An Ultra-High-Resolution Objective Lens for a 200-kV TEM

High resolution TEM imaging has been well established as superb technique for obtaining structural information about materials on an atomic scale. Trends in equipment for high resolution imaging have progressed to the stage where point resolutions below 2 Å can be obtained at 200 kV. This paper describes such a new objective lens for the Philips CM20 Transmission Electron Microscope.In designing a new objective lens, several parameters have to be taken into account. Not only should the coefficient of spherical aberration of the objective lens be minimised, the lens should also allow considerable tilting of the specimen in two directions. The lens should be compatible with X-ray analysis. And last but not least, the design of lens must ensure that the heat transfer of the lens to the specimen environment is minimised.

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High-Resolution Imaging with an Aberration-Corrected Transmission Electron Micrscope

Microscopy and Microanalysis ◽

10.1017/s1431927600030592 ◽

2001 ◽

Vol 7 (S2) ◽

pp. 904-905

Author(s):

M. Lentzen ◽

B. Jahnen ◽

C.L. Jia ◽

K. Urban

Keyword(s):

High Resolution ◽

Phase Contrast ◽

Spherical Aberration ◽

Spatial Coherence ◽

Objective Lens ◽

Pass Band ◽

High Resolution Imaging ◽

Resolution Imaging ◽

High Level ◽

Correction System

In electron microscopy high-resolution imaging of finest object structures is generally hampered by the influence of aberrations of the lens system, especially the high spherical aberration of the objective lens. The delocalization of contrast details induced by aberrations is especially strong for microscopes equipped with a field emission gun providing a high spatial coherence. in recent years a prototype of an aberration correction system has been constructed by Haider et al., following a suggestion by Rose, consisting of two hexapole elements and four additional round lenses. The correction system was adapted to a Philips CM 200 FEG ST microscope with an information limit of 0.13 nm. The alignment is carried out using aberration measurements deduced from Zemlin tableaus. By appropriately exciting the hexapole elements it is possible to reduce or even fully compensate the spherical aberration of the objective lens.With the freedom of a variable spherical aberration Cs new operation modes can be accessed that are not available in standard microscopes. with Cs = 0 and defocus Z = 0 pure amplitude contrast occurs, together with a vanishing contrast delocalization; phase contrast with a single, narrow pass-band up to the information limit can still be achieved by Z = ±7 nm, which introduces a delocalization of R = 0.13 nm. with Cs = 97 μm and Z = −18 nm the broad Scherzer pass-band for phase contrast can be extended to the information limit, with R = 0.35 nm. For the CM 200 Cs = 43 fim and Z = −12 nm still produces a high level of phase contrast, comparable with the extended Scherzer pass-band, but with R = 0.08 nm only. in the latter mode Scherzer’s defocus equals Lichte's defocus of least confusion.

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The Optimum CS Condition for High-Resolution Transmission Electron Microscopy

Microscopy and Microanalysis ◽

10.1017/s1431927600037673 ◽

2000 ◽

Vol 6 (S2) ◽

pp. 1036-1037

Author(s):

Michael A. O'Keefe

Keyword(s):

Electron Microscope ◽

High Resolution ◽

Transmission Electron Microscope ◽

Phase Transfer ◽

Structural Information ◽

Spherical Aberration ◽

Phase Changes ◽

Optical Systems ◽

Objective Lens ◽

Transmission Electron

High-resolution electron microscopists are familiar with the concept of an “optimum defocus” for obtaining highresolution transmission electron microscope images. Scherzer recognized that it is possible to balance the phase changes imposed by the spherical aberration of the TEM objective lens by adjustments to lens defocus. Selection of this focus condition maximizes the same-phase transfer of structural information carried by electrons scattered from the specimen. The upper limit of spatial frequencies transferred with the same phase change determines the resolution of the microscope. The resolution and “optimum defocus” depend only on the electron wavelength of the microscope and the spherical aberration coefficient, CS, of its objective lens. Reduction of Cs is the major route to improved resolution.With the advent of electron-optical systems able to generate negative spherical aberration (usually called “Cs correctors“), it has now become feasible to zero-out objective lens Cs in the high-resolution transmission electron microscope.

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High-Resolution Imaging of Coga/GaAs and Eras/GaAs Interfaces

MRS Proceedings ◽

10.1557/proc-159-89 ◽

1989 ◽

Vol 159 ◽

Author(s):

Jane G. Zhu ◽

Stuart McKeman ◽

Chris J. Palmstrøm ◽

C. Barry Carter

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

High Resolution ◽

Molecular Beam Epitaxy ◽

Molecular Beam ◽

Atomic Scale ◽

High Resolution Imaging ◽

Transmission Electron ◽

Resolution Imaging ◽

Interface Structures

ABSTRACTCoGa/GaAs and ErAs/GaAs grown by molecular-beam epitaxy have been studied using high-resolution transmission electron microscopy (HRTEM). The epitactic interfaces have been shown to be abrupt on the atomic scale. Computer simulations of the HRTEM images have been obtained for different interface structures under various specimen and image conditions. Practical problems in the comparison between the simulated and experimental images are discussed.

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X-ray Microanalysis and High Resolution Imaging of Ge-Au-Ni Metal Layers on Gallium Arsenide

MRS Proceedings ◽

10.1557/proc-25-557 ◽

1983 ◽

Vol 25 ◽

Cited By ~ 5

Author(s):

D. Fathy ◽

O. L. Krivanek ◽

J. C. H. Spence ◽

W. M. Paulson

Keyword(s):

High Resolution ◽

Ohmic Contacts ◽

High Resolution Imaging ◽

X Ray ◽

Specific Contact ◽

High Resolution Tem ◽

Order Of Magnitude ◽

Resolution Imaging ◽

Contact Resistivities ◽

Metal Layers

ABSTRACTOhmic contacts to GaAs have been studied using a high resolution TEM, an SEM and a STEM with an energy dispersive x-ray attachment. Two different deposition sequences of the constituent Au-Ge-Ni metals yielded specific contact resistivities that varied by one order of magnitude. Crosssection images of the interface between the GaAs and the metal Au-Ge-Ni layers following alloying showed protrusions at the interface. Contacts with low specific resistivities showed deeper protrusion and also significantly more Ge and Ni in the GaAs.

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High Resolution Transmission Electron Microscopy at Zero Cs

Microscopy and Microanalysis ◽

10.1017/s1431927600022030 ◽

1998 ◽

Vol 4 (S2) ◽

pp. 382-383

Author(s):

Michael A. O'Keefe

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

High Resolution ◽

Transfer Functions ◽

Spherical Aberration ◽

Objective Lens ◽

Transmission Electron ◽

High Resolution Tem ◽

Model Structures ◽

Image Simulations

Now that correctors for objective lens spherical aberration are becoming feasible, questions have been raised about the usefulness of high-resolution transmission electron microscopy at zero Cs and the possible difficulties of interpretation of such images. In general, high resolution TEM images are interpreted either by comparison with simulations from model structures or by contrast transfer functions (CTFs) to determine the weight (and sense) of spatial contributions to images from corresponding diffracted beams. At zero Cs, HREM image simulations will work, but a projected charge density theory should be used (instead of CTF theory) to interpret images. Both theories use approximations; CTF theory relies on kinematic scattering and PCD theory on zero Cs and limited defocus.

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

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100086386 ◽

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.

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