Yingxue Xi

Previous studies have shown that the external quantum efficiency (EQE) of conventional red Micro-Light emitting diodes(Micro-LEDs) decreases markedly with reducing chip size. This degradation is generally attributed to enhanced non-radiative recombination at sidewall defects, which leads to increased carrier loss in size-scaled LEDs. In this work, AlGaInP quaternary semiconductor epitaxial wafers incorporating multiple quantum wells (MQWs) with different well-layer strain states were grown by metal–organic chemical vapor deposition (MOCVD). Through wafer bonding, photolithography, etching, and metal evaporation, these epitaxial structures were fabricated into Micro-LED arrays with single-pixel pitches of 10, 20, 50, and 100 μm. The experimental results reveal that, with increasing indium (In) composition in the GaInP well layers—corresponding to a gradual increase in lattice mismatch (Δa/a) from 0% to 1%—smaller-sized Micro-LED arrays exhibit superior EQE performance. For devices with a pixel pitch of 10 μm, the EQE of Micro-LED arrays with a 1% lattice mismatch in the well layer is approximately three times higher than that of lattice-matched (0%) counterparts. In contrast, for devices with a pixel pitch of 100 μm, the EQE of lattice-matched (0%) Micro-LED arrays is about 1.3 times higher than that of devices with a 1% lattice mismatch. These results indicate that, to achieve maximum EQE in Micro-LEDs, the strain state of the MQW-layer material must be carefully considered as a priority factor. Optimal device performance requires appropriate matching between LED size and the well-layer growth strain.

This work systematically investigates photonic nanojet (PNJ) planar arrays formed by periodic arrangements of dielectric microstructures with four geometric configurations: cylinders, cones, truncated pyramids, and pyramids, focusing on the effects of geometry, array arrangement, and array sparsity on PNJ formation and coupling behavior. Full-wave finite-difference time-domain simulations were performed to analyze optical field distributions under different array conditions. The results indicate that under approximately infinite array conditions, different geometries exhibit markedly different coupling responses. Cylindrical and truncated pyramid structures are more susceptible to inter-element scattering, leading to pronounced multistage focusing, whereas pyramid and cone structures maintain higher spatial stability due to dominant localized tip-focusing mechanisms. For the central elements, the maximum PNJ intensity is about 16.4 a.u. for cylindrical structures and 33.5 a.u. for truncated pyramid structures, while significantly higher intensities of approximately 47.5 a.u. and 93 a.u. are achieved for pyramid and cone structures, respectively. In contrast, the FWHM remains nearly constant for all geometries under different array conditions, indicating that lateral focusing is primarily governed by geometry rather than array arrangement. By tuning the array spacing, the inter-element coupling strength can be continuously weakened, and different geometries require distinct sparsity levels to reach the weak-coupling limit. These results establish the dominant role of geometric configuration in PNJ planar arrays and provide guidance for their predictable design.

This paper innovatively proposes a high-precision fabrication strategy for silicon-based micro–nano-composite layered structures composed of micron-scale platforms and nanopillars, effectively addressing the challenges of alignment errors and material mismatch during manufacturing. By integrating electron beam lithography (EBL), inductively coupled plasma (ICP) etching, and ultraviolet nanoimprint lithography (NIL) into a unified multi-step workflow, the method achieves exceptional precision and efficiency in producing complex micro–nano-composite architectures. Comprehensive structural characterization is performed using scanning electron microscopy (SEM) and atomic force microscopy (AFM), with probe convolution effects carefully corrected to ensure accurate dimensional analysis. Experimental results confirm the outstanding stability and uniformity of the fabricated structures, exhibiting minimal deviations in both feature size and spatial layout. Nanopillars with diameters ranging from 50 to 200 nm are successfully integrated onto 1-µm square platforms, with the lateral deviation of 50 nm features maintained within 5% or less. Furthermore, the method effectively mitigates thermal stress-induced misalignment during the fabrication of multi-material layers, demonstrating strong potential for scalable production of advanced photonic devices and integrated nanophotonic systems. Overall, this work establishes a robust and versatile technical pathway for the precise manufacturing and quantitative characterization of micro–nano-composite structures, providing a key foundation for the next generation of photonic integration technologies.

This study employs reactive magnetron sputtering technology to fabricate TiN/Y-HfO₂/TiN multilayer thin film devices using titanium targets and yttrium-doped high-purity hafnium targets. A systematic investigation was conducted to explore the influence of hafnium-based thin film thickness on the structural and electrical properties of TiN/Y-HfO₂/TiN thin film devices. Radio frequency magnetron sputtering was utilized to deposit Y-HfO₂ films of varying thicknesses on TiN electrodes by controlling deposition time, with a yttrium doping concentration of 8.24 mol.%. The surface morphology and crystal structure of the thin films were characterized using atomic force microscopy (AFM), Raman spectroscopy, X-ray diffraction (XRD). Results indicate that as film thickness increases, surface roughness and Raman peak intensity increase correspondingly, with the tetragonal phase (t) characteristic peak being most prominent at 65 nm. DC magnetron sputtering was employed to deposit TiN top electrodes, resulting in TiN/Y-HfO₂/TiN thin film devices. Following rapid thermal annealing at 700 °C, electrical properties were evaluated using a ferroelectric tester. Leakage current density exhibited a decreasing trend with increasing film thickness, while the maximum polarization intensity gradually increased, reaching a maximum of 11.5 μC/cm² at 120 nm.

Oxygen defects in Hafnium Oxide (HfO₂)-based ferroelectric thin films not only are related to the cause of ferroelectricity but also affect the ferroelectric properties of the thin films. This paper, therefore, focuses on the fabrication of Zr:HfO₂ thin films by RF (Radio Frequency) magnetron sputtering with Zr-doped HfO₂ as the target and examines how oxygen flow impacts the oxygen vacancies and electrical properties thereof. Additionally, TiN thin-film electrodes were prepared by direct current (DC) magnetron reactive sputtering using nitrogen as the reaction gas, the influences of the substrate temperature on the film deposition rate and crystal phase structure were investigated, and the resultant thin-film electrodes with the lowest resistivity were obtained. Furthermore, the ferroelectric hysteresis loop and leakage current density of metal–insulator–metal (MIM) ferroelectric capacitors formed by annealing the 30 nm thick deposited Zr:HfO₂ sandwiched between the top and bottom TiN electrodes were measured. The results demonstrate that varying oxygen flow has a considerable effect on oxygen vacancies and the Zr doping concentration of deposited Zr:HfO₂ ferroelectric thin films. When the oxygen flow is set to 40 sccm (standard cubic centimeters per minute) and an external electric field strength of 2 mV/cm is applied, the remnant polarization reaches 18 μC/cm², with a decrease in the leakage current density of 10^5–6 orders of magnitude.

Silver nanopillars with strong plasmonic effects are used for localized electromagnetic field enhancement and regulation and have wide potential applications in sensing, bioimaging, and surface-enhanced spectroscopy. Normally, the controlled synthesis of silver nanopillars is mainly achieved using heterometallic nanoparticles, including Au nanobipyramids and Pd decahedra, as seeds for inducing nanostructure growth. However, the seed materials are usually doped in silver nanopillar products. Herein, the synthesis of pure silver nanopillars with hexagonal cross-sections is achieved by employing rebuildable silver nanoparticles as seeds. An environmentally friendly, stable, and reproducible synthetic route for obtaining silver nanopillars is proposed using sodium dodecyl sulfate as the surface stabilizer. Furthermore, the seed particles induce the formation of regular structures at different temperatures, and, specifically, room temperature is beneficial for the growth of nanopillars. The availability of silver nanoparticle seeds using sodium alginate as a carrier at different temperatures was verified. A reproducible method was developed to synthesize pure silver nanopillars from silver nanoparticles at room temperature, which can provide a strategy for designing plasmonic nanostructures for chemical and biological applications.

Double perovskite Cs₂SnI₆ and its doping products (with SnI₂, SnF₂ or organic lithium salts added) have been utilized as p-type hole transport materials for perovskite and dye-sensitized solar cells in many pieces of research, where the mechanism for producing p-type Cs₂SnI₆ is rarely reported. In this paper, the mechanism of forming p-type Li⁺ doped Cs₂SnI₆ was revealed by first-principles simulation. The simulation results show that Li⁺ entered the Cs₂SnI₆ lattice by interstitial doping to form strong interaction between Li⁺ and I⁻, resulting in the splitting of the α spin-orbital of I–p at the top of the valence band, with the intermediate energy levels created and the absorption edge redshifted. The experimental results confirmed that Li⁺ doping neither changed the crystal phase of Cs₂SnI₆, nor introduced impurities. The Hall effect test results of Li⁺ doped Cs₂SnI₆ thin film samples showed that Li⁺ doping transformed Cs₂SnI₆ into a p-type semiconductor, and substantially promoted its carrier mobility (356.6 cm²/Vs), making it an ideal hole transport material.

HfO₂ thin films were deposited on BK-7 glass substrates using an electron beam evaporation deposition (EBD) technique and then post-treated with argon and oxygen ions at an ion energy ranging from 800 to 1200 eV. The optical properties, laser damage resistance, and surface morphology of the thin films exposed to Ar ions and O₂ ions at various energies were studied. It was found that the two ion post-treatment methods after deposition were effective for improving the LIDT of HfO₂ thin films, but the mechanism for the improvement differs. The dense thin films highly resistant to laser damage can be obtained through Ar ion post-treatment at a certain ion energy. The laser-induced damage threshold (LIDT) of thin films after O₂ ion post-treatment was higher in comparison to those irradiated with Ar ion at the same ion energy.

In this paper, comprehensively utilizing the diffraction theory and electromagnetic resonance effect is creatively employed to design a multifunctional metasurface zone plate (MMZP) and achieve the control of polarization states, while maintaining a broadband achromatic converging property in a near-IR region. The MMZP consists of several rings with fixed width and varying heights; each ring has a number of nanofins (usually called meta-atoms). The numerical simulation method is used to analyze the intensity distribution and polarization state of the emergent light, and the results show that the designed MMZP can realize the polarization manipulation while keeping the broadband in focus. For a specific design wavelength (0.7 μm), the incident light can be converted from left circularly polarized light to right circularly polarized light after passing through the MMZP, and the focusing efficiency reaches above 35%, which is more than twice as much as reported in the literature. Moreover, the achromatic broadband focusing property of the MMZP is independent with the polarization state of the incident light. This approach broadens degrees of freedom in micro-nano optical design, and is expected to find applications in multifunctional focusing devices and polarization imaging.