Abstract
The stability and performance of nanoscale junctions are closely related to the local effective temperature. The local effective temperature is mainly caused by the competition between heating and cooling processes in inelastic electron-phonon scat- tering. Local cooling occurs when the rate of energy in cooling exceeds that in heating. Previous research has been done using either specific potential configuration or an adatom to achieve local cooling. We propose an engineer-able local-cooling mechanism in asymmetric two-terminal tunneling junctions, in which one electrode is made of metal, whereas the other is made of a selectable bad-metal, such as heavily-doped polysilicon. The width of energy window of the selectable material, defined as the width covering all possible energy states counting from the conduction band minimum, can be engineered through doping. Interestingly, we have shown that substantial local cooling can be achieved at room temperature when the width of energy window of the low-density electrode is comparable to the energy of the phonon. The unusual local cooling is caused by the narrowed width of energy window, which obstructs the inelastic scattering for heating.
Highlights
IntroductionThe net effect of heating (red lines) and cooling (blue lines) processes are responsible for the local heating
Type consists of its time-reversal processes as a pair
Given a certain vibration mode, what is the optimal material widths of energy window that can provide local cooling in the junction? To answer this question, we set the bias at 5 mV and created contour plots in which the local temperature is plotted as a function of the width of energy window and the normal-mode energy in Fig. 4(a–c), where the electrode temperature T is [200, 300], and 400 K, respectively
Summary
The net effect of heating (red lines) and cooling (blue lines) processes are responsible for the local heating. These phonon emission/absorption process diagrams describe the electrons travel from the right or left electrode gain (lose) energy to relax (cool down) or excite (heat up) phonons in the nano-structure. We show when the width of energy window of the controllable materials is comparable to the energy of the phonon, the current-induced heating processes could be blocked when the electron loses energy and scatters to an energy lower than the band bottom. The cooling power could surpass the heating power and could cause a condition such that the local effective temperature in the scattering region of the device is lower than the electrodes. Thermoelectric cooling (Peltier effect) employs the slope of the transmission function to cool the electrode region rather than device region[29,30]
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