No abstract

Hexagonal boron nitride (hBN) has drawn great attention for its versatile applications in electronics and photonics, and precise estimation of its thickness is critical in many situations. We propose a rapid and broad range (10–500 nm) in situ thickness estimation method for transparent hBN and SiO2 layers on the Si substrate using Raman peak intensity ratios at two wavenumbers and optical microscopy image analysis. We theoretically and experimentally demonstrate our method for a wide range of hBN layer thicknesses, and the estimated results show excellent agreement with the measured results with a percentile estimation error of 2.5%.

Organic photodetectors (OPDs) show their advantages in flexibility, lightweight, and ultrathin form factors, large area compatibility, and low-cost manufacturability, but their absorption wavelengths are typically limited to the visible range. Although internal photoemission is a promising platform to achieve subbandgap photodetection in the near-infrared (NIR) or mid-IR wavelengths, very few studies have been reported for organic-based Schottky barrier photodetectors (SBPDs) operable in the NIR region. In this work, we experimentally demonstrate organic-based broadband NIR SBPDs. Our proposed SBPDs were designed by employing broadband single-channel coherent perfect absorption and therefore show high optical absorption as well as incident angle-and polarization-independent characteristics without any complex patterning processes. Our simple but effective SBPDs might open up new possibilities for OPDs in the extended operation wavelength ranges toward NIR in various sensing and imaging applications.

Passive multilayer coatings for windows have potential to improve energy consumption for indoor temperature regulation. The coatings should block the solar IR energy (800–2500 nm) while maintaining visible light transparency (400–700 nm) to prevent unwanted heating of the interior of a building or a vehicle. It should also efficiently radiate thermal energy to prevent excessive heating. Although solar energy management and radiative cooling techniques have been investigated individually, the combination of the two, a transparent radiative cooler, has emerged only recently. This study theoretically and experimentally demonstrates a transparent radiative cooling window using a combination of planar hyperbolic metamaterials and a uniform layer of polydimethylsiloxane, resulting in high visible transparency (>60%), IR reflectivity (>89%), and thermal emissivity (>95%). Daytime temperature experiments confirm that the cooling window efficiently lowers the interior temperature by as much as 7 °C.

Achieving perfect light absorption at a subwavelength-scale thickness has various advantageous in terms of cost, flexibility, weight, and performance for many different applications. However, obtaining perfect absorbers covering a wide range of wavelengths regardless of incident angle and input polarization without a complicated patterning process while maintaining a small thickness remains a challenge. In this paper, we demonstrate flat, lithography-free, ultrahigh omnidirectional, polarization-independent, broadband absorbers through effective dispersion engineering. The proposed absorbers show day-integrated solar energy absorption up to 96%, which is 32% better than with lossy semiconductor/metal absorbers. The proposed simple yet effective method can be applied to light absorption thin film structures based on various types of highly lossy semiconductor materials, including emerging 2D materials.