Secondary-Electron imaging by Scintillating Gaseous Detection Device

1992 ◽  
Vol 50 (2) ◽  
pp. 1302-1303 ◽  
Author(s):  
G. D. Danilatos
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Secondary Electron ◽  
Environmental Scanning Electron Microscope ◽  
Environmental Scanning ◽  
Specimen Preparation ◽  
Additional Signal ◽  
Gaseous Environment ◽  
Electron Imaging ◽  
Scanning Electron

The environmental scanning electron microscope (ESEM) incorporates the functions of the conventional SEM while it has the added capability of allowing the examination of virtually any specimen in a gaseous environment. The main modes of imaging are all represented in the ESEM, and some developments with regard to the secondary electron (SE) mode are reported herewith.The conventional E-T detector fails to operate in the gaseous conditions of ESEM, but this obstacle has been overcome with the advent of a gaseous detection device (GDD). The principle of operation of this device is based on the monitoring of the products of interaction between signals and gas. Initially, the ionization from the signal/gas interaction was used to produce images of varying contrast and, later, the gaseous scintillation, from the same interaction, was also used to produce images. First, a low bias was applied to various electrodes but later a much higher bias was used for the purpose of achieving additional signal gain. By careful shaping and positioning the respective electrode, it was shown that SE imaging is possible in the ESEM. This has been also independently demonstrated by use of a special specimen preparation.

Recent Advances in Gaseous Detection Modes in the ESEM

1999 ◽  
Vol 5 (S2) ◽  
pp. 268-269
Author(s):  
T. A. Hardt ◽  
W. R. Knowles
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Secondary Electron ◽  
Large Field ◽  
Environmental Scanning ◽  
Electron Detector ◽  
Field Detection ◽  
Gaseous Environment ◽  
Detection Mode ◽  
Scanning Electron

The Environmental Scanning Electron Microscope, or ESEM, is the only class of SEM that can image in a gaseous environment that will maintain a sample in a fully wet state. The use of the patented Gaseous Secondary Electron Detector, or GSED, which amplifies the secondary electron signal with the gas, has allowed the ESEM to image a multitude of samples with true secondary contrast. Recently, several new modes of imaging in a gas have been developed and will allow further expansion of the capabilities of the ESEM.To maintain pressures in the ESEM up to 20 Torr (27 mbar), the use of multiple, differentially pumped apertures, is required. This can place a restriction on the low magnification range. In the large field detection mode, all magnification restrictions are removed. Magnifications as low as lOx may be achieved. This is similar to many conventional SEMs.

A New Mechanism for the Imaging of Crystal Structure in Non-Conductive Materials: An Application of Charge-Induced Contrast in the Environmental Scanning Electron Microscope (ESEM)

1997 ◽  
Vol 3 (S2) ◽  
pp. 1197-1198 ◽  
Author(s):  
Brendan J. Griffin
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Secondary Electron ◽  
Secondary Emission ◽  
Environmental Scanning Electron Microscope ◽  
Electron Interaction ◽  
Environmental Scanning ◽  
Conductive Materials ◽  
Scanning Electron ◽  
Trapped Charge

The mechanism of the contrast in ‘environmental’ or ‘gaseous’ secondary electron images in the environmental scanning electron microscope is at best poorly understood. The original theory suggested a simple gas amplification model in which emitted secondary electrons ionise the chamber gas, leading to signal amplification and finally measurement at a biased detector. This theory is being advanced but little attention has as yet been paid to the factors which influence the actual secondary emission, although unusual contrast effects have been noted in one case. The conven-tional view is that the positive ion product of the gas-electron interaction results in charge neu-tralisation at the sample surface.The implantation and trapping of charge in non-conductive materials was recently described, in reference to electron range measurements. This work demonstrated that trapped charge influ-enced the secondary electron yield, with enhanced secondary electron emission above the region of trapped charge. The consequence is that the distribution of the trapped charge is seen as a bright circle on the surface of the specimen, centred on the point of beam exposure (Fig.l).

Space Charge Artifacts in ESEM Images: Shadowing and Contrast Reversal

2000 ◽  
Vol 6 (S2) ◽  
pp. 774-775
Author(s):  
M. Toth ◽  
M.R. Phillips
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Secondary Electron ◽  
Ion Current ◽  
Environmental Scanning ◽  
Pumping System ◽  
Positive Ions ◽  
Differential Pumping ◽  
Electron Imaging ◽  
Scanning Electron

The environmental scanning electron microscope (ESEM) employs a series of pressure limiting apertures and a differential pumping system to allow for electron imaging at specimen chamber pressures of up to 50 torr. Images rich in secondary electron (SE) contrast can be obtained using the gaseous secondary electron detector (GSED) or ion current (Iion) signals. The GSED and Iion signals are amplified in a gas cascade. SEs emitted from a sample are accelerated through the gas in the specimen chamber by an electric field, EGSED, produced by a positively biased electrode located in the chamber, above the specimen. The accelerated SEs give rise to a cascade ionization process that can amplify the SE signal by up to three orders of magnitude. Electrons produced in the cascade are rapidly swept to the biased electrode and are efficiently removed from the gas. Positive ions produced in the cascade drift away from the electrode with a velocity that is at least three orders of magnitude lower than that of the electrons.

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