An analytical model was developed for the size dependence of surface energy of a nanocavity from the perspective of thermodynamics and continuum medium mechanics. Three components of the liquidlike matrix, vaporlike cavity, and inner surface skin of the cavity were considered for the cavity-matrix structure, and contribution from chemical and structural effects to the surface energy was discussed. It was found that the surface energy increases with the inverse of cavity size and that the cavity shrinks in size, differing from what is usually expected. It was suggested that the surface skin be stronger than the matrix because of the bond order deficiency effect.

Quantum key distribution (QKD) has undergone significant development in recent decades, particularly with respect to free-space (air) and optical fiber channels. Here, we report the first proof-ofprinciple experiment for the BB84 protocol QKD over a water channel. Firstly, we demonstrate again the polarization preservation properties of the water channel in optical transmission according to the measured Mueller matrix, which is close to the unit matrix. The reason for the polarization preservation, revealed by Monte Carlo simulation, is that almost all the received photons are unscattered.Then, we performed the first polarization encoding BB84 protocol QKD over a 2.37m water channel. The results show that QKD can be performed with a low quantum bit error rate (QBER), less than 3.5%, with different attenuation coefficients.

The binary fused silica gratings (BFSGs) with high diffraction efficiency are presented for large astronomical ground-based telescopes. Calculations demonstrate that the BFSGs could obtain high diffraction efficiency in a wider wavelength range and angle of incident (AOI) range compared with volume phase holographic gratings. Several gratings with a size of 60 m m × 60 m m have been fabricated by holographic lithography and reactive ion-beam etching technology. The measured peak diffraction efficiency reaches 94%, and results show that there are 130 nm wavelength bandwidth and 12° AOI bandwidth in which diffraction efficiency is higher than 70%. The stray light causes the diffraction efficiency to decrease by about 0.48%. All measurements have indicated good consistency with the simulation results.

Two-dimensional transition metal dichalcogenides (TMDs) have a promising future in the nanophotonics field due to their unique optoelectronic properties such as large exciton binding energies and carrier mobility. Among these properties, monolayer TMDs exhibit enhanced photoluminescence (PL) by utilizing micro-/nanostructure surface plasmon polariton (SPP) modes. In this work, we present a unique technique to achieve substantial PL enhancement by integrating MoS2 monolayers to gold quasi-periodic nanoterrace morphology with gradient periods on fused silica substrates. Gold quasi-periodic nanostructures were fabricated through cost-effective and fast ion bombardment with iron co-deposition followed by a gold coating technique, and monolayers were deposited by a polymer-assisted technique. Our results show clear evidence that the light emission is enhanced due to the SPP modes produced by the quasi-periodic nanoterrace morphology. Comprehensive spectroscopy studies were performed on monolayer flakes with different laser polarizations, morphology periods, and temperatures to offer detailed insights on the mechanism behind PL enhancement. Together with numerical simulations, our results provided a basis for understanding the PL enhancement effects and shed light on future directions of high-efficiency light-emitting devices such as diodes, lasers, and heterostructure solar cells based on TMD monolayers.