表面吸附污染对多晶铜和金功函数的影响
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摘要
功函数是金属光阴极的一项重要特性,决定了光电子发射量子效率。金属表面在大气环境中容易受表面吸附污染的影响,从而改变表面功函数,并可能影响光电子发射性能。本工作通过光电子能谱的方法,研究常用做光阴极材料的多晶铜和金表面在大气环境中的吸附污染,及其对表面功函数的影响。根据紫外光电子能谱的测量,发现铜和金金属表面存在吸附污染时功函数相比纯净金属表面分别降低约0.1 e V和0.7 e V。利用X射线光电子能谱分析发现有机分子吸附污染使得金样品的表面功函数降低;而对于铜样品表面,导致功函数降低的因素包括有机分子吸附和表面氧化。本研究对光阴极的应用具有指导意义。
Work function is one of the most important properties of metal photocathodes. It will determine the quantum efficiency of photoemission. In the atmosphere environment,there would be adsorptions and contaminations on the metal surface,which may change the work function and even influence photoemission properties. Here,photoelectron spectroscopy methods( XPS and UPS) were introduced to study the surface adsorptions and contaminations of polycrystalline Cu and Au samples and their influence on the work function. According to measurements of ultraviolet photoelectron spectroscopy( UPS),work function decreases of 0. 1 e V and 0. 7 e V were found respectively for Cu and Au with surface contaminations. X-ray photoelectron spectroscopy( XPS) was used to determine the surface chemical states. For Au surface,adsorptions of organic molecules led to a large decrease of work function. For Cu surface,work function decrease was resulted from both organic adsorptions and surface oxidations. This work could help proper applications of metal photocathodes.
Work function is one of the most important properties of metal photocathodes. It will determine the quantum efficiency of photoemission. In the atmosphere environment,there would be adsorptions and contaminations on the metal surface,which may change the work function and even influence photoemission properties. Here,photoelectron spectroscopy methods( XPS and UPS) were introduced to study the surface adsorptions and contaminations of polycrystalline Cu and Au samples and their influence on the work function. According to measurements of ultraviolet photoelectron spectroscopy( UPS),work function decreases of 0. 1 e V and 0. 7 e V were found respectively for Cu and Au with surface contaminations. X-ray photoelectron spectroscopy( XPS) was used to determine the surface chemical states. For Au surface,adsorptions of organic molecules led to a large decrease of work function. For Cu surface,work function decrease was resulted from both organic adsorptions and surface oxidations. This work could help proper applications of metal photocathodes.
引文
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[13]MAO J,PENG T,ZHANG X,et al.Effect of graphitic carbon nitride microstructures on the activity and selectivity of photocatalytic CO2reduction under visible light[J].Catalysis Science&Technology,2013,3(5):1253-1260.
[14]CONTARINI S,HOWLETT S P,RIZZO C,et al.XPS study on the dispersion of carbon additives in silicon carbide powders[J].Applied Surface Science,1991,51(3):177-183.
[15]JOUAN P Y,PEIGNON M C,CARDINAUD C,et al.Characterisation of Ti N coatings and of the Ti N/Si interface by X-ray photoelectron spectroscopy and Auger electron spectroscopy[J].Applied Surface Science,1993,68(4):595-603.
[2]陈丽卿,张伟.氧的电子探针定量分析[J].电子显微学报,1998,17(5):567-568.
[3]柳得橹,张济忠.电子束辐照下碳沉积的分形生长[J].电子显微学报,1996,15(6):529-529.
[4]CHUANG T J,ZHAI R S,CHAN Y L,et al.Chemisorption characteristics of methylnitrene diradicals adsorbed on Cu(110)studied by UPS and PEEM[J].Journal of Electron Spectroscopy and Related Phenomena,2005,144(6):421-424.
[5]KRISCHOK S,STRACKE P,KEMPTER V.Metal(Cu,Pd)adsorption on Mg O:investigations with MIES and UPS[J].Applied Physics A,2005,82(1):167-173.
[6]PASQUALI L,TERZI F,SEEBER R,et al.UPS,XPS,and NEXAFS study of self-assembly of standing 1,4-benzenedimethanethiol SAMs on gold[J].Langmuir,2011,27(8):4713-4720.
[7]PARK Y,CHOONG V,GAO Y,et al.Work function of indium tin oxide transparent conductor measured by photoelectron spectroscopy[J].Applied Physics Letters,1996,68(19):2699.
[8]EASTMAN D E.Photoelectric work functions of transition,rare-earth,and noble metals[J].Physical Review B,1970,2(1):1-2.
[9]MCINTYRE N S,SUNDER S,SHOESMITH D W,et al.Chemical information from XPS-applications to the analysis of electrode surfaces[J].Journal of Vacuum Science&Technology,1981,18(3):714-721.
[10]ROBERT T,BARTEL M,OFFERGELD G.Characterization of oxygen species adsorbed on copper and nickel oxides by X-ray photoelectron spectroscopy[J].Surface Science,1972,33(1):123-130.
[11]GARDNER S D,SINGAMSETTY C S K,BOOTH G L,et al.Surface characterization of carbon fibers using angleresolved XPS and ISS[J].Carbon,1995,33(5):587-595.
[12]BOU M,MARTIN J M,LE MOGNE T,et al.Chemistry of the interface between aluminium and polyethyleneterephthalate by XPS[J].Applied Surface Science,1991,47(2):149-161.
[13]MAO J,PENG T,ZHANG X,et al.Effect of graphitic carbon nitride microstructures on the activity and selectivity of photocatalytic CO2reduction under visible light[J].Catalysis Science&Technology,2013,3(5):1253-1260.
[14]CONTARINI S,HOWLETT S P,RIZZO C,et al.XPS study on the dispersion of carbon additives in silicon carbide powders[J].Applied Surface Science,1991,51(3):177-183.
[15]JOUAN P Y,PEIGNON M C,CARDINAUD C,et al.Characterisation of Ti N coatings and of the Ti N/Si interface by X-ray photoelectron spectroscopy and Auger electron spectroscopy[J].Applied Surface Science,1993,68(4):595-603.