There is still plenty of room at the bottom to generate piezoelectricity. Rice University engineers and their colleagues are leading the way.
A new study describes the discovery of piezoelectricity — the phenomenon by which mechanical energy is converted into electrical energy — across the phase boundaries of two-dimensional materials.
The work appears, led by Rice materials scientists Pulickel Ajayan and Hanyu Zhu and their colleagues at Rice’s George R. Brown School of Engineering, the University of Southern California, the University of Houston, the Wright-Patterson Air Force Base Research Laboratory and Pennsylvania State University. advanced Materials,
This discovery can aid in the development of ever-smaller nanoelectromechanical systems, devices that can be used, for example, small actuators and implantable biosensors, and to power ultrasonic temperature or pressure sensors.
The researchers show that an atomically thin system of metal domains surrounding semiconducting islands creates a mechanical response in a material’s crystal lattice when subjected to an applied voltage.
Rice research scientist Anand Puthirath, co-lead author of the paper, said the presence of piezoelectricity in 2D materials often depends on the number of layers, but synthesizing materials with a precise number of layers has been a difficult challenge.
“Our question was how to create a piezoelectric structure at multiple thickness levels—monolayer, bilayer, trilayer, and even bulk—even from non-piezoelectric materials,” Puthirath said. “The plausible answer was to create one-dimensional, metal-semiconductor junctions in 2D heterostructures, thus introducing crystallographic as well as charge asymmetry at the junction.”
“The lateral junction between phases is very interesting, because it provides atomically sharp boundaries in atomically thin layers, something that our group did about a decade ago,” Ajayan said. “This allows one to engineer materials in 2D to create device architectures that may be unique in electronic applications.”
The junction is less than 10 nanometers thick and forms when tellurium gas is introduced while molybdenum metal forms a film on silicon dioxide in a chemical vapor deposition furnace. This process creates islands of semiconducting molybdenum telluride phases in a sea of metallic phases.
Applying voltage across the junction through the tip of a piezoresponse force microscope generates a mechanical response. It also carefully measures the strength of the piezoelectricity created at the junction.
“The difference between lattice structures and electrical conductivity creates asymmetry at the phase boundary that is essentially independent of thickness,” Puthirath said. This simplifies the preparation of 2D crystals for applications such as miniaturized actuators.
“A heterostructured interface allows more freedom for engineering material properties than a bulk single compound,” Zhu said. “Although asymmetry exists only at the nanoscale, it can significantly affect macroscopic electrical or optical phenomena, which often dominate the interface.”
Research scientist Jiang Zhang and Rice graduate student Rui Xu and University of Southern California postdoctoral researcher Arvind Krishnamurthy are co-lead authors of the paper. Co-authors are graduate student Jiawei Lai, research professor Robert Vajtai and Rice lecturer Venkataraman Swaminathan; Priya Vashisht, professor of chemical engineering and materials science, biomedical engineering, computer science and physics and astronomy at the University of Southern California; Farnaz Safi Samghabadi and Dmitry Litvinov, a graduate student at the University of Houston, John and Rebecca Moores Professor; David Moore and Nicholas Glavin, Air Force Research Laboratory, Wright-Patterson Air Force Base; and Rice alumni Tianyi Zhang and Fu Zhang, graduate students David Sanchez and Mauricio Terrones, Verne M. of Physics at the University of Pennsylvania. Willman Professor.
Zhu is an assistant professor of materials science and nanoengineering. Ajayan is the Benjamin M and Mary Greenwood Anderson Professor of Engineering and Professor of Materials Science and Nanoengineering, Chemistry, and Chemical and Biomolecular Engineering. He is also the chair of Rice’s Department of Materials Science and Nano Engineering.
The Air Force Office of Scientific Research (FA9550-18-1-0072, FA9550-19RYCOR050) and the National Science Foundation (2005096) supported the research.
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material provided by Rice University, Original written by Mike Williams. Note: Content can be edited for style and length.
