摘要:

The microdeformation characteristics of 0.010‐in.‐diam compact bone filaments have been measured under torsional loading conditions. The effects of prestrain, recovery, cyclic loading, and specimen orientation on the nature and extent of the nonelastic flow were determined. Correlations are considered between the mechanical behavior and the composite structure of compact bone.

ISSN:0021-8979    

DOI:10.1063/1.1709926

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A spectrophotometer operating in the ultraviolet region can be used to obtain accurate and precise silicon dioxide thickness determinations on silicon. Excellent accuracy and precision is obtained by considering: (1) the refractive‐index dispersion of the silicon dioxide; and (2) the theoretically calculated phase shifts at the silicon dioxide‐silicon interface based on known optical constants of silicon. Experiments comparing spectrophotometric oxide thickness determinations against VAMFO (variable‐angle monochromatic fringe observation) thickness determinations indicate an accuracy of ±25 Å and a precision of ±15 Å.

ISSN:0021-8979    

DOI:10.1063/1.1709927

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Pines and Schrieffer demonstrated that the two‐stream instability could occur in a high‐mobility semiconductor such as InSb if the conditions &ohgr;p+&tgr;+>10 andT−»T+are satisfied, where &ohgr;p+is the hole‐plasma frequency, &tgr;+is the hole‐collision time andT−andT+are the electron and hole temperatures, respectively. Either condition is difficult to obtain in bulk InSb. The possibility of observing such an instability in a structure consisting of adjacentpandnInSb is considered. The collision condition is reconsidered using a collision term which conserves particles and assuming the somewhat higher electron‐drift velocities (≃electron‐thermal velocity) which are now believed possible. It is concluded that the condition can be relaxed by about an order of magnitude (&ohgr;p+&tgr;+>1). The layered structure could provide the conditionT+«T−if it were in contact with liquid helium while a current, passed only in thenregion, produced both relative streaming and elevated electron temperatures. A comparative stability analysis in the zero‐temperature fluid limit indicates that the surface space‐charge waves of the layered structure can grow at rates only slightly less than those of the bulk space‐charge waves of the corresponding penetrating stream system.

ISSN:0021-8979    

DOI:10.1063/1.1709928

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Optical‐emission fluctuations from three types of GaAs and Ga(AsP)p‐njunction luminescent diodes have been examined. Characteristic time constants of 12×10−3and 0.45×10−3sec are observed in both the optical noise spectra and forward‐current noise spectra of a GaAs diode in which carrier recombinations occur in the junction space‐charge region. More heavily doped junctions (∼1019cm−3), in which tunnel currents predominate, exhibit 1/fnoise. In either case, correlation exists between optical‐emission noise and forward‐current noise, suggesting that carrier transitions responsible for both effects are the same. Only simple photon noise is observed from a Ga(AsP) diode in which junction diffusion currents are significant, although the forward noise spectrum is also 1/fnoise.

ISSN:0021-8979    

DOI:10.1063/1.1709929

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Crystals of In2O3grown from a pure flux have inclusions and striations and, because of oxygen deficiency, are nonstoichiometric and almost black. The addition of MgO to the melt produces crystals that have no inclusions or striations, and that have optical properties characteristic of stoichiometric In2O3. Therefore, Mg acts as an efficient compensator of the oxygen deficiency. This paper describes the effect of MgO on the visible optical absorption spectrum and on the crystal defects. One possible model of the role of Mg in compensating In2O3is discussed briefly.

ISSN:0021-8979    

DOI:10.1063/1.1709930

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A study of cleaved germanium surfaces by transmission electron microscopy and gold transfer replicas provides direct and indirect evidence of plastic deformation introduced by the cleavage process at room temperature. The results are interpreted as showing that dislocations move by glide on {111}‐type planes parallel to the surface and at 70°32′ to the surface. Experiments are also reported using copper plating as a technique for decorating surface damage.

ISSN:0021-8979    

DOI:10.1063/1.1709931

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Defects in a rather perfect synthetic quartz crystal have been surveyed by x‐ray topography. Etching behavior and stress birefringence were also studied. The crystal, grown from az‐plate seed, contained Na and Al in concentrations of 50 ppm by weight. The crystal had grown in thecdirection with low dislocation density (∼ 3000 lines cm−2). The majority of dislocations made about 10° with thecaxis, only 15% had Burgers vectors with ac‐axis component. Cellular growth had developed as growth in thecdirection proceeded. The cell walls were identified with fault surfaces made visible by diffraction contrast. These surfaces were inclined at fairly small angles with [0001] and their intersections with (0001) formed an irregular polygonal network. Dislocations congregated in or near the fault surfaces in the later stages of growth. The fault surfaces outcropped at the grooves between protuberances on the rough external crystal surface of mean orientation (0001). The presence of fault fringes indicates impurity segregation in the cell walls: the fringe contrast could arise from a layer a few microns thick with a lattice parameter a few parts in 105different from that of surrounding material.

ISSN:0021-8979    

DOI:10.1063/1.1709932

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The lifetimes of Gd3+6P7/2and Yb3+2F5/2fluorescence in a glass host have been studied at room temperature as a function of concentration, and in the case of Gd3+as a function of added Eu3+concentration. The results show that the ions ``concentration quench'' by a mechanism involving the migration of excitational energy from ion to ion until a sink in the structure is reached. This result is significant to the preparation of laser materials.

ISSN:0021-8979    

DOI:10.1063/1.1709933

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The ``hexagonal ferrites'' comprise a quasipolytypic series of ferrimagnetic oxides containing Ba, Fe3+, and a divalent metal cation (Me2+). These encompass a family of hexagonal and rhombohedral mixed‐layer structures derived by thec‐axis stacking of two complex invariant building blocks, mainly ``M'' and ``Y''. TheMstacking element is a 5‐anion‐layer block, 11.6 Å in height with the composition BaFe12O19, and theYstacking element is a 6‐anion‐layer block, 14.5 Å high with the composition Ba2Me22+Fe12O22. The largest series,M2Yn(n=0 to 21), involves the stacking of twoMblocks and a variable number ofYblocks. Permutation of theMandYelements allows mixed‐layer polytypism within a given stoichiometry, i.e.,MtoYratio. More than twenty (20) mixed‐layer structures and their polytypes have been examined by electron microscopy after direct replication of the basal face.Basal faces which were etched with dilute hydrochloric acid exhibit etch steps of sub‐unit‐cell heights. The specificMandYstacking sequence of a mixed‐layer structure may be obtained by measuring the step‐height ratio,MYx/MYn−x, of two adjacent steps, provided either the shadow angle or the x‐rayc‐axis dimension is known. In addition it has been found that thec‐axis dimension and the specific stacking sequence may be uniquely determined by counting the individualMandYbuilding blocks which are replicated as separate and distinct etch‐planes on a crystal surface that has been process‐etched.

ISSN:0021-8979    

DOI:10.1063/1.1709934

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Measurement of fundamental and superlattice x‐ray diffraction lines as a function of integrated proton‐bombardment current has been used to determine induced disorder in the surface layers of fully ordered polycrystalline targets of Cu3Au. It is shown that a proton range for induced disorder and the number of disordered atoms created per proton can be inferred from the data.

ISSN:0021-8979    

DOI:10.1063/1.1709935

出版商:AIP    

年代:1967

数据来源: AIP