Spontaneous increase of electric conductivity of nanostructure dielectrics
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1038-O03-01
Spontaneous increase of electric conductivity of nanostructure dielectrics Martiros Lorikyan1,2 1 Yerevan Physics Institute, Yerevan, 0036, Armenia 2 Yerevn Physics Institute, Yerevan, 0036, Armenia
Introduction It is well known that the surface-to-volume ratio of nanoparticles is very large and a significant fraction of atoms or ions are close to the surface of nanoparticles. On the other hand, secondary electron emission (SEE) occurs at or close to the surface of emitters, and, as a result, SEE is very sensitive to the surface properties of materials. Therefore, in the materials with high surface-to-volume ratio, secondary electrons readily get out from the surface and, hence, nanostructure materials may have high SEE characteristics. Actually, it was found in 1972 that under the influence of an external electric field, a high efficient controllable drift and multiplication (CEDM) of electrons takes place in porous KCl and CsI [1,2,3]. It has also been shown that because of polarization of these materials, the CEDM process becomes noticeably suppressed and unstable [4-9]. However, recent detailed investigations have shown that for porous CsI prepared by thermal evaporation, polarization occurs for a time after deposition, then polarization charges spontaneously vanish over time and porous CsI does not display any signs of polarization [10-12] (i.e., CEDM exhibits a high gain, high stability and good spatial localization). Thus, porous CsI spontaneously looses the ability to polarize with time. It was also shown that the time Tpl, during which the spontaneous polarization ‘faculty’ loss phenomenon (SPFL) takes place, strongly depends on the temperature Tk, at which porous CsI is kept after its preparation. When, after preparation, the porous CsI is kept at Tk=180C, SPFL phenomenon takes place within a few hours, whereas at Tk=310C Tpl is at most 1 h [12]. It is very important that after the loss of the polarization ability, porous CsI does no longer exhibits polarization, regardless of temperature, or whether or not it is under voltage and/or ionizing radiation. Thus, immediately after thermal preparation of porous CsI, accumulation of charges starts in it under the action of CEDM, but then these polarization charges spontaneously vanish with time and do not accumulate again, thus ceasing to behave as a dielectric. Later, Chianell et al. [13] observed that the structure of porous CsI used in [1-12] has the form of whiskers 10–50 nm in diameter, i.e. porous CsI has nanostructure. Note that it has been known for a long time that some dielectrics with porous structure are characterized by high-gain electron multiplication in an electric field of positive charges accumulated on their surface, but this effect is not controllable and inertial (Molter effect) [1421]. In this article, using identical experimental conditions the phenomenon of SPFL in porous CsBr and CsI is investigated, and the results are compared. Both materials are of the same purity (99.99%). As a method for investigation of the SPFL pheno
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