Interisland Spacing Research Articles

Electrical conductivity and electron emission from discontinuous metal films of homogeneous structure

The electrical conductivity of discontinuous metal films in weak fields is discussed. All the structural and electrophysical characteristics of the films (the electric field distribution, the island shape, the size distribution of islands and interisland spacings, the field dependence of the conductivity and the influence of temperature on the film resistivity) are investigated using a special chamber in a transmission electron microscope with a device for electron interference. The results obtained allow us to evaluate critically the current theories and to show the important role of the charge effect in the conductivity of discontinuous films in a weak field.

Study of the growth and structure of antimony films on carbon substrates in low and high vacuum

The growth of antimony thin films in low (1 × 10−5 Torr) and high (5 × 10−8 Torr) vacuum has been studied by transmission electron microscopy. The films have been evaporated on amorphous carbon substrates at room temperature. Initially the films took the form of islands which coalesced as they grew in size. Measurements of island density, size and inter-island spacing was made for films of different thicknesses and their variation with film thickness was plotted. The distribution of particle size in a film with an average thickness of 25 Å was measured. These quantities were identical for both vacua. The electrical continuity of a film evaporated on glass has been observed for a film about 120 Å thick. The drop in electrical resistivity is abrupt at that thickness. Electron diffraction patterns have been obtained for selected areas of films of various thickness. It was observed that before continuity was reached all films at both pressures were amorphous in nature. After continuity was reached, the films deposited in high vacuum become crystalline, whereas those deposited in low vacuum retained their amorphous nature.

Behavior of Ultrathin Zirconium Films upon Exposure to Oxygen

Discontinuous films of zirconium, having surface resistivities between 104 and 106 Ω sq−1, were deposited on glass substrates in ultrahigh vacuum and then exposed to oxygen pressures in the range of 5×10−7 to 4×10−8 Torr at temperatures of 25° and −196°C. The change in film resistance with time was monitored and a plot of logR vs logt was constructed. This graph was initially concave upwards, but became linear after a time which was characteristic of monolayer formation. An interpretation of the film behavior was based on the transport of electrons by tunneling through gaps separating the metal islands. The initial change in film resistance was caused by an increase in the zirconium work function. This increase was due to oxygen monolayer formation. The subsequent linear log-log behavior was caused by an increase in the tunneling distance which resulted from oxidation of the metal islands. Values for both the interisland spacing and the room-temperature oxidation rate constant have been calculated from the experimental data. Both impurities and the heat of adsorption interfered with determining a value for the interisland spacing, but when these interferences were eliminated, a distance of 6.9 Å was found for a 104 Ω sq−1 film. The oxidation rate constant for a comparable film at 25°C was 4×10−9 cm with an activation energy of 0.3 kcal mole−1. Pumping speeds also were determined. Zirconium initially pumped oxygen at ≈1500 ml·sec−1·cm−2. The sticking coefficient for oxygen on a partially oxygen covered zirconium surface was approximately 0.05.