An Efficient Annular Dark-Field Detector Capable of Single-Electron Counting Adapted to a High-Resolution Field-Emission SEM

1988 ◽  
Vol 46 ◽  
pp. 190-191
Author(s):  
R. Reichelt ◽  
U. Aebi ◽  
A. Engel
Keyword(s):  
High Resolution ◽  
Electron Energy ◽  
Field Emission ◽  
Major Elements ◽  
Dark Field ◽  
Primary Electron ◽  
Transmission Electron ◽  
Annular Dark Field ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes

Various high resolution scanning electron microscopes (HRSEM) are now commercially available providing probe sizes in the range of 0.5 to 1.5 nm at 30 keV due to their field emission gun 1.2. Equipped with efficient detector systems (which collect different signals and applied to specifically prepared samples) HRSEM challenge the conventional transmission electron microscope (TEM) with high resolution surface images of biological specimens collecting secondary (SE) or backscattered (BSE) electrons. However, the yield of (SE) carrying high resolution information is rather small, i.e. the SE-I yield at 20 keV primary electron energy amounts to < 1% for the major elements (H; C; N; O; P) constituting biological matter. The yield of BSE is greater than the corresponding total SE yield (electron energy >15 keV), but BSE emerge due to high angle elastic scattering from a surface area with a diameter of typically 30% of the deepest electron penetration R (e.g. R≈10 μm for elements mentioned above at 30 keV).

Design of a new objective lens for an HB-501A STEM

1991 ◽  
Vol 49 ◽  
pp. 416-417
Author(s):  
Earl J. Kirkland ◽  
Robert J. Keyse
Keyword(s):  
High Resolution ◽  
Spherical Aberration ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Objective Lens ◽  
Specimen Holder ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
High Resolution Microscopy

An ultra-high resolution pole piece with a coefficient of spherical aberration Cs=0.7mm. was previously designed for a Vacuum Generators HB-501A Scanning Transmission Electron Microscope (STEM). This lens was used to produce bright field (BF) and annular dark field (ADF) images of (111) silicon with a lattice spacing of 1.92 Å. In this microscope the specimen must be loaded into the lens through the top bore (or exit bore, electrons traveling from the bottom to the top). Thus the top bore must be rather large to accommodate the specimen holder. Unfortunately, a large bore is not ideal for producing low aberrations. The old lens was thus highly asymmetrical, with an upper bore of 8.0mm. Even with this large upper bore it has not been possible to produce a tilting stage, which hampers high resolution microscopy.

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.

Towards 1-Ångstrom-resolution STEM

1993 ◽  
Vol 51 ◽  
pp. 996-997
Author(s):  
H.S. von Harrach ◽  
D.E. Jesson ◽  
S.J. Pennycook
Keyword(s):  
High Resolution ◽  
Field Emission ◽  
Phase Contrast ◽  
Spherical Aberration ◽  
A Priori ◽  
Dark Field ◽  
Image Resolution ◽  
Objective Lens ◽  
Annular Dark Field ◽  
First Results

Phase contrast TEM has been the leading technique for high resolution imaging of materials for many years, whilst STEM has been the principal method for high-resolution microanalysis. However, it was demonstrated many years ago that low angle dark-field STEM imaging is a priori capable of almost 50% higher point resolution than coherent bright-field imaging (i.e. phase contrast TEM or STEM). This advantage was not exploited until Pennycook developed the high-angle annular dark-field (ADF) technique which can provide an incoherent image showing both high image resolution and atomic number contrast.This paper describes the design and first results of a 300kV field-emission STEM (VG Microscopes HB603U) which has improved ADF STEM image resolution towards the 1 angstrom target. The instrument uses a cold field-emission gun, generating a 300 kV beam of up to 1 μA from an 11-stage accelerator. The beam is focussed on to the specimen by two condensers and a condenser-objective lens with a spherical aberration coefficient of 1.0 mm.

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.

High-resolution biological microanalysis in the field-emission STEM

1990 ◽  
Vol 48 (2) ◽  
pp. 154-155
Author(s):  
R.D. Leapman ◽  
S.B. Andrews
Keyword(s):  
High Resolution ◽  
Field Emission ◽  
Low Dose ◽  
Dark Field ◽  
X Ray ◽  
Macromolecular Assemblies ◽  
Freeze Dried ◽  
Annular Dark Field ◽  
20 Nm ◽  
Electron Energy Loss

The recent availability of a cryotransfer stage, efficient electron energy loss spectrometers (EELS), and ultrathin window energy-dispersive x-ray spectrometers (EDXS) for the VG Microscopes HB501 field-emission STEM now provides this instrument with the potential for high resolution (<20 nm) biological microanalysis. In practice, limits are normally imposed by the sample itself, due to damage in the electron beam and to changes in structure and composition during freezing, sectioning, transfering and freeze-drying. We have therefore investigated what types of useful high-resolution analytical information can be obtained from rapidly frozen samples, including thin tissue cryosections and frozen isolated macromolecules and macromolecular assemblies.Frozen-hydrated samples were cryotransfered at ~-175C into the VG STEM after which a vacuum of ~3x10-9 mbar was maintained. Samples were freeze-dried by warming to ~-90C over 30 min and were then recooled to below ~-160C to minimize radiation damage and contamination during analysis. Digital annular dark-field images were obtained at low dose (~10 e/Å2) with single electron sensitivity, using a probe current of 2 to10 pA and a beam energy of 100 keV.

Stem Dark-Field Image Using A 200-kV AEM

1996 ◽  
Vol 54 ◽  
pp. 444-445
Author(s):  
T. Tomita ◽  
T. Honda ◽  
M. Kersker
Keyword(s):  
High Resolution ◽  
Field Emission ◽  
Thermal Field ◽  
Imaging System ◽  
Dark Field Image ◽  
Dark Field ◽  
Specimen Thickness ◽  
High Angle ◽  
Long Term Stability ◽  
Annular Dark Field

Interpretation of the high resolution transmission image typically requires simulation since the contrast changes in a complicated way due to changes in focus and specimen thickness. The contrast in images formed by collecting high angle forward scattered electrons in STEM does not change with changes in thickness or defocus.Until recently, high angle annular dark field (HADF) images were obtained only from instruments using cold field emission guns. Recently we have attempted to obtain HADF images using Schottky (ZrO/W(100)) thermal field emission and using a 200kV instrument designed as a comprehensive TEM/STEM. Advantages of the ZrO/W emitter are easy operation, very good short and long term stability, high brightness, and narrow energy spread. This microscope, The JEM2010F with thermal field emission, allows subnanometer analysis with EDS(spot, line, and mapping), EELS, holograms, etc, and has a standard TEM imaging system for high resolution imaging and for various diffraction modes, viz., CBED, selected area, Tanaka, etc.

Condenser-objective lens SE microscopy: application for high - resolution imaging of cell membranes

1987 ◽  
Vol 45 ◽  
pp. 564-567
Author(s):  
R.P. Apkarian
Keyword(s):  
High Resolution ◽  
Primary Electron ◽  
Objective Lens ◽  
Beam Diameter ◽  
Contrast Imaging ◽  
Electron Sources ◽  
Recent Developments ◽  
Brightness Field ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes

Recent developments in high brightness field emission (FE) and LaB6 electron sources for scanning electron microscopes (SEM) equipped with condenser-objective lens specimen stages has resulted in the collection of secondary electron (SE) signals that contain unsurpassed high resolution topographic contrasts. High resolution low loss images were described for a condenser-objective lens SEM when SE contrasts were first being scrutinized. The low energy SE-I imaging mode contains contrasts generated by only specimen specific SE-I and II. The SE-I signal is produced by the primary electron beam interaction with the specimen surface before a scattering event occurs and can be best collected when SE-IIIs are eliminated and SE-IIs are suppressed. High resolution SE-I topographic contrasts include particle contrast (resolution of particles < 10 nm), relief contrast (imaging of very small contours), and edge brightness contrast (sum of beam diameter and SE range).

Advantages of modern field emission Electron Microscopes for characterization of catalytic materials

1995 ◽  
Vol 53 ◽  
pp. 402-403
Author(s):  
L. F. Allard ◽  
S. A. Bradley ◽  
E. Völkl ◽  
S. J. Pennycook
Keyword(s):  
Field Emission ◽  
Collection Efficiency ◽  
Energy Dispersive Spectrometer ◽  
Dark Field ◽  
Supported Metal Catalysts ◽  
X Rays ◽  
Catalytic Materials ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Electron Microscopes

The ability to characterize the structure of a variety of catalytic materials, especially supported metal catalysts, has been dramatically enhanced in recent years by the improved electron microscopy capabilities provided by the new generation of field emission gun transmission (FE-TEM) and dedicated scanning transmission electron microscopes (d-STEM). Although the reciprocity theorem says that a TEM and a dedicated STEM have equivalent, but reciprocal, electron optical geometries so that imaging conditions in one instrument can, in principal, be duplicated in the other, in reality the TEM and d-STEM offer column geometries that are optimized for different kinds of analytical output. For example, the d-STEM permits introduction of an energy dispersive spectrometer, which collects x-rays at a solid angle of 0.2 sr (but at a low take-off angle). A high take-off angle detector in a TEM may give a collection angle of only 0.013 sr. This x-ray collection efficiency coupled with use of annular dark-field techniques makes the imaging and analysis of nanometer-sized metal clusters on supports more effective.

Mn Valency at La0.7Sr0.3MnO3/SrTiO3 (0 0 1) Thin Film Interfaces

2009 ◽  
Vol 15 (3) ◽  
pp. 213-221 ◽  
Author(s):  
Thomas Riedl ◽  
Thomas Gemming ◽  
Kathrin Dörr ◽  
Martina Luysberg ◽  
Klaus Wetzig
Keyword(s):  
Thin Film ◽  
High Resolution ◽  
Scanning Transmission Electron Microscopy ◽  
Atomic Layer ◽  
Dark Field ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
High Resolution Images ◽  
Local Oxygen

AbstractThis article presents a (scanning) transmission electron microscopy (TEM) study of Mn valency and its structural origin at La0.7Sr0.3MnO3/SrTiO3(0 0 1) thin film interfaces. Mn valency deviations can lead to a breakdown of ferromagnetic order and thus lower the tunneling magnetoresistance of tunnel junctions. Here, at the interface, a Mn valency reduction of 0.16 ± 0.10 compared to the film interior and an additional feature at the low energy-loss flank of the Mn-L3 line have been observed. The latter may be attributed to an elongation of the (0 0 1) plane spacing at the interface detected by geometrical phase analysis of high-resolution images. Regarding the interface geometry, high-resolution high-angle annular dark-field scanning TEM images reveal an atomically sharp interface in some regions whereas the transition appears broadened in others. This can be explained by the presence of steps. The performed measurements indicate that, among the various structure-related influences on the valency, the atomic layer termination and the local oxygen content are most important.

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