Darwin on a chip

UT researchers develop (r)evolutionary circuits

Researchers of the MESA+ Institute for Nanotechnology and the CTIT Institute for ICT Research at the University of Twente in The Netherlands have demonstrated working electronic circuits that have been produced in a radically new way, using methods that resemble Darwinian evolution. The size of these circuits is comparable to the size of their conventional counterparts, but they are much closer to natural networks like the human brain. The findings promise a new generation of powerful, energy-efficient electronics, and have been published in the leading British journal Nature Nanotechnology.

One of the greatest successes of the 20th century has been the development of digital computers. During the last decades these computers have become more and more powerful by integrating ever smaller components on silicon chips. However, it is becoming increasingly hard and extremely expensive to continue this miniaturisation. Current transistors consist of only a handful of atoms. It is a major challenge to produce chips in which the millions of transistors have the same characteristics, and thus to make the chips operate properly. Another drawback is that their energy consumption is reaching unacceptable levels. It is obvious that one has to look for alternative directions, and it is interesting to see what we can learn from nature. Natural evolution has led to powerful ‘computers’ like the human brain, which can solve complex problems in an energy-efficient way. Nature exploits complex networks that can execute many tasks in parallel.

Moving away from designed circuits

The approach of the researchers at the University of Twente is based on methods that resemble those found in Nature. They have used networks of gold nanoparticles for the execution of essential computational tasks. Contrary to conventional electronics, they have moved away from designed circuits. By using 'designless' systems, costly design mistakes are avoided. The computational power of their networks is enabled by applying artificial evolution. This evolution takes less than an hour, rather than millions of years. By applying electrical signals, one and the same network can be configured into 16 different logical gates. The evolutionary approach works around - or can even take advantage of - possible material defects that can be fatal in conventional electronics.

Powerful and energy-efficient

It is the first time that scientists have succeeded in this way in realizing robust electronics with dimensions that can compete with commercial technology. According to prof. Wilfred van der Wiel, the realized circuits currently still have limited computing power. “But with this research we have delivered proof of principle: demonstrated that our approach works in practice. By scaling up the system, real added value will be produced in the future. Take for example the efforts to recognize patterns, such as with face recognition. This is very difficult for a regular computer, while humans and possibly also our circuits can do this much better."  Another important advantage may be that this type of circuitry uses much less energy, both in the production, and during use. The researchers anticipate a wide range of applications, for example in portable electronics and in the medical world.

University of Twente

Nanoelectronics Engineers Develop Transistor that Overcomes Fundamental Power Limitations

A new atomically-flat transistor developed by UC Santa Barbara engineers overcomes one of the fundamental limitations of conventional transistors and reduces power dissipation by over 90 percent

One of the greatest challenges in the evolution of electronics has been to reduce power consumption during transistor switching operation. In a study recently reported in Nature, engineers at UC Santa Barbara, in collaboration with Rice University, have demonstrated a new transistor that switches at only 0.1 volts and reduces power dissipation by over 90% compared to state-of-the-art silicon transistors (MOSFETs).

MOSFETs have been the building blocks of everyday electronic products since the 1970s. However, to sustain the ever-growing need for increased transistor densities, miniaturization of MOSFETs has given rise to a power dissipation challenge due to the fundamental limitations of their turn-on characteristics.

"The steepness of a transistor's turn-on is characterized by a parameter known as the subthreshold swing, which cannot be lowered below a certain level in MOSFETs," explained Kaustav Banerjee, Professor of Electrical and Computer Engineering at UC Santa Barbara. A minimum gate voltage change of 60 millivolts at room temperature is required to change the current by a factor of ten in MOSFETs. In essence, the existing state of transistor technology limits the energy efficiency potential of digital circuits in general.

The research group of Professor Banerjee at UC Santa Barbara took a new approach to subverting this fundamental limitation. They employed the quantum mechanical phenomenon of band-to-band tunneling to design a tunnel field effect transistor (TFET) with sub-60mV per decade of subthreshold swing.

"We restructured the transistor's source to channel junction to filter out high energy electrons that can diffuse over the source/channel barrier even in the off state, thereby making the off state current negligibly small," explained Banerjee. At UCSB, Banerjee's Nanoelectronics Research Lab includes Deblina Sarkar, Xuejun Xie, Wei Liu, Wei Cao, Jiahao Kang, and Stephan Kraemer, as well as Yongji Gong and Pulickel Ajayan of Rice University.

Banerjee and his colleagues are motivated by a global electronics industry that loses billions of dollars each year to the impact of power dissipation on chip cost and reliability. "This translates into lower battery lifetime in personal devices like cell phones and laptops, and massive power consumption of servers in large data centers," adds Banerjee, pointing out the global scale of this energy demand.

An industry that relies on conventional semiconductors such as silicon or III-V compound semiconductors as the channel material for TFETs, Banerjee explains, "faces limitations because these materials have high density of surface states, which increase leakage current and degrade the subthreshold swing."

The TFET designed by the UCSB team overcame this challenge in a few ways, most significant being the use of a layered two-dimensional (2D) material called molybdenum disulphide (MoS2). As the current-carrying channel placed over a highly doped germanium (Ge) as the source electrode, MoS2 offers an ideal surface and thickness of only 1.3nm. The resulting vertical heterostructure provides a unique source-channel junction that is strain-free, has a low barrier for current-carrying electrons to tunnel through from Ge to MoS2 through an ultra-thin (~0.34nm) van der Waals gap, and a large tunneling area.

"The crux of our idea is to combine 3D and 2D materials in a unique heterostructure, to achieve the best of both worlds. The matured doping technology of 3D structures is married to the ultra-thin nature and pristine interfaces of 2D layers to obtain an efficient quantum-mechanical tunneling barrier, which can be easily tuned by the gate," commented Deblina Sarkar, lead author of the paper and PhD student in Banerjee's lab.

"We have engineered what is, at present, the thinnest-channel subthermionic transistor ever made," said Banerjee. Their atomically-thin and layered semiconducting channel tunnel FET (or ATLAS-TFET) is the only planar architecture TFET to achieve subthermionic subthreshold swing (~30 millivolts/decade at room temperature) over four decades of drain current, and the only one in any architecture to achieve so at an ultra-low drain-source voltage of 0.1V.

Ajayan, co-author and professor of chemical and biomolecular engineering at Rice University, commented, "This is a remarkable example showing the uniqueness of 2D atomic layered materials that enables device performance which conventional materials will not be able to achieve. This is perhaps the first breakthrough in a series of novel devices that people will now aspire to build using 2D materials."

"The work is a significant step forward in the search for a low voltage logic transistor. The demonstration of sub-thermal operation over four orders of magnitude is impressive, and the on-current also advances the state-of-the-art. There is still a long ways to go, but this work demonstrates the potential of 2D materials to realize the long-sought, low-voltage device," commented Mark Lundstrom, professor of electrical and computer engineering at Purdue University.

"We have demonstrated how to achieve the most important metric of steep subthreshold swing that meets ITRS requirements. Our transistor can be utilized for a number of low-power applications including arenas where the steep subthreshold swing is the main requirement, such as biosensors or gas sensors. With improved performance, the range of applications of this transistor can be further expanded," explained Wei Cao, a PhD student in Banerjee's group and a co-author of the article.

"This work represents an important step of bringing 2D materials closer to real applications in electronics. The use of 2D materials in tunneling transistors started only recently, and this paper gives the whole field yet another strong boost in improving the characteristics of such devices even further," commented Dr. Konstantin Novoselov, a professor of physics at University of Manchester. Novoselov was co-recipient of the 2010 Nobel Prize in Physics, awarded for the discovery of graphene.

"When I first heard Banerjee's idea of using 2D materials for designing inter-band tunneling transistors in 2012, I recognized its merit and immense potential for ultra-low power electronics. I am pleased to see that his vision has been realized," commented James Hwang, professor of electrical engineering at Lehigh University, who was then the AFOSR program manager responsible for funding this research.

UC Santa Barbara, College of Engineering

http://www.nanotechnologyworld.org/#!Nanoelectronics-Engineers-Develop-Transistor-that-Overcomes-Fundamental-Power-Limitations/c89r/5665e4850cf2a72d69b6fec0

Single organic molecule can be altered in a targeted manner using a single electron

A new kind of switch which operates at the nanometre scale has been presented by an international research team. The switch's state can be altered in a targeted manner using a single electron.

 

In electronics, nothing works without transistors: they are the fundamental building blocks on which the logic circuits in our computer chips are based. They usually consist of silicon crystals, doped with other types of atom. One Swiss/Austrian research team (TU Wien, the University of Vienna, the University of Zurich, IBM Zurich) has now succeeded in developing a transistor that functions in a fundamentally different manner and consists solely of a single molecule. Instead of three electrodes, as in a conventional transistor, this switch molecule only requires two. The new nanoswitch has now been presented in the specialist journal 'Nature Nanotechnology'.

Zero or one 

"The key feature of a transistor is that it can assume two different states," explains Robert Stadler from the Institute of Theoretical Physics at TU Wien (at the start of the project he was still working at the Department of Physical Chemistry at the University of Vienna). Depending on which state the transistor is in, it either allows current to flow or not. A conventional transistor made of silicon crystals therefore has three contacts: the current is supplied by one of these, and is able to flow into the second one; whether this actually happens or not depends on the voltage applied at the third contact, which is known as the 'gate contact'.

In order to accommodate ever more transistors in an ever smaller area, transistors have continued to reduce in size over the last few decades. This has drastically improved efficiency in electronics, but does, however, bring with it ever greater technical problems. With conventional silicon technology, physical limitations are encountered as a result. "With extremely small crystals you no longer have sufficient control over the electronic properties, particularly if only a small number of dopants remains and the gate's insulating layer allows increasingly more leakage," explains Stadler. "However, if you switch from crystals to organic molecules at the nanoscale, you then have new opportunities to change the transport characteristics."

From molecule to transistor

At the University of Zurich, chemists have therefore synthesised organometallic molecular structures endowed with individual metal atoms of iron, ruthenium or molybdenum. These designer molecules, which are only around two and a half nanometres long, are then carefully connected using two gold contacts at the IBM research lab in Rüschlikon before voltage can be applied to them.

For one of the molecule types tested, which has a molybdenum atom placed at its core, some quite remarkable properties were observed: similarly to a silicon transistor, this molecule switches back and forth between two different states, which differ by three orders of magnitude as regards their conductivity. Complex computer simulations were required in order to understand the underlying process; these were carried out by Robert Stadler and his doctoral student Georg Kastlunger at the Vienna Scientific Cluster (VSC). This allowed the mechanism to be decoded at a quantum physical level.

"Directly on the molybdenum atom there is a certain space which can be occupied by an electron," says Robert Stadler. "The amount of current that can flow through the molecule at a certain voltage depends on whether or not there is actually an electron occupying this space or not." And this in itself can be controlled. If the space is occupied, relatively little current will flow at a low voltage. At a higher voltage, however, the electron can be dislodged from its special place on the molybdenum atom. As a result, the system switches to a new state with conductivity improved by a factor of around a thousand, causing a sharp increase in the current flow. Both a switching and selection process can therefore be carried out via the two gold contacts, between which the molecule is fixed. A third electrode, as is usually required for a conventional transistor, is no longer necessary, which simplifies the wiring process significantly.

Technology for the chips of the future

The technology itself, however, is still too expensive to put into mass production for commercial computer chips. This is why the experiments were carried out at low temperatures and in an ultra-high vacuum. However, IBM are already working on designs to incorporate several of these molecules in nanopores on a silicon chip, so that they function under normal environmental conditions at room temperature. "This would be simpler and our theoretical methods would undoubtedly be suited to such systems, too," states Stadler with confidence. "Perhaps organic molecules with integrated metal atoms can lead the way to ultra-small switches for new storage systems; in any case, there is the potential for exciting applications, particularly since the omission of the third electrode allows for unrivalled integration densities."

Robert Stadler's group is entirely funded via fellowships from the Austrian Science Fund (FWF). Georg Kastlunger received a one-year scholarship, which was funded in equal parts by the Society of Austrian Chemists (GÖCH), Austrian Academy of Sciences (ÖAW) and the Springer Verlag. The Swiss project partners were funded by the Swiss National Science Foundation.

TU Wien

Nanotechnology World Association

Superconductor survives ultra-high magnetic field

Physicists from the universities of Groningen and Nijmegen (the Netherlands) and Hong Kong have discovered that transistors made of ultrathin layers molybdeendisulfide (MoS2) are not only superconducting at low temperatures but also stay superconducting in a high magnetic field. This is a unique phenomenon with exciting promises for the future. The experiments were the first to have been performed at the High Field Magnet Laboratory in Nijmegen, jointly operated by Radboud University and the FOM foundation. The results are published on 12 November by the journal Science.

Superconductivity is a state in which the electrical resistance of a material disappears completely. Normally, this phenomenon only exists at low temperatures and disappears under a high magnetic field. But in the High Field Magnet Laboratory (HFML), physicists discovered that MoS2 -- which can be bought at the home depot stores as dry lubricant -- remains superconducting under a high magnetic field of 37.5 Tesla.

Strongly pinned electron pairs Superconductivity is induced when free electrons in a material are attracted to each other and form weakly bonded electron pairs. These pairs condensate to a superconducting state only when all possible disturbances in the material are minimal and therefore, superconductivity usually exists at very low temperature. When a material is exposed to a magnetic field, the weak bonding between the electron pair can be easily broken. The rupture of the pair destroys the superconductivity when disturbance from the magnetic field becomes strong enough.

Surprisingly, the superconducting state of MoS2 survives high magnetic fields because the paired electrons are intrinsically associated with an internal high magnetic field, which can reach nearly one hundred Tesla, much higher than the 37.5 Tesla provided by the HFML. For comparison: a conventional fridge magnet has a magnetic field of approximately 0.1 Tesla. Uli Zeitler, physicist at the HFML at Radboud University explains: 'MoS2 behaves in a way that contradicts a law in physics, the so called Pauli paramagnetic limit.'

Information in electron spin Although the current publication is very fundamental, Zeitler does have some ideas for future applications. 'There is information stored inside the charge and spin of electrons, the direction of their internal magnetic field. If you can influence this spin, for instance with an electric field, you can store information in there. And in principle, this technique could be used in the development of a future quantum computer.'

The described experiments are complicated to perform. 'We execute this research at very low temperatures between 0 and 12 Kelvin, about minus 270 degrees Celsius, and under high magnetic fields. But in order to pump enough electrons into MoS2, we first needed relatively high temperatures of about minus 50 degrees Celsius', Zeitler explains.

As the first external user of the newly-built 37.5 T magnet, Justin Ye, a physicist from Zernike Institute of Advanced Material at the University of Groningen is really excited by the result: 'It is a good starting point of this new facility. As the first user I am very happy to obtain this important result with the support from my colleagues in HFML. Following this breakthrough in identifying a new paring mechanism with stunning protection of superconductivity against high magnetic field, I would expect a lot of unexpected results from the future experiments in HFML.'

University of Groningen

Record-setting flexible phototransistor

Developed by UW electrical engineers, this unique phototransistor is flexible, yet faster and more responsive than any similar phototransistor in the world. Photo: Jung-Hun Seo

Inspired by mammals' eyes, University of Wisconsin-Madison electrical engineers have created the fastest, most responsive flexible silicon phototransistor ever made.

The innovative phototransistor could improve the performance of myriad products — ranging from digital cameras, night-vision goggles and smoke detectors to surveillance systems and satellites — that rely on electronic light sensors. Integrated into a digital camera lens, for example, it could reduce bulkiness and boost both the acquisition speed and quality of video or still photos.

Developed by UW-Madison collaborators Zhenqiang "Jack" Ma, professor of electrical and computer engineering, and research scientist Jung-Hun Seo, the high-performance phototransistor far and away exceeds all previous flexible phototransistor parameters, including sensitivity and response time.

The researchers published details of their advance this week in the journal Advanced Optical Materials.

Like human eyes, phototransistors essentially sense and collect light, then convert that light into an electrical charge proportional to its intensity and wavelength. In the case of our eyes, the electrical impulses transmit the image to the brain. In a digital camera, that electrical charge becomes the long string of 1s and 0s that create the digital image.

While many phototransistors are fabricated on rigid surfaces, and therefore are flat, Ma and Seo's are flexible, meaning they more easily mimic the behavior of mammalian eyes.

"We actually can make the curve any shape we like to fit the optical system," Ma says. "Currently, there's no easy way to do that."

One important aspect of the success of the new phototransistors is the researchers' innovative "flip-transfer" fabrication method, in which their final step is to invert the finished phototransistor onto a plastic substrate. At that point, a reflective metal layer is on the bottom.

"In this structure — unlike other photodetectors — light absorption in an ultrathin silicon layer can be much more efficient because light is not blocked by any metal layers or other materials," Ma says.

While many phototransistors are fabricated on rigid surfaces, and therefore are flat, Ma and Seo's are flexible, meaning they more easily mimic the behavior of mammalian eyes.

The researchers also placed electrodes under the phototransistor's ultrathin silicon nanomembrane layer — and the metal layer and electrodes each act as reflectors and improve light absorption without the need for an external amplifier.

"There's a built-in capability to sense weak light," Ma says.

Ultimately, the new phototransistors open the door of possibility, he says.

"This demonstration shows great potential in high-performance and flexible photodetection systems," says Ma, whose work was supported by the U.S. Air Force. "It shows the capabilities of high-sensitivity photodetection and stable performance under bending conditions, which have never been achieved at the same time."

University of Wisconsin-Madison 

Silicon nanoparticle is a new candidate for an ultrafast all-optical transistor

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  Physicists from the Department of Nanophotonics and Metamaterials of ITMO University have experimentally demonstrated the feasibility of designing an optical analog of a transistor based on a single silicon nanoparticle. Because transistors are some of the most fundamental components of computing circuits, the results of the study have crucial importance for the development of optical computers, where transistors must be very small and ultrafast at the same time. The study was published in the scientific journal Nano Letters.

  The performance of modern computers, which use electrons as signal carriers, is largely limited by the time needed to trigger the transistor – usually around 0.1 - 1 nanoseconds (10−9 of a second). Next-generation optical computers, however, rely on photons to carry the useful signal, which heavily increases the amount of information passing through the transistor per second. For this reason, the creation of an ultrafast and compact all-optical transistor is considered to be instrumental in the development of optical computing. Such a nanodevice would enable scientists to control the propagation of an optical signal beam by means of an external control beam within several picoseconds (10−12 of a second).

  In the study, a group of Russian scientists from ITMO University, Lebedev Physical Institute and Academic University in Saint Petersburg put forward a completely new approach to design such optical transistors, having made a prototype using only one silicon nanoparticle.

  The scientists found that they can dramatically change the properties of a silicon nanoparticle by irradiating it with intense and ultrashort laser pulse. The laser thus acts as a control beam, providing ultrafast photoexcitation of dense and rapidly recombining electron-hole plasma whose presence changes the dielectric permittivity of silicon for a few picoseconds. This abrupt change in the optical properties of the nanoparticle opens the possibility to control the direction, in which incident light is scattered. For instance, the direction of nanoparticle scattering can be changed from backward to forward on picoseconds timescale, depending on the intensity of the incident control laser pulse. This concept of ultrafast switching is very promising for designing of all-optical transistor.

  “Generally, researchers in this field are focused on designing nanoscale all-optical transistors by means of controlling the absorption of nanoparticles, which, in essence, is entirely logical. In high absorption mode, the light signal is absorbed by the nanoparticle and cannot pass through, while out of this mode the light is allowed to propagate past the nanoparticle. However, this method did not yield any decisive results,” explains Sergey Makarov, lead author of the study and senior researcher at the Department of Nanophotonics and Metamaterials.“Our idea is different in the sense that we control not the absorption properties of the nanoparticle, but rather its scattering diagram. Let’s say, the nanoparticle normally scatters almost all incident light in the backward direction, but once we irradiate it by a control pulse, it becomes reconfigured and starts scattering light forward.”

  The choice of silicon as a material for the optical transistor was not accidental. Creating an optical transistor requires the use of inexpensive materials appropriate for mass production and capable of changing their optical properties in several picoseconds (in the regime of dense electron-hole plasma) without getting overheated at the same time.

  “The time it takes us to deactivate our nanoparticle amounts to just several picoseconds, while to activate it we need no more than tens of femtoseconds (10−15 of a second). Now we already have experimental data that clearly indicates that a single silicon nanoparticle can indeed play the role of an all-optical transistor. Currently we are planning to conduct new experiments, where, along with a laser control beam, we will introduce a useful signal beam”, concludes Pavel Belov, coauthor of the paper and head of the Department of Nanophotonics and Metamaterials.

  ITMO University

  http://www.nanotechnologyworld.org/

Leti Demonstrates Ultra-scaled Self-aligned Split-gate Memory Cell With 16nm Gate Length

Benefits Especially for Contactless Applications Include Larger Memory Window, Improved Control of Spacer Memory Gate Shape and Length, And Better Functionality

CEA-Leti announced it has fabricated ultra-scaled split-gate memories with gate length of 16nm, and demonstrated their functionality, showing good writing and erasing performances with memory windows over 6V. 

The devices provide several benefits especially for contactless memory applications, such as enlargement of the memory window and increased functionality. Also because of an optimised fabrication step, the devices allow better control of spacer memory gate shape and length.

Split-gate flash memories are made of two transistors: an access transistor and a memory transistor with a charge-trapping layer (nitride, Si nanocrystals etc.). Split-gate architectures use a low-access voltage and minimize drain current during programming, which leads to a decrease of the programming power compared to standard one-transistor NOR memories. Because programming energy decreases when memory gate length decreases, ultra-scaling is particularly relevant for contactless applications.

Memory gate has been reduced down to 16nm thanks to a poly-Si spacer formed on the sidewall of the select transistor. This approach avoids costly lithography steps during fabrication and solves misalignment issues, which are responsible for a strong variation of the electrical performances, such as the memory window.

The main challenges of this self-aligned technology concern the precise control of the spacer memory gate shape and of the memory gate length. Spacer gate has to fulfil two difficult requirements: being as flat as possible in order to get a silicidation surface as large as possible while insuring a functional contact, and getting a steep edge in order to control the drain-junction doping.

Source: http://www-leti.cea.fr/en/Latest-news/Leti-Demonstrates-Ultra-scaled-Self-aligned-Split-gate-Memory-Cell-With-16nm-Gate-Length

On the road to Mottronics

Epitaxial mismatches in the lattices of nickelate
ultra-thin films can be used to tune the energetic
landscape of Mott materials and thereby control
conductor/insulator transitions.

Researchers at the Advanced Light Source Find Key to Controlling the Electronic and Magnetic Properties of Mott Thin Films

“Mottronics” is a term seemingly destined to become familiar to aficionados of electronic gadgets. Named for the Nobel laureate   Nevill Francis Mott, Mottronics involve materials – mostly metal oxides – that can be induced to transition between electrically conductive and insulating phases. If these phase transitions can be controlled, Mott materials hold great promise for future transistors and memories that feature higher energy efficiencies and faster switching speeds than today’s devices. A team of researchers working at Berkeley Lab’s Advanced Light Source (ALS) have  demonstrated the conducting/insulating phases of ultra-thin films of Mott materials can be controlled by applying an epitaxial strain to the crystal lattice.

“Our work shows how an epitaxial mismatch in the lattice can be used as a knot to tune the energetic landscape of Mott materials and thereby control conductor/insulator transitions,” says Jian Liu, a post-doctoral scholar now with Berkeley Lab’s Materials Sciences Division, who is the lead author on a paper describing this work in the journal Nature Communications. “Through epitaxial strain, we forced nickelate films containing only a few atomic layers into different phases with dramatically different electronic and magnetic properties. While some of these phases are not obtainable in conventional ways, we were able to produce them in a form that is ready for device development.”

The Nature Communications paper is titled “Heterointerface engineered electronic and magnetic phases of NdNiO3 thin films.” The corresponding author is Jak Chakhalian, a professor of physics at the University of Arkansas. Co-authors are Mehdi Kargarian, Mikhail Kareev, Ben Gray, Phil Ryan, Alejandro Cruz, Nadeem Tahir, Yi-De Chuang, Jinghua Guo, James Rondinelli, John Freeland and Gregory Fiete.

Jinghua Guo (left) and Yi-De Chuang at Beamline 8.0.1 of the Advanced Light Source were part of a team that discovered a key to controlling the electronic and magnetic properties of Mott materials. (Photo by Roy Kaltschmidt)

Nickel-based rare-earth perovskite oxides, or “nickelates,” are considered to be an ideal model for the study of Mott materials because they display strongly correlated electron systems that give rise to unique electronic and magnetic properties. Liu and his co-authors studied thin films of neodymium nickel oxide using ALS beamline 8.0.1, a high flux undulator beamline that produces x-ray beams optimized for the study of nanoscale materials and strongly correlated physics.

“ALS beamline 8.0.1 provides the high photon flux and energy range that are critical when dealing with nanoscale samples,” Liu says. “The state-of-the-art Resonant X-ray Scattering endstation has a high-speed, high-sensitivity CCD camera that makes it feasible to find and track diffraction peaks off a thin film that was only six nanometers thick.”

The transition between the conducting and insulating phases in nickelates is determined by various microscopic interactions, some of which favor the conducting phase, some which favor the insulating phase. The energetic balance of these interactions determines how easily electricity is conducted by electrons moving between the nickel and oxygen ions. By applying enough epitaxial strain to alter the space between these ions, Liu and his colleagues were able to tune this energetic balance and control the conducting/insulating transition. In addition, they   found strain could also be used to control the nickelate’s magnetic properties, again by exploiting the lattice mismatch.

“Magnetism is another hallmark of Mott materials that often goes hand-in-hand with the insulating state and is used to distinguish Mott insulators,” says Liu. “The challenge is that most Mott insulators, including nickelates, are antiferromagnets that macroscopically behave as non-magnetic materials. “At ALS beamline 8.0.1, we were able to directly track the magnetic evolution of our thin films while tuning the metal-to-insulator transition. Our findings give us a better understanding of the physics behind the magnetic properties of these nickelate films and point to potential applications for this magnetism in novel Mottronics devices.”

This research was primarily supported the U.S. Department of Energy’s Office of Science.

Source: http://newscenter.lbl.gov/science-shorts/2014/02/24/on-the-road-to-mottronics/