摘要
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。
That for practical emitters the measured values of the constant in Richardson's equation are always less than 120 A/cm2T is due to the nonuniformity of work function not to the reflection of electron at the surface potential barrier. For monocrystal faces, the measured and theoretical values agree. In fact, emission comes from those surface electrons already penetrated into the potential barrier before excitation. These surface electrons can neither move freely through vacuum nor through conduction band of the metal, otherwise different crystal faces would not have different work functions. The adsorption of foreign atoms increases the energy and number of the surface electron and then lowers the work function.
关键词
热阴极
逸出功
发射常数
表面势垒
Thermionic cathode
Work function
Emission constant
Surface potential barrier
Surface electron
