In the latest advance in nano-and micro-architected materials, engineers at Caltech have developed a new material made from numerous interconnected microscale knots.
The knots make the material far tougher than identically structured but unknotted materials: they absorb more energy and are able to deform more while still being able to return to their original shape undamaged. These new knotted materials may find applications in biomedicine as well as in aerospace applications due to their durability, possible biocompatibility, and extreme deformability.
“The capability to overcome the general trade-off between material deformability and tensile toughness [the ability to be stretched without breaking] offers new ways to design devices that are extremely flexible, durable, and can operate in extreme conditions,” says former Caltech graduate student Widianto P. Moestopo, now at Lawrence Livermore National Laboratory. Moestopo is the lead author of a paper on the nanoscale knots that was published on March 8 in Science Advances.
Alloys that can return to their original structure after being deformed have a so-called shape memory. This phenomenon and the resulting forces are used in many mechanical actuating systems, for example in generators or hydraulic pumps. However, it has not been possible to use this shape-memory effect at a small nanoscale. Objects made of shape-memory alloy can only change back to their original shape if they are larger than around 50 nanometers.
Researchers led by Salvador Pané, Professor of Materials of Robotics at ETH Zurich, and Xiang-Zhong Chen, a senior scientist in his group, were able to circumvent this limitation using ceramic materials. In a study published in the journal Nature Communications, they demonstrate the shape-memory effect on a layer that is about twenty nanometers thick and made of materials called ferroic oxides. This achievement now makes it possible to apply the shape-memory effect to tiny nanoscale machines.
At first glance, ferroic oxides do not appear to be very suitable for the shape-memory effect: They are brittle in bulk scale, and in order to produce very thin layers of them, they usually have to be fixed onto a substrate, which makes them inflexible. In order to still be able to induce the shape-memory effect, the researchers used two different oxides, barium titanate and cobalt ferrite, of which they temporarily applied thin layers onto a magnesium oxide substrate. The lattice parameters of the two oxides differ significantly from each other. After the researchers had detached the two-layered strip from the supporting substrate, the tension between the two oxides generated a spiral-shaped twisted structure.
Decoding the Brain
Posted in nanotechnology, neuroscience, physics
The ultimate miniature electronic device may be one that manipulates individual electrons with subnanometer and subfemtosecond precision. The past few decades have seen immense progress in the control of ultrafast electronic processes, including in the context of vacuum nanoelectronics, where electrons travel from a nanoscale emitter to a target electrode through a vacuum. Now Hirofumi Yanagisawa at the Japan Science and Technology Agency and colleagues have taken an important step toward optimal spatial control by using the orbitals of a single molecule to shape its electron emission (Fig. 1) [1]. The approach offers the prospect of building highly controllable electron emitters, but also of furthering our understanding of the role of molecular orbitals in the electronic structure of solids.
Fundamental to achieving extreme control over electron emission is defining the spot from which electrons are ejected from the emitter. One approach is to physically shape the material of the emitter into the desired spot pattern. Doing that at the subnanometer scale would entail significant material-and fabrication-related challenges, however. Instead, Yanagisawa and colleagues have demonstrated the clever idea of using the inherent electronic structure of a molecule to route the electrons for emission. In essence, the molecular orbitals are used as a spatial filter to control the emission pattern.
The team’s work grows out of two broad areas of investigation that have progressed significantly over the past few decades. One of these involves the study of femto-and attosecond electron dynamics and the creation of ultrafast electron sources, exemplified by the 2006 demonstration of tight spatial control over femtosecond electron pulses through emission from a nanoscale metallic tip [2– 8]. The second is the study of electron emission patterns originating from molecular structures and nanostructures. Examples include patterns corresponding to the tip structures of nanotubes and nanowires, which change as the tip evolves during nanotube growth [9– 11]. It is by combining the techniques of ultrafast emission and emission microscopy that Yanagisawa and colleagues have demonstrated that the emission patterns can be directly linked to specific molecular orbitals.
Nanotechnology is a field of science and engineering that focuses on the design and manufacture of extremely small devices and structures.
X-ray diffraction has been used for more than a hundred years to understand the structure of crystals or proteins—for instance, in 1952 the well-known double helix structure of the DNA that carries genetic information was discovered in this way. In this technique, the object under investigation is bombarded with short-wavelength X-ray beams. The diffracted beams then interfere and thus create characteristic diffraction patterns from which one can gain information about the shape of the object.
For several years now it has been possible to study even single nanoparticles in this way, using very short and extremely intense X-ray pulses. However, this typically only yields a two-dimensional image of the particle. A team of researchers led by ETH professor Daniela Rupp, together with colleagues at the universities of Rostock and Freiburg, the TU Berlin and DESY in Hamburg, have now found a way to also calculate the three-dimensional structure from a single diffraction pattern, so that one can “look” at the particle from all directions. In the future it should even be possible to make 3D-movies of the dynamics of nanostructures in this way. The results of this research have recently been published in the scientific journal Science Advances.
Daniela Rupp has been assistant professor at ETH Zurich since 2019, where she leads the research group “Nanostructures and ultra-fast X-ray science.” Together with her team she tries to better understand the interaction between very intense X-ray pulses and matter. As a model system they use nanoparticles, which they also investigate at the Paul Scherrer Institute. “For the future there are great opportunities at the new Maloja instrument, on which we were the first user group to make measurements at the beginning of last year. Right now our team there is activating the attosecond mode, with which we can even observe the dynamics of electrons,” says Rupp.
Graphene is a strange material. Understanding its properties is both a fundamental question of science and a promising avenue for new technologies. A team of researchers from the Institute of Science and Technology Austria (ISTA) and the Weizmann Institute of Science has studied what happens when they layer four sheets of it on top of each other and how this can lead to new forms of exotic superconductivity.
Imagine a sheet of material just one layer of atoms thick—less than a millionth of a millimeter. While this may sound fantastical, such a material exists: it is called graphene.
Graphene is an allotrope of carbon in the form of a single layer of atoms in a two-dimensional hexagonal lattice in which one atom forms each vertex. It is the basic structural element of other allotropes of carbon, including graphite, charcoal, carbon nanotubes, and fullerenes. In proportion to its thickness, it is about 100 times stronger than the strongest steel.