# The Work Function Of Atom Metal Contact Charging Electron Transfer Results From The Contact Of Two Contact

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Work function In the case of metal-metal contact charging, electron-transfer results from the contact of two uncharged contact points having different work functions (C. F. Gallo and Lama, 1976). The work function is an intrinsic surface property defined as that minimum energy required to move the weakest bound electron from the surface of a solid to the vacuum energy level (or to infinity) (Hoe et al., 2011a; Ishii et al., 1999). The direction of electron-transfer is expected to go from the material with lower work function to that with a higher work function. The electron-transfer process continues until the Fermi level, which is the level at which the probability of occupancy of states with electrons in the allowed energy state is, of…show more content…
Coulombic forces govern the magnitude of the electrostatic attraction/repulsion forces (Fel) between particles, as defined by Coulomb’s law (in the simplest case of two-point charges) (Seville et al., 1997): "F" _"el" " = " ("q" _"1" "q" _"2" )/("4πϵ" "ϵ" _0 "d" ^"2" ) (2), where q1 and q2 are the electrical charges on the two particles respectively, ε is the relative permittivity, ε0 is the permittivity of free space (given by 8.854 × 10-12 C2/Nm2) and d is the distance of separation between the two particles. If a charged particle encounters an uncharged particle, the first particle will induce an image charge on the surface of the second particle. The electrostatic force (Fc) between these particles is then calculated as: "F" _"c" " = " ("q" ^"2" "(1 -" "d" /√("r" ^"2" "+" "d" ^"2" ) ")" )/("16πϵ" "d" ^"2" ) (3), where q is the electrical charge on the charged particle, r is the radius of the interacting particles, and d is the distance between the charged and uncharged particles. When two solid materials of different in vacuum are separated by a small distance (d), electrons are transferred from the material with the lower work function to the material with the higher one. An equilibrium will be established eventually, in which the two work functions reach the same level. The forces of attraction (Fw) between these two solid materials