Cluster Beam Source Development And Cluster Preparation And Applicatio

Clusters exist widely in nature and human practice,involving in many physical and chemical processes,such as catalysis,combustion,crystal nucleation,growth and so on.The unique properties of clusters are different from individual atoms,molecules and bulk materials due to their structural characteristics.The cluster size is small,the ratio of surface atoms is high,and the geometrical configuration,spin state and interatomic force of surface atoms are completely different from those in bulk phase.At the same time,small size effect and quantum effect are also brought with the size change.With the rise of nanoscience in the past 40 years,clusters,as one of the most important components of nanoscience,have always been a focus of attention.Clusters are widely studied in optics,electricity,superconductivity,catalysis,biology,materials,self-assembly and other fields,showed broad application prospects.Cluster preparation technology is the starting point of cluster research and has always been an important part of cluster science.Compared with the traditional chemical synthesis methods,the gas phase method operates in a high vacuum environment or inert gas atmosphere,without the introduction of external ligand during the synthesis process.The prepared clusters have clean surfaces.Cluster beam technology is the most important method for cluster fabrication in gas phase.Combined with mass spectrometry technology,controllable cluster size fabrication in atomic level can be achieved.With the rise of alloy and composite cluster research,the development of beam source technology that can effectively prepare clusters with controllable size,structure and composition has become the goal of many researchers,especially in recent years.This thesis focuses on the development of cluster beam source and the preparation and application of clusters,carries out the following experimental works:1)We independently developed a cluster beam source combining magnetron sputtering,gas condensation and ultrasonic expansion.The size,structure and composition of clusters can be controlled by the design of a dual-target magnetron sputtering gun,a dual-condensing cavity and the combination of an improved lateral time-of-flight mass spectrometer.A series of mass-selected metallic clusters(Pt,Ag,Au)and alloy clusters(Pt Y,Pt Gd)with highly active rare earth elements were prepared.The developed mass-selected cluster beam source has the characteristics of high beam intensity and high resolution(Ar~+30 n A,resolution above 37).2)A new cluster beam source-low sublimation energy mixed target cluster beam source was designed and constructed.The new one is expected to greatly increase cluster density in the gas phase and the cluster yield.Ag and Zn O clusters were successfully prepared,which verified the feasibility of the cluster preparation by this beam source.The size of the prepared cluster was adjusted by changing the target temperature and the proportion of raw material in the target.3)The successful preparation of multiple atom catalysts(MACs)prove that mass-selected cluster beam source is a suitable method for the preparation of such catalysts.The electrocatalytic performances of the prepared MACs were studied.The electrocatalytic activities of Cu,Pt and Pt Y MACs are correlated with cluster size and composition.The Pt MACs show obvious double atom effect in methanol oxidation reaction(MOR),and the active center is speculated to be located at Pt metal site.The Cu4/C exhibits high catalytic activity for both hydrogen evolution reaction(HER)and CO2 reduction reaction(CO2RR).The catalytic performance of heteronuclear Pt1Y1/C double atom catalyst(DAC)in oxygen reduction reaction(ORR)electrocatalysis exceeds that of homonuclear Pt2/C DAC.The results drive from the variation of MACs geometry and electronic structure.The geometric structure changes the adsorption mode of the adsorbates at the active site,and the electronic structure regulates the adsorption energy of the adsorbates on the catalyst surface.4)The electrocatalytic and gas sensitive properties of the materials were regulated by metal clusters modification.The differences of the two Co-modified N-doped C catalysts prepared by physical and chemical methods for ORR are due to the modification of NC site by Co.The Ag175-WO3 and Au923-ZnO gas sensitive materials were prepared.The modification of Ag175 clusters greatly improves the sensitivity of WO3 nanofibers to NO2.Au923-Zn O material shows gas sensitive response to methylbenzene and good stability at high temperature.The high performance is mainly due to the advantages of cluster prepared by mass-selected cluster beam source:the clean surface and the high activity,which further broadens the application of cluster beam source.