Nanophotonic Materials Research Articles

Self-evolving photonic crystals for ultrafast photonics

Ultrafast dynamics in nanophotonic materials is attracting increasing attention from the perspective of exploring new physics in fundamental science and expanding functionalities in various photonic devices. In general, such dynamics is induced by external stimuli such as optical pumping or voltage application, which becomes more difficult as the optical power to be controlled becomes larger owing to the increase in the energy required for the external control. Here, we demonstrate a concept of the self-evolving photonic crystal, where the spatial profile of the photonic band is dynamically changed through carrier-photon interactions only by injecting continuous uniform current. Based on this concept, we experimentally demonstrate short-pulse generation with a high peak power of 80 W and a pulse width of <30 ps in a 1-mm-diameter GaAs-based photonic crystal. Our findings on self-evolving carrier-photon dynamics will greatly expand the potential of nanophotonic materials and will open up various scientific and industrial applications.

Multigram-Scale Production of Hybrid Au-Si Nanomaterial by Laser Ablation in Liquid (LAL) for Temperature-Feedback Optical Nanosensing, Light-to-Heat Conversion, and Anticounterfeit Labeling.

Recent progress in hybrid optical nanomaterials composed of dissimilar constituents permitted an improvement in the performance and functionality of novel devices developed for optoelectronics, catalysis, medical diagnostics, and sensing. However, the rational combination of contrasting materials such as noble metals and semiconductors within individual hybrid nanostructures via a ready-to-use and lithography-free fabrication approach is still a challenge. Here, we report on a two-step synthesis of hybrid Au-Si microspheres generated by laser ablation of silicon in isopropanol followed by laser irradiation of the produced Si nanoparticles in the presence of HAuCl4. Thermal reduction of [AuCl4]- species to a metallic gold phase, along with its subsequent mixing with silicon under laser irradiation, creates a nanostructured material with a unique composition and morphology, as revealed by electron microscopy, tomography, and elemental analysis. A combination of basic plasmonic and nanophotonic materials such as gold and silicon within a single microsphere allows for efficient light-to-heat conversion, as well as single-particle SERS sensing with temperature-feedback modality and expanded functionality. Moreover, the characteristic Raman signal and hot-electron-induced nonlinear photoluminescence coexisting within the novel Au-Si hybrids, as well as the commonly criticized randomness of the nanomaterials prepared by laser ablation in liquid, were proved to be useful for the realization of anticounterfeiting labels based on a physically unclonable function approach.

Hexagonal boron nitride nanophotonics: a record-breaking material for the ultraviolet and visible spectral ranges.

A global trend towards miniaturization and multiwavelength performance of nanophotonic devices drives research on novel phenomena, such as bound states in the continuum and Mietronics, as well as surveys for high-refractive index and strongly anisotropic materials and metasurfaces. Hexagonal boron nitride (hBN) is one of the promising materials for future nanophotonics owing to its inherent anisotropy and prospects of high-quality monocrystal growth with an atomically flat surface. Here, we present highly accurate optical constants of hBN in the broad wavelength range of 250-1700 nm combining imaging ellipsometry measurements, scanning near-field optical microscopy and first-principles quantum mechanical computations. hBN's high refractive index, up to 2.75 in the ultraviolet (UV) and visible range, broadband birefringence of ∼0.7, and negligible optical losses make it an outstanding material for UV and visible range photonics. Based on our measurement results, we propose and design novel optical elements: handedness-preserving mirrors and subwavelength waveguides with dimensions of 40 nm operating in the visible and UV ranges, respectively. Remarkably, our results offer a unique opportunity to bridge the size gap between photonics and electronics.

Nanophotonics triggered thermally enhanced solar water disinfection bottles for slum dwellers.

Among several existing technologies, solar pasteurization is widely accepted as a reliable and cost-effective method for the removal of microbial pathogens from water. This work reports nanophotonics-triggered thermally enhanced solar water disinfection bottles (nano-SODIS) designed rationally by coating plasmonic carbon nanoparticles (CNP) on the outer surface for the targeted pathogen inactivation from water. The cost-effective CNP nanophotonic material used in this work has high efficiency in harvesting solar radiation and dissipating the heat locally. It has broad absorption efficiency to cover the entire solar spectrum; hence, it is capable to generate multiple scattering. It has also properties of boosting of photon absorption and focusing the light within a constrained spatial region, resulting in powerful and targeted heating that inactivates microorganisms in near proximity. These CNPs were used to coat the nano-SODIS water bottles that achieved the highest temperature of 65-70°C within 90min of exposure to solar radiation with a consequent six-log reduction. The disinfection period was reduced by a factor of 3 compared to the conventional solar disinfection system. The treated water was further assessed for 7days, which confirmed the complete absence of bacteria and no sign of regeneration after storing for a longer period. The SODIS bottles coated with CNP thus overcome the problem of limited solar absorption by acquiring higher broadband absorption potential and thus achieving comparatively high disinfection efficiency. The broad band absorption of CNP was confirmed through UV-DRS absorption spectra. The nano-SODIS bottles designed and constructed in this work are simple, durable, and user friendly in nature and have been deployed in the rural and slums areas of Nagpur, Delhi, and Mumbai, India to provide pathogen-free potable water and to improve the health of local poor communities.

Fabrication of three-dimensional opal nanolattices using template-directed colloidal assembly

Three-dimensional (3D) nanostructures play a crucial role in nanophotonics, lasers, and optical systems. This article reports on the fabrication of 3D nanostructures consisting of opal structures that are spatially aligned to an array of holes defined in the photoresist. The proposed method uses colloidal lithography to pattern a hexagonal array of holes, which are then used to direct the subsequent 3D assembly of colloidal particles. This approach allows the 3D opal structures to be aligned with the 2D array of holes, which can enhance spatial-phase coherence and reduce defects. The polymer patterns can be used as a sacrificial template for atomic layer deposition and create free-standing nanolattices. The final structure consists of a combination of nanolattice, upon which controlled deposition of opal structures is achieved. These structures result in nanostructured materials with high porosity, which is essential to create low-index materials for nanophotonics. A thick layer of titanium oxide with high refractive index is deposited over nanolattices to demonstrate the mechanical stability of underlying structures. These nanolattice structures with precisely controlled height can serve as a low-index layer and can find applications in Bragg reflectors, nanophotonics, and optical multilayers.

A Reconfigurable Nanophotonic Heterostructure Engineered by a DNA Origami Switch.

DNA origami has been widely used to construct nanophotonic structures due to its unparallel capability in assembling photonic nanomaterials with nanometer precision. Nevertheless, the majority of fabricated fluorescence-based nanophotonic systems so far operate in the ultraviolet-visible (UV-Vis) region, which are accompanied by limitations of shallow penetration and potential light damage. Herein, we constructed a reconfigurable nanophotonic heterostructure by integrating an upconversion nanoparticle (UCNP) and a gold nanorod (AuNR) on a DNA origami switch (DOS) template. With the unique anti-Stokes luminescence of UCNP whose excitation wavelength is mostly located in the near-infrared (NIR) region, the obtained reconfigurable nanophotonic system can be excited by 980 laser light and generates visible light emission. In our nanophotonic system, the DNA origami template serves as a switch to reversibly tune the optical properties of UCNP. The construction of this nanophotonic heterostructure expands the toolbox of DNA origami-based nanophotonic systems that may hold great potential in optical biosensing and imaging.

Nanophotonic control of thermal emission under extreme temperatures in air.

Nanophotonic materials offer spectral and directional control over thermal emission, but in high-temperature oxidizing environments, their stability remains low. This limits their applications in technologies such as solid-state energy conversion and thermal barrier coatings. Here we show an epitaxial heterostructure of perovskite BaZr0.5Hf0.5O3 (BZHO) and rocksalt MgO that is stable up to 1,100 °C in air. The heterostructure exhibits coherent atomic registry and clearly separated refractive-index-mismatched layers after prolonged exposure to this extreme environment. The immiscibility of the two materials is corroborated by the high formation energy of substitutional defects from density functional theory calculations. The epitaxy of immiscible refractory oxides is, therefore, an effective method to avoid prevalent thermal instabilities in nanophotonic materials, such as grain-growth degradation, interlayer mixing and oxidation. As a functional example, a BZHO/MgO photonic crystal is implemented as a filter to suppress long-wavelength thermal emission from the leading bulk selective emitter and effectively raise its cutoff energy by 20%, which can produce a corresponding gain in the efficiency of mobile thermophotovoltaic systems. Beyond BZHO/MgO, computational screening shows that hundreds of potential cubic oxide pairs fit the design principles of immiscible refractory photonics. Extending the concept to other material systems could enable further breakthroughs in a wide range of photonic and energy conversion applications.

Efficient near UV-vacuum UV sources based on second-harmonic generation enhanced by high-Q quasi-BICs in all-dielectric metasurfaces of low-index materials

Ultraviolet (UV) nanophotonics is an increasingly important branch of modern photonics due to the fundamental importance and practical applications. This work presents the efficient generation of near UV-vacuum UV radiations based on the second-harmonic generation in all-dielectric metasurfaces exhibiting high-Q quasi-bound states in the continuum (quasi-BICs). For this purpose, lithium niobate (LN) is taken as the nonlinear material comprising the metasurface, which is transparent in the ultraviolet range. Since LN has much lower index compared with the dielectrics commonly used as nanophotonic materials, a specific measure should be taken for supporting high-Q quasi-BICs: the metasurface is constructed with periodic LN nanodisk array on the ultrathin film of the same material deposited on silica, such that the guiding wave couples to the far-field with high Q-factor, resulting in second-harmonic generation with significantly high efficiency up to 0.14 % in the range from near UV to vacuum UV for both transmitted and reflected radiations. The metasurface of similar structure, but with mirror symmetry-broken unit cells, exhibits nearly perfect second-harmonic generation circular dichroism with high efficiency. The presented results can find important applications for ultraviolet nanophotonics due to the significantly high efficiency and strong nonlinear circular dichroism.

DEPENDENCE OF OPTICAL PROPERTIES OF TWO-LAYERED METAL-DIELECTRIC SPHERICAL NANOPARTICLES ON TEMPERATURE

The dependences of the efficiency factors of radiation absorption by spherical hybrid nanoparticles of the core-shell system, respectively, with gold-quartz and quartz-gold materials with core radii r0 = 40, 50, 60, 70 nm and shell thicknesses Δr1 = 10, 20, 30 nm in the wavelength range of 300–3000 nm at temperatures of particles and surrounding quartz T = 300, 1173 K are theoretically calculated and studied. Essential change of radiation absorption by a nanoparticle is established with an increase of temperatures of nanoparticles and environment. The change of optical properties of nanoparticles significantly influences the efficiency of energy absorption of solar or optical radiation by nanoparticles, heating temperature of nanoparticles and environment and further thermal processes. The results are interesting for purposes of creation of high-temperature solid nanostructured absorbers of solar radiation containing absorbing radiation of a nanoparticle and also for creation of new materials for high-temperature nanophotonics.

Nanoscale Photoluminescence Manipulation in Monolithic Porous Silicon Oxide Microcavity Coated with Fluorescent Polyelectrolytes Via Electrostatic Nanoassembling

Porous silicon (PSi) is a promising material for future integrated nanophotonics when coupled with guest emitters [1,2], still facing challenges in terms of homogenous distribution and nanometric thickness of the emitter coating within the silicon nanostructure. Herein, it is shown that the nanopore surface of a porous silicon oxide (PSiO2) microcavity (MC) can be conformally coated with a uniform nm-thick layer of a cationic light-emitting polyelectrolyte, e.g., poly(allylamine hydrochloride) labeled with Rhodamine B (PAH-RhoB), leveraging the self-tuned electrostatic interaction of the positively-charged PAH-RhoB polymer and negatively-charged PSiO2 surface. It is found that the emission of PAH-RhoB in the PSiO2 MC is enhanced (≈2.5×) and narrowed (≈30×) at the resonant wavelength, compared with that of PAH-RhoB in a non-resonant PSiO2 reference structure [3]. The time-resolved photoluminescence analysis highlights a shortening (≈20%) of the PAH-RhoB emission lifetime in the PSiO2 MC at the resonance versus off-resonance wavelengths, and with respect to the reference structure, thereby proving a significant variation of the radiative decay rate. Remarkably, an experimental Purcell factor Fp = 2.82 is achieved. This is further confirmed by the enhance- ment of the photoluminescence quantum yield of the PAH-RhoB in the PSiO2 MC with respect to the reference structure.By building on these results, we envisage many emerging photonic applications of the electrostatic nanoassembly coating technology for introduction of foreign emitters into PSi-based photonic nano-/mesostructures, though not lim- ited to, including ultrasensitive fluorescence-enhanced optical nanosensors, nanolasers, exciton-polaritonic devices, spintronic devices, and quantum optical devices.

Pockels modulation in integrated nanophotonics

Electro-optic modulators provide the electrical control of the intensity, frequency, and phase of an optical signal. They became an indispensable part of our telecommunication network and largely dictate the achievable data bandwidths. Novel active material platforms and recent advantages in fabrication and processing techniques enabled the next generation of electro-optic modulators featuring significantly improved performance in the relevant device metrics, i.e., modulation efficiency, bandwidth, wavelength range of operation, device footprint, and environmental stability. Here, we overview recent achievements of electro-optic modulation, consider tradeoffs between the performance matrices, and conduct an assessment of electro-optic modulators based on the relevant nanophotonic device configurations and material platforms. We highlight the fundamental limitations and practical challenges for different electro-optic materials employed in photonic and plasmonic device platforms.

Epitaxial mid-IR nanophotonic optoelectronics

There are a range of fundamental challenges associated with scaling optoelectronic devices down to the nano-scale, and the past decades have seen significant research dedicated to the development of sub-diffraction-limit optical devices, often relying on the plasmonic response of metal structures. At the longer wavelengths associated with the mid-infrared, dramatic changes in the optical response of traditional nanophotonic materials, reduced efficiency optoelectronic active regions, and a host of deleterious and/or parasitic effects makes nano-scale optoelectronics at micro-scale wavelengths particularly challenging. In this Perspective, we describe recent work leveraging a class of infrared plasmonic materials, highly doped semiconductors, which not only support sub-diffraction-limit plasmonic modes at long wavelengths, but which can also be integrated into a range of optoelectronic device architectures. We discuss how the wavelength-dependent optical response of these materials can serve a number of different photonic device designs, including dielectric waveguides, epsilon-near-zero dynamic optical devices, cavity-based optoelectronics, and plasmonic device architectures. We present recent results demonstrating that the highly doped semiconductor class of materials offers the opportunity for monolithic, all-epitaxial, device architectures out-performing current state of the art commercial devices, and discuss the perspectives and promise of these materials for infrared nanophotonic optoelectronics.

Design and Applications of Liquid Crystal Biophotonic Sensors for Ion Detection

Liquid crystals (LCs) are nanophotonic materials which can interact with light in the molecular scale. While the LCs are widely used in various displays, last decade has witnessed emerging applications of the LCs for nondisplays. Based on the unique stimuli–responsive property and optical property, the applications of the LCs in the field of sensors are widely explored. In addition, ions are widely distributed in nature and bionts, playing critical roles in many physiological activities and ecological cycles. Appropriate amount of ions is beneficial to the human body, while the excess ions can cause irreversible damages. As a result, a variety of LC sensors are proposed to detect the ion concentration in both body fluids and water samples. This article reviews the design principles, applications, and existing problems of the LC ion sensors. The geometries, alignments, and optical signals of the sensors, which can guide the design of the devices, are first discussed. Afterward, two types of LC ion sensors aiming at detecting metal ions and nonmetallic ions, respectively, are illustrated. Finally, the current challenges and potential development directions of the LC ion sensors are introduced briefly.

Lanthanide-doped heterostructured nanocomposites toward advanced optical anti-counterfeiting and information storage

The continuously growing importance of information storage, transmission, and authentication impose many new demands and challenges for modern nano-photonic materials and information storage technologies, both in security and storage capacity. Recently, luminescent lanthanide-doped nanomaterials have drawn much attention in this field because of their photostability, multimodal/multicolor/narrowband emissions, and long luminescence lifetime. Here, we report a multimodal nanocomposite composed of lanthanide-doped upconverting nanoparticle and EuSe semiconductor, which was constructed by utilizing a cation exchange strategy. The nanocomposite can emit blue and white light under 365 and 394 nm excitation, respectively. Meanwhile, the nanocomposites show different colors under 980 nm laser excitation when the content of Tb3+ ions is changed in the upconversion nanoparticles. Moreover, the time-gating technology is used to filter the upconversion emission of a long lifetime from Tb3+ or Eu3+, and the possibilities for modulating the emission color of the nanocomposites are further expanded. Based on the advantage of multiple tunable luminescence, the nanocomposites are designed as optical modules to load optical information. This work enables multi-dimensional storage of information and provides new insights into the design and fabrication of next-generation storage materials.

Probing Optical Nonlinearities of Unconventional Glass Nanocomposites Made of Ionic Liquid Crystals and Bimetallic Nanoparticles.

In this paper, we report the synthesis and characterization of unconventional nanocomposites made of bimetallic nanoparticles dispersed in a liquid crystal glass. Core-shell bimetallic nanoparticles (Ag/Au or Au/Ag) and Ag-Au bimetallic nanoalloys are synthesized using cadmium alkanoate glass-forming liquid crystals as nanoreactors. Optical spectra of the produced glassy nanocomposites exhibit a distinctive absorption peak due to a surface plasmon resonance. In addition, these unusual materials demonstrate a strong nonlinear–optical response probed by means of the Z-scan technique. The use of near-infrared (1064 nm) and visible (532 nm) nanosecond laser pulses reveal a variety of nonlinear–optical mechanisms that depend on the composition of the studied nanocomposites. Our results indicate that metal alkanoate-based glass-forming ionic liquid crystals with embedded plasmonic nanoparticles are promising, yet they are overlooked photonic nanomaterials suitable for optical and nonlinear-optical applications.

Chemical Vapor Deposition of Spherical Amorphous Selenium Mie Resonators for Infrared Meta-Optics.

Applying direct growth and deposition of optical surfaces holds great promise for the advancement of future nanophotonic technologies. Here, we report on a chemical vapor deposition (CVD) technique for depositing amorphous selenium (a-Se) spheres by desorption of selenium from Bi2Se3 and re-adsorption on the substrate. We utilize this process to grow scalable, large area Se spheres on several substrates and characterize their Mie-resonant response in the mid-infrared (MIR) spectral range. We demonstrate size-tunable Mie resonances spanning the 2-16 μm spectral range for single isolated resonators and large area ensembles. We further demonstrate strong absorption dips of up to 90% in ensembles of particles in a broad MIR range. Finally, we show that ultra-high-Q resonances arise in the case where Se Mie-resonators are coupled to low-loss epsilon-near-zero (ENZ) substrates. These findings demonstrate the enabling potential of amorphous Selenium as a versatile and tunable nanophotonic material that may open up avenues for on-chip MIR spectroscopy, chemical sensing, spectral imaging, and large area metasurface fabrication.

Broadband Optical Constants and Nonlinear Properties of SnS2 and SnSe2.

SnS2 and SnSe2 have recently been shown to have a wide range of applications in photonic and optoelectronic devices. However, because of incomplete knowledge about their optical characteristics, the use of SnS2 and SnSe2 in optical engineering remains challenging. Here, we addressed this problem by establishing SnS2 and SnSe2 linear and nonlinear optical properties in the broad (300–3300 nm) spectral range. Coupled with the first-principle calculations, our experimental study unveiled the full dielectric tensor of SnS2 and SnSe2. Furthermore, we established that SnS2 is a promising material for visible high refractive index nanophotonics. Meanwhile, SnSe2 demonstrates a stronger nonlinear response compared with SnS2. Our results create a solid ground for current and next-generation SnS2- and SnSe2-based devices.

Hyperspectral infrared imaging of surface phonon-polaritons in SrTiO3

Polaritons have a demonstrated impact on nanophotonic applications in the midinfrared through visible spectral range. Surface phonon-polaritons (SPhPs) offer a way to bring the potential of polaritons to the longer infrared wavelengths. Strontium titanate (STO) is a perovskite polar dielectric with diverse technologically advantageous properties and it can support SPhPs in a uniquely broad spectral range of the far infrared. Despite these advantages, STO has mostly been overlooked as a nanophotonic material. In this work we investigate SPhP propagation in STO in the far-infrared through midinfrared spectral range using broadband, near-field nanospectroscopy. We developed a tabletop, laser sustained plasma light source that enabled us to obtain amplitude and phase resolved hyperspectral line scan maps of SPhPs across the surface of the STO sample. Analytical modeling of experimental data reveals the dispersion characteristics of SPhPs in STO. This work establishes STO as a platform for perovskite-based broadband far-infrared and terahertz nanophotonics.

Unusually-high growth rate (∼2.8 μm/s) of germania nanowires and its hierarchical structures by an in-situ continuous precursor supply

Low-dimensional nanostructured semiconductors are becoming the promising materials for high-performance nanophotonics, nanoelectronics, and quantum devices. To enable these applications, it requires an efficient methodology to control the dimension of these materials during synthesis processes, and to achieve mass production of these materials with high reproducibility, perfect crystallinity, and low production cost. In this study, an ultra-fast, facile synthesis strategy is presented for reproducible monocrystalline hexagonal germania (GeO2) nanowires (NWs) and hierarchical structures. These GeO2 nanostructures were grown by one-step-annealing of the Ni film-covered GeSn epilayers in a rapid thermal annealing (RTA) system without any gaseous or liquid Ge sources. It was found that after short annealing for 60 s at 675 °C, the long GeO2 NWs of more than 170 μm are obtained, indicating that the growth rate is several magnitude orders higher than that of the common chemical vapor deposition (CVD) methods. The mechanism of the growth was studied by changing the growth temperature, catalyst type, and surface oxidation. The results indicate that this record-fast growth (>2.8 μm/s) of NW is due to the continuously generated in-situ GeO vapors from the Ni-catalyst decomposition of supersaturated GeSn epilayer. This work presents a rapid, and low-cost method to synthesis high-density GeO2 NW and its hierarchical structures which have the potential applications for optoelectronic communication/detection, superhydrophobic surfaces, photocatalyst, and sensing.

Nanophotonic Approaches for Chirality Sensing.

Chiral nanophotonic materials are promising candidates for biosensing applications because they focus light into nanometer dimensions, increasing their sensitivity to the molecular signatures of their surroundings. Recent advances in nanomaterial-enhanced chirality sensing provide detection limits as low as attomolar concentrations (10-18 M) for biomolecules and are relevant to the pharmaceutical industry, forensic drug testing, and medical applications that require high sensitivity. Here, we review the development of chiral nanomaterials and their application for detecting biomolecules, supramolecular structures, and other environmental stimuli. We discuss superchiral near-field generation in both dielectric and plasmonic metamaterials that are composed of chiral or achiral nanostructure arrays. These materials are also applicable for enhancing chiroptical signals from biomolecules. We review the plasmon-coupled circular dichroism mechanism observed for plasmonic nanoparticles and discuss how hotspot-enhanced plasmon-coupled circular dichroism applies to biosensing. We then review single-particle spectroscopic methods for achieving the ultimate goal of single-molecule chirality sensing. Finally, we discuss future outlooks of nanophotonic chiral systems.