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A chip with 2-D dimensional tin oxide (SnO)

Tin Oxide: The First Stable p-type 2-D Semiconductor Material

Researchers at the University of Utah have developed the first stable intrinsic p-type (carrying positive charges) 2-D semiconductor material, tin oxide. If this semiconductor is mated with a n-type (carrying electrons) 2-D semiconductor in a transistor, it opens up the possibility of building power-saving two-dimensional complementary logic circuits like the ones in microprocessors today.

"Now we have everything—we have p-type 2-D semiconductors and n-type 2-D semiconductors," said Ashutosh Tiwari, an associate professor at the University of Utah and the leader of the research, in a press release. "Now things will move forward much more quickly."

The potential for 2-D materials—such as graphene and molybdenum disulfide—as an alternative to the three-dimensional silicon, raises hopes for smaller, faster, lower-power transistors.

However, the path to success for these 2-D materials in transistors has not always been clear, whether it be issues such as graphene not being a natural semiconductor or the charge carrier traps that compromise molybdenum disulfide. But possibly the biggest issue has been that all previous 2-D materials have only been stable n-type semiconductors. It has been possible to dope other 2-D materials, such as molybdenum disulfide and tungsten diselenide, to behave as p-type. However, this new tin oxide represents the first intrinsic p-type semiconductor in a 2D material.

In research described in the journal Advanced Electronic Materials, the Utah University researchers overcame this limitation by layering 2-D tin oxide (SnO) onto a sapphire-and-silicon-dioxide (SiO2) substrate. The researchers were then able to fabricate a few field-effect transistors (FETs) from it.

With this development, the attractive properties of 2-D materials in transistors are more fully exploitable. For instance, in 2-D materials charge transport is basically confined to a single plane, meaning electrical and thermal transport properties that can be much better than those of bulk silicon. That could mean chips that consume less power and throw-off less heat.

In an e-mail interview, Tiwari said that the next step in their research will be to build a CMOS (complementary metal oxide semiconductor) using their new p-type 2-D semiconductor.

This post was corrected on 18 February to indicate that some 2-D materials could act as p-type semiconductors when doped.

A silicon nanowire transistor used as a qubit

Quantum Computing With Ordinary CMOS Transistors

Future quantum computers might not be all that different from the one you’re using now. An international team of researchers have created a the most fundamental part of a quantum computer—the quantum bit, or qubit—using only a CMOS transistor that is not much different from those in today’s microprocessors.

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Electronic Qubit Integrated Into Solid-State Switch

Essential for so-called quantum networks and quantum computers is something called a quantum bit, or qubit, which would replace the traditional bits that are stored or transmitted in today’s computers and optical networks. It consists of an ion with an unpaired electron that has two spin states—up or down, or a 0 and 1 in a binary system. But under some conditions, these qubits can be made to have both the 0 and 1 state simultaneously—a quantum state.

One of the problems researchers have faced in incorporating qubits in optical networks is getting the photons to strongly interact with the qubits in a solid-state device. The aim has been to develop something akin to an electro-optic modulator that uses electronic signals to modulate properties of light in today’s optical networks.

Researchers at the University of Maryland have developed a novel design that may have achieved that aim by “combining the light-trapping of photonic crystals with the electron-trapping of quantum dots.

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Introducing One of the Best Thin-film Transistors Ever

Wide-band gap metal-oxide thin-film transistors (TFTs) have never been quite as popular as the ubiquitous metal-oxide semiconductor field-effect transistors (MOSFET). One of the main issues with TFTs has been that they are limited to n-type semiconductor materials that can only move negative charges through them, limiting their electrical output.

While different architectures have been investigated to overcome this, the problem has remained that there just haven’t been p-type wide-band inorganic semiconductor materials that have done the trick. The result has been that TFTs have been limited to low-power applications, such as display screens.

Now researchers at the University of Alberta in Canada say they have come up with a design that will take nearly any wide-band metal-oxide n-type semiconductor used in thin-film transistors and create a p-type channel, or inversion layer, through which positive charges can travel without the need of some new semiconductor material. As proof of their design, the Canadian researchers have created a TFT capable of conducting both electrons (negative charges) and holes (positive charges) resulting in far greater electrical output.

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Nanotube-Based Tunneling Field Effect Transistor Offers Semiconductor-Free Switching

Researchers at Michigan Technological University (MTU) have developed a method for producing a tunneling field effect transistor (TFET) that overcomes a key obstacle to their adoption: the need to be operated at cryogenic temperatures. Eliminating semiconductor materials in the design of their nanotube-based TFET has allowed the MTU researchers to fabricate a device that can operate at room temperatures and offers the added feature of flexibility.

In research explained in an article published in the Nature journal Scientific Reports, the MTU researchers, led by Yoke Khin Yap, used iron quantum dots in combination with functionalized boron nitride nanotubes (BNNTs) to create flexible tunneling channels in TFET devices.

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Nanomembrane May Bring Rechargeable Lithium-Metal Batteries Back

Researchers at Cornell University, in Ithaca, N.Y., may have found a way to bring the long-moribund prospects of rechargeable lithium-metal batteries back from the dead with a novel nanostructured membrane that could make the batteries both safe and efficient.

In research described in the journal Nature Communications, the Cornell researchers looked anew at the problem that has been plaguing the prospects of rechargeable lithium-metal batteries: growths, referred to as dendrites, that over time branch out of the anode, into the electrolyte, and eventually expand to the point where they actually bridge the gap between the two electrodes and cause the battery to short out—or even worse.

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Cheap Cubic-Boron Nitride Could Enable Next Gen Smart Grid

Researchers at North Carolina State University (NCSU), led by Jay Narayan, have developed a new method for converting hexagonal-boron nitride (h-BN) directly into cubic-boron nitride (c-BN) that is faster and less expensive than previous processes and promises to make a material that is more viable for high-power electronics, transistors and solid-state devices.

Boron nitride (BN) comes in four basic forms. Two of these forms of boron nitride, namely hexagonal-boron nitride (h-BN) and cubic-boron nitride (c-BN), represent the two most attractive forms of BN for electronic applications because their structures and properties are quite similar to both graphite and diamonds. Like diamonds, c-BN has very good thermal properties for integrated circuits as well as high-frequency power capabilities that compare favorably with silicon.

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World's First Single-Atom Optical Switch Fabricated

You may have heard of the single-atom transistor that thumbed its nose at Moore’s Law once and for all. But that transistor was based on the electron, a relative slow poke. What if you could develop a single-atom transistor based on the movement of photons, which travel at the speed of light? Now that would be both small and fast.

Now researchers at ETH Zurich Switzerland have developed the equivalent of a single-atom photonic transistor by fabricating the world’s first single-atom optical switch

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Graphene Cages Cover Silicon Anodes for High Capacity Batteries

Ever since researchers first discovered that the charge life of Li-ion batteries could be improved by a factor of ten by replacing graphite on the anodes with silicon, there has been a steady stream of research aimed at making silicon actually work as an anode material in real-world batteries.

This has not been easy. The main problem has been that as they take on charge, the anodes swell enormously; when they discharge, they shrink, and the silicon cracks. Another issue has been that when lithium ions travel from anode to cathode through the electrolyte, they create a coating on the electrodes that reduces the battery’s performance.

One researcher who has been focused on developing a practical silicon-based anode is Yi Cui from both Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory. Now Cui and a team of researchers from both Stanford and SLAC have developed a new approach to using silicon in the anodes of Li-ion batteries—one that might not only be technologically possible, but also commercially viable.

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Charge Transport in Plastics Increased One Thousand Times

One of the factors that has kept conjugated semiconducting polymers from being even more effective in applications such as organic photovoltaics (OPVs) and organic light-emitting diodes (OLEDs) is the materials’ poor charge carrier mobility. Basically, charge doesn’t move through plastic—even the conjugated variety—as well as it does through silicon. The result is high losses and poor performance.

Nanomaterials such as graphene have been offered up as additives to increase carrier mobility in polymers

Now researchers at Umeå University in Sweden have developed a novel technique for improving the charge transport mobility of a polymer by more than a thousand times. The researchers were able to achieve this enormous increase without any doping of the polymer; instead, they controlled the orientation of the crystallite formations in the polymer.

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IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

Dexter Johnson
Madrid, Spain
Rachel Courtland
Associate Editor, IEEE Spectrum
New York, NY
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