First-principles Study On The Piezoelectric Properties Of Nano Materials

The piezoelectric properties of the material is widely used. People had begun to studythe piezoelectric effect as early as the20th century. In the year of1894, Woldemar Voigtnoted that medium with piezoelectricity on the condition that its structure does not have asymmetrical centre. With the development of technology, as well as the rising of nanomaterials. People could have micro-analysis of the nano material’s piezoelectric propertiesthrough theoretical calculations. Various materials of two-dimensional nano-layers such asMoS₂nanoribbons and h-BN nanoribbons, have good properties of physics and chemical.They are studied extensively.In this article we study the piezoelectric properties of zigzag h-BN nanoribbons,zigzag MoS₂nanoribbons by first-principles calculations. Simultaneously, we also designa structure of graphene nanoribbons with hydrogen atoms’ selective adsorption, then studythe electrode properties. The main research results are shown as follows:The third chapter focuses on the piezoelectric properties of zigzag graphenenanoribbons with hydrogen selective modifications by first-principles calculations. Thestructures of hydrogen modified graphene nanoribbons have been relaxed and thecalculated hydrogen binding energies indicate that these structures are very stable. Owingto the hydrogen atoms’ selective adsorption, the adjacent carbon atoms have differentcharge states and breaking inversion symmetry of nonpiezoelectric graphene. So, thepositive charge center and the negative charge center of the hexatomic carbon ring in thesestructures separate with each other under uniaxial tensile strain, inducing themacroscopical electric polarization. Furthermore, the gradient of strain induced dipolemoment density is relative with the ribbon width, i.e., the wider the ribbon is, the betterpiezoelectric property it has. Besides, the dipole moment density of hydrogen selectivemodified graphene nanoribbons without strain could be controlled by changing edgemodification configuration of hydrogen atoms effectually. The fourth chapter has studied the piezoelectric properties of zigzag h-BNnanoribbons and zigzag MoS₂nanoribbons by first-principles calculations. We find thatthe positive charge center and the negative charge center of the hexatomic B-N ring inthese structures separate with each other under uniaxial tensile strain, inducing themacroscopical electric polarization. The wider the ribbon is, the better piezoelectricproperty it has. Furthermore, a certain width ribbons’ positive and negative values ofdipole moment density will occur flip after strain. Zigzag MoS₂nanoribbons’ chargetransfer caused by stretching occurs in more than one direction, the change of dipolemoment density along x direction relatively small.