O. L. Golubev

Composition of the ion current during field evaporation of some binary and ternary compounds at different temperatures

Experiments on the field evaporation of emitters made of Mo-Re, Ir-Ce, and W-Re binary alloys and Hf-Mo-Re ternary compound are described. It is shown that, depending on emitter preprocessing conditions (high-temperature heating in a high electric field), either atomic ions of almost all components of the alloy with different charge types are emitted simultaneously or ions of only one component of the compound are obtained. Field emitters made of alloys or multicomponent compounds may form a basis for sources of ions differing in mass and composition with the emitter composition remaining the same. Moreover, alloys and multicomponent compounds are promising for sources of ions of such materials of which field emitters are difficult, if at all possible, to prepare.

Control over the number of local emitting nanodimensional protrusions on the surface of a field emitter

A procedure is described that allows the number of emitting nanodimensional protrusions on the surface of a tungsten carbide field emitter to be controlled. According to the proposed approach, a sufficiently large number of nanoprotrusions are grown initially on the emitter surface by means of a thermofield treatment, which usually encounters no difficulties. Then, the applied field strength is decreased in a controlled manner at a certain fixed temperature of the emitter, which allows the number of emitting nanoprotrusions on the surface to be gradually reduced, even to retain a single one.

Variation of ion current composition during field evaporation of some binary and ternary compounds

The process of field evaporation of ion emitters made of binary (Mo-Re) and ternary (Hf-Mo-Re) alloys has been experimentally studied. Depending on the field-ion emitter pretreatment by heating to high temperatures in the presence of strong electric fields, it is possible to ensure the emission of ion fluxes with variable ion type and charge compositions with respect to all components of the initial alloy or compound as well as ions the fluxes of separate components. Using alloys and complex compounds as field-emitter materials, it is possible to create sources of ion fluxes with variable compositions and masses from the same emitter and sources of elements from which it is technically difficult or even impossible to make point emitters directly.

Field evaporation ion sources based on alloys and compounds

Results of experiments aimed at the creation of ion sources employing alloys as materials for field ion emitters are presented. Using alloys and complex compounds as emitter materials, it is possible to obtain ion sources for elements, from which it is difficult or even impossible to make emitters directly. The emitter surface can be enriched by some component of an alloy so as to obtain a source of its ions even if the content of this element in the alloy is as low as fractions of a percent.

Isotopic ratio of evaporated ions, critical ionization distances, and ionization regions in the process of the field evaporation of molybdenum at high temperatures

A magnetic mass spectrometer with a field ion source has been used to study the steady-state field evaporation of molybdenum at a temperature of 1000–2000 K. Ions of all seven molybdenum isotopes have been observed in the process of evaporation; only low-charge ions Mo+2 and Mo+ have been detected. The critical ionization distances and ionization regions for single- and double-charge Mo ions have been identified based on the measured ion energies and the experimentally determined intensity of the evaporation field. It has been demonstrated that ions are produced in the process of field evaporation of surface atoms at certain distances from the emitter surface in a very narrow spatial region.

Possible observation of the isotope effect during field evaporation

The field evaporation of tungsten at high temperatures (T ~ 2000 K) has been studied using a magnetic mass spectrometer equipped with a field ion source. Only low-charge ions (W+2 and W+) have been observed in the course of evaporation for all tungsten isotopes. For singly charged ions only, the number of ions of the heaviest isotope, 186W+, was about one order of magnitude lower than that corresponding to the standard isotope ratio for natural tungsten. An explanation of this anomalous phenomenon is proposed.

Determination of the critical ionization distance and ionization zone during high-temperature field evaporation of molybdenum

Steady-state field evaporation of molybdenum at high emitter temperatures (T ∼ 2000 K) has been studied using a magnetic mass spectrometer equipped with a field ion source. Only low-charge ions (Mo+2 and Mo+) have been observed in the course of evaporation. The measured ion energies and evaporating field strengths (Fev) were used to determine the critical ionization distances (xcr) and ionization zones (Δ) for singly and doubly charged ions. The obtained xcr and Δ values show that the formation of ions takes place at a certain distance from the emitter surface.

Universal method for experimental determination of evaporating electric field strengths for field ion emitters

An original method for experimental determination of evaporating field strengths Fev for field emitters is described. The method is universal and can be used for any field emitters, including nanosize protrusions grown in situ on the surface of such emitters to improve the emission localization. The examples of determining the values of Fev for emitters made of some metals are given and the restrictions of the method are analyzed.

Point sources of electrons and ions based on field emitters from refractory carbides

The process of formation of point sources of charged particles based on growing of the nanoprotrusions on surface of tungsten carbide field emitters was studied. The protrusions were grown by simultaneous action on the emitters of strong electric fields and high temperatures. Such nanoprotrusions allowed to reducemission angles very considerably and to emit both electrons and various ions.

Field evaporation ion sources based on some binary alloys

Results of experiments aimed at the creation of ion sources employing alloys as materials for field emitters are presented. Using even simple alloys it is possible to obtain ion sources for elements, from which it is difficult or impossible to make emitter directly. Using emitter surface enrichment of some component it is possible to obtain an ion source even if the content of this element is as low as fractions of a percent.