Device Architecture Research Articles

Wearable, Battery-Free, Self-Powered Electrochemical Sensors for Personalized Health Monitoring

Recent advances in materials, mechanics, and device architectures form the foundations for rapidly emerging classes of sensors with mechanical characteristics that allow for conformal interfaces with the soft, curvilinear surfaces of the human body. While the field of tissue-integrated biophysical sensors exhibits commendable progress in capturing clinical quality thermal, kinematic, and electrophysiological information, the advancement of complementary biochemical sensors severely lags due to unique challenges associated with seamless integration of delicate biochemical receptors, transducing components, and suitable packaging materials. In this talk, I will discuss non-traditional approaches to address some of these grand challenges. Specifically, I will discuss three technologies that my lab is developing -1) wearable, biofuel cell-inspired sensors for sweat monitoring 2) wearable, soft microfluidics with in-built valving and pumping capabilities for precise, on-demand sensing, and 3) AI-powered, wearable wound monitors for early prediction of chronic wounds.

Flexible Organic Electrochemical Transistor Based on Conjugated Conducting Polymers

— The use of organic electrochemical transistors (OECTs) based on conjugated polymers has gained significant recognition owing to their impressive performance, flexibility, ease of fabrication, and suitability for specific applications where solid-state transistors may not be efficiently employed. Key advantages of OECT technology, such as simple device architecture, robustness in ambient or aqueous environments, straightforward additive manufacturing processes, low operational voltage, and compatibility with flexible, rough, stretchable, and large-area substrates, underscore its significance in various applications. These applications span the sensing of glucose [1], bacteria [2], dopamine [3], DNA [4], lactate [5], cell activities [6], and electrophysiological signals [7]. Notably, the absence of the necessity for a reference electrode, a crucial feature for wearable and textile sensors compared to three electrode-based electrochemical sensors, stands out. In this context, we have fabricated a side-gated OECT on a flexible polyethylene terephthalate (PET) substrate through a scalable screen-printing process where the source, drain, and gate terminals are screen-printed using silver (Ag) conductive ink. The semiconducting channel material employed is polyethylene dioxythiophene: polystyrene sulfonate (PEDOT: PSS), which is spin-coated. Additionally, poly methyl methacrylate (PMMA) has been spin-coated to serve as the dielectric. The OECT operates by volumetric gating of the channel through a gel electrolyte containing poly sodium 4-styrene sulfonate (PSSna), enabling polarization of the gate and channel to induce charge accumulation or depletion, driven by the application of a gate-source voltage. The OECT device structure demonstrated switching from the "ON" to "OFF” state with the application of a positive gate voltage, indicating its functionality as a p-type depletion mode transistor. Additionally, the OECT displayed a transconductance (gm) of 6.25×10-4 A/V, mobility (µ) of 1.242×1010 cm2 /Vs, and a threshold voltage (Vth) of -0.39 V, with the on/off ratio being relatively low at 7.22. The repeatability was confirmed through the fabrication of three devices that exhibited nearly identical behavior. Furthermore, in pursuit of faster response time, lower operating voltage, and miniaturization, additional work involves downscaling the active area length to 100µm from the reported 4mm active area length. The fabrication method not only holds the capability for large-scale production with a high yield in a cost-effective manner but also opens up possibilities for applications requiring swift design changes and digitally enabled direct-write techniques. Future work emphasizes functionalizing the electrolyte used in OECT to detect biomolecules such as glucose, pH, and ion species. Thus, this research underscores the potential usability of fabricated OECTs in various high-performance chemical and biological sensing applications. REFERENCES Tang, H.; Yan, F.; Lin, P.; Xu, J.; Chan, H.L.W. Highly Sensitive Glucose Biosensors Based on OrganicElectrochemical Transistors Using Platinum Gate Electrodes Modified with Enzyme and Nanomaterials.Adv. Funct. Mater. 2011, 21, 2264–2272. [CrossRef]He, R.-X.; Zhang, M.; Tan, F.; Leung, P.H.M.; Zhao, X.-Z.; Chan, H.L.W.; Yang, M.; Yan, F. Detection of bacteria with organic electrochemical transistors. J. Mater. Chem. 2012, 22, 22072–22076. [CrossRef]Gualandi, I.; Tonelli, D.; Mariani, F.; Scavetta, E.; Marzocchi, M.; Fraboni, B. Selective detection of dopamine with an all PEDOT:PSS Organic Electrochemical Transistor. Sci. Rep. 2016, 6, 35419. [CrossRef]Tao, W.; Lin, P.; Hu, J.; Ke, S.; Song, J.; Zeng, X. A sensitive DNA sensor based on an organic electrochemical transistor using a peptide nucleic acid-modified nanoporous gold gate electrode. RSC Adv. 2017, 7, 52118–52124. [CrossRef]Braendlein, M.; Pappa, A.-M.; Ferro, M.; Lopresti, A.; Acquaviva, C.; Mamessier, E.; Malliaras, G.G. Owens, R.M. Lactate Detection in Tumor Cell Cultures Using Organic Transistor Circuits. Adv. Mater. 2017, 1605744.Lin, P.; Yan, F.; Yu, J.; Chan, H.L.W.; Yang, M. The Application of Organic Electrochemical Transistors in Cell-Based Biosensors. Adv. Mater. 2010, 22, 3655–3660Liang, Y.; Ernst, M.; Brings, F.; Kireev, D.; Maybeck, V.; Offenhäusser, A.; Mayer, D. High Performance Flexible Organic Electrochemical Transistors for Monitoring Cardiac Action Potential. Adv. Healthc. Mater. 2018, 1800304. [CrossRef] Figure 1

Understanding the Non-Volatile Resistive Switching Behavior of Lithium Titanium Oxide during Spinel to Rock Salt Conversion for Neuromorphic Computing

Lithium based synaptic device research has been a growing new field in the last few years for enabling robust neuromorphic hardware systems. It can realize parallel analogue computation which is beyond the conventional von Neumann computing architecture which is slow, energy inefficient and expensive to execute complex tasks. In this study, we showcase the remarkable potential of Lithium Titanium Oxide (Li4Ti5O12) spinel, both computationally through Density of States (DoS) analysis using Density Functional Theory (DFT), and experimentally via direct current (DC) polarization investigation of electrochemically lithiated Li4Ti5O12 thin film, examining diverse states of discharge (SoD) in both in-plane and out-of-plane configurations. The observed conductivity jump spans up to six orders of magnitude, transitioning from the Li4Ti5O12 spinel phase to the fully lithiated Li7Ti5O12 rock salt phase. Raman Spectroscopy validates the transformation from the Li4Ti5O12 spinel phase to the Li7Ti5O12 rock salt phase. Moreover, the onset of increase in conductivity during this transformation is corroborated by changes in the oxidation state of Titanium (Ti), as explained with the help of X-Ray Photoelectron Spectroscopy. To actualize these findings, we engineered a three-terminal artificial synaptic device integrating Lithium Phosphorous Oxynitride (LiPON) solid-state electrolyte as the lithium ion source and conductor, while employing Lithium Titanium Oxide (Li4Ti5O12) spinel as the channel material. In device testing, we maintained a source-drain voltage (VSD) of 0.5 V, while sweeping the gate voltage (VG) from -3 V to 3 V, resulting in switching spanning up to 4 orders of magnitude, consistently replicable across multiple cycles. Widening the gate voltage window from ±3 V to ±7V induced an increase in conductance. Furthermore, non-volatile testing affirmed the sustained retention of the conductance state across all tested gate voltage windows, showcasing the device's stability over time. These compelling results portray a promising trajectory for the development of a robust synaptic device architecture reliant on lithium-based all solid-state materials, catalyzing the evolution of high-precision analogue neuromorphic computing systems.

Polarization Characteristics of Massive HVI Debris Clouds Using an Improved Monte Carlo Ray Tracing Method for Remote Sensing Applications

As a signature phenomenon of massive hypervelocity impacts (HVIs) in space, debris clouds provide critical optical information for satellite remote sensing and the assessment of large-scale impacts. However, studies of the optical scattering properties of debris clouds remain limited, and existing vector radiative transfer (VRT) methods struggle to accurately simulate the optical characteristics of these complex scatterers. To address this gap, this paper presents an improved Monte Carlo VRT program (PGS–MC) for multicomponent polydisperse scatterers to precisely evaluate the radiation and polarization characteristics of complex scatterers. Based on the Monte Carlo ray tracing (MCRT) method, our program introduces a particle grouping strategy (PGS) to further emphasize the importance of accounting for optical property discrepancies between different materials and particle sizes, thus significantly improving the fidelity of VRT simulations. Moreover, our program, developed using the compute unified device architecture (CUDA), can be run parallelly on graphics processing units (GPUs), which effectively reduces the computational time. The validation results indicated that the developed PGS–MC program can accurately and efficiently simulate the polarization of complex 3D scatterers. A further investigation showed that the polarization characteristics of debris clouds are highly sensitive to parameters such as the angle between the incident and detection directions, number density, particle size distribution, debris material, and wavelength. In addition, the polarization imaging of debris clouds offers distinct advantages over intensity imaging. This study offers guidance for analyzing the VRT properties of massive HVI debris clouds. Additionally, it provides a practical tool and concrete ideas for modeling the polarization characteristics of various complex scatterers, such as aircraft contrails and clouds, etc.

Bridging Technology and Environment: Sustainable Approaches in Semiconductor Chemical Mechanical Planarization (CMP)

As semiconductor technologies continue to advance in areas such as autonomous driving, artificial intelligence, 5G communications, the Internet of Things, and large-scale data processing, the demand for a reliable semiconductor industry is on the rise.(1) This growing demand necessitates the use of advanced device architectures, which heavily rely on two crucial processes: Chemical Mechanical Planarization (CMP) and post-CMP cleaning.(2) This talk will focus on the development of CMP slurries and post-CMP cleaning solutions, emphasizing their vital roles in these processes. We will delve into the comprehensive development of CMP slurries and post-CMP cleaning solutions, highlighting how synthesis methods can significantly affect the surface chemistry of ceria abrasives and impact the removal rates of SiO2 surfaces during STI CMP.(3, 4) Our research also demonstrates how our cleaning solutions can effectively remove even the most 10 nm-sized ceria particles from SiO2 surfaces,(5) thereby enhancing process efficiency. Furthermore, we will discuss the use of aliphatic amino acids as environmentally friendly corrosion inhibitors in CMP slurries, offering a sustainable alternative to the traditionally used benzotriazole (BTA) and addressing key environmental challenges.(6) In the context of the rapidly expanding semiconductor industry, it becomes critical to address global sustainability concerns and environmental health and safety (EHS) objectives. Our research proposes a comprehensive methodology for evaluating the sustainability of CMP consumables in semiconductor manufacturing, with a primary focus on CMP slurries due to their significant market share and shorter usage lifetimes. This research serves as a foundation for future CMP sustainability analyses, encouraging self-correction strategies within the CMP community to reduce environmental impact. We will also introduce a robust framework for the Life Cycle Assessment (LCA) of CMP consumables, marking a crucial step toward achieving these sustainability goals. In summary, this talk will explore the intricate details of CMP and post-CMP processes, their pivotal roles in the advancement of semiconductor manufacturing, and the imperative task of aligning these processes with environmental and sustainability objectives.This talk is dedicated to the special session in honor of Prof. Babu. S. Babu, Advances in Chemical Mechanical Planarization (CMP), Woodhead Publishing (2021).J. Seo, Journal of Materials Research, 36, 235 (2021).J. Seo, J. W. Lee, J. Moon, W. Sigmund and U. Paik, ACS applied materials & interfaces, 6, 7388 (2014).J. Seo, J. H. Kim, M. Lee, J. Moon, D. K. Yi and U. Paik, Journal of colloid and interface science, 483, 177 (2016).J. Seo, A. Gowda and S. Babu, ECS Journal of Solid State Science and Technology, 7, P243 (2018).H. T. T. Tran, J. Gichovi, E. J. Podlaha and J. Seo, in Electrochemical Society Meeting s 243, p. 1809 (2023).

Artificial Graphene Nanoribbons with Tailored Topological States

Low-dimensional materials functioning at the nanoscale are a critical component for a variety of current and future technologies. From the optimization of light harvesting solar technologies to novel electronic and magnetic device architectures, key physical phenomena are occurring at the nanometer and atomic length-scales and predominately at interfaces. In this presentation, I will discuss low-dimensional material research occurring in the Quantum and Energy Materials (QEM) group at the Center for Nanoscale Materials. Specifically, the synthesis of artificial graphene nanoribbons by positioning carbon monoxide molecules on a copper surface to confine its surface state electrons into artificial atoms positioned to emulate the low-energy electronic structure of graphene derivatives. We demonstrate that the dimensionality of artificial graphene can be reduced to one dimension with proper “edge” passivation, with the emergence of an effectively-gapped one-dimensional nanoribbon structure. Remarkably, these one-dimensional structures show evidence of topological effects analogous to graphene nanoribbons. Guided by first-principles calculations, we spatially explore robust, zero-dimensional topological states by altering the topological invariants of quasi-one-dimensional artificial graphene nanostructures. The robustness and flexibility of our platform allows us to toggle the topological invariants between trivial and non-trivial on the same nanostructure. Our atomic synthesis gives access to nanoribbon geometries beyond the current reach of synthetic chemistry, and thus provides an ideal platform for the design and study of novel topological and quantum states of matter. Figure 1

Fast and accurate phase processing in off-axis digital holography combining adaptive spatial filtering and an embedded GPU platform

Abstract Parallel-phase processing enables rapid phase extraction from off-axis digital holograms. To achieve fast and accurate results, the phase reconstruction processes were parallelized using improved filter algorithms and optimized programming strategies. First, an adaptive filtering method based on the Chan-Vese (CV) model which better suits parallelism was designed to extract the +1 term spectrum. We selected suitable computer unified device architecture (CUDA) libraries according to the characteristics of the key phase reconstruction steps. Acceleration technologies, such as virtual memory and shared memory, were used to improve the computational efficiency. Furthermore, we combined an improved 4f optical imaging system with an embedded graphic processing unit (GPU) platform to design a low-cost phase reconstruction system for off-axis digital holography. To verify the feasibility of our method, the reconstructed quality of the CV filtering method was estimated, and the run times of phase retrieval on the central processing unit (CPU) and embedded GPU were compared for off-axis holograms with different pixel sizes. Additionally, the dynamic fluctuation phase maps of water droplet evaporation were retrieved to demonstrate the real-time capability of the method.

Downscaling of Organic Field-Effect Transistors based on High-Mobility Semiconducting Blends for High-Frequency Operation.

Small molecule/polymer semiconductor blends are promising solutions for the development of high-performing organic electronics. They are able to combine ease in solution processability, thanks to the tunable rheological properties of polymeric inks, with outstanding charge transport properties thanks to high crystalline phases of small molecules. However, because of charge injection issues, so far such good performances are only demonstrated in ad-hoc device architectures, not suited for high-frequency applications, where transistor dimensions require downscaling. Here, the successful integration of the most performing blend reported to date, based on 2,7-dioctyl[1] benzothieno[3,2-b][1]benzothiophene (C8-BTBT) and poly(indacenodithiophene-co-benzothiadiazole) (C16IDT-BT), in OFETs characterized by channel and overlap lengths equal to 1.3 and 1.9µm, respectively, is demonstrated, enabling a transition frequency of 23MHz at -8V. Two key aspects allowed such result: molecular doping, leading to width-normalized contact resistance of only 260Ωcm, allowing to retain an apparent field-effect mobility as high as 3cm2/(Vs) in short channel devices, and the implementation of a high capacitance dielectric stack, enabling the reduction of operating voltages below 10V and the overcoming of self-heating issues. These results represent a fundamental step for the future development of low-cost and high-speed printed electronics for IoT applications.

Enhanced Stability and Performance Lead Halide Perovskite Solar Cells via Hole Transport Materials Additive Strategies

AbstractPast few years has witnessed a rapid surge in the design and fabrication of lead halide perovskite solar cells (LH‐PSCs). Methyl ammonium lead iodide (CH3NH3PbI3) is one of the widely used visible light absorbing material towards the fabrication of LH‐PSCs. The CH3NH3PbI3 has a band gap of around 1.55 eV which makes it a suitable visible light sensitizer for the development of high performance next generation LH‐PSCs. In this work, CH3NH3PbI3 has been explored as visible light absorbing layer with mesoscopic device architecture of (FTO/TiO2/CH3NH3PbI3/spiro‐OMeTAD+MoS2/Au) LH‐PSCs. MoS2 has been utilized as hole transport material additive which not only acted as additive but also enhanced the performance of the LH‐PSCs with long term stability. The FTO/TiO2/CH3NH3PbI3/spiro‐OMeTAD+MoS2/Au showed the interesting efficiency of 14.2 % which is higher than that of the FTO/TiO2/CH3NH3PbI3/spiro‐OMeTAD/Au device (11.9 %). This work offers the fabrication of stable and improved LH‐PSCs with device architecture of FTO/TiO2/CH3NH3PbI3/spiro‐OMeTAD+MoS2/Au.

Electric-Field-Driven Localization of Molecular Nanowires in Wafer-Scale Nanogap Electrodes.

As integrated circuits continue to scale toward the atomic limit, bottom-up processes, such as epitaxial growth, have come to feature prominently in their fabrication. At the same time, chemistry has developed highly tunable molecular semiconductors that can perform the functions of ultimately scaled circuit components. Hybrid techniques that integrate programmable structures comprising molecular components into devices however are sorely lacking. Here we demonstrate a wafer-scale process that directs the localization of a conductive polymer, Mw = 20 kg mol-1 polyaniline, from dilute solutions into 50 nm vertical nanogap device architectures using electric-field-driven self-assembly. The resulting metal-polymer-metal junctions were characterized by electron microscopy, Raman spectroscopy and transport measurements demonstrating that our technique is highly selective, assembling conductive polymers only in electrically activated nanogaps. Our results represent a step toward scalable hybrid nanoelectronics that seamlessly integrate established lithographic top-down fabrication with bottom-up synthesized molecular functional circuit components.

Inkjet-Printed, High-Performance MoS2 Transistors and Unipolar Logic Electronics.

Two-dimensional (2D) semiconductor field-effect film transistors combine large carrier mobility with mechanical flexibility and therefore can be ideally suitable for wearable electronics or at the sensor interfaces of smart sensor systems. However, such applications require large-area solution processing as opposed to single-flake devices, where the critical challenge to overcome is the high interflake resistance values. In this report, using a narrow-channel, near-vertical transport device architecture, we have fabricated inkjet-printed sub-20 nm channel electrolyte-gated transistors with predominantly intraflake carrier transport. Therefore, the electronics transport in these transistors is not dominated by the high interflake resistance, and the intraflake material properties including doping density, defect concentration, contact resistance, and threshold voltage modulation can be examined and optimized independently to achieve a current density as high as 280 μA·μm-1. In addition, through the passivation of the sulfur vacancies with a tailored surface treatment, we demonstrate an impressive On-Off current ratio exceeding 1 × 107, complemented by a low subthreshold swing of 100 mV·decade-1. Next, exploiting these high-performance transistors, unipolar depletion-load-type inverters have been fabricated that show a maximum gain of 31. Furthermore, we have realized NAND, NOR, and OR gates, demonstrating their seamless operation at a frequency of 1 kHz. Therefore, this work represents an important step forward to realize electronic circuits based on printed 2D thin film transistors.

Manganite memristive devices: recent progress and emerging opportunities

Manganite-based memristive devices have emerged as promising candidates for next-generation non-volatile memory and neuromorphic computing applications, owing to their unique resistive switching behavior and tunable electronic properties. This review explores recent innovations in manganite-based memristive devices, with a focus on materials engineering, device architectures, and fabrication techniques. We delve into the underlying mechanisms governing resistive switching in manganite thin films, elucidating the intricate interplay of oxygen vacancies, charge carriers, and structural modifications. This review underscores breakthroughs in harnessing manganite memristors for a range of applications, from high-density memory storage to neuromorphic computing platforms that mimic synaptic and neuronal functionalities. Additionally, we discuss the role of characterization techniques and the need for a unified benchmark for these devices. We provide insights into the challenges and opportunities associated with the co-integration of manganite-based memristive devices with more mature technologies, offering a roadmap for future research directions.

Flux-pulse-assisted readout of a fluxonium qubit

Much attention has focused on the transmon architecture for large-scale superconducting quantum devices; however, the fluxonium qubit has emerged as a possible successor. With a shunting inductor in parallel to a Josephson junction, the fluxonium offers larger anharmonicity and stronger protection against dielectric loss, leading to higher coherence times as compared to conventional transmon qubits. The interplay between the inductive and Josephson energy potentials of the fluxonium qubit leads to a rich dispersive-shift landscape when tuning the external flux. Here, we propose to exploit the features in the dispersive shift to improve qubit readout. Specifically, we report on theoretical simulations showing improved readout times and error rates by performing the readout at a flux-bias point with large dispersive shift. We expand the scheme to include different error channels and show that with an integration time of 155 ns, flux-pulse-assisted readout offers about a 5-times improvement in the signal-to-noise ratio. Moreover, we show that the performance improvement persists in the presence of finite measurement efficiency combined with quasistatic flux noise and also when considering the increased Purcell rate at the flux-pulse-assisted readout point. We suggest a set of reasonable energy parameters for the fluxonium architecture that will allow for the implementation of our proposed flux-pulse-assisted readout scheme. Published by the American Physical Society 2024

KLD: a program to elucidate the localization of the Fermi and Coulomb holes in molecular systems.

The electron localization is a concept that allows scientists to better understand the physical and chemical properties of electronic systems. It is associated with the propensity of electron pairs with opposite spins to accumulate as well as with their response to external perturbations. This paper contains a detailed description of the design and implementation of the program KLD, which was primarily developed in our research group to elucidate electron localization in molecular systems by evaluating the information content of electron-pair density functions. KLD employs two information-based functions as a real space measure of the Fermi and Coulomb holes for same-spin electrons and shows a better resolution as compared to other methods (i.e., ELF). Information about the acceleration of the code is also included in the present work, being noticeable the reduction of wall-time calculation and the error calculation between versions. KLD was designed to be easy to use, extend, and maintain; thus, many principles of modern software development, extensive testing, and package management were adopted. The latest version of the KLD program was created utilizing the Compute Unified Device Architecture (CUDA) version, which allows it to use the computational capacity of NVIDIA Graphics Processing Units (GPUs) for processing purposes. The electron-pair conditional density was calculated from the canonical molecular orbitals obtained at the HF/6-31G(2df,p) level, or alternatively the natural orbitals in the case of explicit correlated wavefunctions computed at the MP2/6-31G(2df,p)//HF/6-31G(2df,p) level.

Realizing Sunlight-Induced Efficiently Dynamic Infrared Emissivity Modulation Based on Aluminum-Doped zinc Oxide Nanocrystals.

Dynamic manipulation of an object's infrared radiation characteristics is a burgeoning technology with significant implications for energy and information fields. However, exploring efficient stimulus-spectral response mechanism and realizing simple device structures remains a formidable challenge. Here, a novel dynamic infrared emissivity regulation mechanism is proposed by controlling the localized surface plasmon resonance absorption of aluminum-doped zinc oxide (AZO) nanocrystals through ultraviolet photocharging/oxidative discharging. A straightforward device architecture that integrates an AZO nanocrystal film with an infrared reflective layer and a substrate, functioning as a photo-induced dynamic infrared emissivity modulator, which can be triggered by weak ultraviolet light in sunlight, is engineered. The modulator exhibits emissivity regulation amount of 0.72 and 0.61 in the 3-5 and 8-13µm ranges, respectively. Furthermore, the modulator demonstrates efficient light triggering characteristic, broad spectral range, angular-independent emissivity, and long cyclic lifespan. The modulator allows for self-adaptive daytime radiative cooling and nighttime heating depending on the ultraviolet light in sunlight and O2 in air, thereby achieving smart thermal management for buildings with zero-energy expenditure. Moreover, the potential applications of this modulator can extend to rewritable infrared displays and deceptive infrared camouflage.

Energy-saving window for versatile multimode of radiative cooling, energy harvesting, and defrosting functionalities

This study presents an energy-saving window that integrates the multi-mode of radiative cooling, droplet-based electricity generator, and defrosting/defogging functionalities with an all-in-one device architecture. Constructed with fluorinated ethylene propylene film and indium tin oxide (ITO)/Ag/ITO layers, the window exhibits a transmittance of 0.652 in the visible spectrum, a reflectance of 0.474 in the near-infrared spectrum, and a long wave infrared emittance of 0.972. This transparent radiative cooler effectively reduces temperatures by 5.2 ℃ on average, compared to the bare glass. Beyond its energy-saving cooling performance, the smart window also serves as a droplet-based electricity generator, producing an impressive instantaneous power of 8.3 W m−2 when impacted by a single water droplet. Besides, in the presence of fog or frost that impairs the visibility of the smart window, the device can switch to the heater mode and improve the visibility by defogging or defrosting. Lastly, this work examines the practical usage of all multi-modes by incorporating the smart window into the scaled-down model house. In this regard, we expect that this work will not only serve as valuable assets for the technological advancement of the academic study field but also make a significant contribution to energy-saving strategies in real-life situations.

How Ammonium Valeric Acid Iodide Additive Can Lead to More Efficient and Stable Carbon‐Based Perovskite Solar Cells: Role of Microstructure and Interfaces?

As perovskite photovoltaic devices can now compete with silicon technology in terms of efficiency, many strategies are investigated to improve their stability. In particular, degradation reactions can be hindered by appropriate device encapsulation, device architecture, and perovskite formulation. Mesoporous device architectures with a carbon electrode offer a plausible solution for the future commercialization of perovskite solar cells. They represent a low‐cost and stable solution with high potential for large‐scale production. Several studies have already demonstrated the potential of the mixed 2D/3D ammonium valeric acid iodide‐based MAPbI3 formulation to increase the lifetime of pure MAPbI3. They can however not describe the mechanisms responsible for the lifetime improvement. Using a full set of characterization techniques in the initial state and as a function of time during damp‐heat aging, new insights into the performance and degradation mechanisms may be observed. With (5‐AVA)0.05MA0.95PbI3, the solar cells are very stable up to 3500 h and the degradation of performances essentially results from the loss of electrical contacts mainly located at the interfaces. In contrast, for the neat MAPbI3, a poor stability is evidenced (T50 = 500 h) and the loss in performance results from the degradation of the bulk perovskite layer itself.

Microchannel pressure sensor for continuous and real-time wearable gait monitoring

A highly sensitive and multi-functional pressure sensor capable of continuous pressure readings is greatly needed, particularly for precise gait pattern analysis. Here, we fabricate a sensitive and reliable pressure sensor by employing eutectic gallium indium (EGaIn) liquid metal as the sensing material and EcoFlex 00-30 silicone as the substrate, via a low-cost process. The device architecture features a microchannel, creating two independent sensing devices, and the mechanical properties of the substrate and sensing material contribute to high stretchability and flexibility, resulting in a sensitivity of 66.07 MPa−1 and a low measurement resolution of 0.056 kPa. The sensor detects applied pressure accurately and can distinguish pressure distribution across a wide area. We demonstrate high efficiency for monitoring human walking gait at various speeds when a single sensor is attached to the foot, and can differentiate between walking postures. This device has strong potential for clinical and rehabilitation applications in gait analysis.

Measurements of Thermal Resistance Across Buried Interfaces with Frequency-Domain Thermoreflectance and Microscale Confinement.

Confined geometries are used to increase measurement sensitivity to thermal boundary resistance at buried SiO2 interfaces with frequency-domain thermoreflectance (FDTR). We show that radial confinement of the transducer film and additional underlying material layers prevents heat from spreading and increases the thermal penetration depth of the thermal wave. Parametric analyses are performed with finite element methods and used to examine the extent to which the thermal penetration depth increases as a function of a material's effective thermal resistance and the degree of material confinement relative to the pump beam diameter. To our surprise, results suggest that the measurement technique is not always the most sensitive to the largest thermal resistor in a multilayer material. We also find that increasing the degree to which a material is confined improves measurement sensitivity to the thermal resistance across material interfaces that are buried 10s of μm to mm below the surface. These results are used to design experimental measurements of etched, 200 nm thick SiO2 films deposited on Al2O3 substrates, and offer an opportunity for thermal scientists and engineers to characterize the thermal resistance across a broader range of material interfaces within electronic device architectures that have historically been difficult to access via experiment.

Improving the crashworthiness of bi-tubular architectures with ABS cores under axial loading: Experimental and numerical investigation

In this study, quasi-static axial compression tests were conducted on mild steel bi-tubular architectures with rectangular nested tube (RNT) and square nested tube (SNT) geometries to evaluate their crushing and crashworthiness performance. A multi-criteria decision-making approach was employed to identify the optimal energy-absorbing architecture. The SNT structure, with the smallest gap size between the inner and outer tubes, exhibited the most desirable energy absorption characteristics among the considered cases. Acrylonitrile butadiene styrene (ABS) cores, with either rhombic or square cell configurations, were used to enhance the energy absorption performance of the SNT structure. A finite element model was created to evaluate the responses of the SNT structure filled with ABS cores. The validity of finite element simulations of the ABS cores and optimal architecture under axial compression were confirmed by comparing them with experimental results. The integration of the cores into the nested architecture enhanced crashworthiness performance and contributed to the control of the structure deformation. The SNT structure filled with rhombic ABS core exhibited superior crashworthiness performance compared to the counterpart filled with square core. The energy absorption of nested SNT structures filled with rhombic ABS core can be 116.93% greater than the corresponding non-filled structure. The crashworthiness indices of ABS-filled structures were highly sensitive to the number of cells and wall thickness of the core. A nested architecture with an ABS core could serve as a novel architecture for energy-absorbing devices.