Electrochemistry on suspended semiconductor nanoparticles

These types of measurements have been confirmed for various semiconductor dispersions (27,131-133) including Ti02, In203, Sn02, CdS, WO3, and Fc203, and demonstrated that the 

Fermi level of particles is a function of irradiation intensity. The photo-onset potentials were shifted toward more negative values as a function of the photon flux. These experiments were supported by a blue shift of the absorption peak in the UV-vis spectra measured immediately after a high-intensity flash (134). This phenomenon is known as the Burstein shift (135). Various potentials were applied to dispersions on an optically transparent electrode, 

In fact, there is a direct correlation between potential separation between peaks A1 and Cl and the observed band gap for various size particles. It is summarized in Table 9.4. 

Based on these results, peak A1 is attributed to electron transfer from the highest occupied molecular orbital (HOMO) to the electrode and peak Cl is attributed to electron transfer from the electrode to the lowest unoccupied molecular orbital (LUMO), thus introducing the concept of electrochemical band gap for semiconductor nanopariicles. Such a band gap was also observed earlier for extremely small metal nanoparticles (4). The decomposition of compound semiconductor particles on charge transfer poses a serious limitation on these studies, which was overcome by carrying out these measurements on 

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