摘要:

Investigation of films formed by vacuum deposition of Nb on single‐crystal MgO has demonstrated the importance of chemical interaction between the substrate and overgrowth in the epitaxial growth process. The interaction layer is composed of an oxygen‐stabilized face‐centered cubic modification of the normally bcc Nb, or the compund NbO, the thickness of which is controlled by the oxygen diffusion process in the layer. The previously observed nucleation‐coalescence process of thin film formation is replaced by ordered chemical reaction. Defect‐producing misorientations between nuclei, predominant in the nucleation‐coalescence case, are not present in the ordered chemical reaction process. Thin films may thus be produced having defect density no higher than that of the substrate crystal. The effect of interaction between the substrate and condensate, although large in the example presented, should not be overlooked in other considerations of the epitaxial process where chemical reaction cannot be ruled out.

ISSN:0021-8979    

DOI:10.1063/1.1709258

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

When a focused electron beam is deflected by a transverse magnetic field through a small angle, the spot shape on the target is distorted. The electron density distribution within it also varies. A novel method of calculating and presenting the characteristics of the distorted spot is presented. The positions of the electrons at the incoming aperture are mapped into the target plane subsequent to the deflection. The resultant density distribution is plotted by the computer.

ISSN:0021-8979    

DOI:10.1063/1.1709259

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The accelerating field of a point‐cathode electron source is divided into two regions, a diverging spherical‐field region located in the immediate vicinity of the point cathode, and a converging‐field region which occupies most of the cathode‐anode space. Analysis of this model gives the Gaussian source size, axial position of the source, and spherical‐ and chromatic‐aberration constants of the pointed‐cathode electron gun. After including diffraction effects, the electron‐optical parameters are optimized for minimum possible source size. The current density which appears to be emitted by the apparent source is introduced as a figure of merit for this type of electron gun, and the performance of field‐emission and Schottky‐emission pointed cathodes are compared. Source diameters below 100 Å are predicted for oriented‐tungsten field‐emission pointed cathodes, with apparent current densities exceeding 104A/cm2; source diameter below 1000 Å are predicted for oriented‐tungsten Schottky‐emission pointed cathodes, with apparent current densities of approximately 100 A/cm2.

ISSN:0021-8979    

DOI:10.1063/1.1709260

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The simulation of field‐ion images by computation of the position of atoms which lie within an outer shell of given thickness on a spherical crystal has been extended to spherical crystals of a variety of structures. These include the hexagonal lattice, the hexagonal close‐packed structure and a few of the common superlattices. The consequences of the invisibility of one atomic species in ordered alloys has been investigated. The results show that computations are in fact necessary for a detailed interpretation of the field‐ion image.

ISSN:0021-8979    

DOI:10.1063/1.1709261

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The customary defocused and Foucault modes of Lorentz microscopy of magnetic films are usually described in terms of geometric optics. However, Wohlleben has shown that geometric optics has a restricted range of validity; a more fundamental approach is provided by wave optics. The defocused and Foucault modes may be discussed in terms of wave optics, and for the defocused mode, it can be shown explicitly that the geometric theory is simply the first approximation to the wave‐optics theory. Consideration of wave optics also leads to the proposal of two additional modes of Lorentz microscopy: Zernike phase‐contrast and interference microscopy; these modescannotbe described on the basis of geometric optics. The most fundamental problems in magnetic films which are amenable to study by Lorentz microscopy are investigations of the fine structures of domain walls and magnetization ripple. These problems are discussed in terms of wave optics for all four modes of Lorentz microscopy; in particular, the intensity distribution of the zero‐width divergent domain wall is explicitly calculated for each mode. For practical experiments, the importance of coherence, i.e., of the illumination source size, is emphasized, and the experimental aid of holography is suggested. Since the Wohlleben limit is valid for all four modes, however, there is no resolution advantage inherent in any one mode. The choice of modes for solution of the domain wall and ripple problems therefore depends upon experimental convenience. It is concluded that the defocused mode seems most promising for practical application; Fresnel diffraction is preferred for the domain‐wall problem, while Fraunhofer diffraction using low‐angle electron‐diffraction techniques is fruitful for the ripple problem.

ISSN:0021-8979    

DOI:10.1063/1.1709262

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

An equation of state, based on a bulk modulus variation with pressure of the formBS=B0S+B0S′P+B0S″P2/2,whereB0S,B0S′, andB0S″are constants, is developed in this analysis. The resultant equation of state is combined with the Rankine‐Hugoniot conservation relations to obtain a Maclaurin series expansion for the shock velocity vs the particle velocityus=c+sup+s′up2+&cellip;.The coefficientsc, s, ands′are given in terms of the unshocked density and quantities available from ultrasonic elastic constant measurements at high pressures. Using new experimental data for sodium, it is shown thats′is nearly zero. For ionic crystals such as KBr a theoretical expression is given forB0S″(in terms ofB0S′). In the case of KBr, the value ofs′is also very close to zero. The smallness ofs′depends on the cancellation of a number of terms brought about by the fact thatB0S″is negative. CsI and xenon are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1709263

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Single‐crystal potassium tetrafluoaluminate‐doped substitutionally with iron has been prepared. The room‐temperature spectrum of isolated iron ions may be described by a conventional spin Hamiltonian with parameters:g∥=2.005,g⊥=1.999,D=0.1471 cm−1,a=0.0020 cm−1, andF=0.007 cm−1. From the linewidths an upper limit to the fluorine hyperfine structure is estimated.

ISSN:0021-8979    

DOI:10.1063/1.1709264

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Appreciable increases in capacitance have been observed in thin single‐crystal CdS platelets when measured under conditions of dc bias. Data have been obtained in the frequency range 20 cps‐20 Mc/sec. Crystals could be roughly divided into two groups (denoted by I and II). Group I crystals, exhibiting an approximateV2dependence of theI‐Vcharacteristic, showed low‐frequency‐capacitance increases of up to a factor of ten under bias. These changes could be explained in terms of SCLC. Group II crystals, exhibitingI‐Vcharacteristic with a voltage exponent much greater than two, showed low‐frequency‐capacitance increases of up to a factor of 1000. This behavior cannot be understood in terms of SCLC flow, and a two‐layer model is proposed which provides a satisfactory explanation.

ISSN:0021-8979    

DOI:10.1063/1.1709265

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Experiments with exploding wires made of constantan, copper, and lithium in atmospheric air have shown that the dwell time of an exploding wire for the examined lengths (3.2, 6.5, 9.7, and 13 cm), diameters (0.005 cm for constantan and copper, and 0.025 cm for lithium), and applied voltages (1 to 20 kV) is a function of the average electric‐field strength along the wire. The function relating dwell time to field strength is not single‐valued, but from a certain critical value there are two dwell times corresponding to each field strength. There is evidence that this duality of the dwell times is due to a change in the type of explosion at the critical gradient. Both types of observed dwell times depend in a simple way on the average field strength.

ISSN:0021-8979    

DOI:10.1063/1.1709266

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Growth of aluminum films on clean Ta(110) surfaces has been investigated by LEED techniques. Five phases of aluminum have been found, which are: (1) disordered Al(111), formed by depositing atT<600°C; (2) Al(111)c(2×2) formed by heating film, deposited atT<300°C, to 700°C; (3) Al(100)c(2×2), formed by heating film, deposited 300<T<600°C, to 700°C; (4) Epitaxial Al(111), formed by depositing film with substrateTin range 600<T<670°C; (5) Diffuse phase, formed by heating any of the preceding to 800°C. Two orientations of each structure have been observed; this results from the close match between primitive unit meshes of aluminum (111), (100) and Ta(110). A mechanism for the growth of Al(111) and Al(100) is suggested. Comparisons with some published LEED data on epitaxy are made.

ISSN:0021-8979    

DOI:10.1063/1.1709267

出版商:AIP    

年代:1967

数据来源: AIP