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3 pages, 152 KiB

Open AccessEditorial

Editorial for the Special Issue “Infrared Nanophotonics: Materials, Devices and Applications”

by Tadaaki Nagao

Micromachines 2020, 11(9), 808; https://doi.org/10.3390/mi11090808 - 26 Aug 2020

Viewed by 1574

Abstract

Infrared light radiates from almost all the matter on earth and its strategic use will be an important issue for the enhancement of human life and the sustainable development of modern industry [...] Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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9 pages, 4938 KiB

Open AccessArticle

Nanoantenna Structure with Mid-Infrared Plasmonic Niobium-Doped Titanium Oxide

by Hai Dang Ngo, Kai Chen, Ørjan S. Handegård, Anh Tung Doan, Thien Duc Ngo, Thang Duy Dao, Naoki Ikeda, Akihiko Ohi, Toshihide Nabatame and Tadaaki Nagao

Micromachines 2020, 11(1), 23; https://doi.org/10.3390/mi11010023 - 24 Dec 2019

Cited by 6 | Viewed by 3361

Abstract

Among conductive oxide materials, niobium doped titanium dioxide has recently emerged as a stimulating and promising contestant for numerous applications. With carrier concentration tunability, high thermal stability, mechanical and environmental robustness, this is a material-of-choice for infrared plasmonics, which can substitute indium tin [...] Read more.

Among conductive oxide materials, niobium doped titanium dioxide has recently emerged as a stimulating and promising contestant for numerous applications. With carrier concentration tunability, high thermal stability, mechanical and environmental robustness, this is a material-of-choice for infrared plasmonics, which can substitute indium tin oxide (ITO). In this report, to illustrate great advantages of this material, we describe successful fabrication and characterization of niobium doped titanium oxide nanoantenna arrays aiming at surface-enhanced infrared absorption spectroscopy. The niobium doped titanium oxide film was deposited with co-sputtering method. Then the nanopatterned arrays were prepared by electron beam lithography combined with plasma etching and oxygen plasma ashing processes. The relative transmittance of the nanostrip and nanodisk antenna arrays was evaluated with Fourier transform infrared spectroscopy. Polarization dependence of surface plasmon resonances on incident light was examined confirming good agreements with calculations. Simulated spectra also present red-shift as length, width or diameter of the nanostructures increase, as predicted by classical antenna theory. Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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10 pages, 2526 KiB

Open AccessArticle

Dark-Field Scattering and Local SERS Mapping from Plasmonic Aluminum Bowtie Antenna Array

by Thang Duy Dao, Chung Vu Hoang, Natsuki Nishio, Naoki Yamamoto, Akihiko Ohi, Toshihide Nabatame, Masakazu Aono and Tadaaki Nagao

Micromachines 2019, 10(7), 468; https://doi.org/10.3390/mi10070468 - 13 Jul 2019

Cited by 8 | Viewed by 4183

Abstract

On the search for the practical plasmonic materials beyond noble metals, aluminum has been emerging as a favorable candidate as it is abundant and offers the possibility of tailoring the plasmonic resonance spanning from ultra-violet to the infrared range. In this letter, in [...] Read more.

On the search for the practical plasmonic materials beyond noble metals, aluminum has been emerging as a favorable candidate as it is abundant and offers the possibility of tailoring the plasmonic resonance spanning from ultra-violet to the infrared range. In this letter, in combination with the numerical electromagnetic simulations, we experimentally study the dark-field scattering spectral mapping of plasmonic resonance from the free-standing Al bowtie antenna arrays and correlate their strong nearfield enhancement with the sensing capability by means of surface-enhanced Raman spectroscopy. The spatial matching of plasmonic and Raman mapping puts another step to realize a very promising application of free-standing Al bowtie antennas for plasmonic sensing. Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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12 pages, 2802 KiB

Open AccessArticle

MEMS-Based Wavelength-Selective Bolometers

by Thang Duy Dao, Anh Tung Doan, Satoshi Ishii, Takahiro Yokoyama, Handegård Sele Ørjan, Dang Hai Ngo, Tomoko Ohki, Akihiko Ohi, Yoshiki Wada, Chisato Niikura, Shinsuke Miyajima, Toshihide Nabatame and Tadaaki Nagao

Micromachines 2019, 10(6), 416; https://doi.org/10.3390/mi10060416 - 21 Jun 2019

Cited by 20 | Viewed by 6252

Abstract

We propose and experimentally demonstrate a compact design for membrane-supported wavelength-selective infrared (IR) bolometers. The proposed bolometer device is composed of wavelength-selective absorbers functioning as the efficient spectroscopic IR light-to-heat transducers that make the amorphous silicon (a-Si) bolometers respond at the desired resonance [...] Read more.

We propose and experimentally demonstrate a compact design for membrane-supported wavelength-selective infrared (IR) bolometers. The proposed bolometer device is composed of wavelength-selective absorbers functioning as the efficient spectroscopic IR light-to-heat transducers that make the amorphous silicon (a-Si) bolometers respond at the desired resonance wavelengths. The proposed devices with specific resonances are first numerically simulated to obtain the optimal geometrical parameters and then experimentally realized. The fabricated devices exhibit a wide resonance tunability in the mid-wavelength IR atmospheric window by changing the size of the resonator of the devices. The measured spectral response of the fabricated device wholly follows the pre-designed resonance, which obviously evidences that the concept of the proposed wavelength-selective IR bolometers is realizable. The results obtained in this work provide a new solution for on-chip MEMS-based wavelength-selective a-Si bolometers for practical applications in IR spectroscopic devices. Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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12 pages, 6027 KiB

Open AccessArticle

A MEMS-Based Quad-Wavelength Hybrid Plasmonic–Pyroelectric Infrared Detector

by Anh Tung Doan, Takahiro Yokoyama, Thang Duy Dao, Satoshi Ishii, Akihiko Ohi, Toshihide Nabatame, Yoshiki Wada, Shigenao Maruyama and Tadaaki Nagao

Micromachines 2019, 10(6), 413; https://doi.org/10.3390/mi10060413 - 21 Jun 2019

Cited by 16 | Viewed by 8300

Abstract

Spectrally selective detection is of crucial importance for diverse modern spectroscopic applications such as multi-wavelength pyrometry, non-dispersive infrared gas sensing, biomedical analysis, flame detection, and thermal imaging. This paper reports a quad-wavelength hybrid plasmonic–pyroelectric detector that exhibited spectrally selective infrared detection at four [...] Read more.

Spectrally selective detection is of crucial importance for diverse modern spectroscopic applications such as multi-wavelength pyrometry, non-dispersive infrared gas sensing, biomedical analysis, flame detection, and thermal imaging. This paper reports a quad-wavelength hybrid plasmonic–pyroelectric detector that exhibited spectrally selective infrared detection at four wavelengths—3.3, 3.7, 4.1, and 4.5 μm. The narrowband detection was achieved by coupling the incident infrared light to the resonant modes of the four different plasmonic perfect absorbers based on Al-disk-array placed on a Al₂O₃–Al bilayer. These absorbers were directly integrated on top of a zinc oxide thin film functioning as a pyroelectric transducer. The device was fabricated using micro-electromechanical system (MEMS) technology to optimize the spectral responsivity. The proposed detector operated at room temperature and exhibited a responsivity of approximately 100–140 mV/W with a full width at half maximum of about 0.9–1.2 μm. The wavelength tunability, high spectral resolution, compactness and robust MEMS-based platform of the hybrid device demonstrated a great advantage over conventional photodetectors with bandpass filters, and exhibited impressive possibilities for miniature multi-wavelength spectroscopic devices. Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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16 pages, 5153 KiB

Open AccessArticle

Efficient Fabrication Process of Ordered Metal Nanodot Arrays for Infrared Plasmonic Sensor

by Masahiko Yoshino, Yusuke Kubota, Yuki Nakagawa and Motoki Terano

Micromachines 2019, 10(6), 385; https://doi.org/10.3390/mi10060385 - 8 Jun 2019

Cited by 5 | Viewed by 3222

Abstract

In this paper, a simple process to fabricate ordered Au nanodot arrays up to 520 nm in diameter that respond to infrared light is developed, and the feasibility of its application to infrared plasmonic sensors is shown. The developed process utilizes thermal dewetting [...] Read more.

In this paper, a simple process to fabricate ordered Au nanodot arrays up to 520 nm in diameter that respond to infrared light is developed, and the feasibility of its application to infrared plasmonic sensors is shown. The developed process utilizes thermal dewetting to agglomerate a coated gold film into nanodots. It was difficult to produce large nanodots that responded to infrared light owing to dot separation. In this paper, therefore, the mechanism of dot agglomeration by thermal dewetting is studied via an experiment and theoretical model, and conditions to form single nanodots are clarified. Furthermore, Au nanodot arrays of 100 nm to 520 nm in diameter were fabricated by this process, and their absorption spectra were analyzed. In addition, an analysis of the change in the peak wavelength against the refractive index indicates the possibility of further improvement of the sensitivity of the infrared plasmon sensors. Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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8 pages, 1749 KiB

Open AccessArticle

Indium–Tin–Oxide Nanostructures for Plasmon-Enhanced Infrared Spectroscopy: A Numerical Study

by Zhangbo Li, Zhiliang Zhang and Kai Chen

Micromachines 2019, 10(4), 241; https://doi.org/10.3390/mi10040241 - 11 Apr 2019

Cited by 6 | Viewed by 4831

Abstract

Plasmonic nanoantennas can significantly enhance the light–matter interactions at the nanoscale, and as a result have been used in a variety of applications such as sensing molecular vibrations in the infrared range. Indium–tin–oxide (ITO) shows metallic behavior in the infrared range, and can [...] Read more.

Plasmonic nanoantennas can significantly enhance the light–matter interactions at the nanoscale, and as a result have been used in a variety of applications such as sensing molecular vibrations in the infrared range. Indium–tin–oxide (ITO) shows metallic behavior in the infrared range, and can be used for alternative plasmonic materials. In this work, we numerically studied the optical properties of hexagonal ITO nanodisk and nanohole arrays in the mid-infrared. Field enhancement up to 10 times is observed in the simulated ITO nanostructures. Furthermore, we demonstrated the sensing of the surface phonon polariton from a 2-nm thick SiO₂ layer under the ITO disk arrays. Such periodic arrays can be readily fabricated by colloidal lithography and dry etching techniques; thus, the results shown here can help design efficient ITO nanostructures for plasmonic infrared applications. Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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7 pages, 4221 KiB

Open AccessArticle

Effect of Etching Depth on Threshold Characteristics of GaSb-Based Middle Infrared Photonic-Crystal Surface-Emitting Lasers

by Zong-Lin Li, Shen-Chieh Lin, Gray Lin, Hui-Wen Cheng, Kien-Wen Sun and Chien-Ping Lee

Micromachines 2019, 10(3), 188; https://doi.org/10.3390/mi10030188 - 14 Mar 2019

Cited by 7 | Viewed by 3187

Abstract

We study the effect of etching depth on the threshold characteristics of GaSb-based middle infrared (Mid-IR) photonic-crystal surface-emitting lasers (PCSELs) with different lattice periods. The below-threshold emission spectra are measured to identify the bandgap as well as band-edge modes. Moreover, the bandgap separation [...] Read more.

We study the effect of etching depth on the threshold characteristics of GaSb-based middle infrared (Mid-IR) photonic-crystal surface-emitting lasers (PCSELs) with different lattice periods. The below-threshold emission spectra are measured to identify the bandgap as well as band-edge modes. Moreover, the bandgap separation widens with increasing etching depth as a result of enhanced diffraction feedback coupling. However, the coupling is nearly independent of lattice period. The relationship between threshold gain and Bragg detuning is also experimentally determined for PCSELs and is similar to that calculated theoretically for one-dimensional distributed feedback lasers. Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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8 pages, 2146 KiB

Open AccessArticle

Design and Fabrication of a Wavelength-Selective Near-Infrared Metasurface Emitter for a Thermophotovoltaic System

by Atsushi Sakurai and Yuki Matsuno

Micromachines 2019, 10(2), 157; https://doi.org/10.3390/mi10020157 - 25 Feb 2019

Cited by 17 | Viewed by 4925

Abstract

In this study, a tungsten-SiO₂-based metal–insulator–metal-structured metasurface for the thermal emitter of the thermophotovoltaic system was designed and fabricated. The proposed emitter was fabricated by applying the photolithography method. The fabricated emitter has high emissivity in the visible to near-infrared region [...] Read more.

In this study, a tungsten-SiO₂-based metal–insulator–metal-structured metasurface for the thermal emitter of the thermophotovoltaic system was designed and fabricated. The proposed emitter was fabricated by applying the photolithography method. The fabricated emitter has high emissivity in the visible to near-infrared region and shows excellent wavelength selectivity. This spectral emissivity tendency agreed well with the result calculated by the finite-difference time-domain method. Additionally, the underlying mechanism of its emission was scrutinized. Study of the fabrication process and theoretical mechanisms of the emission, clarified in this research, will be fundamental to design the wavelength-selective thermal emitter. Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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9 pages, 2484 KiB

Open AccessFeature PaperArticle

Development of a New Laparoscopic Detection System for Gastric Cancer Using Near-Infrared Light-Emitting Clips with Glass Phosphor

by Shunko A. Inada, Hayao Nakanishi, Masahiro Oda, Kensaku Mori, Akihiro Ito, Junichi Hasegawa, Kazunari Misawa and Shingo Fuchi

Micromachines 2019, 10(2), 81; https://doi.org/10.3390/mi10020081 - 24 Jan 2019

Cited by 1 | Viewed by 3061

Abstract

Laparoscopic surgery is now a standard treatment for gastric cancer. Currently, the location of the gastric cancer is identified during laparoscopic surgery via the preoperative endoscopic injection of charcoal ink around the primary tumor; however, the wide spread of injected charcoal ink can [...] Read more.

Laparoscopic surgery is now a standard treatment for gastric cancer. Currently, the location of the gastric cancer is identified during laparoscopic surgery via the preoperative endoscopic injection of charcoal ink around the primary tumor; however, the wide spread of injected charcoal ink can make it difficult to accurately visualize the specific site of the tumor. To precisely identify the locations of gastric tumors, we developed a fluorescent detection system comprising clips with glass phosphor (Yb³⁺, Nd³⁺ doped to Bi₂O₃-B₂O₃-based glasses, size: 2 mm × 1 mm × 3 mm) fixed in the stomach and a laparoscopic fluorescent detection system for clip-derived near-infrared (NIR) light (976 nm). We conducted two ex vivo experiments to evaluate the performance of this fluorescent detection system in an extirpated pig stomach and a freshly resected human stomach and were able to successfully detect NIR fluorescence emitted from the clip in the stomach through the stomach wall by the irradiation of excitation light (λ: 808 nm). These results suggest that the proposed combined NIR light-emitting clip and laparoscopic fluorescent detection system could be very useful in clinical practice for accurately identifying the location of a primary gastric tumor during laparoscopic surgery. Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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20 pages, 21098 KiB

Open AccessArticle

Optical Properties of Au-Based and Pt-Based Alloys for Infrared Device Applications: A Combined First Principle and Electromagnetic Simulation Study

by Min-Hsueh Chiu, Jia-Han Li and Tadaaki Nagao

Micromachines 2019, 10(1), 73; https://doi.org/10.3390/mi10010073 - 20 Jan 2019

Cited by 9 | Viewed by 4254

Abstract

Due to the rapid progress in MEMS-based infrared emitters and sensors, strong demand exists for suitable plasmonic materials for such microdevices. We examine the possibility of achieving this goal by alloying other metals with the noble metals Au and Pt, which have some [...] Read more.

Due to the rapid progress in MEMS-based infrared emitters and sensors, strong demand exists for suitable plasmonic materials for such microdevices. We examine the possibility of achieving this goal by alloying other metals with the noble metals Au and Pt, which have some drawbacks, such as low melting point, structural instability, and high costs. The six different metals (Ir, Mo, Ni, Pb, Ta, and W) which possess good properties for heat resistance, stability, and magnetism are mixed with noble metals to improve the properties. The optical properties are calculated by density functional theory and they are used for further investigations of the optical responses of alloy nanorods. The results show that the studied alloy nanorods have wavelength selective properties and can be useful for infrared devices and systems. Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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8 pages, 2257 KiB

Open AccessArticle

Voltage-Tunable Mid- and Long-Wavelength Dual-Band Infrared Photodetector Based on Hybrid Self-Assembled and Sub-Monolayer Quantum Dots

by Yao Zhai, Guiru Gu and Xuejun Lu

Micromachines 2019, 10(1), 4; https://doi.org/10.3390/mi10010004 - 22 Dec 2018

Cited by 9 | Viewed by 3710

Abstract

In this paper, we report a mid-wave infrared (MWIR) and long-wave infrared (LWIR) dual-band photodetector capable of voltage-controllable detection band selection. The voltage-tunable dual-band photodetector is based on the multiple stacks of sub-monolayer (SML) quantum dots (QDs) and self-assembled QDs. By changing the [...] Read more.

In this paper, we report a mid-wave infrared (MWIR) and long-wave infrared (LWIR) dual-band photodetector capable of voltage-controllable detection band selection. The voltage-tunable dual-band photodetector is based on the multiple stacks of sub-monolayer (SML) quantum dots (QDs) and self-assembled QDs. By changing the photodetector bias voltages, one can set the detection band to be MWIR, or LWIR or both with high photodetectivity and low crosstalk between the bands. Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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9 pages, 2192 KiB

Open AccessArticle

A Trace Carbon Monoxide Sensor Based on Differential Absorption Spectroscopy Using Mid-Infrared Quantum Cascade Laser

by Chen Chen, Qiang Ren, Heng Piao, Peng Wang and Yanzhang Wang

Micromachines 2018, 9(12), 670; https://doi.org/10.3390/mi9120670 - 18 Dec 2018

Cited by 5 | Viewed by 4377

Abstract

Carbon monoxide (CO), as a dangerous emission gas, is easy to accumulate in the complex underground environment and poses a serious threat to the safety of miners. In this paper, a sensor using a quantum cascade laser with an excitation wavelength of 4.65 [...] Read more.

Carbon monoxide (CO), as a dangerous emission gas, is easy to accumulate in the complex underground environment and poses a serious threat to the safety of miners. In this paper, a sensor using a quantum cascade laser with an excitation wavelength of 4.65 μm as the light source, and a compact multiple reflection cell with a light path length of 12 m is introduced to detect trace CO gas. The sensor adopts the long optical path differential absorption spectroscopy technique (LOP-DAST) and obtains minimum detection limit (MDL) of 108 ppbv by comparing the residual difference between the measured spectrum and the Voigt theoretical spectrum. As a comparison, the MDL of the proposed sensor was also estimated by Allan deviation; the minimum value of 61 ppbv is achieved while integration time is 40 s. The stability of the sensor can reach 2.1 × 10⁻³ during the 2 h experimental test and stability of 1.7 × 10⁻² can still be achieved in a longer 12 h experimental test. Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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10 pages, 2075 KiB

Open AccessArticle

A Trace C₂H₂ Sensor Based on an Absorption Spectrum Technique Using a Mid-Infrared Interband Cascade Laser

by Ye Mu, Tianli Hu, He Gong, Ruiwen Ni and Shijun Li

Micromachines 2018, 9(10), 530; https://doi.org/10.3390/mi9100530 - 19 Oct 2018

Cited by 16 | Viewed by 3784

Abstract

In this study, tunable diode laser absorption spectroscopy (TDLAS) combined with wavelength modulation spectroscopy (WMS) was used to develop a trace C₂H₂ sensor based on the principle of gas absorption spectroscopy. The core of this sensor is an interband cascade [...] Read more.

In this study, tunable diode laser absorption spectroscopy (TDLAS) combined with wavelength modulation spectroscopy (WMS) was used to develop a trace C₂H₂ sensor based on the principle of gas absorption spectroscopy. The core of this sensor is an interband cascade laser that releases wavelength locks to the best absorption line of C₂H₂ at 3305 cm⁻¹ (3026 nm) using a driving current and a working temperature control. As the detected result was influenced by 1/f noise caused by the laser or external environmental factors, the TDLAS-WMS technology was used to suppress the 1/f noise effectively, to obtain a better minimum detection limit (MDL) performance. The experimental results using C₂H₂ gas with five different concentrations show a good linear relationship between the peak value of the second harmonic signal and the gas concentration, with a linearity of 0.9987 and detection accuracy of 0.4%. In total, 1 ppmv of C₂H₂ gas sample was used for a 2 h observation experiment. The data show that the MDL is low as 1 ppbv at an integration time of 63 s. In addition, the sensor can be realized by changing the wavelength of the laser to detect a variety of gases, which shows the flexibility and practicability of the proposed sensor. Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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17 pages, 1875 KiB

Open AccessArticle

Midwave FTIR-Based Remote Surface Temperature Estimation Using a Deep Convolutional Neural Network in a Dynamic Weather Environment

by Sungho Kim, Jungho Kim, Jinyong Lee and Junmo Ahn

Micromachines 2018, 9(10), 495; https://doi.org/10.3390/mi9100495 - 27 Sep 2018

Cited by 8 | Viewed by 2939

Abstract

Remote measurements of thermal radiation are very important for analyzing the solar effect in various environments. This paper presents a novel real-time remote temperature estimation method by applying a deep learning-based regression method to midwave infrared hyperspectral images. A conventional remote temperature estimation [...] Read more.

Remote measurements of thermal radiation are very important for analyzing the solar effect in various environments. This paper presents a novel real-time remote temperature estimation method by applying a deep learning-based regression method to midwave infrared hyperspectral images. A conventional remote temperature estimation using only one channel or multiple channels cannot provide a reliable temperature in dynamic weather environments because of the unknown atmospheric transmissivities. This paper solves the issue (real-time remote temperature measurement with high accuracy) with the proposed surface temperature-deep convolutional neural network (ST-DCNN) and a hyperspectral thermal camera (TELOPS HYPER-CAM MWE). The 27-layer ST-DCNN regressor can learn and predict the underlying temperatures from 75 spectral channels. Midwave infrared hyperspectral image data of a remote object were acquired three times a day (10:00, 13:00, 15:00) for 7 months to consider the dynamic weather variations. The experimental results validate the feasibility of the novel remote temperature estimation method in real-world dynamic environments. In addition, the thermal stealth properties of two types of paint were demonstrated by the proposed ST-DCNN as a real-world application. Full article

(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)

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