Shear stiffness and friction mechanics of single-layer graphene measured for the first time

Engineerblogger
Feb 15, 2012

Graphene is an atomic-scale honeycomb lattice made of carbon atoms
Image by Alexander Alus

Graphene is a material that has many potential groundbreaking uses in the electronics and composites industry. Researchers from the University of Bristol have measured and identified for the first time the stress and strain shear modulus and internal friction of graphene sheets.

The research, in collaboration with the US Office of Naval Research, is published in Nano Letters.

Graphene is made up of a single layer of carbon atoms arranged in a hexagonal lattice. It is a promising material for the production of next-generation displays or solar cells because it is flexible, transparent and conductive.

For graphene to be used as nanoelectromechanical resonators or nanosensors, it is essential to know its structural behaviour and limitations as a mechanical material.

Fabrizio Scarpa, Professor of Smart Materials and Structures in the University of Bristol’s Advanced Composites Centre for Innovation and Science (ACCIS), said: “To improve the design of graphene nanosensors it is important to understand the mechanical behaviour and the natural intrinsic damping and internal friction of graphene. Our findings indicate that graphene produced using chemical vapor deposition could be a vital alternative for nanomechanical sensor applications.”

The researchers, using a technique called chemical vapour deposition (CVD), grew graphene films on copper foil in a quartz tube furnace at 1030 oC using a mixture of methane and hydrogen.

The research established some of the elastic properties of CVD-grown, single-layer graphene films on copper. The results revealed a striking difference between single- and multilayered graphene films in both shear modulus and internal friction. This difference may be due to the transition of the shear restoring force from chemical bonding within a layer to interlayer interactions.

The average shear modulus of the films studied compared well with most of the theoretical calculations based on single-layer pristine graphene structures. The high shear modulus and low internal friction point to a low defect density structure approaching that of the pristine graphene.

The findings suggest the use of CVD material in nanomechanical sensor applications could be a vital alternative.

Source: University of Bristol

Additional Information:

• "Shear Modulus of Monolayer Graphene Prepared by Chemical Vapor Deposition," Xiao Liu, Thomas H Metcalf, Jeremy T Robinson, Brian H Houston, and Fabrizio Scarpa, Nano Letters, published online ahead of print 03 January 2012.

Printable Solar-Cell Material Reaches a Milestone

Technology Review
Nov 7, 2011

A new way of manufacturing printable organic solar cells could eventually lead to new kinds of low-cost, cheap, and flexible solar panels.

The work is being led by Alan Heeger, who shared the Nobel Prize in Chemistry with Guillermo Bazan in 2000 for developing the kind of conductive polymers that are already used to make plastic solar cells and organic light-emitting diodes. Both Heeger and Bazan are professors of chemistry at the University of California, Santa Barbara.

Polymer solar cells are inefficient compared to silicon solar cells, but they are much cheaper to make. Organic materials—whether made of polymers or so-called "small molecules," which are organic compounds with a low molecular weight—can be made into inks and printed over large areas. They're also lightweight and flexible, which makes them promising for applications like rooftop installations or solar-cell patches for charging portable electronics.

Using a new small molecule designed by Bazan, Heeger built a solar cell that converts 6.7 percent of the light energy that strikes it into electricity. Bazan expects to reach 9 percent efficiency within a year. Although efficiencies in lab tests tend to be much greater than those in a manufactured cell, this would put these materials on par with the best polymer solar cells on the market. 
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Major Automakers Race To Silicon Valley

Fast Company
June 22, 2011

Silicon Valley: home to Google, Intel, countless tech startups, and... Renault-Nissan? The automotive group announced this week that it is opening a research office directly across from Google's campus by the end of June--and it will focus on the company's most cutting-edge initiatives, including in-vehicle Internet connectivity, user-interface displays, and smart-grid research.

Nissan is one of a number of major automakers to tap Silicon Valley's technological prowess by setting up shop right where the action is. BMW has a technology office in Palo Alto, Mercedes-Benz has a Group and Advanced Engineering office in the area, and Volkswagen has an Electronics Research Laboratory in Belmont, CA.

What will Nissan work on at its new research center? The company says that it will work on devices like the "Carwings" telematics system--a seven-inch touchscreen featuring maps of EV charging stations and real-time energy consumption reports. The system is already found in all Nissan LEAFs. European carmaker Renault will also work on the research and advanced engineering aspects of its electric vehicles, which include the upcoming battery switch station-compatible Fluence ZE and the two-seater Twizy ZE (pictured).

It makes sense for these companies to focus on research in Silicon Valley; it's where the talent is, and the engineering starting wages in Detroit are low compared to California. And there are undeniable attractions to living in the Bay Area versus Detroit, meaning it's easier to lure prospective hotshot employees.

Land is still much cheaper in Detroit, however, so don't expect major automakers to pack up their factories and head for the Bay. But with the proliferation of hybrid, electric, and other advanced vehicle technologies, it only makes sense for car companies to focus on Silicon Valley. Renault-Nissan almost certainly won't be the last.