摘要:

Experiments have been performed to investigate the useful thickness limits for electron transmission under routine operating conditions for silicon and stainless steel. The criterion adopted for this limit was that thickness at which fringe contrast at faults was destroyed by absorption. The results indicate a roughly linear behaviour of this limit at intermediate voltages, then falling off, but less rapidly than a (v/c)2law. At 1 Mev foils of silicon ∼9 μ and stainless steel ∼2 μ thick are adequately transparent for observing defects. The ultimate thickness limit is determined by contrast and chromatic aberration.

ISSN:0031-8086    

DOI:10.1080/14786436808223188

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The flow of liquid helium II in a channel is considered both when the mean velocity of the superfluid component is zero and when that of the normal component is zero. Possible flow regimes and critical velocities are discussed and in both cases the magnitude and form of the mutual friction are calculated using a simple semi-classical approximation. The discussion is extended to the case of heat currents with no net mass flow and compared with experiment. The observation of two different critical velocities below about 1·6°K, but only one near the Λ-point, is accounted for. The observed mutual friction is found to be in reasonable agreement with the values calculated for high and low temperatures. In the Appendix it is shown that, below the Bose condensation temperature, an ideal Bose gas is a type-II superfluid with vanishing Ginzburg–Landau parameter. The angular-momentum defect of the rotating gas is calculated for use in the main paper.

ISSN:0031-8086    

DOI:10.1080/14786436808223189

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The deformation microstructures associated with aluminium after shock loading and cold rolling at room temperature and at liquid nitrogen temperature are presented and discussed. A high density of point defects is produced by shock loading aluminium and it is observed that vacancy-produced dislocation loops are more numerous than those produced by interstitial clustering. Comparison is made with the response of copper and nickel to shock and it is shown that aluminium does not form dislocation cell structures as these metals do under similar loading conditions. The temperature of deformation has little effect on the microstructure in the low pressure range, but as pressure increases the temperature of deformation becomes more important. Mechanisms for the production of defects are discussed.

ISSN:0031-8086    

DOI:10.1080/14786436808223190

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Fission fragment irradiation of a number of semiconducting materials establishes that permanent tracks are formed only when the conductivity is ≲2 × 103(ohm-cm)−1. The intermittent nature of particle tracks is a characteristic of layer structures and further analysis confirms that there is one ‘defect’ per sandwich plane crossed by the fission particle. The intermittency is ascribed to the reduced energy loss of the fission fragment when it travels in the interplanar channel.

ISSN:0031-8086    

DOI:10.1080/14786436808223191

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Thin films of single crystals of both n-type and p-type silicon contain disordered zones ∼ 50 Å in diameter, discernible in the electron microscope after bombardment with ∼ 1013Ne+ions cm−2. As the dose increases these zones become more numerous until eventually (≳ 1014ions cm−2) they overlap, creating a continuous surface layer which electron diffraction shows to be amorphous silicon. The individual zones disappear on annealing between 400 and 500°C, and at ∼630°C the amorphous layer recrystallizes epitaxially upon the underlying silicon, leaving an array of dislocation loops and dipoles.

ISSN:0031-8086    

DOI:10.1080/14786436808223192

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Epitaxial silicon films have been grown on (100) substrates by the pyrolysis of silane using the molecular beam method. For a given set of growth conditions an induction period, corresponding to removal of the residual surface oxide film as SiO, is required before growth centres form. When subsequently the growth conditions are abruptly changed without switching off the beam, it is found that no further induction period is required (i.e. the surface produced by the first stage is ‘clean') and that a second set of growth centres, commensurate with the new growth conditions, is formed. The conclusions of the previous paper (Joyceet al. 1967) are thus substantiated.

ISSN:0031-8086    

DOI:10.1080/14786436808223193

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Stacking faults and dislocation dissociations on {011} and {121} planes in body-centred cubic lattices are examined. The effect of stress on the threefold dissociation of screw dislocations on {121} planes is studied in detail. A change in configuration occurs on reversal of stress, as in tension and compression experiments; this is used to explain slip asymmetry. Mechanisms for the initiation of glide on {011} and {121} planes and for cross-slip between the two types of planes are suggested. The model can explain the observed dependence of slip planes on orientation, temperature and sense of slip. The behaviour depends critically on the energies of the various types of stacking faults. Conditions for twinning to occur, rather than glide, are also determined.

ISSN:0031-8086    

DOI:10.1080/14786436808223194

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

A minimum observed in the high-angle scattering yield for 415 kev protons incident on single-crystal quartz along directions close to that of the [0001] axis has an angular width indicating channelling of the protons by atomic rows. Comparison between the spectra of protons scattered from the quartz and from vitreous silica shows that the channelled protons could travel a mean distance of approximately 1.75 micron before being scattered into the random mode.

ISSN:0031-8086    

DOI:10.1080/14786436808223195

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

An excess of half-jogs or of isolated vacancies of one sign on the core of an edge dislocation in an alkali halide will result in the dislocation being charged. This charge is calculated for a dislocation in equilibrium with both anion and cation vacancies, using a model which includes the free energy of the defects on the dislocation core as well as the electrostatic energy of the dislocation surrounded by its compensating charge cloud. The theory is illustrated for NaCl at around 700°K. In most cases it is likely that the charge is limited not so much by the electrostatic energy as by the way in which the charge can be accommodated on the dislocation.

ISSN:0031-8086    

DOI:10.1080/14786436808223196

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The electrical conductivity of single crystals of pure and Ba2+and Sr2+-doped CsI has been measured over the temperature range 150–550°C. In pure crystals, grown either from aqueous solution or from the melt, a single region of conduction with an activation energy of 1.37ev is observed in the temperature range above 300°C. Comparison of the conductivity with137Cstracer diffusion measurements indicates that the conduction is predominantly due to anion migration.

ISSN:0031-8086    

DOI:10.1080/14786436808223197

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor