Electron holography of p-n junctions

1996 ◽  
Vol 54 ◽  
pp. 974-975
Author(s):  
B.G. Frost ◽  
D.C. Joy ◽  
L.F. Allard ◽  
E. Voelkl
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Field Emission ◽  
Ccd Camera ◽  
Image Plane ◽  
Reference Wave ◽  
Field Of View ◽  
Control Mode ◽  
Objective Lens ◽  
Electron Holography

A wide holographic field of view (up to 15 μm in the Hitachi-HF2000) is achieved in a TEM by switching off the objective lens and imaging the sample by the first intermediate lens. Fig.1 shows the corresponding ray diagram for low magnification image plane off-axis holography. A coherent electron beam modulated by the sample in its amplitude and its phase is superimposed on a plane reference wave by a negatively biased Möllenstedt-type biprism.Our holograms are acquired utilizing a Hitachi HF-2000 field emission electron microscope at 200 kV. Essential for holography are a field emission gun and an electron biprism. At low magnification, the excitation of each lens must be appropriately adjusted by the free lens control mode of the microscope. The holograms are acquired by a 1024 by 1024 slow-scan CCD-camera and processed by the “Holoworks” software. The hologram fringes indicate positively and negatively charged areas in a sample by the direction of the fringe bending (Fig.2).

The influence of the objective lens current in low magnification electron holography

1995 ◽  
Vol 53 ◽  
pp. 614-615
Author(s):  
B.G. Frost ◽  
D.C. Joy ◽  
E. Völkl ◽  
L.F. Allard
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Field Emission ◽  
Focal Plane ◽  
Reference Wave ◽  
Object Wave ◽  
Objective Lens ◽  
Electron Holography ◽  
Emission Electron

In order to align an electron microscope for low magnification holography we usually completely switch off the objective lens and image the sample by the first intermediate lens. In addition, to achieve a highly coherent electron beam we highly excite the condensor lens resulting in a divergent illumination of the sample and the intermediate lens. Now negatively biasing the fiber of a Möllenstedt type biprism placed between the first an second intermediate lenses of our Hitachi HF-2000 field emission electron microscope creates two virtual sources below the back focal plane of the first intermediate lens. These two sources are necessary to form off-axis holograms. Slightly exciting the objective lens and still imaging the sample by the first intermediate lens results in two major changes in our holograms.First: Due to an electron beam less divergent or even convergent illuminating the first intermediate lens when exciting the objective lens (compare Fig. 1 to Fig.2) the angle β at which object wave and reference wave are superimposed decreases.

Development of A 350-KV Holography Electron Microscope and its Applications

1990 ◽  
Vol 48 (1) ◽  
pp. 222-223
Author(s):  
Takeshi Kawasaki ◽  
Junji Endo ◽  
Tsuyoshi Matsuda ◽  
Akira Tonomura
Keyword(s):  
Thin Film ◽  
Electron Beam ◽  
Electron Microscope ◽  
Field Emission ◽  
Source Image ◽  
Electron Holography ◽  
Magnetic Lens ◽  
Lattice Image ◽  
Gold Thin Film ◽  
Spacing Lattice

The 350 kV field-emission electron microscope shown in Fig.1 has been developed to widen the applications of electron holography. A field emission beam is used because it is very bright at first and monochromatic. However, its brightness deteriorates while passing through accelerating electrodes and condenser lenses because of their spherical and chromatic aberrations. A magnetic lens is installed just below a (310)-oriented tungsten tip. A magnetic lens is used so that the electron source image can be located at the most favorable position between the accelerating tube and the first condenser lens to minimize the aberrations and to increase brightness. The measured brightness (probe current) ranges from 1.4x109 A/cm2/sr (0.37 nA) to 6.7x108 A/cm2/sr (2.2 nA) with 10 μA total emission current at 300 kV.These increased brightness and narrow energy spread of the electron beam enable observing fine spacing lattice fringes in a gold thin film. Lattice fringes of 0.065 nm spacing were actually observed in the electron micrograph shown in Fig. 2. The incident electron beam was along the [001] axis, and the (400) and reflected beams were used to form the fringes. A 0.055 nm spacing lattice image is shown in Fig. 3. These fringes resulted from the interference of the electron beam, with an incident axis from the [111] direction into the gold thin film, by the and diffracted beams. This spacing is the shortest observed to date.

Characterization of a Fixed Beam Electron Microscope with a Field Emission Gun

1976 ◽  
Vol 34 ◽  
pp. 526-527
Author(s):  
Wah Chiu ◽  
Robert M. Glaeser
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Field Emission ◽  
Current Density ◽  
Beam Current ◽  
Beam Current Density ◽  
Objective Lens ◽  
Electron Beam Current ◽  
Beam Electron ◽  
Fixed Beam

One of the objectives of our research program is to obtain a 2.0 Å point to point resolution in a fixed beam bright field electron microscope. The resolution in the fixed beam electron microscope is limited by a number of factors: electron beam coherence, energy spread, objective lens stability, mechanical stability, and specimen stability. This paper presents systematic studies of the mentioned factors in our JEM 100B fixed beam electron microscope equipped with a field emission gun operating at ∼ 1800°K.The most important characteristic of a field emission gun is its high brightness in the emitter source. In order to estimate the brightness at the specimen plane, one needs to measure the electron beam current density and the angle of illumination. The electron beam current density has been measured by means of a lithium-drifted silicon detector located below the normal position of the photographic plates. The angle of illumination can be estimated from the size of the condenser aperture and its distance from the specimen plane.

Applications of electron holography to interference microscopy

1991 ◽  
Vol 49 ◽  
pp. 676-677
Author(s):  
Akira Tonomura
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Field Emission ◽  
Phase Distribution ◽  
Phase Measurement ◽  
Interference Microscopy ◽  
Electron Holography ◽  
Electron Wave ◽  
Interference Fringes ◽  
Fluorescent Screen

Electron-holographic interference microscopy, which provides an image of the phase distribution of an electron wave transmitted through a specimen, has become practical with the development of a field-emission electron microscope. This instrument, increasing the brightness of the electron beam by more than two orders of magnitude, allows biprism interference fringes to be directly observed on a fluorescent screen. The coherence of this microscope's electron beam has enabled phase measurement to a precision of 1/100 of the wavelength, and it even makes dynamical observation possible.

Residual Gas Reaction in the Electron Microscope: II The Design of a Gas-Control Chamber for Quantitative Observations

1969 ◽  
Vol 27 ◽  
pp. 82-83
Author(s):  
Chester J. Calbick ◽  
Richard E. Hartman
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Local Environment ◽  
Chamber Pressure ◽  
Objective Lens ◽  
Ion Pump ◽  
Quantitative Studies ◽  
Precise Knowledge ◽  
Differential Pumping ◽  
And Control

Quantitative studies of the phenomenon associated with reactions induced by the electron beam between specimens and gases present in the electron microscope require precise knowledge and control of the local environment experienced by the portion of the specimen in the electron beam. Because of outgassing phenomena, the environment at the irradiated portion of the specimen is very different from that in any place where gas pressures and compositions can be measured. We have found that differential pumping of the specimen chamber by a 4" Orb-Ion pump, following roughing by a zeolite sorption pump, can produce a specimen-chamber pressure 100- to 1000-fold less than that in the region below the objective lens.

A Field Emission System For Transmission Electron Microscopy

1973 ◽  
Vol 31 ◽  
pp. 298-299
Author(s):  
Michel Troyonal ◽  
Huei Pei Kuoal ◽  
Benjamin M. Siegelal
Keyword(s):  
Electron Microscope ◽  
Field Emission ◽  
Optical System ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Objective Lens ◽  
Electron Optical System ◽  
Cross Sectional ◽  
Transmission Electron ◽  
Emission System

A field emission system for our experimental ultra high vacuum electron microscope has been designed, constructed and tested. The electron optical system is based on the prototype whose performance has already been reported. A cross-sectional schematic illustrating the field emission source, preaccelerator lens and accelerator is given in Fig. 1. This field emission system is designed to be used with an electron microscope operated at 100-150kV in the conventional transmission mode. The electron optical system used to control the imaging of the field emission beam on the specimen consists of a weak condenser lens and the pre-field of a strong objective lens. The pre-accelerator lens is an einzel lens and is operated together with the accelerator in the constant angular magnification mode (CAM).

Atomic resolution AEM (ARAEM) of oxide superconductors

1992 ◽  
Vol 50 (1) ◽  
pp. 74-75
Author(s):  
Vinayak P. Dravid ◽  
H. Zhang ◽  
L.D. Marks ◽  
J.P. Zhang
Keyword(s):  
Electron Microscope ◽  
Field Emission ◽  
Atomic Resolution ◽  
Oxide Superconductors ◽  
Electron Holography ◽  
Analytical Electron ◽  
Analytical Electron Microscope ◽  
Point To Point ◽  
Single Instrument ◽  
Better Than

A 200 kV cold field emission gun atomic resolution analytical electron microscope (ARAEM, Hitachi HF-2000) has been recently installed at Northwestern. The ARAEM offers an unprecedented combination of atomic structure imaging of better than 0.20 nm nominal point-to-point resolution and about 0.10 nm line resolution, alongwith nanoscale analytical capabilities and electron holography in one single instrument. The ARAEM has been fully functional/operational and this paper presents some illustrative examples of application of ARAEM techniques to oxide superconductors. Additional results will be presented at the meeting.

Comparison of freeze-fractured yeast replicas using conventional TEM and low-voltage field-emission SEM

1989 ◽  
Vol 47 ◽  
pp. 74-75
Author(s):  
William P. Wergin ◽  
Eric F. Erbe ◽  
Terrence W. Reilly
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Field Emission ◽  
Low Voltage ◽  
Objective Lens ◽  
Specimen Preparation ◽  
Lens System ◽  
Air Drying ◽  
Preparation Techniques ◽  
Scanning Electron

Although the first commercial scanning electron microscope (SEM) was introduced in 1965, the limited resolution and the lack of preparation techniques initially confined biological observations to relatively low magnification images showing anatomical surface features of samples that withstood the artifacts associated with air drying. As the design of instrumentation improved and the techniques for specimen preparation developed, the SEM allowed biologists to gain additional insights not only on the external features of samples but on the internal structure of tissues as well. By 1985, the resolution of the conventional SEM had reached 3 - 5 nm; however most biological samples still required a conductive coating of 20 - 30 nm that prevented investigators from approaching the level of information that was available with various TEM techniques. Recently, a new SEM design combined a condenser-objective lens system with a field emission electron source.

Performance and applications of the holography electron microscope

1993 ◽  
Vol 51 ◽  
pp. 1078-1079
Author(s):  
Akira Tonomura
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Phase Measurement ◽  
Electron Holography ◽  
Imaging Method ◽  
High Contrast ◽  
Magnetic Lens ◽  
High Brightness ◽  
Holographic Imaging ◽  
Dynamic Observation

Electron holography is a two-step imaging method. However, the ultimate performance of holographic imaging is mainly determined by the brightness of the electron beam used in the hologram-formation process. In our 350kV holography electron microscope (see Fig. 1), the decrease in the inherently high brightness of field-emitted electrons is minimized by superposing a magnetic lens in the gun, for a resulting value of 2 × 109 A/cm2 sr. This high brightness has lead to the following distinguished features. The minimum spacing (d) of carrier fringes is d = 0.09 Å, thus allowing a reconstructed image with a resolution, at least in principle, as high as 3d=0.3 Å. The precision in phase measurement can be as high as 2π/100, since the position of fringes can be known precisely from a high-contrast hologram formed under highly collimated illumination. Dynamic observation becomes possible because the current density is high.

Electron Holography Improving Transmission Electron Microscopy

1990 ◽  
Vol 48 (1) ◽  
pp. 208-209
Author(s):  
Hannes Lichte
Keyword(s):  
Electron Microscopy ◽  
Transfer Functions ◽  
Imaging System ◽  
Spherical Aberration ◽  
Image Plane ◽  
Chromatic Aberration ◽  
Object Wave ◽  
Objective Lens ◽  
Electron Holography ◽  
Wave Aberration

Generally, the electron object wave o(r) is modulated both in amplitude and phase. In the image plane of an ideal imaging system we would expect to find an image wave b(r) that is modulated in exactly the same way, i. e. b(r) =o(r). If, however, there are aberrations, the image wave instead reads as b(r) =o(r) * FT(WTF) i. e. the convolution of the object wave with the Fourier transform of the wave transfer function WTF . Taking into account chromatic aberration, illumination divergence and the wave aberration of the objective lens, one finds WTF(R) = Echrom(R)Ediv(R).exp(iX(R)) . The envelope functions Echrom(R) and Ediv(R) damp the image wave, whereas the effect of the wave aberration X(R) is to disorder amplitude and phase according to real and imaginary part of exp(iX(R)) , as is schematically sketched in fig. 1.Since in ordinary electron microscopy only the amplitude of the image wave can be recorded by the intensity of the image, the wave aberration has to be chosen such that the object component of interest (phase or amplitude) is directed into the image amplitude. Using an aberration free objective lens, for X=0 one sees the object amplitude, for X= π/2 (“Zernike phase contrast”) the object phase. For a real objective lens, however, the wave aberration is given by X(R) = 2π (.25 Csλ3R4 + 0.5ΔzλR2), Cs meaning the coefficient of spherical aberration and Δz defocusing. Consequently, the transfer functions sin X(R) and cos(X(R)) strongly depend on R such that amplitude and phase of the image wave represent only fragments of the object which, fortunately, supplement each other. However, recording only the amplitude gives rise to the fundamental problems, restricting resolution and interpretability of ordinary electron images:

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