Charging regime of PMMA studied by secondary electron emission

Issue		Eur. Phys. J. Appl. Phys. Volume 37, Number 1, January 2007


Page(s)		79 - 86
Section		Characterization of Materials: Imaging,\ Microscopy and Spectroscopy
DOI		10.1051/epjap:2006128
Published online		08 November 2006

Eur. Phys. J. Appl. Phys. 37, 79-86 (2007)
DOI: 10.1051/epjap:2006128

Charging regime of PMMA studied by secondary electron emission

M. Boubaya and G. Blaise

Laboratoire de Physique des Solides, Bât. 510, Université Paris XI, 91405 Orsay, France

blaise@lps.u-psud.fr

(Received: 3 May 2005 / Received in final form: 18 May 2006 / Accepted: 13 September 2006 / Published online: 8 November 2006 )

Abstract
Foils of Polymethyl methacrylate (PMMA) 2 mm thick were studied by measuring the total Secondary Electron Emission yield $\sigma$ (SEE yield) in a dedicated Scanning Electron Microscope especially equipped to study the fundamental aspects of the charge transport and trapping in insulating materials. The intrinsic SEE yield $\sigma _{0}$ , (yield of the uncharged material) and the charging kinetics were studied under low current density J=10⁺⁵ pA/cm². The curve of the primary beam energy variation of $\sigma _{0}$ exhibits a maximum intrinsic yield $\sigma _{\rm0max}= 2.2$ at 370 $\pm$ 20 eV and two crossover energies E_I=84 $\pm$ 20 eV and E_II=1465 $\pm$ 20 eV for which $\sigma _{0} = 1$ . For $\sigma _{0} >$ 1 PMMA is positively charged and negatively for $\sigma _{0} <$ 1. As electron injection is proceeding under the low current density used, the SEE yield varies from $\sigma _{0}$ to the steady value $\sigma _{st}=1$ . This value that expresses the equality between the average number of emitted and injected electrons, characterizes the steady charge regime called "Self-Regulated Regime". The evolution of $\sigma$ during the injection process is due to the internal field that blocks or enhances the secondary electron emission, according to the positive or negative nature of the trapped charges. A current density effect, characterized by a steady SEE yield slightly higher than unity, $\sigma _{st }=1.03$ , instead of one, is observed at high energy (for example 4000 eV) for a strong current density J>10⁺⁶ pA/cm². It is interpreted by a field ionisation (Poole-Frenkel type) that enhances the secondary electron emission.

PACS
79.20.Hx - Electron impact: secondary emission.
68.37.Hk - Scanning electron microscopy (SEM) (including EBIC).
61.80.Fe - Electron and positron radiation effects.

© EDP Sciences 2006

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.