When doing 2D modeling, 2D Boundary objects are used to define alternative boundary conditions along a section of a 2D Zone boundary. Where the boundary line and polygon boundary coincide, the boundary condition defined at this object will take precedence over the 2D Zone boundary type. The 2D Boundary must be fully collinear with the boundary of a 2D Zone in order to pass validation.
Piezoelectricity in two-dimensional phase boundaries is being developed by engineers. They may be used to power future nanoelectronics such as sensors and actuators. There’s still plenty of room to generate piezoelectricity at the bottom. Rice University engineers and their colleagues are paving the way.
A new study describes the discovery of piezoelectricity – the phenomenon by which mechanical energy is converted into electrical energy – across phase boundaries of two-dimensional materials. Rice materials scientists Pulickel Ajayan and Hanyu Zhu, along with colleagues from 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, published their findings in Advanced Materials.
The lateral junction between phases is very interesting, since it provides atomically sharp boundaries in atomically thin layers, something our group pioneered almost a decade before. This allows one to engineer materials in 2D to create device architectures that could be unique in electronic applications.
Pulickel Ajayan
The discovery could aid in the development of ever-smaller nanoelectromechanical systems, which could be used to power tiny actuators and implantable biosensors, as well as ultrasensitive temperature and pressure sensors.
When a voltage is applied to an atomically thin system of a metallic domain surrounding semiconducting islands, the researchers demonstrate a mechanical response in the material’s crystal lattice.
The presence of piezoelectricity in 2D materials frequently depends on the number of layers, but synthesizing the materials with a precise number of layers has been a formidable challenge, according to Anand Puthirath, co-lead author of the paper at Rice.
“Our question was how to make a structure that is piezoelectric at multiple thickness levels — monolayer, bilayer, trilayer and even bulk from even non-piezoelectric material,” Puthirath said. “The plausible answer was to make a one-dimensional, metal-semiconductor junction in a 2D heterostructure, thus introducing crystallographic as well as charge asymmetry at the junction.”
“The lateral junction between phases is very interesting, since it provides atomically sharp boundaries in atomically thin layers, something our group pioneered almost a decade before,” Ajayan said. “This allows one to engineer materials in 2D to create device architectures that could 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 the sea of metallic phases.
Applying voltage to the junction via the tip of a piezoresponse force microscope generates a mechanical response. That also carefully measures the strength of piezoelectricity created at the junction.
“The difference in lattice structures and electrical conductivity produces asymmetry at the phase boundary that is essentially independent of thickness,” Puthirath explained. This makes it easier to prepare 2D crystals for applications such as miniaturized actuators.
“A heterostructure interface provides significantly more freedom for engineering material properties than a bulk single compound,” Zhu explained. “Although the asymmetry exists only at the nanoscale, it can have a significant impact on macroscopic electrical or optical phenomena, which are frequently dominated by the interface.”
