Study On The Piezoelectric Response Of Organic-Inorganic Hybrid Ferroelectric Thin Films

The flexible wearable devices based on mechanical energy have aroused people's interest.Traditional inorganic ferroelectrics are not suitable for flexible wearable devices due to their brittleness while the organic ferroelectrics exhibit low power conversion efficiency due to their poor piezoelectric coefficients.The new organic-inorganic hybrid ferroelectrics have aroused people's interest due to their high piezoelectric coefficients and desired flexibility.The new organic-inorganic hybrid ferroelectrics in this paper is hexane-1,6-diammonium pentaiodobismuth([NH3(CH2)6NH3]Bil5,HDA-BiI5).In this paper,the structural properties and semiconductor physical properties of HDA-BiI5 has been investigated.The effect of preparation process on the morphology of HDA-BiI5 films has been investigated.The effect of test conditions of piezoresponse force microscopy(PFM)on the piezoresponse of HDA-BiI5 films has been investigated.The effect of substrate on the piezoresponse of HDA-BiI5 films has been investigated.The details are discussed as follows.The chapter 3 has investigated the structural properties and semiconductor physical properties of HDA-BiI5 and the effect of preparation process on the morphology of HDA-Bil5 films.X-ray diffraction(XRD),thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC)have been used to obtain the structural properties of HDA-BiI5.Scanning electron microscopy(SEM)has been used to investigate the effect of preparing process on the morphology of HDA-BiI5 films.Ultraviolet photoelectron spectroscopy(UPS)and UV-visible absorption spectra(UV-vis)have been used to determine the energy band structure of HDA-BiI5.The results show that the thermal decomposition temperature and Curie temperature of HDA-BiI5 is about 150? and 105?,respectively.The preparing process would affect the crystal size of HDA-BiI5.The work function,valance band edge,band gap and conduction band edge of HDA-BiI5 is-4.94 eV,-6.59 eV,2.00 eV and-4.59 eV,respectively.The chapter 4 has investigated the effect of test conditions of PFM on the piezoresponse of HDA-BiI5 films.The effect of alternating current(AC)driving voltage frequency,direct current(DC)bias voltage and alternating current driving voltage on piezoresponse of HDA-BiI5 films has been investigated.The results show that the frequency of 300 kHz favors vertical PFM piezoresponse while 835 kHz favors horizontal PFM piezoresponse.In addition,the higher DC voltage and AC voltage lead to higher PFM piezoresponse of HD A-Bil5 films.The chapter 5 has investigated the effect of substrate on the piezoresponse of HDA-BiI5 films.The piezoresponse of HDA-BiI5 films deposited on indium tin oxide(ITO),ITO/HT-NiOx and ITO/SnO2 substrates have been compared.In addition,the effect of number of HT-NiOx and SnO2 substrates on the piezoresponse of HDA-BiI5 films has been investigated.The results show that the piezoresponse of HDA-BiI5 films deposited on ITO/HT-NiOx and ITO/SnO2 substrates were both lower than that of films deposited on ITO substrates under the same PFM test conditions.Moreover,the higher number of HT-NiOx and SnO2 substrates leads to weaker piezoresponse of HDA-BiI5 films.