Polarity Of External Electric Field Research Articles

Boosting the performance of single-atom catalysts via external electric field polarization

Single-atom catalysts represent a unique catalytic system with high atomic utilization and tunable reaction pathway. Despite current successes in their optimization and tailoring through structural and synthetic innovations, there is a lack of dynamic modulation approach for the single-atom catalysis. Inspired by the electrostatic interaction within specific natural enzymes, here we show the performance of model single-atom catalysts anchored on two-dimensional atomic crystals can be systematically and efficiently tuned by oriented external electric fields. Superior electrocatalytic performance have been achieved in single-atom catalysts under electrostatic modulations. Theoretical investigations suggest a universal “onsite electrostatic polarization” mechanism, in which electrostatic fields significantly polarize charge distributions at the single-atom sites and alter the kinetics of the rate determining steps, leading to boosted reaction performances. Such field-induced on-site polarization offers a unique strategy for simulating the catalytic processes in natural enzyme systems with quantitative, precise and dynamic external electric fields.

Polarization effect of external electric field on Raman activity and gas sensing of nano zinc oxide

Control and administration of various dangerous gases existing in the environment is very important both for safety in the workplace and for quality of daily life, such as acetone and ethanol, etc. Zinc oxide, a well-known n-type semiconductor with a direct wide band-gap of 3.37 eV, is a very promising gas sensing material. However, zinc oxide's limited selectivity, relatively long response/recovery time, high-power consumption, and lack of long-term stability have restricted its applications in high-standard gas detection. Therefore, increasing gas sensing selectivity is a crucial issue for ZnO application in the gas sensing field. So far, many researches have reported and discussed the effects of morphologies, structures, doping of gas sensing materials, on its sensing performance. In this work, we intend to investigate and theoretically analyze how the polarization of the external electric field affects gas sensing performance and selectivity. Zinc oxide nanoparticles, as a testing gas sensing material, are synthesized by simple precipitation method. Then they are pressed into a disc and polarized under an external electric field with different electric field intensities at different temperatures. The structure and Raman activity for each of the unpolarized ZnO and the polarized ZnO are characterized using X-ray diffraction and Raman spectrometry, respectively. The gas sensing performances of unpolarized and polarized ZnO based sensors to ethanol and acetone are carefully examined using a chemical gas sensing system. The mechanism of external electric field polarization effect on gas sensitivity is discussed. The results reveal that there exists a threshold value for each of voltage and temperature for ZnO polarization under an external electric field. When the voltage and temperature are over 9375 V·cm-1 and 150℃, respectively, the leakage of electricity in ZnO disk happens and the polarization effect gradually disappears. Within the above voltage and temperature limits, Raman peak intensity of the polarized ZnO at 437 cm-1 obviously decreases after external electric field polarization. The response of the polarized ZnO sensor to acetone increases with external electronic field and polarization temperature increasing, while the response to ethanol decreases, which indicates that external electric field polarization can effectively adjust the gas sensing selectivity of nano zinc oxide. Raman analysis indirectly shows that the enhanced gas sensing selectivity of ZnO by the polarization effect of the external electric field is due to oxygen vacancy and zinc vacancy directionally moving under the action of an external electric field. Thus it can be seen that the polarization of the external electric field acting on gas sensing material is a promising effective method to improve gas sensing selectivity.

Anomalous polarization in an electric field and self-polarization in GaAs/AlAs quantum wells and quantum well wires

The response of an electron to an electric field in the infinite quantum wells and the infinite quantum well wires is investigated. Also the self-polarization effect, which can be defined as the influence of the well potential on the impurity electron, is studied for the same structures. The anomalous polarization in the excited states is found to be always exist in the presence of an electric field. Also it is shown that the external electric field polarization is intensified or weakened by an impurity ion depending on its position in the structure.