All‐Screen‐Coatable Photo‐Thermoelectric Imagers for Physical and Thermal Durability Enhancement

Carbon nanotube (CNT) film photo‐thermoelectric (PTE) imagers are suitable for non‐destructive inspection techniques owing to their functionalities. Simultaneously, their practical application remains a crucial bottleneck due to low yield handling in the device fabrication (e.g., disconnections between photo absorbent channels and readout electrodes). However, studies clarifying the above malfunction mechanism and associated dominant factors in device handling, such as specific fabrication or material selection steps, still need to be completed. To address this issue, this work introduces all‐screen‐coatable fabrication techniques for CNT film PTE imagers to enhance their physical and thermal durabilities. First, this work determined that the transfer of CNT films on supporting substrates dominantly governs the mechanical robustness of the channels and that thermal curing in the subsequent fabrication process is an essential factor in the yields of channel‐electrode connections. The proposed approach ensures a transfer‐free direct coating of the CNT film on diverse substrates and is sufficiently durable against thermal curing‐induced disconnections at the channel‐electrode interfaces. The screen‐coating technique is also available for whole device materials of solution‐processable CNT film PTE imagers, simplifying fabrication processes. All‐screen‐coatable CNT film PTE imagers synergize their inherent functional sensing and high‐yield operations toward versatile applications.


Introduction
Non-destructive inspections play indispensable roles in rapidly growing industrial mass-production and social distribution in the borderless Internet of Things age. [1,2]This motivation emphasizes that photo-monitoring enriches non-destructive inspection techniques for non-contact and largearea acquisition of wavelength-specific optical information of target objects. [3,4]oreover, optically broadband and mechanically deformable photo-monitoring devices (e.g., imagers and sensors) effectively govern their use in non-destructive inspections. [5,6]Broadband device operations aggregate multi-wavelength optical information and subsequently identify the material compositions of the targets. [7,8]Deformable device operations provide omni-directional viewing angles without blind spots against even 3D structures by comprehensively surrounding the targets. [9,10]Therefore, studies on developing broadband deformable photo-monitoring devices have gathered attention.[13][14] Among these candidates, a-few-μm-thick carbon nanotube (CNT) films collectively satisfy macroscopic softness and ultra-broadband photo-absorption in millimeterwave (MMW), terahertz-wave (THz), and infrared (IR) regions, where inherent transparency to non-metallic materials eases non-destructive inspections.In particular, their operation under the photo-thermoelectric (PTE) effect allows uncooled photo-detection in the broad MMW-IR bands with sensitivities comparable to those of even solid-state narrowband devices. [15]NT films are available on membrane filters via the suction filtration of aqueous solutions. [16,17]Versatile adhesive transfer from the filter facilitates the freely attachable coupling of the CNT film channel with functional substrates: on curvilinear surfaces, stretchable polyurethane sheets, etc. [18] Previous studies have demonstrated that the CNT film PTE imager maintains its inherent advantageous photo-detection performance, even in such bending or stretching configurations. [19,20]The PTE device design utilizes pn-junction structures to enhance the photo-detection sensitivity along with typical thermoelectric conversion strategies. [21,22]As a simple liquid coating forms a pn-junction within the CNT film channel, [23] the entire device fabrication is available under versatile uncooled and air-exposed all-solution-processable conditions, together with the employment of conducting paste as electrodes. [24]espite their functionalities, existing CNT film PTE imagers still exhibit low-yield operation in device fabrication.Such fabrication defects in a certain number of pixels crucially degrade the inspection accuracy by missing partial optical information of target objects to employ the CNT film PTE imager as a multiple pixels-integrated device for large-area visualization.Although a deeper understanding of the malfunction mechanism in operating CNT film PTE imagers is essential to address this bottleneck, studies on the robustness of the device fabrication still need to be completed.This situation hinders the advantages of all-solution processable fabrication techniques from facilitating large-area high-density pixel integration and subsequent camera device applications.To this end, this work introduces an all-screen-coating device fabrication process for designing CNT film PTE imagers (Figure 1a).The presented approach directly printed the respective material inks on supporting substrates and allowed the device to behave in its inherent nature as a pn-junction-type ultrabroadband PTE sensor (Figure 1b).From the above conceptualization, this work clarifies that channel formation methods predominantly determine the mechanical and thermal robustness of the device.Therefore, the screen-coated device overcomes the fatal structural issues associated with the typical adhesive channel transfer process (Figure 1c), enriching functional inspection techniques with easy handling.

Results and Discussion
As the first step in the screen coating of the CNT film imager, this work prepared a laser-processed thin-film mask and a coating substrate (Figure 2a,b).The substrate was a double-sided adhesive polyimide (PI) tape, and the mask was firmly attached.Figure 2c shows the experimental procedure for screen-coating.
During mechanical ink application across the entire masked area, the window allows the size-and shape-selective formation of ink materials (see "Screen Coating" in the Experimental section).
The solution concentrations govern the ink viscosity (Figure 2d) and subsequent coating yield (Figure 2e) to handle CNTs in screen-coating.Here, a few micrometers of thickness is indispensable for the CNT film to realize highly efficient photo-absorption, even in longer-wavelength light bands. [25]mong the evaluated conditions in this study, utilizing CNTs ink with concentrations over 0.3 wt.% fulfills the above requirement (Figure 2f). Figure 2g compares the film uniformity of the CNTs ink screen coating (0.2-0.5 wt.% concentrations; Figure S1, Supporting Information).Although employing the 0.3 or 0.4 wt.%-CNTs inks allows forming films with thicknesses of 3-4 μm, these samples still exhibit defects: non-uniformity and partial damage.These defects potentially hinder multiple pixels integration and the associated photo-detection performance uniformity among pixels in the fundamental design of the CNT film PTE imager.On the other hand, employing the 0.5 wt.% CNTs ink facilitates high-yield screen-coating without non-uniformity in the thickness and partial damage (Figure 2h; Figure S2, Supporting Information).
Moreover, the screen-coated CNT film PTE imager (with the 0.5 wt.% ink) exhibits the highest photo-detection sensitivity among the prepared conditions in this work.While the appearance and thicknesses of the screen-coated CNT films (0.3-0.5 wt.% inks) are uniform, using higher concentration solutions suppresses the electrical resistance and associated thermal noise in PTE imager operations (Figure S3, Supporting Information).As shown in Figure 2i, even using the 0.5 wt.% CNTs ink requires each bar to move: forward-pushing and return-rolling in the screen-coating process.Although forward-pushing screen coating is insufficient for CNT film formation, this step is necessary to apply the ink across the entire masked area covering the laser-processed region.Then, the return rolling screen-coating firmly adhered the CNTs ink to the mask and substrate (Figure S4 and Videos S1 and S2, Supporting Information).While employing the double-sided PI tape substrate facilitates a freely attachable device configuration of the CNT film PTE imager via adhesive force, the present screen-coating process is also available for diverse substrate materials.As shown in Figure S5 and Video S3 (Supporting Information), the static electricity between the mask and the substrate governs their adhesion and facilitates the associated screen coating of the ink material.The wide selection of substrate materials enriches the CNT film PTE imager's device configuration and subsequent applications.In this work, the current minimum processing resolution of the CNT film in the screen coating method is 100 μm (Figure S6, Supporting Information).Toward realizing further fine processing and higher density device integrations, the use of higher resolution laser cutters potentially enriches the presenting screen coating method.
This work demonstrates the advantageous physical and thermal durability enhancement in the device design of a CNT film PTE imager.][27] "Carbon nanotubes" in the Experimental Section describe the details of these processes.This work focused on the behavior at the CNT film channel-readout electrode interface.Figure 3d,e perform electrode wiring to the channels prepared via both the screen-coating and filtration-transfer methods of CNT film formation.The device design requires using rubber-like readout electrodes, with the inherent softness of the channel, [20] to employ the CNT film PTE imager in flexible and stretchable electronics (Figure S7, Supporting Information).Figure 3f compares the electrode interfaces of the CNT film PTE imager based on the channel formation method.This work also performed screen-coating of the conducting paste for electrode wiring.The electrode interface with the transferred channel exhibited disconnections even when the thickness of the CNT film was greater than that of the screen-coated one.This result implied that the transferred CNT film was not durable against the typical volumetric shrinkage of the rubber-like electrode during thermal curing from the original paste state (Figure S8 and Videos S4 and S5, Supporting Information ).Based on these results, the adhesive channel transfer itself predominantly weakens the mechanical strength of the CNT film, as the evaluation in Figure 3f employs the same substrate and electrode materials for both fabrication processes.This situation hinders the fundamental use of the CNT film PTE imager and further device designs (e.g., multiple pixels-integrated array scanners or cameras) at high fabrication yields.
Figure 3g,h compares the open circuit voltage signals without external irradiation of the 10-pixels CNT film PTE imager fabricated using the filtration-transfer and screen-coating methods, respectively.These signals serve as effective noise in the photoresponses of the CNT film PTE sensor.The CNT film PTE sensor typically exhibits hundreds of μV-a few mV responses against external irradiation. [28]While the screen-coated CNT film PTE imager suppressed noise signals up to hundreds of nanovolts, that of the device fabricated by the filtration-transfer method reached a few millivolts.Therefore, the results prove that filtration transfer-based device fabrication and the associated ease of disconnection at the channel-electrode interface are bottlenecks for operating conventional CNT film PTE sensors.In contrast, the screen-coated channel-electrode interface exhibited a 100% yield for 15 samples regarding avoidance of disconnection (Figure 3i).The results also indicate that employing screencoating maintains the inherent electrical resistance of the channel before and after electrode wiring, suppressing noise signals in the PTE responses of the device.Therefore, the proposed fabrication technique governs the fundamental use of the CNT film PTE imager and the potential further device design.
The device fabrication process of the CNT film PTE imager still requires forming a pn-junction as the photo-detection interface (see "Chemical Carrier Doping" and "PTE Effect" in the Experimental section).In addition to the above channel and electrode, this work performed screen-coating of an aqueous n-type chemical carrier dopant (Figure 4a,b).Although this aqueous type ntype chemical carrier dopant is also available for graphene for a short time, the CNT film advantageously exhibits a stable doped state in the air over time (Figure S9, Supporting Information).This feature further facilitates the high-yield device fabrication and integration of the CNT film PTE imager with the presenting robust screen coating process.Here, Figure S10 (Supporting Information) ensures that the presenting screen coating method is widely available for solution-processable materials and their surfaces, not only for CNT inks and films.
The screen-coated n-type doped region on half of the channel can visually be identified, as shown in Figure 4c.This photograph captures the channel, including the doped region, after thermal curing at 120 °C for 10 min, corresponding to the electrode wiring condition.Note that the device fabrication process of the CNT film PTE imager involves screen-dopant-coating before electrode wiring (Figure S11, Supporting Information).This is because electrodes adjacent to the CNT film potentially weaken the adhesion between the channel and the laser-processed window of the dopant mask.The presented photograph shows the disconnections in the doped channel region.The screen-coating shown in Figure 4c utilized the dopant at 0.7 mol L −1 concentration.Figure 4d shows the screen-dopant-coating at the lower 0.1 mol L −1 concentration.In this case, no disconnections can visually be identified in the doped channel region.Based on these results, the excessive lamination of the complex from the dopant over the channel and its volumetric deformations (against thermal curing for electrode wiring) potentially induce the above disconnections.As the device fabrication process includes electrode wiring after doping, the doped channel region must be durable for the thermal curing of the conducting paste.While the screendopant-coating with a lower concentration avoided channel disconnections, Figure 4e compares the Seebeck coefficients of the CNT film against the dopant concentration (see "Seebeck Coefficient Measurement" in the Experimental section).The results indicate that even the screen-dopant-coating at the concentration of 0.1 mol L −1 employed in Figure 4d can sufficiently convert the Seebeck coefficient of the original p-type pristine CNT film to a negative value in a saturation trend.Thus, this condition satisfies the suitability of the screen-dopant-coating, mechanical durability against thermal curing for electrode wiring, and the fundamental use of the device as a pn-junction-type CNT film PTE imager.
The proposed method introduces a simple mechanical alignment in the dopant application process.Laser processing governs the mask's window size and the channel's associated doping region (Figure 4f). Figure 4g briefly evaluates the mechanical alignment accuracy of the screen-dopant-coating.The graphs presented correspond to the line profiles of the PTE response obtained by scanning a mid-IR (MIR) irradiation spot along the device length direction (see "Signal Readout" and "Photo Sources" in the Experimental section).Here, the pristine channel and the associated undoped CNT film PTE imager exhibited a reverse-polarity photo-response at both the ground-and readout-electrode interfaces (double-peak mapping).In contrast, the CNT film PTE imager with the half-area-doped channel showed single-peak mapping with the highest response intensity at the pn-junction.The doped n-type channel is located on the side of the ground electrode in the device structure.Therefore, the distance between the respective PTE response peaks at the pn-junction and ground-electrode interface in the above mapping corresponds to the effective doping length in the device.The presenting screen-dopant-coating method suppresses a difference between the window design value of the mask and the effective doping length within 100 μm. Figure 4h demonstrates that employing a mask with a longer window allowed doping across the CNT film into the entire n-type channel.The above mechanical alignment of the screen-coating method eases further fabrication design (e.g., multiple pixels integration) because this device handles wavelength bands of up to hundreds of micrometers and even a few millimeters.
The proposed all-screen-coatable CNT film PTE imager is wellsuitable as a non-destructive inspection technique owing to its optical and mechanical properties.Figure 5a,b presents the fundamentals of the device used as the imager.This work fabricated a 20-pixels-integrated CNT film PTE imager using the screen-coating method.For the experimental setup of transmissive imaging, the target was located between the device and the photosource, and the scanning direction was perpendicular to the pixel-array direction.As MMW-near-IR (NIR) irradiation exhibits transparency to non-metallic opaque materials, device operation in these bands results in non-destructive imaging inspections.Figure 5c shows an example of non-destructive imaging inspection with device operation in the NIR band.The target was an opaque glass and concealed a hazardous knife on its rear side.In the obtained PTE image, the vertical and horizontal axes correspond to the pixel array-and scanning directions, respectively.The image visualizes the shape of the concealed knife by comprehensively detecting the local attenuation of the transmission signals owing to reflection on the target.For employing the multiple pixels-integrated imagers, inherent PTE response intensities of the respective pixels are different depending on their position.This is simply because the output power distribution in the beam spot of the photosource increases toward the center.This situation potentially induces unnecessary color gradation in the PTE image, thereby degrading the inspection accuracy.However, signal calibration using each device pixel's response intensity distribution ratio maintains the PTE image's color balance (Figure S12, Supporting Information).
Based on these results, Figure 5d demonstrates that employing the proposed device allows for the non-destructive extraction and distinction of the material composition of a multi-layered structure via ultra-broadband multi-wavelength imaging.The inherent optical properties of the CNT film PTE imager and the high yield operation of multiple integrated pixels are crucial in acquiring clear non-destructive images in each tested band.The target comprises a silicon body on an opaque glass coating, a defective hole, and contaminants (metal and plastic), assuming a simple quality inspection of a semiconductor component.As these materials exhibit different transparencies in each band, aggregating multi-wavelength images leads to the detection and identification of concealed features.In this work, four types of photo sources (visible light (Vis), NIR, far-IR (FIR), and MMW) were used: 1) The PTE image obtained under Vis irradiation first visualizes the outline of the opaque glass.
2) The PTE image against NIR irradiation, only exhibiting transparency to opaque glass for the above material composition, then identifies the existence of the concealed defective hole in the target.
3) The PTE image against FIR irradiation, further exhibiting transparency to semiconductors, subsequently detects the position of the silicon chips.4) The PTE image against higher transparent MMW irradiation finally distinguishes between the metal and the plastic contaminants not identifiable in other bands.
Although each PTE image provides specific information about the target, its individual use is insufficient for fully understanding the material composition.Therefore, the proposed device allows the aggregation of multi-wavelength PTE images to reconstruct concealed, composite, and layered targets.
The all-screen-coated CNT film PTE imager sheet also collectively satisfies mechanical softness and optical stability owing to the device's robustness, especially in the channel-electrode interfaces presented earlier.This feature further facilitates the device's use in a 3D imaging inspection module.Figure 5e develops a source-coupled 360°PTE endoscope by firmly wrapping the freely deformable device sheet around a cylindrical probing module with built-in NIR light-emitting diodes (LEDs).The endoscope performs the inherent broadband-sensitive photomonitoring of the CNT film PTE imager even in an omnidirectional viewing angle, and the all-in-one packaging of optical systems leads to advantageous mobile module operations.Here, the target is a metallic pipe joint, whose inner surface is covered with an opaque coating (Figure 5f).The module then identifies and visualizes the concealed light-absorbing impurities concealed beneath the coating by comprehensively detecting local reductions in NIR reflection signals from the inner metallic surface of the target in a non-destructive, omni-directional, and mobile PTE endoscopy manner (see Figure 5g; Figure S13, Supporting Information; "3D Printing and 3D Imaging" in Experimental Section).

Conclusion
In conclusion, this work determined the mechanism of the lowyield operation of the CNT film PTE sensor and introduced an all-screen-coatable device fabrication process to address this crucial issue.As the transfer deteriorates the mechanical strength of the channel and induces disconnections at the electrode junctions during thermal curing, the present approach ensures a robust coating of the CNT film on functional substrates.
The subsequent multiple pixels-integrated CNT film PTE imager functions at a high yield and maximizes its potential and inherent suitability as a fundamental tool in ubiquitous non-destructive inspection applications.

Experimental Section
Screen Coating: In this work, the device fabrication process utilized a mechanical coater (Smart desktop coater TC-100s, Mitsui Electric Co. Ltd.), a bar applicator (OSP-1.5),and 50 μm-thick polyethylene terephthalate (PET) masks (Film separator, NO.760H, TERAOKA SEISAKUSHO Co. Ltd.).The coating substrate comprised the aforementioned 25 μm thick double-sided adhesive PI tape and a supporting glass.This work also performed laser processing of the masks with a desktop CO 2 laser system CL1, Oh-Laser Co. Ltd.).The irradiation wavelength was 10.6 μm, and the minimum processing resolution was 300 μm.The processing conditions were as follows: 15 W irradiation was at a speed of 30 cm s −1 .The screen coating speed was set constant at 1 mm s −1 .The detailed experimental procedure of the screen coating was as follows: set the substrate on the supporting glass, firmly attached the mask to the substrate, dropped ink materials on the mask, applied the ink across the entire mask area via mechanical forward pushing, and returned rolling of the screen bar, dried, and detached the mask from the substrate.
Carbon Nanotubes: This work employed single-walled semiconducting-metallic-mixed carbon nanotube (CNT) aqueous dispersions (ZEONANO SG101, Zeon Co.) at a concentration range of 0.2-0.5 wt.%.The CNTs synthesis utilized a super growth method, [16] and the CNT dimensions were as follows: 3 nm diameter and several hundreds of μm length.For the self-aligned selective suction filtration of the CNT films, the experimental setup employed 70 μm-thick membrane filters (200 nm pore, C020A025A, Advantec Ltd.), 5 μm-thick polyimide (PI) masks (Kapton, Dupont-Toray Co.), and a vacuum pump (MVP015, Pfeiffer Vacuum Technology AG).The CNT films have a non-oriented structure.The subsequent adhesive transfer of the CNT films used a 25 μm-thick double-sided adhesive PI tape (NO.760H,TERAOKA SEISAKUSHO Co. Ltd.).The adhesive transfer process of the CNT film was as follows: dried the suction-filtered CNT film, adhered the PI tape to the supporting membrane filter of the CNT film, and peeled off the PI tape from the membrane.The rubber-like readout electrode in this study comprised a silver powder-binder resin-mixed conductive paste (ELEPASTE NP1, TAIYO INK MFG Co. Ltd.).The curing condition was set at 120 °C for 10 min.
Chemical Carrier Doping: This work employed the liquid coating chemical carrier doping method to form pn-junctions in the originally p-type CNT film channels.The aqueous dopant comprised potassium hydroxide (0.5 m KOH, Tokyo Chemical Industry Co. Ltd.) and 15-crown 5-ether (C0859, Tokyo Chemical Industry Co. Ltd.).The crown ether selectively traped the cation (K + ) and the freely acting anion (OH − ) injected electrons into the CNT films. [29]eebeck Coefficient Measurement: This work employed micro-ceramic heaters (MS-M1000, SAKAGUCHI E.H. VOC Co.), K-type thermocouples (T-35K, SAKAGUCHI E.H. VOC Co.), and a digital multiplexer (DAQ970A, KEYSIGHT TECHNOLOGIES Inc.) to measure the Seebeck coefficient of the CNT films.The experimental system generated a temperature difference between the heaters (5 °C) and readouts thermoelectric voltage response signals via the K-type thermocouples probing on the edge of the samples.[15] The K-type thermocouple comprised an alumel-terminal (−18 μVK −1 ) and a chromel-terminal (22 μVK −1 ).
Photo-Thermoelectric Effect: The photo-thermoelectric (PTE) effect synergied different energy conversion mechanisms (photo-induced heating and thermoelectric) to electrically detect external irradiation.Against external irradiation, the PTE effect triggered thermoelectric conversion at the photodetection interface, where the temperature locally increased over the remaining regions owing to photo-absorption.In other words, the photodetection under the PTE effect provided direct-current (DC) voltage signals as the response.The intensity of the PTE response was proportional to the Seebeck coefficient of the material employed for the photodetection interface. [30]When the photodetection interface consisted of heterogeneous material bonding junctions, its Seebeck coefficient was equal to the difference between the Seebeck coefficients of each constituent material (effective Seebeck coefficient). [31]Based on the above, heterogeneous bonding junctions, comprising materials with positive and negative Seebeck coefficient values, often served as the photodetection interface to enhance the effective Seebeck coefficient and the associated PTE response. [32]or the presenting device structure, the following equation describes the photo-induced PTE response: where ∆V, S p CNT film , S n CNT film , and ∆T are the photoinduced PTE response (DCV), Seebeck coefficients of p-type and n-type CNT film channel, photoinduced temperature gradient across the channel, respectively. [23]gainst external irradiation with a large beam spot covering the entire device region, the CNT film PTE sensor also exhibits negative polarity photoresponses as follows: ΔV = (S n CNT film − S Electrode ) × ΔT where S Electrode is the Seebeck coefficient of the readout and ground electrodes. [23]Equations 2 and 3, respectively, correspond to PTE conversion at the readout electrode-CNT film channel (p-type) junction and the CNT film channel (n-type)-ground electrode junction.Based on each Seebeck coefficient value: S p CNT film (50 μV K −1 ), S n CNT film (−40 μV K −1 ), and S Electrode (1.5 μV K −1 ) , [19] the polarity of the effective Seebeck coefficients and the associated PTE responses are positive for the pn-junction and negative for the channel-electrode junctions.As the absolute values of the effective Seebeck coefficient (S Eff ) of the pn-junction are higher than that of the channel-electrode junctions, the PTE response at the pn-junction serves dominantly even against the large-area irradiation and the device provides photo-induced positive DCV signal values.
Signal Readout: This work employed a multiplexer data logger (34980A-34923A/T, KEYSIGHT TECHNOLOGIES Inc.) to read out DCV photo-response signals of the device.The scan resolution and speed of the data logger were 100 nV and 6.6 Hz, respectively.Up to 80 channels were available for a terminal block of the data logger.Up to eight terminal blocks were available for the data logger.The data logger directly connected to both ends (ground and readout) of each CNT film PTE sensor continuously recorded DCV photo-response signals of the device and transferred them to LabVIEW programs in a PC via a General Purpose Interface Bus (GPIB) cables.For spatial scanning measurements (e.g., imaging or PTE response line mapping of the device), this work also utilized motorized digital stepping stages (Motorized Stage, Sigma Koki Co.) and a stage controller (SHOT-304GS, Sigma Koki Co.).The minimum stepping resolution of the stage was 500 nm, and the scan step was set at 100 μm here.For the above measurements, this work collectively operateed the CNT film PTE sensor, the data logger, the stages, and the stage controller by synchronously linking them via the GPIB cables.
3D Printing and 3D Imaging: This work performed 3D resin printing (Value 3D Magix MF-2500 EP II, MUTOH INDUSTRIES Ltd.) with 3D CAD software (AUTODESK TINKER CAD) to fabricate the supporting substrate of the source-coupled multi-view stereoscopic PTE endoscope.The available resins were polylactic acid and acrylonitrile-butadiene-styrene.The minimum processing resolution was 50 μm in XY and 100 μm in Z directions.In 3D image reconstructions (Figure 5g), the spatial coordinates correspond to the CAD design of the inspecting target (XY: plane coordinates of each pixel in the endoscope module, Z: scan direction coordinates).MATLAB software then combined the above spatial setup with the color gradation induced by the PTE response of each pixel in the endoscope module for respective scan coordinates.

Figure 1 .
Figure 1.Conceptual diagram of the all-screen-coatable CNT film PTE imager.a) Schematic flow of the device fabrication.b) Multiple pixels-integrated ultra-broadband, soft, and thin-film image sensor array sheet.c) Durability comparison of the channel-electrode interfaces.

Figure 2 .
Figure 2. Screen-coating of CNT solutions.a,b) Photographs of a laser-processed mask (a), and a masked coating substrate (b).c) Screen coating process.d) CNT solutions with different concentrations.e-h) Comparisons of the screen-coated films (e), the film thickness (f), the uniformity of the film thickness (g), and the coating yield (h), for each concentration of the CNT solutions.i) Photographic and thickness comparisons of the screen coating methods.

Figure 3 .
Figure 3. Physically and thermally robust CNT film PTE sensor fabrication via screen-coating.a) Laser-processed mask for the suction filtration.b) Selfaligned CNT filtration process.c) Adhesive transfer process of the CNT films.d-f) Photographic comparisons of the CNT films (d), the CNT film PTE imagers (e), and the durability of the channel-electrode interfaces (f) for each coating method.g,h) Comparison of the open-circuit voltage of 10-pixels CNT film PTE imagers fabricated by the filtration-transfer method (g), and the screen-coating method (h).i) Changes in the electrical resistance of the CNT films before and after each device fabrication method.

Figure 4 .
Figure 4. Screen coating of the n-type chemical carrier dopant onto the CNT film PTE sensor.a) CNT film on a coating substrate covered with a doping mask.b) Screen-coating-based doping process.c,d) Photographs of n-type-doped regions in the CNT films with higher (c: 0.7 mol L −1 ) and lower (d: 0.1 mol L −1 ) concentration dopant solutions.e) Change in the Seebeck coefficient of the CNT film against the n-type dopant concentrations.f) CNT films with different lengths of the n-type doping regions.g) PTE response line mapping of the CNT film PTE imagers.h) Change in PTE response line mapping of the CNT film PTE imagers against n-type doping lengths.

Figure 5 .
Figure 5. Applications of multi-functional non-destructive imaging inspection with the all-screen-coated CNT film PTE imager.a) Photograph of the 20 pixels-integrated (1 mm-pitch) CNT film PTE imager, being employed in (c) and (d).b) Experimental setup of transmissive one axial scan imaging.c) Demonstration of the non-destructive transmissive one axial scan NIR imaging.d) Demonstration of ultra-broadband and multi-wavelength nondestructive transmissive imaging of a composite layered object.e) Photographs of the sources-coupled 360°PTE endoscope with the all-screen-coated CNT film imager sheet.f) IR transparency of the inner coating film of the target metallic pipe joint in (e).g) Non-destructive omni-directional image reconstruction of the target.