Bogdan Barwiński

Temperature coefficient of resistance in discontinuous gold films on sapphire substrate near percolation threshold

Abstract The results of measurements of the temperature coefficient of resistance in discontinuous gold films on a sapphire substrate below and above the percolation threshold are presented. When the percolation threshold is reached the temperature coefficient of resistance undergoes a drastic change. It changes abruptly from negative to positive, because the mechanism of conduction is different below (thermally activated tunnelling) and above (metallic) this threshold.

A point field emission tungsten cathode obtained by faceting of the tungsten surface induced by ultrathin gold film: Observations by means of scanning field emission microscope (SFEM)

The paper describes a simple procedure of the preparation of a point field emission tungsten cathode for applications to ultra high vacuum devices. Scanning field emission microscope (SFEM) was used as the testing method. The point electron source was obtained by the reconstruction of the tip caused by annealing in the presence of electric field. In order to facilitate the process of the reconstruction, an ultrathin gold film was evaporated onto the tip surface before annealing. As the result of the combined action of all these factors one obtains, so called build-up, ultra sharp tip, which is a point field emission electron source.

Reconstruction of the {111} face on a tungsten tip observed by means of a scanning field emission microscope (SFEM)

The paper describes a simple procedure of a preparation of tungsten tip for an application to ultra high vacuum scanning tunnelling microscope (UHV STM). Scanning field emission microscope was used as a testing method. A microtip with one atom on its apex was obtained by a reconstruction of the {111} face. The reconstruction is caused by annealing in the presence of a high electric field as well as by annealing without the field.

The charge transfer between metal and an adsorbed atom observed by means of a scanning field emission microscope (SFEM)

Abstract This paper describes the application of a scanning field emission microscope to observe oscillations in the charge density surrounding an adsorbed impurity on a surface of a tungsten tip. It presents records of SFEM images of a selected part of the tip. The time interval between two successive scannings was ≅ 34 s. The images present fluctuations of a local field emission current which are interpreted as local variations in the electronic structure of the surface at the adsorbed molecule. These fluctuations are explained assuming the existence of the atomic-like oscillations of the local density of states which arise from the presence of the adsorbed molecule. This behavior was predicted earlier by Eigler, Weiss, Schweizer and Lang [Phys. Rev. Lett. 66 (1991) 1189].

Influence of the dielectric overcoat on the low frequency noise in discontinuous metal films

The influence of a NaCl coating on the low frequency noise (1×10−3 −2.0 Hz) in discontinuous silver films was examined. It is shown that this overcoat causes an increase of the power of the noise and does not change the form of the noise power spectrum.

Temperature dependence of current noise in discontinuous silver films near the percolation threshold

The temperature dependence of the electric current fluctuations in discontinuous silver films on evaporated NaCl substrates has been studied below the percolation threshold, i.e. in the insulating region of conduction. The results are explained assuming that the current fluctuations in the film are induced mainly by two mechanism. The first is characterized by an exponential function of reciprocal temperature (Ea = 0.4 eV) and the second by an evidently weaker function of temperature in the examined range (130–300 K). As a plausible explanation it is assumed that the stronger dependence is a result of surface diffusion of silver nuclei on the substrate, and the weaker dependence is induced by the changes of the potential barrier height due to the fluctuation of the number of electron occupied localized states at the metal-insulator interface (similarly to that proposed by M. Celasco, A. Masoero, P. Mazzetti and A. Stepanescu [Phys. Rev. B 17 (1978) 2564]).

Shaping of tungsten field emission cathode. Observations by means of scanning field emission microscope (SFEM)

Abstract The paper describes a procedure of shaping of the surface of tungsten field emitters, which produces tips with decreased both extraction voltage and the emitting area in comparison with analogous factors for tungsten tips cleaned by the standard flash heating up to 2300 K. It has been shown, that for prepared in the proposed way tips, field emission occurs mainly from a few spots, which we have found as related to 〈111〉 and 〈100〉 directions of tungsten crystal. Scanning field emission microscopy (SFEM) was proposed as the method testing quality of field emitters.