Total secondary-electron yield of metals measured by a dynamic method

Abstract

The secondary electron emission of dielectrics usually is measured by the pulse method, in which the dielectric is irradiated with short pulses of electrons. Attempts to use a dynamic method, in which the dielectric is irradiated continuously, have failed because the dielectric becomes charged and this charge interferes with the emission process. The dynamic method can, however, be applied to metals where volume charges are prevented. This article reports dynamic measurements of the total secondary emission yield from stainless steel, platinum, and aluminum and compares them with results from the current pulse method. In order to apply the dynamic method to metals a simple but important change in the setup was introduced: a dielectric slab was placed between the electrode and the metallic sample, which permitted the sample surface potential and therefore the energy of the incident electrons to change continuously. Unlike for dielectrics, the emission curves for metals are identical when obtained by the two methods. However, for a sample with deliberately oxidized surfaces the total secondary emission yield is smaller when measured with the dynamic method as compared with the pulse method, just as happens for dielectrics.

On some contrast reversals in SEM: Application to metal/insulator systems

“…1 applies only to a hypothetical specimen composed of the specific quartz as investigated by Salow [15] and the specific platinum as investigated by Pintão and Hessel [16]. The other consequence is that the real contrast reversal of images 2c and d results from a crossing of yield curves specific to the two components, quartz and Cr, of the investigated TEG-FET circuit.…”

“…To overcome the difficulty of using a published data set for a prediction or a simulation of SEM images, the best strategy would be to perform in-situ measurements of the SEE yields of specimen's components. This experimental strategy may consist in implementing, into scanning microscopes, attachments derived from that used in dedicated SEE measurements [6,16] such as that described by Iyasu et al [9] for conductors or, with slight changes, that of El Gomati and Assa'd [24] for any kind, conductive or insulating, of specimen. This strategy would be applied to specimens composed of a few components such as those involved in the research and developments of microelectronic systems and it may be limited to acquisition of only one measured pair of values, [d max ; E1 max ], for each component, these experimental values being inserted next into calculated-reduced yield curves, in order to obtain a normal yield curve, d ¼ f(E1) [19].…”

“…Fig. 1, the starting data of interest are that of Salow for quartz [15] and that of Pintão and Hessel for platinum [16]. The next two models, constant loss model [3,17] and parabolic model [18][19][20], have been used to smoothen the experimental uncertainties and to extrapolate the results above the investigated energy range.…”

“…In the author's opinion, these deviations are partly due to the inherent uncertainties of experiments but they also result from the physics involved in the SEE yield. In a three-step process, SE generation, transport and escape, the generation is the only step dependent on the intrinsic properties (chemical formulae) of the investigated material but SE transport and escape are very [15] for quartz and from Pintão and Hessel [16] for Pt. The lines correspond to a fitting procedure derived from the parabolic model or the constant loss model.…”

Initial Assessment of Electron and X-Ray Production and Charge Exchange in the NDCX-II Accelerator

“…Secondary electron yield for this energy range is well below 1 (see for example Ref. [1]). Furthermore, (assuming the secondary emission process to be local with regard to surface location) any secondaries emitted through this process will be on field lines which would take them inward away from the wall only downstream (relative to ion beam propagation) of their emission point; so these electrons quickly return to their birth location.…”