In recent years ferroelectric polymers have attracted much attention due to their potentials in flexible electronics. To satisfy the requirements of low operation voltage and low power consumption, it is required to reduce the ferroelectric film thickness down to, for example, 100 nm. However, decreased film thickness results in low crystallinity and thus worse electrical performance. One possible solution is to realize the epitaxial growth of ferroelectric thin films via effective control of structure and orientation of ferroelectric crystals. Here we report our work on poly­(tetrafluoro­ethylene)-template-induced ordered growth of ferroelectric thin films. We focus on the study of thermal stability of ferroelectric phase in these ferroelectric films. Our work indicates that epitaxial growth effectively increases the crystallinity and the melting and ferroelectric phase transition temperatures and implies the extended application of ferroelectric devices at higher temperature.

Generating intense ultrashort pulses with high-quality spatial modes is crucial for ultrafast and strong-field science and can be achieved by nonlinear supercontinuum generation (SCG) and pulse compression. In this work, we propose that the generation of quasi-stationary solitons in periodic layered Kerr media can greatly enhance the nonlinear light-matter interaction and fundamentally improve the performance of SCG and pulse compression in condensed media. With both experimental and theoretical studies, we successfully identify these solitary modes and reveal their unified condition for stability. Space-time coupling is shown to strongly influence the stability of solitons, leading to variations in the spectral, spatial and temporal profiles of femtosecond pulses. Taking advantage of the unique characteristics of these solitary modes, we first demonstrate single-stage SCG and the compression of femtosecond pulses from 170 to 22 fs with an efficiency >85%. The high spatiotemporal quality of the compressed pulses is further confirmed by high-harmonic generation. We also provide evidence of efficient mode self-cleaning, which suggests rich spatiotemporal self-organization of the laser beams in a nonlinear resonator. This work offers a route towards highly efficient, simple, stable and highly flexible SCG and pulse compression solutions for state-of-the-art ytterbium laser technology.

Ferroelectric polymers are a kind of promising materials for low-cost flexible memories. However, the relatively high thermal annealing temperature restricts the selection of some flexible polymer substrates. Here we report an alternative method to obtain ferroelectric poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) thin films under low process temperatures. Spin-coated P(VDF-TrFE) thin films were solvent vapor processed at 30 °C for varied times. Structural analyses indicated that solvent vapor annealing induced crystallization to form a ferroelectric β phase, and electrical measurements from both macroscopic ferroelectric switching and microscopic vertical piezoresponse force microscopy further proved the films enduring solvent vapor annealing for suitable short times possessed good ferroelectric and piezoelectric properties. To illuminate the application of solvent vapor annealing on ferroelectric devices, we further fabricated ferroelectric capacitor memory devices with a structure of Al/P(VDF-TrFE)/Al2O3/p-Si/Al where the ferroelectric layer was solvent vapor annealed. Ferroelectric capacitors showed obvious bistable operation and comparable ON/OFF ratio and retention performance. Our work makes it possible to structure ferroelectric devices on flexible substrates that require low process temperatures.

Organic semiconducting/ferroelectric blend films attracted much attention due to their electrical bistability and rectification properties and thereof the potential in resistive memory devices. During film deposition from the blend solution, spinodal decomposition induced phase separation, resulting in discrete semiconducting phase whose electrical property could be modulated by the continuous ferroelectric phase. However, blend films processed by common spin coating method showed extremely rough surfaces, even comparable to the film thickness, which caused large electrical leakage and thus compromised the resistive switching performance. To improve film roughness and thus increase the productivity of these resistive devices, we developed temperature controlled spin coating technique to carefully adjust the phase separation process. Here we reported our experimental results from the blend films of ferroelectric poly(vinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) and semiconducting poly(3-hexylthiophene) (P3HT). We conducted a series of experiments at various deposition temperatures ranging from 20 to 90 °C. The resulting films were characterized by AFM, SEM, and VPFM to determine their structure and roughness. Film roughness first decreased and then increased with the increase of deposition temperature. Electrical performance was also characterized and obviously improved insulating property was obtained from the films deposited between 50 and 70 °C. By temperature control during film deposition, it is convenient to efficiently fabricate ferroelectric/semiconducting blend films with good electrical bistability.