Borui Chen

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.

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.

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.

Ultra-broadband enhancement of nonlinear optical processes from randomly patterned super absorbing metasurfaces

Broadband light trapping and field localization is highly desired in enhanced light-matter interaction, especially in harmonic generations. However, due to the limited resonant bandwidth, most periodic plasmonic nanostructures cannot cover both fundamental excitation wavelength and harmonic generation wavelength simultaneously. Therefore, most previously reported plasmonic nonlinear optical processes are low in conversion efficiency. Here, we report a strong enhancement of second harmonic generation based on a three-layered super absorbing metasurface structure consisting of a dielectric spacer layer sandwiched by an array of random metallic nanoantennas and a metal ground plate. Intriguingly, the strong light trapping band (e.g. >80%) was realized throughout the entire visible to near-infrared spectral regime (i.e., from 435 nm to 1100 nm), enabling plasmonically enhanced surface harmonic generation and frequency mixing across a broad range of excitation wavelengths, which cannot be achieved with narrow band periodic plasmonic structures. By introducing hybrid random antenna arrays with small metallic nanoparticles and ultra-thin nonlinear optical films (e.g. TiO2) into the nanogaps, the nonlinear optical process can be further enhanced. This broadband light-trapping metastructure shows its potential as a building block for emerging nonlinear optical meta-atoms.

Using resistive readout to probe ultrafast dynamics of a plasmonic sensor

Surface plasmons in a DC current lead to an increase in scattering processes, resulting in a measurable increase in electrical resistance of a plasmonic nano-grating. This enables a purely electronic readout of plasmonically mediated optical absorption. We show that there is a time-dependence in these resistance changes on the order of 100ps that we attribute to electron-phonon and phonon-phonon scattering processes in the metal of the nano-gratings. Since plasmonic responses are strongly structurally dependent, an appropriately designed plasmoelectronic detector could potentially offer an extremely fast response at communication wavelengths in a fully CMOS compatible system.

Novel plasmonic polarimeter for biomedical imaging applications

Using polarized light in medical imaging is a valuable tool for diagnostic purposes since light traveling through scattering tissues such as skin, blood, or cartilage may be subject to changes in polarization. We present a new detection scheme and sensor that allows for directly measuring the polarization of light electronically using a plasmonic sensor. The sensor we fabricated consists of a plasmonic nano-grating that is embedded in a Wheatstone circuit. Using resistive losses induced by optically excited plasmons has shown promise as a CMOScompatible plasmonic light detector. Since the plasmonic response is sensitive to polarization with respect to the grating orientation, measuring the resistance change under incident light supplies a direct electronic measure of the polarization of light without polarization optics. Increased electron scattering introduced by plasmons in an applied current results in a measurable decrease in electrical conductance of a grating, allowing a purely electronic readout of a plasmonic excitation. Accordingly, because of its plasmonic nature, such a detector is dependent on both the wavelength and polarization of incident light with a response time limited by the surface plasmon lifetime.

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).

Plasmoelectronic sensor for real-time on-chip wavelength selective biosensing

Using resistive losses induced by optically excited surface plasmons has shown promise as a CMOS-compatible plasmonic light detector. Increased electron scattering introduced by surface plasmons in an applied current results in a measurable decrease in electrical conductance of a grating, allowing a purely electronic readout of surface plasmon excitation. Accordingly, because of its plasmonic nature, such a detector is dependent on both the wavelength and polarization of incident light with a response time limited by the surface plasmon lifetime. Our ultrafast measurements with electronic read-out indicate that the response time of this detector is on the order of 1ps. Thus such a detector would enable time-resolved biomedical applications such as real-time monitoring of protein structural dynamics for pharmacological applications and research.

Using plasmon-induced resistance changes in a tunable metal grating for all-electronic readout

In this work, we take advantage of the resistive losses induced by plasmons excited at optical frequencies to design, fabricate and characterize a metal grating based CMOS-compatible light detector. A change of resistance is caused by increased electron scattering introduced by localized and delocalized surface plasmons in an applied current. We realize a spectral and polarization dependent detector that can be read out electronically. The optical response of the sensor can be tuned from the visible to IR regime by changing the geometry of the metal grating, which enables a variety of applications for an on-chip ultra-wideband plasmonic detector.

Flat metallic surface with sub-10-nm gaps using modified atomic-layer lithography

We developed a novel atomic layer lithography procedure to fabricate large area flat metallic surfaces with sub-10-nm features, which is particularly useful for fabrication of nanostructures with strongly localized field enhancement.