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3 pages, 155 KiB

Open AccessEditorial

Special Issue on the State-of-the-Art Optical Properties and Applications of Metallic Nanostructures in Asia

by Hai-Pang Chiang

Nanomaterials 2024, 14(4), 322; https://doi.org/10.3390/nano14040322 - 6 Feb 2024

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Abstract

With developments in nanofabrication technology, the optical properties and applications of metallic nanostructures have attracted increased research interest in recent years [...] Full article

(This article belongs to the Special Issue State-of-the-Art Optical Properties and Applications of Metallic Nanostructures in Asia)

Research

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17 pages, 5683 KiB

Open AccessArticle

Structure of an In Situ Phosphorus-Doped Silicon Ultrathin Film Analyzed Using Second Harmonic Generation and Simplified Bond-Hyperpolarizability Model

by Wei-Ting Chen, Ting-Yu Yen, Yang-Hao Hung and Kuang-Yao Lo

Nanomaterials 2022, 12(23), 4307; https://doi.org/10.3390/nano12234307 - 4 Dec 2022

Cited by 4 | Viewed by 1945

Abstract

In fabricating advanced silicon (Si)-based metal–oxide semiconductors, the ability to inspect dopant distribution in Si ultrathin films (tens of nm) is crucial for monitoring the amount of dopant diffusion. Here, we perform an anisotropic reflective second harmonic generation (SHG) measurement to demonstrate the [...] Read more.

In fabricating advanced silicon (Si)-based metal–oxide semiconductors, the ability to inspect dopant distribution in Si ultrathin films (tens of nm) is crucial for monitoring the amount of dopant diffusion. Here, we perform an anisotropic reflective second harmonic generation (SHG) measurement to demonstrate the sensitivity of SHG to phosphorus (P) concentration within the range of

2.5 \times 10^{17}

to

1.6 \times 10^{20}

atoms/cm³. In addition, we propose an analysis method based on a simplified bond-hyperpolarizability model to interpret the results. The bond vector model that corresponds to the P vacancy clusters is built to calculate the SHG contribution from substitutionally incorporated P atoms. The effect of incorporating P into the Si lattice is reflected in the effective hyperpolarizability, lattice tilt, and deformation of this model. The fitting results of the intuitively defined coefficients exhibit a high correlation to the P concentration, indicating the potential of this model to resolve the properties in complex material compositions. Finally, a comparison with Fourier analysis is made to evaluate the advantages and disadvantages of this model. Combined anisotropic reflective SHG (Ani-RSHG) and the simplified bond-hyperpolarizability model (SBHM) can analyze the crystal structure of doped ultrathin films and provide a non-destructive nanophotonic way for in-line inspection. Full article

(This article belongs to the Special Issue State-of-the-Art Optical Properties and Applications of Metallic Nanostructures in Asia)

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14 pages, 4219 KiB

Open AccessArticle

Rigorous Analysis and Systematical Design of Double-Layer Metal Superlens for Improved Subwavelength Imaging Mediated by Surface Plasmon Polaritons

by Jing Wang, Zhichao Li and Weina Liu

Nanomaterials 2022, 12(20), 3553; https://doi.org/10.3390/nano12203553 - 11 Oct 2022

Cited by 4 | Viewed by 2048

Abstract

A double-layer metal superlens was rigorously analyzed and systematically designed to improve subwavelength imaging ability. It was revealed that transmission properties of the imaging system could be accurately interpreted by the five-layer waveguide mode theory—each amplification peak among the spatial frequency range of [...] Read more.

A double-layer metal superlens was rigorously analyzed and systematically designed to improve subwavelength imaging ability. It was revealed that transmission properties of the imaging system could be accurately interpreted by the five-layer waveguide mode theory—each amplification peak among the spatial frequency range of evanescent waves was associated with a corresponding surface plasmon polariton (SPP) mode of an insulator-metal-insulator-metal-insulator (IMIMI) structure. On the basis of such physical insight, evanescent waves of higher spatial frequency were effectively amplified via increasing propagation constants of symmetrically coupled short-range SPP (s-SRSPP) and antisymmetrically coupled short-range SPP (a-SRSPP), and evanescent waves of lower spatial frequency were appropriately diminished by approaching to cut off symmetrically coupled long-range SPP (s-LRSPP). A flat and broad optical transfer function of the imaging system was then achieved, and improved subwavelength imaging performance was validated by imaging an ideal thin object of two slits with a 20-nm width distanced by a 20-nm spacer, under 193-nm illumination. The resolution limit of the designed imaging system with double-layer superlens was further demonstrated to be at least ~λ/16 for an isolated two-slit object model. This work provided sound theoretical analysis and a systematic design approach of double-layer metal superlens for near-field subwavelength imaging, such as fluorescent micro/nanoscopy or plasmonic nanolithography. Full article

(This article belongs to the Special Issue State-of-the-Art Optical Properties and Applications of Metallic Nanostructures in Asia)

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14 pages, 2417 KiB

Open AccessArticle

Laser-Induced Plasmonic Nanobubbles and Microbubbles in Gold Nanorod Colloidal Solution

by Shang-Yang Yu, Chang-Hsuan Tu, Jiunn-Woei Liaw and Mao-Kuen Kuo

Nanomaterials 2022, 12(7), 1154; https://doi.org/10.3390/nano12071154 - 31 Mar 2022

Cited by 6 | Viewed by 2296

Abstract

In this work, we studied the initiated plasmonic nanobubbles and the follow-up microbubble in gold nanorod (GNR) colloidal solution induced by a pulsed laser. Owing to the surface plasmon resonance (SPR)-enhanced photothermal effect of GNR, several nanobubbles are initiated at the beginning of [...] Read more.

In this work, we studied the initiated plasmonic nanobubbles and the follow-up microbubble in gold nanorod (GNR) colloidal solution induced by a pulsed laser. Owing to the surface plasmon resonance (SPR)-enhanced photothermal effect of GNR, several nanobubbles are initiated at the beginning of illumination and then to trigger the optical breakdown of water at the focal spot of a laser beam. Consequently, microbubble generation is facilitated; the threshold of pulsed laser energy is significantly reduced for the generation of microbubbles in water with the aid of GNRs. We used a probing He-Ne laser with a photodetector and an ultrasonic transducer to measure and investigate the dynamic formations of nanobubbles and the follow-up microbubble in GNR colloids. Two wavelengths (700 nm and 980 nm) of pulsed laser beams are used to irradiate two kinds of dilute GNR colloids with different longitudinal SPRs (718 nm and 966 nm). By characterizing the optical and photoacoustic signals, three types of microbubbles are identified: a single microbubble, a coalesced microbubble of multiple microbubbles, and a splitting microbubble. The former is caused by a single breakdown, whereas the latter two are caused by discrete and series-connected multiple breakdowns, respectively. We found that the thresholds of pulsed energy to induce different types of microbubbles are reduced as the concentration of GNRs increases, particularly when the wavelength of the laser is in the near-infrared (NIR) region and close to the SPR of GNRs. This advantage of a dilute GNR colloid facilitating the laser-induced microbubble in the NIR range of the bio-optical window could make biomedical applications available. Our study may provide an insight into the relationship between plasmonic nanobubbles and the triggered microbubbles. Full article

(This article belongs to the Special Issue State-of-the-Art Optical Properties and Applications of Metallic Nanostructures in Asia)

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14 pages, 8702 KiB

Open AccessArticle

Physical Properties and the Reconstruction of Unstable Decahedral Silver Nanoparticles Synthesized Using Plasmon-Mediated Photochemical Process

by Jui-Chang Chen, Yu-Te Chu, Shi-Hise Chang, Ya-Tin Chuang and Cheng-Liang Huang

Nanomaterials 2022, 12(7), 1062; https://doi.org/10.3390/nano12071062 - 24 Mar 2022

Cited by 4 | Viewed by 2002

Abstract

Plasmon-mediated shape transformation from quasi-spherical silver nanoparticles (AgNPs) to silver nanoprisms (AgNPrs) and decahedral silver nanoparticles (D-AgNPs) under irradiation of blue LEDs (λ = 456 ± 12 nm, 80 mW/cm²) was studied at temperatures ranging between 60, 40, 30, 20, 10, [...] Read more.

Plasmon-mediated shape transformation from quasi-spherical silver nanoparticles (AgNPs) to silver nanoprisms (AgNPrs) and decahedral silver nanoparticles (D-AgNPs) under irradiation of blue LEDs (λ = 456 ± 12 nm, 80 mW/cm²) was studied at temperatures ranging between 60, 40, 30, 20, 10, and 0 °C. It was found that reaction temperature affected transformation rates and influenced the morphology distribution of final products. The major products synthesized at temperatures between 60 °C and 0 °C were AgNPrs and D-AgNPs, respectively. The D-AgNPs synthesized at such low temperatures are unstable and become blunt when light irradiation is removed after the photochemical synthesis. These blunt nanoparticles with pentagonal multiple-twinned structures can be further used as the seeds to reconstruct complete D-AgNPs after irradiating blue LEDs at various bath temperatures. Our results showed that these rebuilt D-AgNPs are much more stable when at higher bath temperatures. Furthermore, the rebuilt D-AgNPs (edge lengths ~41 nm) can grow into larger D-AgNPs (edge lengths ~53 nm) after the irradiation of green LEDs. Surface-enhanced Raman spectra of CV in AgNP colloids showed that D-AgNP colloids have better SERS enhancements factors than AgNPrs. Full article

(This article belongs to the Special Issue State-of-the-Art Optical Properties and Applications of Metallic Nanostructures in Asia)

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14 pages, 3332 KiB

Open AccessArticle

Ultrahigh Sensitivity of a Plasmonic Pressure Sensor with a Compact Size

by Chung-Ting Chou Chao, Yuan-Fong Chou Chau, Sy-Hann Chen, Hung Ji Huang, Chee Ming Lim, Muhammad Raziq Rahimi Kooh, Roshan Thotagamuge and Hai-Pang Chiang

Nanomaterials 2021, 11(11), 3147; https://doi.org/10.3390/nano11113147 - 21 Nov 2021

Cited by 28 | Viewed by 2602

Abstract

This study proposes a compact plasmonic metal-insulator-metal pressure sensor comprising a bus waveguide and a resonator, including one horizontal slot and several stubs. We calculate the transmittance spectrum and the electromagnetic field distribution using the finite element method. When the resonator’s top layer [...] Read more.

This study proposes a compact plasmonic metal-insulator-metal pressure sensor comprising a bus waveguide and a resonator, including one horizontal slot and several stubs. We calculate the transmittance spectrum and the electromagnetic field distribution using the finite element method. When the resonator’s top layer undergoes pressure, the resonance wavelength redshifts with increasing deformation, and their relation is nearly linear. The designed pressure sensor possesses the merits of ultrahigh sensitivity, multiple modes, and a simple structure. The maximum sensitivity and resonance wavelength shift can achieve 592.44 nm/MPa and 364 nm, respectively, which are the highest values to our knowledge. The obtained sensitivity shows 23.32 times compared to the highest one reported in the literature. The modeled design paves a promising path for applications in the nanophotonic field. Full article

(This article belongs to the Special Issue State-of-the-Art Optical Properties and Applications of Metallic Nanostructures in Asia)

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22 pages, 7265 KiB

Open AccessArticle

Improved Refractive Index-Sensing Performance of Multimode Fano-Resonance-Based Metal-Insulator-Metal Nanostructures

by Yuan-Fong Chou Chau, Chung-Ting Chou Chao, Siti Zubaidah Binti Haji Jumat, Muhammad Raziq Rahimi Kooh, Roshan Thotagamuge, Chee Ming Lim and Hai-Pang Chiang

Nanomaterials 2021, 11(8), 2097; https://doi.org/10.3390/nano11082097 - 18 Aug 2021

Cited by 43 | Viewed by 3049

Abstract

This work proposed a multiple mode Fano resonance-based refractive index sensor with high sensitivity that is a rarely investigated structure. The designed device consists of a metal–insulator–metal (MIM) waveguide with two rectangular stubs side-coupled with an elliptical resonator embedded with an air path [...] Read more.

This work proposed a multiple mode Fano resonance-based refractive index sensor with high sensitivity that is a rarely investigated structure. The designed device consists of a metal–insulator–metal (MIM) waveguide with two rectangular stubs side-coupled with an elliptical resonator embedded with an air path in the resonator and several metal defects set in the bus waveguide. We systematically studied three types of sensor structures employing the finite element method. Results show that the surface plasmon mode’s splitting is affected by the geometry of the sensor. We found that the transmittance dips and peaks can dramatically change by adding the dual air stubs, and the light–matter interaction can effectively enhance by embedding an air path in the resonator and the metal defects in the bus waveguide. The double air stubs and an air path contribute to the cavity plasmon resonance, and the metal defects facilitate the gap plasmon resonance in the proposed plasmonic sensor, resulting in remarkable characteristics compared with those of plasmonic sensors. The high sensitivity of 2600 nm/RIU and 1200 nm/RIU can simultaneously achieve in mode 1 and mode 2 of the proposed type 3 structure, which considerably raises the sensitivity by 216.67% for mode 1 and 133.33% for mode 2 compared to its regular counterpart, i.e., type 2 structure. The designed sensing structure can detect the material’s refractive index in a wide range of gas, liquids, and biomaterials (e.g., hemoglobin concentration). Full article

(This article belongs to the Special Issue State-of-the-Art Optical Properties and Applications of Metallic Nanostructures in Asia)

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10 pages, 3093 KiB

Open AccessArticle

The Effect of Quasi-Spherical Gold Nanoparticles on Two-Photon Induced Reactive Oxygen Species for Cell Damage

by Jiunn-Woei Liaw, Chia-Yu Kuo and Shiao-Wen Tsai

Nanomaterials 2021, 11(5), 1180; https://doi.org/10.3390/nano11051180 - 30 Apr 2021

Cited by 8 | Viewed by 2262

Abstract

The performance of quasi-spherical gold nanoparticles (GNPs) on the generation of reactive oxygen species (ROS) to cause cell damage, as irradiated by a two-photon laser, is studied. In this mechanism, hot electrons are generated from GNPs as irradiated by the two-photon laser, reacting [...] Read more.

The performance of quasi-spherical gold nanoparticles (GNPs) on the generation of reactive oxygen species (ROS) to cause cell damage, as irradiated by a two-photon laser, is studied. In this mechanism, hot electrons are generated from GNPs as irradiated by the two-photon laser, reacting with the molecules in the medium to produce ROS. We used laser scanning confocal microscopy with a low-fluence femtosecond Ti:Sapphire laser of 800 nm to observe the generated ROS in A431 cells, which were incubated with GNPs in advance. Subsequently, the cell morphology, cytoskeleton, and viability were investigated. In comparison with the control (no GNPs), the expression of ROS in these GNP-treated cells was enhanced after irradiation by the two-photon laser. Additionally, the disruption of cytoskeletons and the follow-up apoptosis of these GNP-treated cells are significantly increased as the number of laser shots increases. Moreover, we used N-acetyl-L-cysteine (NAC), an antioxidant, to inhibit the formation of ROS, to clarify whether the cytoskeletal disruption is caused by ROS rather than photothermal effects. Our results show that after two-photon irradiation, the ROS expression in these cells treated with GNPs plus NAC was significantly reduced. In addition, the cytoskeletal damage of these cells treated with GNPs and NAC was less than that of those treated with GNPs but without NAC; their cell viability after three days was almost the same with the control. These results illustrate that the induced ROS from the two-photon excited GNPs is the main cause of cell damage. The study may pave a way for the use of GNPs as a photosensitized therapeutic agent for two-photon photodynamic therapy on tumor treatment. Full article

(This article belongs to the Special Issue State-of-the-Art Optical Properties and Applications of Metallic Nanostructures in Asia)

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10 pages, 5234 KiB

Open AccessEditor’s ChoiceArticle

Enhanced Heat-Electric Conversion via Photonic-Assisted Radiative Cooling

by Jeng-Yi Lee, Chih-Ming Wang, Chieh-Lun Chi, Sheng-Rui Wu, Ya-Xun Lin, Mao-Kuo Wei and Chu-Hsuan Lin

Nanomaterials 2021, 11(4), 983; https://doi.org/10.3390/nano11040983 - 11 Apr 2021

Cited by 7 | Viewed by 2685

Abstract

In this paper, an inorganic polymer composite film is proposed as an effective radiative cooling device. The inherent absorption is enhanced by choosing an appropriately sized SiO₂ microsphere with a diameter of 6 μm. The overall absorption at the transparent window of [...] Read more.

In this paper, an inorganic polymer composite film is proposed as an effective radiative cooling device. The inherent absorption is enhanced by choosing an appropriately sized SiO₂ microsphere with a diameter of 6 μm. The overall absorption at the transparent window of the atmosphere is higher than 90%, as the concentration of SiO₂–PMMA composite is 35 wt%. As a result, an effective radiative device is made by a spin coating process. Moreover, the device is stacked on the cold side of a thermoelectric generator chip. It is found that the temperature gradient can be increased via the effective radiative cooling process. An enhanced Seebeck effect is observed, and the corresponding output current can be enhanced 1.67-fold via the photonic-assisted radiative cooling. Full article

(This article belongs to the Special Issue State-of-the-Art Optical Properties and Applications of Metallic Nanostructures in Asia)

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10 pages, 4045 KiB

Open AccessArticle

Scattering Analysis and Efficiency Optimization of Dielectric Pancharatnam–Berry-Phase Metasurfaces

by Chen-Yi Yu, Qiu-Chun Zeng, Chih-Jen Yu, Chien-Yuan Han and Chih-Ming Wang

Nanomaterials 2021, 11(3), 586; https://doi.org/10.3390/nano11030586 - 26 Feb 2021

Cited by 7 | Viewed by 3143

Abstract

In this study, the phase modulation ability of a dielectric Pancharatnam–Berry (PB) phase metasurface, consisting of nanofins, is theoretically analyzed. It is generally considered that the optical thickness of the unit cell of a PB-phase metasurface is λ/2, i.e., a half-waveplate for [...] Read more.

In this study, the phase modulation ability of a dielectric Pancharatnam–Berry (PB) phase metasurface, consisting of nanofins, is theoretically analyzed. It is generally considered that the optical thickness of the unit cell of a PB-phase metasurface is λ/2, i.e., a half-waveplate for polarization conversion. It is found that the λ/2 is not essential for achieving a full 2π modulation. Nevertheless, a λ/2 thickness is still needed for a high polarization conversion efficiency. Moreover, a gradient phase metasurface is designed. With the help of the particle swarm optimization (PSO) method, the wavefront errors of the gradient phase metasurface are reduced by fine-tuning the rotation angle of the nanofins. The diffraction efficiency of the gradient phase metasurface is thus improved from 73.4% to 87.3%. This design rule can be utilized to optimize the efficiency of phase-type meta-devices, such as meta-deflectors and metalenses. Full article

(This article belongs to the Special Issue State-of-the-Art Optical Properties and Applications of Metallic Nanostructures in Asia)

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16 pages, 3526 KiB

Open AccessArticle

Photocatalytic Activity of Magnetic Nano-β-FeOOH/Fe₃O₄/Biochar Composites for the Enhanced Degradation of Methyl Orange Under Visible Light

by Zheng Zhang, Guanghua Wang, Wenbing Li, Lidong Zhang, Benwei Guo, Ling Ding and Xiangcheng Li

Nanomaterials 2021, 11(2), 526; https://doi.org/10.3390/nano11020526 - 18 Feb 2021

Cited by 29 | Viewed by 3828

Abstract

A novel nano-β-FeOOH/Fe₃O₄/biochar composite with enhanced photocatalytic performance and superparamagnetism was successfully fabricated via an environmentally friendly one-step method. The structural properties of the prepared composite were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron [...] Read more.

A novel nano-β-FeOOH/Fe₃O₄/biochar composite with enhanced photocatalytic performance and superparamagnetism was successfully fabricated via an environmentally friendly one-step method. The structural properties of the prepared composite were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and a vibrating sample magnetometer. The XPS spectrum of the as-prepared composites confirmed the presence of Fe-O-C bonds between β-FeOOH and biochar, which could be conducive to transfer photo-generated electrons. UV-vis spectroscopy confirmed the existence of an electron–hole connection between β-FeOOH and biochar, which promoted the rapid interface transfer of photogenerated electrons from β-FeOOH to biochar. These novel structures could enhance the response of biochar to accelerate the photoelectrons under visible light for more free radicals. Electron spin resonance analysis and free radical quenching experiments showed that •OH was the primary active species in the photodegradation process of methyl orange by nano-β-FeOOH/Fe₃O₄/biochar. In the synergistic photocatalytic system, β-FeOOH/Fe₃O₄/biochar exhibited excellent catalytic activity for the degradation of azo dye (methyl orange), which is 2.03 times higher than that of the original biochar, while the surface area decreased from 1424.82 to 790.66 m²·g⁻¹. Furthermore, β-FeOOH/Fe₃O₄/biochar maintained a stable structure and at least 98% catalytic activity after reuse, and it was easy to separate due to its superparamagnetism. This work highlights the enhanced photocatalytic performance of β-FeOOH/Fe₃O₄/biochar material, which can be used in azo dye wastewater treatment. Full article

(This article belongs to the Special Issue State-of-the-Art Optical Properties and Applications of Metallic Nanostructures in Asia)

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Review

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21 pages, 7072 KiB

Open AccessReview

Plasmonic Metal Nanostructures Meet Triplet–Triplet Annihilation-Based Photon Upconversion Systems: Performance Improvements and Application Trends

by Jotaro Honda, Kosuke Sugawa, Hironobu Tahara and Joe Otsuki

Nanomaterials 2023, 13(9), 1559; https://doi.org/10.3390/nano13091559 - 5 May 2023

Cited by 2 | Viewed by 2453

Abstract

Improving the performance of upconversion systems based on triplet–triplet annihilation (TTA-UC) can have far-reaching implications for various fields, including solar devices, nano-bioimaging, and nanotherapy. This review focuses on the use of localized surface plasmon (LSP) resonance of metal nanostructures to enhance the performance [...] Read more.

Improving the performance of upconversion systems based on triplet–triplet annihilation (TTA-UC) can have far-reaching implications for various fields, including solar devices, nano-bioimaging, and nanotherapy. This review focuses on the use of localized surface plasmon (LSP) resonance of metal nanostructures to enhance the performance of TTA-UC systems and explores their potential applications. After introducing the basic driving mechanism of TTA-UC and typical sensitizers used in these systems, we discuss recent studies that have utilized new sensitizers with distinct characteristics. Furthermore, we confirm that the enhancement in upconverted emission can be explained, at least in part, by the mechanism of “metal-enhanced fluorescence”, which is attributed to LSP resonance-induced fluorescence enhancement. Next, we describe selected experiments that demonstrate the enhancement in upconverted emission in plasmonic TTA-UC systems, as well as the emerging trends in their application. We present specific examples of studies in which the enhancement in upconverted emission has significantly improved the performance of photocatalysts under both sunlight and indoor lighting. Additionally, we discuss the potential for future developments in plasmonic TTA-UC systems. Full article

(This article belongs to the Special Issue State-of-the-Art Optical Properties and Applications of Metallic Nanostructures in Asia)

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