The (1-1-2) and (1-0-0) planes of a tungsten crystal were bombarded at normal incidence with primary electrons and the intensity of the full-velocity secondary beams measured as a function of azimuth, co-latitude ($\theta$), and primary voltage. A new magnetic deflection method of analyzing the secondaries permitted observations at co-latitudes down to zero. The crystal was outgassed 1550 hours at temperatures up to 1600°C at pressures of ${10}^{-7\mathrm{}}$ mm of Hg or less. Strong sharp beams were observed in the $A{A}^{\prime }$ azimuth (Fig. 1) of the (1-1-2) plane at all wave-lengths which were used, and were found to be governed in every case by the volume equation $n_2\lambda =\frac{d}{6^{\frac{1}{2}}}+2\left(\frac{d}{6^{\frac{1}{2}}}\right)sin(30\mathrm{}°-\theta )$ and in no case by the surface equation. This is the first time that such a pronounced deviation from the usual theory has been observed. The final average experimental value for $W_a$ was 5.52 volts which, combined with photoelectric and thermionic data yields a value for $W_i$ of about 1 volt. The values obtained for $W_a$ were unusually consistent. A few beams of the usual type obeying both interference equations were observed in the $B$ and $C$ azimuths of the (1-1-2) plane and also in an azimuth 30° from $B$. They were all quite broad, however, and consequently no attempt was made to estimate $W_a$ from them. Beams were found in the case of the (1-0-0) plane which could be detected for various wave-lengths within the immediate neighborhood of their predicted location and which showed a tendency to vary in latitude in obedience with the volume equation, but became too weak to observe if the wave-length chosen was very far from the predicted value. Slight variations in the angle of incidence were found to have a very great effect on the observations. Some of those portions of the observations which differ from typical results obtained in similar investigations with other metals can be correlated qualitatively with the peculiarities of the tungsten crystal lattice. It seems likely that the explanation of the peculiarly governed beams observed in the $A{A}^{\prime }$ azimuth of the (1-1-2) plane and of Kikuchi's "N-pattern" for mica is somehow contained in the relation of atomic plane population to interplanar distance.

Close

PrevNext

View figure in article