How to Construct Machines as Small as Cells

If you want to build a fully functional nanosized robot, you need to incorporate a host of capabilities, from complicated electronic circuits and photovoltaics to sensors and antennas. But just as importantly, if you want your robot to move, you need it to be able to bend.

Cornell researchers have created micron-sized shape memory actuators that enable atomically thin two-dimensional materials to fold themselves into 3D configurations. All they require is a quick jolt of voltage. And once the material is bent, it holds its shape – even after the voltage is removed. As a demonstration, the team created what is potentially the world’s smallest self-folding origami bird. And it’s not a lark.

The group’s paper, “Micrometer-Sized Electrically Programmable Shape Memory Actuators for Low-Power Microrobotics,” published in Science Robotics and was featured on the cover. The paper’s lead author is postdoctoral researcher Qingkun Liu. The project is led by Itai Cohen, professor of physics, and Paul McEuen, the John A. Newman Professor of Physical Science, both in the College of Arts and Sciences.

We humans, our defining characteristic is we’ve learned how to build complex systems and machines at human scales, and at enormous scales as well,” said McEuen. “But what we haven’t learned how to do is build machines at tiny scales. And this is a step in that basic, fundamental evolution in what humans can do, of learning how to construct machines that are as small as cells.”

McEuen and Cohen’s ongoing collaboration has so far generated a throng of nanoscale machines and components, each seemingly faster, smarter and more elegant than the last.

We want to have robots that are microscopic but have brains on board. So that means you need to have appendages that are driven by complementary metal-oxide-semiconductor (CMOS) transistors, basically a computer chip on a robot that’s 100 microns on a side,” Cohen said.

Imagine a million fabricated microscopic robots releasing from a wafer that fold themselves into shape, crawl free and go about their tasks, even assembling into more complicated structures. That’s the vision.


Graphene Smart Textiles Lower Body Temperature During Heatwave

New research on the two-dimensional (2D) material graphene has allowed researchers to create smart adaptive clothing which can lower the body temperature of the wearer in hot climates.

A team of scientists from The University of Manchester’s National Graphene Institute have created a prototype garment to demonstrate dynamic thermal radiation control within a piece of clothing by utilising the remarkable thermal properties and flexibility of graphene. The development also opens the door to new applications such as, interactive infrared displays and covert infrared communication on textiles.

The human body radiates energy in the form of electromagnetic waves in the infrared spectrum (known as blackbody radiation). In a hot climate it is desirable to make use the full extent of the infrared radiation to lower the body temperature which can be achieved by using infrared-transparent textiles. As for the opposite case, infrared-blocking covers are ideal to minimise the energy loss from the body. Emergency blankets are a common example used to deal with treating extreme cases of body temperature fluctuation.

The collaborative team of scientists demonstrated the dynamic transition between two opposite states by electrically tuning the infrared emissivity (the ability to radiate energy) of graphene layers integrated onto textiles.

The new research published today in journal Nano Letters, demonstrates that the smart optical textile technology can change its thermal visibility.

Ability to control the thermal radiation is a key necessity for several critical applications such as temperature management of the body in excessive temperature climates. Thermal blankets are a common example used for this purpose. However, maintaining these functionalities as the surroundings heats up or cools down has been an outstanding challenge”, explained Professor Coskun Kocabas, who led the research.

The successful demonstration of the modulation of optical properties on different forms of textile can leverage the ubiquitous use of fibrous architectures and enable new technologies operating in the infrared and other regions of the electromagnetic spectrum for applications including textile displays, communication, adaptive space suits, and fashion“, he added.


Beyond Moore’s Law

A team of researchers based in Manchester, the Netherlands, Singapore, Spain, Switzerland and the USA has published a new review on a field of computer device development known as spintronics, which could use graphene as a building block for next-generation electronics. Recent theoretical and experimental advances and phenomena in studies of electronic spin transport in graphene and related two-dimensional (2D) materials have emerged as a fascinating area of research and development.

Spintronics is the combination of electronics and magnetism at nanoscale and could allow electronic development at speeds exceeding Moore’s law, which observes that computer processing power roughly doubles every two years, while the price halves. Spintronic devices may offer higher energy efficiency and lower dissipation as compared to conventional electronics, which rely on charge currents. In principle, we could have phones and tablets operating with spin-based transistors and memories, greatly improving speed and storage capacity.

Since its isolation in 2004, graphene has opened the door for other 2D materials. Researchers can then use these materials to create stacks of 2D materials called heterostructures. These can be combined with graphene to create new ‘designer materials‘ to produce applications originally limited to science fiction. As published in APS Journal Review of Modern Physics, the review focuses on the new perspectives provided by heterostructures and their emergent phenomena, including proximity-enabled spin-orbit effects, coupling spin to light, electrical tunability and 2D magnetism. The average person already encounters spintronics in laptops and PCs, which are already using spintronics in the form of the magnetic sensors in the reading heads of hard disk drives. These sensors are also used in the automotive industry.

The continuous progress in graphene spintronics, and more broadly in 2D heterostructures, has resulted in the efficient creation, transport and detection of spin information using effects previously inaccessible to graphene alone” said Dr Ivan Vera Marun, Lecturer in Condensed Matter Physics at The University of Manchester.

As efforts on both the fundamental and technological aspects continue, we believe that ballistic spin transport will be realised in 2D heterostructures, even at room temperature. Such transport would enable practical use of the quantum mechanical properties of electron wave functions, bringing spins in 2D materials to the service of future quantum computation approaches.”

Controlled spin transport in graphene and other two-dimensional materials has become increasingly promising for applications in devices. Of particular interest are custom-tailored heterostructures, known as van der Waals heterostructures, that consist of stacks of two-dimensional materials in a precisely controlled order.

Billions of spintronic devices such as sensors and memories are already being produced. Every hard disk drive has a magnetic sensor that uses a flow of spins, and magnetic random access memory (MRAM) chips are becoming increasingly popular.


Atom-Thin Processor

An international team of researchers has reported a breakthrough in fabricating atom-thin processors — a discovery that could have far-reaching impacts on nanoscale chip production and in labs across the globe where scientists are exploring 2D materials for ever-smaller and –faster semiconductors.

The team, headed by New York University Tandon School of Engineering Professor of Chemical and Biomolecular Engineering Elisa Riedo, outlined the research results in the latest issue of Nature Electronics.They demonstrate that lithography using a probe heated above 100 degrees Celsius outperformed standard methods for fabricating metal electrodes on 2D semiconductors such as molybdenum disulfide (MoS₂). Such transitional metals are among the materials that scientists believe may supplant silicon for atomically small chips.

The team’s new fabrication method — called thermal scanning probe lithography (t-SPL) — offers a number of advantages over today’s electron beam lithography (EBL). First, thermal lithography significantly improves the quality of the 2D transistors, offsetting the Schottky barrier, which hampers the flow of electrons at the intersection of metal and the 2D substrate. Also, unlike EBL, the thermal lithography allows chip designers to easily image the 2D semiconductor and then pattern the electrodes where desired. Also, t-SPL fabrication systems promise significant initial savings as well as operational costs: They dramatically reduce power consumption by operating in ambient conditions, eliminating the need to produce high-energy electrons and to generate an ultra-high vacuum. Finally, this thermal fabrication method can be easily scaled up for industrial production by using parallel thermal probes.


How To Replace The Thick Glass Lenses by 2D Metalens

In optics, the era of glass lenses may be waning. In recent years, physicists and engineers have been designing, constructing and testing different types of ultrathin materials that could replace the thick glass lenses used today in cameras and imaging systems. Critically, these engineered lenses — known as metalenses — are not made of glass. Instead, they consist of materials constructed at the nanoscale into arrays of columns or fin-like structures. These formations can interact with incoming light, directing it toward a single focal point for imaging purposes.

But even though metalenses are much thinner than glass lenses, they still rely on “high aspect ratio” structures, in which the column or fin-like structures are much taller than they are wide, making them prone to collapsing and falling over. Furthermore, these structures have always been near the wavelength of light they’re interacting with in thickness — until now. In a paper published in the journal Nano Letters, a team from the University of Washington (UW) and the National Tsing Hua University in Taiwan announced that it has constructed functional metalenses that are one-tenth to one-half the thickness of the wavelengths of light that they focus. Their metalenses, which were constructed out of layered 2D materials, were as thin as 190 nanometers — less than 1/100,000ths of an inch thick.

This is the first time that someone has shown that it is possible to create a metalens out of 2D materials,” said senior and co-corresponding author Arka Majumdar, a UW assistant professor of physics and of electrical and computer engineering.

Their design principles can be used for the creation of metalenses with more complex, tunable features, added Majumdar, who is also a faculty researcher with the UW’s Molecular Engineering & Sciences Institute and Institute for Nano-Engineered Systems.