Secondary Electron Detector with the Unipotential Lens Structure for Variable Pressure/Environmental SEM

2012 ◽  
Vol 186 ◽  
pp. 24-27
Author(s):  
Witold Słówko ◽  
Michał Krysztof
Keyword(s):  
Main Part ◽  
Secondary Electron ◽  
High Vacuum ◽  
Variable Pressure ◽  
Original Structure ◽  
Intermediate Chamber ◽  
Wide Range ◽  
Optimum Solution ◽  
Environmental Sem ◽  
Gas Pressures

To extend capabilities of classic instruments toward the VP/E technique, authors designed the vacuum-detector system in the form of a simple attachment, which can be mounted to a classic SEM, without changes in its original structure. The main part of the system is the vacuum and detection head, combining the intermediate chamber and electron detectors of chosen kinds. Authors investigate the SE detector showing the unipotential lens structure to find optimum solution for a wide range of gas pressures from high vacuum to pressures exceeding 10 mbar.

Things That Go “Bump” in the VPSEM - and How We Image with Them

2001 ◽  
Vol 7 (S2) ◽  
pp. 772-773
Author(s):  
Brendan J Griffin
Keyword(s):  
Secondary Electron ◽  
Full Range ◽  
High Vacuum ◽  
Electron Interaction ◽  
Variable Pressure ◽  
Imaging Model ◽  
Wide Range ◽  
Electron Microscopes ◽  
Electron Imaging ◽  
Scanning Electron Microscopes

Variable pressure scanning electron microscopes (VPSEM) differ from conventional SEM by operating at pressures ranging from the ‘high vacuum’ SEM levels of 10-6 torr up to typically around 2 torr. The environmental SEM or ESEM is a commercial variant which employs an unique multistage pressure-limiting aperture (PLA) system to attain specimen chamber operating pressures of up to 50 torr. Early instruments used air or argon as the imaging gas but more commonly today water vapour is used. A wide range of gases have been employed, including potentially explosive hydrogen-methane mixtures. The choice of gas is operator-based and can be varied during the imaging session.Early VPESM were restricted to backscattered electron imaging (BSE) until the development of the gaseous secondary electron detector in the ESEM. Gaseous secondary electron detectors are now available for all models of VPSEM and together with compatible cathodoluminescence and EDS XRay detectors, the full range of SEM-based imaging options is present.The principal distinguishing feature of VPSEM is, of course, that samples can be examined uncoated. Gas-electron interaction generates a positive ion supply that can minimise conventional charging artefacts, in a simple imaging model.

scholarly journals Environmental SEMs: A New Way to Look at Samples

1995 ◽  
Vol 3 (8) ◽  
pp. 14-15
Author(s):  
Don Chernoff ◽  
Mohammad Salim Mujallid
Keyword(s):  
High Vacuum ◽  
Chamber Pressure ◽  
Variable Pressure ◽  
New Class ◽  
The Past ◽  
Order Of Magnitude ◽  
Differential Pumping ◽  
New Applications ◽  
Magnitude Increase ◽  
Environmental Sem

A new class of SEM has evolved over the past few years which provides some startling capabilities never before available to electron microscopists. These instruments, typically referred to as environmental SEMs or variable pressure SEMs. have opened up a host of new applications that are difficult or impossible with a standard SEM. Many of the constraints of sample preparation and handling that exist with a conventional SEM do not apply to environmental SEMs.An environmental SEM functions like a conventional SEM except that you can introduce air or any other gas into the chamber and raise the chamber pressure above the normal high vacuum range of 10-5 or 10-6 Torr. Inmost instruments the vacuum can be raised to as much as 1 Torr. This represents a 6 order of magnitude increase in chamber pressure. Environmental SEMs can achieve this high chamber pressure without damage to the electron source by using differential pumping apertures in the column.

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).

Replication of Wet Objects and Cells

1974 ◽  
Vol 32 ◽  
pp. 102-103
Author(s):  
S. Basu ◽  
D. F. Parsons
Keyword(s):  
Water Vapor Pressure ◽  
High Vacuum ◽  
Polystyrene Latex ◽  
Vacuum System ◽  
Saturated Water Vapor ◽  
Replication Method ◽  
New Methods ◽  
Saturated Water ◽  
Water Vapors ◽  
Intermediate Chamber

We are approaching the invasiveness of cancer cells from the studies of their wet surface morphology which should distinguish them from their normal counterparts. In this report attempts have been made to provide physical basis and background work to a wet replication method with a differentially pumped hydration chamber (Fig. 1) (1,2), to apply this knowledge for obtaining replica of some specimens of known features (e.g. polystyrene latex) and finally to realize more specific problems and to improvize new methods and instrumentation for their rectification. In principle, the evaporant molecules penetrate through a pair of apertures (250, 350μ), through water vapors and is, then, deposited on the specimen. An intermediate chamber between the apertures is pumped independently of the high vacuum system. The size of the apertures is sufficiently small so that full saturated water vapor pressure is maintained near the specimen.

Design of a UHV STEM for Through-The-Lens Electron Spectroscopy

1990 ◽  
Vol 48 (2) ◽  
pp. 380-381
Author(s):  
A. J. Bleeker ◽  
P. Kruit
Keyword(s):  
Secondary Electron ◽  
High Vacuum ◽  
Secondary Electron Emission ◽  
Auger Spectroscopy ◽  
Scanning Transmission Electron Microscope ◽  
Point Of View ◽  
Ultra High Vacuum ◽  
Scanning Transmission ◽  
Auger Spectra ◽  
Coincidence Measurements

Combining of the high spatial resolution of a Scanning Transmission Electron Microscope and the wealth of information from the secondary electrons and Auger spectra opens up new possibilities for materials research. In a prototype instrument at the Delft University of Technology we have shown that it is possible from the optical point of view to combine STEM and Auger spectroscopy [1]. With an Electron Energy Loss Spectrometer attached to the microscope it also became possible to perform coincidence measurements between the secondary electron signal and the EELS signal. We measured Auger spectra of carbon aluminium and Argon gas showing energy resolutions better than 1eV [2]. The coincidence measurements on carbon with a time resolution of 5 ns yielded basic insight in secondary electron emission processes [3]. However, for serious Auger spectroscopy, the specimen needs to be in Ultra High Vacuum. ( 10−10 Torr ). At this moment a new setup is in its last phase of construction.

Principles of Low-Vacuum SEM

1992 ◽  
Vol 50 (2) ◽  
pp. 1304-1305
Author(s):  
Klaus-Ruediger Peters
Keyword(s):  
New Technologies ◽  
High Vacuum ◽  
Optical Microscope ◽  
Specimen Surface ◽  
Electrical Field ◽  
Gaseous Environment ◽  
New Information ◽  
Gas Molecules ◽  
New Interactions ◽  
Gas Pressures

Only recently it became possible to expand scanning electron microscopy to low vacuum and atmospheric pressure through the introduction of several new technologies. In principle, only the specimen is provided with a controlled gaseous environment while the optical microscope column is kept at high vacuum. In the specimen chamber, the gas can generate new interactions with i) the probe electrons, ii) the specimen surface, and iii) the specimen-specific signal electrons. The results of these interactions yield new information about specimen surfaces not accessible to conventional high vacuum SEM. Several microscope types are available differing from each other by the maximum available gas pressure and the types of signals which can be used for investigation of specimen properties.Electrical non-conductors can be easily imaged despite charge accumulations at and beneath their surface. At high gas pressures between 10-2 and 2 torr, gas molecules are ionized in the electrical field between the specimen surface and the surrounding microscope parts through signal electrons and, to a certain extent, probe electrons. The gas provides a stable ion flux for a surface charge equalization if sufficient gas ions are provided.

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.

Direct STEM ADF imaging of gold on silicon (111)

1989 ◽  
Vol 47 ◽  
pp. 472-473
Author(s):  
P. Xu ◽  
E. J. Kirkland ◽  
J. Silcox
Keyword(s):  
Film Growth ◽  
Heavy Atom ◽  
High Vacuum ◽  
Dark Field ◽  
Thin Metal Film ◽  
Base Pressure ◽  
Ultra High Vacuum ◽  
Specimen Preparation ◽  
Dark Field Imaging ◽  
Wide Range

Many studies of thin metal film growth and the formation of metal-semiconductor contacts have been performed using a wide range of experimental methods. STEM annular dark field imaging could be an important complement since it may allow direct imaging of a single heavy atom on a thin silicon substrate. This would enable studies of the local atomic arrangements and defects in the initial stage of metal silicide formation.Preliminary experiments were performed in an ultra-high vacuum VG HB501A STEM with a base pressure of 1 × 10-10 mbar. An antechamber directly attached to the microscope for specimen preparation has a base pressure of 2×l0-10 mbar. A thin single crystal membrane was fabricated by anodic etching and subsequent reactive etching. The specimen was cleaned by the Shiraki method and had a very thin oxide layer left on the surface. 5 Å of gold was deposited on the specimen at room temperature from a tungsten filament coil monitored by a quartz crystal monitor.

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.

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