Wise Old (Owl) Chips
Graphene is a promising material for use in future transistors. It consists of one-atom-thick planar sheets, which are packed in honeycomb crystal lattice structures. The problem is that graphene doesn’t have a band gap, meaning it can’t be turned off in a system.

Rice University, Cornell University and others have devised a new, and wise, way to turn graphene into working circuits. Researchers have developed 100nm, 2D circuits using these materials. And they have also used the technology to pattern a structure in the shape of Rice’s mascot, the owl.

An atom-thick Rice Owl (scale bar equals 100 micrometers) was created to show the ability to make fine patterns in hybrid graphene/hexagonal boron nitride (hBN). In this image, the owl is hBN and the lighter material around it is graphene. The ability to pattern a conductor (graphene) and insulator (hBN) into a single layer may advance the ability to shrink electronic devices. (Credit: Zheng Liu/Rice University)

Researchers have combined graphene and hexagonal boron nitride (h-BN) as an insulator to make 2D circuits. With proper control, the band gap and magnetic properties of these materials can be controlled. These materials have fundamental limitations, however. And they cannot be easily integrated with conventional lithography, according to researchers.

To enable the technology, researchers have devised a “patterned regrowth” process. This enables the spatially controlled synthesis of lateral junctions between electrically conductive graphene and insulating h-BN, as well as between intrinsic and doped graphene, according to researchers.

Using chemical vapor deposition (CVD), researchers first deposited a sheet of h-BN. A mask was placed over the h-BN. The exposed material was etched away with argon gas. Then, graphene was grown via CVD in the open spaces. The hybrid layer could then be picked up and placed on any substrate.

The resulting films form continuous sheets across these hetero-junctions. At present, researchers have demonstrated 100nm technology. “It should be possible to make fully functional devices with circuits at 30, even 20 nanometers wide, all in two dimensions,” said Rice researcher Jun Lou, on the university’s Web site.

Researchers Dive Into Nano Tunnels
The Karlsruhe Institute of Technology (KIT) and Rice University claim to have dug the world’s smallest nano tunnels.

Researchers have devised metal particles, which can bore or form tunnels into graphite materials. Engineered nanoporous tunnel networks in graphite may find applications in medicine and battery technology. They also could pave the way toward nanopatterning of graphene to enable graphene nanoribbons.

In the lab, researchers devised layered carbon atoms to form graphite. The tunnels are made applying nickel nanoparticles to the graphite. These materials are heated in hydrogen gas. The surface of the metal particles serves as a catalyst removing the carbon atoms of the graphite.

Graphite consists of layered carbon atoms. A metal particle bores into the graphite sample from the edges of these layers. (Photo: KIT)

Through capillary forces, the nickel particle is drawn into the hole that forms and bores through the material. The size of the tunnels obtained in the experiments was in the range of 1nm to 50nm.

On its Web site, Maya Lukas and Velimir Meded from KIT said: “The tunnels below these upper layers, however, leave atomic structures on the surface whose courses can be traced and which can be assigned to the nanotunnels by means of the very detailed scanning tunneling microscopy images and based on computerized simulations.”

Good Genes Enable Storage
The EMBL-European Bioinformatics Institute (EMBL-EBI) has devised a DNA storage technology. The technology could make it possible to store at least 100 million hours of high-definition video in a cup of DNA.

DNA is generating interest as a storage technology because of its ability to handle high-density information encoding. But previous DNA-based information storage efforts have only encoded small amounts of information.

Researchers have devised a scalable DNA storage technology. They encoded computer files totaling 739 kilobytes of hard-disk storage, with an estimated 5.2 × 106 bits into a DNA code. Researchers synthesized, sequenced and reconstructed the DNA to its original files with 100% accuracy.

“We knew we needed to make a code using only short strings of DNA, and to do it in such a way that creating a run of the same letter would be impossible. So we figured, let’s break up the code into lots of overlapping fragments going in both directions, with indexing information showing where each fragment belongs in the overall code, and make a coding scheme that doesn’t allow repeats. That way, you would have to have the same error on four different fragments for it to fail—and that would be very rare,” said Ewan Birney, associate director of EMBL-EBI, on the research group’s Web site.

In one experiment, the group sent various encoded information to Agilent Technologies. “We downloaded the files from the Web and used them to synthesize hundreds of thousands of pieces of DNA – the result looks like a tiny piece of dust,” said Emily Leproust of Agilent. In turn, Agilent mailed the sample to EMBL-EBI, where the researchers were able to sequence the DNA and decode the files without errors.

—Mark LaPedus

SOI Enables Strong Nanowires
Strained silicon nanowires are promising transistor structures, thanks to their electrostatic control and enhanced transport properties, but realizing high strain levels for such nanowires is a challenge.

Paul Scherrer Institut and others have developed a method to create new and strong silicon nanowire structures. Researchers have devised nanowires, which are under a tension level that is more than twice as high as that used in today’s components.

Researchers achieved 4.5% of elastic strain, or 7.6 GPa uniaxial tensile stress, in 30nm wide nanowires. This exceeds the limit that can be obtained using SiGe-based virtual substrates.

This approach is based on strain accumulation mechanisms in suspended dumbbell-shaped bridges, which are patterned on strained silicon-on-insulator (SOI) substrates. Potentially, this method can be applied to any tensile pre-strained layer, provided the layer can be released from the substrate, according to researchers. This enables the fabrication of a variety of strained semiconductors with properties for applications in nanoelectronics, photonics and photovoltaics.

“There is actually no magic behind building up tension in a wire—you just have to pull strongly on both ends,” said Hans Sigg of the Laboratory for Micro- and Nanotechnology, on Paul Scherrer Institut’s Web Site. “The challenge is to implement such a wire in a stressed state into an electronic component.”

Salad Dressing Chip Production Process
The University of Chicago, New York University and Syracuse University have devised a way to heal defects in materials at the atomic level.

Researchers created defects in single-layer crystals and then watched them self-heal using curved microscopic particles. The research could pave the way for improvements in graphene and carbon nanotubes.

To enable such a feat, researchers utilized “soft matter,” which includes semi-solid substances such as gels, foams and liquid crystals. Researchers equated the microemulsions used in this effort to mayonnaise-based ranch dressing.

“Mayonnaise is made from a mixture of olive oil and vinegar,” said Syracuse physicist Mark Bowick, on the University of Chicago’s Web site. “You have to beat the ingredients for a long time to disperse tiny droplets of the vinegar in the oil to make an emulsion.”

A surfactant is required to keep droplets mixed evenly throughout the oil. “In ranch dressing, the surfactant used is ground-up mustard seed particles, which arrange themselves at the interface between the water and the oil,” Bowick said. “The mustard seed particles collect on the surface of the water droplets.”

To study curved crystals, researchers emulated ranch dressing by adding microscopic acrylic glass particles to an emulsion of glycerol droplets. The glass particles collected on the surface of individual glycerol droplets. The particles’ positive electric charges repel each other, causing them to arrange themselves in a honeycomb pattern, with each particle equally distant from the others, according to researchers.

The curved crystal pattern generates 12 defects. Researchers then added an extra particle, called an interstitial, in the middle of the crystal. On a curved surface, the particle added halfway between two defects would create another defect. The strain on the crystalline structure caused by these two defects would “flow” away from site and would disappear, according to researchers.

In the lab, researchers proved the technology. Using optical tweezers, researchers inserted interstitials in a lattice of similar colloidal particles sitting on flat or curved oil-glycerol interfaces. Unlike in flat space, the curved crystals self-heal through a collective particle rearrangement that redistributes the increased density associated with the interstitial.

Thanks For The Memories
Rice University is helping to launch memory technology into space, enabling it to go “where no memory has gone before.” The university has devised 3D, two-terminal memories on transparent flexible sheets, based on the switching properties of silicon oxide.

The resistive memories are made of silicon oxide with a graphene terminal crossbar. A voltage is able to run across the thin sheet of silicon oxide strips from a 5nm channel, turning it into conductive silicon.

New memory material. Source: Rice University.

The devices show potential for radiation-hardened applications, as they can withstand heat up to about 700 degrees Celsius. In fact, the devices built at Rice are now being evaluated at the International Space Station (ISS). The chips were launched as part of a Russian cargo mission to the ISS that arrived Aug. 1. The devices will remain on the station for two years.

The discovery followed recent work at Rice on graphitic-based memories, in which researchers saw strips of graphite on a silicon oxide substrate break and heal when a voltage was applied.

Using graphene as crossbar terminals, Rice shows silicon oxide can be used as a reliable memory. The memories are flexible, transparent and can be built in 3-D configurations. Through in-situ transmission electron microscopy, Rice was able to image the real-time formation and evolution of the filament in a silicon oxide resistive switch.

More DSA Breakthroughs In The Lab
Using directed self-assembly (DSA), Karlsruhe Institute of Technology (KT) and others have built 3D structures from a 2D template. In addition, researchers have devised a new etching method to produce 3D structures in silicon for the processing of light signals in telecommunications.

First, polystyrene is applied to a silicon surface. After drying, spheres automatically form in a dense monolayer on the silicon. Upon metal coating and the removal of the spheres, a honeycomb etching mask remains on the silicon surface.

Deep below the silicon surface, the SPRIE method produces regular structures in the micrometer range that refract light. Source: KIT/CFN.

The university calls this step SPRIE or sequential passivation and reactive ion etching. Instead of a simple hole with vertical smooth walls, every etching step produces a spherical depression with a curved surface.

“Optical telecommunication takes place at a wavelength of 1.5 µm. With our etching method, we produce a corrugated structure in the micrometer range along the wall,” said Martin Wegener, Professor of the Institute of Applied Physics and Institute of Nano-technology of KT and coordinator of the DFG Center for Functional Nanostructures (CFN), on KT’s site.

—Mark LaPedus

Researchers study behavior of ferroelectrics
Today’s memories based on ferroelectric materials are difficult to scale and are mainly used for niche applications like SRAM replacements in battery-backed systems.

The U.S. Department of Energy’s Brookhaven National Laboratory, Lawrence Berkeley National Laboratory and others have revealed details about the atomic structure and behavior of ferroelectric materials. This could lead the way to next-generation or universal memories based on ferroelectric materials.

Brookhaven has devised a technique called electron holography to capture images of the electric fields created by the ferroelectric materials’ atomic displacement. The laboratory also demonstrated a method for identifying the behavior and stability of ferroelectrics.

Direct polarization images of individual ferroelectric nano cubes captured with electron holography. The fringing field, or “footprint” of electric polarization, can be seen clearly in (a), but it vanishes when the material is subjected to high temperatures (b). The lower images show that no fringing field can be observed before application of electricity (c), but a clear field emanates after current is applied (d).

Understanding the atomic-scale properties will help guide implementation of these particles. “Electron holography is an interferometry technique using coherent electron waves,” said Brookhaven physicist Myung-Geun Han. “When electron waves pass through a ferroelectric sample, they are influenced by local electric fields, yielding a so-called phase-shift. The interference pattern between the electrons that pass through electric fields and those that don’t creates what’s called an electron hologram, which allows us to directly ‘see’ those local electric fields around individual ferroelectric nano particles.”

With this technique, researchers revealed that the electric polarity could remain stable for individual ferroelectric materials. This means that each nanoparticle can be used as a data bit.
“Properly used, ferroelectrics could ramp up memory density and store an unparalleled multiple terabytes of information on just one square inch of electronics,” Han said. “This brings us closer to engineering such devices.”

The ferroelectric nanoparticles tested, semiconducting germanium telluride and insulating barium titanate, were engineered at Lawrence Berkeley National Laboratory. They were brought to Brookhaven Lab for the electron holography experiments. Additional experiments using x-ray diffraction were conducted at Argonne National Laboratory’s Advanced Photon Source.

The University of California at Berkeley, the University of New Orleans and Central Michigan University also collaborated with the work. The research was funded by Department of Energy’s Office of Science. The research will be published in Nature Materials.

Researchers devise molecular spintronic devices
A molecular switch can be used to store information in a single molecule. Adding spin functionality to molecular switches is a key technology to enable a next-generation memory device.
The research was conducted by Karlsruhe Institute of Technology, Institut de Physique et Chimie des Matériaux de Strasbourg, Chiba University and Synchrotron SOLEIL.

To enable these devices, researchers devised spin-crossover complexes. This consists of a transition metal ion that can be switched between a low-spin (LS) and a high-spin (HS) state by external stimuli. The two configurations may lead to different conductances.

As part of the process, researchers made use of individual Fe-phen molecules at low temperature with high lateral and energy resolution. The Fe-phen molecules, which were adsorbed onto a copper surface, exhibited the coexistence of HS and LS states.

But the strong coupling of the materials to the substrate prevents a spin state from being written electrically. Introducing an interfacial copper nitride layer allows switching between the HS and the LS state. The combined changes in conductance and spin state demonstrate how to confer memristive to spintronic properties, realizing multifunctional spintronic capacity in single molecules.

The paper has been published in Nature Communications.

—Mark LaPedus