摘要:

A low‐energy electron diffraction apparatus has been built and used to study the adsorption of simple gases on platinum (100), (110), and (111) faces. Some simple structures formed on various faces are described. Adsorption of oxygen on the (110) face is shown to lead to a rearrangement of the top layer of Pt atoms. On the basis of single scattering it is shown that the adsorbate‐substrate combination leads to reflections to be expected from each lattice considered separately. When double scattering is permitted, reflections appear in positions given by the sums and differences of the reciprocal lattice vectors of the separate lattices. This double scattering or multiple reflection is shown to play an important role in low‐energy electron diffraction. In particular, two sets of complex diffraction patterns formed by oxygen on the Pt (100) face are shown to have an easy interpretation in terms of multiple reflection. The simple oxygen structures formed are rotated with respect to the Pt substrate but form coincidence lattices with it.

ISSN:0021-8979    

DOI:10.1063/1.1713766

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The resonance frequencies of various single crystals of salicylidene aniline were measured for different modes of vibration, and the velocities of sound waves in these materials were deduced. Values are given for the electric equivalent circuit parameters and elastic constants in such crystals.

ISSN:0021-8979    

DOI:10.1063/1.1713767

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Plastic deformation produced by phosphorus diffusion into a (001) silicon surface has been studied by transmission electron microscopy. The lattice parameter differences in regions of steep solute concentration gradient are accommodated by a crossed grid of edge dislocations having Burgers vectora/2[110] anda/2[1¯10]. The long edge dislocations end at nodes, which suggests that they are formed by dislocation reactions between pairs of dislocations that can glide into the crystal on {111} planes.

ISSN:0021-8979    

DOI:10.1063/1.1713768

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Two sources of error are discussed. The first, due to previous plastic flow in one direction, causes an x‐ray line shift whether or not a real macrostress is present, and is due to a particular distribution of microstress. The second source is stacking faults. The first error is unavoidable, but the second can be eliminated by the proper x‐ray technique.

ISSN:0021-8979    

DOI:10.1063/1.1713769

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A study was made of the perfection and the factors controlling perfection of copper crystals grown by a Bridgman technique. Crystals grown from 99.999+% and from (OFHC) copper were acid sawed and polished, and dislocation densities determined by etch pit techniques. The orientation of the growth direction of unseeded crystals of both purities was random. There was a correlation between perfection and growth direction for the 99.999+% copper crystals in that the more perfect crystals had growth direction far from the [111] zone. Dislocation densities as low as 103/cm2, with no subboundaries, were obtained in some of the purer as‐grown crystals. The OFHC crystals were much less perfect and contained many subboundaries. After annealing slices of the purer crystals at 1075°C, dislocation densities as low as 102/cm2were obtained. The vacancy condensation mechanism for dislocation generation apparently was not significant in accounting for the residual dislocation density in these crystals.

ISSN:0021-8979    

DOI:10.1063/1.1713770

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Self‐damage accumulation at 22.5°K has been studied in alpha plutonium enriched and unenriched in238Pu. The enriched specimen was held at this low temperature for a period equivalent to about 14 000 h in terms of damage accumulated in the unenriched specimen. The resistivity of the enriched specimen increased to a maximum of 141.5 &mgr;&OHgr;‐cm and then decreased gradually with additional time. The increase has been attributed to self‐irradiation damage consisting of interstitials and vacancies, and the decrease is discussed in terms of possible effects due to phase transformation, internal stresses, magnetic ordering, impurities, and clustering of defects. Annealing behavior differed widely in the two plutonium specimens studied and this is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1713771

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The relation between the concentration of intrinsic paramagnetic states (theE′ centers) of silica (silica glass) produced by irradiation and the concentration of OH−ions in the silica was investigated by introducing OH−ions into silica, initially free of these ions, in a controlled manner. Optical absorption and electron spin resonance measurements were used to establish the relation. The results of the investigation showed that in synthetic silicas the concentration ofE′ centers varied linearly with the concentration of hydroxyl units, the sum of the concentrations of hydroxyl units andE′ centers being constant. A ``vacancy'' model for the silica structure is proposed. In terms of this model the estimated saturation concentration ofE′ centers is of the same order as the concentration of ``vacancies,'' ∼1020cm−3. The saturation concentration of hydroxyl units is also ∼1020cm−3. Silica made by fusing natural quartz crystals differs from the synthetic silica with respect to the optical bands and the electron spin resonance spectra produced by irradiation. The effects of introducing hydroxyl units into natural quartz silica initially free of hydroxyl units is also different. These differences between natural quartz silica and synthetic silica are related to the models which have been suggested for theE′ centers. The models which are suggested are in agreement with the results of other experiments.

ISSN:0021-8979    

DOI:10.1063/1.1713772

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

X‐ray diffraction profiles of calcium fluoride show broadening which is partly caused by small crystallites and partly by deformation. Annealing eliminates most of the broadening and is accompanied by a parameter change that takes place between room temperature and 250°C and is probably associated with the precipitation of calcium oxide. By cold working the annealed calcium fluoride, it was possible to produce a specimen showing profile integral breadths equal to the original material, but which analysis showed to be caused almost entirely by strain.

ISSN:0021-8979    

DOI:10.1063/1.1713773

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Internal friction measurements following application of hydrostatic pressure were used to study residual pressure effects in polycrystalline aluminum. Application of 4‐kbar pressure was observed to increase irreversibly the amplitude‐dependent damping of 99.99% and 99.996% Alcoa aluminum at a strain amplitude of approximately 3×10−5by amounts up to 60 and 35 times the initial values, respectively. With successive pressure‐anneal cycles an abrupt disappearance of the residual pressure effect was sometimes observed. The effect was studied as a function of grain size by annealing cold‐worked aluminum at different temperatures. Measurements before and after application of 6‐kbar pressure to zone‐refined polycrystalline aluminum showed no changes in damping that could be ascribed to the effect of pressure. Polycrystalline alloys prepared by doping zone‐refined aluminum to 99.99% purity by addition of copper, iron, or silicon showed no residual pressure effect. Vacuum‐melted polycrystalline 99.996% aluminum showed no residual pressure effect. Zone‐refined aluminum melted in air or under a hydrogen atmosphere showed residual pressure effects. The residual pressure effect observed in refined aluminum is attributed to quenched‐in hydrogen present in the lattice. The pressure‐sensitive defects are considered to be hydrogen‐filled cavities.

ISSN:0021-8979    

DOI:10.1063/1.1713774

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Single crystals of LaF3have been grown by the Cˇzochalski technique. Crystal clarity and perfection were strongly dependent on the amount of oxide impurity. Trivalent rare‐earth doping was easily achieved, and divalent doping was possible with the easily reduced rare earths such as europium and samarium.

ISSN:0021-8979    

DOI:10.1063/1.1713775

出版商:AIP    

年代:1964

数据来源: AIP