Tag Archives: letter-materials-tech

More materials for electronic applications could be identified, thanks to the discovery of a new metal-organic framework (MOF) that displays electrical semiconduction with a record high photoresponsivity, by a global research collaboration involving the University of Warwick.

Research published today in Nature Communications shows how high photoconductivity and semiconductor behaviour can be added to MOFs – which already have a huge international focus for their applications in gas storage, sensing and catalysis.

The new work, conducted by Universities in Brazil, the United Kingdom and France – including researchers at Warwick’s Department of Chemistry – found that the new MOF has a photoresponsivity of 2.5 × 105 A.W-1- the highest ever observed.

The MOF has been prepared using cobalt (II) ions and naphthalene diimides and acid as ligands. The structure shows anisotropic redox conduction, according to the directions of the crystal lattice. The conduction mechanism is sensitive to light, and may be modified or modulated according to the incident wavelength.

Photoactive and semiconducting MOFs are rare but desirable for electrical and photoelectrical devices.

These results are the first of this kind concerning MOFs and are the starting point for the possibility of discovery of even more functional materials, displaying properties suitable for practical applications.

The potential for use in electronic components and photoconversion devices, such as solar cells and photocatalysts provides a very exciting future for such materials.

Professor Richard Walton, from Warwick’s Department of Chemistry, commented:

“The material we have discovered paves the way for new applications of a topical family of materials in many areas ranging from technology to energy conversion. We illustrate how MOFs that combine organic and inorganic components can produce unique functional materials from readily available chemicals.

“Our work was underpinned by Warwick’s strengthening collaborative links with Brazilian universities and our exceptional equipment for materials analysis “

Think keeping your coffee warm is important? Try satellites. If a satellite’s temperature is not maintained within its optimal range, its performance can suffer which could mean it could be harder to track wildfires or other natural disasters, your Google maps might not work and your Netflix binge might be interrupted. This might be prevented with a new material recently developed by USC Viterbi School of Engineering engineers.

When satellites travel behind the Earth, the Earth can block the sun’s rays from reaching the satellites—cooling them down. In space, a satellite can face extreme temperature variation as much as 190 to 260 degrees Fahrenheit. It’s long been a challenge for engineers to keep satellite temperatures from fluctuating wildly. Satellites have conventionally used one of two mechanisms: physical “shutters” or heat pipes to regulate heat. Both solutions can deplete on-board power reserves. Even with solar power, the output is limited. Furthermore, both solutions add mass, weight and design complexity to satellites, which are already quite expensive to launch.

Taking cues from humans who have a self-contained system to manage internal temperature through homeostasis, a team of researchers including Michelle L. Povinelli, a Professor in the Ming Hsieh Department of Electrical Engineering at the USC Viterbi School of Engineering, and USC Viterbi students Shao-Hua Wu and Mingkun Chen, along with Michael T. Barako, Vladan Jankovic, Philip W.C. Hon and Luke A. Sweatlock of Northrop Grumman, developed a new material to self-regulate the temperature of the satellite. The team of engineers with expertise in optics, photonics, and thermal engineering developed a hybrid structure of silicon and vanadium dioxide with a conical design to better control the radiation from the body of the satellite. It’s like a textured skin or coating.

Vanadium dioxide functions as what is known as a “phase-change” material. It acts in two distinct ways: as an insulator at low temperatures and a conductor at high temperatures. This affects how it radiates heat. At over 134 degrees Fahrenheit (330 degrees Kelvin), it radiates as much heat as possible to cool the satellite down. At about two degrees below this, the material shuts off the heat radiation to warm the satellite up. The material’s conical structure (almost like a prickly skin) is invisible to the human eye at about less than half the thickness of a single human hair–but has a distinct purpose of helping the satellite to switch its radiation on and off very effectively.

Results

The hybrid material developed by USC and Northrop Grumman is twenty times better at maintaining temperature than silicon alone. Importantly, passively regulating heat and temperature of satellites could increase the life span of the satellites by reducing the need to expend on-board power.

Applications on Earth

Besides use on a satellite, the material could also be used on Earth for thermal management. It could be applied to a building over a large area to more efficiently maintain a building’s temperature.

The study, “Thermal homeostasis using microstructured phase-change materials,” is published in Optica. The research was funded by Northrop Grumman and the National Science Foundation. This development is part of a thematic research effort between Northrop Grumman, NG Next Basic Research and USC known as the Northrop Grumman Institute of Optical Nanomaterials and Nanophotonics (NG-ION2).

The researchers are now working on developing the material in the USC microfabrication facility and will likely benefit from the new capabilities in the recently-dedicated John D. O’Brien Nanofabrication Laboratory in the USC Michelson Center for Convergent Bioscience.

University of Alabama at Birmingham physicists have taken the first step in a five-year effort to create novel compounds that surpass diamonds in heat resistance and nearly rival them in hardness.

They are supported by a five-year, $20 million National Science Foundation award to create new materials and improve technologies using the fourth state of matter — plasma.

Plasma — unlike the other three states of matter, solid, liquid and gas — does not exist naturally on Earth. This ionized gaseous substance can be made by heating neutral gases. In the lab, Yogesh Vohra, a professor and university scholar in the UAB Department of Physics, uses plasma to create thin diamonds film. Such films have many potential uses, such as coatings to make artificial joints long-lasting or to maintain the sharpness of cutting tools, developing sensors for extreme environments or creating new super-hard materials.

To make a diamond film, Vohra and colleagues stream a mix of gases into a vacuum chamber, heating them with microwaves to create plasma. The low pressure in the chamber is equivalent to the atmosphere 14 miles above the Earth’s surface. After four hours, the vapor has deposited a thin diamond film on its target.

In a paper in the journal Materials, Vohra and colleagues in the UAB College of Arts and Sciences investigated how the addition of boron, while making a diamond film, changed properties of the diamond material.

It was already known that, if the gases are a mix of methane and hydrogen, the researchers get a microcrystalline diamond film made up of many tiny diamond crystals that average about 800 nanometers in size. If nitrogen is added to that gas mixture, the researchers get nanostructured diamond, made up of extremely tiny diamond crystals averaging just 60 nanometers in size.

In the present study, the Vohra team added boron, in the form of diborane, or B2H6, to the hydrogen/methane/nitrogen feed gas and found surprising results. The grain size in the diamond film abruptly increased from the 60-nanometer, nanostructured size seen with the hydrogen/methane/nitrogen feed gas to an 800-nanometer, microcrystalline size. Furthermore, this change occurred with just minute amounts of diborane, only 170 parts per million in the plasma.

Using optical emission spectroscopy and varying the amounts of diborane in the feed gas, Vohra’s group found that the diborane decreases the amounts of carbon-nitrogen radicals in the plasma. Thus, Vohra said, “our study has clearly identified the role of carbon-nitrogen species in the synthesis of nanostructured diamond and suppression of carbon-nitrogen species by addition of boron to the plasma.”

Since the addition of boron can also change the diamond film from a nonconductor into a semiconductor, the UAB results offer a new control of both diamond film grain size and electrical properties for various applications.

Over the next several years, Vohra and colleagues will probe the use of the microwave plasma chemical vapor deposition process to make thin films of boron carbides, boron nitrides and carbon-boron-nitrogen compounds, looking for compounds that survive heat better than diamonds and also have a diamond-like hardness. In the presence of oxygen, diamonds start to burn at about 1,100 degrees Fahrenheit.

A research group in Japan announced that it has quantified for the first time the impacts of three electron-scattering mechanisms for determining the resistance of silicon carbide (SiC) power semiconductor devices in power semiconductor modules. The university-industry team consisting of researchers from the University of Tokyo and Mitsubishi Electric Corporation has found that resistance under the SiC interface can be reduced by two-thirds by suppressing electron scattering by the charges, a discovery that is expected to help reduce energy consumption in electric power equipment by lowering the resistance of SiC power semiconductors.

Electron scattering under the silicon carbide (SiC) interface is limited by three factors: roughness of the SiC interface, charges under the SiC interface and atomic vibration. Credit: 2017 Mitsubishi Electric Corporation.

Electron scattering under the silicon carbide (SiC) interface is limited by three factors: roughness of the SiC interface, charges under the SiC interface and atomic vibration. Credit: 2017 Mitsubishi Electric Corporation.

Electric power equipment used in home electronics, industrial machinery, trains and other apparatuses requires a combination of maximized efficiency and minimized size. Mitsubishi Electric, a leading Japanese electronics and electrical equipment manufacturer, is accelerating use of SiC devices for power semiconductor modules, which are key components in electric power equipment. SiC power devices offer lower resistance than conventional silicon power devices, so to further lower their resistance it is important to understand correctly the characteristics of the resistance under the SiC interface.

“Until now, however, it had been difficult to measure separately resistance-limiting factors that determine electron scattering,” says Satoshi Yamakawa, senior manager of the SiC Device Development Center at Mitsubishi Electric’s Advanced Technology R&D Center.

Electron scattering focusing on atomic vibration was measured using technology from the University of Tokyo. The impact that charges and atomic vibration have on electron scattering under the SiC interface was revealed to be dominant in Mitsubishi Electric’s analyses of fabricated devices. Although it has been recognized that electron scattering under the SiC interface is limited by three factors, namely, the roughness of the SiC interface, the charges under the SiC interface and the atomic vibration, the contribution of each factor had been unclear. A planar-type SiC metal-oxide-semiconductor field-effect transistor (SiC-MOSFET), in which electrons conduct away from the SiC interface to around several nanometers, was fabricated to confirm the impact of the charges.

“We were able to confirm at an unprecedented level that the roughness of the SiC interface has little effect while charges under the SiC interface and atomic vibration are dominant factors,” says Koji Kita, an associate professor at the University of Tokyo’s Graduate School of Engineering and one of scientists leading the research.

Using an earlier planar-type SiC-MOSFET device for comparison, resistance was reduced by two-thirds owing to suppression of electron scattering, which was achieved by making the electrons conduct away from the charges under the SiC interface. The previous planar-type device has the same interface structure as that of the SiC-MOSFET fabricated by the electronics maker.

For the test, Mitsubishi Electric handled the design, fabrication and analysis of the resistance-limiting factors and the University of Tokyo handled the measurement of electron-scattering factors.

“Going forward, we will continue refining the design and specifications of our SiC MOSFET to further lower the resistance of SiC power devices,” says Mitsubishi Electric’s Yamakawa.

This research achievement was announced at the 63rd International Electron Devices Meeting (IEDM) in San Francisco, California, on December 4, 2017.

Smartphones and computers wouldn’t be nearly as useful without room for lots of apps, music and videos.

Devices tend to store that information in two ways: through electric fields (think of a flash drive) or through magnetic fields (like a computer’s spinning hard disk). Each method has advantages and disadvantages. However, in the future, our electronics could benefit from the best of each.

“There’s an interesting concept,” says Chang-Beom Eom, the Theodore H. Geballe Professor and Harvey D. Spangler Distinguished Professor of Materials Science and Engineering at the University of Wisconsin-Madison. “Can you cross-couple these two different ways to store information? Could we use an electric field to change the magnetic properties? Then you can have a low-power, multifunctional device. We call this a ‘magnetoelectric’ device.”

In research published recently in the journal Nature Communications, Eom and his collaborators describe not only their unique process for making a high-quality magnetoelectric material, but exactly how and why it works.

Physics graduate student Julian Irwin checks equipment in the lab of materials science and engineering Professor Chang-Beom Eom, where researchers have produced a material that could exhibit the best qualities of both solid-state and spinning disk digital storage. Credit: Sarah Page/UW-Madison College of Engineering

Physics graduate student Julian Irwin checks equipment in the lab of materials science and engineering Professor Chang-Beom Eom, where researchers have produced a material that could exhibit the best qualities of both solid-state and spinning disk digital storage. Credit: Sarah Page/UW-Madison College of Engineering

Magnetoelectric materials — which have both magnetic and electrical functionalities, or “orders” — already exist. Switching one functionality induces a change in the other.

“It’s called cross-coupling,” says Eom. “Yet, how they cross-couple is not clearly understood.”

Gaining that understanding, he says, requires studying how the magnetic properties change when an electric field is applied. Up to now, this has been difficult due to the complicated structure of most magnetoelectric materials.

In the past, says Eom, people studied magnetoelectric properties using very “complex” materials, or those that lack uniformity. In his approach, Eom simplified not only the research, but the material itself.

Drawing on his expertise in material growth, he developed a unique process, using atomic “steps,” to guide the growth of a homogenous, single-crystal thin film of bismuth ferrite. Atop that, he added cobalt, which is magnetic; on the bottom, he placed an electrode made of strontium ruthenate.

The bismuth ferrite material was important because it made it much easier for Eom to study the fundamental magnetoelectric cross-coupling.

“We found that in our work, because of our single domain, we could actually see what was going on using multiple probing, or imaging, techniques,” he says. “The mechanism is intrinsic. It’s reproducible — and that means you can make a device without any degradation, in a predictable way.”

To image the changing electric and magnetic properties switching in real time, Eom and his colleagues used the powerful synchrotron light sources at Argonne National Laboratory outside Chicago, and in Switzerland and the United Kingdom.

“When you switch it, the electrical field switches the electric polarization. If it’s ‘downward,’ it switches ‘upward,'” he says. “The coupling to the magnetic layer then changes its properties: a magnetoelectric storage device.”

That change in direction enables researchers to take the next steps needed to add programmable integrated circuits — the building blocks that are the foundation of our electronics — to the material.

While the homogenous material enabled Eom to answer important scientific questions about how magnetoelectric cross-coupling happens, it also could enable manufacturers to improve their electronics.

“Now we can design a much more effective, efficient and low-power device,” he says.

Crosstalk and noise can become a major source of reliability problems of CNT based VLSI interconnects in the near future. Downscaling of component size in integrated circuits (ICs) to nanometer scale coupled with high density integration makes it challenging for researchers to maintain signal integrity in ICs. There are high chances of occurrence of crosstalk between adjacent wires. This crosstalk in turn, will increase the peak noise in the transient signals that pass through the interconnects. As multiple occurrences of crosstalk happen, the noise propagates through multiple stages of wires and the problem worsens to logic failure.

But thanks to semiconducting CNTs, which till now have found applications in the fabrication of futuristic field effect transistors, when placed around an interconnect, can reduce crosstalk to a large extent. Basically, semiconducting CNTs are non-conducting, have small dielectric constant, medium to large band gaps and hence can act as insulating shields to electric fields.

As semiconducting CNTs are one dimensional nanowires, they have very high anisotropic properties along their axis as well as their radius. The dielectric polarizability, which is the measure of number of polarizable bonds in a material, is found to be very smaller along the CNT radius compared to its axis. So, semiconducting CNTs are less polarizable along their radius which further suggests that they have small dielectric constants. The famous Clausius-Mossotti relation can be used to derive the dielectric constant from the dielectric polarizability. Further, this relation also tells that the dielectric constant of a CNT increases with its radius. So, obviously small diameter semiconducting CNTs are the ideal candidates as the low-k dielectric medium between two CNT interconnects.

The contact geometry is modified in such a way that more metal atoms are present at the centre where metallic CNTs are present. The contact has lesser number of metal atoms at the periphery where semiconducting CNTs are present. This helps in building a Schottky barrier at the contact semiconducting CNT interface and hence, inhibits any carrier movement.

Finally, experimental results show that the radial dielectric constant can be as low as 2.82 if (2,2) CNTs are used as shields. The coupling capacitance between adjacent wires is dependent on the interconnect thickness as well as the semiconducting CNT shield thickness. Crosstalk between CNT wires can be reduced by 28% if semiconducting CNTs are used. The crosstalk induced peak noise was also found to be 25% lesser for semiconducting CNT shielded interconnects at different input voltages of 0.8V, 0.5V and 0.3V.

For the first time, physicists have developed a technique that can peer deep beneath the surface of a material to identify the energies and momenta of electrons there.

The energy and momentum of these electrons, known as a material’s “band structure,” are key properties that describe how electrons move through a material. Ultimately, the band structure determines a material’s electrical and optical properties.

The team, at MIT and Princeton University, has used the technique to probe a semiconducting sheet of gallium arsenide, and has mapped out the energy and momentum of electrons throughout the material. The results are published today in the journal Science.

By visualizing the band structure, not just at the surface but throughout a material, scientists may be able to identify better, faster semiconductor materials. They may also be able to observe the strange electron interactions that can give rise to superconductivity within certain exotic materials.

“Electrons are constantly zipping around in a material, and they have a certain momentum and energy,” says Raymond Ashoori, professor of physics at MIT and a co-author on the paper. “These are fundamental properties which can tell us what kind of electrical devices we can make. A lot of the important electronics in the world exist under the surface, in these systems that we haven’t been able to probe deeply until now. So we’re very excited — the possibilities here are pretty vast.”

Ashoori’s co-authors are postdoc Joonho Jang and graduate student Heun Mo Yoo, along with Loren Pfeffer, Ken West, and Kirk Baldwin, of Princeton University.

Pictures beneath the surface

To date, scientists have only been able to measure the energy and momentum of electrons at a material’s surface. To do so, they have used angle-resolved photoemission spectroscopy, or ARPES, a standard technique that employs light to excite electrons and make them jump out from a material’s surface. The ejected electrons are captured, and their energy and momentum are measured in a detector. Scientists can then use these measurements to calculate the energy and momentum of electrons within the rest of the material.

“[ARPES] is wonderful and has worked great for surfaces,” Ashoori says. “The problem is, there is no direct way of seeing these band structures within materials.”

In addition, ARPES cannot be used to visualize electron behavior in insulators — materials within which electric current does not flow freely. ARPES also does not work in a magnetic field, which can greatly alter electronic properties inside a material.

The technique developed by Ashoori’s team takes up where ARPES leaves off and enables scientists to observe electron energies and momenta beneath the surfaces of materials, including in insulators and under a magnetic field.

“These electronic systems by their nature exist underneath the surface, and we really want to understand them,” Ashoori says. “Now we are able to get these pictures which have never been created before.”

Tunneling through

The team’s technique is called momentum and energy resolved tunneling spectroscopy, or MERTS, and is based on quantum mechanical tunneling, a process by which electrons can traverse energetic barriers by simply appearing on the other side — a phenomenon that never occurs in the macroscopic, classical world which we inhabit. However, at the quantum scale of individual atoms and electrons, bizarre effects such as tunneling can occasionally take place.

“It would be like you’re on a bike in a valley, and if you can’t pedal, you’d just roll back and forth. You would never get over the hill to the next valley,” Ashoori says. “But with quantum mechanics, maybe once out of every few thousand or million times, you would just appear on the other side. That doesn’t happen classically.”

Ashoori and his colleagues employed tunneling to probe a two-dimensional sheet of gallium arsenide. Instead of shining light to release electrons out of a material, as scientists do with ARPES, the team decided to use tunneling to send electrons in.

The team set up a two-dimensional electron system known as a quantum well. The system consists of two layers of gallium arsenide, separated by a thin barrier made from another material, aluminum gallium arsenide. Ordinarily in such a system, electrons in gallium arsenide are repelled by aluminum gallium arsenide, and would not go through the barrier layer.

“However, in quantum mechanics, every once in a while, an electron just pops through,” Jang says.

The researchers applied electrical pulses to eject electrons from the first layer of gallium arsenide and into the second layer. Each time a packet of electrons tunneled through the barrier, the team was able to measure a current using remote electrodes. They also tuned the electrons’ momentum and energy by applying a magnetic field perpendicular to the tunneling direction. They reasoned that those electrons that were able to tunnel through to the second layer of gallium arsenide did so because their momenta and energies coincided with those of electronic states in that layer. In other words, the momentum and energy of the electrons tunneling into gallium arsenide were the same as those of the electrons residing within the material.

By tuning electron pulses and recording those electrons that went through to the other side, the researchers were able to map the energy and momentum of electrons within the material. Despite existing in a solid and being surrounded by atoms, these electrons can sometimes behave just like free electrons, albeit with an “effective mass” that may be different than the free electron mass. This is the case for electrons in gallium arsenide, and the resulting distribution has the shape of a parabola. Measurement of this parabola gives a direct measure of the electron’s effective mass in the material.

Exotic, unseen phenomena

The researchers used their technique to visualize electron behavior in gallium arsenide under various conditions. In several experimental runs, they observed “kinks” in the resulting parabola, which they interpreted as vibrations within the material.

“Gallium and arsenic atoms like to vibrate at certain frequencies or energies in this material,” Ashoori says. “When we have electrons at around those energies, they can excite those vibrations. And we could see that for the first time, in the little kinks that appeared in the spectrum.”

They also ran the experiments under a second, perpendicular magnetic field and were able to observe changes in electron behavior at given field strengths.

“In a perpendicular field, the parabolas or energies become discrete jumps, as a magnetic field makes electrons go around in circles inside this sheet,” Ashoori says.

“This has never been seen before.”

The researchers also found that, under certain magnetic field strengths, the ordinary parabola resembled two stacked donuts.

“It was really a shock to us,” Ashoori says.

They realized that the abnormal distribution was a result of electrons interacting with vibrating ions within the material.

“In certain conditions, we found we can make electrons and ions interact so strongly, with the same energy, that they look like some sort of composite particles: a particle plus a vibration together,” Jang says.

Further elaborating, Ashoori explains that “it’s like a plane, traveling along at a certain speed, then hitting the sonic barrier. Now there’s this composite thing of the plane and the sonic boom. And we can see this sort of sonic boom — we’re hitting this vibrational frequency, and there’s some jolt happening there.”

The team hopes to use its technique to explore even more exotic, unseen phenomena below the material surface.

“Electrons are predicted to do funny things like cluster into little bubbles or stripes,” Ashoori says. “These are things we hope to see with our tunneling technique. And I think we have the power to do that.”

A team of Hokkaido University researchers has developed a novel material synthesis method called proton-driven ion introduction (PDII) which utilizes a phenomenon similar to “ion billiards.” The new method could pave the way for creating numerous new materials, thus drastically advancing materials sciences.

The synthesis method is based on a liquid-free process that allows for intercalation – insertion of guest ions into a host material – and ion substitution with those in the host material by driving ions with protons. This study, led by Assistant Professor Masaya Fujioka and Professor Junji Nishii at the university’s Research Institute for Electric Science, was published in the Journal of the American Chemical Society on November 16th.

Conventionally, intercalation and ion substitution have been conducted in an ion solution, but the process is regarded as cumbersome and problematic. In a liquid-based process, solvent molecules can be inserted into the host materials along with guest ions, degrading the crystal quality. It is also difficult to homogeneously introduce ions into host materials, and some host materials are not suitable when used with liquids.

In the PDII method, a high voltage of several kilovolts is applied to a needle-shaped anode placed in atmospheric hydrogen to generate protons via the electrolytic disassociation of hydrogen. The protons migrate along the electric field and are shot into the supply source of the desired ions – similar to balls in billiards – and the ions are driven out of the source to keep it electrically neutral. Ions forced out of the source are introduced, or intercalated, into a nanometer-level gap in the host material.

In this study, by using different materials as ion supply sources, the team succeeded in homogenously introducing lithium ions (Li+), sodium ions (Na+), potassium ions (K+), copper ions (Cu+) and silver ions (Ag+) into nanometer-level gaps in tantalum (IV) sulfide (TaS2), a layered material, while maintaining its crystallinity. Furthermore, the team successfully substituted Na+ of Na3V2(PO4)3 with K+, producing a thermodynamically metastable material, which cannot be obtained using the conventional solid-state reaction method.

“At present, we have shown that hydrogen ions (H+), Li+, Na+, K+, Cu+ and Ag+ can be used to introduce ions in our method, and we expect a larger variety of ions will be usable. By combining them with various host materials, our method could enable the production of numerous new materials,” says Masaya Fujioka. “In particular, if a method to introduce negatively charged ions and multivalent ions is established, it will spur the development of new functional materials in the solid ion battery and electronics fields.”

The stacked color sensor


November 16, 2017

The human eye has three different types of sensory cells for the perception of colour: cells that are respectively sensitive to red, green and blue alternate in the eye and combine their information to create an overall colored image. Image sensors, for example in mobile phone cameras, work in a similar way: blue, green and red sensors alternate in a mosaic-like pattern. Intelligent software algorithms calculate a high-resolution colour image from the individual colour pixels.

However, the principle also has some inherent limitations: as each individual pixel can only absorb a small part of the light spectrum that hits it, a large part of the light is lost. In addition, the sensors have basically reached the limits of miniaturization, and unwanted image disturbances can occur; these are known as color moiré effects and have to be laboriously removed from the finished image.

Transparent only for certain colors

Researchers have therefore been working for a number of years on the idea of stacking the three sensors instead of placing them next to each other. Of course, this requires that the sensors on top let through the light frequencies that they do not absorb to the sensors underneath. At the end of the 1990s, this type of sensor was successfully produced for the first time. It consisted of three stacked silicon layers, each of which absorbed only one colour.

This actually resulted in a commercially available image sensor. However, this was not successful on the market because the absorption spectra of the different layers were not distinct enough, so part of the green and red light was absorbed by the blue-sensitive layer. The colors therefore blurred and the light sensitivity was thus lower than for ordinary light sensors. In addition, the production of the absorbing silicon layers required a complex and expensive manufacturing process.

Empa researchers have now succeeded in developing a sensor prototype that circumvents these problems. It consists of three different types of perovskites – a semiconducting material that has become increasingly important during the last few years, for example in the development of new solar cells, due to its outstanding electrical properties and good optical absorption capacity. Depending on the composition of these perovskites, they can, for example, absorb part of the light spectrum, but remain transparent for the rest of the spectrum. The researchers in Maksym Kovalenko’s group at Empa and ETH Zurich used this principle to create a color sensor with a size of just one pixel. The researchers were able to reproduce both simple one-dimensional and more realistic two-dimensional images with an extremely high color fidelity.

Accurate recognition of colors

The advantages of this new approach are clear: the absorption spectra are clearly differentiated and the colour recognition is thus much more precise than with silicon. In addition, the absorption coefficients, especially for the light components with higher wavelengths (green and red), are considerably higher in the perovskites than in silicon. As a result, the layers can be made significantly smaller, which in turn allows smaller pixel sizes. This is not crucial in the case of ordinary camera sensors; however, for other analysis technologies, such as spectroscopy, this could permit significantly higher spatial resolution. The perovskites can also be produced using a comparatively cheap process.

However, more work is still needed in order to further develop this prototype into a commercially usable image sensor. Key areas include the miniaturisation of pixels and the development of methods for producing an entire matrix of such pixels in one step. According to Kovalenko, this should be possible with existing technologies.

Perovskites are such a promising material in research that the prestigious journal Science has published a special edition about them. It includes a review article by the Empa/ETH research group led by Maksym Kovalenko about the current state of research and potential uses of lead halide perovskites nanocrystals.

These have properties that make them a promising candidate for the development of semiconductor nanocrystals for various optoelectronic applications such as television screens, LEDs and solar cells: they are inexpensive to manufacture, have a high tolerance to defects and can be tuned precisely to emit light in a specific colour spectrum.

AKHAN Semiconductor, a technology company specializing in the fabrication and application of lab-grown, electronics-grade diamond, announced today the issuance by the Japan Patent Office of a patent covering a method for the fabrication of diamond semiconductor materials, core to applications in automotive, aerospace, consumer electronics, military, defense, and telecommunications systems, amongst others.

“We are ecstatic to be awarded this key patent in Japan. Its issuance protects our proprietary interests in diamond semiconductor in one of the nations leading the globe in diamond research,” said Adam Khan, Founder & Chief Executive Officer, AKHAN Semiconductor, Inc. “Following this year’s issuances of a Taiwan diamond semiconductor patent, and a major US diamond transparent electronics patent, the Japan patent issuance is a further testament to AKHAN’s leadership in the diamond semiconductor space.”

Japan, which has actively funded millions of dollars into diamond electronics research since 2002, earlier this year announced marked progress in the development of diamond semiconductor device performance. The AKHAN granted and issued patent, JP6195831 (B2), is a foreign counterpart of other issued and pending patents owned by AKHAN Semiconductor, Inc. that are used in the company’s Miraj Diamond Platform products. As a key landmark patent, the claims protect uses far beyond the existing applications, including microprocessor applications. Covering the base materials common to nearly all semiconductor components, the intellectual property can be realized in everything from diodes, transistors, and power inverters, to fully functioning diamond chips such as integrated circuitry.

AKHAN’s flagship Miraj Diamond Glass for mobile display and camera lens is 6x stronger, 10x harder, and runs over 800x cooler than leading glass competitors like Gorilla Glass by coating standard commercial glass such as aluminosilicate, BK7, and Fused Silica with lab-grown nanocrystalline diamond. Diamond-based technology is capable of increasing power density as well as creating faster, lighter, and simpler devices for consumer use. Cheaper and thinner than its silicon counterparts, diamond-based electronics could become the industry standard for energy efficient electronics.

“This patent adds to the list of other key patents in the field of Diamond Semiconductor that are owned by the company, including the ability to fabricate transparent electronics, as well as the ability to form reliable metal contacts to diamond semiconductor systems,” said Carl Shurboff, President and Chief Operating Officer, AKHAN Semiconductor, Inc. “This patent bolsters the supporting evidence of AKHAN’s leadership in manufacturing diamond semiconductor products, and supports ongoing efforts with our major defense, aerospace and space system development partners.”