Category Archives: Process Materials

Versum Materials, Inc. (NYSE: VSM), a materials supplier to the semiconductor industry, announced today that it would expand its manufacturing capacity at its Delivery Systems and Service (DS&S) headquarters in Allentown, Pennsylvania. To support customer demand and the growth in its DS&S business, new positions will be created for highly skilled technicians, engineers, quality control personnel, and manufacturing and support staff.

The timing of the expansion aligns with the 25th anniversary of manufacturing at the Allentown location. The 31,000-square-foot, state-of-the-art facility was established in 1992 as the Semiconductor Equipment Manufacturing Center (SEMC) of Air Products, which Versum Materials spun-off from in October 2016. The facility will be rebranded Vultee Street as part of this announcement.

The manufacturing capacity expansion will serve the semiconductor, LCD and LED markets around the globe with gas and chemical delivery equipment designed to meet their precise purity and safety requirements. This investment will increase the production of Versum Materials’ line of GASGUARD ultra-high purity specialty gas equipment and CHEMGUARD chemical delivery equipment.

Last year, Versum Materials increased capacity at its DS&S manufacturing location in Ansan, South Korea, where in addition to the above-mentioned equipment, it produces a line of GASKEEPER specialty gas equipment designed specifically for the region.

“We are excited about our prospects for growth in the industry and supporting our valued customers with state-of-the-art, high-purity equipment. We are enhancing our manufacturing capacity to keep pace with our customers’ increasing requirements for more flexibility and shorter lead times,” said Jeff White, vice president and general manager of DS&S.

The company expects the expansion of the Allentown facility to be complete this spring. A list of open positions can be found on the company’s career page.

Materion Corporation (NYSE:MTRN) announced today that it has completed the previously announced acquisition of the target materials business of the Heraeus Group, of Hanau, Germany, for approximately $30 million.

The acquisition strengthens Materion’s position in precious and non-precious target materials for the architectural and automotive glass, photovoltaic, display and semiconductor markets. The business, now operating within the Materion Advanced Materials business segment, is expected to generate approximately $50 to $60 million in new value-added sales on an annualized basis and be accretive to 2017 earnings. Materion Advanced Materials reported value-added sales of $176.3 million in 2016.

Through this transaction, Materion’s Advanced Materials segment gains target manufacturing capability in Europe, Asia and the U.S., as well as new technologies and a highly specialized workforce of 135 employees.

Donald G. Klimkowicz, President, Materion Advanced Materials, commented, “Beyond accelerating and solidifying our global materials offering in semiconductor and display, the acquisition provides diversification, critical mass and new opportunities in other growing target-related areas where Materion has not enjoyed as strong a position including glass and photovoltaic. This truly is a winning combination.”

Added Materion Chief Executive Officer Richard J. Hipple, “This transaction is the latest in a series of advanced materials acquisitions made by Materion since 2005 to augment our growth and further our diversification into a leading advanced materials organization. I am very excited about the prospects for future growth that this acquisition brings us in existing and new markets, and how closely the values and culture of the Heraeus employees who join us match with our own. We welcome them to the Materion family.”

Materion Corporation is headquartered in Mayfield Heights, Ohio. The Company, through its wholly owned subsidiaries, supplies highly engineered advanced enabling materials to global markets. Products include precious and non-precious specialty metals, inorganic chemicals and powders, specialty coatings, specialty engineered beryllium alloys, beryllium and beryllium composites, and engineered clad and plated metal systems.

Ionotronic devices rely on charge effects based on ions, instead of electrons or in addition to electrons. These devices open new opportunities for creating electrically switchable memories. However, there are still many technical challenges to overcome before this new kind of memories can be produced.

Researchers at Aalto University in Finland have visualized how oxygen ion migration in a complex oxide material causes the material to alter its crystal structure in a uniform and reversible fashion, prompting large modulations of electrical resistance. They performed simultaneous imaging and resistance measurements in a transmission electron microscope using a sample holder with a nanoscale electrical probe. Resistance-switching random access memories could utilize this effect.

Researchers performed imaging and resistance measurements in a transmission electron microscope using a sample holder with a nanoscale electrical probe. Credit: Mikko Raskinen / Aalto University

Researchers performed imaging and resistance measurements in a transmission electron microscope using a sample holder with a nanoscale electrical probe. Credit: Mikko Raskinen / Aalto University

Sample holder helps control migration of ions 

“In a transmission electron microscope, a beam of high-energy electrons is transmitted through a very thin specimen. Various detectors collect the electrons after their interaction with the sample, providing detailed information about the atomic structure and composition of the material. The technique is extremely powerful for nanomaterials characterization, but if used conventionally, it does not allow for active material manipulation inside the microscope. In our study, we utilized a special sample holder with a piezo-controlled metallic probe to make an electrical nanocontact. This in situ method allowed us to apply short voltage pulses and thereby control the migration of oxygen ions in our sample,” explains Academy of Finland Research Fellow Lide Yao.

The researchers found that migration of oxygen ions away from the contact area results in an abrupt change in the oxide lattice structure and an increase of electrical resistance. Reversal of the voltage polarity fully restores the original material properties. Electro-thermal simulations, performed by PhD candidate Sampo Inkinen, showed that a combination of current-induced sample heating and electric-field-directed ion migration causes the switching effect.

Ionotronic concept for manipulation of several material properties

“The material that we investigated in this study is a complex oxide. Complex oxides can exhibit many interesting physical properties including magnetism, ferroelectricity, and superconductivity, and all these properties vary sensitively with the oxidation state of the material. Voltage-induced migration of oxygen ions does change the amount of oxidation, triggering strong material responses. While we have demonstrated direct correlations between oxygen content, crystal structure, and electrical resistance, the same ionotronic concept could be utilized to control other material properties,” says Professor Sebastiaan van Dijken, who is a coauthor on the paper with Yao.

“In the current study, we employed a special sample holder for simultaneous measurements of the atomic-scale structure and electrical resistance. We are now developing an entirely new and unique holder that would allow for transmission electron microscopy measurements while the specimen is irradiated by intense light. We plan to investigate atomic scale processes in perovskite solar cells and other optoelectronic materials with this setup in the future,” adds Yao.

Versum Materials, Inc. (NYSE: VSM), a materials supplier to the semiconductor industry, announced today that Edward “Ed” Shober has been appointed to the position of senior vice president of its Materials segment. Mr. Shober will be responsible for the company’s Process Materials (PM) and Advanced Materials (AM) global businesses, which produce specialty chemicals and materials utilized in the next generation of semiconductors and displays for smart devices, as well as high-purity, specialty gases used in the semiconductor manufacturing process. Mr. Shober has led the AM business since 2011 and has more than 20 years’ experience serving Versum Materials’ customers in the semiconductor industry.

“Ed will continue to support our culture of operating as an agile organization that is relentlessly focused on building on our global technology leadership and establishing a reputation for quality, safety and reliability,” stated Guillermo Novo, President and CEO of Versum Materials. “Because of Ed’s customer relationships, leadership, experience and technical capabilities, we are confident that’s Ed’s transition will be seamless for our customers and his industry knowledge will continue to be an invaluable asset to our team.”

Mr. Shober joined Air Products in 1994, leading engineering activities in the electronics engineering and electronics package plants organizations. In 1999, he was named vice president of engineering and operations for TRiMEGA, a joint venture between Air Products and Kinetic Systems providing turnkey solutions to semiconductor fabs, and served as TRiMEGA’s chief operating officer from 2001-2004. Mr. Shober went on to lead DA NanoMaterials, Air Products’ joint venture with DuPont, as its chief operating officer from 2004-2007 and chief executive officer from 2007-2010. In October 2011, he served as the director of Advanced Materials Integration, Electronics Division, until assuming leadership of Air Products’ Advanced Materials business. He previously served as the vice president of Advanced Materials for the Materials Technologies business of Air Products since 2012. Mr. Shober holds a Bachelor of Science degree in civil/structural engineering from Brown University.

GlobalFoundries_Ajit_ManochSEMI, the global association connecting and representing the worldwide electronics manufacturing supply chain, today announced the appointment of Ajit Manocha as its president and CEO. He will succeed Denny McGuirk, who announced his intention to retire last October. The SEMI International Board of Directors conducted a comprehensive search process, selecting Manocha, an industry leader with over 35 years of global experience in the semiconductor industry.  Manocha will begin his new role on March 1 at SEMI’s new Milpitas headquarter offices.

“Ajit has a deep understanding of our industry’s dynamics and the interdependence of the electronics manufacturing supply chain,” said Y.H. Lee, chairman of SEMI’s board of directors. “From his early days developing dry etch processes at AT&T Bell Labs, to running global manufacturing for Philips/NXP, Spansion, and, as CEO of GLOBALFOUNDRIES, Ajit has been formative to our industry’s growth. Ajit is the ideal choice to drive our SEMI 2020 plan and beyond, ensuring that SEMI provides industry stewardship and engages its members to advance the interests of the global electronics manufacturing supply chain.”

“Beyond his experience leading some of our industry’s top fabs, Ajit has long been active at SEMI and has served on boards of several global associations and consortia,” said Denny McGuirk, retiring president and CEO of SEMI. “Ajit’s experience in technology, manufacturing, and industry stewardship is a powerful combination. I’m very excited to be passing the baton to Ajit as he will continue to advance the growth and prosperity of SEMI’s members.”

“I have tremendous respect for the work SEMI does on behalf of the industry,” said Ajit Manocha, incoming president and CEO of SEMI. “I am excited to be joining SEMI at a time when our ecosystem is rapidly expanding due to extensive innovation on several fronts.  From applications based on the Internet and the growth of mobile devices to artificial intelligence/machine learning, autonomous vehicles, and the Internet of Things, there is a much broader scope for SEMI to foster heterogeneous collaboration and fuel growth today than ever before.  I am looking forward to leading the global SEMI organization as we strive to maximize value for our members across this extended global ecosystem.”

Manocha was formerly CEO at GLOBALFOUNDRIES, during which he also served as vice chairman and chairman of the Semiconductor Industry Association (SIA).  Earlier, Manocha served as EVP of worldwide operations at Spansion. Prior to Spansion, he was EVP and chief manufacturing officer at Philips/NXP Semiconductors. Manocha also held senior management positions within AT&T Microelectronics. He began his career at AT&T Bell Laboratories as a research scientist where he was granted several patents related to microelectronics manufacturing. Manocha holds a bachelor’s degree from the University of Delhi and a master’s degree in physical chemistry from Kansas State University.

An Steegen reveals some of the secrets of semiconductor scaling – a pipeline full of materials, device architectures and advanced techniques that promise to further extend semiconductor scaling.

BY AN STEEGEN, Executive Vice President Semiconductor Technology & Systems, imec

The explosive growth of data traffic fuels the demand for ever more processing power and storage capacity. Moore’s Law continues to be necessary, but innova- tions are needed beyond this law to help managing the devices power, performance, area and cost.

The end of happy scaling?

Data traffic explosion, fueled by the Internet of Things, social media and server applications, has created a continuous need for advanced semiconductor technologies. Servers, mobile devices, and IoT devices drive the require- ments for processing and storage. “At the same time, this trend is also creating more diversification,” said An Steegen, Executive Vice President Semiconductor Technology & Systems at Imec (Leuven, Belgium). “IoT devices, for example, will need low-power signal acquisition and processing, and embedded non-volatile memory technol- ogies. For mobile and server applications, on the contrary, further dimensional scaling, continuous transistor archi- tecture innovations and memory hierarchy diversification are among the key priorities.”

But will we be able to continue traditional semiconductor scaling, as initiated by Gordon Moore more than 50 years ago? “For a long time, we have lived in the happy scaling era, where every technology node reshrinks and redoubles the number of transistors per area, for the same cost,” Steegen said. “But the last 10-12 years, we have not been following that happy scaling path. The number of transistors still doubles, but device scaling provides us with diminishing returns. We’ve seen these dark periods of ‘dark silicon’ before, but, fortunately, we’ve always managed to get out of these periods. Again, the technology box will provide new features to help manage power, performance and area node by node as we move to the next generation.”

The technology box for dimensional scaling

On the dimensional scaling side, extreme ultraviolet lithography (EUVL) is considered an important enabler for continuing Moore’s Law. “Ideally, we would need it at the 10nm node, where we will start replacing single exposures with multiple exposures. More realistically, it will hopefully be ready to lower the costs for the 7nm technology,” said Steegen. “At imec, we already showed that EUVL is capable of printing 7nm logic dimensions with one single exposure.” Still, issues need to be resolved, related to, for example, the line-edge roughness. “At the same time, to enhance dimensional scaling, we increasingly make use of scaling boosters, such as self-aligned gate contact or buried power rail. These tricks allow a standard cell height to be reduced from 9 to 6 tracks, leading to a bit density increase and large die cost reduction – a nice example of design- technology co-optimization.”

Improving power/performance in the front-end of line

FinFET technology has been the killer device for the 14 and 10nm technology nodes. But for the 7-5nm, Steegen foresees challenges: “At these nodes, FinFET technology can’t meet the 20% performance scaling and 40% power gain anymore. To go beyond 7nm will require horizontal gate-all-around nanowires, which promise better electro- static control. In such a configuration, the drive current per footprint can be maximized by vertically stacking multiple horizontal nanowires. In 2016, at IEDM, we demonstrated for the first time the CMOS integration of vertically stacked gate-all-around Si nanowire MOSFETs. Vertical nanowires, although requiring a more disruptive process flow, could be a next step. Or junction-less gate- all-around nanowire FET devices, which, as shown at the 2016 VLSI conference, appear as an attractive option for advanced logic, low-power circuits and analog/RF applications.” Further down the road, from the 2.5nm node onwards, fin/nanowire devices are expected to run out of steam. “Sooner or later, we will need to find the next switch,” she said. “Promising approaches are tunnel-FETs, which can provide a 3x drive current improvement, and spin-wave majority gates.” Spin-wave majority gates with micro-sized dimensions have already been reported. But to be CMOS-competitive, they must be scaled and handle waves with nanometer-sized wavelengths. An Steegen: “In 2016, imec proposed a method to scale these spin-wave devices into nanometer dimensions, opening routes towards building spin-wave majority gates that promise to outperform CMOS-based logic technology in terms of power and area reduction.”

Extending or replacing Cu in the back-end-of-line

Looking ahead, it might as well be the interconnect that will threaten further device scaling. Therefore, the back- end-of-line (BEOL) and the struggle to keep scaling the BEOL needs attention as well. “We look at ways to extend the life of Cu, for example with liners of ruthenium (Ru) or cobalt (Co). On the longer term, we will probably need alternative metals, such as Co for local interconnects or vias,” says Steegen.

The future memory hierarchy

Besides a central processing unit, memory to store all the data and instructions is another key element of the classical Von Neumann computer architecture. The ever increasing performance of computation platforms and the consumer’s hunger for storing and exchanging ever more data drive the need to keep on scaling memory technol- ogies. Besides this scaling trend, existing memories that make up today’s memory hierarchy are challenged with the need for new types of memory.

Steegen said: “STT-MRAM, for example, is an emerging memory concept that has the potential to become the first embedded non-volatile memory technology on advanced logic nodes for advanced applications. It is also an attractive technology for future high-density stand-alone applications. It promises non-volatility, high-speed, low-voltage switching and nearly unlimited read/write endurance. But its scalability towards higher densities has always been challenging. Recently, we have been able to demon- strate a high-performance perpendicular magnetic tunnel junction device as small as 8nm, combined with a manufacturable solution for a highly scalable STT-MRAM array.” The future memory landscape also requires a new type of memory able to fill the gap between DRAM and solid-state memories: the storage class memory. This memory type should allow massive amounts of data to be accessed in very short latency. Imec is working there on MRAM and resistive RAM (RRAM) approaches.

Beyond classical scaling – towards system- technology co-optimization

A challenge for traditional Von Neumann computing is to increase the data transfer bandwidth between the processing chip and the memory. And this is where 3D approaches enter the scene. Said Steegen: “With advanced CMOS scaling, new opportunities for 3D chip integration arise. For example, it becomes possible to realize different partitions of a system-on-chip (SoC) circuit and hetero- geneously stacking these partitions with high inter- connect densities. At the smallest partitions, chips are no longer stacked as individual die, but as full wafers bonded together.” An increased bandwidth is also enabled by optical I/O. In this context, imec continues its efforts to realize building blocks (e.g. optical modulators, Ge photodetectors) with 50Gb/s channel data rate for its Si photonics platform.

Moore’s Law will continue, but not only through the conventional routes of scaling. “We have moved from pure technology optimization (involving novel materials and device architectures) to design-technology co-optimi- zation (e.g. the use of scaling boosters to reduce cell height). And we are already thinking ahead about a next phase, system-technology co-optimization. And to keep computing power improving, we are exploring ways beyond the classical Von Neumann model, such as neuro- morphic computing, a brain-inspired computer concept and quantum computing, which exploits the laws of quantum physics. There are plenty of creative ideas that will allow the industry to further extend semiconductor scaling,” Steegen concluded.

AN STEEGEN is imec’s Executive Vice President Semiconductor Technology & Systems. In that role, she heads the research hub’s efforts to define and enable next-generation ICT technology and to feed the industry roadmaps.

Heat transport is of similar fundamental importance and its control is for instance necessary to efficiently cool the ever smaller chips. An international team including theoretical physicists from Konstanz, Junior Professor Fabian Pauly and Professor Peter Nielaba and their staff, has achieved a real breakthrough in better understanding heat transport at the nanoscale. The team used a system that experimentalists in nanoscience can nowadays realize quite routinely and keeps serving as the “fruit fly” for breakthrough discoveries: a chain of gold atoms. They used it to demonstrate the quantization of the electronic part of the thermal conductance. The study also shows that the Wiedemann-Franz law, a relation from classical physics, remains valid down to the atomic level. The results were published in the scientific journal “Science” on 16 February 2017.

This is an artists' view of the quantized thermal conductance of an atomically thin gold contact. Credit: Created by Enrique Sahagun

This is an artists’ view of the quantized thermal conductance of an atomically thin gold contact. Credit: Created by Enrique Sahagun

To begin with, the test object is a microscopic gold wire. This wire is pulled until its cross section is only one atom wide and a chain of gold atoms forms, before it finally breaks. The physicists send electric current through this atomic chain, that is through the thinnest wire conceivable. With the help of different theoretical models the researchers can predict the conductance value of the electric transport, and also confirm it by experiment. This electric conductance value indicates how much charge current flows when an electrical voltage is applied. The thermal conductance, that indicates the amount of heat flow for a difference in temperature, could not yet be measured for such atomic wires.

Now the question was whether the Wiedemann-Franz law, that states that the electric conductance and the thermal conductance are proportional to each other, remains valid also at the atomic scale. Generally, electrons as well as atomic oscillations (also called vibrations or phonons) contribute to heat transport. Quantum mechanics has to be used, at the atomic level, to describe both the electron and the phonon transport. The Wiedemann-Franz law, however, only describes the relation between macroscopic electronic properties. Therefore, initially the researchers had to find out how high the contribution of the phonons is to the thermal conductance.

The doctoral researchers Jan Klöckner and Manuel Matt did complementary theoretical calculations, which showed that usually the contribution of phonons to the heat transport in atomically thin gold wires is less than ten percent, and thus is not decisive. At the same time, the simulations confirm the applicability of the Wiedemann-Franz law. Manuel Matt used an efficient, albeit less accurate method that provided statistical results for many gold wire stretching events to calculate the electronic part of the thermal conductance value, while Jan Klöckner applied density functional theory to estimate the electronic and phononic contributions in individual contact geometries. The quantization of the thermal conductance in gold chains, as proven by experiment, ultimately results from the combination of three factors: the quantization of the electrical conductance value in units of the so-called conductance quantum (twice the inverse Klitzing constant 2e2/h), the negligible role of phonons in heat transport and the validity of the Wiedemann-Franz law.

For quite some time it has been possible to theoretically calculate, with the help of computer models as developed in the teams of Fabian Pauly and Peter Nielaba, how charges and heat flow through nanostructures. A highly precise experimental setup, as created by the experimental colleagues Professor Edgar Meyhofer and Professor Pramod Reddy from the University of Michigan (USA), was required to be able to compare the theoretical predictions with measurements. In previous experiments the signals from the heat flow through single atom contacts were too small. The Michigan group succeeded in improving the experiment: Now the actual signal can be filtered out and measured.

The results of the research team make it possible to study heat transport not only in atomic gold contacts but many other nanosystems. They offer opportunities to experimentally and theoretically explore numerous fundamental quantum heat transport phenomenona that might help to use energy more efficiently, for example by exploiting thermoelectricity.

Engineers at the University of California San Diego have developed a material that could reduce signal losses in photonic devices. The advance has the potential to boost the efficiency of various light-based technologies including fiber optic communication systems, lasers and photovoltaics.

The discovery addresses one of the biggest challenges in the field of photonics: minimizing loss of optical (light-based) signals in devices known as plasmonic metamaterials.

SEM images of a 'lossless' metamaterial that behaves simultaneously as a metal and a semiconductor. Credit: Ultrafast and Nanoscale Optics Group at UC San Diego

SEM images of a ‘lossless’ metamaterial that behaves simultaneously as a metal and a semiconductor. Credit: Ultrafast and Nanoscale Optics Group at UC San Diego

Plasmonic metamaterials are materials engineered at the nanoscale to control light in unusual ways. They can be used to develop exotic devices ranging from invisibility cloaks to quantum computers. But a problem with metamaterials is that they typically contain metals that absorb energy from light and convert it into heat. As a result, part of the optical signal gets wasted, lowering the efficiency.

In a recent study published in Nature Communications, a team of photonics researchers led by electrical engineering professor Shaya Fainman at the UC San Diego Jacobs School of Engineering demonstrated a way to make up for these losses by incorporating into the metamaterial something that emits light — a semiconductor.

“We’re offsetting the loss introduced by the metal with gain from the semiconductor. This combination theoretically could result in zero net absorption of the signal — a ‘lossless’ metamaterial,” said Joseph Smalley, an electrical engineering postdoctoral scholar in Fainman’s group and the first author of the study.

In their experiments, the researchers shined light from an infrared laser onto the metamaterial. They found that depending on which way the light is polarized — which plane or direction (up and down, side to side) all the light waves are set to vibrate — the metamaterial either reflects or emits light.

“This is the first material that behaves simultaneously as a metal and a semiconductor. If light is polarized one way, the metamaterial reflects light like a metal, and when light is polarized the other way, the metamaterial absorbs and emits light of a different ‘color’ like a semiconductor,” Smalley said.

Researchers created the new metamaterial by first growing a crystal of the semiconductor material, called indium gallium arsenide phosphide, on a substrate. They then used high-energy ions from plasma to etch narrow trenches into the semiconductor, creating 40-nanometer-wide rows of semiconductor spaced 40 nanometers apart. Finally, they filled the trenches with silver to create a pattern of alternating nano-sized stripes of semiconductor and silver.

“This is a unique way to fabricate this kind of metamaterial,” Smalley said. Nanostructures with different layers are often made by depositing each layer separately one on top of another, “like a stack of papers on a desk,” Smalley explained. But the semiconductor material used in this study (indium gallium arsenide phosphide) can’t just be grown on top of any substrate (like silver), otherwise it will have defects. “Rather than creating a stack of alternating layers, we figured out a way to arrange the materials side by side, like folders in a filing cabinet, keeping the semiconductor material defect-free.”

As a next step, the team plans to investigate how much this metamaterial and other versions of it could improve photonic applications that currently suffer from signal losses.

A new spin on electronics


February 15, 2017

Modern computer technology is based on the transport of electric charge in semiconductors. But this technology’s potential will be reaching its limits in the near future, since the components deployed cannot be miniaturized further. But, there is another option: using an electron’s spin, instead of its charge, to transmit information. A team of scientists from Munich and Kyoto is now demonstrating how this works.

The extremely thin, electrically conducting layer between the materials lanthanum-aluminate (LaAlO2) and strontium-titanate (SrTiO3) transports spin-information from the point of injection to a detector. Credit: Christoph Hohmann / Nanosystems Initiative Munich

The extremely thin, electrically conducting layer between the materials lanthanum-aluminate (LaAlO2) and strontium-titanate (SrTiO3) transports spin-information from the point of injection to a detector. Credit: Christoph Hohmann / Nanosystems Initiative Munich

Computers and mobile devices continue providing ever more functionality. The basis for this surge in performance has been progressively extended miniaturization. However, there are fundamental limits to the degree of miniaturization possible, meaning that arbitrary size reductions will not be possible with semiconductor technology.

Researchers around the world are thus working on alternatives. A particularly promising approach involves so-called spin electronics. This takes advantage of the fact that electrons possess, in addition to charge, angular momentum – the spin. The experts hope to use this property to increase the information density and at the same time the functionality of future electronics.

Together with colleagues at the Kyoto University in Japan scientists at the Walther-Meißner-Institute (WMI) and the Technical University of Munich (TUM) in Garching have now demonstrated the transport of spin information at room temperature in a remarkable material system.

A unique boundary layer

In their experiment, they demonstrated the production, transport and detection of electronic spins in the boundary layer between the materials lanthanum-aluminate (LaAlO2) and strontium-titanate (SrTiO3). What makes this material system unique is that an extremely thin, electrically conducting layer forms at the interface between the two non-conducting materials: a so-called two-dimensional electron gas.

The German-Japanese team has now shown that this two-dimensional electron gas transports not only charge, but also spin. “To achieve this we first had to surmount several technical hurdles,” says Dr Hans Hübl, scientist at the Chair for Technical Physics at TUM and Deputy Director of the Walther-Meißner-Institute. “The two key questions were: How can spin be transferred to the two-dimensional electron gas and how can the transport be proven?”

Information transport via spin

The scientists solved the problem of spin transfer using a magnetic contact. Microwave radiation forces its electrons into a precession movement, analogous to the wobbling motion of a top. Just as in a top, this motion does not last forever, but rather, weakens in time – in this case by imparting its spin onto the two-dimensional electron gas.

The electron gas then transports the spin information to a non-magnetic contact located one micrometer next to the contact. The non-magnetic contact detects the spin transport by absorbing the spin, building up an electric potential in the process. Measuring this potential allowed the researchers to systematically investigate the transport of spin and demonstrate the feasibility of bridging distances up to one hundred times larger than the distance of today’s transistors.

Based on these results, the team of scientists is now researching to what extent spin electronic components with novel functionality can be implemented using this system of materials.

Quantum mechanics, the physics that governs nature at the atomic and subatomic scale, contains a host of new physical phenomena to explore quantum states at the nanoscale. Though tricky, there are ways to exploit these inherently fragile and sensitive systems for quantum sensing. One nascent technology in particular makes use of point defects, or single-atom misplacements, in nanoscale materials, such as diamond nanoparticles, to measure electromagnetic fields, temperature, pressure, frequency and other variables with unprecedented precision and accuracy.

Quantum sensing could revolutionize medical diagnostics, enable new drug development, improve the design of electronic devices and more.

For use in quantum sensing, the bulk nanodiamond crystal surrounding the point defect must be highly perfect. Any deviation from perfection, such as additional missing atoms, strain in the crystalline lattice of the diamond, or the presence of other impurities, will adversely affect the quantum behavior of the material. Highly perfect nanodiamonds are also quite expensive and difficult to make.

A cheaper alternative, say researchers at Argonne National Laboratory and the University of Chicago, is to take defect-ridden, low-quality, commercially manufactured diamonds, and then “heal” them.

In a paper published this week in APL Materials, from AIP Publishing, the researchers describe a method to heal diamond nanocrystals under high-temperature conditions, while visualizing the crystals in three dimensions using an X-ray imaging technique.

“Quantum sensing is based on the unique properties of certain optically active point defects in semiconductor nanostructures,” said F. Joseph Heremans, an Argonne National Laboratory staff scientist and co-author on the paper.

These defects, such as the nitrogen-vacancy (NV) centers in diamond, are created when a nitrogen atom replaces a carbon atom adjacent to a vacancy in the diamond lattice structure. They are extremely sensitive to their environment, making them useful probes of local temperatures, as well as electric and magnetic fields, with a spatial resolution more than 100 times smaller than the thickness of a human hair.

Because diamonds are biologically inert, quantum sensors based on diamond nanoparticles, which can operate at room temperature and detect several factors simultaneously, could even be placed within living cells, where they could, according to Heremans, “image systems from the inside out.”

Heremans and his colleagues, including Argonne’s Wonsuk Cha and Paul Fuoss, as well as David Awschalom of the University of Chicago, set out to map the distribution of the crystal strain in nanodiamonds and to track the healing of these imperfections by subjecting them to high temperatures, up to 800 degrees Celsius in an inert helium environment.

“Our idea of the ‘healing’ process is that gaps in the lattice are filled as the atoms move around when the crystal is heated to high temperatures, thereby improving the homogeneity of the crystal lattice,” said Stephan Hruszkewycz, also a staff scientist at Argonne and lead author on the paper.

This nanodiamond healing was monitored with a 3-D microscopy method called Bragg coherent diffraction imaging, performed by subjecting the crystals to a coherent X-ray beam at the Advanced Photon Source at Argonne. The X-ray beam that scatters off the nanodiamonds was detected and used to reconstruct the 3-D shape of the nanocrystal, “and, more importantly, the strain state of the crystal,” Hruszkewycz said.

The researchers found that nanodiamonds “shrink” during the high-temperature annealing process, and surmise that this occurs because of a phenomenon called graphitization. This phenomenon occurs when the surface of the material is converted from the normal diamond lattice arrangement into graphite, a single layer of chicken-wire-like arranged carbon atoms.

The study marks the first time that Bragg coherent diffraction imaging has been shown to be useful at such high temperatures, a capability that, Hruszkewycz said, “enables the exploration of structural changes in important nanocrystalline materials at high temperatures that are difficult to access with other microscopy techniques.”

Hruszkewycz added that the research represents “a significant step towards developing scalable methods of processing inexpensive, commercial nanodiamonds for quantum sensing and information processing.”