Bem, Daniel B. (1991) The Electrical Transport Properties of Organic Semiconductor Polypropylene Doped with Various Concentrations of Bromine. Masters thesis, Kenyatta University.
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Abstract
Electrical transport pro~erties of undoped and bromine-doped polypropylene were studied by investigating the temperature dependence of dark electrical conductivity and thermoelectric power. The doping process involved letting the polypropylene samples absorb liquid bromine molecules and, by varying the -immersion time, it was possible to obtain samples of different bromine concentrations. The samples with concentrations, by weight uptake, of 0.00%, 0.7%, 1.6%, 2.2%, 3.5%, 4.2%, 5.9%, 6.8% and 7.2% were prepared. The isotadticity of these samples was confirmed by infrared spectroscopy. Conductivi ty (a ) values were calculated in the temperature range 208K to 373K. The conductivity is found to increase sharply upto 5% concentration, beyond which it tends to a constant value. Below room temperature the lncr versus, inverse temperature curves are straight lines each of which has two gradients, which is in conformity with the expected contribution to the resultant conductivity from extrinsic and intrinsic conduction. The activation energy (Eg), for both regions, was calculated with the aid of the equation a = (50 exp (-\/2kBT), where 0'0 is the pre exponential constant. The Eg values .for the extrinsic (lower temperature) regime lie between 0.22 ± 0.04 eV and 0.92 ± 0.02 eV, while in the intrinsic conduction regime, values varied from 0.91 ± 0.03 eV to 3.45 ± 0.04 eV. The values calculated for thermopower (8) were found to be positive which is an indication of a P-type conduction process with holes as the majority carriers. The equation 8 = (kB/e)[Es/2kBT + B], where B is a constant which depends upon the scattering mechanism, was used to explain the linear temperature dependent thermopower and for the determination of the thermal activation energy of carrier generation (Es)' Es values ~anged from 0.20 ± 0.04 ev to 0.97 ± 0.08 eV. The hopping, tunneling and small polaron models of the conduction process have been employed to explain the observed phenomena.
| Item Type: | Thesis (Masters) |
|---|---|
| Subjects: | Q Science > QC Physics T Technology > TK Electrical engineering. Electronics Nuclear engineering |
| Divisions: | Africana |
| Depositing User: | Tim Khabala |
| Date Deposited: | 06 Mar 2018 12:47 |
| Last Modified: | 06 Mar 2018 12:47 |
| URI: | http://thesisbank.jhia.ac.ke/id/eprint/3420 |
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