The ability to regulate the emission angle of thermal source is crucial for improving the efficiency of many energy conversion systems. Here, we design a structure of Ge/Al<sub>2</sub>O<sub>3</sub>/Au which can realize the spatial regulation of thermal emission. It has been shown that nearly perfect absorption could be attained and the range of emission angle could be tuned without structural patterning. By utilizing Berreman mode and intrinsic loss of Al<sub>2</sub>O<sub>3</sub>, we could attain the expansion of the range of emission angle.
Three-dimensional helical nanostructures have attracted a great deal of attention by the virtue of anomalous properties in mechanics, electricity, electromagnetism and optics due to their intriguing shapes. This paper mainly introduces the fabrication of novel gold nanosprings by using the rolled-up technique and studies their mechanical and piezoresistive properties. Cutting across 80 nm thick gold film deposited on silicon substrate with defective nanofiber probes, we fabricate nanosprings with variable size. Maximum elastic elongation and electromechanical resonance of one gold nanospring are measured. Furthermore, we survey its piezoresistive property. It can be inferred that low stiffness, large displacement and strong piezoresistive effect of gold nanospring make it an excellent candidate for potential application as micro electro-mechanical sensor.
By combining the advantages of high resolution in optical imaging and deep penetration depth in ultrasound imaging, photoacoustic(PA) imaging enables high resolution deep imaging in vivo. A nanoprobe with high conversion efficiency is usually used in order to increase the amplitude of the photoacoustic signal. Here, highly efficient PA conversion is demonstrated in metal-insulator-metal(MIM) nanostructures. A magnetic resonance can be formed to achieve nearly 100% absorption of incident light near the resonant wavelength. In this paper, the absorbance of the MIM structure in the visible and near-infrared wavelength is demonstrated at first. Then, multiphysics coupling approach is used to solve the electromagnetic, thermodynamic and transient acoustic pressure physics. The results show that the photoacoustic signal amplitude of the MIM structures is much higher than that of the same structures without the top metal strips. Due to its high PA conversion efficiency, the MIM nanostructures can generate strong PA signals with low laser incident power, resulting in better biocompatibility. In this way, it can be applied not only as a PA probe to biomedical PA imaging, photoacoustic tomography, but also to medical related fields such as photothermotherapy and precision drug delivery.
Knowledge of temperatures at the nanoscale is essential for studying and controlling the heat-induced local thermal responses. The temperature rise of a heated nanoparticle (NP) near the interface of two kinds of media with different thermal conductivities is numerically investigated. We find that the temperature rise becomes size independent if it is scaled by the temperature rise in the case where the particle-interface distance is zero and the distance is scaled by the equivalent radius of the NP. This universal scaling behavior can be understood with the principle of dimensional homogeneity. An empirical equation is retrieved to predict the actual particle temperature at a given position. Our results may benefit precise control of heat at the nanoscale with applications in plasmonic absorbers, immunotargeted photothermal cancer cell killing, etc.
We propose a tunable unidirectional long-range surface plasmon polaritons (LRSPP) launcher based on subwavelength metallic nanoslits in the visible range. The direction of the generated LRSPPs could be tuned simply by varying the incident angles. The extinction ratio reaches up to 28 dB with a wide angular width of 30º. The influences of the launcher geometry on its performance are investigated in this study as well. The broadband property of the launcher is also demonstrated.
Absorption properties of film-coupled log-periodic optical antennas in the near-infrared region are numerically investigated. The maximum absorption for TE and TM polarizations at normal incidence reach to 95% and 93%, respectively, and the optimal absorption of around 90% can be simultaneously obtained for both cases. It is shown that the main absorption peak is independent to light polarizations at normal incidence. Moreover, the log-periodic antenna-assisted absorption represents district polarization selectivity at high-order resonances. For oblique incidence, only the incident light of specific wavelengths within a narrow incidence angle can be almost entirely trapped inside the absorber, indicating special direction and wavelength selectivity of the absorber. All these features would lead to potential applications in photovoltaic technology, sensing, etc.