A University of Texas at Arlington research team has discovered a nanotechnology to cool electrons to -228 C without external means and at room temperature, an advancement UTA claims could enable electronic devices to function with very little energy.
The process involves passing electrons through a quantum well in order to cool them and keep them from reheating. The team details its research in an Open Access research paper published in the journal Nature Communications on Wednesday, Sept. 10, entitled “Energy-filtered cold electron transport at room temperature” (Nat. Commun. 5:4745 doi: 10.1038/5745, Published 10 September 2014) coauthored by Pradeep Bhadrachalam, Ramkumar Subramanian, Vishva Ray, Liang-Chieh Ma, and Seong Jin Koh of the at the University of Texas at Arlington’s Department of Materials Science and Engineering and Nanotechnology Research Center; and Weichao Wang, Jiyoung Kim, and Kyeongjae Cho of the University of Texas at Dallas Department of Materials Science and Engineering in Richardson, Texas.
In the article, the scientists explain that Fermi-Dirac electron thermal excitation is an intrinsic phenomenon that limits functionality of various electron systems, noting that efforts to manipulate electron thermal excitation have been successful when the entire system is cooled to cryogenic temperatures.
In this study, they show that electron thermal excitation can be effectively suppressed at room temperature, and that energy-suppressed electrons, whose energy distribution corresponds to an effective electron temperature of ~45K, can be transported throughout device components without external cooling. This is accomplished using a discrete level of a quantum well, which filters out thermally excited electrons and permits only energy-suppressed electrons to participate in electron transport.
The researchers note that a quantum well (~2nm of Cr2O3) is formed between source (Cr) and tunneling barrier (SiO2) in a double-barrier-tunnelling-junction structure having a quantum dot as the central island. Cold electron transport is detected from extremely narrow differential conductance peaks in electron tunneling through CdSe quantum dots, with full widths at half maximum of only ~15mV at room temperature.
This study’s focus was on a much higher temperature regime than have previous studies: ie: room temperature. They show that electron thermal excitation can be effectively suppressed at room temperature and the energy-suppressed electrons, whose energy distribution corresponds to an effective electron temperature of ~45K, can be transported throughout device components without any external cooling. The coauthors observe that electron energy filtering and its associated cold electron transport have profound technical implications. If the method can be properly implemented into an electron system/device whose operation temperature or performance is limited by the Fermi-Dirac thermal excitation the electron energy filtering could significantly relieve those thermal limitations.
“We are the first to effectively cool electrons at room temperature. Researchers have done electron cooling before, but only when the entire device is immersed into an extremely cold cooling bath,” Seong Jin Koh, an associate professor in the UT Arlington Materials Science & Engineering Department who led the research, in a release. “Obtaining cold electrons at room temperature has enormous technical benefits. For example, the requirement of using liquid helium or liquid nitrogen for cooling electrons in various electron systems can be lifted.”
“Electrons are thermally excited even at room temperature, which is a natural phenomenon. If that electron excitation could be suppressed, then the temperature of those electrons could be effectively lowered without external cooling,” Dr. Koh continues. “The team used a nanoscale structure, which consists of a sequential array of a source electrode, a quantum well, a tunneling barrier, a quantum dot, another tunneling barrier, and a drain electrode, to suppress electron excitation and to make electrons cold. Cold electrons promise a new type of transistor that can operate at extremely low-energy consumption. Implementing our findings to fabricating energy-efficient transistors is currently under way.
Khosrow Behbehani, dean of the UT Arlington College of Engineering, comments that this research is representative of the University’s role in fostering innovations that benefit the society, such as creating energy-efficient green technologies for current and future generations.
“Dr. Koh and his research team are developing real-world solutions to a critical global challenge of utilizing the energy efficiently and developing energy-efficient electronic technology that will benefit us all every day,” Dr. Behbehani observes. “We applaud Dr. Koh for the results of this research and look forward to future innovations he will lead.”
Usha Varshney, program director in the National Science Foundations Directorate for Engineering, which funded the research, says that the research findings could be vast. “When implemented in transistors, these research findings could potentially reduce energy consumption of electronic devices by more than 10 times compared to the present technology,” Dr. Varshney notes. “Personal electronic devices such as smartphones, iPads, etc., can last much longer before recharging.”
The UTA release notes that in addition to potential commercial applications, there are many military uses for the technology. Batteries weigh a lot, and less power consumption means reducing the battery weight of electronic equipment that soldiers are carrying, which will enhance their combat capability. Other potential military applications include electronics for remote sensors, unmanned aerial vehicles and high-capacity computing in remote operations.
The study coauthors conclude that future research could include identifying key elements that will allow electrons to be cooled even further, and that the most important challenge of this future research will be to keep the electron from gaining energy as it travels across device components. This would require research into how energy-gaining pathways could be effectively blocked.
University of Texas at Arlington
National Science Foundation
University of Texas at Arlington
National Science Foundation