Beam transfer characteristics of a commercial environmental SEM and a low vacuum SEM

Danilatos, G. D.; Rattenberger, Johannes; Dracopoulos, Vassilios

doi:10.1111/j.1365-2818.2010.03455.x

Cited by 31 publications

(37 citation statements)

References 11 publications

(30 reference statements)

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“…These excess losses are measured relative to the losses incurred by a thin PLA, which represents the best physically possible configuration in a conventional type of differential pumping system. The use of such a reference system was previously postulated in working out the figure of merit (Danilatos et al, 2011). The validity of this assumption is now demonstrated by computational means in the next section.…”

Section: Figure Of Meritmentioning

confidence: 91%

“…This condition can be used for the definition of a 'thin' aperture, as was also proposed in previous reports (Danilatos, 2000(Danilatos, , 2009Danilatos et al, 2011).…”

Section: Thick and Thin Aperture -Optimum Reference Systemmentioning

confidence: 98%

“…Until this is conclusively done in the actual conditions of a laboratory, an alternative approach is available by the use of the DSMC method to compute the same, if the geometry and boundary conditions are known. The gas flow for one commercial instrument (the 'FEI Quanta 600 FEG') operating either as an ESEM or as a LVSEM has been previously presented but only a few values were provided (computed) for ε (Danilatos et al, 2011). We now extend the same approach in the complete range of operating pressures for both modes of its operation.…”

Section: Computation Of the Figure Of Merit By Dsmc -Real Situationmentioning

confidence: 99%

“…This is a continuation in part of a previous report on the efficiency of electron beam transfer from the high vacuum of the electron optics column to the relatively high pressure environment of 'low vacuum' and environmental scanning electron microscopes (LVSEM and ESEM; Danilatos et al, 2011). In the previous work, the direct simulation Monte Carlo (DSMC) method (Bird, 1995) was employed to determine the gas flow field properties and, in particular, the gas density variation along the beam path.…”

Section: Introductionmentioning

confidence: 99%

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Figure of merit for environmental SEM and its implications

Danilatos¹

2011

Journal of Microscopy

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Summary A recently introduced figure of merit for environmental and low vacuum scanning electron microscopes has now been computed in the full operational pressure range for one commercial instrument. The direct simulation Monte Carlo method has been used in lieu of experimental measurements. The theory of this figure of merit is further consolidated. It is shown that a thin pressure limiting aperture can indeed be used as an optimum reference system for all instruments employing differential pumping in the transfer of an electron beam from high vacuum to high pressure. The implications of the results obtained are discussed both in relation to existing commercial instruments and associated literature to pave the way for future progress in the field.

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Section: Figure Of Meritmentioning

confidence: 91%

“…This condition can be used for the definition of a 'thin' aperture, as was also proposed in previous reports (Danilatos, 2000(Danilatos, , 2009Danilatos et al, 2011).…”

Section: Thick and Thin Aperture -Optimum Reference Systemmentioning

confidence: 98%

Section: Computation Of the Figure Of Merit By Dsmc -Real Situationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Figure of merit for environmental SEM and its implications

Danilatos¹

2011

Journal of Microscopy

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“…Up to date, the obvious solution practiced by manufacturers of ESEM is to significantly increase the diameter of PLA. However, this introduces severe disadvantages, such as electron beam loss, increased pumping, restricted pressure range, inaccessible low energy beam at high pressure and overall limited instrument performance [4,5].…”

Section: Introductionmentioning

confidence: 99%

Dynamic Correction of Higher-Order Deflection Aberrations in the Environmental SEM

Oral

Neděla

Danilatos³

2015

Microsc Microanal

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Pushing the limits of environmental scanning electron microscopy

Rattenberger

Fitzek

Schroettner

et al. 2016

European Microscopy Congress 2016: Proceedings

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In environmental scanning electron microscopy (ESEM) electrical insulating, wet and biological samples can be investigated without additional sample preparation. The imaging gas inside the chamber suppresses charging and outgassing of the sample but it also decreases the signal to noise ratio (SNR) [1]. Especially applications in the kPa regime are limited by poor image quality (e.g. wetting experiments). Recent publications on high pressure capabilities of state of the art microscopes have shown that they are working far away from physical limits and that there is plenty of room for improvements [2]. The key to high image quality at high pressures is to reduce scattering of the primary beam electrons inside the imaging gas as far as possible while maintaining ideal operation conditions for the SE‐detector [3]. In the FEI Quanta 600 ESEM the gaseous environment in the sample chamber is separated by a differential pumping system and two pressure limiting apertures (PLA) from the high vacuum inside the electron column. Nevertheless, a lot of gas streams through the PLA upwards and a significant amount of scattering takes place even before the electron beam is entering the sample chamber [2]. Based on the insights of Monte Carlo and finite element simulations a new aperture holder was designed that significantly reduces this gas flow and therefore also the primary beam scattering. The PLAs are exchangeable and smaller diameters further increase the SNR at the expense of a smaller field of view. In a conventional ESEM the secondary electron detector is a positively biased electrode which attracts and accelerates the secondary electrons. On their way to the detector the secondary electrons undergo collision ionization which amplifies the signal and generates positively biased gas ions. With increasing chamber pressure this SE signal amplification strongly decreases because the electron mean free path decreases and the SEs do not gain enough energy between collisions to ionize the imaging gas anymore. By replacing the position and modifying the shape of the detector it can be optimized for high pressure applications. Nearby a needle detector with very small tip radius (R < 10 µm) the electric field is strong enough for SE amplification and by positioning the needle on the sample table it operates at ideal conditions regardless of pressure and working distance. The distance sample to PLA and sample to detector is no longer coupled. A by‐product of this design is that the conventional position of the backscatter electron detector (BSE) at the end of the column is no longer blocked by the SE detector. With this outstanding signal to noise ratio at high chamber pressures the limits of conventional ESEM technology can be crossed. Wetting experiments at low acceleration voltages and low dwell times are possible as well as imaging liquid samples without cooling (see figure 1,2). In figure 3 a BSE image of gold nanoparticle in oil at 10 kPa chamber pressure can be seen and the overall improvements are shown in figure 4.

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Beam transfer characteristics of a commercial environmental SEM and a low vacuum SEM

Cited by 31 publications

References 11 publications

Figure of merit for environmental SEM and its implications

Figure of merit for environmental SEM and its implications

Dynamic Correction of Higher-Order Deflection Aberrations in the Environmental SEM

Pushing the limits of environmental scanning electron microscopy

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