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We have shown that Ni metal particles when melted in the presence of C60 form graphitic layers around themselves with the Ni remaining as pure metal and without any evidence of carbide formation. We have successfully encapsulated particles over several orders of magnitude of size from ∼10 nm to several microns. The process has been observed taking place in real time using transmission electron microscopy (TEM). The process was not observed when graphite powder was used instead of C60 powder and the Ni similarly heated to melting point, using the electron beam. Heating a mixture of Ni and C60 powders together in a conventional manner also produced encapsulated Ni particles. This suggests that the encapsulation method is thermal in nature although the electron beam does offer the ability to control the process for individual particles. Further research has shown that the encapsulation process can also occur at temperatures as low as 800° C by a catalytic route. We have extended the work of heating a metal in the presence of fullerenes and have effectively encapsulated other metals such as Fe, Co, Ho, Cu and Au.

A detailed analysis of the microstructure of layered semiconductor heterostructures is only possible if the interface between the various layers can be accurately located. Microstructural features whose characterisation is dependent on the location of the interface include the planarity and width of the layers, the composition profile and the geometry of misfit dislocations (in the particular case of lattice mismatched heterostructures). We report on an investigation to image, at high resolution in the transmission electron microscope, the interface in an In0.2Ga0.8As/GaAs structure grown by molecular beam epitaxy. The difficulty in locating the interface, due to similarity in electron optical behaviour of GaAs and In0.2Ga0.8As when imaged in a <110> direction, was overcome by incorporating into the structure a “marker layer” of AlAs two unit cells thick (11.4 Å in total) between the GaAs and the In0.2Ga0.8As layers. Lattice fringe images of an In0.2Ga0.8As/AlAs/GaAs structure are presented which show, at near atomic resolution, the location of the misfit dislocations relative to the In0.2Ga0.8As/GaAs interface.

The separation of Shookley partial dislocations in Si and Ge has been measured for dislocations at and near screw orientation using the weak-beam method of electron microscopy. The separations appear to fall into two categories. The first category has dissociations which agree with those expected from previous measurements for dislocation orientations above 30°, and the stacking fault between the partials is intrinsic in character. The second category has dissociations which are wider than those in the first category, and the stacking fault is extrinsic in character. A model to explain these observations is proposed.

A study is made of the accuracy with which two-beam lattice fringe images of modulated structures can be interpreted, with particular reference to spinodally decomposed alloys. The dependence of the image upon foil thickness, lens parameters and atomic segregation is discussed and the importance these parameters have upon similar images from any region of slowly varying interplanar spacings is outlined.

Basal dislocations in CdS have been studied using the weak-beam method of electron microscopy. Networks of dissociated nodes and long lengths of dissociated dislocations were observed, from which the stacking fault energy was determined to be γ = 85 ± 21 mJ m-2. Dissociated dislocations were observed gliding while dissociated, both partials being visible during the motion. This motion was recorded on video tape, and shows conclusively that the dislocations glide while dissociated.

We have prepared and studied seventeen thin films ranging in composition from pure silver to pure magnesium fluoride. Using mass thicknesses based on quartz crystal oscillators and physical thicknesses obtained from a stylus profilometer, we have measured the void volume fraction of the films as a function of their composition. We have shown the Ag–MgF_2 system to be capable of incorporating a high volume fraction of voids. We report on the results of electron microscope studies of the films, which show the dependence of film microstructure on composition, thickness, and the nature of its substrate.

Multislice calculations have been performed to obtain weak beam images for both extrinsic and intrinsic inclined stacking faults in silicon. A comparison of these results with results from kinematical and two-beam column approximation calculations is made. The multislice results are found to be different, particularly for the intrinsic case where, unlike the other two calculation methods, an appreciable asymmetry between ± g image pairs is predicted. This is thought to be due to the better modelling in the multislice calculation of the atomic potential in the region of the fault.The effects of small tilts (i.e. changes in excitation error) and beam divergence on the intrinsic stacking fault contrast are also investigated using the multislice technique. The results indicate that it should be relatively easy to observe experimentally the ± g weak beam image asymmetry predicted above.

The effect of gas-phase doping with boron and phosphorus on the structure of glow-discharge amorphous hydrogenated silicon has been studied by means of energy-filtered electron diffraction. The reduced density function was calculated and the network was found to contract upon doping. At levels of less than 20 at.% neither boron nor phosphorus segregated from the network. At high phosphorus doping levels an amorphous chemically ordered structure corresponding to Si2P was formed. At high boron doping levels, evidence for the presence of boron icosahedra was obtained.

In most previous reports material with corticotrophin releasing factor (CRF) activity has been obtained from hypothalami after extraction with dilute aqueous acid. Such conditions allow substantial proteolytic degradation. By adopting conditions designed to precipitate proteases and by using information on the nature of CRF gained from earlier studies, rapid large scale extraction and partial purification of porcine hypothalamic CRF in high yield was achieved. After extraction with 0·2 m-HCl: acetone (1: 1, v/v), centrifugation and ultrafiltration, considerable preliminary purification of the CRF activity was achieved by adsorption onto carboxymethylcellulose and subsequent elution at increased salt concentration. Following ion-exchange chromatography of the extract on carboxymethylcellulose, CRF activity was obtained in good yield (minimal effective dose of about 1–2 μg/ml) for ACTH release in an in-vitro CRF bioassay utilizing a coupled isolated pituitary cell–adrenal cell system. The data indicated that the previously reported heterogeneous corticotrophin releasing factors of low activity may be a consequence of proteolytic degradation.

Abstract: The critical thicknesses of InxGa1-xAs/GaAs and GaAs/InxGa1-xAs/GaAs strained-layer systems were determined by transmission electron microscopy using the lift-off technique. The onset of misfit dislocation generation has been observed for the first time and the geometries of the misfit dislocations in both uncapped and capped layers correspond to the predicted models. A comparison is given between the predicted and experimental critical thicknesses.

The dissociation widths of extended dislocations in CdTe, CdS and ZnTe have been measured using the weak-beam technique of electron microscopy, for α and β dislocations separately. Values of the stacking-fault energies have been determined. The experimental results agree with the modified ionic charge model of dislocations in the II-VI semiconductors, and not with the pure ionic model.

The motion of α and β dislocations in CdS under the influence of an electron beam has been studied in the transmission electron microscope. The enhanced mobility of the α dislocations with respect to the β dislocations is explained in terms of point-defect locking, and the observations give further evidence that the dislocations are of the glide set. The observed dislocation vibration is explained in terms of the interaction of charged double kinks with the dislocation line.

The weak-beam technique of electron microscopy has been used to investigate plate-like G.P. zones in aluminium-copper alloys. For aluminium-1-48 and 3-97 wt% copper alloys aged at 80, 100 and 130°C, G.P. (I) zones of about 35 to 100 Å in diameter were observed. In dark-field images, using the (002) reflection with |s| ⋍ 0-45 to 1-1 × 10-2 Å-1 the zones appeared as pairs of bright lines, the separation of which depends on the magnitude of [s]. Similarly in alloys containing G.P. (II) zones, the images showed pairs of bright lines with a slightly wider separation than the G.P. (1) zone images, sometimes accompanied by a series of closely spaced fringes. The pairs of bright lines were interpreted as corresponding to individual G.P. (I) and (II) zones by comparison with computed image profiles. The experimental images are in good agreement with images computed for a model having a displacement field corresponding to a circular edge loop lying on the habit plane of the G.P. zones, with a Burgers vector equal to 0.2o, where аo, is the lattice parameter of aluminium. These results are compared with Gerold's model of G.P. zones.

The disappearance of microtwins in the high- Tc, superconductor Y1Ba2Cu3O7-x under the influence of electron irradiation is reported, and is shown to occur when the structure transforms from the orthorhombic to the tetragonal phase. Convergent-beam electron diffraction studies establish the crystallography of this transformation. The observations are explained in terms of an increase in x under electron irradiation. The space group of the orthorhombic structure is determined as Pm2m.

The structure of amorphous alloy films of a-Si1-xCx: H has been investigated as a function of x using energy-filtered electron diffraction. The films were prepared by d.c. magnetron plasma deposition from mixtures of silane and methane. Electron-energy-loss spectroscopy was used to determine film composition and to measure the plasmon frequency as a function of x. A film of a-Sic prepared by vacuum evaporation was also studied. For plasma-deposited films with x < 0·5, the radial distribution function shows peaks corresponding to C-C, Si-C and Si-Si bonding and also shows that carbon substitutes for silicon in a random tetrahedral network with some carbon-carbon bonding. For x > 0·5 the radial distribution function shows major peaks corresponding to C-C and Si-C bonding, with no observable Si-Si bonding. The presence of regions rich in carbon is inferred from this and from the plasmon results. For x = 1 the films show a structure in which the degree of fourfold bonding increases with substrate temperature. The a-Sic film shows only silicon-carbon bonding, in agreement with published work.

A detailed analysis of the microstructure of layered semiconductor heterostructures is only possible if the interface between the various layers can be accurately located. Microstructural features whose characterisation is dependent on the location of the interface include the planarity and width of the layers, the composition profile and the geometry of misfit dislocations (in the particular case of lattice mismatched heterostructures). We report on an investigation to image, at high resolution in the transmission electron microscope, the interface in an InGaAs/GaAs structure grown by molecular beam epitaxy. The difficulty in locating the interface, due to similarity in electron optical behaviour of GaAs and InGaAs when imaged in a 〈110〉 direction, was overcome by incorporating into the structure a 'marker layer' of AlAs two unit cells thick (11.4 Å in total) between the GaAs and the InGaAs layers. Lattice fringe images of an InGaAs/AlAs/GaAs structure are presented which show, at near atomic resolution, the location of the misfit dislocations relative to the InGaAs/GaAs interface. [ABSTRACT FROM AUTHOR]

Using standard imaging techniques of electron microscopy it is not possible to resolve the partial dislocations having the equilibrium separation for dissociated dislocations in the pure face-centred cubic metals. Consequently the stacking-fault energy γ cannot be determined from direct measurements of the separations of the partials. In this paper it is demonstrated that such determinations are possible using the weak-beam method of electron microscopy. The separations of Shockley partial dislocations in silver and copper have been measured, as a function of dislocation line orientation, using this method. From these measurements, the values γsilver= 16·3+1·7 erg cm-2 and γcopper= 41±9 erg cm-2 have been obtained from analyses based on anisotropic elasticity theory.

A method for determining the position of dislocation lines accurately from dislocation images is reported and applied to the case of measuring the separation of partial dislocations. A theoretical analysis of the method is given, and the predictions verified by many-beam computed image profiles. The separation of partial dislocations in Cu + 10at. % Al has been determined using the method. The separation was found to be 120±20 Å. Other applications of the method are suggested.

Recently several very clear lattice fringe images have been published in which the perturbing influence of lattice defects is evident in the form of bending and terminating fringes. Detailed analyses of these images have been given, based on the assumption that there exists a one-to-one correspondence between fringe distribution and lattice plane distribution. From studies of the properties of calculated images, doubt has been cast upon the validity of such a straightforward interpretation. Analysis of these calculated images suggested that a change in the diffraction geometry could produce changes in the number of terminating fringes and in the fringe bending which were not related to the lattice plane geometry in any simple way. In this paper a summary of the predicted image properties arising from the calculations is given. By examining lattice fringe images of inclined dislocations in deformed Ge, these properties are verified experimentally. As a result it is shown that it is not correct to analyse fringe images on the basis of a one-to-one correspondence with lattice planes because the fringe distribution and number of terminating fringes are dependent upon the diffraction geometry.

The 'weak-beam' technique of Cockayne, Ray and Whelan (1969) for imaging dislocations in the electron microscope has been applied to dislocations in silicon. These are shown to be dissociated into partial dislocations, the dissociation width corresponding to a stacking-fault energy of about 55 erg cm-2.

The weak-beam technique of electron microscopy (Cockayne, Ray and Whelan 1969) has been used to image the fourfold dissociation of superlattice dislocations in a DO3-ordered Fe-26 at.% Al alloy. Values of 77±12 and 85±16 erg cm-2 have been obtained for the first and second nearest-neighbour antiphase boundary energies, respectively.

The 'weak-beam' technique of Cockayne, Ray and Whelan (1969) for resolving very closely spaced dislocations in the electron microscope has been applied to the dissociation of BZ-type superlattice dislocations in highly ordered Fe-35 at. % Al. By plotting the separation of the partials as a function of orientation a value of 105±15 erg om-2 has been obtained for the antiphase boundary energy.