N. M. Blashenkov

Singly charged tungsten and tantalum ions observed during high-temperature field evaporation

High-temperature field evaporation of tungsten and tantalum emitters in the temperature range from room temperature to 2500 K is studied using a static magnetic mass spectrometer equipped with a field source of ions. At room temperature, triply charged W3+ and Ta3+ ions alone are observed in the mass spectra. However, as the emitter temperature grows, the charge of the ions decreases. At T ≈ 1000 K, doubly charged W2+ and Ta2+ ions dominate in the spectra, and singly charged W+ and Ta+ ions appear in the temperature range 1900 < T < 2500 K. The evaporation rate of the singly charged ions is one to two orders of magnitude lower than the evaporation rate of the doubly charged particles. The energy parameters of field evaporation for differently charged tungsten ions are found.

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.

Detecting Singly Charged Ions during Field Evaporation of Tantalum at High Temperatures

The field evaporation of tantalum from point emitters in a broad range of temperatures from T = 300 to 2500 K was studied using a static magnetic mass spectrometer equipped with a special field ion source. The room-temperature mass spectrum of field-evaporated particles displayed only the peaks of triply charged ions (Ta3+). As the temperature was increased, the charge of field-evaporated ions exhibited a decrease: at T ∼ 1000 K, the peaks of doubly charged ions (Ta2+) prevailed. The peaks of singly charged ions (Ta+) were detected for the first time at temperatures in the interval 1900 K < T < 2500 K. The rate of evaporation of singly charged tantalum ions was several orders of magnitude lower than that of doubly charged ions.

A specialized isotope mass spectrometer for noninvasive diagnostics of Helicobacter pylori infection in human beings

A specialized isotope mass spectrometer for noninvasive diagnostics of Helicobacter pylori infection in human beings based on the carbon-13 isotope breath test has been designed and constructed. Important stages of the work included (i) calculating a low-aberration mass analyzer, (ii) manufacturing and testing special gas inlet system, and (iii) creating a small-size collector of ions. The proposed instrument ensures 13C/12C isotopic ratio measurement to within 1.7‰ (pro mille) accuracy, which corresponds to requirements for a diagnostic tool. Preliminary medical testing showed that the mass spectrometer is applicable to practical diagnostics. The instrument is also capable of measuring isotopic ratios of other light elements, including N, O, B (for BF2+ ions), Ar, Cl, and S.

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.

Nonequilibrium surface ionization of water molecules in a high electric field in the presence of resonance absorption of near-infrared radiation

The results of experiments undertaken to establish the connection between the current of ions desorbed from the surface in the presence of an electric field and the frequency of the infrared radiation incident on that surface are described. It is shown that resonance absorption of infrared radiation by adsorbed molecules increases the efficiency of the surface ionization process.

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.

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.