摘要:

Arrangements of superconducting materials have been investigated to obtain objective lenses with the lowest possible spherical aberration coefficient (Cs) for the electron microscope. Various configurations of Nb3Sn in ferromagnetic containers giving current loops of small radii which produce axially symmetric magnetic fields with high peak intensities and narrow halfwidths were studied. The axial field distributions were measured (bismuth probe) and optical parameters and spherical aberration coefficients were calculated. Available superconducting materials appear to set a limit ofCs≃ 0.4 mm andCs≃ 1.8 mm for 100 kV and 1000 kV electrons, respectively (bore diam, 5 mm).

ISSN:0003-6951    

DOI:10.1063/1.1754619

出版商:AIP    

年代:1966

数据来源: AIP

摘要:

This Letter reports avalanche noise studies on microplasma‐free guard‐ring avalanche diodes. The low and high frequency approximations of Hines' theory are compared with experimental results at 1 kHz and 3 to 9 GHz, respectively. Good agreement is found between experiment and theory at both low and high frequencies. The open‐circuit spectral voltage density is white up to the avalanche frequency &ohgr;aand decreases inversely with current. For &ohgr; ≫ &ohgr;athe spectral noise power density falls off with &ohgr;4.

ISSN:0003-6951    

DOI:10.1063/1.1754620

出版商:AIP    

年代:1966

数据来源: AIP

摘要:

Experimental findings have been interpreted by Copeland as indicating that the multiplication rate &agr;(E) of carriers in GaAs has a narrow peak between 3 and 10 kV/cm. It is argued here that theory can account for a sizeable &agr; at these low fields, but that, rather than having a maximum and decreasing to zero again, &agr; will continue to rise. The proposed variation of &agr; appears to be more consistent with experimental results.

ISSN:0003-6951    

DOI:10.1063/1.1754621

出版商:AIP    

年代:1966

数据来源: AIP

摘要:

Using a nozzle‐type molecular beam with highly uniform velocity and high intensity and a sensitive time‐of‐flight detection system allows the measurement of the complete distribution of speeds after scattering the incident beam from a solid surface. With a ``dirty'' metal target at room temperature and argon as beam gas, it is found that the thermal spread of velocities in the scattered beam is at least three times larger than the thermal spread of velocities in the incident beam. While a complete thermal accommodation of the incident atoms would result in the same speed distribution for all scattering angles, the measurements show an angular dependence of the thermal spread and the mean speed of the scattered atoms.

ISSN:0003-6951    

DOI:10.1063/1.1754622

出版商:AIP    

年代:1966

数据来源: AIP