Tunnel electron transfer between nanoparticles

R [15]. For particles Ag with R = 5nm this correction lifts Fermi level to 0.22 eV in comparison with level for bulk metal [15]. The surface-determined size effect for Fermi energy of metal nanoparticles results in mutual charging of nanoparticles of different sizes by the tunnel electron transfer between nanoparticles. Such charging processes, as it will be shown below (Subsection 4.4), greatly influence catalytic reactions induced by assembly of metal nanoparticles with size distribution immobilized in solid dielectric matrix. 

Unusually small value of pc in this system speaks that the true concentration of Ag in the areas of a film, where Ag nanocrystals are formed, strongly differs from the average concentration determined in experiment. Systems with concentration of M/SC nanoparticles close to pc are of special interest. In such systems the essential increase in conductivity as compared to that of pure polymer results from processes of tunnel electron transfer between nanoparticles. Conductivity of composite system with regard to electron tunneling between M/SC nanoparticles has been considered in work [88] on the basis of the following model. In the model, the spherical particle of radius Rq is surrounded with the sphere of radius Rd describing the delocalization for conductivity electrons of the particle and partial transition of electronic density in an environment (Figure 10.6a). 

Specific catalytic properties of synthesized Pd-PPX nanocomposites have been explained by the tunnel charge transfer between nanoparticles. As mentioned in Section 2, the energy of Fermi level of small metal particle depends on its size [14], At the same time, M nanoparticles immobilized in PPX matrix have rather wide size distribution in the range 2-8 nm (Section 3). Electron transfer between particles of different size results in their mutual charging that leads to equalization of their electrochemical potentials [15],... 

The increase in catalytic activity with the rise of metal content can be explained by the mutual charging of Cu nanoparticles by tunnel electron transfer between particles of different size. Presumably, negative charged particles formed in this case, among positively charged ones, facilitate initiation of the chain reaction (I) via dissociation of CC14. 

The specific low-frequency dielectric losses are found out in composite films, containing M nanoparticles. It is assumed that these losses are caused by interaction of an electromagnetic field with the dipoles reorientation in the environment connected with tunnel electrons transfer between the nanoparticles or traps of the environment. 

It is believed that surface localized electron-hole pairs produced under light in SC nanoparticles participate in photo-induced processes of charge transfer between nanoparticles. These processes most probably of quantum tunnel type determine photoconductivity of composite films containing SC nanoparticles in a dielectric matrix. The photocurrent response time in this case should correspond to the lifetime ip of such pairs, which is of the order nanosecond and even more [6]. This rather long ip makes photo-induced tunnel current in composite film possible. 

Experimental data relating to the conductivity of composite films with M/SC nanoparticles are described by the classical percolation model in terms of tunnel processes. Chemisorption of chemical compounds on the surface of M/SC nanoparticles in films and the subsequent reactions with participation of chemisorbed molecules change the concentration of conducting electrons and/or barriers for their tunnel transfer between the nanoparticles with the result of strong influence on the film conductivity. Such films are used as conductometric sensors for detecting various substances in an atmosphere. 

Probably, in these reactions as well as in reaction under action of Cu-PPX film [116], catalytic activity increases due to appearance of negatively charged Cu nanoparticles formed by the tunnel transfer of electrons between... 

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