摘要:

Calculations have been performed on the contrast available in thick specimens. Ten modes of operation have been considered, six in the conventional electron microscope (CEM) and four in the scanning transmission electron microscope (STEM). Electrons passing through the specimen fall into four categories, elastically scattered, inelastically scattered, unscattered, and those scattered both elastically and inelastically. For the various operation modes these groups are taken in combinations to form practical signal intensities. In the calculation of practical intensities, the angular distribution of plurally scattered electrons is considered. The fraction of each scattered group passing through the microscope aperture has been calculated for various types of illumination. The practical intensities are used to calculate the contrast available in stained and unstained specimens. For very thick specimens bright field offers the best combination of contrast and signal intensity. Other contrast modes show a reversal in the sign of contrast for thicknesses close to one mean free path for elastic scattering. The equations for signal intensity and contrast are quite general, and apply to all values of voltage and instrumental resolution.

ISSN:0021-8979    

DOI:10.1063/1.1663833

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Three experimental methods for measuring the noise‐equivalent absorption of an x‐ray image intensifier are described. In all cases, the image intensifier is irradiated with a source of x rays or &ggr; rays, and the output is monitored with a photomultiplier. In one method the rms value of the photomultiplier current is observed as a function of the bandwidth of the measuring circuit. In the second method, the scintillation pulse spectrum is recorded, and its moments computed to give the required information. In the third method, the response to a series of short bursts of radiation is measured. The noise‐equivalent absorption is determined from the standard deviation of a large number of observations, automatically recorded. The three methods are described and compared, and typical results are shown.

ISSN:0021-8979    

DOI:10.1063/1.1663834

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The thermal expansion along the growth axis of crystalline TTF‐TCNQ was determined between 5 and 300 K. The total change in length over this range was found to be approximately 3%.

ISSN:0021-8979    

DOI:10.1063/1.1663835

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The subthreshold electron velocity‐field characteristic has been measured at room temperature for a range of bulk and epitaxial samples ofn‐type InP having low‐field Hall mobilities in the range 3600–4950 cm2/V s. The threshold field for current instabilities is found to be between 10.5 and 11.5 kV/cm and the peak velocity is 2.5×107cm/s.

ISSN:0021-8979    

DOI:10.1063/1.1663836

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Results of resistivity measurements and x‐ray studies of four additional superconducting metastable simple cubic alloys are presented. It is found that, in general, superconducting phases with simple cubic structure occur at average valence electron concentrations of 4.5 and 6.5 valence electrons per atom, and average valence electron densities of 0.16 and 0.26 electrons/Å3. An inverse relation between the transition temperatureTcand the lattice spacing is pointed out which applies generally for both antimony‐ and tellurium‐base alloys.

ISSN:0021-8979    

DOI:10.1063/1.1663837

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Gallium arsenide Schottky‐barrier field‐effect transistors have been fabricated in ann‐type film produced by sulfur implantation in a Cr‐doped semi‐insulating GaAs substrate. The conditions of the implantation and the resulting electrical properties of the film are presented. The FET devices are described and the measured current‐voltage characteristics of this device are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1663838

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The ordinary and extraordinary refractive indices of congruently melting LiNbO3in the wavelength range 0.40463–3.05148 &mgr;m are reported.

ISSN:0021-8979    

DOI:10.1063/1.1663839

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A method using coincident rf sputtering and rf discharge decomposition is shown capable of producing single‐crystal, epitaxial, nonequilibrium solid solutions of Si in GaAs with the composition of Si far exceeding the limits reported for the bulk equilibrium phase diagram. Measured values of alloy composition and lattice parameter indicate close correspondence to Vegard's law. High‐temperature annealing of epitaxial films demonstrates the ultimate instability of the alloys.

ISSN:0021-8979    

DOI:10.1063/1.1663840

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A Doppler shift in wavelength can result in a very slight change in the index of refraction of a transparent material due to disperison. This effect, if not accounted for, produces an error of a few percent in the velocities determined using the recently developed velocity interferometer for diffusely reflecting surfaces.

ISSN:0021-8979    

DOI:10.1063/1.1663841

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Results of Hall‐effect and resistivity measurements on semi‐insulating undoped AgGaS2are reported. Both shallow (∼0.11 eV) and deep (∼0.72 eV) acceptor levels were observed from p‐type crystals. Crystal resistance is not readily changed by heat treatment.

ISSN:0021-8979    

DOI:10.1063/1.1663842

出版商:AIP    

年代:1974

数据来源: AIP