Home About us Contact
|
Home About us Contact | ||
|
|
||
Semiconductor Behavior (semiconductor + behavior)
Selected AbstractsSemiconductor Behavior of a Metal-Organic Framework (MOF)CHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2007Mercedes Alvaro Dr. Abstract Upon light excitation MOF-5 behaves as a semiconductor and undergoes charge separation (electrons and holes) decaying in the microsecond time scale. The actual conduction band energy value was estimated to be 0.2,V versus NHE with a band gap of 3.4,eV. Photoinduced electron transfer processes to viologen generates the corresponding viologen radical cation, while holes of MOF-5 oxidizes N,N,N,,N, -tetramethyl- p -phenylenediamine. One application investigated for MOF-5 as a semiconductor has been the shape-selective photocatalyzed degradation of phenol in aqueous solutions. [source] The Influence of Doping Levels and Surface Termination on the Electrochemistry of Polycrystalline DiamondELECTROANALYSIS, Issue 6 2004Matthew Abstract The influence of surface chemistry and boron doping density on the redox chemistry of Fe(CN) at CVD polycrystalline diamond electrodes is considered. It is demonstrated that for this couple both the doping density and the surface chemistry are important in determining the rate of charge transfer at the electrode/electrolyte interface. For hydrogen terminated CVD diamond metallic electrochemical behavior is always observed, even at boron doping densities as low as 7×1018,cm,3. In contrast, the electrochemical behavior of oxygen terminated CVD diamond varies with doping density, a metallic response being observed at high doping density and semiconductor behavior at low doping density. It is shown that the results attained may be explained by a surface state mediated charge transfer mechanism, thus demonstrating the importance of controlling surface chemistry in electroanalytical applications of diamond. [source] Nanofiber organic semiconductors: The effects of nanosize on the electrical charge transport and optical properties of bulk polyanilinesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2009F. Yakuphanoglu Abstract The electrical transport, optical, and microstructural properties of bulk polyaniline (PANI) and nano-PANIs were investigated. A field emission scanning electron microscopy (SEM) image of bulk PANI showed macroscopic and aggregated granular particles. A SEM image of the nanostructured PANI showed the formation of one-dimensional nano/microstructures. The formation of nanofibers was observed from the transmission electron microscopy image. The electrical conductivities of the bulk and nanostructured PANIs increased with increasing temperature, which indicated semiconductor behavior. The electrical conductivities of the bulk and nanostructured PANIs at room temperature were found to be 2.12 × 10,5 and 1.80 × 10,2 S/cm, respectively. The electrical conductivity of the nanostructured PANI was about 850 times higher than that of the bulk PANI. The obtained band gaps of the bulk and nanostructured PANIs were determined from diffuse reflectance measurements and were found to be 3.27 and 2.41 eV, respectively. The refractive index of the PANI samples changed from 1.3 to 1.61. The obtained results indicate that the electrical and optical properties of the PANI were inherently dependent on the nanostructure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Ultrahigh-Temperature Semiconductors Made from Polymer-Derived CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2010Hee-Yeon Ryu We report the semiconductor behavior of polymer-derived ceramics at high temperatures extending up to 1300°C, far above that of any known material. The conductivity depends strongly on the N/O molar ratio, reaching its highest value when the ratio is approximately unity. The temperature dependence of the conductivity for these specimens, ,, shows good agreement with the Mott's variable range hopping (VRH) mechanism for three,dimensional conduction in amorphous materials as described by. The comparison yields the following range of values for the density of states, N(E)=4.9 × 1017,5.9 × 1018 (eV·cm3),1, hopping energy, W=0.017,0.047 eV, and hopping distance, R=13.4,21.8 nm. The charge carrier mobilities predicted by the VRH model are in excellent agreement with the values measured in the Hall experiment. The long hopping distances are an unusual feature of this ceramic, suggesting long-range wave functions that may arise from clusters of SiCNO atoms that can exist in the form of a nanodomain network. Specimens that are either rich in oxygen (at the expense of nitrogen) or rich in nitrogen, have conductivities that are four to eight orders of magnitude lower than the ,equimolar compositions. One oxygen-rich specimen shows band-gap controlled semiconductivity with an activation energy of 1.1 eV. Taken together, these results suggest that the electronic properties of the SiCNO ceramics are controlled by complex interactions between C and other atoms (Si, N, and O). These results are at variance with the simple picture where "free carbon" is assumed to determine the electronic behavior. [source] | |||||||||||||