Secondary electron imaging at gas pressures in excess of 1kPa

Abstract

Environmental scanning electron microscopy (ESEM) enables electron imaging of gas-mediated, direct-write nanolithography processes, liquids, and hydrated biomaterials. However, ESEM is limited by poor image quality at gas pressures in excess of ∼600Pa. Here the authors achieve high quality secondary electron imaging at 2kPa of H2O by optimizing boundary conditions that govern beam scatter and the energy distribution of low energy electrons in the gas, dielectric breakdown of the gas, and detector collection efficiency. The presented high pressure imaging method will enable imaging of hydrated materials at close to room temperature, and gas-mediated surface modification processes occurring at high pressures.

Advances in gas-mediated electron beam-induced etching and related material processing techniques

“…Either a capillary is positioned near the electron beam impact point at the substrate surface, and used to inject the gas into a chamber that is pumped continuously using a high vacuum pumping system [39,40]. Alternatively, the entire vacuum chamber, or a subchamber [18] is filled with a precursor gas, as is done in environmental electron microscopy [41][42][43][44]. Ideally, the precursor gas does not etch the substrate spontaneously 1 .…”

Figure of merit for environmental SEM and its implications

“…It may be due to relying more on unconfirmed assumptions than on rigorous quantitative analysis of the system. The present findings suggest that previous works expounding on the purpose and capabilities of ESEM (Cameron & Donald 1994;Stokes et al 2004;Stokes 2006;Griffin 2007;Stokes & Baken 2007;Toth et al 2007;Stokes 2008;Stokes et al 2008) should be looked at in a new light, and also in view of related prior works by the present author (Danilatos & Robinson, 1979;Danilatos, 1980Danilatos, , 1988Danilatos, , 1990Danilatos, , 1992Danilatos, , 1993aDanilatos, ,b, 2004.…”

“…5 shows the variation of particle thickness q and stagnation gas thickness θ against the chamber pressure p 0 for two cases of specimen positioning at z = −1 and 0 mm. A closest specimen position reported has been at z = 1.4 mm (Toth et al, 2007), so that 1 mm is thought to represent a close to best practical position choice. At the same time, we include the 'zero' distance for the hypothetical case of imaging at this distance also, for comparison purposes and parity with the reference 'thin' aperture, although the existing detectors available do not normally allow imaging at this point.…”

High‐quality imaging in environmental scanning electron microscopy – optimizing the pressure limiting system and the secondary electron detection of a commercially available ESEM

“…Ways to quantify the efficiency of the pressure limiting system and to quantify the image quality have been presented earlier by Fitzek et al (2015). Inefficiencies in the design of the pressure limiting system and better designs for high-pressure SE detectors have been pointed out in several publications (Danilatos et al, 2001;Knowles et al, 2005;Toth et al, 2007;Danilatos, 2009;Danilatos et al, 2011;Dracopoulos & Danilatos, 2013). In this work a new design for the pressure limiting system is presented, which takes these insights into account.…”