Kou Li

The optical nature of ultra‐broadband millimeter‐wave–visible‐light non‐destructive inspection requires noise suppression of sensors and their appropriate operations for higher‐intensity laser irradiation to flexibly choose photo‐sources. While carbon nanotube (CNT) soft photo‐thermoelectric sensors facilitate compact ultra‐broadband monitoring, their conventional designs focus on noise. In short, efforts are insufficient for evaluating photo‐response dynamic ranges and the fundamental behavior for higher‐intensity irradiation. This work clarifies the surface adhesiveness of substrates dominantly controls response dynamic ranges of CNT sensors against higher‐intensity photo‐irradiation. The proposed CNT sensor design strategy experimentally demonstrates that higher‐intensity irradiation transfers the inherent pn‐junction photo‐detection interface to undesired n‐type channels. This work suggests adhesive chemicals of the device substrate surface function as unnecessary electron‐donating groups on the entire pn‐junction CNT film triggered by irradiation‐induced heating. The device properly maintains the photo‐detection interface for higher‐intensity irradiation by appropriately designing the material composition and size for CNTs on non‐adhesive substrates. This work realizes the associated CNT sensor operation at 10–100 mV response ranges customizable within diverse instruments. The optimized CNT sensor on non‐adhesive substrates finally expands its photo‐response upper‐limit (112 mV) from that (9.98 mV) on adhesive tapes. Such approaches develop user‐friendly CNT film photo‐thermoelectric sensors and ubiquitous social non‐destructive inspection.

Longer‐wavelength (LW) computer vision (CV) monitoring techniques hold great potential as non‐destructive testing tools for daily necessities and industrial products, utilizing effective optical properties. Carbon nanotube (CNT) film photo‐thermoelectric image sensors facilities, such CV systems as broadband wavelength range operations over existing narrow‐band detectors at comparable sensitivity with them owing to the inherent advantageous material properties. Nevertheless, insufficient pixel integration of CNT image sensors requires extensive and time‐costing optical spatial scanning for CV measurements, limiting practical inspection applications at real‐time industrial sites. To this end, this work demonstrates LW computed tomography (CT, a representative CV method) monitoring system employing a 2D pixel‐array integrated CNT film PTE camera sheet and multi‐wavelength photo‐sources. The camera fabrication process utilizes air‐jet dispense‐printing and achieves high‐yield integration of CNT film pixels (20 mm‐15 mm‐sq. for pixel area, 60 pixels total). This work then performs structure reconstruction and material identification of a visibly opaque multi‐layered composite 3D object according to optical properties in the 976 nm–10.3 µm wavelength range by LW CT with the device. The presented CNT film camera completes its LW operation in ≈11 min for each wavelength, a 36.9 % time reduction compared to previous CT systems using 1D pixel‐array sensors.

Infrared (IR) detection technologies are central to applications ranging from molecular fingerprinting to next‐generation wireless communication systems. However, developing uncooled, high‐sensitivity IR photodetectors remains challenging due to the low photon energy in this spectral range. This study reports a rational design strategy for enhancing the photothermoelectric (PTE) response by using semiconducting single‐walled carbon nanotubes (CNTs) with precisely tailored electronic and thermal transport properties. The PTE sensitivity is increased through structural sorting, controlled chemical doping, and passivation, relative to devices fabricated with unsorted CNTs. This enhancement arises from a synergistic interplay between plasmon‐enabled photothermal excitation and optimized thermoelectric transport properties, including an increased effective Seebeck coefficient and suppressed thermal conductivity, which together enable stronger temperature gradients upon IR irradiation. These findings establish a design principle for integrating light absorption, heat management, and charge transport in nanostructured materials, supporting the development of efficient, scalable, ambient‐operable IR sensing platforms.

While recent industrial automation trends emphasize the importance of non-destructive inspection by material-identifying millimeter-wave, terahertz-wave, and infrared (MMW, THz, IR) monitoring, fundamental tools in these wavelength bands (such as sensors) are still immature. Although inorganic semiconductors serve as diverse sensors with well-established large-scale fine-processing fabrication, the use of those devices is insufficient for non-destructive monitoring due to the lack of photo-absorbent properties for such major materials in partial regions across MMW–IR wavelengths. To satisfy the inherent advantageous non-destructive MMW–IR material identification, ultrabroadband operation is indispensable for photo-sensors under compact structure, flexible designability, and sensitive performances. This review then introduces the recent advances of carbon nanotube film-based photo-thermoelectric imagers regarding usable and high-yield device fabrication techniques and scientific synergy among computer vision to collectively satisfy material identification with three-dimensional (3D) structure reconstruction. This review synergizes material science, printable electronics, high-yield fabrication, sensor devices, optical measurements, and imaging into guidelines as functional non-destructive inspection platforms. The motivation of this review is to introduce the recent scientific fusion of MMW–IR sensors with visible-light computer vision, and emphasize its significance (non-invasive material-identifying sub-millimeter-resolution 3D-reconstruction with 660 nm–1.15 mm-wavelength imagers at noise equivalent power within 100 pWHz^−1/2) among the existing testing methods.

While non-destructive in-line monitoring at manufacturing sites is essential for safe distribution cycles of pharmaceuticals, efforts are still insufficient to develop analytical systems for detailed dynamic visualisation of foreign substances and material composition in target pills. Although spectroscopies, expected towards pharma testing, have faced technical challenges in in-line setups for bulky equipment housing, this work demonstrates compact dynamic photo-monitoring systems by selectively extracting informative irradiation-wavelengths from comprehensive optical references of target pills. This work develops a non-destructive in-line dynamic inspection system for pharma agent pills with carbon nanotube (CNT) photo-thermoelectric imagers and the associated ultrabroadband sub-terahertz (THz)–infrared (IR) multi-wavelength monitoring. The CNT imager in the proposed system functions in ultrabroadband regions over existing sensors, facilitating multi-wavelength photo-monitoring against external sub-THz–IR-irradiation. Under recent advances in the investigation of functional optical materials (e.g., gallium arsenide, vanadium oxide, graphene, polymers, transition metal dichalcogenides), CNTs play advantageous leading roles in collectively satisfying informative efficient photo-absorption and solution-processable configurations for printable device fabrication into freely attachable thin-film imagers in pharma monitoring sites. The above non-destructive dynamic monitoring system maintains in-line experimental setups by integrating the functional thin-film imager sheets and compact multiple photo-sources. Furthermore, permeable sub-THz–IR-irradiation, which provides different transmittance values specific to non-metallic materials per wavelength or composition, identifies constituent materials for pharma agents themselves and concealed foreign substances in a non-contact manner. This work finally inspects invisible detailed features of pharma pills with the non-destructive in-line dynamic photo-monitoring system by incorporating performances of CNT imagers and compact optical setups.

Carbon nanotube (CNT) film-based photo-thermoelectric (PTE) imagers perform functional electromagnetic-wave monitoring, potentially facilitating multimodal non-destructive inspection device usage. The CNT film compositions govern the fundamental device performance, and satisfying high PTE conversion efficiency (higher response and lower noise) is essential for sensitive operations. Although typical sensitive design focuses on minimizing noise, the associated leveling-off response intensity (up to a few millivolts) induces technical limitations in device operations. These issues include mismatching for coupling with compact wireless circuits, being indispensable for on-site inspection applications, and require high-intensity responses at least a few millivolt orders. This work develops chemically enriched PTE imagers comprising semiconducting-separated CNT (semi-CNT) films. While semi-CNTs provide greater intensity thermoelectric responses than semi-metal mixture compositions in the conventional PTE device, the presented imager employs p-/n-type chemical carrier doping to relax inherent significant bottlenecking noise. Such doping enhances material properties for PTE conversion with semi-CNTs up to 4060 times. The imager satisfies similar performances to conventional CNT film devices, including ultrabroadband sensitive photo-detection (with minimum noise sensitivity of 5 pWHz^−1/2) under repeatedly deformable configurations, and advantageously exhibits response signal intensity exceeding a few–tens of millivolts. These features enable remote on-site non-destructive PTE imaging inspection with palm-sized wireless circuits.

While photo-thermoelectric (PTE) sensors and their ultrabroadband monitoring facilitate non-destructive testing, their conventional fabrication is insufficient for high-yield integration. Specifically, PTE devices faced challenges in their crucial spatial-misalignment for separate fabrication processes per constituent. Herein, this work demonstrates mechanically alignable and all-dispenser-printable integration of carbon nanotube (CNT) functional PTE sensor devices by designing them with solution-processable ink-materials. This technique first accurately prints CNT channels, essential in PTE conversion, using higher-concentration inks, and integrates remaining constituents (dopants and conductive pastes) into single device structures at high-yield. This work further demonstrates that employing higher-concentration CNT inks, suitable for mechanical channel printing, also designs sensitive PTE sensors. These sensors serve stably as integrated devices on diverse functional substrates, facilitating ubiquitous non-destructive monitoring depending on features. Therefore, this work designs such CNT PTE integrated devices and the associated functional inspection appropriately for structures, sizes, and external environments (e.g., temperature and humidity) of monitoring targets.

Photo‐thermoelectric (PTE) conversion with soft carbon nanotube (CNT) thin‐films potentially facilitates non‐destructive inspections as image sensor devices through ultrabroadband optical monitoring and freely attachable 3D omni‐directional views. Toward real‐time and large‐area measurements, printing fabrication methods are effective for multi‐pixel integrations of all‐solution‐processable CNT film PTE sensors. However, the conventional printing method of CNT PTE sensors yields fatally low‐efficient in fabricating each pixel due to insufficient diffusion of n‐type liquid dopants on the pristine p‐type film channels. Herein, this work demonstrates high‐yield fabrications of pn‐junction type PTE sensors by employing p‐/n‐type CNT inks. For such conceptualization, the presenting strategy first develops all‐solution‐processable n‐type CNT inks. Specifically, this work fabricates the n‐type inks by simply mixing the pristine p‐type CNT source solution and chemical liquid agents (hydroxide and crown‐ether) at high‐yield via ultrasonic vibration. The presenting CNT solution functions stability as n‐type materials on various supporting substrates by several fabrication methods in the counterpart junction with pristine p‐type film channels. Available fabrication methods and formable substrates are as follows: printing (screen, air‐jet dispense), coating (spin, casting), and manual application on papers, polymer sheets (parylene, polyimide, polyurethane, and polyethylene terephthalate), glass, and semiconductor wafers. Furthermore, the all‐solution‐processable pn‐junction CNT film PTE sensor fabricated by printing of p‐/n‐type inks sufficiently satisfies superior inherent optical properties. Following these, the presenting uniform high‐yield pn‐junction fabrication, 100 % forming at an error ratio of response signal intensities within 8.54 %, potentially facilitates large‐scale integrations of ultrabroadband deformable thin‐film PTE sensor sheets and the associated functional non‐destructive inspections.