Electron Diffraction Photographs Research Articles

Line interaction in X-ray and electron diffraction photographs

The mutual effect of two neighbouring lines on X-ray and electron diffraction patterns is treated theoretically. The theory is in qualitative agreement with the experimental results of electron diffraction photographs (taken on plates) but cannot be used to correct these quantitatively on account of the practical difficulty of making the necessary measurements. In certain X-ray photographs (taken on films) there arises an effect, not treated by the theory, which for low values of Bragg angle acts in an opposite sense. The general conclusion is that for precision measurements close groups of lines should be treated with circumspection or altogether avoided.

ON THE DISCOLOURATION OF ALUMINIUM SURFACE IN BOILING WATER (PRAT 2)

In the Part 1 of this report, we discussed about the conditions in which the discolouration occurres and summarized them in three simple items. In this part, we intended to solve this phenomenon by comparing the sample which is boiled in distillated water (not discoloured) with that boiled in well water (discoloured).The analyses of well-water indicate that PH is 7.5, alkalinity is 301.24ppm, acidity is 17.2apm and iron ion is 0.17ppm. In comparison with this data, the analyses of service-water of Sakai City show that PH is 7.1, alkalinity is 50ppm, acidity is 3.0ppm and iron ion is 0.05ppm.Photo. 2 are the electron diffraction photographs of the surface of aluminum. No. 1 shows the photo. of the bare aluminum before boiling. No. 2 shows the photo. of the bare aluminum which was polished and etched in 20%HNO3. No. 3 shows the photo. of the surface of aluminum after boiling in the well-water. No. 4 shows that after boiling in the distillated water. In comparison No. 3 with No. 4, we found the remarkable difference, but from this photographs we could find no clew of discolouration. We detected, however, that the crystalline alumina was formed on the sarface of aluminum which was boiled in the distillated water.From the results of the Part 1 and the analyses of well-water, the factor of discolouration seemed to be the iron ion included in the well-water. Then, we examined the discolouration of the samples that was boiled in the distillated water in which the small amount of FeSO4 or FeSO3 was contained. The results was negative as shown in Photo. 3. Namely, no discolouration was occurred before the concentration of iron ion reached to 1, 000mg/l. As the concentration of iron ion is 0.17mg/l in the well-water, however, the discolouration seemes to be not the simple action of iron ion as above experimeht, as if iron ion may be the factor of discolouration.Moreover, the next experiment certainly indicates that the mechanism of the discolouration is not the simple substitution of iron ion for aluminum ion. The experiment included that two aluminum samples were immersed in the well-water and conected to the each pole of the D. C. source (1V and 2V) and then boiled for 1 hour. For the results, the anode aluminum is more blackened than cathode one as shown in the Photo. 4. From this results, the discolouration seems to occur rather by adsorption than by substitution.We measured the single electrode potential of samples refered to Pt and solutional current in boiling distillated water and well-water, etc. Fig. 1-4 shows the results. From this curve also, we could not yet point out the factor of this phenomenon.Finally, we examined the corrosion resistance of the samples which were boild in the distillated water and well-water. Thee results are shown in Fig. 5-7. From this results, it seems to be say that the sample boiled in the distillated water is most resistant to any corrosive solution but the discoloured sample boiled in the well-watter is more resistant to the alukali solution than the bare aluminum, although it has the lowest resistance to the acid solution and 3%NaCl solution. From these facts, again, it seems to be reasonable to suppose that the blackning factor may be the iron ion.

Optical demonstration of electron-diffraction effects due to small particle size

1. In a recent paper by Rees & Spink (1950), 'The shape transform in electron diffraction by small crystals', photographs are reproduced showing the reflexions on the 1120 ring of zinc oxide (ZnO). They show clearly that each reflexion on the ring is accompanied by a number of subsidiary maxima, which extend in a radial direction, perpendicular to the ring circumference. As set forth in the paper, these maxima are due to the fact that the individual crystallites are thin needles of diameter 100-500A., considerably elongated in the direction of the hexagonal axis.~ 'The shape transform of such crystals in reciprocal space will therefore extend appreciably only in the reciprocal-lattice plane normal to c*, and the resulting diffractions will be streaked at angles determined by the orientation of the crystal with respect to the beam and the indices of the particular reflexion.' Similar effects in ZnO photographs were observed by Hfllier & Baker (1946) and are also visible in the accompanying photograph of ZnO~: (Fig. 1 (a)). I t shows the elongation of the individual spots (the division in subsidiary maxima is not so well visible), and moreover the varying direction of the striae with regard to the corresponding diffraction circle. If we restrict ourselves to the innermost circles with indices (10i0), (0002), (10il), (10i2) and (11~0), we see that the individual striae have directions respectively perpendicular [for (10i0) and (1150)], parallel [for (0002)] and inclined [for (1011) and (10i2)] to the diffraction circles. This is indicated once again in a schematic way in the accompanying drawing (Fig. 1 (b)). 2. This remarkable effect can be illustrated in a ' qualitative' way by means of the apparatus for optical demonstration of electron-diffraction photographs, as constructed several years ago by the author in collaboration with Ploos van Amstel (Burgers & van Amstel, 1936), With its help the understanding of complicated geometrical features of diffraction photographs can often be facilitated. The principle of the demonstration is based on the

Structure of Amorphous Aluminium Oxide Films

ALUMINIUM generally is covered with an oxide layer which gives excellent protection against corrosion. Preston and Bircumshaw1 and other workers, using the electron diffraction method, showed that the layers are not crystalline. Their electron diffraction photographs show two diffuse rings which have not yet been explained satisfactorily. In air and at temperatures below the transition into the crystalline phase, the oxide layer grows very slowly, and only up to about 100 A. in thickness. Consequently, as the layer is too thin for X-ray methods, electron diffraction techniques have to be used.

Internal Motion and Molecular Structure Studies by Electron Diffraction. III. Structure of CH2CF2 and CF2CF2

The interatomic distances and vibrational amplitudes projected on the lines connecting pairs of atoms at equilibrium have been determined for CH2CF2 and CF2CF2 by an objective procedure for analyzing electron diffraction photographs. Distances involving hydrogen atoms have been evaluated and the procedure for resolving radial distribution peaks involving more than one distance is illustrated. The effects on the accuracy of the method of various characteristics such as sample spread and multiple scattering have been analyzed.

Internal Motion and Molecular Structure Studies by Electron Diffraction. II. Interpretation and Method

The application of a recently developed objective procedure to the analysis of electron diffraction photographs from more complex molecules is discussed in terms of the further development of the details of some of the theoretical and experimental aspects of the procedure. The topics discussed are the physical significance of measured vibrational amplitudes, the method for drawing a background line, the calibration of photographic plates, and the computation of intensity curves by means of IBM machines.

An Electron Diffraction Investigation of the Structures of Neopentyl Chloride and Silico-Neopentyl Chloride: The Determination of Intensities through the Use of a Rotating Sector

Constructional details and operational data on an electron diffraction apparatus, in which a rotating sector has been incorporated, are presented. Its range of application and limitations are listed, and methods for the reduction of microphotometer records are discussed. Electron diffraction photographs of neopentyl chloride and silico-neopentyl chloride were taken with and without sectors. Their structures were deduced by a combination of the visual and photometric procedures. Attempts were made to estimate quantitatively the equivalent temperature factors for libration about the C–C and Si–C bonds. Best values for the interatomic distances and their possible interpretations are presented in the concluding section.

Determination of the crystal structure of gold leaf by electron diffraction

It is found that the radii of the rings of Debye-Scherrer electron-diffraction photographs obtained from gold leaf are not in exact agreement with the theoretical values. This is ascribed to the crystal lattice being distorted by surface-tension forces.

The Use of Punched Cards in Molecular Structure Determinations II. Electron Diffraction Calculations

Special files of punched cards for use with the electrical accounting machines of the International Business Machines Corporation in evaluating the Fourier sums and integrals used in the determination of the structure of gas molecules from electron diffraction photographs are described.

Structure of Graphite

Laidler and Taylor1 directed attention to the presence of lines in the X-ray diffraction photographs of graphite which could not be explained by the structure proposed by Bernal2, and by Hassel and Mark3: these lines are given by graphites from many different sources, natural and artificial. Similar extra lines on electron diffraction photographs of graphite had been observed by Finch and Wilman4. Edwards and Lipson5 thought that they may be caused by anomalies in the structure of graphite similar to those found in cobalt6, but occurring at regular intervals, and proposed a new structure which would account for these extra lines7. In this, the flat, honeycomb net planes are stacked parallel to each other, but instead of having the ababab sequence of the Bernal structure, they have an abcabc sequence: this gives a unit cell with a c-axis one and a half times the usual one. From intensity data they calculated that this new structure represented about 14 per cent of the graphite, the remainder being made up of 80 per cent of the ordinary structure and 6 per cent of a disordered structure. It is interesting to note that this new structure was the first structure suggested for graphite, by Debye and Scherrer8 in 1917.

LXIII. The precision of measurement of broad spectrum lines, with special reference to electron-diffraction photographs

Abstract The factors affecting the precision of measurement of the position of spectrum lines by visual and microphotometric methods are discussed. A statistical study of an extensive set of data shows that as a useful working rule the standard deviation of a single reading of the position of a line by means of a measuring microscope may be taken as 0-3 times the square root of the line width, if all lengths are measured in microns, whereas the standard deviation of a micro-photometer reading is about half this. The systematic errors of such measurements and methods for their determination are also discussed. The validity of these estimates of systematic and random error has been confirmed by a comparison of the radii of electron-diffraction circles with theory.

Molecular Structure of Nitrogen Dioxide and Nitric Acid by Electron Diffraction

New electron diffraction photographs have been taken of NO2 extending the region previously investigated to include larger angles of scattering. An interference ring was found at (1/λ) sin ½θ = 0.49 followed by another ring appearing at 0.94 as determined by visual measurements. The outer portion of the pattern consists of two rather broad rings and two well-defined minima. Theoretical intensities of scattering were computed for various nitrogen valence angles, assuming the positions of the two oxygens to be equivalent. The best fit, and probably the correct structure, gives the angle O–N–O = 130±2° with the N–O distance 1.21±.02A. Photographs were obtained from pure nitric acid vapor at 70°—85°C. The interference maxima were measured visually as far out as the eighth maximum at (1/λ) sin ½θ = 1.83; a prominent minimum was seen at 1.54. Theoretical intensities were computed for various likely models, disregarding the scattering by the hydrogen atom. Good agreement was obtained for a planar model having an NO2 group with the same structure found for nitrogen dioxide. The third oxygen atom O′ is located at a distance of 1.41±0.02A from the nitrogen atom and equidistant from the other oxygen atoms. A model having the nitrogen atom slightly out of the plane containing the oxygen atoms also gave good agreement with the experimental results. This model however is considered less probable in view of Raman spectra data which apparently require a planar structure for O′–NO2.

The Radial Distribution Method in Electron Diffraction

A new radial distribution function for use in interpreting the electron diffraction photographs of gas molecules has been obtained. Instead of replacing the inverted Fourier integral by a sum the integration is performed by assuming that the shapes of the maxima and minima are those of cosine functions. The amount of scattering matter r2D(r) is calculated rather than the density D(r). Comparison between radial distribution functions calculated by this method and by other methods is made for a diatomic molecule, a nonlinear triatomic molecule (to test resolving power), a linear triatomic molecule and carbon tetrachloride.

Internuclear Distances inSe2,Te2, and HgCl by Electron Diffraction

Electron diffraction photographs have been obtained from the gas molecules ${\mathrm{Se}}_{2}$, ${\mathrm{Te}}_{2}$, and HgCl. The internuclear distances found for ${\mathrm{Se}}_{2}$ and ${\mathrm{Te}}_{2}$ were 2.19\ifmmode\pm\else\textpm\fi{}0.03A and 2.59\ifmmode\pm\else\textpm\fi{}0.02A, respectively, while for HgCl a separation of 2.23\ifmmode\pm\else\textpm\fi{}0.03A was obtained. Additional photographs were taken of Hg${\mathrm{Cl}}_{2}$ indicating an Hg-Cl distance of 2.27\ifmmode\pm\else\textpm\fi{}0.03A near to the above value for HgCl. Comparison is made with band spectrum data on the internuclear distances for ${\mathrm{Se}}_{2}$ and ${\mathrm{Te}}_{2}$.

Interatomic Distances of the Alkali Halide Molecules by Electron Diffraction

A determination of the interatomic distances of the alkali halide gas molecules has been made by the electron diffraction method. Heating the salts to a temperature of approximately 1200\ifmmode^\circ\else\textdegree\fi{}C provided a molecular beam of sufficient density to give electron diffraction photographs. The nuclear distances were obtained from visual measurements of the interference maxima. Data from ${\mathrm{I}}_{2}$ and ${\mathrm{Cl}}_{2}$ provided a calibration of the visual measurements since the internuclear distances for these molecules are well known from band spectra. The interatomic distances for the sodium, potassium and rubidium halides were found to be about 10 percent less than the corresponding known distances in the crystal lattice. For the case of the caesium halides the distances obtained were approximately 14 percent smaller than the separations found in the crystals. Tables showing complete data on twelve molecules are given.

The Molecular Structure of P4O6, P4O8, P4O10 and As4O6 by Electron Diffraction

Molecular structures of P4O6 and As4O6 were determined from electron diffraction data. P4O6 was found to have the symmetry of the point group Td with an angle P–O–P of 128.5±1.5°, and a P–O distance of 1.67±0.03A. In this structure the phosphorus oxygen distances and the phosphorus valence angles were preserved with resulting deformation of the oxygen valence angle. The separation of the arsenic atoms in As4O6 was found to be 3.20±0.05A. Because of the predominant scattering of the arsenic atoms it was difficult to determine the oxygen valence angle, As–O–As. Values of 120°, 127.5° and 140° gave approximate agreement between the observed and calculated positions of maxima. Electron diffraction photographs obtained from P4O10 differ considerably from those found for P4O6. It was not possible to explain all of the features of the P4O10 diffraction pattern by a model having the symmetry of the point group Td and it is thought that the structure might be one of lower symmetry. Data were obtained on P4O8 which indicated that it has approximately the same electron diffraction pattern as P4O10.

An Extension of the Analytic Method of Analysis of Electron Diffraction Photographs of Gases

An Extension of the Analytic Method of Analysis of Electron Diffraction Photographs of Gases

Texture of thinly rolled tungsten foil

Electron diffraction photographs of very thinly rolled tungsten foil show the presence of a pronounced rolling texture, the crystallites lying with a cube plane parallel to the plane of the foil and a cube edge (with very little spreading) at 45° to the direction of rolling. On oxidation, an oxide layer is formed consisting of crystallites oriented at random.

An Apparatus for "Optical" Demonstration of some Geometrical Features of Electron Diffraction Photographs

Article An Apparatus for "Optical" Demonstration of some Geometrical Features of Electron Diffraction Photographs was published on December 1, 1936 in the journal Zeitschrift für Kristallographie - Crystalline Materials (volume 95, issue 1-6).

The Crystal Structure of Polonium by Electron Diffraction

Electron diffraction photographs (λ=0.062A) were obtained from about 10—7 g of polonium that had been volatilized in a stream of hydrogen and condensed over an area of about 3 mm2 on a thin collodion film. Diffraction patterns were also obtained from bismuth and tellurium since it was expected that polonium would have a similar crystal structure. Analysis of these patterns shows that the structure of polonium closely resembles that of tellurium, the lattice being pseudohexagonal with a=4.25A, c=7.06A, or 14.12A, and the calculated density 9.39 assuming 3 Po in the pseudo unit of structure. The true lattice is probably monoclinic with a=7.42A, b=4.29A, c=14.10A and β quite close to 90°, a suggested value being β=92°; the calculated density for 12 Po in the unit of structure is 9.24. A structure, based upon the space group C23–C2, in which each polonium atom has four nearest neighbors gives moderate agreement between observed and calculated intensities of reflection.