As the field increases, field emission will inevitably
become a more significant part of the overall emission. So
the emission may not be solely thermionic anymore. The key
question is whether such an emission still produces an overall
cooling effect. A number of theoretical studies have tried
to answer this question from various angles. Most of these
studies suggest that a mixed thermionic and field emission at
room temperature can still result in an overall cooling of the
surface.13,16–18,20,29–34 For example, most recently, Musho
et al. published a quantum simulation of thermionic electron
emission from diamond thin films and concluded that such
film is capable of emitting hot electrons at low temperatures.25
However, there are also researchers doubt if efficient
thermionic cooling can be achieved at room temperature.34
Even though the work presented here does not provide a defi-
nite experimental data to answer this key question, as it is
limited by the experimental setting on both temperature measurement
and the applied external electric field, the experimental
evidence obtained thus far does show a very large
cooling effect at relative high temperature, as well as a trend
line that provides some clues on what might happen at lower
temperatures. Again, the large cooling effect observed is a
direct result of the large emission current. A low work function
surface combined with an even larger field effect should
be able to help produce strong electron emission at relative
low temperatures. Thus, if the trend of cooling dependence
on emission current continues to a certain degree at lower
temperatures, then significant cooling could be achievable
with devices based on the scheme presented in this study.