Electron and light emission from island metal films and generation of hot electrons in nanoparticles

We review experimental and theoretical works devoted to electron and photon emission from island metal films (IMFs) representing ensembles of small me tal particles deposited onto a dielectric substrate and coupled via penetra ble potential barriers. Electrons and photons are emitted when the films ar e energized by passage of current through them or by laser irradiation. In either case the primary recipient of the energy is the electron gas, which can be heated up to temperatures much higher than the particle lattice temp erature. A theoretical substantiation of the model of hot electrons in nano particles is presented. The major physical factor that permits generation o f hot electrons in IMFs is the dramatic reduction (by orders of magnitude) of the electron-lattice energy transfer in the particles whose size is smal ler than the mean free path of electrons in the volume. In such particles w ith a ballistic motion of electrons, the energy is being lost mainly in sur face scattering acts which are less effective in energy transfer than gener ation of volume phonons. Thus, the electron temperature can become substant ially higher than the lattice temperature provided the absorbed power densi ty is high enough and the lattice of the island is intensively cooled by th e substrate. The model of hot electrons is used to interpret experimental d ata. Non-equilibrium electron heating in IMFs can be observed even under st ationary conditions, so the island metal films basically differ in their el ectronic properties from continuous metal films and bulk metals where hot e lectrons can be obtained only for very short times (less than or equal to 1 0(-11) s), Thus, the island metal films represent an important variety of n anomaterials having rather unusual physical properties. IMFs can be utilize d to fabricate cathodes having interesting application potentialities in va cuum microelectronics, information display technologies and infrared image conversion. Hot electrons generated in nanoparticles may also play a signif icant role in various dispersed systems exposed to energy fluxes. (C) 2000 Elsevier Science B.V. All rights reserved.