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Still "Plenty of Room at the Bottom": Nanoscience at Caltech Twenty Years On
Still "Plenty of Room at the Bottom": Nanoscience at Caltech Twenty Years On
April 03, 2024
The Kavli Nanoscience Institute at Caltech, a 21st century center for science and engineering at the nanoscale, celebrated its 20th anniversary with a special symposium and a fireside chat between President Thomas F. Rosenbaum and 2022 Kavli Prize Laureate George M. Whitesides (PhD '64) from Harvard University on March 7–8, 2024.
Throughout history, people have marveled at large things. Blue-ribbon-winning giant pumpkins, 7-foot humans, the Great Pyramid of Giza, and the cosmos itself have all captured humanity's imagination. But from the invention of the optical microscope in the 16th century to the silicon-based microchip in the mid-20th century, scientists and engineers have become equally intrigued by very very small things. Now, with the advent of sophisticated microscopy instruments, tiny objects as small as several nanometers in size can be measured by researchers such as those at Caltech's Kavli Nanoscience Institute (KNI), which celebrated its 20th anniversary with a special symposium and a fireside chat between Caltech President Thomas F. Rosenbaum and 2022 Kavli Prize Laureate George M. Whitesides (PhD '64) from Harvard University on March 7–8th, 2024.
Just how small is a nanometer? If you're thinking "small," think smaller. Nano, Greek for dwarf, is one billionth of a meter: 0.000000001 (10-9 meters). A single sheet of ordinary paper is 10,000 times as thick as a nanometer, as is the diameter of a single strand of human hair. One nanometer is the length of about 10 atoms depending on the atom. Or to keep it close to home, consider this: Your fingernail grows by about 1 nanometer every second.
Despite their vanishingly small size, nanoscale materials can be incredibly strong—more impact-resistant than Kevlar, for example—and can perform amazing feats that we are only beginning to harness, such as the ability to refract light backward.
Nanotechnology—currently defined as the design, fabrication, or use of structures between 1 and 100 nanometers—is said to have begun in 1981, with the development of the scanning tunneling microscope (STM), which is capable of scanning over and imaging individual atoms. It was predicted decades earlier by the late Caltech professor Richard Feynman in a 1959 speech to the American Physical Society, "Plenty of Room at the Bottom," where he spoke of miniaturizing computers and storing the 120,000 volumes in the Caltech library "on just one library card."
Although Caltech scientists began experimenting with nanotechnologies as soon as they were available, it was not until the formation of the KNI and the construction of the KNI Cleanroom in 2003 that a single place existed on campus that housed instrumentation capable of virtually all aspects of nanofabrication: photo-, ion- and electron beam lithography, deposition, wet and dry etching, electron microscopy, and more. In turn, this facilitated collaborations among researchers on campus focused on nanoscale phenomena. Fred Kavli of the Kavli Foundation was instrumental in brainstorming the future of nanoscience with the Caltech faculty and administration, and providing initial funding along with the Gordon and Betty Moore Foundation. Later funding has come from the Fletcher Jones Foundation, Chuck and Judy Wheatley, and the Space Solar Power Project.
KNI has given Caltech scientists on campus and at JPL, as well as researchers from other universities and companies, the ability to work at the nanoscale. Today, about 10 percent of Caltech's faculty or members of their research groups use KNI's instruments. The facility draws researchers from across scientific disciplines, including applied physics, materials science, biology, chemistry, engineering, and astronomy. "Once users are fully trained and signed off to use the equipment, they have 24/7 access to the facility," explains Tiffany Kimoto, KNI's executive director. "We also have had several corporate users over the years who have used our facilities, including Samsung, Meta, Nokia, and several start-ups, especially those founded by Caltech personnel."
"It is exhilarating to think about everything that is possible at the nanoscale, and how many more challenges remain," says Julia R. Greer, the Fletcher Jones Foundation Director of the KNI and Ruben F. and Donna Mettler Professor of Materials Science, Mechanics and Medical Engineering. "We are getting really close to fabricating, manipulating, and imaging samples at the atomic level, which propels new discoveries just about every day."
Projects undertaken at KNI include prototyping new materials that can resist impact or store energy, growing and characterizing quantum materials and two-dimensional van der Waals materials for topological quantum devices and nanophotonics, identifying rare proteins, and building nanodevices that connect single photons to individual atoms and nanodevices that can store and release photons on demand. These are just some of the ways Caltech researchers have been working on science's cutting edge with KNI's help. To learn more about these efforts over the past 20 years of KNI's existence, click through this slideshow.
Electronics of the Future
The information age would not have been possible without microchips—semiconductor transistors on silicon chips that drive digital electronics. In 1965, Gordon Moore (PhD '54) predicted that the number of transistors that could fit on a microprocessor would double every 18 months to 2 years, and for decades, technology has met or exceeded that rate. Now the chase is on to identify new materials that can support faster, smaller, lighter, and more powerful electronic capabilities without thermal degradation from the power output. Several candidates are being investigated at the KNI, including graphene, a one-atom thick sheet of graphitic carbon that is an excellent electrical and thermal conductor; metasurface optics that manipulate light between tiny folded surfaces; electro-optical frequency division that uses a pair of laser beams to create precise frequencies that can be used as time standards; and optical frequency combs that can substitute multiple lasers, each operating at a specific frequency, for a single multifrequency optical source the size of a match box.
Credit: 彭嘉傑 via Wikimedia Commons
Quantum Information
Within the limits of ordinary human senses, the material world can be explained quite well by classical physics. But once it became possible to detect phenomena at the atomic and subatomic level, quantum mechanics was required to describe these phenomena. As nanoscale science progresses, it has become possible to not only observe atomic and subatomic behaviors, but to manipulate them with nanoscale devices. This has opened the door to the possibility of quantum computing, which is expected to solve problems that are impossible for conventional computers. KNI researchers are experimenting with a variety of ways to store quantum information, including through sound waves (phonons), light waves (photons), nuclear spin waves, and surface plasmons (the sea of electrons bridging the space between a metal surface and the material above it).
Nanophotonics
In 2009, KNI resarchers created a optomechanical crystal capable of trapping light and sound vibrations together, opening up the opportunity to send large amounts of information and to detect and weigh individual macromolecules. The creation of tiny optical cavities has allowed scientists to produce light waves, known as solitons, that circulate indefinitely rather than dissipating. These tiny boxes of light have been engineered at the KNI with periodic nano-patterning that causes rare-earth ytterbium ions to bounce back and forth such that photon emissions can be detected and collected. In the process of working with ytterbium, a new phenomenon was discovered: atoms that are transparent to certain frequencies of light. A laser's light will usually bounce off an atom, but as the frequency is adjusted, it can create what researchers call "collectively induced transparency." Just how this new area of physics operates is still under study.
Credit: Lance Hayashida/Caltech
Understanding the Brain
Figuring out what is going on inside the brain is an enormous scientific challenge that draws researchers from many different disciplines. KNI founding director Michael Roukes, the Frank J. Roshek Professor of Physics, Applied Physics, and Bioengineering, has played a key role in organizing the effort, securing funding from President Barack Obama's BRAIN (Brain Research through Advancing Innovative Neurotechnology) Initiative in both 2014 and 2016, and organizing a TEDxCaltech event on the brain in 2013. Roukes's research has led to a method for mapping brain circuits called integrated photonics. Tiny optical microchips can be implanted inside the brain where they can be used to monitor neurons and also to control their activity. Prior to this, only brain circuits lying close to the surface of the brain could be monitored. Roukes's goal is to record the behavior of every neuron in a cubic millimeter of brain tissue (roughly 100,000 neurons).
Credit: Roukes et. al.
Nano-architected materials and devices
One reason why KNI's establishment and continued operation is so widely celebrated in science is that researchers have the ability to use the facility to create new materials, or old materials in new configurations with different capabilities. One such nano-architected material, built from tiny carbon struts, is more impact resistant than Kevlar. Other nano-architected materials have the capacity to refract light backward, a phenomenon not found in nature, and to create metamaterials that can be tuned to take on a variety of shapes. Known materials, such as a sponge, have the ability to take on different shapes depending on conditions: one shape when wet, another when dry. But these carefully architected lattices can be finely controlled to take on a variety of "in-between" states. Some nanoscale devices have benefited from machine learning, where multiple iterations of a design are printed out until the device is optimized to, for example, separate light by wavelength and polarization, a technology that could be added to cameras to increase their resolution and efficiency.
New Energy Solutions
It has become imperative to develop alternative energy sources, such as solar and wind power, that are efficient, safe, and renewable, and that minimize waste. To that end, Caltech researchers, using KNI's instruments, have made pioneering strides in something quite new: space-based solar power. The Space Solar Power Project, funded by the Donald Bren Foundation, at first anonymously in 2013, and then publicly in 2021, is working toward harnessing solar power with space-based solar collectors and beaming it back to Earth 24 hours a day, without interference from weather or darkness. A demonstration mission was launched in January 2023, and by May 2023, power was wirelessly transmitted from space for the first time to a receiver on the roof of the Gordon and Betty Moore Laboratory of Engineering on the Caltech campus. Nanomaterials are also being pioneered to extend the lifetime of rechargeable lithium batteries, and to make them more energy-dense.