Zhejun Liu

Nanocavity Enhancement for Ultra‐Thin Film Optical Absorber

A fundamental strategy is developed to enhance the light-matter interaction of ultra-thin films based on a strong interference effect in planar nanocavities, and overcome the limitation between the optical absorption and film thickness of energy harvesting/conversion materials. This principle is quite general and is applied to explore the spectrally tunable absorption enhancement of various ultra-thin absorptive materials including 2D atomic monolayers.

Extremely Cost-Effective and Efficient Solar Vapor Generation under Nonconcentrated Illumination Using Thermally Isolated Black Paper

Passive solar vapor generation represents a promising and environmentally benign method of water purification/desalination. However, conventional solar steam generation techniques usually rely on costly and cumbersome optical concentration systems and have relatively low efficiency due to bulk heating of the entire liquid volume. Here, an efficient strategy using extremely low‐cost materials, i.e., carbon black (powder), hydrophilic porous paper, and expanded polystyrene foam is reported. Due to the excellent thermal insulation between the surface liquid and the bulk volume of the water and the suppressed radiative and convective losses from the absorber surface to the adjacent heated vapor, a record thermal efficiency of ≈88% is obtained under 1 sun without concentration, corresponding to the evaporation rate of 1.28 kg (m2 h)−1. When scaled up to a 100 cm2 array in a portable solar water still system and placed in an outdoor environment, the freshwater generation rate is 2.4 times of that of a leading commercial product. By simultaneously addressing both the need for high‐efficiency operation as well as production cost limitations, this system can provide an approach for individuals to purify water for personal needs, which is particularly suitable for undeveloped regions with limited/no access to electricity.

Magneto-optical Kerr effect in perpendicularly magnetized Co/Pt films on two-dimensional colloidal crystals

Magneto-optical Kerr effect and optical reflectance are measured in the visible region for perpendicularly magnetized Co/Pt films on self-assembly array of two-dimensional closely packed polystyrene spheres. Peaks and valleys are observed in the magneto-optical Kerr and the optical reflectance spectra and their positions scale with the sphere diameter. In explanation of the above scenario, not only the Mie optical scattering of single nanocaps but also the surface plasmon resonance should be considered. This work will facilitate development of magnetoplasmonic nanosensors.

Refractive index engineering of metal-dielectric nanocomposite thin films for optical super absorber

Using metal-dielectric nanocomposite materials, we developed thin-film resonant and nonresonant absorbers with tunable absorption band. A compact double-side vertically graded metal-dielectric nanocomposite absorber was fabricated by gradually varying metal-dielectric nanocomposite ratios. The optical impedance of this metal-dielectric nanocomposite structure can be engineered to realize the antireflection characteristics. A broad-band and angle-insensitive super absorption over 81% was obtained in visible to near-infrared spectral region (i.e., 400 nm to 1100 nm), which is broader than recently reported plasmonic metamaterial absorbers in the similar spectral region.

Reversibly tunable coupled and decoupled super absorbing structures

We differentiate the spacer-dependent peak shift in coupled and decoupled super absorbing structures based on magnetic resonance and interference mechanism, respectively, which is experimentally validated by low-cost and large-area structures fabricated using lithography-free processes. The reversible real-time spectral tunability is then demonstrated by incorporating a thermally tunable polymeric spacer layer.

Cold Vapor Generation beyond the Input Solar Energy Limit

Abstract 100% efficiency is the ultimate goal for all energy harvesting and conversion applications. However, no energy conversion process is reported to reach this ideal limit before. Here, an example with near perfect energy conversion efficiency in the process of solar vapor generation below room temperature is reported. Remarkably, when the operational temperature of the system is below that of the surroundings (i.e., under low density solar illumination), the total vapor generation rate is higher than the upper limit that can be produced by the input solar energy because of extra energy taken from the warmer environment. Experimental results are provided to validate this intriguing strategy under 1 sun illumination. The best measured rate is ≈2.20 kg m−2 h−1 under 1 sun illumination, well beyond its corresponding upper limit of 1.68 kg m−2 h−1 and is even faster than the one reported by other systems under 2 sun illumination.

Surface dispersion engineering of Ag–Au alloy films

By controlling the content ratio of Ag and Au during the metal co-sputtering process, we demonstrate that the surface dispersion properties of alloy metal films can be manipulated with no need to tune the geometric parameters for surface patterns. This inexpensive technology provides a different way to engineer the surface dispersion properties of plasmonic metamaterial components on a chip.

Extremely cost-effective and efficient solar vapor generation using thermally isolated black paper

We report an efficient strategy using extremely low-cost materials. Due to the excellent thermal insulation, a record thermal efficiency of ∼88% was obtained under one sun without concentration, corresponding to the evaporation rate of 1.28 kg/(m2·h).