Prediction of Optical Properties in Particulate Media Using Double Optimization of Dependent Scattering and Particle Distribution.

The prediction of optical properties dominated by light scattering in particulate media composed of high-concentration and polydisperse particles is greatly important in various optical applications. However, the accuracy and efficiency of light propagation simulations are still limited by the huge computational burden and complex interactions between dense and polydisperse particles. Here, we proposed a new optimization strategy that can effectively and accurately predict optical properties based on Monte Carlo simulation with particle size and dependent scattering corrections. Both the scattering parameters of particles and the experimental reflectance spectrum are fully examined for verification. Furthermore, using the weighted solar reflectance of particulate media as a representative optical property, both numerical simulations and experiments confirm the superiority and universality of the proposed optimization approach in a variety of materials systems. Moreover, our work can guide the design of particulate media with specific optical features insightfully and will be applicable in many fields involving multiparticle scattering.

Characterizing Local Electronic States of Twin Boundaries in Copper.

Grain boundaries (GBs) and twin boundaries (TBs) in copper (Cu) are two major planar defects that influence electrical conductivity due to their complex electron transport characteristics, involving electron scattering and electron concentration. Understanding their local electronic states is crucial for the design of future conductor materials. In this study, we characterized electron behaviors at TBs and GBs within one Cu grain using atomic force microscopy. Our findings revealed that, compared with GBs, TBs exhibit better current transport capability (direct-current mode) and larger electromagnetic loss (high-frequency microwave mode). Both kelvin probe force microscopy and theoretical analysis suggested that TBs with smaller lattice disorder possess lower density of states at the Fermi level. The reduced density of states may result in decreased electron scattering and a lower electron concentration at TBs. The latter can be highlighted by the high-frequency skinning effect, manifested as larger electromagnetic loss and weaker high-frequency conductivity.

Radio-Frequency Conductivity Characteristics and Corresponding Mechanism of Graphene/Copper Multilayer Structures.

High-radio-frequency (RF) conductivity is required in advanced electronic materials to reduce the electromagnetic loss and power dissipation of electronic devices. Graphene/copper (Gr/Cu) multilayers possess higher conductivity than silver under direct current conditions. However, their RF conductivity and detailed mechanisms have rarely been evaluated at the micro scale. In this work, the RF conductivity of copper-copper (P-Cu), monolayer-graphene/copper (S-Gr/Cu), and multilayer-graphene/copper (M-Gr/Cu) multilayer structures were evaluated using scanning microwave impedance microscopy (SMIM) and dielectric resonator technique. The results indicated that the order of RF conductivity was M-Gr/Cu < P-Cu < S-Gr/Cu at 3 GHz, contrasting with P-Cu < M-Gr/Cu < S-Gr/Cu at DC condition. Meanwhile, the same trend of M-Gr/Cu < P-Cu < S-Gr/Cu was also observed using the dielectric resonator technique. Based on the conductivity-related Drude model and scattering theory, we believe that the microwave radiation can induce a thermal effect at S-Gr/Cu interfaces, leading to an increasing carrier concentration in S-Gr. In contrast, the intrinsic defects in M-Gr introduce additional carrier scattering, thereby reducing the RF conductivity in M-Gr/Cu. Our research offers a practical foundation for investigating conductive materials under RF conditions.

Diatomite-Based Recyclable and Green Coating for Efficient Radiative Cooling.

Radiative cooling is a promising strategy to address energy challenges arising from global warming. Nevertheless, integrating optimal cooling performance with commercial applications is a considerable challenge. Here, we demonstrate a scalable and straightforward approach for fabricating green radiative cooling coating consisting of methyl cellulose matrix-random diatomites with water as a solvent. Because of the efficient scattering of the porous morphology of diatomite and the inherent absorption properties of both diatomite and cellulose, the aqueous coating exhibits an excellent solar reflectance of 94% in the range of 0.25-2.5 µm and a thermal emissivity of 0.9 in the range of 8-14 µm. During exposure to direct sunlight at noon, the obtained coating achieved a maximum subambient temperature drop of 6.1 °C on sunny days and 2.5 °C on cloudy days. Furthermore, diatomite is a naturally sourced material that requires minimal pre-processing, and our coatings can be prepared free from harmful organic compounds. Combined with cost-effectiveness and environmental friendliness, it offers a viable path for the commercial application of radiative cooling.

Effect of Copper Surface Roughness on the High-Temperature Structural Stability of Single-Layer-Graphene.

Graphene (Gr) has shown great potential in the field of oxidation protection for metals. However, numerous studies have shown that Gr will suffer structural degradation on metal surface during high-temperature oxidation, which significantly limited the effectiveness of their oxidation protection. Therefore, understanding the degradation mechanism of Gr is of great interest to enhance their structural stability. Here, the effect of copper (Cu) surface roughness on the high-temperature structural stability of single-layer graphene (SLG) was examined using Cu covered with SLG as a model material. SLG/Cu with different roughness values was obtained via high-temperature annealing of the model material. After high-temperature oxidation at 500 °C, Raman spectra analysis showed that the defect density of the oxidized SLG increased from 41% to 81% when the surface roughness varied from 37 nm to 81 nm. Combined with density functional theory calculations, it was found that the lower formation energy of the C-O bond on rough Cu surfaces (0.19 eV) promoted the formation of defects in SLG. This study may provide guidance for improving the effectiveness of SLG for the oxidation protection of metallic materials.

Strain to shine: stretching-induced three-dimensional symmetries in nanoparticle-assembled photonic crystals.

Stretching elastic materials containing nanoparticle lattices is common in research and industrial settings, yet our knowledge of the deformation process remains limited. Understanding how such lattices reconfigure is critically important, as changes in microstructure lead to significant alterations in their performance. This understanding has been extremely difficult to achieve due to a lack of fundamental rules governing the rearrangements. Our study elucidates the physical processes and underlying mechanisms of three-dimensional lattice transformations in a polymeric photonic crystal from 0% to over 200% strain during uniaxial stretching. Corroborated by comprehensive experimental characterizations, we present analytical models that precisely predict both the three-dimensional lattice structures and the macroscale deformations throughout the stretching process. These models reveal how the nanoparticle lattice and matrix polymer jointly determine the resultant structures, which breaks the original structural symmetry and profoundly changes the dispersion of photonic bandgaps. Stretching induces shifting of the main pseudogap structure out from the 1st Brillouin zone and the merging of different symmetry points. Evolutions of multiple photonic bandgaps reveal potential optical singularities shifting with strain. This work sets a new benchmark for the reconfiguration of soft material structures and may lay the groundwork for the study of stretchable three-dimensional topological photonic crystals.