高灵敏及高分辨KPFM及其相关技术(英文版)(精)/纳米光子学丛书

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Chapter 3 Kelvin Probe Force Microscopy 3.1Fundamentals of KPFM (1) Work function In solidstate physics，the workfunction［1］ is the minimum energy (usually measured in electronvolts) needed to remove an electron from a solid to a point immediately outside the solid surface (or the energy needed to move an electron from the Fermi level into vacuum). Here “immediately” means that the final electron position is far from the surface on the atomic scale but still close to the solid on the macroscopic scale. The work function is a characteristic property for any solid phase of a substance with a conduction band (whether empty or partly filled). For a metal，the Fermi level is inside the conduction band，indicating that the band is partly filled. For an insulator， the Fermi level lies within the band gap， indicating an empty conduction band; in this case，the minimum energy to remove an electron is about the sum of half the band gap and the electron affinity，Figure 31 give a band diagram of an insulator. Figure 31Simple band diagram with denoted vacuum energy EVAC，conduction band EC ，Fermi energy EF，valence band EV，electron affinity Eea，work function Φ and band gap Eg (For colored figure please scan the QR code on page 15) Φ is measured by CPD,VAB exists between the surfaces of two solids A and B of work functions ΦA and ΦB，when connected electrically，since ΦB-ΦA=eVAB.(3.1) For the two solids at same temperature， the method involves a prior knowledge of the work function of one of the solids if that of the other is to be measured absolutely. (2) Contact potential difference Contact potential difference (CPD) is a method of measuring work function changes of a surface. The technique usually involves capacitor plates which are caused to vibrate as the voltage potential on the plates is measured. One capacitor plate is used as a reference which should remain inert to adsorption electrons. The other plate will be