Wide-band underwater acoustic absorption based on locally resonant unit and interpenetrating network structure

The interpenetrating network structure provides an interesting avenue to novel materials. Locally resonant phononic crystal （LRPC） exhibits excellent sound attenuation performance based on the periodical arrangement of sound wave scatters. Combining the LRPC concept and interpenetrating network glassy structure, this paper has developed a new material which can achieve a wide band underwater strong acoustic absorption. Underwater absorption coefficients of different samples were measured by the pulse tube. Measurement results show that the new material possesses excellent underwater acoustic effects in a wide frequency range.Moreover, in order to investigate impacts of locally resonant units,some defects are introduced into the sample. The experimental result and the theoretical calculation both show that locally resonant units being connected to a network structure play an important role in achieving a wide band strong acoustic absorption.

Using BODIPY Unit to Design Molecular Acceptors with Absorption Wavelength of >1000 nm for Organic Photodetectors

Near-infrared(NIR)organic photodetectors(OPDs)are promising in flexible electronic and imaging sensor applications.However,high-performance NIR-II OPDs with photoresponse wavelength beyond 1000 nm are rare due to the lack of narrow bandgap molecular acceptors.In this work,an A-D-A′-D-Atype molecular acceptor with an onset absorption wavelength of 1150 nm was developed.Its narrow bandgap was benefited by the balanced resonance of the boron-nitrogen covalent bond(B–N)and boron-nitrogen coordination bond(B←N)in thienyl-fused 4-difluoro-4-bora-3a,4a-diaza-s-indacene(BODIPY)unit,as well as the strong intramolecular charge transfer(ICT)effect.The molecule showed a strong NIR absorption with an absorption peak at 1019 nm and an optical bandgap as low as 1.07 eV.Using the molecule as an electron acceptor in OPD device fabrication,a wide photoresponse wavelength range of 300 to∼1150 nm was achieved.At bias of−0.1 V,the device showed a low dark current density of 4.59×10^(−8) A cm^(−2) and high responsivity of 0.29 A W^(−1) at 970 nm,achieving a high peak specific detectivity of 2.39×1012 Jones and remaining a high specific detectivity of 1.59×10^(12) Jones at 1064 nm.These results demonstrate a feasible design of ultra-narrow bandgap molecular acceptors based on BODIPY unit induction of highly sensitive NIR-II OPDs.