Thermodynamics of Moist Air for Vacuum Technology

2021 ◽  
Vol 105 (1) ◽  
pp. 299-307
Author(s):  
Vladimir Horak ◽  
Bui Thanh Phan ◽  
Lenka Dobšáková
Keyword(s):  
Mass Conservation ◽  
Environmental Scanning ◽  
Moist Air ◽  
State Behavior ◽  
Vacuum Chambers ◽  
Vacuum Technology ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron ◽  
Thermodynamic Processes

The paper is focused on the developing a predictive mathematical model for describing thermodynamic processes connected with the moist air depressurization in vacuum chambers. Equations of the mathematical description are based on principles of the energy and mass conservation, which are complemented by the moist air thermodynamics, the state behavior of water and vapor, including principles of the critical flow. The described problem has been solved using the MATLAB software. In the paper, two cases are applied and discussed: the vacuum drying and the specimen chamber of an environmental scanning electron microscope. The specific requirements are especially important for environmental scanning electron microscopes, where it is possible to observe samples, which contain water, in their natural condition. If the air pressure, temperature and humidity do not have suitable values, observed sample may be dried or damaged.

Techniques and Applications for Imaging Biological Samples in a Low Vacuum Environmental Scanning Electron Microscope

2001 ◽  
Vol 7 (S2) ◽  
pp. 782-783
Author(s):  
C. J. Gilpin.
Keyword(s):  
Water Vapour ◽  
Biological Samples ◽  
Vapour Pressure ◽  
Water Vapour Pressure ◽  
Environmental Scanning ◽  
Sample Collection ◽  
Electron Microscopes ◽  
A Site ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

Of all the commercially available scanning electron microscopes which operate at “low vacuum” the ESEM is the most suitable for examining biological samples. in order to maintain samples with liquid water present the specimen chamber must be capable of operating at a pressure of at least 4.6 Torr (611 pascals) of water vapour pressure (the vapour pressure of water at 0°C). Use of lower pressures or a chamber gas other than water vapour will result in evaporation of water from the sample at a rate dependant on the partial pressure difference between the sample and its surrounding environment. Tables of relative humidity as a function of water vapour pressure and temperature are readily available to calculate desired settings for the microscope.One of the difficulties associated with examining fresh biological material is the need to have the microscope and sample available in the same location at the same time.If sample collection occurs at a site remote from the microscope inevitable necrotic changes will occur before examination can be carried out.

Analysis of Interesting Materials in the Environmental SEM: You Put What in Your Microscope?

2001 ◽  
Vol 7 (S2) ◽  
pp. 776-777
Author(s):  
John F. Mansfield
Keyword(s):  
Electron Microscope ◽  
Chemical Engineering ◽  
Materials Science ◽  
Variable Pressure ◽  
Environmental Scanning ◽  
Specimen Preparation ◽  
Wide Range ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

The environmental scanning electron microscope (ESEM™) and variable pressure electron microscope (VPSEM) have become accepted tools in the contemporary electron microscopy facility. Their flexibility and their ability to image almost any sample with little, and often no, specimen preparation has proved so attractive that each manufacturer of scanning electron microscopes now markets a low vacuum model.The University of Michigan Electron Microbeam Analysis Laboratory (EMAL) operates two variable pressure instruments, an ElectroScan E3 ESEM and a Hitachi S3200N VPSEM. The E3 ESEM was acquired in the early 1990s with funding from the Amoco Foundation and it has been used to examine an extremely wide variety of different materials. Since EMAL serves the entire university community, and offers support to neighboring institutions and local industry, the types of materials examined span a wide range. There are users from Materials Science & Engineering, Chemical Engineering, Nuclear Engineering, Electrical Engineering, Physics, Chemistry, Geology, Biology, Biophysics, Pharmacy and Pharmacology.

In environmental Scanning Electron Microscopy, the secondary electron signal reveals surface information not accessible by conventional backscattered electron signals

1989 ◽  
Vol 47 ◽  
pp. 78-79
Author(s):  
Klaus-Ruediger Peters
Keyword(s):  
High Vacuum ◽  
Environmental Scanning Electron Microscopy ◽  
Environmental Scanning ◽  
Specimen Preparation ◽  
Dynamic Events ◽  
Backscattered Electron ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

Environmental scanning electron microscopes (ESEM) operate at high as well as at low vacuum (<2.5 kPa: ~20 Torr) but utilize all advantages of conventional high vacuum SEM (large specimen size, high depth of focus and specimen tilt capability, TV-rate scanning for imaging dynamic events). They have the advantage of imaging wet specimens as well as insulators without the need of any specimen preparation. Previously, environmental scanning microscopy was restricted to the BSE signal collected with BSE detectors. SE signals cannot be collected with the Everhart-Thornley detector because it cannot operate at low vacuum. Using positively biased electron collectors, it is now possible to collect an SE signal. However, the origin and quality of this signal need to be further characterized.An ElectroScan ESEM was used equipped with SE and BSE detectors and operated at 7-30 kV with partial water pressures of 0.1-2.5 kPa (∼1-20 Torr).

Ceramics in the environmental Scanning Electron Microscope

1993 ◽  
Vol 51 ◽  
pp. 910-911
Author(s):  
Stuart McKeman
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Low Voltage ◽  
Ceramic Materials ◽  
Environmental Scanning Electron Microscope ◽  
Environmental Scanning ◽  
Dynamic Experiments ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

Several recent advances have had a major potential impact on the microscopy of ceramic materials. The ability of modern scanning electron microscopes to image uncoated materials, at low voltage for example, whilst still maintaining high resolution should make possible a wide variety of experiments that were hitherto impossible to contemplate. This ability to look at the unmodified surface of a ceramic enables iterative or dynamic experiments to be done with a lot more confidence in the results than has been possible before. A second advance has been the introduction of microscopes capable of operating at higher pressures than was previously possible. This makes possible the ability to image specimens in a variety of different environments. The environmental scanning electron microscope (ESEM) exploits of both of these novel areas. The aim of this review is to highlight areas where the unique capabilities of the ESEM may be applied to advance our understanding of ceramics.

Experimental evaluation of environmental scanning electron microscopes at high chamber pressure

2015 ◽  
Vol 260 (2) ◽  
pp. 133-139 ◽  
Author(s):  
H. FITZEK ◽  
H. SCHROETTNER ◽  
J. WAGNER ◽  
F. HOFER ◽  
J. RATTENBERGER
Keyword(s):  
Experimental Evaluation ◽  
Chamber Pressure ◽  
Environmental Scanning ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

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.

Current State of Biological High-Resolution Scanning Electron Microscopy

1988 ◽  
Vol 46 ◽  
pp. 180-181 ◽  
Author(s):  
Klaus-Ruediger Peters
Keyword(s):  
High Performance ◽  
Low Voltage ◽  
Backscattered Electrons ◽  
Lens Position ◽  
Low Voltage Operation ◽  
Signal Collection ◽  
Probe Size ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

A new generation of high performance field emission scanning electron microscopes (FSEM) is now commercially available (JEOL 890, Hitachi S 900, ISI OS 130-F) characterized by an "in lens" position of the specimen where probe diameters are reduced and signal collection improved. Additionally, low voltage operation is extended to 1 kV. Compared to the first generation of FSEM (JE0L JSM 30, Hitachi S 800), which utilized a specimen position below the final lens, specimen size had to be reduced but useful magnification could be impressively increased in both low (1-4 kV) and high (5-40 kV) voltage operation, i.e. from 50,000 to 200,000 and 250,000 to 1,000,000 x respectively.At high accelerating voltage and magnification, contrasts on biological specimens are well characterized1 and are produced by the entering probe electrons in the outmost surface layer within -vl nm depth. Backscattered electrons produce only a background signal. Under these conditions (FIG. 1) image quality is similar to conventional TEM (FIG. 2) and only limited at magnifications >1,000,000 x by probe size (0.5 nm) or non-localization effects (%0.5 nm).

Observation of GaAs/AlAs Superlattice Structures in both Secondary and Backscattcred Electron Imaging Modes with an Ultrahigh Resolution Scanning Electron Microscope

1990 ◽  
Vol 48 (1) ◽  
pp. 404-405
Author(s):  
K. Ogura ◽  
A. Ono ◽  
S. Franchi ◽  
P.G. Merli ◽  
A. Migliori
Keyword(s):  
Gaas Layer ◽  
Objective Lens ◽  
Superlattice Structure ◽  
Backscattered Electron ◽  
Instrumental Resolution ◽  
Electron Microscopes ◽  
Superlattice Structures ◽  
Electron Imaging ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

In the last few years the development of Scanning Electron Microscopes (SEM), equipped with a Field Emission Gun (FEG) and using in-lens specimen position, has allowed a significant improvement of the instrumental resolution . This is a result of the fine and bright probe provided by the FEG and by the reduced aberration coefficients of the strongly excited objective lens. The smaller specimen size required by in-lens instruments (about 1 cm, in comparison to 15 or 20 cm of a conventional SEM) doesn’t represent a serious limitation in the evaluation of semiconductor process techniques, where the demand of high resolution is continuosly increasing. In this field one of the more interesting applications, already described (1), is the observation of superlattice structures.In this note we report a comparison between secondary electron (SE) and backscattered electron (BSE) images of a GaAs / AlAs superlattice structure, whose cross section is reported in fig. 1. The structure consist of a 3 nm GaAs layer and 10 pairs of 7 nm GaAs / 15 nm AlAs layers grown on GaAs substrate. Fig. 2, 3 and 4 are SE images of this structure made with a JEOL JSM 890 SEM operating at an accelerating voltage of 3, 15 and 25 kV respectively. Fig. 5 is a 25 kV BSE image of the same specimen. It can be noticed that the 3nm layer is always visible and that the 3 kV SE image, in spite of the poorer resolution, shows the same contrast of the BSE image. In the SE mode, an increase of the accelerating voltage produces a contrast inversion. On the contrary, when observed with BSE, the layers of GaAs are always brighter than the AlAs ones , independently of the beam energy.

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