The pre-exponential voltage-exponent as a sensitive test parameter for field emission theories.

For field electron emission (FE), an empirical equation for measured current I m as a function of measured voltage V m has the form I m = CV m k exp[-B/V m], where B is a constant and C and k are constants or vary weakly with V m. Values for k can be extracted (i) from simulations based on some specific FE theory, and in principle (ii) from current-voltage measurements of sufficiently high quality. This paper shows that a comparison of theoretically derived and experimentally derived k-values could provide a sensitive and useful tool for comparing FE theory and experiment, and for choosing between alternative theories. Existing methods of extracting k-values from experimental or simulated current-voltage data are discussed, including a modernized 'least residual' method, and existing knowledge concerning k-values is summarized. Exploratory simulations are reported. Where an analytical result for k is independently known, this value is reliably extracted. More generally, extracted k-values are sensitive to details of the emission theory used, but also depend on assumed emitter shape; these two influences will need to be disentangled by future research, and a range of emitter shapes will need examination. Other procedural conclusions are reported. Some scientific issues that this new tool may eventually be able to help investigate are indicated.

GaBi alloy liquid metal ion source for microelectronics research.

A GaBi alloy liquid metal ion source has been studied. From an analysis of the source mass spectra as a function of emission current, a mechanism is suggested for the production of single- and double-charged ions. There is good agreement with the results of Swanson's investigations of a pure Bi source.

Fundamental new results in the energetics and thermodynamics of charged metal surfaces.

There should be close scientific relationships between the following: the bonding energy of an atom or molecule at a curved surface; the Laplace-Young equation (the 'equation for pressure difference across a curved surface'); the Kelvin equation (the 'equation for vapour pressure above a curved surface'); and the thermodynamics of surface diffusion. This paper briefly reports some surprising new theoretical results obtained by reviewing these relationships, and inserting 'atomic-type' surface electrostatic energy terms into the expression for system potential energy. The two main results are as follows. First, the field dependence of atomic bonding energy is shown to be associated with a change in the electrical capacitance between the specimen and its surroundings, when the atom is removed. Good agreement is found between old experiments and the new theory. Second, when atomic-type effects are taken into account, new terms appear in the formula for pressure difference across a charged curved surface. These describe a field-dependent correction to the 'surface tension' term and a curvature-dependent correction to the Maxwell field stress term. The main consequences are: the concepts of 'surface tension' and 'surface free energy' become no longer equivalent; a small correction is needed to the Raleigh criterion for the stability of charged droplets; and a mathematical Taylor cone is no longer a hydrodynamic equilibrium shape.

New results in the theory of Fowler-Nordheim plots and the modelling of hemi-ellipsoidal emitters.

This paper reports further progress in understanding the theory of emission-area extraction from Fowler-Nordheim plots, and reports some useful interim results derived by modelling field electron emission from hemi-ellipsoidal emitters. The mathematical nature of the relationship between a new approach to emission-area extraction, recently proposed, and older approaches is demonstrated. The new approach is extended to cover field dependence in emission area. Preliminary results are reported from an investigation into the effects of making erroneous assumptions about the tunnelling barrier seen by the electron and the absence of field dependence in emission area. If wrong theoretical assumptions are made, then emission area can be overpredicted by a factor of as much as 10 or 20. On the other hand, if correct theoretical assumptions are made, then the extracted emission area is close to an emission area derived directly from the model calculations. The problematical nature of the concept of emission area, when emission area is a function of field, is pointed out.

Field-induced electron emission from electrically nanostructured heterogeneous (ENH) materials.

This paper discusses the origins of field-induced electron emission from thin films of electrically nanostructured heterogeneous (ENH) materials. Such materials exhibit low macroscopic field (LMF) electron emission: as thin films on a conducting substrate, they emit electrons into vacuum when LMFs, typically about 1-10 V/microm, are applied. An ENH material comprises: a dielectric matrix, which may contain nanoscale inclusions of higher electrical conductivity; conducting channels that open in the dielectric between the inclusions (if present) and between them and the substrate; and an electron emitting channel that opens into vacuum. Electrically nanostructured heterogeneous materials can have a variety of different detailed structures and theories, but all can exhibit LMF emission under suitable circumstances. This paper provides an updated summary of an integrating overview recently presented to explain LMF emission. A central feature is that electrical nanostructure within the film can create internal field enhancement, thereby producing a high local field at the vacuum interface: this enables thermalised electrons to escape rapidly into vacuum by tunnelling. The question of what aspect of the system controls the emission current is a separate issue. Various features and implications of the theory are set out.