Xie Zeng

Broadband absorption engineering of hyperbolic metafilm patterns

We experimentally realize a patterned hyperbolic metafilm with engineered and freely tunable absorption band from near-IR to mid-IR spectral regions based on multilayered metal/dielectric hyperbolic metamaterial waveguide taper.

Rainbow Trapping in Hyperbolic Metamaterial Waveguide

We propose a hyperbolic metamaterial waveguide to realize a highly efficient rainbow trapping effect, which can be used to develop practical on-chip optical super absorbers with a tunable absorption band.

Dielectric-Grating-Coupled Surface Plasmon Resonance From the Back Side of the Metal Film for Ultrasensitive Sensing

We propose a dielectric grating that can launch surface plasmon resonance (SPR) modes efficiently on the other side of flat metal films, which is similar to the conventional prism coupling mechanism. Importantly, this structure can excite SPR under the normal incident light, which is particularly suitable for the integration with optical fiber tips. By launching the SPR mode near the wavelength of 1.55 μm with a very narrow resonance line width (~4 nm), this structure is promising for the development of high-performance portable, flexible, and real-time refractometric sensing applications.

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.

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.

Wide-Angle and Polarization-Insensitive Perfect Absorber for Organic Photovoltaic Layers

In this letter, we computationally explore a wide-angle and polarization-insensitive perfect absorber based on hybrid metal-dielectric-metal structures. By introducing an organic photovoltaic layer between top metallic nanopatterns and a continuous metal bottom plate, an enhanced angle-and polarization-insensitive absorption can be obtained in the spectral range 400-700 nm, which is promising to realize improved thin-film organic photovoltaic devices. The physical mechanism of the perfect absorber is explained theoretically and numerically by the critical coupling principle.

Nanocavity absorption enhancement for two-dimensional material monolayer systems.

Here we propose a strategy to enhance the light-matter interaction of two-dimensional (2D) material monolayers based on strong interference effect in planar nanocavities, and overcome the limitation between optical absorption and the atomically-thin thickness of 2D materials. By exploring the role of spacer layers with different thicknesses and refractive indices, we demonstrate that a nanocavity with an air spacer layer placed between a graphene monolayer and an aluminum reflector layer will enhance the exclusive absorption in the graphene monolayer effectively, which is particularly useful for the development of atomically-thin energy harvesting/conversion devices.

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.

Flat metallic surface gratings with sub-10 nm gaps controlled by atomic-layer deposition

Atomic layer lithography is a recently reported new technology to fabricate deep-subwavelength features down to 1-2 nm, based on combinations of electron beam lithography (EBL) and atomic layer deposition (ALD). However, the patterning area is relatively small as limited by EBL, and the fabrication yield is not very high due to technical challenges. Here we report an improved procedure to fabricate flat metallic surfaces with sub-10 nm features based on ALD processes. To demonstrate the scalability of the new manufacturing method, we combine the ALD process with large area optical interference patterning, which is particularly promising for the development of practical applications for nanoelectronics and nanophotonics with extremely strong confinement of electromagnetic fields.