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).

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.

Environmental SEM in a Multi-User Biological Sciences E.M. Unit

1999 ◽  
Vol 5 (S2) ◽  
pp. 286-287
Author(s):  
Christopher J. Gilpin ◽  
Mohamed S. Baguneid
Keyword(s):  
Biological Sciences ◽  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
High Vacuum ◽  
Environmental Scanning Electron Microscopy ◽  
Environmental Scanning ◽  
Environmental Sem ◽  
Imaging Mechanisms ◽  
Scanning Electron ◽  
The Ideal

Environmental scanning electron microscopy (ESEM) has matured into a mainstream technique in many areas of microscopy. Instrumentation has evolved and our understanding of some of the imaging mechanisms has progressed. However the majority of laboratories where ESEMs are located are based around the materials sciences. Despite the fact that ESEM is the only SEM instrument that permits liquid water to be present whilst imaging, the housing of such a microscope in biological EM units has been relatively rare. This authors laboratory is a multi-user EM unit based in a School of Biological Sciences. There exists the opportunity for basic biological scientists, clinical and pre-clinical medical and dental researchers to make use of such a resource. Indeed as the ESEM is housed alongside a conventional high vacuum instrument and a cryo high vacuum instrument there exists the ideal opportunity to carry out comparative studies.This study will examine a range of biological samples using ESEM, cryo SEM and dry high vacuum SEM.

The application of environmental SEM to marine biology

1992 ◽  
Vol 50 (1) ◽  
pp. 834-835
Author(s):  
Richard Ray
Keyword(s):  
Biological Material ◽  
Marine Biology ◽  
High Vacuum ◽  
Environmental Scanning ◽  
Conductive Film ◽  
Critical Point Drying ◽  
New Development ◽  
High Resolution Images ◽  
Environmental Sem ◽  
Scanning Electron

Preparation of marine biological material for standard scanning electron microscopy (SEM) requires extensive manipulation, including fixation, removal of salts, dehydration, and either air drying or critical-point drying because the SEM operates at high vacuum. Non-conducting samples including biological material must be coated with a conductive film of metal before the specimen can be imaged.The Electroscan Corporation (Wilmington, MA) recently introduced a new development in SEM technology—the environmental scanning electron microscope (ESEM). This instrument uses a unique secondary electron detector capable of forming high resolution images at pressures in the range of 0.1 to 20 torr. If water vapor is used as the specimen environment, wet samples including wet biofilms can be observed directly. This paper illustrates the use of the ESEM to view bacteria, dinoflagellates, and diatoms on surfaces.

An experimental measurement on the mechanism of charge balance in the environmental SEM

1995 ◽  
Vol 53 ◽  
pp. 622-623
Author(s):  
D. W. Phifer ◽  
D. C. Joy
Keyword(s):  
Dielectric Breakdown ◽  
High Vacuum ◽  
Incident Beam ◽  
Sample Surface ◽  
Environmental Scanning ◽  
Charge Balance ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Environmental Sem ◽  
Scanning Electron

Increasingly, electron microscopes are being used to look at non-conducting samples. These samples are prone to buildup of surface charge that must be drained away to prevent distortion of the image (due to the large potential buildup) and damage to the sample surface (due to dielectric breakdown). In conventional high vacuum scanning electron microscopes, the microscopist control beam energy to produce an acceptable yield of electrons while minimizing sample charging on non-conducting samples. This charge balance is achieved by reducing incident beam voltage to produce detectable interactions without excessive charge buildup on the sample surface. Electron yields at the low voltages required are sufficient for imaging when using a field emission gun, but it is not, in general, possible to perform microanalysis because the x ray lines of interest cannot be excited. The environmental scanning electron microscope (ESEM) has demonstrated the ability to overcome this problem by placing the sample in a low vacuum environment.

Detector strategies for environmental scanning electron microscopy

1992 ◽  
Vol 50 (2) ◽  
pp. 1296-1297
Author(s):  
Klaus-Ruediger Peters
Keyword(s):  
High Vacuum ◽  
Environmental Scanning Electron Microscopy ◽  
Charge Carriers ◽  
Environmental Scanning ◽  
Surface Information ◽  
X Ray ◽  
Detector Electrode ◽  
Electrons And Ions ◽  
Low Energy Electrons ◽  
Environmental Sem

Environmental SEM operate at specimen chamber pressures of ∼20 torr (2.7 kPa) allowing stabilization of liquid water at room temperature, working on rugged insulators, and generation of an environmental secondary electron (ESE) signal. All signals available in conventional high vacuum instruments are also utilized in the environmental SEM, including BSE, SE, absorbed current, CL, and X-ray. In addition, the ESEM allows utilization of the flux of charge carriers as information, providing exciting new signal modes not available to BSE imaging or to conventional high vacuum SEM.In the ESEM, at low vacuum, SE electrons are collected with a “gaseous detector”. This detector collects low energy electrons (and ions) with biased wires or plates similar to those used in early high vacuum SEM for SE detection. The detector electrode can be integrated into the first PLA or positioned at any other place resulting in a versatile system that provides a variety of surface information.

Universal ESEM

1993 ◽  
Vol 51 ◽  
pp. 786-787
Author(s):  
G.D. Danilatos
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
High Vacuum ◽  
Natural Extension ◽  
Necessary Condition ◽  
Environmental Scanning ◽  
Detection Systems ◽  
Small Gain ◽  
Detection Medium ◽  
Scanning Electron

The environmental scanning electron microscope (ESEM) has evolved as the natural extension of the scanning electron microscope (SEM), both historically and technologically. ESEM allows the introduction of a gaseous environment in the specimen chamber, whereas SEM operates in vacuum. One of the detection systems in ESEM, namely, the gaseous detection device (GDD) is based on the presence of gas as a detection medium. This might be interpreted as a necessary condition for the ESEM to remain operational and, hence, one might have to change instruments for operation at low or high vacuum. Initially, we may maintain the presence of a conventional secondary electron (E-T) detector in a "stand-by" position to switch on when the vacuum becomes satisfactory for its operation. However, the "rough" or "low vacuum" range of pressure may still be considered as inaccessible by both the GDD and the E-T detector, because the former has presumably very small gain and the latter still breaks down.

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.

The Energy Spectra of Secondary Electrons

2000 ◽  
Vol 6 (S2) ◽  
pp. 750-751
Author(s):  
David C Joy ◽  
David Braski
Keyword(s):  
Surface Layer ◽  
Electron Microscope ◽  
Secondary Electron ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Energy Spectra ◽  
Yield Coefficient ◽  
Sem Images ◽  
Secondary Electrons ◽  
Scanning Electron

It has been estimated that more than 90% of all scanning electron microscope (SEM) images ever published have been obtained using secondary electrons (SE) which are defined as being those electrons emitted with energies between 0 and 50eV. The properties of these secondary electron are therefore of considerable interest and importance. However, although secondary electrons have been intensively studied since their discovery by Starke in 1901 the majority of the work has been aimed at determining the SE yield coefficient and its variation with energy for elements and compounds. The energy spectrum of secondary electrons has received far less attention although it is evident that the form of the spectrum must have an effect on the image contrast observed in the SEM because SE detectors are energy selective devices. The few studies that have been made have mostly concentrated on spectra obtained from clean samples observed under ultra-high vacuum conditions. This is understandable, because it is certain that the presence of a surface layer of contamination will change the SE spectrum to some degree or other, but it is unfortunate because all specimens in real SEMs are dirty and it is information about this situation that is required.

X-Ray Energy Dispersive Spectroscopy in the Environmental Scanning Electron Microscope

1998 ◽  
Vol 4 (S2) ◽  
pp. 182-183
Author(s):  
John F. Mansfield ◽  
Brett L. Pennington
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Energy Dispersive Spectroscopy ◽  
Primary Electron ◽  
Environmental Scanning ◽  
Primary Electron Beam ◽  
X Ray ◽  
Environmental Sem ◽  
Scanning Electron

The environmental scanning electron microscope (Environmental SEM) has proved to be a powerful tool in both materials science and the life sciences. Full characterization of materials in the environmental SEM often requires chemical analysis by X-ray energy dispersive spectroscopy (XEDS). However, the spatial resolution of the XEDS signal can be severely degraded by the gaseous environment in the sample chamber. At an operating pressure of 5Torr a 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 25 μm in an Environmental SEM operating at an accelerating voltage of 30kV, with a water vapor pressure of 3Torr and a working distance of 15mm.

Biological Applications of Environmental Scanning Electron Microscopy

1997 ◽  
Vol 3 (S2) ◽  
pp. 383-384
Author(s):  
C. J. Gilpin
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Water Vapor Pressure ◽  
Environmental Scanning Electron Microscopy ◽  
Peltier Effect ◽  
Natural State ◽  
Environmental Scanning ◽  
Sample Chamber ◽  
And Control ◽  
Scanning Electron

The environmental scanning electron microscope (ESEM) first marketed by ElectroScan and now by FEI/Philips has been recognized as the only scanning electron microscope which allows liquid water to be present in the sample chamber at temperatures above freezing. As most biological material contains a high percentage of water it would seem essential to use this technology to examine specimens in their natural state. The purpose of this presentation is to describe in detail the way in which the microscope should be used to maximize the information obtainable from a variety of biological samples. This tutorial will also consider methods which can be applied to “difficult” samples whose structure becomes altered during what would be considered a normal imaging schedule.The main features of the microscope are the use of the Peltier effect cooling stage and control of chamber water vapor pressure to enable wet specimens to be imaged.

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