Examinations of low-density polymer foams with a low-voltage FESEM

1987 ◽  
Vol 45 ◽  
pp. 390-391 ◽  
Author(s):  
C. W. Price ◽  
P. L. McCarthy ◽  
S. A. Letts ◽  
F. M. Kong
Keyword(s):  
Low Voltage ◽  
Cell Structure ◽  
Low Density ◽  
Polymer Foams ◽  
Structural Detail ◽  
Conductive Coatings ◽  
Thin Membranes ◽  
Beam Currents ◽  
Beam Damage ◽  
Fracture Specimens

The cell structure of low-density polymer foams is extremely delicate, and the application of conductive coatings for SEM examinations can obliterate much of the fine structural detail. In extreme cases, the structure can be significantly altered by the coating. This problem has been found to be particularly critical in low-density polymer foams. The thin membranes of polymer foams also are exceptionally susceptable to electron-beam damage. Consequently, both the improved low-voltage resolution and the low beam currents now available on an SEM equipped with a field-emission gun (FESEM) have proven to be highly beneficial for the examination of low-density polymer foams. This will be demonstrated for polystyrene foams; equally successful results have been obtained on other types of polymer foams.The simplest technique to examine the cell structure of polystyrene foams is to fracture specimens and examine the fracture surface. Since polystyrene is nonconductive, it must be coated to be examined in the conventional SEM.

Recent developments in low-voltage SEM of polymers

1993 ◽  
Vol 51 ◽  
pp. 866-867
Author(s):  
S.J. Krause ◽  
W.W. Adams
Keyword(s):  
Low Voltage ◽  
Chromatic Aberration ◽  
Thermal Electron ◽  
Analytical Technique ◽  
Recent Developments ◽  
Beam Currents ◽  
New Generation ◽  
First Time ◽  
Voltage Scanning ◽  
Beam Damage

Over the past decade low voltage scanning electron microscopy (LVSEM) of polymers has evolved from an interesting curiosity to a powerful analytical technique. This development has been driven by improved instrumentation and in particular, reliable field emission gun (FEG) SEMs. The usefulness of LVSEM has also grown because of an improved theoretical and experimental understanding of sample-beam interactions and by advances in sample preparation and operating techniques. This paper will review progress in polymer LVSEM and present recent results and developments in the field.In the early 1980s a new generation of SEMs produced beam currents that were sufficient to allow imaging at low voltages from 5keV to 0.5 keV. Thus, for the first time, it became possible to routinely image uncoated polymers at voltages below their negative charging threshold, the "second crossover", E2 (Fig. 1). LVSEM also improved contrast and reduced beam damage in sputter metal coated polymers. Unfortunately, resolution was limited to a few tenths of a micron due to the low brightness and chromatic aberration of thermal electron emission sources.

High-pressure freezing of cells in suspension for low-voltage scanning electron microscopy (LVSEM)

1991 ◽  
Vol 49 ◽  
pp. 64-65
Author(s):  
Marek Malecki ◽  
James Pawley ◽  
Hans Ris
Keyword(s):  
Electron Microscopy ◽  
High Pressure ◽  
Low Voltage ◽  
Culture Media ◽  
Cell Structure ◽  
Freeze Substitution ◽  
Ice Crystal ◽  
High Pressure Freezing ◽  
Cell Culture Media ◽  
Voltage Scanning

The ultrastructure of cells suspended in physiological fluids or cell culture media can only be studied if the living processes are stopped while the cells remain in suspension. Attachment of living cells to carrier surfaces to facilitate further processing for electron microscopy produces a rapid reorganization of cell structure eradicating most traces of the structures present when the cells were in suspension. The structure of cells in suspension can be immobilized by either chemical fixation or, much faster, by rapid freezing (cryo-immobilization). The fixation speed is particularly important in studies of cell surface reorganization over time. High pressure freezing provides conditions where specimens up to 500μm thick can be frozen in milliseconds without ice crystal damage. This volume is sufficient for cells to remain in suspension until frozen. However, special procedures are needed to assure that the unattached cells are not lost during subsequent processing for LVSEM or HVEM using freeze-substitution or freeze drying. We recently developed such a procedure.

High-Resolution, Low-Voltage SEM of Cell Wall Regeneration of Yeast Shizosaccharomyces Pombe Protoplasts

1988 ◽  
Vol 46 ◽  
pp. 208-211
Author(s):  
M. Osumi ◽  
N. Yamada ◽  
T. Nagatani
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Low Voltage ◽  
Cell Wall Regeneration ◽  
The Past ◽  
The Poor ◽  
Probe Size ◽  
Beam Damage ◽  
Biological Field ◽  
Scanning Electron

Even though many early workers had suggested the use of lower voltages to increase topographic contrast and to reduce specimen charging and beam damage, we did not usually operate in the conventional scanning electron microscope at low voltage because of the poor resolution, especially of bioligical specimens. However, the development of the “in-lens” field emission scanning electron microscope (FESEM) has led to marked inprovement in resolution, especially in the range of 1-5 kV, within the past year. The probe size has been cumulated to be 0.7nm in diameter at 30kV and about 3nm at 1kV. We have been trying to develop techniques to use this in-lens FESEM at low voltage (LVSEM) for direct observation of totally uncoated biological specimens and have developed the LVSEM method for the biological field.

Low-voltage, high-resolution scanning electron microscopy of polymers

1987 ◽  
Vol 45 ◽  
pp. 466-467 ◽  
Author(s):  
S. J. Krause ◽  
W.W. Adams ◽  
S. Kumar ◽  
T. Reilly ◽  
T. Suziki
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Low Voltage ◽  
Chromatic Aberration ◽  
Image Resolution ◽  
Resolution Limit ◽  
Crossover Point ◽  
New Generation ◽  
Beam Damage ◽  
Scanning Electron

Scanning electron microscopy (SEM) of polymers at routine operating voltages of 15 to 25 keV can lead to beam damage and sample image distortion due to charging. Imaging polymer samples with low accelerating voltages (0.1 to 2.0 keV), at or near the “crossover point”, can reduce beam damage, eliminate charging, and improve contrast of surface detail. However, at low voltage, beam brightness is reduced and image resolution is degraded due to chromatic aberration. A new generation of instruments has improved brightness at low voltages, but a typical SEM with a tungsten hairpin filament will have a resolution limit of about 100nm at 1keV. Recently, a new field emission gun (FEG) SEM, the Hitachi S900, was introduced with a reported resolution of 0.8nm at 30keV and 5nm at 1keV. In this research we are reporting the results of imaging coated and uncoated polymer samples at accelerating voltages between 1keV and 30keV in a tungsten hairpin SEM and in the Hitachi S900 FEG SEM.

Low - Voltage Scanning Electron Microscopy Imaging, Secondary and Backscatter, With Microchannel Plate Detector

1990 ◽  
Vol 48 (1) ◽  
pp. 442-442
Author(s):  
Galen Powers ◽  
Ray Cochran
Keyword(s):  
Low Voltage ◽  
Beam Current ◽  
Microchannel Plate ◽  
Normal Operation ◽  
Microscopy Imaging ◽  
Backscatter Signal ◽  
Vacuum Interface ◽  
Width Measurements ◽  
Working Distance ◽  
Beam Currents

The capability to obtain symmetrical images at voltages as low as 200 eV and beam currents less than 9 pico amps is believed to be advantageous for metrology and study of dielectric or biological samples. Symmetrical images should allow more precise and accurate line width measurements than currently achievable by traditional secondary electron detectors. The low voltage and current capability should allow imaging of samples which traditionally have been difficult because of charging or electron beam damage.The detector system consists of a lens mounted dual anode MicroChannel Plate (MCP) detector, vacuum interface, power supplies, and signal conditioning to interface directly to the video card of the SEM. The detector has been miniaturized so that it does not interfere with normal operation of the SEM sample handling and alternate detector operation. Biasing of the detector collection face will either add secondaries to the backscatter signal or reject secondaries yielding only a backscatter image. The dual anode design allows A−B signal processing to provide topological information as well as symmetrical A+B images.Photomicrographs will show some of the system capabilities. Resolution will be documented with gold on carbon. Variation of voltage, beam current, and working distance on dielectric samples such as glass and photoresist will demonstrate effects of common parameter changes.

scholarly journals Kinked Bisamides as Efficient Supramolecular Foam Cell Nucleating Agents for Low-Density Polystyrene Foams with Homogeneous Microcellular Morphology

Polymers ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1094
Author(s):  
Bastian Klose ◽  
Daniel Kremer ◽  
Merve Aksit ◽  
Kasper P. van der Zwan ◽  
Klaus Kreger ◽  
...  
Keyword(s):  
Cell Size ◽  
Self Assembly ◽  
Large Scale ◽  
Elevated Temperatures ◽  
Foam Cell ◽  
Cell Structure ◽  
Expansion Ratio ◽  
Low Density ◽  
Nucleating Agents ◽  
Foam Density

Polystyrene foams have become more and more important owing to their lightweight potential and their insulation properties. Progress in this field is expected to be realized by foams featuring a microcellular morphology. However, large-scale processing of low-density foams with a closed-cell structure and volume expansion ratio of larger than 10, exhibiting a homogenous morphology with a mean cell size of approximately 10 µm, remains challenging. Here, we report on a series of 4,4′-diphenylmethane substituted bisamides, which we refer to as kinked bisamides, acting as efficient supramolecular foam cell nucleating agents for polystyrene. Self-assembly experiments from solution showed that these bisamides form supramolecular fibrillary or ribbon-like nanoobjects. These kinked bisamides can be dissolved at elevated temperatures in a large concentration range, forming dispersed nano-objects upon cooling. Batch foaming experiments using 1.0 wt.% of a selected kinked bisamide revealed that the mean cell size can be as low as 3.5 µm. To demonstrate the applicability of kinked bisamides in a high-throughput continuous foam process, we performed foam extrusion. Using 0.5 wt.% of a kinked bisamide yielded polymer foams with a foam density of 71 kg/m3 and a homogeneous microcellular morphology with cell sizes of ≈10 µm, which is two orders of magnitude lower compared to the neat polystyrene reference foam with a comparable foam density.

Clay Aerogel Composite Materials

2010 ◽  
Vol 63 ◽  
pp. 147-151 ◽  
Author(s):  
David A. Schiraldi ◽  
Matthew D. Gawryla ◽  
Saeed Alhassan
Keyword(s):  
Mechanical Properties ◽  
Composite Materials ◽  
Environmentally Friendly ◽  
Porous Ceramics ◽  
Low Density ◽  
Polymer Foams ◽  
Freeze Dried ◽  
Aerogel Composite ◽  
Environmentally Friendly Process

A simple, inexpensive, and environmentally-friendly process for converting mixtures of clays and polymers has been developed. Polymer and clay are combined in water, and the mixtures are freeze dried to produce materials which have bulk densities typically in the range of 0.03 – 0.15 g/cm3. These low density polymer/clay aerogel materials possess good mechanical properties similar to those of traditional polymer foams, can be reinforced with fibers, modified with nanoparticles, biomineralized, or converted into porous ceramics.

scholarly journals Progress in development of low density polymer foams for the ICF Program

1985 ◽  
Author(s):  
S.A. Letts ◽  
L.M. Lucht ◽  
R.J. Morgan ◽  
R.C. Cook ◽  
T.M. Tillotson ◽  
...  
Keyword(s):  
Low Density ◽  
Polymer Foams

scholarly journals Low-voltage scanning electron microscopy

1983 ◽  
Vol 41 ◽  
pp. 488-491
Author(s):  
J. B. Pawley ◽  
M. P. Winters
Keyword(s):  
Electron Probe ◽  
Current Flow ◽  
Low Voltage ◽  
Semiconductor Industry ◽  
X Rays ◽  
Probe Diameter ◽  
Small Probe ◽  
Important Improvement ◽  
Voltage Scanning ◽  
Beam Damage

There are two reasons for the renewed interest in using the SEM at beam voltages, Vb, around 1kV (LVSEM). The most common one arises from applications in the semiconductor industry and emphasizes the reduction in charging artifacts and in subsurface beam damage. The second reason postulates that the increased contrast in the topographic component of the secondary electron signal will permit an important improvement in topographic spatial resolution if only a sufficiently small probe diameter can be obtained. We shall treat these two areas separately and then mention some of the strategies that have been adopted to make LVSEM work.Surfaces are very important in the manufacture of modern semiconductor devices and the ability of the electron probe to induce current flow (EBIC), to detect variations in surface voltage, Vs, and to excite characteristic x rays in addition to its ability to image topography in an easily understandable way guaranteed the SEM a major role in programs of semiconductor development and failure analysis. There were two problems, however, charging and beam-induced damage to the specimen.

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