Gaseous scintillation detection and amplification in variable pressure scanning electron microscopy

Abstract

Absolute charge calibration of scintillating screens for relativistic electron detection Rev. Sci. Instrum. 81, 033301 (2010); 10.1063/1.3310275Silicon photodiodes for low-voltage electron detection in scanning electron microscopy and electron beam lithography J.This work investigates the generation and detection of gaseous scintillation signals produced in variable pressure scanning electron microscopy through electron-gas molecule excitation reactions. Here a gaseous scintillation detection ͑GSD͒ system is developed to efficiently detect photons produced via excitation reactions in electron cascades. Images acquired using GSD are compared to those obtained using conventional gaseous secondary electron detection ͑GSED͒ and demonstrate that images rich in secondary electron ͑SE͒ contrast can be achieved using the gaseous scintillation signal. A theoretical model, based on existing Townsend theories, is developed. It describes the production and amplification of photon signals generated by cascading SEs, high energy backscattered electrons, and primary beam electrons. Photon amplification ͑the total number of photons produced per sample emissive electron͒ is then investigated and compared to conventional electronic amplification over a wide range of microscope operating parameters, scintillating imaging gases, and photon collection geometries. These studies revealed that argon gas exhibited the largest GSD gain, followed by nitrogen then water vapor, exactly opposite to the trend observed for electron amplification data. It was also found that detected scintillation signals exhibit larger SE signal-to-background levels compared to those of conventional electronic signals detected via GSED. Finally, dragging the electron cascade towards the light pipe assemblage of GSD systems, or electrostatic focusing, dramatically increases the collection efficiency of photons.

High bandwidth secondary electron detection in variable pressure scanning electron microscopy using a Frisch grid

“…Electronic amplification (A e ) was measured using the same techniques as those previously employed by [16,26]. For specifics on the techniques please refer to section III.B.…”

Scintillation SE detector for variable pressure scanning electron microscopes

“…The detectors of the group (i) can be designed for the detection of charged particles generated predominantly by SEs or by BSEs or generated by a mixture of these electrons (Danilatos, 1990; Morgan & Phillips, 2006a). It is also possible to detect photons, originated in excitation processes in cascade collisions of signal electrons with gaseous environment (Danilatos, 1988, 1990; Morgan & Phillips, 2006b). Both the charged particles and the photon detection systems contain electrodes that are placed near the specimen and are usually positively biased in respect to the specimen so the electrostatic field causing the cascade amplification of electrons is created (Knowles, 1995; Heinz, 2004a; Morgan & Phillips, 2006a,b; Thiel et al , 2006).…”

“…It is also possible to detect photons, originated in excitation processes in cascade collisions of signal electrons with gaseous environment (Danilatos, 1988, 1990; Morgan & Phillips, 2006b). Both the charged particles and the photon detection systems contain electrodes that are placed near the specimen and are usually positively biased in respect to the specimen so the electrostatic field causing the cascade amplification of electrons is created (Knowles, 1995; Heinz, 2004a; Morgan & Phillips, 2006a,b; Thiel et al , 2006). In specific conditions, the cascade amplification of electrons can be enhanced by a magnetic field (Thiel et al ., 2006).…”

Controlled dehydration of a biological sample using an alternative form of environmental SEM

“…Due to the high pressure of gases in the specimen chamber of ESEM the conditions for secondary electron detection are completely different from those in a conventional SEM. The construction of detectors must be based on different physical principles, as described by Jacka et al (2003), Jirák et al (2008) and Morgan and Phillips (2006). The most efficient detectors of secondary electrons in the high‐pressure conditions in the specimen chamber of ESEM use the principle of gas ionization that proceeds as a cascade between a grounded specimen holder and a detector signal electrode supplied with a positive voltage, placed under the pole piece of the objective lens (Danilatos, 1990; Meredith et al , 1996) or inside the objective lens (Thiel, 2006).…”