Amino acid crystals are an attractive piezoelectric material as they have an ultrahigh piezoelectric coefficient and have an appealing safety profile for medical implant applications. Unfortunately, solvent-cast films made from glycine crystals are brittle, quickly dissolve in body fluid, and lack crystal orientation control, reducing the overall piezoelectric effect. Here, we present a material processing strategy to create biodegradable, flexible, and piezoelectric nanofibers of glycine crystals embedded inside polycaprolactone (PCL). The glycine-PCL nanofiber film exhibits stable piezoelectric performance with a high ultrasound output of 334 kPa [under 0.15 voltage root-mean-square (Vrms)], which outperforms the state-of-the-art biodegradable transducers. We use this material to fabricate a biodegradable ultrasound transducer for facilitating the delivery of chemotherapeutic drug to the brain. The device remarkably enhances the animal survival time (twofold) in mice-bearing orthotopic glioblastoma models. The piezoelectric glycine-PCL presented here could offer an excellent platform not only for glioblastoma therapy but also for developing medical implantation fields.

Epitaxial $c$ -axis oriented $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_3$ (BFO) thin films were deposited on conductive $\mathrm{Sr}\mathrm{Ru}{\mathrm{O}}_3$ (SRO) on (001) $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ substrates by pulsed laser deposition. A Pt/BFO/SRO capacitor was constructed by depositing a top Pt electrode. The leakage current density versus. electric field characteristics were investigated from $80\text{to}350\mathrm{K}$ . It was found that the leakage mechanisms were a strong function of temperature and voltage polarity. At temperatures between 80 and $150\mathrm{K}$ , space-charge-limited current was the dominant leakage mechanism for both negative and positive biases. On the other hand, at temperatures between 200 and $350\mathrm{K}$ the dominant leakage mechanisms were Poole-Frenkle emission and Fowler-Nordheim tunneling for negative and positive biases, respectively.

Epitaxial $c$ -axis oriented $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_3$ (BFO) thin films were deposited on (001) Nb-doped $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ (Nb-STO) substrates by pulsed laser deposition. Introducing Bi vacancies caused the BFO thin film to evolve to a $p$ -type semiconductor and formed a $p\text{-}n$ heterojunction with an $n$ -type semiconductor Nb-STO. The current density versus voltage $\left(J\text{-}V\right)$ and capacitance versus voltage $\left(C\text{-}V\right)$ characteristics of the heterojunction were investigated. A typical rectifying $J\text{-}V$ effect was observed with a large rectifying ratio of $5\times {10}^4$ . Reverse $C\text{-}V$ characteristics exhibited a linear $1∕C^2$ versus $V$ plot, from which a built-in potential of $0.6\mathrm{V}$ was deduced. The results show a potential application of BFO/Nb-STO heterojunction for oxide electronics.

Highly (100) textured graded manganese (Mn) doped ${\mathrm{Ba}}_{\text{0.5}}{\mathrm{Sr}}_{\text{0.5}}{\mathrm{TiO}}_3$ [BST (50/50)] thin films were deposited on lanthanum aluminate substrates using sol-gel technique. We have demonstrated that the graded acceptor doping is a promising technique to reduce the temperature coefficient of capacitance (TCC), loss tangent, and leakage current of BST thin films. In the temperature range between 175 and 260 K the reported TCC of Mn graded BST (50/50) films is less than ${\text{5.55×10}}^{\text{−4}}/\mathrm{K},$ which is comparable to the best capacitors known so far. The lower temperature coefficient of the capacitance of the Mn graded films has been argued to be due to the induced compositional heterogeneity resulting into a distribution of the Curie temperature.

We have studied the effect of tensile strain on the superconductivity in FeSe films. 50, 100, and 200 nm FeSe films were grown on MgO, ${\text{SrTiO}}_3$ , and ${\text{LaAlO}}_3$ substrates by using a pulsed laser deposition technique. X-ray diffraction analysis showed that the tetragonal phase is dominant in all of our FeSe films. The 50 nm FeSe films on MgO and ${\text{SrTiO}}_3$ are under tensile strain, while the 50 nm FeSe film on ${\text{LaAlO}}_3$ and the other thick FeSe films are unstrained. Superconducting transitions have been observed in unstrained FeSe films with $T_{\text{onset}}\approx 8\text{K}$ , which is close to the bulk value. However, no sign of superconductivity has been observed in FeSe films under tensile strain down to 5 K. This is evidence to show that tensile strain suppresses superconductivity in FeSe films.