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.

Development of a Field Emission VP-SEM and Some Initial Applications

2001 ◽  
Vol 7 (S2) ◽  
pp. 882-883
Author(s):  
Masako Nishimura ◽  
Sukehiro Itoh ◽  
Steve Joens
Keyword(s):  
Field Emission ◽  
Chamber Pressure ◽  
Variable Pressure ◽  
Natural State ◽  
Backscattered Electrons ◽  
Pumping System ◽  
Multi Stage ◽  
Gas Molecules ◽  
Residual Gas ◽  
Differential Pumping

The use of variable pressure SEMs (VP-SEMs) is increasing in various fields of science and industry, allowing microscopy in a variable pressure environment of 1 ∼ 270 Pa utilizing backscattered electrons for imaging. The VP-SEM allows microscopy of insulated samples without the need for sample preparation. Charging artifacts can be minimized as well. When the VP-SEM is operated with a cooling stage, which allows cooling of samples at −20° and above, vaporization of water from samples is reduced. This permits microscopy of wet samples at close to the natural state for extended periods of time.Poor S/N ratio and deterioration of resolution, both of which are due to collisions among residual gas molecules and primary/backscattered electrons, have limited the performance of VP-SEMs. For resolving these limitations, we have completed the development of a new field emission VP-SEM which operates with a stable Schottky field emission source, a new environmental secondary electron detector (ESED), and a multi-stage differential pumping system. Fig. 1 shows a sectional view of the column with the differential pumping system. This design allows stable gun vacuum conditions with variable specimen chamber pressure 10 through 3,000 Pa, permitting a pressure difference from the gun by 1011 Pa without problems.

Alumina-Forming Austenitic Alloys for Advanced Recuperators

2007 ◽  
Author(s):  
Bruce A. Pint ◽  
John P. Shingledecker ◽  
Michael P. Brady ◽  
Philip J. Maziasz
Keyword(s):  
Alumina Scale ◽  
Turbine Engines ◽  
Exhaust Gas ◽  
Materials Selection ◽  
The Past ◽  
Austenitic Alloys ◽  
Order Of Magnitude ◽  
Selection For ◽  
Sufficient Strength ◽  
Magnitude Increase

Materials selection for thin-walled recuperators has been extensively investigated over the past decade. In the latest generation of recuperated turbine engines, type 347 stainless steel has been replaced by higher alloyed steels and Ni-base chromia-forming alloys. However, high (linear) rates of chromia evaporation in exhaust gas fundamentally limits the oxidation lifetime of these chromia-forming alloys. One solution is to use alumina-forming alloys that are more resistant to this environment. The lower scale growth kinetics and resistance to evaporation in the presence of water vapor suggests an order of magnitude increase in lifetime for alumina-forming alloys. A significant problem with this strategy was the large drop in creep strength with the addition of sufficient Al to form an external alumina scale. However, new Fe-base austenitic compositions have been developed with sufficient strength for this application above 700°C.

Quantitative Microscopy for Analysis of Hydrogel Pore Structure

2001 ◽  
Vol 7 (S2) ◽  
pp. 834-835 ◽  
Author(s):  
Andrew J. Marshall ◽  
Buddy D. Ratner
Keyword(s):  
Pore Structure ◽  
Soft Tissues ◽  
Three Dimensional ◽  
Chamber Pressure ◽  
Quantitative Microscopy ◽  
Sem Images ◽  
New Class ◽  
Hydrophilic Nature ◽  
Porous Biomaterials ◽  
Environmental Sem

Introduction Applications for porous biomaterials include scaffolds for tissue engineering and spatial control of wound healing. Porous hydrogels are of particular interest due to their hydrophilic nature, elasticity, and mechanical compatibility with soft tissues. We present an optical technique for quantitatively analyzing the pore structure of porous hydrogel materials. The technique presented here is especially useful for analyzing a new class of porous hydrogels with spherical pore shape. Many important properties of the three-dimensional pore structure of these materials can be quantitatively described by analyzing a twodimensional slice (thin section) of material.Materials and MethodsPorous cross-linked hydrogels were prepared using a previously described method. Briefly, poly(hydroxyethyl methacrylate) (polyHEMA) was polymerized around a pore template of close-packed poly(methyl methacrylate) (PMMA) microspheres (Sekisui Plastics, grade MB-8C or MB-20C). The microspheres were then leached out with 90% v/v acetone.Scanning electron microscope (SEM) images were obtained using an FEI 2020 Environmental SEM with a gun voltage of 15 kV and a chamber pressure of 5 torr.

Evaluation of the Variable Pressure Correction Technique for X-ray Microanalysis in the ESEM

1999 ◽  
Vol 5 (S2) ◽  
pp. 292-293
Author(s):  
R. A. Carlton ◽  
C. E. Lyman ◽  
J. E. Roberts
Keyword(s):  
Electron Beam ◽  
High Vacuum ◽  
Chamber Pressure ◽  
Variable Pressure ◽  
Pressure Correction ◽  
X Ray ◽  
Correction Technique ◽  
The Wire ◽  
Chamber Gas ◽  
Beam Broadening

The purpose of this study is to evaluate the variable pressure correction technique (VPCT) as a solution to the problem of extraneous x-ray peaks due to electron beam broadening in the chamber gas of the ESEM. The basis of VPCT is the observation that target x-ray counts decrease with increasing chamber pressure; whereas, x-ray counts due to beam broadening increase. If data are collected at two or more chamber pressures, the number of x-ray counts for an element can be corrected to that expected at zero gas pressure (high vacuum). Tests of NIST SRM 482 have shown EDS x-ray analysis in the ESEM (within the chamber pressure range of 1 to 8 torr) to have comparable accuracy and precision values to those of EDS in the traditional SEM. The samples used in the these studies, however, were quite large (ca. 500 μm in diameter) and so extraneous EDS peaks, due to the electron beam broadening effect of the chamber gas, were minimized.The 60% Au / 40% Cu wire of SRM 482 was pressed into a hole in the surface of an Al specimen stub so as to produce a flat surface with a sharp interface between the wire and the stub. Spectra were collected at 5 and 150 μm from the junction of the wire and the Al stub at chamber pressures of 2, 4, and 8 torr.

A New High Resolution Field Emission SEM with Variable Pressure Capabilities

2001 ◽  
Vol 7 (S2) ◽  
pp. 880-881 ◽  
Author(s):  
Peter Gnauck ◽  
Volker Drexel ◽  
J. Greiser
Keyword(s):  
High Resolution ◽  
Field Emission ◽  
Low Voltage ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Chamber Pressure ◽  
Variable Pressure ◽  
Natural State ◽  
Electron Microscopes ◽  
Scanning Electron

To examine non conductive samples in their natural state (i.e. without significant sample preparation) at high resolution in the SEM the technique of low voltage field emission scanning electron microscopy (LVFESEM) is used. Due to the limitation in accelerating voltage (U<1kV) this technique is limited in respect of chemical analysis. Furthermore it is not possible to examine humid and outgassing samples in high vacuum. in recent years the application of variable pressure scanning electron microscopes (VPSEM) became an important technique in materials science as well as in life science. Due to the capability of maintaining a high chamber pressure humid, outgassing and non-conductive samples, can be examined in their natural state without significant sample modification or preparation. Especially compound materials with different electron yields can be imaged without any charging effects (Fig. 2), [2]. This paper describes a high resolution field emission electron microscope, that combines low voltage and variable pressure capabilities.The high pressure capabilities of the instrument are realized by eliminating the high vacuum requirements of SEM in the microscope chamber. This is done by separating the vacuum environment in the chamber from the ultra high vacuum environment in the gun area.

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.

On the Measurement of Total Elastic Cross-sections in the ESEM or VPSEM Using X-Ray Microanalysis

2000 ◽  
Vol 6 (S2) ◽  
pp. 788-789
Author(s):  
Raynald Gauvin ◽  
David C. Joy
Keyword(s):  
Elastic Scattering ◽  
Cross Sections ◽  
Beam Current ◽  
Chamber Pressure ◽  
Variable Pressure ◽  
Scattering Cross ◽  
Exponential Decay Law ◽  
Scattering Cross Sections ◽  
Environmental Sem ◽  
Beam Broadening

It is of paramount importance to know the total elastic-scattering cross sections of the gases which are present in the specimen chamber of the variable pressure scanning electron microscope (VP-SEM) or in the environmental SEM (ESEM) since these values are needed to compute the width of the beam broadening skirt by the use of Monte Carlo simulations. However, these values are not well known for even the most common gases because the vibrational modes of the molecules add another contribution to the usual value of the elastic scattering cross-section. To overcome this difficulty a method has been proposed to measure total elastic cross-sections which is based on a measurement on the unscattered beam current as a function of the chamber pressure using a Faraday cup. The total elastic cross-sections are then deduced using the well-known exponential decay law.

Residual Gas Reaction in the Electron Microscope: II The Design of a Gas-Control Chamber for Quantitative Observations

1969 ◽  
Vol 27 ◽  
pp. 82-83
Author(s):  
Chester J. Calbick ◽  
Richard E. Hartman
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Local Environment ◽  
Chamber Pressure ◽  
Objective Lens ◽  
Ion Pump ◽  
Quantitative Studies ◽  
Precise Knowledge ◽  
Differential Pumping ◽  
And Control

Quantitative studies of the phenomenon associated with reactions induced by the electron beam between specimens and gases present in the electron microscope require precise knowledge and control of the local environment experienced by the portion of the specimen in the electron beam. Because of outgassing phenomena, the environment at the irradiated portion of the specimen is very different from that in any place where gas pressures and compositions can be measured. We have found that differential pumping of the specimen chamber by a 4" Orb-Ion pump, following roughing by a zeolite sorption pump, can produce a specimen-chamber pressure 100- to 1000-fold less than that in the region below the objective lens.

Atomic-level imaging of the surface structure of Ag2O

1984 ◽  
Vol 42 ◽  
pp. 656-657
Author(s):  
William Krakow
Keyword(s):  
High Vacuum ◽  
Atomic Level ◽  
Ultra High Vacuum ◽  
Research Groups ◽  
Resolution Electron ◽  
Surface Reconstructions ◽  
Order Of Magnitude ◽  
High Resolution Electron Microscope ◽  
Saturated Structure ◽  
Transmission And Reflection

In recent years electron microscopy has been used to image surfaces in both the transmission and reflection modes by many research groups. Some of this work has been performed under ultra high vacuum conditions (UHV) and apparent surface reconstructions observed. The level of resolution generally has been at least an order of magnitude worse than is necessary to visualize atoms directly and therefore the detailed atomic rearrangements of the surface are not known. The present author has achieved atomic level resolution under normal vacuum conditions of various Au surfaces. Unfortunately these samples were exposed to atmosphere and could not be cleaned in a standard high resolution electron microscope. The result obtained surfaces which were impurity stabilized and reveal the bulk lattice (1x1) type surface structures also encountered by other surface physics techniques under impure or overlayer contaminant conditions. It was therefore decided to study a system where exposure to air was unimportant by using a oxygen saturated structure, Ag2O, and seeking to find surface reconstructions, which will now be described.

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.

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