Angle selective backscattered electron contrast in the low-voltage scanning electron microscope: Simulation and experiment for polymers

Q Wan,R.C Masters,D Lidzey,K.J Abrams,M Dapor,R.A Plenderleith,S Rimmer,F Claeyssens,C Rodenburg

doi:10.1016/j.ultramic.2016.09.006

Abstract

Recently developed detectors can deliver high resolution and high contrast images of nanostructured carbon based materials in low voltage scanning electron microscopes (LVSEM) with beam deceleration. Monte Carlo Simulations are also used to predict under which exact imaging conditions purely compositional contrast can be obtained and optimised. This allows the prediction of the electron signal intensity in angle selective conditions for back-scattered electron (BSE) imaging in LVSEM and compares it to experimental signals. Angle selective detection with a concentric back scattered (CBS) detector is considered in the model in the absence and presence of a deceleration field, respectively. The validity of the model prediction for both cases was tested experimentally for amorphous C and Cu and applied to complex nanostructured carbon based materials, namely a Poly(N-isopropylacrylamide)/Poly(ethylene glycol) Diacrylate (PNIPAM/PEGDA) semi-interpenetration network (IPN) and a Poly(3-hexylthiophene-2,5-diyl) (P3HT) film, to map nano-scale composition and crystallinity distribution by avoiding experimental imaging conditions that lead to a mixed topographical and compositional contrast

Highlights

Low-voltage scanning electron microscopes (LVSEMs) have substantially benefited from the development of the field-emission gun and high sensitivity detectors in last few decades [1]; resulting in a significant increase of resolution from 100 nm to o0.5 nm [2]
Monte Carlo simulations of amorphous C, Cu, PNIPAM/PEGDA semi-interpenetration network (IPN) and P3HT film angular distributions of emitted electrons in a low voltage SEM have been shown
We report how to transform the simulated angular distributions to account for particular microscope settings enabling a direct comparison to experimental data and establish the angular range for which the model can be used

Summary

Introduction

Low-voltage scanning electron microscopes (LVSEMs) have substantially benefited from the development of the field-emission gun and high sensitivity detectors in last few decades [1]; resulting in a significant increase of resolution from 100 nm to o0.5 nm [2]. The LVSEM is commonly used as a high resolution imaging for surface topography and insulators [3]. This coating hides the surface detail and can create artificial signals due to the electron range differences in the sample material and the coating [7]. The LVSEM technique allows careful control of the primary voltage which allows for the imaging of non-conductive insulating materials, even in the absence of a coating [8]. The BSE signal can be optimised for uncoated insulating samples and, generally, reaches a maximum value around primary energy setting of 1–2 keV [4,10]

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Conclusion