BLOGS

A finished device: Optical microscope image of the transistor (left) and an ultra-scaled vertical nanowire (right). (Courtesy: Y Shao)

Topics: Electrical Engineering, Materials Science, Nanoengineering, Nanomaterials, Nanotechnology, Semiconductor Technology

A new transistor made from semiconducting vertical nanowires of gallium antimonide (GaSb) and indium arsenide (InAs) could rival today’s best silicon-based devices. The new transistors are switched on and off by electrons tunnelling through an energy barrier, making them highly energy-efficient. According to their developers at the Massachusetts Institute of Technology (MIT) in the US, they could be ideal for low-energy applications such as the Internet of Things (IoT).

Electronic transistors use an applied voltage to regulate the flow of electricity – that is, electrons – within a semiconductor chip. When this voltage is applied to a conventional silicon transistor, electrons climb over an energy barrier from one side of the device to the other, and it switches from an “off” state to an “on” one. This type of switching is the basis of modern information technology, but there is a fundamental physical limit on the threshold voltage required to get the electrons moving. This limit, which is sometimes termed the “Boltzmann tyranny” because it stems from the Boltzmann-like energy distribution of electrons in a semiconductor, puts a cap on the energy efficiency of this type of transistor.

Highly precise process

In the new work, MIT researchers led by electrical engineer Jesús A del Alamo made their transistor using a top-down fabrication technique they developed. This extremely precise process uses high-quality, epitaxially-grown structures and both dry and wet etching to fabricate nanowires just 6 nm in diameter. The researchers then placed a gate stack composed of a very thin gate dielectric and a metal gate on the sidewalls of the nanowires. Finally, they added point contacts to the source, gate and drain of the transistors using multiple planarization and etch-back steps.

Vertical-nanowire transistors defeat the Boltzmann tyranny, Isabelle Dumé, Physics World

Power with a twist: Twisted ropes made from single-walled carbon nanotubes could store enough energy to power sensors within the human body while avoiding the chemical hazards associated with batteries. (Courtesy: Shigenori UTSUMI)

Topics: Applied Physics, Battery, Carbon Nanotubes, Chemistry, Materials Science, Nanoengineering

Mechanical watches and clockwork toys might seem like relics of a bygone age, but scientists in the US and Japan are bringing this old-fashioned form of energy storage into the modern era. By making single-walled carbon nanotubes (SWCNTs) into ropes and twisting them like the string on an overworked yo-yo, Katsumi Kaneko, Sanjeev Kumar Ujjain , and colleagues showed that they can store twice as much energy per unit mass as the best commercial lithium-ion batteries. The nanotube ropes are also stable at a wide range of temperatures, and the team says they could be safer than batteries for powering devices such as medical sensors.

SWCNTs are made from sheets of pure carbon just one atom thick that have been rolled into a straw-like tube. They are impressively tough – five times stiffer and 100 times stronger than steel – and earlier theoretical studies by team member David Tománek and others suggested that twisting them could be a viable means of storing large amounts of energy in a compact, lightweight system.

Twisted carbon nanotubes store more energy than lithium-ion batteries, Margaret Harris, Physics World.

Researchers have synthesized sheets of gold that are one atom thick. Credit: imaginima/Getty

Topics: Graphene, Materials Science, Nanoengineering, Nanomaterials, Solid-State Physics

It is the world’s thinnest gold leaf: a gossamer sheet of gold just one atom thick. Researchers have synthesized¹ the long-sought material, known as goldene, which is expected to capture light in ways that could be useful in applications such as sensing and catalysis.

Goldene is a gilded cousin of graphene, the iconic atom-thin material made of carbon that was discovered in 2004. Since then, scientists have identified hundreds more of these 2D materials. But it has been particularly difficult to produce 2D sheets of metals, because their atoms have always tended to cluster together to make nanoparticles instead.

Researchers have previously reported single-atom-thick layers of tin² and lead³ stuck to various substances, and they have produced gold sheets sandwiched between other materials. But “we submit that goldene is the first free-standing 2D metal, to the best of our knowledge”, says materials scientist Lars Hultman at Linköping University in Sweden, who is part of the team behind the new research. Crucially, the simple chemical method used to make goldene should be amenable to larger-scale production, the researchers reported in Nature Synthesis on 16 April¹.

“I’m very excited about it,” says Stephanie Reich, a solid-state physicist and materials scientist at the Free University of Berlin, who was not involved in the work. “People have been thinking for quite some time how to take traditional metals and make them into really well-ordered 2D monolayers.”

In 2022, researchers at New York University Abu Dhabi (NYUAD) said that they had produced goldene, but the Linköping team contends that the prior material probably contained multiple atomic layers, on the basis of the electron microscopy images and other data that were published in ACS Applied Materials and Interfaces⁴. Reich agrees that the 2022 study failed to prove that the material was singler-layer goldene. The principal authors of the NYUAD study did not respond to Nature’s questions about their work.

Meet ‘goldene’: this gilded cousin of graphene is also one atom thick, Mark Peplow, Nature

TSMC is building Two New Facilities to Accommodate 2nm Chip Production

Topics: Applied Physics, Chemistry, Electrical Engineering, Materials Science, Nanoengineering, Semiconductor Technology

Realize that Moore’s “law” isn’t like Newton’s Laws of Gravity or the three laws of Thermodynamics. It’s simply an observation based on experience with manufacturing silicon processors and the desire to make money from the endeavor continually.

As a device engineer, I had heard “7 nm, and that’s it” so often that it became colloquial folklore. TSMC has proven itself a powerhouse once again and, in our faltering geopolitical climate, made itself even more desirable to mainland China in its quest to annex the island, sadly by force if necessary.

Apple will be the first electronic manufacturer to receive chips built by Taiwan Semiconductor Manufacturing Company (TSMC) using a two-nanometer process. According to Korea’s DigiTimes Asia, inside sources said that Apple is "widely believed to be the initial client to utilize the process." The report noted that TSMC has been increasing its production capacity in response to “significant customer orders.” Moreover, the report added that the company has recently established a production expansion strategy aimed at producing 2nm chipsets based on the Gate-all-around (GAA) manufacturing process.

The GAA process, also known as gate-all-around field-effect transistor (GAA-FET) technology, defies the performance limitations of other chip manufacturing processes by allowing the transistors to carry more current while staying relatively small in size.

Apple to jump queue for TSMC's industry-first 2-nanometer chips: Report, Harsh Shivam, New Delhi, Business Standard.

Researchers are working to overcome challenges related to nanoscale optoelectronic interconnects, which use light to transmit signals around an integrated circuit. IMAGE: PROVIDED BY NCNST

Topics: Biology, Materials Science, Nanoengineering, Nanomaterials, Nanotechnology, Quantum Mechanics

The promise of nanotechnology, the engineering of machines and systems at the nanoscale, is anything but tiny. Over the past decade alone, there has been an explosion in research on how to design and build components that solve problems across almost every sector, and nanotechnology innovations have led to huge advancements in our quest to address humanity’s grand challenges, from healthcare to water to food security.

Like any area of scholarship, there are still so many unknowns. And yet, there are more talented scientists and engineers endeavoring to better comprehend and harness the power of nanotechnology than ever before. The future is bright for nanotechnology and its applications.

In celebration of its 20th anniversary, the National Center for Nanoscience and Technology, China (NCNST), a subsidiary of the prestigious Chinese Academy of Sciences, partnered with Science Custom Publishing to survey nanoscience experts from the journal and across the globe about the most knotty and fascinating questions that still need to be answered if we are to advance nanotechnology in society.

The Tiny Ten: Experts weigh in on the top 10 challenges remaining for nanoscience & nanotechnology, Science Magazine

In this image, optical pulses (solitons) can be seen circling through conjoined optical tracks. (Image: Yuan, Bowers, Vahala, et al.) An animated gif is at the original link below.

Topics: Applied Physics, Astronomy, Electrical Engineering, Materials Science, Nanoengineering, Optics

(Nanowerk News) When we last checked in with Caltech's Kerry Vahala three years ago, his lab had recently reported the development of a new optical device called a turnkey frequency microcomb that has applications in digital communications, precision timekeeping, spectroscopy, and even astronomy.

This device, fabricated on a silicon wafer, takes input laser light of one frequency and converts it into an evenly spaced set of many distinct frequencies that form a train of pulses whose length can be as short as 100 femtoseconds (quadrillionths of a second). (The comb in the name comes from the frequencies being spaced like the teeth of a hair comb.)

Now Vahala, Caltech's Ted and Ginger Jenkins, Professor of Information Science and Technology and Applied Physics and executive officer for applied physics and materials science, along with members of his research group and the group of John Bowers at UC Santa Barbara, have made a breakthrough in the way the short pulses form in an important new material called ultra-low-loss silicon nitride (ULL nitride), a compound formed of silicon and nitrogen. The silicon nitride is prepared to be extremely pure and deposited in a thin film.

In principle, short-pulse microcomb devices made from this material would require very low power to operate. Unfortunately, short light pulses (called solitons) cannot be properly generated in this material because of a property called dispersion, which causes light or other electromagnetic waves to travel at different speeds, depending on their frequency. ULL has what is known as normal dispersion, and this prevents waveguides made of ULL nitride from supporting the short pulses necessary for microcomb operation.

In a paper appearing in Nature Photonics ("Soliton pulse pairs at multiple colors in normal dispersion microresonators"), the researchers discuss their development of the new micro comb, which overcomes the inherent optical limitations of ULL nitride by generating pulses in pairs. This is a significant development because ULL nitride is created with the same technology used for manufacturing computer chips. This kind of manufacturing technique means that these microcombs could one day be integrated into a wide variety of handheld devices similar in form to smartphones.

The most distinctive feature of an ordinary microcomb is a small optical loop that looks a bit like a tiny racetrack. During operation, the solitons automatically form and circulate around it.

"However, when this loop is made of ULL nitride, the dispersion destabilizes the soliton pulses," says co-author Zhiquan Yuan (MS '21), a graduate student in applied physics.

Imagine the loop as a racetrack with cars. If some cars travel faster and some travel slower, then they will spread out as they circle the track instead of staying as a tight pack. Similarly, the normal dispersion of ULL means light pulses spread out in the microcomb waveguides, and the microcomb ceases to work.

The solution devised by the team was to create multiple racetracks, pairing them up so they look a bit like a figure eight. In the middle of that '8,' the two tracks run parallel to each other with only a tiny gap between them.

Conjoined 'racetracks' make new optical devices possible, Nanowerk.

A mathematical tool called a fast Fourier transform maps the structure in a way that reveals the 12-fold symmetry of the quasicrystal. The fast Fourier transform of the electron microscope image of the quasicrystal is shown on the left, while the transform of the simulated crystal is shown on the right. Image credit: Mirkin Research Group, Northwestern University, and Glotzer Group, University of Michigan.

Topics: Biology, DNA, Nanoengineering, Nanomaterials, Nanotechnology

ANN ARBOR—Nanoengineers have created a quasicrystal—a scientifically intriguing and technologically promising material structure—from nanoparticles using DNA, the molecule that encodes life.

The team, led by researchers at Northwestern University, the University of Michigan, and the Center for Cooperative Research in Biomaterials in San Sebastian, Spain, reports the results in Nature Materials.

Unlike ordinary crystals, which are defined by a repeating structure, the patterns in quasicrystals don’t repeat. Quasicrystals built from atoms can have exceptional properties—for example, absorbing heat and light differently, exhibiting unusual electronic properties such as conducting electricity without resistance, or their surfaces being very hard or very slippery.

Engineers studying nanoscale assembly often view nanoparticles as a kind of ‘designer atom,’ which provides a new level of control over synthetic materials. One of the challenges is directing particles to assemble into desired structures with useful qualities, and in building this first DNA-assembled quasicrystal, the team entered a new frontier in nanomaterial design.

“The existence of quasicrystals has been a puzzle for decades, and their discovery appropriately was awarded a Nobel Prize,” said Chad Mirkin, the George B. Rathmann Professor of Chemistry at Northwestern University and co-corresponding author of the study. “Although there are now several known examples, discovered in nature or through serendipitous routes, our research demystifies their formation and, more importantly, shows how we can harness the programmable nature of DNA to design and assemble quasicrystals deliberately.”

Nanoparticle quasicrystal constructed with DNA, Kate McAlpine, University of Michigan