Nanoporous semiconductors

As an indication of the types of infonnation gleaned from all-electron methods, we focus on one recent approach, the FLAPW method. It has been used to detennine the band stmcture and optical properties over a wide energy range for a variety of crystal stmctures and chemical compositions ranging from elementary metals [ ] to complex oxides [M], layered dichalcogenides [, and nanoporous semiconductors The k p fonnulation has also enabled calculation of the complex band stmcture of the A1 (100) surface... 

On structure/property-relations in nanoporous semiconductors of the cetineite-type... 

In the search for a new class of nanomaterials, i.e. crystalline nanoporous semiconductors, a lot of efforts are made to synthesize new compounds with a zeolite-like open framework structure consisting of typical semiconductor elements like As, Sb, Se, etc.11-41 In 1995 Wang and Liebau reported the preparation and structure of oxoselenoantimonates (III) with a zeolite-like channel structure15 61, which are related to the natural mineral cetineite.171 This mineral with composition (K Na)3+x(Sb203)3(SbS3)(0H) (2.8-x)H20 with x = 0.5, first described in 1987 by Sabelli and Vezzalini181, was found in Le Cetine mine in Tuscany, Italy. 

In conclusion we showed how the optical excitation energies in isostructural cetineites, the experimental ones as well as the theoretical values, depend on the chemical composition. Based on this, in mixed phase (Na,K S) the band gap can be tuned by varying the Na K-ratio. These results give an insight into the structure/property-relation and show that the optical properties can be tuned chemically in this novel class of nanoporous semiconductors. 

On Structure/Property Relations in Nanoporous Semiconductors of the Cetineite- 683... 

Enzel et al. [37] applied AFM to nanoporous semiconductors based on tin (IV) sulfide and tin (IV) selenide. The surface structure of these materials displayed regular patterns of micropores, in agreement with expectations from the crystallographic projections of their bulk structures. AFM studies of silica have dealt with, e.g., amorphous silica gels [38] or... 

Anderson N. A., Hao E., Ai X., Hastings G. and Lian T. (2001), Ultrafast and long-lived photoinduced charge separation in MEH-PPV/nanoporous semiconductor thin film composites , Chem. Phys. Lett. 347, 304-310. 

The simplest photoelectrochemical cells consist of a semiconductor working electrode and a metal counter electrode, both of which are in contact with a redox electrolyte. In the dark, the potential difference between the two electrodes is zero. The open circuit potential difference between the two electrodes that arises from illumination of the semiconductor electrode is referred to as the photovoltage. When the semiconductor and counter electrode are short circuited, a light induced photocurrent can be measured in the external circuit. These phenomena originate from the effective separation of photogenerated electron-hole pairs in the semiconductor. In conventional photoelectrochemical studies, the interface between the flat surface of a bulk single crystalline semiconductor and the electrolyte is two dimensional, and the electrode is illuminated from the electrolyte side. However, in the last decade, research into the properties of nanoporous semiconductor electrodes interpenetrated by an electrolyte solution has expanded substantially. If a nanocrystalline electrode is prepared as a film on a transparent conducting substrate, it can be illuminated from either side. The obvious differences between a flat (two dimensional) semiconductor/ electrolyte junction and the (three dimensional) interface in a nanoporous electrode justify a separate treatment of the two cases. 

In this chapter, the characterization of the three types of systems described earlier have been considered single crystal and polycrystalline bulk electrodes (Sect. 2.1.3), dye-sensitized and quantum dot electrodes (Sect. 2.1.4), and macro-porous and nanoporous semiconductors (Sect. 2.1.5). Some essential features, common to all these systems, are introduced in the following subsection. The... 

P. E. de Jongh in Photoelectrochemistry of nanoporous semiconductor electrodes, Ph.D. Thesis,. University of Utrecht, 1999. 

J. Bisquert, G. GarciaBelmonte, F. Fabregat-Santiago, ModeUing the electric potential distribution in the dark in nanoporous semiconductor electrodes, J. Solid State Electrochem. 1999, 3(6), 337-347. 

Fabregat-Santiago F, Mora-Sero I, Garcia-Belmonte G, Bisquert J (2003) Cyclic voltammetry studies of nanoporous semiconductors. Capacitive and reactive properties of nanocrystalline T102 electrodes in aqueous electrolyte. J Phys Chem B 107(3) 758-768... 

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