Band-gaps entries

A pioneering study of the electrical conductivity of poly(2,5-dibutoxy-p-phenylene ethynylene), a fully soluble PPE derivative, was conducted by the groups of Shinar and Barton (Table 1, entry 3) [38]. The polymer employed displayed a band gap. Eg, of 2.5 eV, which is typical for 2,5-dialkyloxy-PPEs. A conductivity of 10 Scm was reported for the undoped polymer. This value was later confirmed in an independent study by Lo Sterzo et al.,who reported a conductivity of 4-10 Scm for the same polymer [39]. It was reported that upon exposure to I2 vapor at a pressure of 1 Torr, the room-temperature conductivity of poly(2,5-dibutoxy-p-phenylene ethynylene) increased by about three orders of magnitude to 10 Scm [38]. It increased further and imme-... 

Rather problematic with TiCk in terms of the attainable process efficiency is its rather wide band gap (3.0-3.2 eV). Consequently, only a small fraction ( 5%) of the overall solar spectrum can be harnessed by this material. Thus, the early work (as in Table 5, Entries 16 and 17, Refs. 236 and 237 respectively) has also included attempts at extending the light response of TiCk from the UV to the visible range see, for example, Refs. 260, 290-296. Reviews of these works are available, see Refs. 20, 32, 297 and 298. For reasons mentioned earlier, we exclude for our discussion, studies oriented toward chemical modification of the TiCk surface with a dye. As sum-... 

Entry number Oxide semiconductor Energy band gap, eV Comments Reference (s)... 

Entry number Oxide semiconductor (s) Energy band gap(s)a, eV Comments Refer- ence... 

Entry number Oxide Energy band gap eV Comments Refer- ence(s)... 

Entry number Metal chalcogenide(s) Band gap energy eV Comments Reference(s)... 

The optical properties of nanomaterials are also different from those of their bulk counterpart due to the effect of surface plasmon resonance. This process appears when the entry free electrons in the conduction band produce an in-phase oscillation, called surface plasmon resonance. In this context, the increase of band gap in semiconductor nanoparticles generates a shift toward shorter wavelengths of the absorption edge. At resonance, light is tightly confined to the surface of the nanostructure until it eventually is absorbed inside the metal or scattered back into photons (Vollath 2008). 

Ladder structures that are composed exclusively of aromatic carbon centers have been the focus of theoretical calculations and diverse synthetic efforts for a long time. Polyacenes are a major focus in this interest [40,41]. Polyacenes are band molecules composed exclusively of annelated six-member carbon rings. Linear polyacenes, poly(n)acenes, are, as polymers with low band gap energy, poorly accessible as a result of their high reactivity (oxidation, dimerization) [42-44]. Hitherto only oligo-( )acenes up to hexa- and heptacene [45,46] have been known and characterized. A synthetic entry to the corresponding polymer does not yet exist, although there are... 

Table 15 LDA, Hcurtree-Fock (HF), and experimental (Exp.) values for various electronic properties for four semiconductors. The width is the total valence-band width, the gap is the smallest gap between valence and conduction bands, and ECOh Is the cohesive energy. The last two entries are band-energy differences at the point (k = 0). All energies are given in eV (the cohesive energy in eV/atom), and the results are from ref. 86...

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