Transmission Electron Holography of Polymer Microstructure

1998 ◽  
Author(s):  
Matthew R. Libera
Keyword(s):  
Electron Holography ◽  
Polymer Microstructure ◽  
Transmission Electron

Mean inner potential measurements of polymer latexes by transmission electron holography

1996 ◽  
Vol 54 ◽  
pp. 168-169
Author(s):  
Young-Chung Wang ◽  
Matthew Libera
Keyword(s):  
Refractive Index ◽  
Polymeric Materials ◽  
High Energy ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Phase Imaging ◽  
Rest Energy ◽  
Polymer Microstructure ◽  
Transmission Electron ◽  
Energy Dependent

Because polymeric materials consist primarily of light elements, weak contrast is often observed when imaging polymer microstructure in a transmission electron microscope. Preferential staining of microstructural features by heavy elements such as osmium, ruthenium, or uranium is commonly used to induce amplitude contrast. Because of its ability to recover the entire exit-face electron wavefunction, transmission electron holography raises the possibility of using phase contrast to measure polymer microstructure without the need for heavy-element stains. Under kinematic scattering conditions, the phase shift, ΔΦ, imposed on an incident high-energy electron wave is given by the product of the electron-optical refractive index, neo, and the specimen thickness, t: Δφ=(2π/λ)(neo−1)t. The refractive index is related to the specimen’s mean coulombic (inner) potential Φ0: neo−1 = (e |Φ0|/E) [(E0+E)/(2E0+E)] = CEΦ0 where e is the electron charge, E is the kinetic energy of the incident electrons, E0 is the rest energy, and CE is an energy-dependent constant. Quantitative measurements of Φ0 and neo can be made using holographic phase imaging to determine from specimens of known thickness.

Electron holography in materials science

1991 ◽  
Vol 49 ◽  
pp. 670-671
Author(s):  
Hannes Lichte ◽  
Edgar Voelkl
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Materials Science ◽  
Fourier Spectrum ◽  
Object Wave ◽  
Electron Holography ◽  
Reconstruction Procedure ◽  
Numerical Reconstruction ◽  
Transmission Electron ◽  
Unique Interpretation

The object wave o(x,y) = a(x,y)exp(iφ(x,y)) at the exit face of the specimen is described by two real functions, i.e. amplitude a(x,y) and phase φ(x,y). In stead of o(x,y), however, in conventional transmission electron microscopy one records only the real intensity I(x,y) of the image wave b(x,y) loosing the image phase. In addition, referred to the object wave, b(x,y) is heavily distorted by the aberrations of the microscope giving rise to loss of resolution. Dealing with strong objects, a unique interpretation of the micrograph in terms of amplitude and phase of the object is not possible. According to Gabor, holography helps in that it records the image wave completely by both amplitude and phase. Subsequently, by means of a numerical reconstruction procedure, b(x,y) is deconvoluted from aberrations to retrieve o(x,y). Likewise, the Fourier spectrum of the object wave is at hand. Without the restrictions sketched above, the investigation of the object can be performed by different reconstruction procedures on one hologram. The holograms were taken by means of a Philips EM420-FEG with an electron biprism at 100 kV.

Reconstruction of electron holograms recorded in a non-FEG, non-biprism TEM

1995 ◽  
Vol 53 ◽  
pp. 618-619
Author(s):  
Z.L. Wang
Keyword(s):  
Electron Microscope ◽  
Single Crystal ◽  
Experimental Technique ◽  
Transmission Electron Microscope ◽  
The Other ◽  
Electron Holography ◽  
Transmission Electron ◽  
Coherent Sources ◽  
Imaging Theory ◽  
Normal Specimen

An experimental technique for performing electron holography using a non-FEG, non-biprism transmission electron microscope (TEM) has been introduced by Ru et al. A double stacked specimens, one being a single crystal foil and the other the specimen, are loaded in the normal specimen position in TEM. The single crystal, which is placed onto the specimen, is responsible to produce two beams that are equivalent to two virtual coherent sources illuminating the specimen beneath, thus, permitting electron holography of the specimen. In this paper, the imaging theory of this technique is described. Procedures are introduced for digitally reconstructing the holograms.

Application of electron holography to material science studies on magnetic domain states of small particles

1993 ◽  
Vol 51 ◽  
pp. 1028-1029
Author(s):  
T. Hirayama ◽  
Q. Ru ◽  
T. Tanji ◽  
A. Tonomura
Keyword(s):  
Magnetic Field ◽  
Material Science ◽  
Science Studies ◽  
Phase Distribution ◽  
Carbon Film ◽  
Objective Lens ◽  
Electron Holography ◽  
Transform Method ◽  
Transmission Electron ◽  
Thin Carbon

The observation of small magnetic materials is one of the most important applications of electron holography to material science, because interferometry by means of electron holography can directly visualize magnetic flux lines in a very small area. To observe magnetic structures by transmission electron microscopy it is important to control the magnetic field applied to the specimen in order to prevent it from changing its magnetic state. The easiest method is tuming off the objective lens current and focusing with the first intermediate lens. The other method is using a low magnetic-field lens, where the specimen is set above the lens gap.Figure 1 shows an interference micrograph of an isolated particle of barium ferrite on a thin carbon film observed from approximately [111]. A hologram of this particle was recorded by the transmission electron microscope, Hitachi HF-2000, equipped with an electron biprism. The phase distribution of the object electron wave was reconstructed digitally by the Fourier transform method and converted to the interference micrograph Fig 1.

On the Faceting of Polar Ceramic Surfaces: Microscopy and Holography Studies of MGO(111) Surfaces

1996 ◽  
Vol 54 ◽  
pp. 366-367
Author(s):  
M. Gajdardziska-Josifovska ◽  
B. G. Frost ◽  
E. Völkl ◽  
L. F. Allard
Keyword(s):  
Electron Microscopy ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Electron Holography ◽  
Flat Surfaces ◽  
Transmission Electron ◽  
Excess Surface ◽  
Polar Surfaces ◽  
Salt Structure ◽  
Crystallographic Planes

Polar surfaces are those crystallographic faces of ionically bonded solids which, when bulk terminated, have excess surface charge and a non-zero dipole moment perpendicular to the surface. In the case of crystals with a rock salt structure, {111} faces are the exemplary polar surfaces. It is commonly believed that such polar surfaces facet into neutral crystallographic planes to minimize their surface energy. This assumption is based on the seminal work of Henrich which has shown faceting of the MgO(111) surface into {100} planes giving rise to three sided pyramids that have been observed by scanning electron microscopy. These surfaces had been prepared by mechanical polishing and phosphoric acid etching, followed by Ar+ sputtering and 1400 K annealing in ultra-high vacuum (UHV). More recent reflection electron microscopy studies of MgO(111) surfaces, annealed in the presence of oxygen at higher temperatures, have revealed relatively flat surfaces stabilized by an oxygen rich reconstruction. In this work we employ a combination of optical microscopy, transmission electron microscopy, and electron holography to further study the issue of surface faceting.

Characterization of JEOL 3000f TEM Equipped for Electron Holography

2000 ◽  
Vol 6 (S2) ◽  
pp. 228-229
Author(s):  
M. A. Schofield ◽  
Y. Zhu
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Design Of Experiment ◽  
Electron Holography ◽  
Fringe Spacing ◽  
Interference Fringes ◽  
Transmission Electron ◽  
Careful Design

Quantitative off-axis electron holography in a transmission electron microscope (TEM) requires careful design of experiment specific to instrumental characteristics. For example, the spatial resolution desired for a particular holography experiment imposes requirements on the spacing of the interference fringes to be recorded. This fringe spacing depends upon the geometric configuration of the TEM/electron biprism system, which is experimentally fixed, but also upon the voltage applied to the biprism wire of the holography unit, which is experimentally adjustable. Hence, knowledge of the holographic interference fringe spacing as a function of applied voltage to the electron biprism is essential to the design of a specific holography experiment. Furthermore, additional instrumental parameters, such as the coherence and virtual size of the electron source, for example, affect the quality of recorded holograms through their effect on the contrast of the holographic fringes.

Electron Refraction of Amorphous Nanospheres

1997 ◽  
Vol 3 (S2) ◽  
pp. 1055-1056
Author(s):  
Y.C. Wang ◽  
T.M. Chou ◽  
M. Libera
Keyword(s):  
Refractive Index ◽  
Electron Scattering ◽  
Unit Volume ◽  
High Energy ◽  
Covalent Bonding ◽  
Electron Holography ◽  
High Energy Electron ◽  
Electron Wave ◽  
Transmission Electron ◽  
The Mean

The phase shift imparted to an incident high-energy electron wave in a TEM is related to the specimen’s electron-refractive properties. These, in turn, are related to the electrostatic potential and, by Fourier transform (1), to the electron scattering factors fei(s) for the various atom species i in the specimen and scattering vectors s. The average refractive index is determined by the mean electrostatic (inner) potential, Φo, and can be modelled as Φo = (C/Ω) Σfei(s0) [equation 1] where C = 47.878 (V-Å2) and the summation runs over all of the atoms in the unit volume Ω (2). Calculated fei(s) data are available from the literature (e.g. 3). These calculations have only been done for neutral atoms and some fully ionized cations and anions. They do not account for electron redistribution due to covalent bonding to which Φo is quite sensitive (4).This research is making Φo measurements using transmission electron holography. Holograms were collected using a 200keV Philips CM20 FEG TEM equipped with a non-rotatable biprism (5) and a Gatan 794 Multiscan camera.

Visualization of different carrier concentrations in n-type-GaN semiconductors by phase-shifting electron holography with multiple electron biprisms

Microscopy ◽  
2019 ◽  
Vol 69 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Kazuo Yamamoto ◽  
Kiyotaka Nakano ◽  
Atsushi Tanaka ◽  
Yoshio Honda ◽  
Yuto Ando ◽  
...  
Keyword(s):  
Focused Ion Beam ◽  
Ion Beam ◽  
Phase Shifting ◽  
Active Layer Thickness ◽  
Electron Holography ◽  
Wide Field ◽  
Transmission Electron ◽  
Dopant Level ◽  
Phase Profile ◽  
Phase Resolution

Abstract Phase-shifting electron holography (PS-EH) using a transmission electron microscope (TEM) was applied to visualize layers with different concentrations of carriers activated by Si (at dopant levels of 1019, 1018, 1017 and 1016 atoms cm−3) in n-type GaN semiconductors. To precisely measure the reconstructed phase profiles in the GaN sample, three electron biprisms were used to obtain a series of high-contrast holograms without Fresnel fringes generated by a biprism filament, and a cryo-focused-ion-beam (cryo-FIB) was used to prepare a uniform TEM sample with less distortion in the wide field of view. All layers in a 350-nm-thick TEM sample were distinguished with 1.8-nm spatial resolution and 0.02-rad phase-resolution, and variations of step width in the phase profile (corresponding to depletion width) at the interfaces between the layers were also measured. Thicknesses of the active and inactive layers at each dopant level were estimated from the observed phase profile and the simulation of theoretical band structure. Ratio of active-layer thickness to total thickness of the TEM sample significantly decreased as dopant concentration decreased; thus, a thicker TEM sample is necessary to visualize lower carrier concentrations; for example, to distinguish layers with dopant concentrations of 1016 and 1015 atoms cm−3. It was estimated that sample thickness must be more than 700 nm to make it be possible to detect sub-layers by the combination of PS-EH and cryo-FIB.

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