Optical studies on hopping-transport mechanism of excess electrons in liquefied nitrogen

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Abstract
Hopping conduction in liquefied nitrogen is investigated using a modified optical Schlieren system. The mobility of the electronic charge carriers is found to lie in the range 0.14–0.60 cm2/V sec. These values are two or three orders of magnitude larger than that of negative ions (10−4–10−3 cm2/V sec) and also two or three orders smaller than the predictable maximum value of free electrons 102–103 cm2/V sec in liquefied nitrogen. The results suggest that electrons emitted from the cathode move by a hopping-transport mechanism, such as the polaron- and a quantum-tunneling-type conduction. The sensitivity of the present optical Schlieren system was measured by a Mach Zehnder technique, and the observable change of the refractive index is greater than 2×10−5.