Previous studies of the gas sensitivity of CuPC (copper phthalocyanine) and ZnPC have been extended to include CoPC and NiPC, with particular reference to ammonia detection. Ammonia sensitivity is found to depend on the crystal structure of the films, ammonia concentration and temperature. The alpha - beta phase transition is found to give different film morphologies for ZnPC and NiPC. alpha -NiPC is the only PC studied that shows an increase in resistance on exposure to air. The other PCs show enhanced conductivity resulting from hole injection associated with oxygen adsorption. Surface conduction dominates bulk properties for all the PCs. Ammonia adsorption decreases conductivity due to the catalytic removal of surface oxygen but the response of the various PCs varies by two orders of magnitude. The low response of ZnPC is thought to be associated with the formation of a ZnPC-NH3 surface complex. CoPC and NiPC offer the highest response for low ammonia concentrations in air and the improved linearity of the response-concentration characteristics with SiO2 sublayers suggests that these may be viable materials for the fabrication of an integrated NH3 detector.

The toroidally aligned filaments which are commonly observed to be formed by the ablation of a hydrogen fuelling pellet have been studied in TEXT. The ablatant forms the first distinguishable filament near a critical radius, which appears to be that of the q=2 surface. The positions of the other filaments can be predicted from the ballistic motion of the pellet and a simple time dependent model for pellet ablation. These experimental results indicate that a time dependent model may be required as a refinement of present ablation models.

No abstract

The electrical characteristics of thermally evaporated triclinic lead phthalocyanine thin films are studied. A number of parameters is evaluated on the basis of the theory of space-charge-limited conduction and the following values are obtained: permittivity E = 3.16 x lo-'' F m-'; hole mobility p x 6.05 x lo-'' m2 V-' s-';room temperature hole concentration p o z 1.60 x 10" m -3 ; concentration of traps per unit energy range at the valence band edge Po z 2.79 x J -' m^3; temperature parameter of trapping distribution IT; x 770 K; total trap concentration N, x 2.97 x The room temperature electrical conductivity o = 1.55 x lO-'OS m-'. C -U measurements confirm that the Au-PbPc interface does not form a Schottky barrier. At low temperatures the capacitance of Au-PbPc-Au devices is temperature insensitive, increasing rapidly above 300 K and saturating at about 400 K. Measurements of thermoelectric power confirm that semiconduction is p-type. Die elektrischen Eigenschaften von thermisch aufgedampften dunnen triklinen Blei-Phtalozyaninschichten werden untersucht. Eine Anzahl von Parametern wird auf der Grundlage der Theorie des raumladungsgegrenzten Stromes berechnet und folgende Werte erhalten: Dielektrizitatskonstante E = 3,16 x lo-" F m -I ; Locherbeweglichkeit p z 6,05 x lo-'' m 2 V-'s-'; Raumtemperaturlocherkonzentration p o z 1,60 x 10" m-3; Konzentration der Haftstellen pro Energieeinheit an der Valenzbandkante Po z 2,79 x J-' m -3 ; Temperaturparameter der Haftstellenverteilung ?; = 770 K; Gesarnthaftstellenkonzentration N, z 2,97 x loz3 ~t -~. Die elektrische Leitfahigkeit bei Zimmertemperatur betragt u = 1,55 x 10l o S m -I . C-U-Messungen bestatigen, dal3 die Au-PbPc-Grenzflache keine Schottky-Barnere bildet. Bei tiefen Temperaturen ist die Kapazitat von Au-PbPc-Au-Bauelementen temperaturunabhangig, steigt oberhalb 300 K schnell an und sattigt bei etwa 400 K. Messungen der Thermospannung bestatigen den p-Halbleitungstyp.