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.

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.

scholarly journals Beyond switches: Rotaxane- and catenane-based synthetic molecular motors

2008 ◽  
Vol 80 (1) ◽  
pp. 17-29 ◽  
Author(s):  
Euan R. Kay ◽  
David A. Leigh
Keyword(s):  
Molecular Motors ◽  
Physical Science ◽  
Statistical Physics ◽  
Biological Process ◽  
Molecular Level ◽  
Molecular Machines ◽  
Interlocked Molecules ◽  
Recent Developments ◽  
New Generation ◽  
First Time

Nature uses molecular motors and machines in virtually every significant biological process, but learning how to design and assemble simpler artificial structures that function through controlled molecular-level motion is a major challenge for contemporary physical science. The established engineering principles of the macroscopic world can offer little more than inspiration to the molecular engineer who creates devices for an environment where everything is constantly moving and being buffeted by other atoms and molecules. Rather, experimental designs for working molecular machines must follow principles derived from chemical kinetics, thermodynamics, and nonequilibrium statistical physics. The remarkable characteristics of interlocked molecules make them particularly useful for investigating the control of motion at the molecular level. Yet, the vast majority of synthetic molecular machines studied to date are simple two-state switches. Here we outline recent developments from our laboratory that demonstrate more complex molecular machine functions. This new generation of synthetic molecular machines can move continuously and progressively away from equilibrium, and they may be considered true prototypical molecular motors. The examples discussed exemplify two, fundamentally different, "Brownian ratchet" mechanisms previously developed in theoretical statistical physics and realized experimentally in molecular-level devices for the first time in these systems.

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.

Low-voltage Scanning Electron Microscopy of polymers

1986 ◽  
Vol 44 ◽  
pp. 676-677 ◽  
Author(s):  
O. W. Vaz ◽  
S. J. Krause
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Low Voltage ◽  
Polymer Surface ◽  
Image Distortion ◽  
Crossover Point ◽  
Voltage Scanning ◽  
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. These problems may be avoided by imaging polymer samples at a “crossover point”, which is located at low accelerating voltages (0.1 to 2.0 keV), where the number of electrons impinging on the sample are equal to the number of outgoing electrons emerging from the sample. This condition permits the polymer surface to remain electrically neutral and prevents image distortion due to “charging” effects. In this research we have examined Teflon (polytetrafluorethylene) samples and studied the effects of accelerating voltage and sample tilting on charging phenomena. We have also determined the approximate position of the “crossover point”.

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.

Low-voltage high-resolution SEM of biological samples

1989 ◽  
Vol 47 ◽  
pp. 72-73
Author(s):  
James B. Pawley
Keyword(s):  
Secondary Electron ◽  
Low Voltage ◽  
Focal Length ◽  
Semiconductor Industry ◽  
Focal Length Lens ◽  
Small Probe ◽  
Beam Voltage ◽  
Recent Developments ◽  
Topographical Feature ◽  
Beam Damage

There are three reasons for the recent upsurge of interest in using the SEM at a beam voltage (Vo) around 1 kV (LVSEM). The most common one arises from applications in the semiconductor industry and emphasizes the reduction in charging artifacts and in subsurface beam damage obtainable at low VoThe second reason derives from the belief that, given instrumentation capable of producing a sufficiently small probe, the increased contrast in the topographic component of the secondary electron signal will permit an important improvement in real topographic spatial resolution.The third reason is that recent developments in instrumentation have shown that by coupling a cold field-emission source with a short focal length lens, it is indeed possible to obtain small probe diameters at low voltage. Although they are considerably larger than probes obtained at higher voltage, they are nonetheless smaller than the smallest topographical feature yet imaged in the secondary electron (SE) mode. (Fig 1)

Low-Voltage Scanning Electron Microscopy in polymer characterization

1987 ◽  
Vol 45 ◽  
pp. 468-469 ◽  
Author(s):  
V. K. Berry
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Low Voltage ◽  
Polymer Surfaces ◽  
Conducting Materials ◽  
Theoretical Considerations ◽  
Voltage Scanning ◽  
Beam Damage ◽  
Scanning Electron

The application of low voltage scanning electron microscopy (LVSEM) to the characterization of polymers and non-conducting materials, other than semiconductors, has not been well explored yet. Some of the theoretical considerations and practical limitations which prevented the development of commercial instruments have mostly been addressed with the result that machines are now available which are optimized for low voltage (≥ 0.5 kV) operation. The advantages of working at low voltages are beginning to be recognized outside the semi-conductor industry. When we image uncoated polymer surfaces at low beam energies (0.5-1.5 kV), no beam damage or charging artifacts are experienced, because in this region the emitted electrons are equal to or more than the incident electrons and there is no deposition of charge underneath the surface due to the lower penetration of the incident electrons.

Trends in Electron Energy Loss Spectroscopy

1977 ◽  
Vol 35 ◽  
pp. 228-229
Author(s):  
C. Colliex ◽  
P. Trebbia
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Electron Energy Loss Spectroscopy ◽  
Materials Science ◽  
Analytical Technique ◽  
Recent Developments ◽  
Quantitative Results ◽  
Electron Microscopes ◽  
Electron Energy Loss ◽  
Primary Electrons

The physical foundations for the use of electron energy loss spectroscopy towards analytical purposes, seem now rather well established and have been extensively discussed through recent publications. In this brief review we intend only to mention most recent developments in this field, which became available to our knowledge. We derive also some lines of discussion to define more clearly the limits of this analytical technique in materials science problems.The spectral information carried in both low ( 0<ΔE<100eV ) and high ( >100eV ) energy regions of the loss spectrum, is capable to provide quantitative results. Spectrometers have therefore been designed to work with all kinds of electron microscopes and to cover large energy ranges for the detection of inelastically scattered electrons (for instance the L-edge of molybdenum at 2500eV has been measured by van Zuylen with primary electrons of 80 kV). It is rather easy to fix a post-specimen magnetic optics on a STEM, but Crewe has recently underlined that great care should be devoted to optimize the collecting power and the energy resolution of the whole system.

Processing of human melanoma cells for correlative TEM, LVSEM, and LM

1991 ◽  
Vol 49 ◽  
pp. 106-107
Author(s):  
Marek Malecki ◽  
J. Victor Small ◽  
James Pawley
Keyword(s):  
Electron Microscopy ◽  
Low Voltage ◽  
Fluorescent Microscopy ◽  
Blood Stream ◽  
Surface Topology ◽  
Integrin Receptors ◽  
Transmission Electron ◽  
Develop Technology ◽  
Voltage Scanning ◽  
Mechanisms Of Adhesion

The relative roles of adhesion and locomotion in malignancy have yet to be clearly established. In a tumor, subpopulations of cells may be recognized according to their capacity to invade neighbouring tissue,or to enter the blood stream and metastasize. The mechanisms of adhesion and locomotion are themselves tightly linked to the cytoskeletal apparatus and cell surface topology, including expression of integrin receptors. In our studies on melanomas with Fluorescent Microscopy (FM) and Cell Sorter(FACS), we noticed that cells in cultures derived from metastases had more numerous actin bundles, then cells from primary foci. Following this track, we attempted to develop technology allowing to compare ultrastructure of these cells using correlative Transmission Electron Microscopy(TEM) and Low Voltage Scanning Electron Microscopy(LVSEM).

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