Effects of Electron-ion Recombination on Contrast in ESEM Images

2001 ◽  
Vol 7 (S2) ◽  
pp. 794-795
Author(s):  
M. Toth ◽  
B. L. Thiel ◽  
A. M. Donald
Keyword(s):  
Secondary Electron ◽  
Image Formation ◽  
Environmental Scanning ◽  
Operating Parameters ◽  
Ion Recombination ◽  
Conventional Models ◽  
Working Distance ◽  
Present Experimental Evidence ◽  
Scanning Electron

We present experimental evidence for the effects of electron-ion recombination on contrast formation in secondary electron (SE) images obtained using an environmental scanning electron microscope (ESEM). Inclusion of the effects of SE-ion recombination in the theory of ESEM image formation accounts for contrast reversal observed, under appropriate conditions, in SE images of conductors (ie, in the absence of localized specimen charging) and of insulators that exhibit localized charging. Previously unexplained dynamic contrast caused by temporal charging can be understood if both conventional models of the effects of charging on SE emission, and the proposed role of SEion recombination in ESEM image formation are accounted for.In an ESEM, the extent of charging exhibited by insulating specimens can be controlled by varying the type and pressure (P) of the imaging gas, and operating parameters that determine the extent to which the gas is ionized (eg, detector bias, VGSED, and working distance, WD).

Electron behavior in the gaseous environment of the ESEM chamber

1996 ◽  
Vol 54 ◽  
pp. 838-839 ◽  
Author(s):  
S.A. Wight
Keyword(s):  
Secondary Electron ◽  
High Vacuum ◽  
Beam Current ◽  
Chamber Pressure ◽  
Environmental Scanning ◽  
Carbon Block ◽  
Faraday Cup ◽  
X Ray ◽  
Gaseous Environment ◽  
Working Distance

Measurements of electrons striking the sample in the Environmental Scanning Electron Microscope (ESEM) are needed to begin to understand the effect of the presence of the gas on analytical measurements. Accurate beam current is important to x-ray microanalysis and it is typically measured with a faraday cup. A faraday cup (Figure 1) was constructed from a carbon block embedded in non-conductive epoxy with a 45 micrometer bore platinum aperture over the hole. Currents were measured with an electrometer and recorded as instrument parameters were varied.Instrument parameters investigated included working distance, chamber pressure, condenser percentage, and accelerating voltage. The conditions studied were low vacuum with gaseous secondary electron detector (GSED) voltage on; low vacuum with GSED voltage off; and high vacuum (GSED off). The base conditions were 30 kV, 667 Pa (5 Torr) water vapor, 100,000x magnification with the beam centered inside aperture, GSED voltage at 370 VDC, condenser at 50%, and working distance at 19.5 mm. All modifications of instrument parameters were made from these conditions.

Novel and Advanced Applications of the Low Vacuum and Environmental Scanning Electron Microscope (SEM)

1997 ◽  
Vol 3 (S2) ◽  
pp. 385-386 ◽  
Author(s):  
Brendan J. Griffin
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Secondary Electron ◽  
Electron Gun ◽  
Environmental Scanning ◽  
Electron Detector ◽  
Environmental Sem ◽  
Practical Sense ◽  
Advanced Applications ◽  
Scanning Electron

The environmental SEM is an extremely adaptive instrument, allowing a range of materials to be examined under a wide variety of conditions. The limitations of the instrument lie mainly with the restrictions imposed by the need to maintain a moderate vacuum around the electron gun. The primary effect of this has been, in a practical sense, the limited low magnification available. Recently this has been overcome by modifications to the final pressure limiting aperture and secondary electron detector (Fig.l). The modifications are simple and users should be brave in this regard.A variety of electron detectors now exist including various secondary, backscattered and cathodoluminescence systems (Figs 2-5). These provide an excellent range of options; the ESEM must be regarded as a conventional SEM in that a range of imaging options should be installed. In some cases, e.g. cathodoluminescence, the lack of coating provides an advantage unique to the low vacuum SEMs.

Field Emission SEM with a Newly Developed FEGUN and Conical Strongly Excited Objective Lens

2000 ◽  
Vol 6 (S2) ◽  
pp. 764-765
Author(s):  
H. Kazumori ◽  
A. Yamada ◽  
M. Mita ◽  
T. Nokuo ◽  
M. Saito
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Scanning Electron Microscope ◽  
Secondary Electron ◽  
Objective Lens ◽  
Probe Current ◽  
Large Samples ◽  
Low Emission ◽  
Working Distance ◽  
Scanning Electron

A newly developed cold FE-GUN which enables to us to obtain large probe current and low emission noise, and conical strongly excited objective lens has been installed on the JSM-6700F Scanning Electron Microscope (SEM). In the range of accelerating voltages from 0.5 to 15kV, this instrument has got much better resolution as compared with in-lens type SEM (Ohyama et al 1986)(Fig. 1). We can obtain high-resolution secondary electron images with large samples (ex. 150mm ϕ×10mmH).Our old type objective lens (Kazumori et al 1994) has the limitation of working distance (WD), but the new lens enables us to work at very short WD at accelerating voltage of 15kV. As a result the spherical (Cs) and chromatic (Cc) aberration constants are 1.9mm and 1.7mm respectively at a WD of 3mm.In order to get large probe current, we increased emission current and got near the distance between the t ip of emi tter and the pr inciple plane of condenser lens.

An Experimental Study of Pig Blood–Lime Mortar Used on Ancient Architecture in China

2014 ◽  
Vol 997 ◽  
pp. 496-499 ◽  
Author(s):  
Peng Zhao ◽  
De Qing Xie ◽  
Guang Yan Li ◽  
Yun Sheng Zhang
Keyword(s):  
Building Materials ◽  
Early Stage ◽  
Architectural History ◽  
Environmental Scanning Electron Microscopy ◽  
Environmental Scanning ◽  
Historical Buildings ◽  
Lime Mortar ◽  
Mechanism Of Interaction ◽  
Scanning Electron

Portland cement has low chemical and physical affinity for traditional building materials. This hinders the restoration of historical buildings and modern rustic architecture where blue bricks are used. Pig blood–lime mortar is one of the most important technological inventions in the Chinese architectural history. Mortar in this work was fabricated according to formulas of the literature, and some analyses were conducted for further understanding their microstructure. Environmental scanning electron microscopy was utilized to analyze mechanism of interaction between key components of ancient mortar bonding materials. Results show that pig blood accelerates the formation of microstructure at early stage. Pig blood plays the role of biological templates which regulates the growth of calcium carbonate crystal.

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.

Imaging peristome movement in the environmental SEM

1993 ◽  
Vol 51 ◽  
pp. 790-791
Author(s):  
J.C. Long ◽  
D.M.J. Mueller
Keyword(s):  
Water Vapor ◽  
Signal Amplification ◽  
Secondary Electron ◽  
New Technology ◽  
High Vacuum ◽  
Natural State ◽  
Environmental Scanning ◽  
Spore Dispersal ◽  
Environmental Sem ◽  
Scanning Electron

The ElectroScan Environmental Scanning Electron Microscope is a powerful new tool in the study of spore dispersal mechanisms in bryophytes. The ESEM is similar in many ways to a conventional SEM, but with a few important differences. While the ESEM column remains at high vacuum (10−7torr), the specimen chamber typically operates in a water vapor environment at low vacuum (1 to 20 torr). The secondary electron signal is generated by gaseous signal amplification and is collected by the Environmental Secondary Detector.This new technology has significant implications regarding sample preparation and specimen requirements. First, there is no need to dry the sample, thus observations in the natural state are possible. Second, the water vapor dissipates charge build up, therefore a conductive coating is not necessary.The ESEM lends itself directly to the understanding of spore dispersal in mosses, which involves the sensitivity of the peristome to changes in ambient moisture (hygroscopicity).

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