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 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.

Accurate measurements of mean inner potential of crystal wedges using electron holography

1992 ◽  
Vol 50 (1) ◽  
pp. 134-135
Author(s):  
M. Gajdardziska-Josifovska ◽  
M. R. McCartney ◽  
J. K. Weiss
Keyword(s):  
Phase Change ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Electron Wave ◽  
Flat Surfaces ◽  
Numerical Reconstruction ◽  
Digital Holograms ◽  
The Mean ◽  
Energy Dependent ◽  
Magnetic Electron

The phase of an electron wave which has interacted with a material is measured in electron holography experiments with respect to a coherent reference wave which has travelled through vacuum. In non-magnetic electron-transparent materials, and under kinematical diffracting conditions, the phase change (Δφ) of the transmitted electron wave depends only on the thickness (t) and the mean inner potential (Ui) of the material: Δφ = c |Ui| t; c being an energy-dependent constant. This phase change measured from electron holograms has been used previously to determine the mean inner potential of amorphous and polycrystalline films of known thicknesses. Refraction effects in RHEED patterns have also been used to determine the mean inner potential of several crystals with flat surfaces. The reported accuracies in these studies have ranged from 2.5% to 9.5%, although uncertainties in specimen thickness and the unknown effects of surface contamination and/or reconstruction are very likely sources of systematic errors. This paper shows that numerical reconstruction of digital holograms, combined with use of cleaved crystal wedges, enables measurement of the mean inner potential of crystals with enhanced accuracy.

Direct imaging of spatially varying potential and charge across internal interfaces in solids

1995 ◽  
Vol 53 ◽  
pp. 316-317
Author(s):  
V. Ravikumar ◽  
R. P. Rodrigues ◽  
V. P. Dravid
Keyword(s):  
Electrostatic Potential ◽  
Defect Density ◽  
Measurement Techniques ◽  
High Energy ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Direct Imaging ◽  
Local Mean ◽  
Spatially Varying

The importance of spatially varying potential (and thus charge) across lattice discontinuities in solids has been recognized in many technologically important systems, especially those containing electrically active interfaces, e.g. electroceramics. The presence of spatially varying potential across electroceramic interfaces has been indirectly deduced and analyzed using predominantly bulk measurement techniques like I-V, C-V curves and impedance spectroscopy. Direct imaging of spatially varying electrostatic potential profile and determination of the sign, magnitude and spatial distribution of the associated interface- and space- charge (and therefore defect density) in electroceramics have remained elusive.We have utilized the technique of transmission high energy electron holography to directly image and quantify the electrostatic potential across grain boundaries (GBs) in SrTiO3, a functional electroceramic. The phase of the exit wave function at the GB region can be altered by : (i) variation in local mean inner potential (related to the change in density of atoms at the GB), (ii) differential diffraction conditions across the interface, (iii) change in the local specimen thickness and, (iv) presence of local electrostatic (electrical charge) and magnetic potential.

Measurement of Polystyrene Mean Inner Potential by Transmission Electron Holography of Latex Spheres

1998 ◽  
Vol 4 (2) ◽  
pp. 146-157 ◽  
Author(s):  
Y.C. Wang ◽  
T.M. Chou ◽  
M. Libera ◽  
E. Voelkl ◽  
B.G. Frost
Keyword(s):  
Phase Image ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Polystyrene Spheres ◽  
Reconstruction Procedure ◽  
A Value ◽  
Transmission Electron ◽  
Phase Images ◽  
The Mean ◽  
Beam Damage

This study describes the use of transmission electron holography to determine the mean inner potential of polystyrene. Spherical nanoparticles of amorphous polystyrene are studied so that the effect of specimen thickness on the phase shift of an incident electron wave can be separated from the intrinsic refractive properties of the specimen. A recursive four-parameter χ-squared minimization routine is developed to determine the sphere center, radius, and mean inner potential (Φ0) at each pixel in the phase image. Because of the large number of pixels involved, the statistics associated with determining a single Φ0 value characteristic of a given sphere are quite good. Simulated holograms show that the holographic reconstruction procedure and the χ-squared analysis method are robust. Averaging the Φ0 data derived from ten phase images from ten different polystyrene spheres gives a value of Φ0PS = 8.5 V (σ) = 0.7 V). Specimen charging and electron-beam damage, if present, affect the measurement at a level below the current precision of the experiment.

Resolution of a Transmitted Electron Image Formed by A Scanning Electron Microscope

1970 ◽  
Vol 28 ◽  
pp. 386-387
Author(s):  
S. Takashima ◽  
H. Hashimoto ◽  
S. Kimoto
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Specimen Thickness ◽  
Probe Diameter ◽  
Transmission Electron ◽  
Electron Image ◽  
Conventional Transmission Electron Microscope ◽  
Scanning Electron

The resolution of a conventional transmission electron microscope (TEM) deteriorates as the specimen thickness increases, because chromatic aberration of the objective lens is caused by the energy loss of electrons). In the case of a scanning electron microscope (SEM), chromatic aberration does not exist as the restrictive factor for the resolution of the transmitted electron image, for the SEM has no imageforming lens. It is not sure, however, that the equal resolution to the probe diameter can be obtained in the case of a thick specimen. To study the relation between the specimen thickness and the resolution of the trans-mitted electron image obtained by the SEM, the following experiment was carried out.

Void-Lattice Formation in Natural Fluorite by Electron Irradiation

1976 ◽  
Vol 34 ◽  
pp. 614-615 ◽  
Author(s):  
L.E. Murr
Keyword(s):  
Electron Microscope ◽  
Electron Irradiation ◽  
Heavy Ion ◽  
High Energy ◽  
Stoichiometric Ratio ◽  
Direct Observations ◽  
Transmission Electron ◽  
Anion Vacancies ◽  
Cation And Anion Vacancies ◽  
Lattice Formation

The production of void lattices in metals as a result of displacement damage associated with high energy and heavy ion bombardment is now well documented. More recently, Murr has shown that a void lattice can be developed in natural (colored) fluorites observed in the transmission electron microscope. These were the first observations of a void lattice in an irradiated nonmetal, and the first, direct observations of color-center aggregates. Clinard, et al. have also recently observed a void lattice (described as a high density of aligned "pores") in neutron irradiated Al2O3 and Y2O3. In this latter work, itwas pointed out that in order that a cavity be formed,a near-stoichiometric ratio of cation and anion vacancies must aggregate. It was reasoned that two other alternatives to explain the pores were cation metal colloids and highpressure anion gas bubbles.Evans has proposed that void lattices result from the presence of a pre-existing impurity lattice, and predicted that the formation of a void lattice should restrict swelling in irradiated materials because it represents a state of saturation.

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.

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