Imperfections may improve graphene sensors

November 29, 2011

Although they found that graphene makes very good chemical sensors, researchers at the University of Illinois at Urbana-Champaign have discovered an unexpected "twist"--that the sensors are better when the graphene is "worse"--more imperfections improved performance.

"This is quite the opposite of what you would want for transistors, for example," explained Eric Pop, an assistant professor of electrical and computer engineering and a member of the interdisciplinary research team. "Finding that the less perfect they were, the better they worked, was counter intuitive at first."

The research group, which includes researchers from both chemical engineering and electrical engineering, and from a startup company, Dioxide Materials, reported their results in the November 23, 2011 issue of Advanced Materials.

"The objective of this work was to understand what limits the sensitivity of simple, two-terminal graphene chemiresistors, and to study this in the context of inexpensive devices easily manufactured by chemical vapor deposition (CVD)," stated lead authors Amin Salehi-Khojin and David Estrada.

The researchers found that the response of graphene chemiresistors depends on the types and geometry of their defects.

"Nearly-pristine graphene chemiresistors are less sensitive to analyte molecules because adsorbates bind to point defects, which have low resistance pathways around them," noted Salehi-Khojin, a research scientist at Dioxide Materials and post-doctoral research associate in the Department of Chemical and Biomolecular Engineering (ChemE) at Illinois. "As a result, adsorption at point defects only has a small effect on the overall resistance of the device. On the other hand, micrometer-sized line defects or continuous lines of point defects are different because no easy conduction paths exist around such defects, so the resistance change after adsorption is significant."

"This can lead to better and cheaper gas sensors for a variety of applications such as energy, homeland security and medical diagnostics" said Estrada who is a doctoral candidate in the Department of Electrical and Computer Engineering.

According to the authors, the two-dimensional nature of defective, CVD-grown graphene chemiresistors causes them to behave differently than carbon nanotube chemiresistors. This sensitivity is further improved by cutting the graphene into ribbons of width comparable to the line defect dimensions, or micrometers in this study.

"What we determined is that the gases we were sensing tend to bind to the defects," Pop said. "Surface defects in graphene are either point-, wrinkle-, or line-like. We found that the points do not matter very much and the lines are most likely where the sensing happens."

"The graphene ribbons with line defects appear to offer superior performance as graphene sensors," said ChemE professor emeritus and Dioxide Materials CEO Richard Masel. "Going forward, we think we may be able engineer the line defects to maximize the material's sensitivity. This novel approach should allow us to produce inexpensive and sensitive chemical sensors with the performance better than that of carbon nanotube sensors."
-end-
Additional authors of the paper, Polycrystalline Graphene Ribbons as Chemiresistors," include Kevin Y. Lin, Myung-Ho Bae, and Feng Xiong. This work was supported by Dioxide Materials, by ONR grants N00014-09-1-0180 and N00014-10-1-0061, and the NDSEG Graduate Fellowship (D.E.).

University of Illinois College of Engineering

Related Graphene Articles from Brightsurf:

How to stack graphene up to four layers
IBS research team reports a novel method to grow multi-layered, single-crystalline graphene with a selected stacking order in a wafer scale.

Graphene-Adsorbate van der Waals bonding memory inspires 'smart' graphene sensors
Electric field modulation of the graphene-adsorbate interaction induces unique van der Waals (vdW) bonding which were previously assumed to be randomized by thermal energy after the electric field is turned off.

Graphene: It is all about the toppings
The way graphene interacts with other materials depends on how these materials are brought into contact with the graphene.

Discovery of graphene switch
Researchers at Japan Advanced Institute of Science and Technology (JAIST) successfully developed the special in-situ transmission electron microscope technique to measure the current-voltage curve of graphene nanoribbon (GNR) with observing the edge structure and found that the electrical conductance of narrow GNRs with a zigzag edge structure abruptly increased above the critical bias voltage, indicating that which they are expected to be applied to switching devices, which are the smallest in the world.

New 'brick' for nanotechnology: Graphene Nanomesh
Researchers at Japan advanced institute of science and technology (JAIST) successfully fabricated suspended graphene nanomesh (GNM) by using the focused helium ion beam technology.

Flatter graphene, faster electrons
Scientists from the Swiss Nanoscience Institute and the Department of Physics at the University of Basel developed a technique to flatten corrugations in graphene layers.

Graphene Flagship publishes handbook of graphene manufacturing
The EU-funded research project Graphene Flagship has published a comprehensive guide explaining how to produce and process graphene and related materials (GRMs).

How to induce magnetism in graphene
Graphene, a two-dimensional structure made of carbon, is a material with excellent mechani-cal, electronic and optical properties.

Graphene: The more you bend it, the softer it gets
New research by engineers at the University of Illinois combines atomic-scale experimentation with computer modeling to determine how much energy it takes to bend multilayer graphene -- a question that has eluded scientists since graphene was first isolated.

How do you know it's perfect graphene?
Scientists at the US Department of Energy's Ames Laboratory have discovered an indicator that reliably demonstrates a sample's high quality, and it was one that was hiding in plain sight for decades.

Read More: Graphene News and Graphene Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.