The study of ideal absorbers, which can efficiently absorb light over a broad range of wavelengths, is of fundamental importance, as well as critical for many applications from solar steam generation and thermophotovoltaics to light/thermal detectors. As a result of recent advances in plasmonics, plasmonic absorbers have attracted a lot of attention. However, the performance and scalability of these absorbers, predominantly fabricated by the top-down approach, need to be further improved to enable widespread applications. We report a plasmonic absorber which can enable an average measured absorbance of ~99% across the wavelengths from 400 nm to 10 μm, the most efficient and broadband plasmonic absorber reported to date. The absorber is fabricated through self-assembly of metallic nanoparticles onto a nanoporous template by a one-step deposition process. Because of its efficient light absorption, strong field enhancement, and porous structures, which together enable not only efficient solar absorption but also significant local heating and continuous stream flow, plasmonic absorber–based solar steam generation has over 90% efficiency under solar irradiation of only 4-sun intensity (4 kW m−2). The pronounced light absorption effect coupled with the high-throughput self-assembly process could lead toward large-scale manufacturing of other nanophotonic structures and devices.

Self-assembly of highly efficient, broadband plasmonic absorbers for solar steam generation.

Self-assemblyof highly efficient, broadband plasmonic absorbersfor solar steam generation

Electromagnetic Response and Energy Conversion for Functions and Devices in Low‐Dimensional Materials

Compact solid-state sources of terahertz (THz) radiation are being sought for sensing, imaging, and spectroscopy applications across the physical and biological sciences. We demonstrate that coherent continuous-wave THz radiation of sizable power can be extracted from intrinsic Josephson junctions in the layered high-temperature superconductor Bi2Sr2CaCu2O8. In analogy to a laser cavity, the excitation of an electromagnetic cavity resonance inside the sample generates a macroscopic coherent state in which a large number of junctions are synchronized to oscillate in phase. The emission power is found to increase as the square of the number of junctions reaching values of 0.5 microwatt at frequencies up to 0.85 THz, and persists up to ∼50 kelvin. These results should stimulate the development of superconducting compact sources of THz radiation.

http://absimage.aps.org/image/MAR08/MWS_MAR08-2007-004672.pdf

Emission of Coherent THz-Radiation from Superconductors.

Inspired by nanoscience and nanoengineering, numerous nanostructured materials developed by multidisciplinary approaches exhibit excellent photoelectronic properties ranging from ultraviolet to terahertz frequencies. As a new class of building block, nanoscale elements in terms of quantum dots, nanowires, and nanolayers can be used for fabricating photodetectors with high performance. Moreover, in conjunction with traditional photodetectors, they exhibit appealing performance for practical applications including high density of integration, high sensitivity, fast response, and multifunction. Therefore, with the perspective of photodetectors constructed by diverse low-dimensional nanostructured materials, recent advances in nanoscale photodetectors are discussed here; meanwhile, challenges and promising future directions in this research field are proposed.

Nanostructured Photodetectors: From Ultraviolet to Terahertz.

Terahertz (THz) technologies are promising for diverse areas such as medicine, bioengineering, astronomy, environmental monitoring, and communications. However, despite decades of worldwide efforts, the THz region of the electromagnetic spectrum still continues to be elusive for solid state technology. Here, we report on the development of a powerless, compact, broadband, flexible, large-area, and polarization-sensitive carbon nanotube THz detector that works at room temperature. The detector is sensitive throughout the entire range of the THz technology gap, with responsivities as high as ∼2.5 V/W and polarization ratios as high as ∼5:1. Complete thermoelectric and opto-thermal characterization together unambiguously reveal the photothermoelectric origin of the THz photosignal, triggered by plasmonic absorption and collective antenna effects, and suggest that judicious design of thermal management and quantum engineering of Seebeck coefficients will lead to further enhancement of device performance.

http://nanojapan.rice.edu/Downloads/Papers/2014_NanoLetters_Lloyd,%20Meagan%20and%20He,%20Xiaowei.pdf

Carbon Nanotube Terahertz Detector

Carbon nanotubes (CNTs) have emerged as promising materials for visible, infrared, and terahertz photodetectors Further development of these photodetectors requires a fundamental understanding of the mechanisms that govern their behavior as well as the establishment of figures of merit for technology applications Recently, a number of CNT detectors have been shown to operate based on the photothermoelectric effect Here we present a figure of merit for these detectors, which includes the properties of the material and the device In addition, we use a suite of experimental characterization methods for the thorough analysis of the electrical, thermoelectric, electrothermal, and photothermal properties of the CNT thin-film devices Our measurements determine the quantities that enter the figure of merit and allow us to establish a path toward future performance improvements

Figure of Merit for Carbon Nanotube Photothermoelectric Detectors.

The increasing interest in mobile and wearable technology demands the enhancement of functionality of clothing through incorporation of sophisticated architectures of multifunctional materials. Flexible electronic and photonic devices based on organic materials have made impressive progress over the past decade, but higher performance, simpler fabrication, and most importantly, compatibility with woven technology are desired. Here we report on the development of a weaved, substrateless, and polarization-sensitive photodetector based on doping-engineered fibers of highly aligned carbon nanotubes. This room-temperature-operating, self-powered detector responds to radiation in an ultrabroad spectral range, from the ultraviolet to the terahertz, through the photothermoelectric effect, with a low noise-equivalent power (a few ${\mathrm{nW}/\mathrm{Hz}}^{1/2}$) throughout the range and with a $ZT$-factor value that is twice as large as that of previously reported carbon nanotube-based photothermoelectric photodetectors. Particularly, we fabricated a $\ensuremath{\sim}1$-m-long device consisting of tens of ${p}^{+}\text{\ensuremath{-}}{p}^{\ensuremath{-}}$ junctions and weaved it into a shirt. This device demonstrated a collective photoresponse of the series-connected junctions under global illumination. The performance of the device did not show any sign of deterioration through 200 bending tests with a bending radius smaller than 100 $\ensuremath{\mu}\mathrm{m}$ as well as standard washing and ironing cycles. This unconventional photodetector will find applications in wearable technology that require detection of electromagnetic radiation.

https://link.aps.org/accepted/10.1103/PhysRevMaterials.2.015201

Carbon nanotube woven textile photodetector

Nanostructured dopant-based silicon (Si) transistors are promising candidates for high-performance photodetectors and quantum information devices. For highly doped Si with donor bands, the energy depth of donor levels and the energy required for tunneling processes between donor levels are typically on the order of millielectron volts, corresponding to terahertz (THz) photon energy. Owing to these properties, highly doped Si quantum dots (QDs) are highly attractive as THz photoconductive detectors. Here, we demonstrate THz detection with a lithographically defined and highly phosphorus-doped Si QD. We integrate a 40 nm-diameter QD with a micrometer-scale broadband logarithmic spiral antenna for the detection of THz photocurrent in a wide frequency range from 0.58 to 3.11 THz. Furthermore, we confirm that the detection sensitivity is enhanced by a factor of ~880 compared to a QD detector without an antenna. These results demonstrate the ability of a highly doped-Si QD coupled with an antenna to detect broadband THz waves. By optimizing the dopant distribution and levels, further performance improvements are feasible.

/pdf/terahertz-detection-with-an-antenna-coupled-highly-doped-e09rcqeh7p.pdf

Terahertz detection with an antenna-coupled highly-doped silicon quantum dot.

A detailed analysis of micro- and nanoantennas is crucial for enhancing the performance of photodetectors in the mid- and far-infrared (IR) region. In contrast to the rapid progress in IR detectors based on nanodevices, the local nanoscale properties of antennas for the purpose of near-field coupling with these detectors have not been well investigated. In this work, we fabricated and studied a logarithm-spiral (log-spiral) antenna with an arm termination, which was designed as a low-loss, wide-band antenna for highly efficient near-field interaction with nanoscale IR detectors. By using a scattering-type near-field optical microscope (s-SNOM) combined with a highly stable quantum cascade laser, we observed a nanoscale spatial distribution of amplitudes generated via IR illumination on the antenna surface. Experimental and simulated results revealed a clear dependence on IR-light polarization corresponding to the rotationally symmetric structure of the spiral antenna. Furthermore, phase mapping measurements indicated a π reversal of the out-of-plane phase between two adjacent antenna probes regardless of polarization direction, providing a possibility of efficient near-field coupling with nanoscale detectors. These results demonstrate that s-SNOM imaging offers a powerful tool for gaining useful information regarding mutual coupling between optical antennas and nanostructures.

Naoki Fujimura

Papers

Carbon Nanotube Terahertz Detector

Figure of Merit for Carbon Nanotube Photothermoelectric Detectors.

Carbon nanotube woven textile photodetector

Terahertz detection with an antenna-coupled highly-doped silicon quantum dot.

Near-field infrared investigations of an arm-terminated spiral structure with bow-tie probe