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1.
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. 相似文献
2.
The possibility of realization of barrier-free field evaporation regime for ions from polar solutions in the conditions when the flux of ions from the liquid is limited by their diffusion and drift from the bulk to the surface is considered. The strength of the electric field extracting ions is estimated by simulating electric fields in an ion source with a track membrane as the interface with allowance for the sizes of channels in the membrane and their density. It is shown that when time-dependent electric fields are used, the regime of barrier-free field evaporation can be realized with an appropriate choice of geometrical parameters of the membrane. 相似文献
3.
P. Sigmund 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(5):569-578
The 50th anniversary of the appearance of a series of seminal papers by O.B. Firsov is taken as an occasion to have a look at some central aspects of the stopping of slow ions in matter. A brief characterization of Firsov’s model of electronic energy loss is given in comparison with alternative views. The main part of the paper is devoted to central problems such as scaling behavior, Z 1 and Z 2 structure, deviations from velocity proportionality, threshold behavior, metal-insulator and gas-solid differences, and correlation between nuclear and electronic stopping. 相似文献
4.
5.
We set up model transport equations that describe the behavior of molecular (diatomic and polyatomic) gases with a molecule
collision rate proportional to the molecular velocity. In deriving these equations we allow for the internal (rotational)
degrees of freedom, while the vibrational degrees of freedom are assumed “frozen.” We also set up an exact equation for the
problem of the temperature jump with allowance for slow evaporation from the liquid surface into the saturated vapor atmosphere.
Finally, we derive explicit formulas for calculating the coefficients of the temperature jump and gas-density jump above a
flat surface and do the necessary numerical calculations.
Zh. éksp. Teor. Fiz. 114, 956–971 (September 1998) 相似文献
6.
Resolved fine structure spliting of Gd in YSb yields a fourth order crystalline field parameter b4 = (29±3)G. A correlation between b4 and the crystalline field experienced by other rare-earth ions in the same host is demonstrated. 相似文献
7.
Using an electromembrane source, mass-spectrometric investigations into the field evaporation of ions from KI solutions in
a water-glycerol mixture and in ethylene glycol are performed. The concentration of negatively charged solvent ions (deprotonated
molecules) on the emitting surface of the liquid is determined. It is shown that, under the conditions of intense field evaporation
of ions, the surface concentration of deprotonated glycerol and ethylene glycol molecules is several orders of magnitude higher
than their equilibrium concentration in the absence of an electric field. The high concentration of solvent ions is associated
with an increase in the autoprotolysis constant in a strong electric field. 相似文献
8.
9.
High-temperature field emission of Re, Pt, Ta, and W is studied by field-emission methods. Metal ions are found to evaporate mainly from the tops of thermal-field microprotrusions produced by high electric fields and temperatures on the emitter surface. For fi eld intensities of up to F=1–2 V/Å and temperatures of 1500–2000 K, the ion currents i are recorded from the entire emitter surface. They range from several tenths of nanoamperes to several nanoamperes. The activation energies of field evaporation determined from the Arrhenius plots logi=f(1/T) are found to be appreciably lower than those calculated within the charge exchange model for known parameters of the process and the metals evaporated. Reasons for such a difference in the activation energies and mechanisms of ion evaporation at high F and T are discussed. 相似文献
10.
V. A. Kel'man 《Russian Physics Journal》1975,18(8):1089-1092
The method of intersecting modulated beams was used to measure the absolute excitation functions of 3s-3p and 3p-4s transitions of MgII in collisions of electrons with magnesium ions at energies between the threshold of excitation and 100 eV. 相似文献
11.
I. Espe B. Skaali P. O. Tjøm S. M. Lee M. Rozkoš B. Elbek 《Czechoslovak Journal of Physics》1980,30(4):395-416
The experimental data have been compared with the result of extensive compound nucleus calculations based on the statistical theory. The shapes and the absolute cross sections for the high energy parts of the proton- and -spectra are reproduced with a level density parametera 0·11 A MeV–1 and a moment of inertiaJ1·3J
rig. The same parameters fairly well reproduce the angular distributions corresponding to the high energy parts of the spectra whereas deviations between theory and experiment are observed for the lower energies where particles emitted by higher order processes contribute. The observed total cross section for emission of an -particle is 500 mb or 1·7 times calculated value. For protons the corresponding numbers are 2313 mb and 3·0. The increase in cross section is ascribed to the process in which several particles are evaporated. Various methods are discussed for determination of the average orbital angular momentum of the emitted particle or the average spin of the daughter nucleus.On leave fromFaculty of Matematics and Physics, Charles University, Prague, Czechoslovakia. 相似文献
12.
Contrary to opinions expressed by earlier investigators, thorough examination of the existing models for field evaporation indicates that they are capable of predicting changes in the relative abundance of ionic species as temperature is changed and evaporation rate is held constant, without assuming atomic tunneling or slowness of electronic transition. However, this need not imply that atomic tunneling and slowness of electronic transition do not exist. Furthermore, the inclusion of energy level shifts in field evaporation theory results in the prediction of higher charge states than would be otherwise expected. This is in agreement with the observations of various investigators on copper and other metals. The examination further reveals that very significant differences in the predicted variation of evaporation rate with field exist between the image-hump and intersection models. This suggests a means by which one can attempt to determine experimentally the “correct” model to apply in a given situation. Furthermore, rigorous interpretation of the intersection model in conjunction with the experimental data of Tsong and Müller can result in significantly different values for the distance of the equilibrium position of the surface atom from the metal surface and the polarizability of the surface atom, than obtained using linear approximations. 相似文献
13.
14.
I. Espe B. Skaali P. O. Tjøm S. M. Lee M. Rozkoš B. Elbek 《Czechoslovak Journal of Physics》1979,29(11):1208-1214
Highly excited compound nuclei of74Kr have been formed by bombardment of58Ni with 70 MeV16O ions. The spectra of protons and -particles resulting from the decay of the compound nucleus (and several daughter nuclei) have been recorded at laboratory angles from 30° to 155°. The CM differential cross sections corresponding to definite energies for the particles emitted were calculated from the data. The charged particle spectra and the angular distributions show that evaporation processes are dominant. A study of spectral shapes and angular distributions has to some extent made it possible to distinguish primary particles from those evaporated after the emission of one or several particles.On leave fromFaculty of Mathematics and Physics, Charles University, Prague, Czechoslovakia. 相似文献
15.
P. Sigmund 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(1):45-54
The principle of reciprocity, i.e., the invariance of the
inelastic excitation in ion-atom collisions against interchange of
projectile and target, has been applied to the electronic stopping cross
section of low-velocity ions and tested empirically on
ion-target combinations supported by a more or less adequate amount of
experimental data. Reciprocity is well obeyed (within ~10%) for
many systems studied, and deviations exceeding ~20% are
exceptional. Systematic deviations such as gas-solid or metal-insulator
differences have been looked for but not identified on the present basis.
A direct consequence of reciprocity is the equivalence of Z1 with
Z2 structure for random slowing down. This feature is reasonably well
supported empirically
for ion-target combinations involving carbon, nitrogen, aluminium and
argon.
Reciprocity may be utilized as a criterion to reject questionable
experimental data. In cases where a certain
stopping cross section has not been or cannot be measured, the
stopping cross section for the inverted system may be available and
serve as a first estimate.
It is suggested to build in reciprocity as a fundamental requirement into
empirical interpolation schemes directed at the stopping of low-velocity
ions. Examination of the SRIM and MSTAR codes reveals cases where
reciprocity is obeyed accurately, but deviations of up to a factor of two
are common. In case of heavy ions such as gold, electronic stopping
cross sections predicted by SRIM are asserted to be almost an order of
magnitude too high. 相似文献
16.
We show how a classical approach can be used to model electronic processes taking place when slow highly charged ions collide with surfaces. In particular we derive expressions for the distance of the first charge flow and for the image energy gain of an ion of chargeq outside a surface described by a workfunctionW and a static dielectric constant ?. 相似文献
17.
A metal-surface microtopography formed by low-temperature field evaporation is analyzed by the methods of field-ion microscopy
and computer modeling. It is shown that the anisotropy of the field evaporation and the regional distribution of the brightness
of the ion-microscope image correspond to the configuration of the first Brillouin zones.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 7, 516–520 (10 April 1997) 相似文献
18.
Hu SX 《Physical review letters》2007,98(13):133201
Using the time-dependent wave-packets method, we have quantum mechanically investigated the three-body recombination process for electron energies varying from 10 to 0.01 eV. The classical "bottleneck" prediction on the probable population was confirmed by our S-wave quantum calculations for electron kinetic energies (K(E)) as low as 0.1 eV. But for K(E)<0.1 eV, the quantum three-body recombination tends to populate lower n levels than the classical theory predicted. We also find that, in the same n level, the recombination tends to populate higher angular-momentum states with K(E) decreasing. These results may shed light on the intrinsic dynamics of both ultracold plasmas and frozen Rydberg gases. 相似文献
19.
S. Martin J. Bernard L. Chen A. Denis J. Désesquelles 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(1):1-6
Electron capture by Ar8+ in collisions with C60 fullerene has been investigated using coincident measurements of the number n of ejected electrons, the mass and charge of multicharged Cr+
60
recoil ions and their fragments Ci+
m and the final charge state of outgoing projectiles Ar(8-s)+ (). The number of captured electrons r is the sum of the numbers of stabilized and emitted electrons: r
=
n
+
s. The ratio n
/
s decreases by a factor three with s increasing from 1 to 7 showing that the multiply excited states populated by capture of a large number of electrons are rather
stable against auto-ionisation. Each kinetic energy spectrum of Ar+ and Ar2+ projectiles is composed of two peaks which we attribute to collisions “inside” and “outside” the C60 cage. The measured energy shift of the projectile keV is consistent with the corresponding energy loss keV in a carbon foil with an equivalent thickness. Inside collisions are characterized by a strong dissociation of recoil
ions into light monocharged fragments and by a high multiplicity of ejected electrons.
Received: 25 March 1998 / Received in final form and Accepted: 9 June 1998 相似文献
20.
The electronic stopping and straggling of low velocity point charge in the electron gas subjected to magnetic ordering is analysed within the linear response theory. The electrons were described by the Lindhard dielectric function ?(k,ω). The magnetic interactions were included in the model along the Stoner treatment of itinerant electrons. The effect caused by phase transition was shown to be negligible comparing to the experimental result. 相似文献