Fundamental physics of vacuum electron sources

Abstract

The history of electron emission is reviewed from a standpoint of the work function that determines the electron emission capability and of applications in the fields of scientific instruments and displays. For years, in thermionic emission, a great deal of effort has been devoted to the search for low work function materials with high melting temperature, while reduction of the local change in time of the work function rather than the work function itself has been the main issue of field emission investigations. High brightness and long life are the central targets of emission material investigations for scientific instrument applications, while high current density and low power consumption are the guiding principles for display applications.In most of the present day industries, thermionic emission materials are exclusively used in such fields requiring high current and high reliability as cathode ray tubes, transmission and receiving tubes, x-ray sources and various electron beam machines. Field electron emission sources, however, since applied to high resolution electron microscopes in the 1970s have recently become dominant in research and development in the fields of scientific instruments as well as in the fields of various electron tubes and beam machines.The main issue in this report is to analyse the work function on the atomic scale and thereby to understand the fundamental physics behind the work function, the change in time of the local work function leading to field emission current fluctuation and the relationship between microscopic (on atomic scale) and macroscopic work functions.Our attempt is presented here, where the work function on the atomic scale is measured by utilizing a scanning tunnelling microscopy technique, and it is made clear how far the local work function extends its influence over neighbouring sites. As a result, a simple relationship is established between microscopic and macroscopic work functions.

Spectral properties of Cs and Ba on Cu(111) at very low coverage: Two-photon photoemission spectroscopy and electronic structure theory

“…Very little experimental or theoretical information exists, however, that would connect the atomic chemisorption structure of Ba with its effect on the macroscopic work function of metals. 31,32 The paper is organized as follows: in Sec. II the experimental apparatus for the 1PP and 2PP measurements is briefly described.…”

On some contrast reversals in SEM: Application to metal/insulator systems

“…SE transport is governed by interactions of a few-eV electrons with impurities, dislocations, grain boundaries and also with atomic vibrations for insulators and the corresponding attenuation length, s, significantly varies from one specimen to another. SE escape probability, A, changes with any slight change of work function (or electron affinity) that is very sensitive to the surface composition, structure and environment [23]. This opinion is supported by the fact that reduced yield curves, d/d max ¼ f(E1/E1 max ), of different forms of a given compound such as SiO 2 (amorphous or glasses or quartz) are nearly identical even when derived from very diverging, d ¼ f(E1), curves: see Figs.…”

Localized and Delocalized Features of Microscopic Work Functions

“…Thus, we believe that the microscopic work function is crucially important to control the surface processes such as electron emission 7) and surface chemical reactions 8) , which are known to be markedly in‰uenced by the work function. Since the proposal of the measurements of the local work function through the local tunneling barrier height (LBH) by Binnig and Rohrer 9) , the microscopic work function has been intensively investigated by using scanning probe microscopy techniques 10) .…”