scholarly journals Time Dependent Study of the Positive ion Current in the Environmental Scanning Electron Microscope (ESEM)

2001 ◽  
Vol 7 (S2) ◽  
pp. 788-789
Author(s):  
S.W. Morgan ◽  
M.R. Phillips
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Sample Surface ◽  
Primary Electron ◽  
Environmental Scanning Electron Microscope ◽  
Environmental Scanning ◽  
Secondary Electrons ◽  
Positive Ions ◽  
Cascade Amplification ◽  
Scanning Electron

The Environmental Scanning Electron Microscope (ESEM) is capable of image generation in a gaseous environment at sample chamber pressures of up to 20 torr. in an ESEM, low energy secondary electrons emitted from a sample surface, by virtue of the primary electron beam, are accelerated towards the positively biased metallic ring (typically +30 to +550V) Gaseous Secondary Electron Detector (GSED). As these electrons accelerate towards the ring they undergo ionizing collisions with gas molecules producing positive ions and additional electrons known as environmental secondary electrons. The environmental electrons further ionize the gas on their way to the ring producing a cascade amplification of the original signal. The amplified signal induced in the ring is used to form an image. The electric field generated between the GSED ring and the grounded stage causes the positive ions produced in the cascade to drift towards the sample, effectively neutralizing negative charge build up on the surface of a non-conducting sample.

In Situ Study of Live Specimens in an Environmental Scanning Electron Microscope

2013 ◽  
Vol 19 (4) ◽  
pp. 914-918 ◽  
Author(s):  
Eva Tihlaříková ◽  
Vilém Neděla ◽  
Makoto Shiojiri
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Water Layer ◽  
Sample Surface ◽  
Primary Electron ◽  
Environmental Scanning Electron Microscope ◽  
Working Environment ◽  
Environmental Scanning ◽  
Scanning Electron

AbstractIn this paper we introduce new methodology for the observation of living biological samples in an environmental scanning electron microscope (ESEM). The methodology is based on an unconventional initiation procedure for ESEM chamber pumping, free from purge–flood cycles, and on the ability to control thermodynamic processes close to the sample. The gradual and gentle change of the working environment from air to water vapor enables the study of not only living samples in dynamic in situ experiments and their manifestation of life (sample walking) but also its experimentally stimulated physiological reactions. Moreover, Monte Carlo simulations of primary electron beam energy losses in a water layer on the sample surface were studied; consequently, the influence of the water thickness on radiation, temperature, or chemical damage of the sample was considered.

Review of Techniques for Overcoming XEDS Problems in the Environmental Scanning Electron Microscope

1997 ◽  
Vol 3 (S2) ◽  
pp. 1207-1208
Author(s):  
John Mansfield
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Primary Electron ◽  
Environmental Scanning Electron Microscope ◽  
Significant Fraction ◽  
Environmental Scanning ◽  
Primary Electron Beam ◽  
Environmental Sem ◽  
Scanning Electron

Full characterization of materials in the environmental scanning electron microscope (Environmental SEM) often requires chemical analysis by X-ray energy dispersive spectroscopy (XEDS). However, a major problem arises because the spatial resolution of the XEDS signal is severely degraded by the gaseous environment in the sample chamber. The significant fraction of the primary electron beam is scattered after it passes through the final pressure limiting aperture and before it strikes the sample. Bolon and Griffin have both published data that illustrates this effect very well. Bolon revealed that 45% of the primary electron beam was scattered by more than 25μm in an Environmental SEM operating at an accelerating voltage of 30kV, with a water vapor pressure of 3Torr and a working distance of 15mm. Griffin’s work demonstrated that even at higher voltages (30 kV), shorter working distances (<10mm) and lower chamber pressures (2Torr), there is a significant fraction of the electron beam scattered out to over 400 μm away from the point where the primary beam strikes the sample.

Contrast formation mechanisms in the environmental scanning electron microscope

1999 ◽  
Vol 5 (S2) ◽  
pp. 274-275
Author(s):  
M. Toth ◽  
M.R. Phillips
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Charge Trapping ◽  
Sample Surface ◽  
Environmental Scanning Electron Microscope ◽  
Hydride Vapor Phase Epitaxy ◽  
Environmental Scanning ◽  
Formation Mechanisms ◽  
Electron Dose ◽  
Scanning Electron

Uncoated, non-conductive samples can be imaged and analyzed in the environmental scanning electron microscope (ESEM) due to effective charge neutralization at the sample surface by ionized gas molecules. Under some gas pressure and electron dose conditions, ESEM images of uncoated, poorly conductive samples often contain contrast not present in secondary or backscattered electron images of the (coated) samples obtained in conventional SEMs. It has been proposed that the contrast is related to charge trapping at defects and impurities. It has also been suggested that UV cathodoluminescence (CL) may contribute to contrast in the ESEM. In this paper, we present experimental evidence of contrast formation in the ESEM due to charge trapping in Dy doped zircon, electron trapping at oxygen vacancies in sapphire and the absence of signal generation by 360nm UV CL.The specimens used in this study were (i) cross-sectioned Titanium in-diffusion doped sapphire single crystal, (ii) Dy doped synthetic Zircon7 and (iii) 43 μm epitaxial GaN grown on c-pane sapphire by hydride vapor phase epitaxy.

Distribution and Behaviour of Positive Ions in the Environmental Scanning Electron Microscope (ESEM)

2000 ◽  
Vol 6 (S2) ◽  
pp. 776-777 ◽  
Author(s):  
John P. Craven ◽  
Frank S. Baker ◽  
Bradley L. Thiel
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Environmental Scanning Electron Microscope ◽  
Environmental Scanning ◽  
Positive Ions ◽  
Electron Detection ◽  
Gas Molecules ◽  
Charged Ions ◽  
Positively Charged ◽  
Scanning Electron

Electron detection in the environmental scanning electron microscope relies upon the presence of a small pressure of a gaseous phase inside the microscope chamber. The presence of this gas controls two important mechanisms by which the microscope functions. The conventional gaseous secondary electron detector (GSED) applies a variable positive bias (0 to +600 V) directly above the specimen. Electrons ejected from the specimen surface due to the incident scanning probe are accelerated by this field towards the positively biased detector. Whilst traversing the gap between specimen and detector the electrons undergo ionizing collisions with gas molecules. These result in an amplification of the incident electron signal through the production of ejected ‘daughter’ electrons and leave behind positively charged ions. After production these ions are repelled by the detector bias and drift back towards the microscope stage where they aid charge neutralization on the surface of the specimen.

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