| Zinc oxide(ZnO)has the advantages of high exciton binding energy and thermal stability,which is widely used in the strain sensing and gas sensing field.Developing a nove ZnO-based composite thin film sensors,exploring the electron transport mechanism in the thin film structure,and expanding its practical applications in the sensing field has become a research focus.In this paper,several ZnO-based composite thin films with different structures are prepared.The electrical properties are tested under external environmental conditions including pressure and bending.The effect of different pressures and bending amounts on the I-V curves of the composite thin films are analyzed.The charge transfer principles and interfacial carrier transport processes inside the thin film structures are discussed.Meanwhile,the energy band structure and electronic properties of the ZnO-based composite structure after gas adsorption are studied in combination with theoretical simulations and experiments,the details of this paper are as follows:(1)ZnO/CuO and ZnO/rGO/CuO composite structures are designed and prepared by depositing ZnO and CuO films on the front and back side of dust-free cloth using magnetron method,respectively.The microstructure morphologies and electrical properties are characterized.Experimental results reveal that both composite structures exhibit significant p-n junction rectification characteristics under pressure and bending.Compared with the ZnO/CuO structure,the current response of ZnO/rGO/CuO composite structure is significantly enhanced and the I-V curves are symmetrically distributed,which is due to the reduction of GO to rGO during the sputtering process,resulting in more conductive fiber channels constructed by rGO on the dust-free fabric substrate.The I-V curves gradually change linearly with the increase of external pressure,indicating that the structure changes from Schottky contact to ohmic contact.(2)ZnO-based multilayer composite thin film structures with noble metal modification are fabricated by further introducing noble metals Ag and Au into the ZnO/rGO/CuO composite structure,and the I-V characteristics of various structures are studied comparatively.The results show that the noble metal modification can effectively enhance the current response value of the composite structure and the value is further increased with the increase of pressure and bending amount.Compared with the single-sided modification,the noble metal double-sided modified structures(ZnO/Ag/rGO/Ag/CuO and ZnO/Au/rGO/Au/CuO)have the best response performance.The current response of the ZnO/Au/rGO/Au/CuO structure reaches 1525.08 at10 mm bending amount.We suggest that the noble metal nanoparticles can change the internal electric field between ZnO and CuO and effectively regulate the height of the interfacial potential barrier and the position of the depletion region to enhance the interfacial carrier mobility.(3)The electronic properties of ZnO-based composite structures after gas adsorption are studied by density functional theory(DFT).By constructing single-and double-layer ZnO/Ga N heterojunction models and comparing the energy band structure,density of states,charge transfer and other properties after gas adsorption,it is found that the heterojunction has excellent selectivity for different gas molecules.The introduced vacancy defects not only change the conductivity type of the system but also have a large effect on the surface charge distribution.The ZnO/rGO/ZnO composite films are experimentally prepared by magnetron sputtering technique,and the I-V characteristics of different gases after adsorption are tested.It is found that the response to toluene is the highest,but the response to methanol is the lowest.Combined with the theoretical simulation results,we analyze that the change of I-V characteristic curves of ZnO/rGO/ZnO composite films after gas adsorption is mainly due to the transfer of electrons from the heterojunction surface to the gas molecules as electron acceptors,which in turn affects the carrier concentration. |
