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Our results show the impact of alkyl chain lengths (Cn) on mesocrystal formation related to the contour length ratio of periphery Lp to wedge Lw. Energy landscapes for Cn dendrons at Lp/Lw ≈ 1 are more intricate than those with longer or shorter Cn.

In this paper, a capacitively-fed, ultra-wideband (UWB), and low-profile monocone antenna is proposed for vehicle-to-everything (V2X) applications. The proposed antenna consists of a monocone design with an inner set of vias. Additionally, an outer ring is added with a small gap from the monocone and shorted with six folded wires of different lengths to extend the operating band. The proposed antenna covers the frequency range from 0.75 GHz to 7.6 GHz and has a 164% fractional bandwidth, with a gain value varying between 2 and 10 dBi. The dimensions of the antenna are 0.37λL× 0.37λL× 0.067λL. The antenna was fabricated using a 3D printer with low-cost polylactic acid plastic (PLA) material and then sprayed with aerosol copper nanoparticles. The efficiency was approximately 90% throughout the frequency bands of interest. Finally, the proposed antenna was installed on a vehicle and tested with an OBU (onboard unit) and a RSU (roadside unit) in the field. The results show a longer wireless communication range for V2X applications.

The widespread use of Internet-of-things (IoT) devices has inspired researchers to adopt unique material design strategies to realize efficient indoor organic photovoltaic (OPV) systems. However, despite acceptor halogenation being an effective strategy for modulating OPV properties, studies on the systematic examination of nonfullerene acceptor- (NFA-) OPVs under dim indoor light using the halogenation approach are scarce. This study evaluates the performance of NFA-OPVs under indoor light by employing a halogenation approach with Y6-derivatives. The choice of the chlorination or fluorination unit in an NFA significantly affects the indoor performance of OPVs. The champion OPV devices with a chlorinated acceptor demonstrated excellent power conversion efficiency (PCE) of 25.5% compared to that of the fluorinated acceptor (PCE: 22.5%) under 1000-lx light-emitting-diode (LED) illumination. Moreover, suitable energy levels, satisfactory spectral matching, and improved surface morphology of the chlorinated acceptors resulted in the excellent indoor performance of the OPVs. In addition, acceptor chlorination resulted in high crystallinity and planarity, which facilitated suppressed trap-assisted recombination and low open-circuit voltage (VOC) loss of OPV devices in an indoor environment.

Automated Vehicles (AVs) are attracting attention as a safer mobility option thanks to the recent advancement of various sensing technologies that realize a much quicker Perception–Reaction Time than Human-Driven Vehicles (HVs). However, AVs are not entirely free from the risk of accidents, and we currently lack a systematic and reliable method to improve AV safety functions. The manual composition of accident scenarios does not scale. Simulation-based methods do not fully cover the peculiar AV accident patterns that can occur in the real world. Artificial Intelligence (AI) techniques are employed to identify the moments of accidents from ego-vehicle videos. However, most AI-based approaches fall short in accounting for the probable causes of the accidents. Neither of these AI-driven methods offer details for authoring accident scenarios used for AV safety testing. In this paper, we present a customized Vision Transformer (named ViT-TA) that accurately classifies the critical situations around traffic accidents and automatically points out the objects as probable causes based on an Attention map. Using 24,740 frames from Dashcam Accident Dataset (DAD) as training data, ViT-TA detected critical moments at Time-To-Collision (TTC) ≤ 1 s with 34.92 higher accuracy than the state-of-the-art approach. ViT-TA’s Attention map highlighting the critical objects helped us understand how the situations unfold to put the hypothetical ego vehicles with AV functions at risk. Based on the ViT-TA-assisted interpretation, we systematized the composition of Functional scenarios conceptualized by the PEGASUS project for describing a high-level plan to improve AVs’ capability of evading critical situations. We propose a novel framework for automatically deriving Logical and Concrete scenarios specified with 6-Layer situational variables defined by the PEGASUS project. We believe our work is vital towards systematically generating highly reliable and trustworthy safety improvement plans for AVs in a scalable manner.

We present a direct approach to fabricating the perfect neutral layer for block copolymer (BCP) self-assembled thin films. An irreversible physisorption of polystyrene

While hole extraction is crucial for the external quantum efficiency of conventional n-i-p colloidal quantum dot (CQD) solar cells (CQDSCs), sulfur-passivated p-type CQDs (pCQDs) have been the best...

A simple approach to utilizing physically adsorbed layers consisting of nonfunctional random and block copolymer chains is suggested for surface neutrality toward lamella-forming polystyrene-b-poly...

While perovskite solar cells (PSCs) have emerged as promising low-cost solar power generators, most reported high-performance PSCs employ electron transport layers (ETLs, mainly TiO2) treated at hi...

A non-invasive, image-based analytic method utilizing scattering-type scanning near-field optical microscopy (s-SNOM) is suggested to evaluate the phase separation behavior of lamella-forming polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer films. Taking advantage of the penetrability of the tip-enhanced IR signal into the films, the spatio-spectral maps of each component are constructed. Subsequently, the effect of a sole and combinatorial applications of the self-assembly procedures, such as solvent vapor annealing (SVA) and/or thermal annealing (TA), on the spatial distribution of PS or PMMA components is quantitatively assessed in terms of the areal portions of the PS domain, PMMA domain, and the mixed zone that is adjacent to the domain border. Additionally, by statistically comparing the local concentration profiles, the chemical contrast between the domains turns out to be dependent upon the annealing procedures (namely, SVA and SVA + TA). This technique can pave the way to an uncomplicated but precise investigation of the polymer nanostructure-based thin film devices whose performances are critically governed by the spatial arrangement of the chemical elements.

Self-assembled block copolymer (BCP) thin films necessarily require a distinct chemical contrast between the blocks (or microdomain homogeneity) for the purpose of high-resolution pattern transfer applications. Despite its importance, however, there has been difficulty in measuring the chemical distribution associated with the self-assembling processes, i.e. solvent vapor annealing (SVA) or thermal annealing (TA). Herein, we present a simple yet effective method to probe the chemical distribution over polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) films that underwent the SVA or SVA + TA processes. An IR nanospectroscopy using scattering-type scanning near-field optical microscopy (s-SNOM), in concert with X-ray scattering analyses, provides the relative chemical concentration of the perpendicular lamellar patterns. The chemical mapping for the components based on the s-SNOM reveals that the SVA process leaves a considerable portion of the intermixed zones of PS and PMMA blocks, whereas the subsequent TA process facilitates the chain segregation towards high-contrast chemical distribution. Interestingly, such a microdomain homogeneity critically affects the quality of the unidirectional Al2O3 lines that were substituted from topographically guided lamellae. Our results substantiate an important insight into understanding the chain redistribution behavior in the self-assembled BCP films using non-destructive s-SNOM technique.

Ultrathin random copolymer mats with cross-linkable glycidyl methacrylate units, consisting of styrene (S) and 2-vinylpyridine (2VP), are prepared on bare substrates to tune substrate interactions....

Instability, glass transition temperature (Tg), and thermal expansion of polystyrene (PS) films are evaluated with respect to the thickness of a silicon oxide (SiOx) interlayer that mediates favora...

We present a direct approach to fabricating the perfect neutral layer for block copolymer (BCP) self-assembled thin films. An irreversible physisorption of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) itself onto the bottom substrates, though extremely thin, offers such a compositional randomness for the substrates, directing the balanced interfacial interactions toward both blocks of the top-layer PS-b-PMMA. Owing to the neutral property from the skin layers, the chemically identical BCP self-assembles into perpendicular microdomains on the adsorbed layer composed of itself, as identified in symmetric PS-b-PMMA films. Intriguingly, the compositional randomness turns out to be valid when the correlation length (ξ) of the BCP layer adsorbed on the substrates is shorter than equilibrium lamellar spacing (L0) of the BCP. Our strategy provides its versatility applicable to various substrates without any necessity of specific random copolymer brushes or mats, enabling the design of a neutral platform fo...

As automated vehicles have been considered one of the important trends in intelligent transportation systems, various research is being conducted to enhance their safety. In particular, the importance of technologies for the design of preventive automated driving systems, such as detection of surrounding objects and estimation of distance between vehicles. Object detection is mainly performed through cameras and LiDAR, but due to the cost and limits of LiDAR’s recognition distance, the need to improve Camera recognition technique, which is relatively convenient for commercialization, is increasing. This study learned convolutional neural network (CNN)-based faster regions with CNN (Faster R-CNN) and You Only Look Once (YOLO) V2 to improve the recognition techniques of vehicle-mounted monocular cameras for the design of preventive automated driving systems, recognizing surrounding vehicles in black box highway driving videos and estimating distances from surrounding vehicles through more suitable models for automated driving systems. Moreover, we learned the PASCAL visual object classes (VOC) dataset for model comparison. Faster R-CNN showed similar accuracy, with a mean average precision (mAP) of 76.4 to YOLO with a mAP of 78.6, but with a Frame Per Second (FPS) of 5, showing slower processing speed than YOLO V2 with an FPS of 40, and a Faster R-CNN, which we had difficulty detecting. As a result, YOLO V2, which shows better performance in accuracy and processing speed, was determined to be a more suitable model for automated driving systems, further progressing in estimating the distance between vehicles. For distance estimation, we conducted coordinate value conversion through camera calibration and perspective transform, set the threshold to 0.7, and performed object detection and distance estimation, showing more than 80% accuracy for near-distance vehicles. Through this study, it is believed that it will be able to help prevent accidents in automated vehicles, and it is expected that additional research will provide various accident prevention alternatives such as calculating and securing appropriate safety distances, depending on the vehicle types.

Although the power conversion efficiency (PCE) of inorganic perovskite-based solar cells (PSCs) has been considerably less than that of organic-inorganic hybrid PSCs due to their wider bandgap, inorganic perovskites are great candidates for the front cell in tandem devices. Herein, we demonstrate the great potential of low-temperature solution-processed two-terminal hybrid tandem solar cell devices based on spectrally matched inorganic perovskite and organic bulk heterojunction for the front and back cells, respectively. By matching optical properties of front and back cells in the hybrid tandem device by using CsPbI2Br and PTB7-Th:IEICO-4F BHJ as the active materials, we achieved a remarkably enhanced PCE in the hybrid tandem (18.04%) as compared to that of the single-junction device (12.46% for CsPbI2Br and 11.02% for PTB7- Th:IEICO-4F). Notably, the PCE of our hybrid tandem device is thus far the highest PCE among the reported tandem devices based on perovskite and organic material. Moreover, the long-term stability of inorganic perovskite devices under stress of humidity was improved in the hybrid tandem device due to the hydrophobicity of the PTB7-Th:IEICO-4F back cell. In addition, the potential promise of this type of hybrid tandem device was calculated, where a PCE of as much as 2 ~28% is possible by improving the external quantum efficiency and reducing energy loss in the sub-cells.

The structural orientation of an amphiphilic crystalline polymer to a highly ordered microphase-separated lamellar structure on a hydrophobic surface is presented. It is formed by the surface graft polymerization of poly(ethylene glycol)behenyl ether methacrylate onto poly(trimethylsilyl) propyne in the presence of allylamine. In particular, allylamine plays a pivotal role in controlling the crystalline phase, configuration, and permeation properties. The resulting materials are effectively used to improve the CO2 capture property of membranes. Upon the optimization of the reaction conditions, a high CO2 permeability of 501 Barrer and a CO2 /N2 ideal selectivity of 77.2 are obtained, which exceed the Robeson upper bound limit. It is inspiring to surpass the upper bound limit via a simple surface modification method.

We present a compelling evidence for thickness dependence on the order-to-disorder transition (ODT) behavior in cylinder- and lamella-forming polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) films. Such an asymmetric wetting condition that confines the films with selective interactions of the PS/air and P2VP/substrate interfaces generates a parallel orientation of cylindrical and lamellar microdomains. We evaluated thickness-dependent phase transition as a function of interlattice distance (L0) using ex situ grazing incidence small-angle X-ray scattering (GISAXS) and transmission electron microscopy (TEM). Below an onset thickness (t0) above which the ODT temperatures (TODTs) of the films are independent of film thickness, the TODTs of cylinder- and lamella-forming PS-b-P2VP films remarkably increase as the film thickness decreases. Our results confirmed that preferential wetting at the PS/air and P2VP/substrate interfaces in very thin films substantially leads to an ordered state over accessible temperatu...

We propose a simple and quantitative method to evaluate thickness of crosslinked surface layer (tx) for superabsorbent poly(acrylic acid) (PAA) materials using a fluorescent dye of rhodamine B (RhB). The electrostatic attraction between the cationic amine group of dye and the anionic carboxylate group of PAA allows us to measure the fluorescent contrast since the surface-crosslinking causes a significant decrease in concentration of carboxylate group compared to that of inner region. Our method utilizing the distinct adsorption difference of RhB visualizes the crosslinked surface (or shell) layer and successfully demonstrates a direct characterization of tx in a dry state of superabsorbent materials, regardless of irregular particle shape.

We modulated the grafting density (σ) and chain length of polystyrene (PS) brushes on substrates to probe their effect on the glass transition temperature (Tg) in overlaying PS thin films. The Tg of PS films was analyzed as a function of brush thickness (or σRg2), where Rg is the radius of gyration of PS brushes. Our results indicate that PS films below 90 nm exhibit a nonmonotonic dependence of Tg on grafting density with the maximum Tg occurring near the regime of wetting–dewetting transition of the overlaying melt. The maximum Tg was found to be higher than the value of bulk PS system. Computer simulation results suggest that such trends arise as a consequence of the environment of enhanced friction presented by the brush layer and the overlap between the polymer film and the grafted layer.

Fullerene-free all-small-molecule organic photovoltaic cells (SM-OPVs) have attracted considerable attention because of well-defined molecular structures with low batch-to-batch variation. Porphyrin derivatives have recently emerged as one of the promising conjugated building blocks for the small-molecule (SM) donors. Herein, we first report fullerene-free SM-OPVs employing porphyrin-based donors. Three zinc porphyrin (PZn)-based SM donors, which have strong bimodal absorption in the visible region and near-infrared region, are synthesized. Constructing bulk-heterojunction (BHJ) active layers using the PZn donors and a SM acceptor, IDIC, which have complementary absorption, achieved panchromatic photon-to-current-conversion from 400 to 900 nm. The manipulation of side chains in the PZn donors considerably influenced the molecular ordering and nanomorphology of the BHJ active layers. PZn-based fullerene-free SM-OPV devices with promising power conversion efficiency of 6.13% were achieved, which also offers...

Versatile control of cylindrical nanostructures formed by supramolecular assembly of end-functionalized polymer blends is demonstrated not only in their orientation over large areas but also in their surface chemical functionalities. Two binary blends consisting of supramolecular analogues of diblock copolymers with complementary end-sulfonated and aminated groups are investigated, viz., mono-end-functionalized polymers of (i) one-end-sulfonated polystyrene (SPS) and one-end-aminated poly(butadiene) (APBD) and (ii) one end-aminated polystyrene (APS) and one end-sulfonated poly(butadiene) (SPBD). The orientation of the cylinders with respect to the substrate surface depends on the solvent annealing time; either hexagonally ordered vertical cylinders or in-plane ones are readily obtained by controlling the solvent annealing time. Selective chemical etching of one of the polymers provides four different chemically modified nanostructures, viz., hexagonally ordered cylindrical holes and cylindrical posts with either sulfonate or amine surface functional groups. Additional supramolecular assembly is successfully achieved by solution coating either polymers or organic dyes that complementarily interact with the functional groups on the nanostructures. Furthermore, the supramolecularly assembled nanostructures are controlled by confining them to topographically pre-patterned Si substrates with pattern geometries of various shapes and sizes to produce globally ordered vertical or in-plane cylinders with chemical functionalities on their surfaces.

We modulated the grafting density (σ) of a random copolymer brush of poly(styrene-r-methyl methacrylate) on substrates to probe its effect on the formation of perpendicularly aligned lamellae of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA). Supported by coarse-grained simulation results, we hypothesized that an increase in σ will allow us to systematically tune the block copolymer interfacial interactions with the substrates from being preferential to one of the blocks to being neutral toward both blocks and will thereby facilitate enhanced regimes of perpendicularly aligned lamellae. We verified such a hypothesis by using a simple grafting-to approach to modify the substrates and characterized the thickness window for perpendicular lamellae as a function of brush thickness (or σ) on the grafted substrates using scanning force microscopy (SFM) images and grazing incidence small-angle X-ray scattering (GISAXS) measurements. The experimental results validated our hypothesis and suggested that the σ o...

We investigated the orientation of gyroid structures in thin films of high-molecular-weight (HMW) polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) upon a solvent vapor annealing (SVA) process with tetrahydrofuran nonselective to the PS and PMMA blocks. During the SVA process, the swollen PS-b-PMMA films produced the gyroid structures that were developed through a cylindrical morphology from a poorly ordered structure. The interfacial interactions exerted by the substrates significantly influenced the orientation of cylinders, like the parallel and perpendicular orientations on the selective and neutral substrates, respectively, while the solvent vapor generated perpendicular cylinders at the surface. In the final formation of gyroid structures, we identified the two distinct [211] and [111] planes on the surface throughout the interior of the films, which were directed from cylinders on the selective and neutral substrates, respectively. To provide the insight of the molecular mechanisms taking place d...

In this paper, we propose a monocone roof-top broadband antenna for V2X (Vehicle to Everything) wireless communication. The proposed antenna consists of four elements – monocone, ground ring, center post, and parasitic disk. The antenna performance is characterized with respect to reflection coefficient and radiation pattern. The simulated and measured data indicate that the proposed antenna can support 0.7 GHz to 6 GHz. Radiation patterns show omnidirectional and high-gain characteristics on the horizontal plane. The simulated magnitude of reflection coefficient is similar to that of the measured data.

The structural orientation of an amphiphilic crystalline polymer to a highly ordered microphase-separated lamellar structure on a hydrophobic surface is presented. It is formed by the surface graft polymerization of poly(ethylene glycol)behenyl ether methacrylate onto poly(trimethylsilyl) propyne in the presence of allylamine. In particular, allylamine plays a pivotal role in controlling the crystalline phase, configuration, and permeation properties. The resulting materials are effectively used to improve the CO

A Ka-band push-push voltage-controlled oscillator (VCO) using a parasitic capacitance cancelling technique is presented. To enhance the oscillation frequency ( f osc ) and the tuning range (TR), the parasitic capacitance of the VCO is cancelled with negative capacitance (NC). To realise NC, a negative impedance circuit (NIC) is analysed and designed. Because of self-resonance frequency, NC is realised using an open-circuit stable NIC. For further enhancement of the f osc , the VCO is developed in a push-push operation. The proposed VCO is fabricated in a commercial 0.15 μm GaAs pHEMT process. It shows 12.4% of the TR at 31.6 GHz with 11 dBm output power. With the NIC, the centre frequency of the VCO increases from 20.1 to 31.6 GHz and the TR increases from 5.7 to 12.4% compared with a VCO without the NIC.

Wrinkling is a well-known example of instability-driven surface deformation that occurs when the accumulated compressive stress exceeds the critical value in multilayered systems. A number of studies have investigated the instability conditions and the corresponding mechanisms of wrinkling deformation. Force balance analysis of bilayer systems, in which the thickness of the capping layer is importantly considered, has offered a useful approach for the quantitative understanding of wrinkling. However, it is inappropriate for multilayer wrinkling (layer number > 3) consisting of heterogeneous materials (e.g. polymer/metal or inorganic), in which the thickness variation in the substrate is also crucial. Therefore, to accommodate the additive characteristics of multilayered systems, we thermally treated tri- or quad-layer samples of polymer/metal multilayers to generate surface wrinkles and used a cumulative energy balance analysis to consider the individual contribution of each constituent layer. Unlike the composite layer model, wherein the thickness effect of the capping layer is highly overestimated for heterogenously stacked multilayers, our approach precisely reflects the bending energy contribution of the given multilayer system, with results that match well with experimental values. Furthermore, we demonstrate the feasibility of this approach as a metrological tool for simple and straightforward estimation of the thermomechanical properties of polymers, whereby a delicate change in the Young's modulus of a thin polymeric layer near its glass transition temperature can be successfully monitored.

Parathyroid hormone (PTH) which increases osteoblast numbers and bone formation by activating bone-lining cells to osteoblasts plays an important role in calcium and phosphate homeostasis and bone remodeling by activating PTH receptors. To determine the structural origin of a minimum activity domain of hPTH, we initiated a detailed structural determination of the hPTH(H14) in aqueous solution using NMR spectroscopy. Circular dichroism and NMR data demonstrated that hPTH(H14) maintains a typical helical conformation in both membrane-mimicking environments and 30% TFE solution. The solution structure clearly showed that the residues from Ser(3) to Leu(11) of hPTH(H14) formed a stable helical structure, especially having charged side-chains oriented in opposite directions relative to one another for optimum interaction with the receptor molecule.

Room-temperature ionic liquids (RTILs) containing bis-imidazolium salts were explored to control their optical properties of them in an organic device. The neat bis-imidazolium salts showed ionic conductivity of 3.5 × 10−4 S/cm at room-temperature and the electrochemical window was exhibited within ±2.5 V in a two electrode cell. The bis-imidazolium salts were transparent yellow and showed fluorescence upon excitation with light in the range of 360 to 500 nm. A two electrode organic ionic liquid cell was fabricated using a mixture of PEO200BIm-TFSI and electroactive molecules to control the emission property of the ionic liquid by electrochemical methods. The first example of the ionic liquid containing electro-fluorescence switch was explored with an electroactive benzyl viologen (BzV) blend of bis-imidazolium ionic liquid.