The twin lens system - A high resolution objective lens at 300 kV

1986 ◽  
Vol 44 ◽  
pp. 610-613
Author(s):  
B. Bormans ◽  
P. Hagemann
Keyword(s):  
Chromatic Aberration ◽  
Objective Lens ◽  
Finite Element Program ◽  
Medium Voltage ◽  
Voltage Electron ◽  
System A ◽  
Element Program ◽  
Electron Microscopes ◽  
Single Field ◽  
Better Than

Point resolution of better than 0.2 nm is today achievable in medium voltage electron microscopes. Crucial for this achievement is the objective lens design which has to provide sufficiently low spherical and chromatic aberration figures. In addition to the lens itself, its integration into the overall microscope optics has to ensure a reproducible and accurate alignment.Cleaver has shown that symmetrical lenses have lower aberrations than their asymmetrical counterparts by a factor of 1.5 or 2. Theoretical optimization of this lens at 300 kV can be carried out using a first-order finite element program, as developed by Munro. The symmetrical single-field condenser objective with saturated pole-piece tips produces particularly good values with Cs = 1.0 mm and Cc = 1.4 mm at 300 kV. In this lens the specimen is placed in the centre of the magnetic field.

The Reduction of Chromatic Aberrations Due to Instrumental Instabilities

1971 ◽  
Vol 29 ◽  
pp. 14-15
Author(s):  
J. S. Lally ◽  
R. Evans
Keyword(s):  
Electron Microscope ◽  
High Voltage ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Usual Practice ◽  
Voltage Electron ◽  
Short Focal Length ◽  
Chromatic Aberrations ◽  
Electron Microscopes

One of the instrumental factors often limiting the resolution of the electron microscope is image defocussing due to changes in accelerating voltage or objective lens current. This factor is particularly important in high voltage electron microscopes both because of the higher voltages and lens currents required but also because of the inherently longer focal lengths, i.e. 6 mm in contrast to 1.5-2.2 mm for modern short focal length objectives.The usual practice in commercial electron microscopes is to design separately stabilized accelerating voltage and lens supplies. In this case chromatic aberration in the image is caused by the random and independent fluctuations of both the high voltage and objective lens current.

Current and future aberration correctors for the improvement of resolution in electron microscopy

2009 ◽  
Vol 367 (1903) ◽  
pp. 3665-3682 ◽  
Author(s):  
M. Haider ◽  
P. Hartel ◽  
H. Müller ◽  
S. Uhlemann ◽  
J. Zach
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Low Voltage ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Voltage Electron ◽  
System A ◽  
Transmission Electron ◽  
Correction System

The achievable resolution of a modern transmission electron microscope (TEM) is mainly limited by the inherent aberrations of the objective lens. Hence, one major goal over the past decade has been the development of aberration correctors to compensate the spherical aberration. Such a correction system is now available and it is possible to improve the resolution with this corrector. When high resolution in a TEM is required, one important parameter, the field of view, also has to be considered. In addition, especially for the large cameras now available, the compensation of off-axial aberrations is also an important task. A correction system to compensate the spherical aberration and the off-axial coma is under development. The next step to follow towards ultra-high resolution will be a correction system to compensate the chromatic aberration. With such a correction system, a new area will be opened for applications for which the chromatic aberration defines the achievable resolution, even if the spherical aberration is corrected. This is the case, for example, for low-voltage electron microscopy (EM) for the investigation of beam-sensitive materials, for dynamic EM or for in-situ EM.

Design of objective lens for 200-kV high-resolution electron microscopes

1983 ◽  
Vol 41 ◽  
pp. 314-315
Author(s):  
K. Tsuno ◽  
T. Honda ◽  
Y. Harada ◽  
M. Naruse
Keyword(s):  
Optical Properties ◽  
Computer Technology ◽  
Axial Magnetic Field ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Resolution Electron ◽  
Correction Of Astigmatism ◽  
Three Stages ◽  
Electron Microscopes ◽  
Stage 1

Developement of computer technology provides much improvements on electron microscopy, such as simulation of images, reconstruction of images and automatic controll of microscopes (auto-focussing and auto-correction of astigmatism) and design of electron microscope lenses by using a finite element method (FEM). In this investigation, procedures for simulating the optical properties of objective lenses of HREM and the characteristics of the new lens for HREM at 200 kV are described.The process for designing the objective lens is divided into three stages. Stage 1 is the process for estimating the optical properties of the lens. Firstly, calculation by FEM is made for simulating the axial magnetic field distributions Bzc of the lens. Secondly, electron ray trajectory is numerically calculated by using Bzc. And lastly, using Bzc and ray trajectory, spherical and chromatic aberration coefficients Cs and Cc are numerically calculated. Above calculations are repeated by changing the shape of lens until! to find an optimum aberration coefficients.

Atomic structure imaging of the Si/SiO2 interface with high-resolution electron microscopy

1986 ◽  
Vol 44 ◽  
pp. 390-391
Author(s):  
J.L. Batstone ◽  
J.M. Gibson ◽  
Alice.E. White ◽  
K.T. Short
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Atomic Structure ◽  
High Resolution Electron Microscopy ◽  
Medium Voltage ◽  
Voltage Electron ◽  
Resolution Electron ◽  
Structural Image ◽  
Electron Microscopes ◽  
Point To Point

High resolution electron microscopy (HREM) is a powerful tool for the determination of interface atomic structure. With the previous generation of HREM's of point-to-point resolution (rpp) >2.5Å, imaging of semiconductors in only <110> directions was possible. Useful imaging of other important zone axes became available with the advent of high voltage, high resolution microscopes with rpp <1.8Å, leading to a study of the NiSi2 interface. More recently, it was shown that images in <100>, <111> and <112> directions are easily obtainable from Si in the new medium voltage electron microscopes. We report here the examination of the important Si/Si02 interface with the use of a JEOL 4000EX HREM with rpp <1.8Å, in a <100> orientation. This represents a true structural image of this interface.

Toward The Simultaneous Correction of Spherical and Chromatic Aberration in Electron Optics by Means of an Electrostatic Electron Mirror

1990 ◽  
Vol 48 (1) ◽  
pp. 206-207
Author(s):  
Gertrude. F. Rempfer
Keyword(s):  
Chromatic Aberration ◽  
Transverse Magnetic ◽  
Objective Lens ◽  
Ion Imaging ◽  
Corrected Image ◽  
Electric And Magnetic Fields ◽  
Chromatic Aberrations ◽  
Improved Performance ◽  
Electron Microscopes ◽  
Image Planes

Optimum performance in electron and ion imaging instruments, such as electron microscopes and probe-forming instruments, in most cases depends on a compromise either between imaging errors due to spherical and chromatic aberrations and the diffraction error or between the imaging errors and the current in the image. These compromises result in the use of very small angular apertures. Reducing the spherical and chromatic aberration coefficients would permit the use of larger apertures with resulting improved performance, granted that other problems such as incorrect operation of the instrument or spurious disturbances do not interfere. One approach to correcting aberrations which has been investigated extensively is through the use of multipole electric and magnetic fields. Another approach involves the use of foil windows. However, a practical system for correcting spherical and chromatic aberration is not yet available.Our approach to correction of spherical and chromatic aberration makes use of an electrostatic electron mirror. Early studies of the properties of electron mirrors were done by Recknagel. More recently my colleagues and I have studied the properties of the hyperbolic electron mirror as a function of the ratio of accelerating voltage to mirror voltage. The spherical and chromatic aberration coefficients of the mirror are of opposite sign (overcorrected) from those of electron lenses (undercorrected). This important property invites one to find a way to incorporate a correcting mirror in an electron microscope. Unfortunately, the parts of the beam heading toward and away from the mirror must be separated. A transverse magnetic field can separate the beams, but in general the deflection aberrations degrade the image. The key to avoiding the detrimental effects of deflection aberrations is to have deflections take place at image planes. Our separating system is shown in Fig. 1. Deflections take place at the separating magnet and also at two additional magnetic deflectors. The uncorrected magnified image formed by the objective lens is focused in the first deflector, and relay lenses transfer the image to the separating magnet. The interface lens and the hyperbolic mirror acting in zoom fashion return the corrected image to the separating magnet, and the second set of relay lenses transfers the image to the final deflector, where the beam is deflected onto the projection axis.

Characterization of Grain Boundaries and Interfaces by High Resolution Transmission Electron Microscopy

1989 ◽  
Vol 153 ◽  
Author(s):  
William Krakow
Keyword(s):  
High Resolution ◽  
Grain Boundaries ◽  
Ohmic Contacts ◽  
Dielectric Material ◽  
Medium Voltage ◽  
Voltage Electron ◽  
Resolution Electron ◽  
Interfacial Structures ◽  
Tilt Boundaries ◽  
Electron Microscopes

AbstractSeveral examples will be given of high resolution electron microscope images of both grain boundaries and interfaces and the methods which have been applied to understanding their atomic structure. Specific expitaxial interfacial structures considered are: Pd2Si/Si used for ohmic contacts, Al on Si overlayers and CaF2/Si where the CaF2, is an attractive possibility as a dielectric material. For the case of grain boundaries specific examples of both twist and tilt boundaries in Au will be given to show the imaging capability with the new generation of medium voltage electron microscopes.

Instrumentation at the National Center for Electron Microscopy: The atomic resolution microscope

1983 ◽  
Vol 41 ◽  
pp. 310-311 ◽  
Author(s):  
R. Gronsky ◽  
G. Thomas
Keyword(s):  
Electron Microscopy ◽  
Atomic Resolution ◽  
Objective Lens ◽  
Contrast Transfer Function ◽  
Voltage Electron ◽  
Variable Voltage ◽  
New Instrument ◽  
Performance Specifications ◽  
Electron Microscopes ◽  
Point To Point

The Atomic Resolution Microscope (ARM) is one of two unique high voltage electron microscopes at the Lawrence Berkeley Laboratory's National Center for Electron Microscopy (NCEM). This paper reports on the latest results from this new instrument which was manufactured by JEOL, Ltd. to the performance specifications of the NCEM, delivered in January of 1983, and soon to be open to access by the entire microscopy community. Details of its history and development are given in reference 1; its performance specifications are reviewed below.Adopting as a design definition for resolution the first zero crossover of th% phase contrast transfer function at Scherzer defocus, the ARM (Fig. 1) maintains 1.7Å point-to-point resolution over its 400kV to 1000kV operating range. Consequently the microscope can be tuned to a voltage which is below the threshold for knock-on damage in a specimen and used to directly image its contiguous-atom structure. The key to this variable-voltage, high-resolution performance is a top-entry objective stage, which, in addition to ± 40° biaxial tilting, incorporates a height (Z)-control to alter specimen position within the objective lens.

Electron Microscopic Observation of Crystal Lattice Images

1972 ◽  
Vol 30 ◽  
pp. 548-549
Author(s):  
Tsutomu Komoda
Keyword(s):  
Electron Microscope ◽  
Spherical Aberration ◽  
Electron Microscopic Observation ◽  
Chromatic Aberration ◽  
Operating Conditions ◽  
Optimum Operating ◽  
Objective Lens ◽  
Electron Microscopic ◽  
Electron Microscopes ◽  
Lattice Resolution

Electron microscope images of crystal lattices have been observed by many authors since the first achievement by Menter in 1956. During these years, the optimum operating conditions with electron microscopes have been investigated for the high resolution lattice imaging. Finally minute lattice spacings around 1 Å have been resolved by several authors by using contemporary instruments. The major lattice planes with low index in crystals are almost within a range of spacing capable to be resolved by electron microscopy (1-3 Å). Therefore, the observing techniques are now essential for practical studies in the area of crystallography as well as metal physics.Although the point to point resolution of the electron microscope is restricted due to the spherical aberration of the objective lens in addition to the diffraction, the lattice resolution is mainly limited due to the chromatic aberration under the normal illumination.

High Voltage Microscopy of Thick Specimens

1968 ◽  
Vol 26 ◽  
pp. 322-323
Author(s):  
Raymond K. Hart
Keyword(s):  
High Voltage ◽  
Effective Means ◽  
Chromatic Aberration ◽  
High Voltage Electron Microscopy ◽  
Voltage Electron ◽  
Physical Problems ◽  
Small Constant ◽  
Anomalous Transmission ◽  
Electron Microscopes ◽  
Image Production

The aspect of high voltage electron microscopy which makes it inviting to solve both biological and physical problems is the ability of this technique to probe thicker specimens and at higher resolution than is currently possible with conventional electron microscopes. Naturally, there will be a thickness limit above which an electron beam will cease to be an effective means of obtaining useful microscopical data. The ultimate limit will be determined by the specimen induced chromatic aberration, resolution, contrast processes, and transmitted intensity available for image production.Recently Uyeda and Nonoyama have determined the maximum usable thickness of molybdenite for operating voltages up to 1.2 MeV. They showed that this thickness is approximately proportional to kβ2, where k is a small constant and β is the ratio of the velocity of an electron to that of light. Aluminum has also been observed to follow this β2 relationship. Even thicker specimens have been viewed with fair clarity, indicating that anomalous transmission effects can occur in crystalline material. These are thought to be due to directional dependence of the absorption coefficient. For aluminum, the thickness of specimens showing anomalous transmission would fall above curve A in Figure 1.

Objective Lens Properties of Very High Excitation

1968 ◽  
Vol 26 ◽  
pp. 320-321 ◽  
Author(s):  
S. Suzuki ◽  
K. Akashi ◽  
H. Tochigi
Keyword(s):  
Thermal Emission ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Technical Advances ◽  
Single Field ◽  
Very High ◽  
Illuminating System ◽  
Excellent Stability

Recently the image quality of the electron microscope has been highly improved, because of technical advances made for the exclusion of mechanical and electrical instabilities in the instrument itself. To further improve the resolution, it is important to minimize the chromatic aberration, as well as the spherical aberration. This is true, even though the accelerating voltage has excellent stability; because of the unavoidable velocity fluctuations of electrons, resulting from thermal emission from the cathode, and the energy-loss in the specimen.Therefore, the specimen should be immersed deeply into the lens field, to make these aberrations small. The result will be very high lens excitation. In 1962, Professor E. Ruska and Dr. W. Riecke had investigated the single field condenser-objective lens at the center of which the specimen is placed. Prior to that, in 1960, Dr. S. Suzuki, one of the authors, had pointed out that this new objective lens, in which the specimen is placed at the image side from the center of the lens field,(of the condenser-objective lens: but no special illuminating system is necessary.

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