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.

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.

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

Tags: carbon nanotubes, directed self assembly, DSA, graphene, International Space Station, Karlsruhe Institute Of Technology, microemulsions, nanowires, New York University, Paul Scherrer Institut, Rice University, self-healing, silicon on insulator, SOI, Syracuse University, University of Chicago

This entry was posted on Tuesday, October 9th, 2012 at 12:01 am and is filed under News Stories. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.