.The theoretical predictions about the edge-selective growth of M（Cp）₂ are confirmed by the Fourier transform infrared measurements（FTIR）of CO signals on successive ALD-coated Pt nanoparticles.The combination of theoretical and experimental study demonstrates the robust edge-selective growth of M（Cp）₂ on Pt nanoparticles.The selective growth mechanism of iron oxide on Pt nanoparticles in ALD using tert-Butyl ferrocene（TBF）and O₂/O₃ as the precursors are studied.When using O₂ as the co-reactant,the ALD reaction can only take place above 250℃in which the Fe Ox will be deposited on（100）and edge sites.When using O₃ instead of O₂,the reaction can take place at 150℃and low coordinated sites of Pt are selected to be covered.Lastly,we develop a selective ALD method based on the precisely control of ALD parameters and fabricate Pt atoms decorated Co O_x nanoclusters structure.The structure is realized through the precisely control of the ALD process by tuning the deposition temperature and counter reactant.As a result,the Pt growth on the Al₂O₃ support is suppressed and Pt atoms are exclusively studded on the Co O_x nanoclusters.The Pt/Co O_xcatalysts show nearly 100%CO conversion and selectivity at room temperature.Meanwhile,the composite catalyst has ultralow Pt loading of～0.8 wt%.The selective deposition of Pt on Co maximizes Pt atoms dispersion and utilization,as well as the highly active Pt/Co O_xinterfaces that contributes to the excellent catalytic performance.Meanwhile,it is found that the Co O spices at low chemical state is critical to improve the activity.The kinetics studies show that the composite Pt-Co catalysts show weaker CO adsorption and lower O₂activation barrier.The first principle simulations also indicate that the Pt/Co O exhibits lower CO oxidation barrier.