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New materials that exhibit strong second-order optical nonlinearities at a desired operational frequency are of paramount importance for nonlinear optics. Giant second-order susceptibilityχ⁽²⁾has been obtained in semiconductor quantum wells (QWs). Unfortunately, the limited confining potential in semiconductor QWs causes formidable challenges in scaling such a scheme to the visible/near-infrared (NIR) frequencies for more vital nonlinear-optic applications. Here, we introduce a metal/dielectric heterostructured platform, i.e., TiN/Al₂O₃epitaxial multilayers, to overcome that limitation. This platform has an extremely highχ⁽²⁾of approximately 1500 pm/V at NIR frequencies. By combining the aforementioned heterostructure with the large electric field enhancement afforded by a nanostructured metasurface, the power efficiency of second harmonic generation (SHG) achieved 10⁻⁴at an incident pulse intensity of 10 GW/cm², which is an improvement of several orders of magnitude compared to that of previous demonstrations from nonlinear surfaces at similar frequencies. The proposed quantum-engineered heterostructures enable efficient wave mixing at visible/NIR frequencies into ultracompact nonlinear optical devices.

 

The integration of layer-by-layer (LbL) and self-assembly methods has the potential to achieve precision assembly of nanocomposite materials. Knowledge of how nanoparticles move across and within stacked materials is critical for directing nanoparticle assembly. Here, we investigate nanoparticle self-assembly within two different LbL architectures: (1) a bilayer composed of two immiscible polymer thin-films, and (2) a bilayer composed of polymer and graphene that possesses a “hard-soft” interface. Polymer-grafted silver nanocubes (AgNCs) are employed as a model nanoparticle system for systematic experiments – characterizing both assembly rate and resulting morphologies – that examine how assembly is affected by the presence of an interface. We observe that polymer grafts can serve to anchor AgNCs at the bilayer interface and to decrease particle mobility, or can promote particle transfer between layers. We also find that polymer viscosity and polymer mixing parameters can be used as predictors of assembly rate and behavior. These results provide a pathway for designing more complex multilayered nanocomposites. 

Transvaginal ultrasound is widely used for ovarian cancer screening but has a high false‐positive rate. Photoacoustic imaging provides additional optical contrast to supplement ultrasound and might be able to improve the accuracy of screening. Two copper sulfide (CuS) nanoparticle types (nanodisks and triangular nanoprisms) are reported as photoacoustic contrast agents for imaging ovarian cancer. Both CuS nanoprisms and nanodisks are ≈6 nm thick and ≈26 nm wide and are coated with poly(ethylene glycol) to make them colloidally stable in phosphate‐buffered saline for at least two weeks. The CuS nanodisks and nanoprisms reveal strong localized surface plasmon resonances with peak maxima at 1145 and 1098 nm, respectively. Both nanoparticle types have strong and stable photoacoustic intensity with detection limits below 120 pm. The circular CuS nanodisk remains in the circulation of nude mice (n= 4) and xenograft 2008 ovarian tumors (n= 4) 17.9‐fold and 1.8‐fold more than the triangular nanoprisms, respectively. Finally, the photoacoustic intensity of the tumors from the mice (n= 3) treated with CuS nanodisks is threefold higher than the baseline. The tumors treated with nanodisks have a characteristic peak at 920 nm in their spectrum to potentially differentiate the tumor from adjacent tissues.