V. Kalendra

Electrical Properties of Composites of Polystyrene and Multi-Walled Carbon Nanotubes

The dependencies of electrical conductivity on the electrical field and temperature of high-resistivity polystyrene/carbon nanotube (CNT) composites were investigated. The electrical conductivity of the samples and their thermal activation energy were systematically dependent on the CNT doping level. Several unusual phenomena were observed which could be explained by the inhomogeneous distribution of CNTs in the polystyrene matrix. At higher levels of CNT doping, an interconnected conducting network is formed. If the amount of CNT is equal to or less than 0.6%, “islands” of CNT become separated by the layers of polystyrene, which limit charge transport. At low voltages, there is a sharper decrease in conductance as the voltage decreases.

The effect of irradiation with high-energy protons on 4H-SiC detectors

The effect of irradiation of 4H-SiC ionizing-radiation detectors with various doses (as high as 1016 cm−2) of 24-GeV protons is studied. Isotopes of B, Be, Li, He, and H were produced in the nuclear spallation reactions of protons with carbon. Isotopes of Al, Mg, Na, Ne, F, O, and N were produced in the reactions of protons with silicon. The total amount of the produced stable isotopes varied in proportion with the radiation dose from 1.2 × 1011 to 5.9 × 1013 cm−2. It is shown that, at high radiation doses, the contact characteristics of the detectors change appreciably. The potential-barrier height increased from the initial value of 0.7–0.75 eV to 0.85 eV; the rectifying characteristics of the Schottky contacts deteriorated appreciably. These effects are attributed to the formation of a disordered structure of the material as a result of irradiation.

Variation of the properties of 4H-SiC radiation detectors upon irradiation by 24 GeV protons

We had investigated effects of the high-energy proton irradiation on the properties of radiation detectors fabricated as Schottky diodes on 4H-SiC. The doses of 24 GeV protons ranged from 1013 cm-2 up to 1016 cm-2. Numbers and activities of radionuclides and isotopes produced after the irradiation were analysed. Activities of 7Be and 22Na were found to be proportional to the irradiation dose and ranged from 1.3 up to 890 Bq and from 1.9 up to 950 Bq, respectively. The contact properties were investigated by means of the current-voltage analysis. At lower irradiation doses a slight decrease of the effective potential barrier height from about 0.75 eV down to < 0.7 eV took place. The reverse current of the diodes grew by up to one order of magnitude. At the doses above 3x1015 cm-2 opposite changes were observed. Irradiation by up to 1x1016 protons/cm-2, resulted in the increase of the potential barrier height up to ~ 0.85 eV, followed by the drop of the reverse current by up to two orders of magnitude. The observed effects were explained by the appearance of the disordered material structure because of the high-energy particle bombardment.