Subscribe free to our newsletters via your
. Solar Energy News .




TECH SPACE
Edgy Look at 2D Molybdenum Disulfide
by Lynn Yarris for Berkeley News
Berkeley CA (SPX) May 14, 2014


A new SHG imaging technique allows rapid and all-optical determination of the crystal orientations of 2D semiconductor membranes at a large scale, providing the knowledge needed to use these materials in nanoelectronic devices.

The drive to develop ultrasmall and ultrafast electronic devices using a single atomic layer of semiconductors, such as transition metal dichalcogenides, has received a significant boost. Researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have recorded the first observations of a strong nonlinear optical resonance along the edges of a single layer of molybdenum disulfide.

The existence of these edge states is key to the use of molybdenum disulfide in nanoelectronics, as well as a catalyst for the hydrogen evolution reaction in fuel cells, desulfurization and other chemical reactions.

"We observed strong nonlinear optical resonances at the edges of a two-dimensional crystal of molybdenum disulfide" says Xiang Zhang, a faculty scientist with Berkeley Lab's Materials Sciences Division who led this study. "These one-dimensional edge states are the result of electronic structure changes and may enable novel nanoelectronics and photonic devices.

These edges have also long been suspected to be the active sites for the electrocatalytic hydrogen evolution reaction in energy applications. We also discovered extraordinary second harmonic light generation properties that may be used for the in situ monitoring of electronic changes and chemical reactions that occur at the one-dimensional atomic edges."

Zhang, who also holds the Ernest S. Kuh Endowed Chair Professor at the University of California (UC) Berkeley and directs the National Science Foundation's Nano-scale Science and Engineering Center, is the corresponding author of a paper in Science describing this research. The paper is titled "Edge Nonlinear Optics on a MoS2 Atomic Monolayer." Co-authors are Xiaobo Yin, Ziliang Ye, Daniel Chenet, Yu Ye, Kevin O'Brien and James Hone.

Emerging two-dimensional semiconductors are prized in the electronics industry for their superior energy efficiency and capacity to carry much higher current densities than silicon. Only a single molecule thick, they are well-suited for integrated optoelectronic devices.

Until recently, graphene has been the unchallenged superstar of 2D materials, but today there is considerable attention focused on 2D semiconducting crystals that consist of a single layer of transition metal atoms, such as molybdenum, tungsten or niobium, sandwiched between two layers of chalcogen atoms, such as sulfur or selenium.

Featuring the same flat hexagonal "honeycombed" structure as graphene and many of the same electrical advantages, these transition metal dichalcogenides, unlike graphene, have direct energy bandgaps. This facilitates their application in transistors and other electronic devices, particularly light-emitting diodes.

Full realization of the vast potential of transition metal dichalcogenides will only come with a better understanding of the domain orientations of their crystal structures that give rise to their exceptional properties. Until now, however, experimental imaging of these three-atom-thick structures and their edges have been limited to scanning tunneling microscopy and transmission electron microscopy, technologies that are often difficult to use.

Nonlinear optics at the crystal edges and boundaries enabled Zhang and his collaborators to develop a new imaging technique based on second-harmonic generation (SHG) light emissions that can easily capture the crystal structures and grain orientations with an optical microscope.

"Our nonlinear optical imaging technique is a non-invasive, fast, easy metrologic approach to the study of 2D atomic materials," says Xiaobo Yin, the lead author of the Science paper and a former member of Zhang's research group who is now on the faculty at the University of Colorado, Boulder.

"We don't need to prepare the sample on any special substrate or vacuum environment, and the measurement won't perturb the sample during the imaging process. This advantage allows for in-situ measurements under many practical conditions. Furthermore, our imaging technique is an ultrafast measurement that can provide critical dynamic information, and its instrumentation is far less complicated and less expensive compared with scanning tunneling microscopy and transmission electron microscopy."

For the SHG imaging of molybdenum disulfide, Zhang and his collaborators illuminated sample membranes that are only three atoms thick with ultrafast pulses of infrared light. The nonlinear optical properties of the samples yielded a strong SHG response in the form of visible light that is both tunable and coherent. The resulting SHG-generated images enabled the researchers to detect "structural discontinuities" or edges along the 2D crystals only a few atoms wide where the translational symmetry of the crystal was broken.

"By analyzing the polarized components of the SHG signals, we were able to map the crystal orientation of the molybdenum disulfide atomic membrane," says Ziliang Ye, the co-lead author of the paper and current member of Zhang's research group. "This allowed us to capture a complete map of the crystal grain structures, color-coded according to crystal orientation. We now have a real-time, non-invasive tool that allows us explore the structural, optical, and electronic properties of 2D atomic layers of transition metal dichalcogenides over a large area."

This research was supported by the DOE Office of Science through the Energy Frontier Research Center program, and by the U.S. Air Force Office of Scientific Research Multidisciplinary University Research Initiative.

For more about the research of Xiang Zhang go here

.


Related Links
Berkeley Lab
Space Technology News - Applications and Research






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





TECH SPACE
New revolutionary sensor links pressure to color change
Riverside CA (SPX) May 06, 2014
Imagine an automobile crash test that uses test dummies painted all over with a substance that can change color according to the levels of stress that various parts of the dummies' bodies will endure. Such a "color map" could provide vital information to engineers designing safer automobiles. Or imagine baseball gloves that when worn show the batters if they are using the appropriate amoun ... read more


TECH SPACE
Plants' Oil-Desaturating Enzymes Pair Up to Channel Metabolites

SE Asia palm oil problems could hit consumers worldwide

Boeing, Embraer team for biofuel use

Fueling aviation with hardwoods

TECH SPACE
Exoskeleton to remote-control robot

Robots may need to include parental controls

DARPA-Funded DEKA Arm System Earns FDA Approval

Robot mimics cartwheel movement of desert spider

TECH SPACE
Offshore wind supported with U.S. federal funding

GDF Suez, others, selected to build offshore wind farms

U.S. moves closer to first-ever offshore wind farm

Irish 'green paper' outlines transition to a low-carbon economy

TECH SPACE
Two-stroke scooters are 'super-polluters': study

Toyota posts record annual profit of $17.9 bn

Life-changer or death sentence? Madrid's electric bikes

Google says driving forward on autonomous car

TECH SPACE
Energy device for flexible electronics packs a lot of power

Why Hasn't The US Gone After Gazprom?

Vietnam sea spat part of China's larger strategy: experts

Alaska governor signs natural gas bill pipeline measure

TECH SPACE
Obama sends Vietnam nuclear deal to Congress

Fewer US nuclear plants could curb climate change fight

Westinghouse Expands to Meet Latin America's Energy Needs

Exelon buys Pepco for $6.83 bn in energy deal

TECH SPACE
Caltech's Sustainability Institute Gets Funding to Solve Global Energy Problems

US House approves major Africa power bid

Changing Renewable Energy Target would damage investment and throw away jobs

Germany now EU's worst polluter as CO2 emissions rise

TECH SPACE
Emerald ash borers were in US long before first detection

China demand for luxury furniture 'decimating rosewood'

Super-charged tropical trees of Borneo vitally important for global carbon cycling

Arctic study sheds light on tree-ring divergence problem




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.