Field evaporation rates of tungsten

Abstract

Essential parameters of the theory of field evaporation are the higher ionization potentials of the metal 2 I,, the surface atom's distance zo from the effective electronic surface plane of the metal, the polarizability a of the surface atom in its site, the energy difference A , between the atomic and the ionic states of the surface atom, the rate and temperature dependent activation energy Q,, and the pre-exponential factor G of the Arrhenius equation.It is shown how these data can be obtained from field evaporation rate measurements.Experiments with the (110) plane of tungsten were carried out in a range from 10-2 t o lo7 layers/s using both dc and pulsed field evaporation techniques. The following data are obtained: 2 In = 51.8 eV, t: I, = 83.0 eV, xo N, 0 A, a = 3.44 A3, A, = 5.6 eV, and V = lo7 s-l. It is also shown that the well known reduction of the evaporation field by the imaging gas is to a considerable extent due t o the field induced adsorption of the gas. Die wesentlichen Parameter der Theorie der Feldverdampfung sind die hoheren Ionisierungspotentiale des Metalls I,, der Abstand xo des Oberflachenatoms von der effektiven elektronischen Oberflachenebene des Metalls, die Polarisierbarkeit a des Oberflachenatoms in seiner Lage, die Energiedifferenz A , zwischen dem atomaren und dem ionisierten Zustand des Oberfllichenatoms, die geschwindigkeits-und temperaturabhangige Aktivierungsenergie Q, und der priiexponentielle Faktor 5 der Arrheniusgleichung. E s wird gezeigt, wie diese Daten durch Messung der Geschwindigkeit der Feldverdampfung erhalten werden konnen. Versuche mit der (llO)-8lliche von Wolfram wurden in einem Bereich von 10+ bis lo7 Atomlagen/s angestellt unter Benutzung von Gleichspannungs-und Impuls-3 Feldverdampfungsmethoden. Die folgenden Daten wurden erhalten: 2 I , = 51,8 eV, 4 ? l 2 In = 83,O eV, zo w 0 A, a = 3,44 A3. A, = 5,6 eV und Y = lo7 5-l. Es wird weiter n gezeigt, daS die bekannte Herabsetzung des Verdampfungsfeldes durch das Abbildungsgas im betrlchtlichen NaSe durch die feldinduzierte Adsorption des Gases bedingt ist. n 3 4 1E n 11.

On the Field Evaporation Behavior of a Model Ni-Al-Cr Superalloy Studied by Picosecond Pulsed-Laser Atom-Probe Tomography

“…The ionic model upon which these theories are based treats the temperature dependence of the evaporation field to be exclusively from the heat of sublimation, which, from Kirchhoff 's equation, displays very little temperature dependence from absolute zero to the melting point of metals~Zemansky, 1957!. Brandon predicted an increase in the rate of evaporation with increasing temperature-predictions that were validated ex-perimentally~Brandon, 1966a; Southon, 1968;Tsong & Müller, 1970;Ernst, 1979;Kellogg, 1981aKellogg, , 1982Wada, 1984;Miller & Smith, 1989!. While no fully satisfactory theoretical treatment of field evaporation is currently available~Miller & Smith, 1989;Tsong, 1990!, modification of the image hump theory of field evaporation led to an expression for the temperature sensitivity of the evaporation field at constant evaporation rate~Brandon, 1964rate~Brandon, , 1965rate~Brandon, , 1966a!.…”

Étude de l'énergie de liaison d'ad-atomes de transition sur un substrat de transition par microscopie ionique à champ

“…xi est donc pratiquement nul. L'explication donnée par Tsong et Mueller [8] est que les atomes sont évaporés à partir de sites en coin, la surface étant schématisée sur la figure 4a. Pour x; = ro rayon atomique, la surface aurait la position indiquée sur la figure 4b ce qui est effectivement moins vraisemblable.…”

A new approach for explanation of specimen rupture under high electric field

“…8 represents the experimental field dependence of the field evaporation rate at 78 K [23]. At a geometrical field of 65 V/nm, F g ÀF a ¼ 3.1 V/nm, i.e.…”