Center for Functional Nanomaterials Seminar

Epitaxial Strontium Titanate (STO) thin film has been attracted a great interest for its application in microwave tunable devices like phase shifters or tunable filters. It has been shown that the high permittivity can be obtained by the control of mechanical misfit strain in thin films, by different ways like using different substrates, changing deposition condition, changing the film thickness and other methods like post-annealing and two-step method, which have been used to deposit the thin films in this talk. We studied the strain-controled epitaxial ferroelectric SrTiO3 thin film by transmission electron microscopy. The effect of planer defects on strain relaxation and thin film growth are discussed.
Transmission electron microscopy investigations have been performed on bismuth layer structure ferroelectrics (BLSFs). Ferroelectric domains (including 90o and 180o domains) and antiphase boundary are observed in dark field image. It is found that structure of domain is affected by different occupies at A site or B site instead of the number of perovskite octahedral between adjacent Bi2O2 layers. The special role of 90o domain wall with the interaction with charge defects in switching is discussed. In addition, the near edge fine structures of the electron loss spectroscopy (EELS) arises from different layers are investigated in bismuth layer structure ferroelectrics SrBi2Ta2O9. The EELS spectra are interpreted by comparing with the calculation using linearnized augment plane wave (LAPW) method within the local density approximation (LDA).