Harnessing nanoscale electrical currents powered by light to power emerging technologies

Traditional microelectronic architectures, with transistors to control electrical currents along wires, power everything from advanced computers to everyday devices.

But as integrated circuits offer diminishing returns in speed and adaptability, scientists at Los Alamos National Laboratory are developing light-based systems at the nanoscale that could enable breakthroughs in ultrafast microelectronics, sensing infrared at room temperature (e.g. night vision) and a wide variety of technological applications.

“Most modern technologies, from computers to applications such as energy harvesting, rely on the ability to move electrons,” said Jacob Pettine, a Los Alamos physicist at the Center for Integrated Nanotechnologies (CINT). “But how we control this charge flow remains very limited by conventional materials and structures.”

Nanoantennas capture and focus light

As described in an article just published in Nature, the research team designed and fabricated nanometer-sized asymmetric gold structures on an atomically thin layer of graphene. The gold structures are nicknamed “nanoantennas” because of the way they capture and focus light waves, forming optical “hot spots” that excite electrons in graphene. Only the graphene electrons very close to the hot spots are excited, the rest of the graphene remaining much less excited.

The research team adopted a teardrop shape of gold nanoantennas, where breaking the inversion symmetry defines directionality along the structure. The hot spots are located only at the pointed ends of the nanoantennas, leading to a pathway on which the excited hot electrons flow with a clear directivity: a charging current, controllable and tunable at the nanoscale by exciting different combinations of hot spots.

“These metasurfaces provide a simple way to control the amplitude, location and direction of hotspots and charging current at the nanoscale with sub-picosecond response speed,” said Hou-Tong Chen, scientist at CINT overseeing the research. “Then you can think about more detailed features.”

Promising applications for controllable and adjustable charging current

The conceptual demonstration of these optoelectronic metasurfaces presents a number of promising applications. The generated charging current can be naturally used as a signal for photodetection, especially important in the long-wavelength infrared region. The system can serve as a source of terahertz radiation, useful in a range of applications from ultra-fast wireless communications to spectroscopic characterization of materials. The system could also provide new opportunities for controlling nanomagnetism, in which specialized currents could be designed for adaptable magnetic fields at the nanoscale.

This new capacity could also prove important for ultra-fast information processing, particularly in computing and microelectronics. The ability to use laser pulses and metasurfaces for adaptive circuits could enable the distribution of slower, less versatile transistor-based computer and electronic architectures. Unlike conventional circuits, adaptive structured light fields could offer completely new design possibilities.

“These results lay the foundation for versatile modeling and optical control of currents at the nanoscale,” Pettine said. “Alongside valuable laboratory applications, vector metasurfaces can enable advancements in many different technological areas.”