A molecular ferroelectric thin film of imidazolium perchlorate on silicon.

Molecular ferroelectrics have garnered significant attention due to their structural tunability, low synthesis temperature, and high flexibility. Herein, we successfully synthesized imidazole perchlorate (ImClO4) single crystals and high-quality, highly-oriented thin films on Si substrates. These films demonstrated a high inverse piezoelectric coefficient of 55.7 pm/V. Two types of domain bands were observed: type-I bands tilted ~60° relative to the horizontal axis, and type-II bands positioned perpendicular to the horizontal axis. Under a + 20 V bias, type-I bands showed a reduction and detachment of 180° domain walls to form a needle-like domain. It extended toward the band boundary after applying -20 V bias, which grew along the boundary upon contact. In contrast, type-II bands showed straight domain wall motion and displayed a higher piezoresponse than type-I bands. The growth of  high quality molecular ferroelectric thin films on Si substrates paves the way for the development of on-chip devices.

Enhanced Ultrasound Transmission through Skull Using Flexible Matching Layer with Gradual Acoustic Impedance.

Transcranial ultrasound imaging and therapy have gained significant attention due to their noninvasive nature, absence of ionizing radiation, and portability. However, the presence of the skull, which has a high acoustic impedance, presents a challenge for the penetration of ultrasound into intracranial tissue. This leads to a low transmission of ultrasound through the skull, hindering energy focusing and imaging quality. To address this challenge, we propose a novel approach that utilizes a flexible matching layer with gradual acoustic impedance to enhance ultrasound transmission through the skull. This matching layer is constructed using Poly(dimethylsiloxane) (PDMS)/tungsten powders as the structural component responsible for the gradual impedance, while agarose serves as the flexible matrix. Our simulation and experimental results demonstrate that the matching layer with an exponential gradual acoustic impedance significantly improves the ultrasound transmission coefficient across a wide frequency range compared to traditional quarter wavelength matching layers. Specifically, at 2 MHz, the maximum transmission coefficient reaches 49.5%, more than four times higher than that of the skull without a matching layer (only 11.7%). Additionally, the good flexibility of our matching layer ensures excellent adhesion to the curved surface of the skull, further enhancing its application potential in transcranial ultrasound imaging and therapy. The improved transmission performance allows for a lower ultrasound transmission power, effectively addressing overheating and safety issues.