Home > Press > 2D oxide flakes pick up surprise electrical properties: Rice University lab detects piezoelectric effects in nanosheets due to defects
![]() |
Electrets — electrons trapped in defects in two-dimensional molybdenum dioxide — give the material piezoelectric properties, according to Rice University researchers. The defects (blue) appear in the material during formation in a furnace, and generate an electric field when under pressure. (Credit: Ajayan Research Group/Rice University) |
Abstract:
Rice University researchers have found evidence of piezoelectricity in lab-grown, two-dimensional flakes of molybdenum dioxide.
Their investigation showed the surprise electrical properties are due to electrons trapped in defects throughout the material, which is less than 10 nanometers thick. They characterize these charges as electrets, which appear in some insulating materials and generate internal and external electric fields.
Piezoelectricity is likewise a property of materials that respond to stress by generating an electric voltage across their surfaces or generate mechanical strain in response to an applied electric field. It has many practical and scientific uses, from the conversion of a wiggling guitar string into an electrical signal to scanning microscopes like those used to make the new finding.
The researchers at Rice’s Brown School of Engineering found their micron-scale flakes exhibit a piezoelectric response that is as strong as that observed in such conventional 2D piezoelectric materials as molybdenum disulfide.
The report by Rice materials scientist Pulickel Ajayan and collaborators appears in Advanced Materials.
The key appears to be defects that make molybdenum dioxide’s crystal lattice imperfect. When strained, the dipoles of electrons trapped in these defects seem to align, as with other piezoelectric materials, creating an electric field leading to the observed effect.
“Super thin, 2D crystals continue to show surprises, as in our study,” Ajayan said. “Defect engineering is a key to engineer properties of such materials but is often challenging and hard to control.”
“Molybdenum dioxide isn’t expected to show any piezoelectricity,” added Rice postdoctoral researcher Anand Puthirath, a co-corresponding author of the paper. “But because we’re making the material as thin as possible, confinement effects come into the picture.”
He said the effect appears in molybdenum dioxide flakes grown by chemical vapor deposition. Stopping the growth process at various points gave the researchers some control over the defects’ density, if not their distribution.
Lead author and Rice alumna Amey Apte added the researchers’ single-chemical, precursor-based vapor deposition technique “helps in the reproducibility and clean nature of growing molybdenum oxide on a variety of substrates.”
The researchers found the piezoelectric effect is stable at room temperature for significant timescales. The molybdenum dioxide flakes remained stable at temperatures up to 100 degrees Celsius (212 degrees Fahrenheit). But annealing them for three days at 250 C (482 F) eliminated the defects and halted the piezoelectric effect.
Puthirath said the material has many potential applications. “It can be used as an energy harvester, because if you strain this material, it will give you energy in the form of electricity,” he said. “If you give it voltage, you induce mechanical expansion or compression. And if you want to mobilize something at the nanoscale, you can simply apply voltage and this will expand and move that particle the way you want.”
Co-authors of the paper are Rice alumna Sandhya Susarla, now a postdoctoral scholar at Lawrence Berkeley National Laboratory; graduate students Kosar Mozaffari and Farnaz Safi Samghabadi, research assistant professor Long Chang and Dmitri Litvinov, a professor of electrical and computer engineering, at the University of Houston; Jordan Hachtel and Juan Carlos Idrobo of Oak Ridge National Laboratory; and David Moore and Nicholas Glavin of the Air Force Research Laboratory at Wright-Patterson Air Force Base, Ohio. Apte is now at the Intel Corp., Chandler, Arizona.
Ajayan and Pradeep Sharma, the M.D. Anderson Chair Professor and department chair of mechanical engineering at the University of Houston, are co-corresponding authors. Ajayan is chair of Rice’s Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry.
The Air Force Office of Scientific Research and the Department of Energy's Office of Science supported the research. Microscopy research was performed at Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences.
####
About Rice University
Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation’s top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,962 undergraduates and 3,027 graduate students, Rice’s undergraduate student-to-faculty ratio is just under 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for lots of race/class interaction and No. 4 for quality of life by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger’s Personal Finance.
Follow Rice News and Media Relations via Twitter @RiceUNews.
For more information, please click here
Contacts:
Jeff Falk
713-348-6775
Mike Williams
713-348-6728
Copyright © Rice University
If you have a comment, please Contact us.Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
Related Links |
Emerging applications of elemental 2D materials:
Rice Department of Materials Science and NanoEngineering:
George R. Brown School of Engineering:
Related News Press |
News and information
Controlling chemical catalysts with sculpted light January 15th, 2021
New way to control electrical charge in 2D materials: Put a flake on it January 15th, 2021
Laboratories
Controlling chemical catalysts with sculpted light January 15th, 2021
New class of cobalt-free cathodes could enhance energy density of next-gen lithium-ion batteries December 21st, 2020
2 Dimensional Materials
New way to control electrical charge in 2D materials: Put a flake on it January 15th, 2021
Govt.-Legislation/Regulation/Funding/Policy
Controlling chemical catalysts with sculpted light January 15th, 2021
Researchers realize efficient generation of high-dimensional quantum teleportation January 14th, 2021
Chemists invent shape-shifting nanomaterial with biomedical potential It converts from sheets to tubes and back in a controllable fashion January 13th, 2021
Possible Futures
Scientists' discovery is paving the way for novel ultrafast quantum computers January 15th, 2021
Physicists propose a new theory to explain one dimensional quantum liquids formation January 15th, 2021
Controlling chemical catalysts with sculpted light January 15th, 2021
Discoveries
Physicists propose a new theory to explain one dimensional quantum liquids formation January 15th, 2021
Announcements
Controlling chemical catalysts with sculpted light January 15th, 2021
Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers/Posters
Controlling chemical catalysts with sculpted light January 15th, 2021
Military
Stretching diamond for next-generation microelectronics January 5th, 2021
Spontaneous robot dances highlight a new kind of order in active matter January 1st, 2021
Battery Technology/Capacitors/Generators/Piezoelectrics/Thermoelectrics/Energy storage
Record-setting thermoelectric figure of merit achieved for metal oxides December 29th, 2020
New imaging method views soil carbon at near-atomic scales December 25th, 2020
New class of cobalt-free cathodes could enhance energy density of next-gen lithium-ion batteries December 21st, 2020
Stretchable micro-supercapacitors to self-power wearable devices December 11th, 2020
![]() |
||
![]() |
||
The latest news from around the world, FREE | ||
![]() |
![]() |
||
Premium Products | ||
![]() |
||
Only the news you want to read!
Learn More |
||
![]() |
||
Full-service, expert consulting
Learn More |
||
![]() |