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在实用热阴极中,测量得的发射常数值经常小于120A/cm~2T~2。这是由于逸出功有一分布所致,而不是由于电子遇到表面势垒时的反射。用单晶面测量时,理论和实验值便相符了。事实上发射来源于已穿透进势垒的表面电子。这些电子既不能进入真空,也不能在金属导带中自由运动,否则不同晶面便不可能有不同的逸出功。异族元素的吸附增加表面电子的数目和能量,因而使逸出功下降。
In practical hot cathodes, the measured emission constant is often less than 120 A / cm ~ 2 T ~ 2. This is due to a distribution of work function, not due to the electron’s reflection when it encounters a surface barrier. When measured from a single crystal face, the theoretical and experimental values match. In fact the emission originates from the surface electrons that have penetrated the barrier. These electrons can neither enter the vacuum nor move freely in the metal conduction band, otherwise different crystal faces can not have different work functions. Absorption of interracial elements increases the number and energy of surface electrons, thereby decreasing the work function.