Effect of Ambient Oxygen on the Semiconductivities of Evaporated Films of Mesonaphthodianthrene and Mesonaphthodianthrone

Abstract

The electrical conductivity of an "evaporated" film of mesonaphthodianthrene increases when the film is exposed t o oxygen. The increase in conductivity is associated with changes in the semiconductivity activation energies. The activation energy for the oxygen-free anthrene (bulk conduction) is 0.74 ev while that associated with oxygen adsorption (surface conduction) is 0.40 ev. In marked contrast, the conductivity of an evaporated film of mesonaphthodianthrone decreases when exposed t o oxygen. An oxygen-free film of the anthrone has different activation energies in different ternperatlire regions, the activation energies being 0.73 ev and 0.43 ev in the higher and lower temperature regions, respectively. The conduction associated with the lower activation energy decreases when the film is exposed to oxygen.The effect of oxygen on the semiconductivities of mesonaphthodianthrene and mesonaphthodianthrone are compared with the effect of oxygen 011 their electron spin resonance spectra. INTRODUCTIONThe adsorption of gas inolecules on the surface of metals and sen~iconductors modifies the electrical properties associated with the surface (e.g. work function, contact potential, surface conductance, etc.) especially when the surface reaction involves an electrontransfer mechanism. While in the case of inorganic semiconductors there is a large body of scientific literature dealing with such effects, in the case of organic selniconductors comparatively few papers exist, in spite of the fact that adsorption on organic crystal surfaces call also involve electron-transfer mechanisms. Pick and Wissinan observed that the electrical conductivity of a napthalene single crystal was affected inarkedly by ambient oxygen (1). The influence of ambient oxygen on the photocoilductivity of the anthracene crystal has been studied by many investigators (2, 3, 4). The effect of oxygen on the photocoi~ductivity of phthalocyanine is also ltnown (5).Recently Matsunaga found that a sharp absorption peak appeared in the electron spin resonance spectrum of mesonaphthodiantlirene powder when it was exposed to air (6). This suggests that some ltind of electron transfer is taking place between the hydrocarbon crystal and oxygen molecules adsorbed on the surface. I t seemed, therefore, interesting to investigate the influence of ambient oxygen on the electrical conductivities of thin films formed by evaporation (evaporated films) of these compounds. A brief account of our findings on this subject has been presented in a previous note wherein it was pointed out that ambient oxygen does indeed exert an influence on the electrical conductivities of such filins (7). E X P E R I M E N T A L ~iIesonaphthodianthrene (I) and mesonapl~thodianthrone (11) were both purified by repeated sublimation in a high vacuum. Iminediately after the final sublimation, a small amount of the powder of the sample was sealed in the conductivity apparatus,

Photoinduced Doping of Organic Field Effect Transistors Studied by Displacement Current Measurement and Infrared Absorption Spectroscopy in Multiple Internal Reflection Geometry

“…It is widely believed that such p-type OSCs are unintentionally doped by oxygen from air. [1][2][3] The properties of organic electronic devices such as sensors, transistors, and light-emitting diodes are affected by oxygen gas. [4][5][6] In an oxygen doping process, an electron is transferred to an oxygen molecule, and a molecular cation and an oxygen anion are formed.…”

The Effect of the Ambient Oxygen on the Electrical Properties of an Evaporated Film of Pentacene

“…I n previous papers we have shown that the semiconductivities of films of mesonaphthodianthrene formed by sublimation are increased markedly by exposure to oxygen (4,5). I t was further shown that oxygen produces a new conduction mechanism with a lower activation energy, and we have attributed the effect to the formation of a complex between oxygen and the surface ~nolecules.…”

Direct Production of a Novel Iron‐Based Nanocomposite from the Laser Pyrolysis of Fe(CO)5/MMA Mixtures: Structural and Sensing Properties

“…However, for explaining the observed sensitivity one should take into account not only the Fe 2 O 3 content but also the polymeric/carbonaceous matrix: (i) the particle coating maintains a good dispersion between the small grains (coatings prevents grain growth and agglomeration) thus avoiding sintering; (ii) the carbonaceous shell could act like a stabilizer for the oxide phase at higher temperatures; (iii) the appearance of nanometric-size channels, due to the loss of gas and shrinkage in volume could favor gas penetration onto the Fe 2 O 3 interface [40]; (iv) the probably low contribution of the carbonaceous component of the calcined composite to the semiconductivity of the thick film should not be neglected. In fact it is already known that, depending on the chemical process and on the heating temperature, amorphous carbon could present different degrees of semiconductivity [41].…”