Raman Anisotropy And Piezoelectric Properties Of SnO₂ Microwires And Two-Dimensional WS₂

The piezoelectric effect is the process of converting mechanical energy into electrical signals.The principle is that when strain is applied to the piezoelectric device,the two Schottky barriers formed by the piezoelectric material and the electrode will be modulated by polarized charges of opposite polarity.Thereby adjusting the current size.Piezoelectric applications are very extensive,such as strain sensors,energy converters,human-machine communication,wearable devices,etc.With the development of wearable device technology,traditional piezoelectric materials cannot meet their needs for lighter and thinner.Therefore,researchers have conducted piezoelectric research on two-dimensional materials characterized by lightness and thinness.In the research,it was found that MoSe₂,In₂Se₃,WSe₂,etc.,which have excellent photoelectric effects,all have piezoelectric signals.Unfortunately,the signals are weak and difficult to use on the application layer.In this article,we artificially enhance the signal of WS₂,which has a weak piezoelectric signal.The enhanced signal is 8 times of the original state.This not only taps the potential of the two-dimensional piezoelectric material,but also allows its signal to reach the level of the application layer.On the other hand,the study of piezoelectric effect is also a current research hotspot.When the piezoelectric effect,the photoelectric effect and the semiconductor are coupled,the strength of the piezoelectric effect of the device can be adjusted through the laser,which is equivalent to adding a controllable grid,which is the piezoelectric effect.In this article,we not only discovered that SnO₂ microwires have a strong piezoelectric effect,but more importantly,we found that its photoelectric effect is also excellent.The specific research content of this article is as follows:（1）One-dimensional microwires with a low-symmetric crystal structure exhibit excellent Raman anisotropy and piezoelectric effects,and can realize a variety of novel device functions,such as polarization-sensitive photoelectric detection,strain sensing,and energy conversion.Here,we report for the first time that one-dimensional tin dioxide（SnO₂）microwires have polarized Raman spectroscopy,highly anisotropic angle-resolved photocurrent,and remarkable piezoelectric properties.The study found that its piezoelectric factor can be as high as 4100,which means that strain has a strong"gating"effect on current modulation.Under periodic stretching and release,the SnO₂ micron wire outputs a large oscillating piezoelectric current of 750 p A.In addition,when the piezoelectric effect is used to control the photoelectric effect,the response speed of ultraviolet light is also significantly increased by an order of magnitude,reaching 2 ms.The high anisotropy and outstanding piezoelectricity in this work have opened up new applications of SnO₂ micron wires in unique angular resolution,stretchable electronics and optoelectronics.（2）Because two-dimensional piezoelectric materials have mechanical flexibility and an atomic layer thickness,they are suitable for emerging applications,such as wearable electronic devices,human-machine interfaces,and strain sensors.The main disadvantages of two-dimensional piezoelectric materials are their low degree of in-plane polarization and weak piezoelectric effect.In our research,we found the piezoelectric effect in the single layer WS₂for the first time.In addition,when in-plane uniaxial deformation is applied along the direction of the armchair of WS₂,the symmetry of the crystal structure is reduced,and stronger in-plane polarization can be induced.Raman anisotropy can be generated through angle-resolved polarization Raman spectroscopy.In the piezoelectric test,the engineered WS₂ showed an order of magnitude higher dynamic piezoelectric signal.This research demonstrates a new strategy for artificially designing single-layer WS₂,which achieves greater anisotropy,higher polarization,and stronger piezoelectric effect by applying in-plane deformation.It opens up a new path for the application of piezoelectric and angle-resolving related electronics based on two-dimensional materials.