Using the methods of field electron microscopy, the change in the form of the field emitter from Ta was studied when exposed to high temperatures T and strong electric fields F. The aim of the study was to obtain a stable form of the emitter surface that would give a stationary ion current during field evaporation. Such a stable form was found at a certain combination of T and F, it could provide a stable constant ion current, but of relatively small magnitude.

Using the methods of field electron microscopy, the change in the form of the field emitter from Ta was studied when exposed to high temperatures T and strong electric fields F. The aim of the study was to obtain a stable form of the emitter surface that would give a stationary ion current during field evaporation. Such a stable form was found at a certain combination of T and F, it could provide a stable constant ion current, but of relatively small magnitude.

Field emission microscopy was used to study Si condensation on a W surface by varying substrate temperature T and number n of monoatomic layers of the precipitated condensate. A low-temperature Si monolayer with a pure W structure formed at lower temperatures of T ~ 600 K, while another structure of a high-temperature surface silicide monolayer formed at T ≥ 1000 K. The orienting effect additionally differed between the low-temperature monolayer and surface silicide during further growth of Si layers. Pure Si crystallites formed starting from the third monolayer ( n ≥ 3) in the case of condensation on the low-temperature monolayer and starting from n ≥ 300 monolayers in the case of condensation on surface silicide. Estimates were obtained for the activation energy Q dif of Si diffusion into the W lattice and the desorption energy Q des of Si atoms from the W surface.

Condensation and adsorption of Ni with a thickness from several tenths of a monoatomic layer to several hundred layers on the surface of a single-crystal W tip has been studied by field emission microscopy in a wide range of surface temperature T . In contrast to adsorption of Si on W, adsorption of Ni on W does not induce any W surface reconstruction in the entire range of substrate temperatures T . Phenomena of bulk diffusion and field reconstruction of the surface are not observed as well. At multilayer Ni coatings, Ni crystallites with peculiar structure and faceting grow on the W surface (on close-packed and loose W faces at small and large T values, respectively). The presence of a strong external electric field makes it possible to retain crystallites on the W surface at temperatures much higher than their dissolution temperature in the absence of an external field.

Steady-state field evaporation of tungsten at high temperatures (T ~ 2000 K) has been studied using a magnetic mass spectrometer equipped with the field ion source. Only low-charged ions (W+2 and W+) have been observed in the course of evaporation. The distribution of the ion currents by tungsten isotopes correspondents to standart isotopic ratio for natural tungsten. Some deviations from standart isotopic ratio were observed owing to fluctuations and unstable nature of evaporation process. O.L. Golubev, N.M. Blashenkov

Field evaporation of tungsten at T ~ 2000 K was studied using a sector magnetic mass spectrometer with a field ion source and a field emission microscope. Only low-charge ions W +2 and W + of all W isotopes were observed in the process of evaporation. The mass distribution of ion currents of isotopes agreed roughly with the standard isotopic ratio for natural tungsten, although certain deviations from it, which were attributed to fluctuations and the erratic nature of evaporation process, were also detected.

Using the methods of the field emission microscopy, the condensation of Si on the W surface at various temperatures T of the substrate and numbers n of monatomic layers of the deposited condensate is studied. At low temperatures of T ~ 600 K, a low-temperature Si monolayer with the structure of pure W is formed on the surface, whereas another structure of a high-temperature monolayer, namely, surface silicide, is formed at T ≥ 1000 K. The low-temperature monolayer and surface silicide also differ in their orienting effect when constructing the Si layers. In the case of condensation on a low-temperature monolayer, crystallites of Si are formed starting already from the third monolayer at n ≥ 3, whereas the Si crystallites grow during the condensation on surface silicide starting from n ≥ 300 monolayers.

Using the methods of the field emission microscopy, the condensation of Si on the W surface at various temperatures T of the substrate and numbers n of monoatomic layers of the deposited condensate is studied. At low temperatures T ~ 600 K, a low-temperature Si-monolayer with the structure of pure W is formed on the surface, whereas another structure of a high-temperature monolayer, namely surface siliside is formed at T > 1000 K. The low-temperature monolayer and surface siliside are differ in their orienting effect when constructing the Si layers. In the case of condensation on a low-temperature monolayer, crystallites of Si are formed starting already from the third monolayer at n > 3, whereas the Si crystallites grow during the condensation on surface siliside starting from n > 300 monolayers. The energy activation of the volume diffusion Qdif of the Si-atoms into W and desorption Qdes from W surface are determined.

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.

Изотопное отношение испаряемых ионов, критические расстояния ионизации и зоны ионизации в

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 (F ev) were used to determine the critical ionization distances (x cr) and ionization zones (Δ) for singly and doubly charged ions. The obtained x cr and Δ values show that the formation of ions takes place at a certain distance from the emitter surface.

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.

An original method for experimental determination of evaporating field strengths F ev 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 F ev for emitters made of some metals are given and the restrictions of the method are analyzed.

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.

High-temperature field evaporation of metals and alloys and its connection with surface ionization are considered. The main parameters of the evaporation process (dependence of the evaporation rate on the emitter temperature and on the electric field at the emitter surface, the charge of the ions being evaporated and its temperature dependence, kinetic parameters of the evaporation process, as well as the state of the emitter surface under simultaneous action of high fields and temperatures) are analyzed. The similarity and the difference between field evaporation at high temperatures and surface ionization in a strong electric field are determined.

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.

Using field emission microscopy, the shape modification of the tungsten carbide emitter simultaneously exposed to high electric fields and high temperatures is studied. It is shown that in this case the emitter shape changes observed on the emitter surface are the same as those observed in the pure metal emitters. The possibility to grow a single nanoprotrusion on the emitter surface which can emit charged particles with stability similar to that for the carbon material emitters is demonstrated. The values of the emission current, current density, emission angle, and reduced brightness are comparable to those for the carbon nanotube emitters, and the advantage of this single nanoprotrusion is its complete reproducibility and capability to emit not only electrons but also ions.

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.

The procedure of the growing of a single nanoprotrusion on a tungsten carbide field emitter surface was described. This aim is achieved by simultaneous action high electric fields and enough high temperatures on the emitters (thermofield treatment) at special regime. The values of emission current, current density, emission angle and reduced brightness of the single nanoprotrusions-emitters are comparable with the values typical for the emitters from carbon nanotubes.

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.