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Advance in programmable synthetic materials: Reading sequence of metal atoms in MOFs allows encoding of multiple chemical functions

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Home > Press > Advance in programmable synthetic materials: Reading sequence of metal atoms in MOFs allows encoding of multiple chemical functions

Rods of multivariate MOFs (left) can be programmed with different metal atoms (colored balls) to do a series of chemical tasks, such as controlled drug release, or to encode information like the ones and zeros in a digital computer. CREDIT
UC Berkeley image by Omar Yaghi and Zhe Ji
Rods of multivariate MOFs (left) can be programmed with different metal atoms (colored balls) to do a series of chemical tasks, such as controlled drug release, or to encode information like the ones and zeros in a digital computer. CREDIT
UC Berkeley image by Omar Yaghi and Zhe Ji

Abstract:
Artificial molecules could one day form the information unit of a new type of computer or be the basis for programmable substances. The information would be encoded in the spatial arrangement of the individual atoms – similar to how the sequence of base pairs determines the information content of DNA, or sequences of zeros and ones form the memory of computers.

Advance in programmable synthetic materials: Reading sequence of metal atoms in MOFs allows encoding of multiple chemical functions


Berkeley, CA | Posted on August 11th, 2020

Researchers at the University of California, Berkeley, and Ruhr-Universität Bochum (RUB) have taken a step towards this vision. They showed that atom probe tomography can be used to read a complex spatial arrangement of metal ions in multivariate metal-organic frameworks.

Metal-organic frameworks (MOFs) are crystalline porous networks of multi-metal nodes linked together by organic units to form a well-defined structure. To encode information using a sequence of metals, it is essential to be first able to read the metal arrangement. However, reading the arrangement was extremely challenging. Recently, the interest in characterizing metal sequences is growing because of the extensive information such multivariate structures would be able to offer.

Fundamentally, there was no method to read the metal sequence in MOFs. In the current study, the research team has successfully done so by using atom probe tomography (APT), in which the Bochum-based materials scientist Tong Li is an expert. The researchers chose MOF-74, made by the Yaghi group in 2005, as an object of interest. They designed the MOFs with mixed combinations of cobalt, cadmium, lead, and manganese, and then decrypted their spatial structure using APT.

Li, professor and head of the Atomic-Scale Characterisation research group at the Institute for Materials at RUB, describes the method together with Dr. Zhe Ji and Professor Omar Yaghi from UC Berkeley in the journal Science, published online on August 7, 2020.

Just as sophisticated as biology

In the future, MOFs could form the basis of programmable chemical molecules: for instance, an MOF could be programmed to introduce an active pharmaceutical ingredient into the body to target infected cells and then break down the active ingredient into harmless substances once it is no longer needed. Or MOFs could be programmed to release different drugs at different times.

“This is very powerful, because you are basically coding the behavior of molecules leaving the pores,” Yaghi said.

They could also be used to capture CO2 and, at the same time, convert the CO2 into a useful raw material for the chemical industry.

“In the long term, such structures with programmed atomic sequences can completely change our way of thinking about material synthesis,” write the authors. “The synthetic world could reach a whole new level of precision and sophistication that has previously been reserved for biology.”

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The work was supported by the Center of Excellence for Nanomaterials and Clean Energy Applications at King Abdulaziz City for Science and Technology.

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Robert Sanders
510-915-3097

@UCBerkeley

Copyright © University of California, Berkeley

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Physicists make electrical nanolasers even smaller

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Home > Press > Physicists make electrical nanolasers even smaller

Electrically pumped surface plasmon-polariton nanolaser CREDIT
Dmitry Fedyanin
Electrically pumped surface plasmon-polariton nanolaser CREDIT
Dmitry Fedyanin

Abstract:
Researchers from the Moscow Institute of Physics and Technology and King’s College London cleared the obstacle that had prevented the creation of electrically driven nanolasers for integrated circuits. The approach, reported in a recent paper in Nanophotonics, enables coherent light source design on the scale not only hundreds of times smaller than the thickness of a human hair but even smaller than the wavelength of light emitted by the laser. This lays the foundation for ultrafast optical data transfer in the manycore microprocessors expected to emerge in the near future.

Physicists make electrical nanolasers even smaller


Moscow, Russia | Posted on September 18th, 2020

Light signals revolutionized information technologies in the 1980s, when optical fibers started to replace copper wires, making data transmission orders of magnitude faster. Since optical communication relies on light — electromagnetic waves with a frequency of several hundred terahertz — it allows transferring terabytes of data every second through a single fiber, vastly outperforming electrical interconnects.

Fiber optics underlies the modern internet, but light could do much more for us. It could be put into action even inside the microprocessors of supercomputers, workstations, smartphones, and other devices. This requires using optical communication lines to interconnect the purely electronic components, such as processor cores. As a result, vast amounts of information could be transferred across the chip nearly instantaneously.

Getting rid of the limitation on data transmission will make it possible to directly improve microprocessor performance by stacking more processor cores, to the point of creating a 1,000-core processor that would be virtually 100 times faster than its 10-core counterpart, which is pursued by the semiconductor industry giants IBM, HP, Intel, Oracle, and others. This in turn will make it possible to design a true supercomputer on a single chip.

The challenge is to connect optics and electronics at the nanoscale. To achieve this, the optical components cannot be larger than hundreds of nanometers, which is about 100 times smaller than the width of a human hair. This size restriction also applies to on-chip lasers, which are necessary for converting information from electrical signals to optical pulses that carry the bits of the data.

However, light is a kind of electromagnetic radiation with a wavelength of hundreds of nanometers. And the quantum uncertainty principle says there is a certain minimum volume that light particles, or photons, can be localized in. It cannot be smaller than the cube of the wavelength. In crude terms, if one makes a laser too small, the photons will not fit into it. That said, there are ways around this restriction on the size of optical devices, which is known as the diffraction limit. The solution is to replace photons with surface plasmon-polaritons, or SPPs.

SPPs are collective oscillations of electrons that are confined to the surface of a metal and interact with the surrounding electromagnetic field. Only a few metals known as plasmonic metals are good to work with SPPs: gold, silver, copper, and aluminum. Just like photons, SPPs are electromagnetic waves, but at the same frequency they are much better localized — that is, they occupy less space. Using SPPs instead of photons makes it possible to “compress” light and thus overcome the diffraction limit.

The design of truly nanoscale plasmonic lasers is already possible with current technologies. However, these nanolasers are optically pumped, that is, they have to be illuminated with external bulky and high-power lasers. This may well be convenient for scientific experiments, but not outside the laboratory. An electronic chip intended for mass production and real-life applications has to incorporate hundreds of nanolasers and operate on an ordinary printed circuit board. A practical laser needs to be electrically pumped, or, in other words, powered by an ordinary battery or DC power supply. So far such lasers are only available as devices that operate at cryogenic temperatures, which is not suitable for most practical applications, since maintaining liquid nitrogen cooling is not typically possible.

The physicists from the Moscow Institute of Physics and Technology (MIPT) and King’s College London have proposed an alternative to the conventional way electrical pumping works. Usually the scheme of electrical pumping of nanolasers requires an ohmic contact made of titanium, chromium, or a similar metal. Moreover, that contact has to be a part of the resonator — the volume where the laser radiation is generated. The problem with that is titanium and chromium strongly absorb light, which harms resonator performance. Such lasers suffer from high pump current and are susceptible to overheating. This is why the need for cryogenic cooling emerges, along with all the inconveniences it entails.

The proposed new scheme for electrical pumping is based on a double heterostructure with a tunneling Schottky contact. It makes the ohmic contact with its strongly absorbing metal redundant. The pumping now happens across the interface between the plasmonic metal and semiconductor, along which SPPs propagate. “Our novel pumping approach makes it possible to bring the electrically driven laser to the nanoscale, while retaining its ability to operate at room temperature. At the same time, unlike other electrically pumped nanolasers, the radiation is effectively directed to a photonic or plasmonic waveguide, making the nanolaser fit for integrated circuits,” Dr. Dmitry Fedyanin from the Center for Photonics and 2D Materials at MIPT commented.

The plasmonic nanolaser proposed by the researchers is smaller — in each of its three dimensions — than the wavelength of the light it emits. Moreover, the volume occupied by SPPs in the nanolaser is 30 times smaller than the light wavelength cubed. According to the researchers, their room-temperature plasmonic nanolaser could be easily made even smaller, making its characteristics even more impressive, but that would come at the cost of the inability to effectively extract the radiation into a bus waveguide. Thus, while further miniaturization would render the device poorly applicable to on-chip integrated circuits, it would be still convenient for chemical and biological sensors and near-field optical spectroscopy or optogenetics.

Despite its nanoscale dimensions, the predicted output power of the nanolaser amounts to over 100 microwatts, which is comparable to much larger photonic lasers. Such a high output power allows each nanolaser to be used to transmit hundreds of gigabits per second, eliminating one of the most formidable obstacles to higher-performance microchips. And that includes all sorts of hi-end computing devices: supercomputer processors, graphic processors, and perhaps even some gadgets to be invented in the future.

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The study was supported by a grant of the Russian Foundation for Basic Research.

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Contacts:
Varvara Bogomolova
7-916-147-4496

@mipt_eng

Copyright © Moscow Institute of Physics and Technology

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Nano-microscope gives first direct observation of the magnetic properties of 2D materials: Discovery means new class of materials and technologies

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Home > Press > Nano-microscope gives first direct observation of the magnetic properties of 2D materials: Discovery means new class of materials and technologies

New diamond-based nano-microscope opens up potential for 2D materials. CREDIT
David A. Broadway
New diamond-based nano-microscope opens up potential for 2D materials. CREDIT
David A. Broadway

Abstract:
Australian researchers and their colleagues from Russia and China have shown that it is possible to study the magnetic properties of ultrathin materials directly, via a new microscopy technique that opens the door to the discovery of more two-dimensional (2D) magnetic materials, with all sorts of potential applications.

Nano-microscope gives first direct observation of the magnetic properties of 2D materials: Discovery means new class of materials and technologies


Melbourne, Australia | Posted on September 18th, 2020

Published in the journal Advanced Materials, the findings are significant because current techniques used to characterise normal (three-dimensional) magnets don’t work on 2D materials such as graphene due to their extremely small size – a few atom thick.

“So far there has been no way to tell exactly how strongly magnetic a 2D material was,” said Dr Jean-Philippe Tetienne from the University of Melbourne School of Physics and Centre for Quantum Computation and Communication Technology.

“That is, if you were to place the 2D material on your fridge’s door like a regular fridge magnet, how strongly it gets stuck onto it. This is the most important property of a magnet.”

To address the problem, the team, led by Professor Lloyd Hollenberg, employed a widefield nitrogen-vacancy microscope, a tool they recently developed that has the necessary sensitivity and spatial resolution to measure the strength of 2D material.

“In essence, the technique works by bringing tiny magnetic sensors (so-called nitrogen-vacancy centres, which are atomic defects in a piece of diamond) extremely close to the 2D material in order to sense its magnetic field,” Professor Hollenberg explained.

To test the technique, the scientists chose to study vanadium triiodide (VI3) as large 3D chunks of VI3 were already known to be strongly magnetic.

Using their special microscope, they have now shown that 2D sheets of VI3 are also magnetic but about twice as weak as in the 3D form. In other words, it would be twice as easy to get them off the fridge’s door.

“This was a bit of a surprise, and we are currently trying to understand why the magnetisation is weaker in 2D, which will be important for applications,” Dr Tetienne said.

Professor Artem Oganov of Skolkovo Institute of Science and Technology (Skoltech) in Moscow said the findings have the potential to trigger new technology.

“Just a few years ago, scientists doubted that two-dimensional-magnets are possible at all. With the discovery of two-dimensional ferromagnetic VI3, a new exciting class of materials emerged. New classes of material always mean that new technologies will appear, both for studying such materials and harnessing their properties.”

The international team now plan to use their microscope to study other 2D magnetic materials as well as more complex structures, including those that are expected to play a key role in future energy-efficient electronics.

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Other organizations involved in the research include University of Basel, RMIT University, Nanjing University of Posts and Telecommunications, Moscow Institute of Physics and Technology, Northwestern Polytechnical University, and Renmin University of China.

####

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Contacts:
Lito Vilisoni Wilson
61-466-867-909

@unimelb

Copyright © University of Melbourne

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Who stole the light? Self-induced ultrafast demagnetization limits the amount of light diffracted from magnetic samples at soft x-ray energies

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Home > Press > Who stole the light? Self-induced ultrafast demagnetization limits the amount of light diffracted from magnetic samples at soft x-ray energies

Schematic sketch of the scattering experiment with two competing processes. The soft x-ray beam (blue arrow, from left) hits the magnetic sample (circular area) where it scatters from the microscopic, labyrinth-like magnetization pattern. In this process, an x-ray photon is first absorbed by a Cobalt 3p core electron (a). The resulting excited state can then relax spontaneously (b), emitting a photon in a new direction (purple arrow). This scattered light is recorded as the signal of interest in experiments. However, if another x-ray photon encounters an already excited state, stimulated emission occurs (c). Here, two identical photons are emitted in the direction of the incident beam (blue arrow towards right). This light carries only little information on the sample magnetization and is usually blocked for practical reasons. CREDIT
MBI Berlin
Schematic sketch of the scattering experiment with two competing processes. The soft x-ray beam (blue arrow, from left) hits the magnetic sample (circular area) where it scatters from the microscopic, labyrinth-like magnetization pattern. In this process, an x-ray photon is first absorbed by a Cobalt 3p core electron (a). The resulting excited state can then relax spontaneously (b), emitting a photon in a new direction (purple arrow). This scattered light is recorded as the signal of interest in experiments. However, if another x-ray photon encounters an already excited state, stimulated emission occurs (c). Here, two identical photons are emitted in the direction of the incident beam (blue arrow towards right). This light carries only little information on the sample magnetization and is usually blocked for practical reasons. CREDIT
MBI Berlin

Abstract:
Free electron X-ray lasers deliver intense ultrashort pulses of x-rays, which can be used to image nanometer-scale objects in a single shot. When the x-ray wavelength is tuned to an electronic resonance, magnetization patterns can be made visible. When using increasingly intense pulses, however, the magnetization image fades away. The mechanism responsible for this loss in resonant magnetic scattering intensity has now been clarified.

Who stole the light? Self-induced ultrafast demagnetization limits the amount of light diffracted from magnetic samples at soft x-ray energies


Berlin, Germany | Posted on September 18th, 2020

Just as in flashlight photography, short yet intense flashes of x-rays allow to record images or x-ray diffraction patterns which “freeze” motion that is slower than the duration of the x-ray pulse. The advantage of x-rays over visible light is that nanometer scale objects can be discerned due to the short wavelength of x-rays. Furthermore, if the wavelength of the x-rays is tuned corresponding to particular energies for electronic transitions, one can obtain unique contrast, allowing for example to make the magnetization of different domains within a material visible. The fraction of x-rays scattered from a magnetic domain pattern, however, decreases when the x-ray intensity in the pulse is increased. While this effect had been observed already in the very first images of magnetic domains recorded at a free electron x-ray laser in 2012, a variety of different explanations had been put forward to explain this loss in scattered x-ray intensity.

A team of researchers from MBI Berlin, together with colleagues from Italy and France, has now precisely recorded the dependence of the resonant magnetic scattering intensity as a function of the x-ray intensity incident per unit area ( the “fluence”) on a ferromagnetic domain sample. Via integration of a device to detect the intensity of every single shot hitting the actual sample area, they were able record the scattering intensity over three orders of magnitude in fluence with unprecedented precision, in spite of the intrinsic shot-to-shot variations of the x-ray beam hitting the tiny samples. The experiments with soft x-rays were carried out at the FERMI free-electron x-ray laser in Trieste, Italy.

Magnetization is a property directly coupled to the electrons of a material, which make up the magnetic moment via their spin and orbital motion. For their experiments, the researchers used patterns of ferromagnetic domains forming in cobalt-containing multilayers, a prototypical material often used in magnetic scattering experiments at x-ray lasers. In the interaction with x-rays, the population of electrons is disturbed and energy levels can be altered. Both effects could lead to a reduction in scattering, either through a transient reduction of the actual magnetization in the material due to the reshuffling of electrons with different spin, or by not being able to detect the magnetization anymore because of the shift in the energy levels. Furthermore, it has been debated whether the onset of stimulated emission at high x-ray fluences administered during a pulse of about 100 femtoseconds duration can be responsible for the loss in scattering intensity. The mechanism in the latter case is due to the fact that in stimulated emission, the direction of an emitted photon is copied from the incident photon. As a result, the emitted x-ray photon would not contribute to the beam scattered away from the original direction, as sketched in Fig.1.

In the results presented in the journal Physical Review Letters, the researchers show that while the loss in magnetic scattering in resonance with the Co 2p core levels has been attributed to stimulated emission in the past, for scattering in resonance with the shallower Co 3p core levels this process is not significant. The experimental data over the entire fluence range is well described by simply considering the actual demagnetization occurring within each magnetic domain, which the MBI researchers had previously characterized with laser-based experiments. Given the short lifetime of the Co 3p core levels of about a quarter femtosecond which is dominated by Auger decay, it is likely that the hot electrons generated by the Auger cascade in concert with subsequent electron scattering events lead to a reshuffling of spin up and spin down electrons transiently quenching the magnetization. As this reduced magnetization manifests itself already within the duration of the x-ray pulses used (70 and 120 femtosecond) and persists for a much longer time, the latter part of the x-ray pulse interacts with a domain pattern where the magnetization has actually faded away. This is in line with the observation that less reduction of the magnetic scattering is observed when hitting the magnetic sample with the same number of x-ray photons within a shorter pulse duration (Fig.2). In contrast, if stimulated emission were the dominant mechanism, the opposite behavior would be expected.

Beyond clarifying the mechanism at work, the findings have important ramifications for future single shot experiments on magnetic materials at free electron x-ray lasers. Similar to the situation in structural biology, where imaging of protein molecules by intense x-ray laser pulses can be impeded by the destruction of the molecule during the pulse, researchers investigating magnetic nanostructures also have to choose the fluence and pulse duration wisely in their experiments. With the fluence dependence of resonant magnetic scattering mapped out, researchers at x-ray lasers now have a guideline to design their future experiments accordingly.

####

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Physicists make electrical nanolasers even smaller September 18th, 2020

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Nano-microscope gives first direct observation of the magnetic properties of 2D materials: Discovery means new class of materials and technologies September 18th, 2020

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