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要提高电子显微镜的分辨率就必须减少像差,其中最主要的是球差和色差,球差早已有人提出用六极透镜系统来消除,并取得了一些成果。引起色差的原因有:电子枪加速电压的波动,透镜电流的波动及阴极发射出来的热电子具有能量分散度。所以,研究不同温度下阴极热发射电子的能谱曲线是很有意义的。作者利用金属钨W和拒斥场法。测量了不同温度下,W的电子能量分布(峰值和半宽度)随温度的变化。要得到电子束的能谱曲线,须先测出电子束的积分曲线,再对该曲线微分即得能谱曲线。实验装置是一同轴圆筒型的理想二极管及其测量系统,实验结果用计算机进行处理。由能谱分布曲线看出:电子的能量分布服从麦克斯韦分布;能谱半宽度随温度升高而增大,峰值对应的电压也随温度升高而增大。说明温度愈高,W的热电子能散度愈大,色差也越大。这些结果对正确使用W阴极,以及进一步提高各种电子光学仪器的分辨率有参考意义和实用价值。
To improve the resolution of the electron microscope must reduce the aberration, of which the most important are the spherical aberration and color difference, spherical aberration has long been proposed to eliminate the hexapole system, and achieved some results. The causes of color differences are: gun acceleration voltage fluctuations, lens current fluctuations and the cathode emits hot electrons with energy dispersion. Therefore, it is significant to study the energy spectrum curve of cathode thermal emission electrons at different temperatures. The author uses metallic tungsten W and repelling field methods. The temperature dependence of the electron energy distribution (peak and half width) of W at different temperatures was measured. To get the energy spectrum of the electron beam curve, you must first measure the integral curve of the electron beam, and then differentiate the curve to obtain the energy spectrum curve. Experimental device is a coaxial cylinder ideal diode and its measurement system, the experimental results were processed by a computer. The distribution of energy spectrum shows that the energy distribution of electrons obeys Maxwellian distribution, the half-width of energy spectrum increases with the increase of temperature, and the voltage corresponding to the peak also increases with the increase of temperature. Explain that the higher the temperature, the greater the W divergence, the greater the color difference. These results have reference and practical value for proper use of W cathode and further improvement of the resolution of various electronic optical instruments.