Thickness measurement of cobalt foils using ultramicrotome cuts and electron microscopy

A method of thickness measurement of cobalt foils using transverse ultramicrotome cuts of foils embedded in Araldite is described. A new two-stage gelatine-carbon replica technique was developed. For a foil with inhornogeneous thickness, the method enables an exact determination of the position on the foil of the spot where thickness is measured. Although glass knives only were available for cutting, the accuracy of thickness measurement was better than ±1000 Å.     

FMR in surface oxidized iron single crystals

Ferromagnetic resonance absorption has been observed at room temperature in iron single crystals of whisker type (grown along [100] direction). The surface of the samples has been oxidized in air at 760 Torr at approx. 350 °C for periods up to 240 min. With the increasing degree of oxidation the resonance linewidth broadens and the resonance field shifts to lower values. Moreover, in oxidized samples an additional resonance peak situated above, the main resonance occurs, with intensity, position and linewidth depending on the period of oxidation. The ferrimagnetic resonance absorption in the iron oxide surface layer could be responsible for the occurence of this peak.     

Honeycomb domain structure

A theory is given of a new structure produced when demagnetizing uniaxial single crystals (e.g. magnetoplumbite) in a field normal to thec axis. The experimental results fully support the theory on the assumption that domain structures produced under normal conditions are metastable. Methods are given by which stable structures can be prepared from such metastable ones. On the basis of these results opinions are expressed as to the nucleation of plate and honeycomb structures, produced either by reducing the field from saturation or by cooling below the Curie point.

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In conclusion the authors would like to thank C. Novák from the Institute of Technical Physics, Czechoslovak Academy of Sciences, for checking the calculation of the harmonic analysis and Z. Málek and J. Eousek for carefully reading the paper and for valuable remarks.     

Refined Prediction and Observation of Dislocation Structures in Low Σ Symmetric Grain Boundaries

The grain boundary dislocation structures of three Fe–4at.% Si bicrystals with an additional misorientation of the order of 2° were studied by transmission electron microscopy (TEM), one S5 [001] (310) and two S9 [110] (1 [`1]\overline 1 4). It was found that in the S5 case two Burgers vectors of the structure are not simple basic complete displacement shift lattice (DSC) vectors and are larger than any one of them. This enabled formation of the preferred grain boundary dislocation (GBD) structure with a hexagonal net composed of three screw dislocations and an independent set of parallel edge dislocations. In the S9 case the GBD structure comprises three apparently independent sets of parallel dislocations. The Burgers vectors of two sets could be established as basic DSC vectors in screw and edge orientation, respectively, with respect to the GB plane. For the third set formed by separated groups of four dislocations no corresponding basic DSC vector exists. This case needs further investigation. The previously published table of predicted GBD structures for symmetrical coincidence boundaries up to S11 was refined according to the new results.     

Preparation of metal foils from deformed specimens of small dimensions for transmission electron microscopy

A method of preparing thin metal foils from Fe-Si single crystals suitable for transmission electron microscopy is described in this paper. In contrast to methods used hitherto foils can be prepared from platelets having a very small area (0·07 cm²), the place in the specimen under observation can be located with an accuracy of ±0·1 mm and its orientation with respect to the edges of the platelet can be ascertained.     

Etching of slip produced antiphase domain boundaries in iron-silicon alloys

A method for revealing the slip produced antiphase domain boundaries in nearly stoichiometric ordered Fe₃Si alloys by chemical etching in a solution of HF + H₂O₂ + H₂O is reported. The method was applied to determine the character of superlattice dislocations in strained crystals. Perfect superlattice dislocations were found at the beginning of deformation. Imperfect superlattice dislocations producing antiphase domain boundaries were found at higher deformations.     

Threshold peak structures in the vibrational excitation of HCl by low-energy electron impact

A new model which describes dissociative electron attachment and vibrational excitation for the HCl molecule is proposed. The model is based on ab initio scattering data calculated in the fixed nuclei approximation by Morgan et al. [J. Phys. B 23 (1990) 99]. The cross sections for vibrational excitation exhibit interesting oscillatory structures in the threshold peak region.