Heat engines provide most of our mechanical power and are essential for long-range transportation. However, whereas significant progress has been made in the miniaturization of motors driven by electrostatic forces, it has proven difficult to reduce the size of conventional liquid or gas driven heat engines below 10^7 um^3 (10 million cubic microns). Here we demonstrate an all-silicon reciprocating heat engine with a volume of less than 0.5 um^3.(half of one cubic micron) The device draws heat from a DC current using the piezoresistive effect and converts it into mechanical energy by expanding and contracting at different temperatures. It is shown that the engine can even increase the mechanical energy of a resonator when its motion is governed by random thermal fluctuations. When the thermodynamic cycle of the heat engine is reversed, it operates as a refrigerator or heat pump that can reduce motional noise in mechanical systems. In contrast to the Peltier effect, the direction of the thermal current does not depend on the direction of the electrical current.
We have demonstrated a solid-state piezoresistive heat engine and refrigerator that can be reduced to microscopic dimensions. The device might drive micromechanical oscillators, motors and sensors. However, even though man-made heat engines outperform biological engines on the macroscopic scale and are essential for long-rang transportation, it remains to be seen whether they can ever compete with biological or artifcial molecular motors on the microscale. Anyhow, their manufacturability and the possibility to operate them over a wider range of environmental conditions are signifcant advantages.
Previous work by others to make Quantum machine using cold atoms