低能聚焦电子束诱导的金属表面局域荷电效应
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摘要
鉴于低能电子束微纳成像与分析的重要应用,本文着重研究低能电子束同金属样品的相互作用。低能电子束入射至金属表面,当总散射电子产率>1且入射束流密度较高时,发现测得透射束流会随时间而发生不同程度的衰减失稳现象。建立微观空穴态复合模型讨论分析了透射束流衰减现象的物理机制,并推测透射束流衰减的原因。由于金属表面缺陷和吸附等将使得样品中所激发的空穴态寿命增加,降低了同自由电子复合几率,导致表面局域电荷积累,从而在宏观统计上导致电子发射效率的降低以及透射束流的衰减。
Low energy electron beams have important applications onmicroscaleand even nanoscale imaging and analysis. To explore deeper mechanisms of applications,the interactions between a low energy beam and metal surface are studied. It was found that the transmission currents would decay with time byhigh current density electron beams with low energy when the total scattered electron yield was greater than 1. The physical mechanism of the decay was investigated with a micro-electron-hole recombination model.Incident electrons couldexcite long lifetime holes on metal surface,and the holes wouldinduce the decayof the transmission current. It was speculated that the defects and adsorptions on metal surface would increase the lifetime of the excited holes and reduce the electronhole recombination rate,which led to local charges accumulationonthe metal surface. In macroscopic scale,it could be observed that the electron emission rate and the transmission current decayed with time.
Low energy electron beams have important applications onmicroscaleand even nanoscale imaging and analysis. To explore deeper mechanisms of applications,the interactions between a low energy beam and metal surface are studied. It was found that the transmission currents would decay with time byhigh current density electron beams with low energy when the total scattered electron yield was greater than 1. The physical mechanism of the decay was investigated with a micro-electron-hole recombination model.Incident electrons couldexcite long lifetime holes on metal surface,and the holes wouldinduce the decayof the transmission current. It was speculated that the defects and adsorptions on metal surface would increase the lifetime of the excited holes and reduce the electronhole recombination rate,which led to local charges accumulationonthe metal surface. In macroscopic scale,it could be observed that the electron emission rate and the transmission current decayed with time.
引文
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[25]VIET PHAM T,RAO M,ANDREASSON P,et al.Photocarrier generation in CuxO thin films deposited by radio frequency sputtering[J].Applied Physics Letters,2013,102(3):032101.
[2]KJELLMAN T,ASAHINA S,SCHMITT J,et al.Direct observation of plugs and intrawall pores in SBA-15using low voltage high resolution scanning electron microscopy and the influence of solvent properties on plug-formation[J].Chemistry of Materials,2013,25(20):4105-4112.
[3]LEWIS P,MICKLETHWAITE S,HARRINGTON J,et al.Exploring backscattered imaging in low voltage FESEM[J].Journal of Cell Biology,2015,644(1):012019.
[4]TSURUMI D,HAMADA K,KAWASAKI Y.Highly reproducible secondary electron imaging under electron irradiation using high-pass energy filtering in low-voltage scanning electron microscopy[J].Microscopy and Microanalysis,2012,18(2):385-389.
[5]WUHRER R,MORAN K,IOP.Low voltage imaging and X-ray microanalysis in the SEM:challenges and opportunities[C].IOP Conference Series:Materials Science and Engineering,in 14thEuropean Workshop on Modern Developments and Applications in Microbeam Analysis,2016(109):012019.
[6]ELLIOTT S L,BROOM R F,HUMPHREYS C J.Dopant profiling with the scanning electron microscope—A study of Si[J].Journal of Applied Physics,2002,91(11):9116-9122.
[7]CAZAUX J.e-Induced secondary electron emission yield of insulators and charging effects[J].Nuclear Instruments&Methods in Physics Research Section BBeam Interactions with Materials and Atoms,2006,244(2):307-322.
[8]KANAYA K,ONO S,ISHIGAKI F.Secondary-electron emission from insulators[J].Journal of Physics DApplied Physics,1978,11(17):2425-2437.
[9]CAZAUX J.Some considerations on the secondary electron emission,delta,from e(-)irradiated insulators[J].Journal of Applied Physics,1999,85(2):1137-1147.
[10]KUMAGAI K,YAO Y Z,CHEN J,et al.Image instability during the electrical measurement in scanning electron microscope[J].Physica Status Solidi C:Current Topics in Solid State Physics,2011,8(4):1407-1411.
[11]HOWIE A.Threshold energy effects in secondary electron emission[J].Microscopy and Microanalysis,2000,6(4):291-296.
[12]PESTY F,GAROCHE P.Low-energy electron beam on an insulator surface:impact of the charging process on the diffraction by mica muscovite[J].Surface Science,2005,580(1/2/3):153-162.
[13]URA K,AOYAGI S.Static capacitance contrast of LSI covered with an insulator film in low accelerating voltage scanning electron microscope[J].Journal of Electron Microscopy,2000,49(1):157-162.
[14]MULLEROVA I,EL-GOMATI M M,FRANK L.Imaging of the boron doping in silicon using low energy SEM[J].Ultramicroscopy,2002,93(3/4):223-243.
[15]FUJII H,OKUMURA T,AKAHASHI M.Low-energy electron beam induced charging and secondary electron emission properties of FEP film used on satellite surfaces[J].Electrical Engineering in Japan,2014,188(1):9-17.
[16]LI S,ZHAO C,MIN D,et al.Simulation of low-energy electron beam irradiated PTFE based on bipolar charge transport model[J].Ieee Transactions on Dielectrics and Electrical Insulation,2016,23(5):3016-3025.
[17]LI W Q,ZHANG H B.The surface potential of insulating thin films negatively charged by a low-energy focused electron beam[J].Micron,2010,41(5):416-422.
[18]ZHANG H B,LI W Q,CAO M.Space charge characteristics of an insulating thin film negatively charged by a low-energy electron beam[J].Journal of Electron Microscopy,2012,61(2):85-97.
[19]黄晓旭,吴桂林,钟虓?,等.先进材料多维多尺度高通量表征技术[J].电子显微学报,2016,35(6):567-568.
[20]GROSS B,HESSEL R,Electron-emission from electronirradiated dielectrics[J].Ieee Transactions on Electrical Insulation,1991,26(1):18-25.
[21]DING Z J,LI H M,TANG X D,et al.Monte Carlo simulation of absolute secondary electron yield of Cu[J].Applied Physics A:Materials Science&Processing,2004,78(4):585-587.
[22]CIMINO R,GONZALEZ L A,LARCIPRETE R,et al.Detailed investigation of the low energy secondary electron yield of technical Cu and its relevance for the LHC[J].Physical Review Special Topics-Accelerators and Beams,2015,18(5):051002.
[23]WARREN J T,O'HARA K E,WOLFE J P.Two-body decay of thermalized excitons in Cu2O[J].Physical Review B,2000,61(12):8215-8223.
[24]GERLACH A,BERGE K,GOLDMANN A,et al.Lifetime ofdholes at Cu surfaces:theory and experiment[J].Physical Review B,2001,64(8):085423.
[25]VIET PHAM T,RAO M,ANDREASSON P,et al.Photocarrier generation in CuxO thin films deposited by radio frequency sputtering[J].Applied Physics Letters,2013,102(3):032101.