Anisotropic Generation and Detection of Coherent Ag Phonons in Black Phosphorus

Black phosphorus (BP) has attracted great attention due to its layer-tuned direct bandgap, in-plane anisotropic properties, and novel optoelectronic applications. In this work, the anisotropic characteristics of BP crystal in terms of the Raman tensor and birefringence are studied by investigating polarization dependence in both the generation and detection of Ag mode coherent phonons. While the generated coherent phonons exhibit the typical linear dichroism of BP crystal, the detection process is found here to be influenced by anisotropic multiple thin film interference, showing wavelength and sample thickness sensitive behaviors. We additionally find that the Ag1 and Ag2 optical phonons decay into lower frequency acoustic phonons through the temperature-dependent anharmonic process.

Photonic paper: Multiscale assembly of reflective cellulose sheets in Lunaria annua

Bright, iridescent colors observed in nature are often caused by light interference within nanoscale periodic lattices, inspiring numerous strategies for coloration devoid of inorganic pigments. Here, we describe and characterize the septum of the Lunaria annua plant that generates large (multicentimeter), freestanding iridescent sheets, with distinctive silvery-white reflective appearance. This originates from the thin-film assembly of cellulose fibers in the cells of the septum that induce thin-film interference–like colors at the microscale, thus accounting for the structure’s overall silvery-white reflectance at the macroscale. These cells further assemble into two thin layers, resulting in a mechanically robust, iridescent septum, which is also significantly light due to its high air porosity (>70%) arising from the cells’ hollow-core structure. This combination of hierarchical structure comprising mechanical and optical function can inspire technological classes of devices and interfaces based on robust, light, and spectrally responsive natural substrates.

Катодолюминесценция пленок ZnO на ромбоэдрической плоскости сапфира с буферным слоем золота

Luminescent properties of ZnO films grown on R-plane sapphire coated with a buffer layer of gold nanoislands were studied. Luminescence spectra of the samples show a set of oscillations resulted from classical thin-film interference. Such a set of oscillations can be represented as a barcode with each bar position corresponding to the wavelength of each oscillation and bar width corresponding to the oscillation intensity. High repeatability and simplicity of production of such ZnO-based thin-film structures together with high sensitivity of interference phenomena to the ambient environment make them prospective for different chemo- and biosensing applications.