High resolution at low voltage: A new approach

1989 ◽  
Vol 47 ◽  
pp. 76-77
Author(s):  
Arthur V. Jones
Keyword(s):  
Low Voltage ◽  
Emission Sources ◽  
New Approach ◽  
Design Concepts ◽  
Probe Diameter ◽  
Low Voltage Operation ◽  
Sufficient Intensity ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Immersion Type

With the introduction of field-emission sources and “immersion-type” objective lenses, the resolution obtainable with modern scanning electron microscopes is approaching that obtainable in STEM and TEM-but only with specific types of specimens. Bulk specimens still suffer from the restrictions imposed by internal scattering and the need to be conducting. Advances in coating techniques have largely overcome these problems but for a sizeable body of specimens, the restrictions imposed by coating are unacceptable.For such specimens, low voltage operation, with its low beam penetration and freedom from charging artifacts, is the method of choice.Unfortunately the technical dificulties in producing an electron beam sufficiently small and of sufficient intensity are considerably greater at low beam energies — so much so that a radical reevaluation of convential design concepts is needed.The probe diameter is usually given by

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).

Toward High-Resolution Low-Voltage SEM

1988 ◽  
Vol 46 ◽  
pp. 218-219
Author(s):  
Zhifeng Shao
Keyword(s):  
Low Voltage ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Limiting Factor ◽  
Operating Voltage ◽  
Probe Radius ◽  
Non Local ◽  
Electron Microscopes ◽  
Image Position ◽  
Scanning Electron Microscopes

Recently, low voltage (≤5kV) scanning electron microscopes have become popular because of their unprecedented advantages, such as minimized charging effects and smaller specimen damage, etc. Perhaps the most important advantage of LVSEM is that they may be able to provide ultrahigh resolution since the interaction volume decreases when electron energy is reduced. It is obvious that no matter how low the operating voltage is, the resolution is always poorer than the probe radius. To achieve 10Å resolution at 5kV (including non-local effects), we would require a probe radius of 5∽6 Å. At low voltages, we can no longer ignore the effects of chromatic aberration because of the increased ratio δV/V. The 3rd order spherical aberration is another major limiting factor. The optimized aperture should be calculated as

Chromatic aberration and low-voltage SEM

1987 ◽  
Vol 45 ◽  
pp. 546-547
Author(s):  
Zhifeng Shao ◽  
A.V. Crewe
Keyword(s):  
Electron Energy ◽  
Low Voltage ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Primary Electron ◽  
Probe Size ◽  
Non Local ◽  
Optical Treatment ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes

For scanning electron microscopes, it is plausible that by lowering the primary electron energy, one can decrease the volume of interaction and improve resolution. As shown by Crewe /1/, at V0 =5kV a 10Å resolution (including non-local effects) is possible. To achieve this, we would need a probe size about 5Å. However, at low voltages, the chromatic aberration becomes the major concern even for field emission sources. In this case, δV/V = 0.1 V/5kV = 2x10-5. As a rough estimate, it has been shown that /2/ the chromatic aberration δC should be less than ⅓ of δ0 the probe size determined by diffraction and spherical aberration in order to neglect its effect. But this did not take into account the distribution of electron energy. We will show that by using a wave optical treatment, the tolerance on the chromatic aberration is much larger than we expected.

The Observation of NBC Precipitates In Steels In The Nanometer Range Using A Field Emission Gun Scanning Electron Microscope

1997 ◽  
Vol 3 (S2) ◽  
pp. 1243-1244 ◽  
Author(s):  
Raynald Gauvin ◽  
Steve Yue
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Field Emission ◽  
Incident Electron Energy ◽  
Beam Diameter ◽  
Probe Diameter ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

The observation of microstructural features smaller than 300 nm is generally performed using Transmission Electron Microscopy (TEM) because conventional Scanning Electron Microscopes (SEM) do not have the resolution to image such small phases. Since the early 1990’s, a new generation of microscopes is now available on the market. These are the Field Emission Gun Scanning Electron Microscope with a virtual secondary electron detector. The field emission gun gives a higher brightness than those obtained using conventional electron filaments allowing enough electrons to be collected to operate the microscope with incident electron energy, E0, below 5 keV with probe diameter smaller than 5 nm. At 1 keV, the electron range is 60 nm in aluminum and 10 nm in iron (computed using the CASINO program). Since the electron beam diameter is smaller than 5 nm at 1 keV, the resolution of these microscopes becomes closer to that of TEM.

State of the development of multipole correctors for a probe-forming system and a high-resolution 200kV TEM

1995 ◽  
Vol 53 ◽  
pp. 596-597
Author(s):  
M. Haider ◽  
J. Zach
Keyword(s):  
High Resolution ◽  
Low Voltage ◽  
Spherical Aberration ◽  
Limiting Factors ◽  
Objective Lens ◽  
Probe Diameter ◽  
Physical Limit ◽  
Low Energies ◽  
Routine Basis ◽  
Electron Microscopes

The development of modern high resolution electron microscopes has shown the emergence of new modern microscopes which are easy to operate and, more importantly, with which one can attain high resolution on a routine basis. However, the physical limit set by the inherent aberrations of electron lenses could not be overcome by simply optimising the geometry of the pole pieces. The only direct way to get rid of the aberrations of the round lenses is to use a corrector with which the resolution limiting aberrations can be compensated.For the observation of uncoated biological surfaces we started a project to develop a Low Voltage Scanning Electron Microscope (LVSEM). The main problem with using low energies is to design electron optics with which one can achieve high resolution in the range of 1 nm at energies of 1 keV and below. Hence, the two main axial aberrations of such a probe forming system: the chromatic and the spherical aberration Cc and C3, respectively, have to be considered as the limiting factors of the probe diameter. Therefore, the compensation of these two aberrations is the best choice as one does not want to run into other limitations if, for example, the geometry of the objective lens is scaled down in order to obtain small aberration coefficients.

scholarly journals Depth Information Available from the Backscattered Electron Signal

1995 ◽  
Vol 3 (6) ◽  
pp. 8-9
Author(s):  
V.N.E. Robinson
Keyword(s):  
Surface Topography ◽  
Atomic Number ◽  
Secondary Electron ◽  
Low Voltage ◽  
Depth Information ◽  
New Techniques ◽  
Backscattered Electron ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

Although the secondary electron (SE) signal is still the most commonly used signal in scanning electron microscopes (SEMs), the backscattered electron (BSE) signal is now in wide use. Imaging both atomic number and surface topography have been the major applications of BSE detectors, with some applications in channelling, magnetic contrast and similar specialized applications. Over the last few years, low voltage BSE imaging has been used for imaging surface features to a depth of a few nm. But the BSE signal contains much more information and new techniques are being developed to take advantage of its versatility.

Low-voltage high-resolution Scanning Electron Microscopy of semiconductors

1989 ◽  
Vol 47 ◽  
pp. 82-83
Author(s):  
S.J. Krause ◽  
G.N. Maracas ◽  
W.J. Varhue ◽  
D.C. Joy
Keyword(s):  
High Resolution ◽  
High Performance ◽  
Low Voltage ◽  
Image Recording ◽  
Surface Charging ◽  
New Information ◽  
Negative Surface ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

The advent of scanning electron microscopes (SEMs) with reliable, high performance field emission guns (FEG) has afforded many opportunities to obtain new information at low voltages not available at higher voltages in traditional SEMs equipped with tungsten hairpin or LaB6 filaments. The FEG SEMs are able to operate at low voltages with both high brightness and high resolution (HR) due to the small source size and low energy spread of the beam. Resolution of 4 nm down to 1.5 nm are routinely possible in the energy range from 1 to 5 keV along with standard image recording times of 1 to 2 minutes. The low voltage capabilities have allowed insulating materials, such as polymers, composites, and ceramics to be imaged at high resolutions at energies below the second crossover, usually around 1 to 2 keV, without experiencing image artifacts from negative surface charging normally found in uncoated insulators at higher operating voltages.

Low-voltage fesem study of TiO2 surface structure and metallization

1996 ◽  
Vol 54 ◽  
pp. 136-137
Author(s):  
F. Cosandey
Keyword(s):  
Surface Structure ◽  
Field Emission ◽  
Science Studies ◽  
Low Voltage ◽  
Nanometer Scale ◽  
Recent Developments ◽  
Resolution Imaging ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Electron Range

Recent developments of Field Emission Scanning Electron Microscopes (FESEM) are now permitting material science studies of surfaces with nanometer scale resolution. For the study of oxide materials with low conductivity it is particularly important to image surfaces at low voltage in order to minimize both the electron range and charging. The unique electron optic design of the LEO (ex ZEISS) 982 GEMINI microscope combining retarding field and electrostatic lens concepts with Schottky field emission source is particularly well optimize for high resolution imaging of materials at low voltage. In this study, we are presenting results on performance evaluation of the LEO 982 FESEM microscope with a study of TiO2 surface structure and metallization.

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