We present a systematic study on the fabrication, characterization and high temperature surface enhanced Raman spectroscopy (SERS) performance of SiO2 coated silver nanoparticles (Ag@SiO2) on a flat ...substrate, aiming to obtain a thermally robust SERS substrate for monitoring high temperature reactions. We confirm that a 10–15 nm SiO2 coating provides a structure stability up to 900 °C without significantly sacrificing the enhancement factor, while the uncoated particle cannot retain the SERS effect above 500 °C. The finite difference time domain (FDTD) simulation results supported that the SiO2 coating almost has no influence on the distribution of the electric field but only physically trapped the most enhanced spot inside the coating layer. On this thermally robust substrate, we confirmed that the SERS of horizontally aligned single walled carbon nanotubes is stable at elevated temperatures, and demonstrate an in situ Raman monitoring of the atmosphere of the annealing process of nanodiamonds, in which the interconverting process of C–C bonds is unambiguously observed. We claim that this is a first experimental proof that the high temperature SERS effect can be preserved and applied in a chemical reaction at temperature above 500 °C. This versatile substrate also enables novel opportunities for observing growth, etching, and structure transformation of many 0D and 2D nano-materials.
The increasing demands of computational power have accelerated the development of 3D circuits in the semiconductor industry. To resolve the accompanying thermal issues, two-phase microchannel heat ...exchangers using have emerged as one of the promising solutions for cooling purposes. However, the direct boiling in microchannels and rapid bubble growth give rise to highly unstable heat flux on the channel walls. In this regard, it is hence desired to control the supply of vapor bubbles for the elimination of the instability. In this research, we investigate a controllable bubble generation technique, which is capable of periodically producing bubble seeds at the sub-micron scale. These nanobubbles were generated in a solid-state nanopore filled with a highly concentrated electrolyte solution. As an external electric field was applied, the localized Joule heating inside the nanopore initiated the homogeneous bubble nucleation. The bubble dynamics was analyzed by measuring the ionic current variation through the nanopore during the bubble nucleation and growth. Meanwhile, we theoretically examined the bubble growth and collapse inside the nanopore by a moving boundary model. In both approaches, we demonstrated that by altering the pore size, the available sensible heat for the bubble growth can be manipulated, thereby offering the controllability of the bubble size. This unique characteristic renders nanopores suitable as a nanobubble emitter for microchannel heat exchangers, paving the way for the next generation microelectronic cooling applications.
The need for ever faster and more efficient computation and communication devices has spurred interest in the field of all-optical modulators. Here a small-size hybrid plasmonic-photonic all-optical ...waveguide modulator utilizing a subwavelength Au/VO 2 nanostructure is proposed as a high-modulation optically actuatable modulator. Using finite-difference-time-domain simulations, a nanoscale (320 nm × 300 nm cross-section) optimized modulator is designed. The modulator design has an extinction ratio as high as 26.85 dB/μm, and a length of only 550 nm.
Circularly polarized emission (CPE) plays an important role in the designs of advanced displays and photonic integrated circuits. Unfortunately, the control of CPE handedness is limited by the chiral ...metasurfaces employed to emit chiral light. Particularly, the switching of the handedness with chiral metasurfaces relies on flipping the metasurfaces, which adds some constraints to practical applications. Herein, we propose an angle-sensitive chiral metamirror with Mie resonators to realize handedness switching. The Mie resonator supports a magnetic dipole having large field enhancement. This chiral metamirror is applied to excite CPEs with opposite handedness at emission angles within 10°. In contrast to the conventional methods, this work proposes a more efficient approach to manipulate the handedness of CPE.
Wavelength-selective photodetectors with dual and multiple narrowband spectral responses in the infrared range are essential in the development of hyperspectral imaging technology and have attracted ...great attention due to their potential applications in a variety of areas such as resource remote sensing and mineral exploration. Here, we introduce an efficient optimization of Tamm-plasmon (TP) structure-based hot electron photodetection devices in the telecommunications wavelengths. The devices consist of a Si/SiO2 distributed Bragg reflector (DBR) multilayer structure atop of an Au/n-Si Schottky diode. The DBR structure is optimized using Differential Evolution (DE) algorithm for wavelength-selectivity and ultra-narrow linewidths at arbitrarily wavelengths. DE shows excellent capability and efficiency in solving a high dimensional continuous optimization problem with competitive speed. The optimized TP structure by DE exhibits near-unity absorptance at the designed wavelengths and requires a relatively short computation time on a standard computer of approximately one and three days to search the optimized TP structures for single and dual absorption peak photodetection, respectively. This result shows that DE is efficient for multilayer structure optimization. Finally, a mechanism for selective photodetection of the two sensitive wavelengths is proposed by tuning the height of the Au/n-Si Schottky barrier with a bias voltage. This wavelength selection mechanism opens the way for dual absorption peaks photodetection.
•Differential Evolution algorithm-based optimization of single- and dual-peak absorption for use in photodetection.•High selectivity and near-unity absorptance realization.•Dual-peak photodetection selectivity scheme based on bias-controlled Schottky barrier height.
Plasmonic-waveguide lasers, which exhibit subdiffraction limit lasing and light propagation, are promising for the next-generation of nanophotonic devices in computation, communication, and ...biosensing. Plasmonic lasers supporting waveguide modes are often based on nanowires grown with bottom-up techniques that need to be transferred and aligned for use in optical circuits. Here, we demonstrate a monolithically fabricated ZnO/Al plasmonic-waveguide nanolaser compatible with the fabrication requirements of on-chip circuits. The nanolaser is designed with a plasmonic metal layer on the top of the laser cavity only, providing highly efficient energy transfer between photons, excitons, and plasmons, and achieving lasing in the ultraviolet region up to 330 K with a low threshold intensity (0.20 mJ/cm2 at room temperature). This work demonstrates the realization of a plasmonic-waveguide nanolaser without the need for transfer and positioning steps, which is the key for on-chip integration of nanophotonic devices.
A tapered fiber sensor was developed to detect the presence of condensed water and frost. The rough surface of the tapered fiber efficiently scattered the light propagating through the tapered fiber. ...The scattering loss is selective to the medium surrounding the tapered region of the fiber. Compared to the transmission intensity in the air, liquid water on the tapered fiber causes a 40% increase in transmission, whereas the presence of frost decreases the light transmission by 15%. Frost induces roughness on the surface of the tapered fiber and as a result increases light scattering and transmission losses. In contrast, liquid water uniformly covers the tapered fiber surface and reduces the light scattering. Furthermore, the amount of frozen water on the tapered surface is related to the duration of the transmission intensity peak during the defrosting process. The proposed detection scheme based on a rough tapered fiber can be utilized in real-time remote monitoring systems of the frost formation in large refrigeration systems.
An axicon fiber tip combined with a camera device is developed to sensitively detect refractive indexes in solutions. The transparent axicon tips were made by etching optical fibers through a wet ...end-etching method at room temperature. When the axicon fiber tip was immersed in various refractive index media, the angular spectrum of the emitted light from the axicon fiber tip was changed. Using a low numerical aperture lens to collect the directly transmitted light, a high intensity sensitivity was achieved when the tip cone angle was about 35 to 40 degrees. We combined the axicon fiber tip with a laser diode and a smartphone into a portable refractometer. The front camera of the smartphone was used to collect the light emitted from the axicon fiber tip. By analyzing the selected area of the captured images, the refractive index can be distinguished for various solutions. The refractive index sensitivity was up to 56,000%/RIU, and the detection limit was 1.79 × 10
RIU. By measuring the refractive index change via the axicon fiber tip, the concentration of different mediums can be sensitively detected. The detection limits of the measurement for sucrose solutions, saline solutions, and diluted wine were 8.86 × 10
°Bx, 0.12‱, and 0.35%, respectively.
A hybrid plasmonic structure consisting of adjacent U-shaped cavities separated by a nanochannel is proposed for tunable and narrow-band selection of light. The hybrid cavity-channel structure ...achieves absorption resonance with a bandwidth, defined as the full-width at half-maximum, of 1.5 nm and tunable property in the near-infrared and infrared regions. The hybrid structure resonance originates in the coupling of horizontal surface plasmon mode of the U-cavity with channel mode, which sustains stationary-surface-plasmons in the channel with antinodes at the channel entrances enabling light concentration and nodes at the channel exits enabling light confinement. As a result of the coupling, a sharp and strong absorption resonance is readily adjustable by varying the geometrical parameters of the U-cavity while keeping the channel parameters unchanged.
When applying a voltage bias across a thin nanopore, localized Joule heating can lead to single-bubble nucleation, offering a unique platform for studying nanoscale bubble behavior, which is still ...poorly understood. Accordingly, we investigate bubble nucleation and collapse inside solid-state nanopores filled with electrolyte solutions and find that there exists a clear correlation between homo/heterogeneous bubble nucleation and the pore diameter. As the pore diameter is increased from 280 to 525 nm, the nucleation regime transitions from predominantly periodic homogeneous nucleation to a nonperiodic mixture of homogeneous and heterogeneous nucleation. A transition barrier between the homogeneous and heterogeneous nucleation regimes is defined by considering the relative free-energy costs of cluster formation. A thermodynamic model considering the transition barrier and contact-line pinning on curved surfaces is constructed, which determines the possibility of heterogeneous nucleation. It is shown that the experimental bubble generation behavior is closely captured by our thermodynamic analysis, providing important information for controlling the periodic homogeneous nucleation of bubbles in nanopores.
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