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This study proposes a model of mobility and negative bias stress stability degradation mechanism of zinc oxynitride (ZnON) thin-film transistors (TFTs) with various anion compositions. The subgap density of states (DOS) for ZnON TFTs were extracted using monochromatic photonic capacitance–voltage measurement. The extracted subgap DOS indicated an additional nitrogen-related subgap peak was observed in ZnON TFTs with an excessive nitrogen condition, which might originate from a nitrogen divacancy formation. Furthermore, the shifted threshold voltage components after the bias stress test were quantitatively divided as subgap DOS and interface trapping.

Sunlight-based desalination is one of the most environment-friendly, low-cost methods for obtaining freshwater on the planet. We implemented a biomimetic three-dimensional (3D) solar evaporator, improved by a solar-induced air-flow updraft. A carbon-coated polyvinyl alcohol (PVA) foam allowed us to achieve perfect absorption of ultrabroadband sunlight and continuously provide water to tall 3D structures. Integrating the convection flower (Amorphophallus titanum) and solar chimney structure, we proposed a bio-inspired 3D solar evaporator system that generates an updraft airflow. This updraft replaces saturated vapor between neighboring PVA foams with dry air, resulting in a significant increase in the effectiveness of dry air-water contact interfaces. Under the 1 sun condition (1 kW m-2), we achieve a high solar-vapor conversion efficiency of 95.9%.

Hardware-oriented neuromorphic computing is gaining great deal of interest for highly parallel data processing and superb energy efficiency, as the candidate for replacement of conventional von Neumann computing. In this work, a novel synaptic transistor constructing the neuromorphic system is proposed, fabricated, and characterized. Amorphous indium-gallium-zinc-oxide ( $\alpha $ -IGZO) and Al2O3 are introduced as the channel and gate dielectric materials, respectively. Along with the high functionality and low-temperature processing viability, geometric peculiarity featuring extended gate structure improves the performances of the proposed transistor as synaptic component in the neuromorphic system. The insight into the substantial effect of optimal device structure design on energy efficiency is highlighted.

A newly developed nanopatterned broadband antireflective (AR) coating was fabricated on the front side of a glass/indium tin oxide/perovskite solar cell (PSC) by depositing a single interference layer onto a two-dimensional (2D)-patterned moth-eye-like nanostructure. The optimized developed AR nanostructure was simulated in a finite-difference time domain analysis. To realize the simulated developed AR nanostructure, we controlled the SiO2 moth-eye structure with various diameters and heights and a MgF2 single layer with varying thicknesses by sequentially performing nanosphere lithography, reactive ion etching, and electron-beam evaporation. Optimization of the developed AR nanostructure, which has a 100 nm-thick MgF2 film coated onto the SiO2 moth-eye-like nanostructure (diameter 165 nm and height 400 nm), minimizes the reflection loss throughout the visible range. As a result, the short-circuit current density (JSC) of the newly AR-coated PSC increases by 11.80%, while the open-circuit voltage (VOC) remains nearly constant. Therefore, the power conversion efficiency of the newly developed AR-decorated PSC increases by 12.50%, from 18.21% for a control sample to 20.48% for the optimum AR-coated sample. These results indicate that the newly developed MgF2/SiO2 AR nanostructure can provide an advanced platform technology that reduces the Fresnel loss and therefore increases the possibility of the commercialization of glass-based PSCs.

Given that light is known to function as a zeitgeber, having the greatest influence on the human circadian rhythm, it is necessary to assess the effects of light on humans with the goal of maintaining the circadian rhythm. Herein, we fabricated a simple circadian light meter that directly measures the non-visual effects of light using optical filters that mimic the non-visual action spectrum. The fabricated light meter was calibrated and verified through the values obtained from a conventional illuminance spectrophotometer. Furthermore, during 24 h of everyday life, 11 participants wore hats equipped with the developed light meter so that we could investigate the effects of the light environment to which they were exposed to, both indoors and outdoors. For comparison, natural outdoor illumination was also measured with the same light meter. Based on the considerable difference between the light exposure levels during the daytime and nighttime, it is possible that the participant’s melatonin levels would be impacted by the light exposure measured by the light meter. Consequently, based on the light exposure measurements made in this study, the proposed circadian light meter would be a valuable tool for real world circadian lighting studies that require actual light dose to the eyes of the test subjects.

Accurate circuit simulation reflecting physical and electrical stress is of importance in indium gallium zinc oxide (IGZO)-based flexible electronics. In particular, appropriate modeling of threshold voltage (VT) changes in different bias and bending conditions is required for reliability-aware simulation in both device and circuit levels. Here, we present SPICE compatible compact modeling of IGZO transistors and inverters having an atomic layer deposition (ALD) Al2O3 gate insulator on a polyethylene terephthalate (PET) substrate. Specifically, the modeling was performed to predict the behavior of the circuit using stretched exponential function (SEF) in a bending radius of 10 mm and operating voltages ranging between 4 and 8 V. The simulation results of the IGZO circuits matched well with the measured values in various operating conditions. It is expected that the proposed method can be applied to process improvement or circuit design by predicting the direct current (DC) and alternating current (AC) responses of flexible IGZO circuits.

Solar steam generation is a promising solar energy harvesting technology to address the global clean energy and water deficiency cost-effectively. In this work, we present a compact plasmonic nanostructure-nanoparticle composite based on haze/GO-rGO/Au enabling multiple purposes such as broadband solar absorption, solar steam generation, and solar desalination. The graphene oxide-reduced GO (GO-rGO) combination allows broadband optical absorption, and the presence of 5 nm Au nanoparticles creates high-density localized hotspots for enhanced photothermal effect as evidenced through Raman signal enhancement studies. Anodized aluminum oxide-based haze nanostructures provide maximum light interaction volume through multiple nanogaps and porosity through vertically aligned nanowires of 20-26 nm width and 5-10 μm depth for water channelization. The haze sample coated with GO-rGO/Au shows high solar absorbance of 92.5% over the 300-2500 nm wavelength range covering the whole solar spectrum (ultraviolet-visible-near-infrared). We have achieved 50 and 71.1% of solar-to-thermal conversion efficiencies in a single-layer microscale sample for saline and freshwater, respectively, with a maximum surface temperature of 95.7 °C. The efficiencies increase to 64 and 77% for two layers of the sample at 5 suns (5 kW m-2) illumination.

Solar thermoelectric generators (STEGs), which convert solar thermal energy into electricity, are studied as an environmentally friendly energy source. The unique properties of aerogels (i.e., high thermal insulation and solar light transmission) are essential factors in the solar-receiving components of STEGs. Herein, STEG power generation is enhanced through optical and thermal management using a highly transparent aerogel window. The aerogel window (thickness: 5 mm) exhibits an extremely low thermal conductivity and a high solar transmittance of 96.5%, higher than that of soda-lime glass (89.9% at 0.5 mm thickness) in the wavelength range of 300–2500 nm. Furthermore, we use a copper oxide (CuO) nanoflake structure as a cost-effective solar absorber for the STEG. Under 1-sun (1 k W m−2) illumination, power generation of the STEG with the aerogel window is 21% and 17% higher than that of glass-covered and uncovered STEGs, respectively. To demonstrate the performance of aerogel in an open environment, we measure the power generation of aerogel-covered, glass-covered, and uncovered STEGs under wind conditions. Under 1-sun illumination and a wind speed of 3 m s−1, the power generation of the STEG with the aerogel window is 54% and 71% higher than that of glass-covered and uncovered STEGs, respectively.

In this study, we analyzed the threshold voltage shift characteristics of bottom-gate amorphous indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) under a wide range of positive stress voltages. We investigated four mechanisms: electron trapping at the gate insulator layer by a vertical electric field, electron trapping at the drain-side GI layer by hot-carrier injection, hole trapping at the source-side etch-stop layer by impact ionization, and donor-like state creation in the drain-side IGZO layer by a lateral electric field. To accurately analyze each mechanism, the local threshold voltages of the source and drain sides were measured by forward and reverse read-out. By using contour maps of the threshold voltage shift, we investigated which mechanism was dominant in various gate and drain stress voltage pairs. In addition, we investigated the effect of the oxygen content of the IGZO layer on the positive stress-induced threshold voltage shift. For oxygen-rich devices and oxygen-poor devices, the threshold voltage shift as well as the change in the density of states were analyzed.

Metallic nanostructure-based solar absorbers are widely used owing to their controllable range of absorption wavelengths and various potential applications. Metal-versatile solar absorbers that are not limited to noble metals are essential to reduce production costs. In this study, broadband solar absorbing surfaces were fabricated based on Ni or Au-deposited self-aggregated alumina nanowire structures. A high solar absorptance was obtained for both the Ni-deposited nanowire structures (~0.90) and Au-deposited nanowire structures (~0.92), indicating the advantage of using nickel instead of the noble metal. These high solar absorptance were theoretically analysed by comparing the electric field distributions obtained from finite-difference time-domain (FDTD) simulations and the dielectric functions of Ni and Au. In addition, efficient solar steam generation platform was designed using these broadband solar absorbers and aerogel thermal insulator. The solar steam generation efficiency was improved through heat localisation using an aerogel as a thermal insulator and a polyvinyl alcohol (PVA) sponge as a water supplier. The efficiencies of the solar steam generation platforms using black Ni and Au films under an illumination of 5 kW m−2 were 83.8% and 78.3%, respectively.

Deep learning is now widely used as an efficient tool for medical image classification and segmentation. However, conventional machine learning techniques are still more accurate than deep learning when only a small dataset is available. In this study, we present a general data augmentation strategy using Perlin noise, applying it to pixel-by-pixel image classification and quantification of various kinds of image patterns of diffuse interstitial lung disease (DILD). Using retrospectively obtained high-resolution computed tomography (HRCT) images from 106 patients, 100 regions-of-interest (ROIs) for each of six classes of image patterns (normal, ground-glass opacity, reticular opacity, honeycombing, emphysema, and consolidation) were selected for deep learning classification by experienced thoracic radiologists. For extra-validation, the deep learning quantification of the six classification patterns was evaluated for 92 HRCT whole lung images for which hand-labeled segmentation masks created by two experienced radiologists were available. FusionNet, a convolutional neural network (CNN), was used for training, test, and extra-validation on classifications of DILD image patterns. The accuracy of FusionNet with data augmentation using Perlin noise (89.5%, 49.8%, and 55.0% for ROI-based classification and whole lung quantifications by two radiologists, respectively) was significantly higher than that with conventional data augmentation (82.1%, 45.7%, and 49.9%, respectively). This data augmentation strategy using Perlin noise could be widely applied to deep learning studies for image classification and segmentation, especially in cases with relatively small datasets.

The coupling of the surface plasmon near-field into the sensing medium is key to the sensitivity of surface plasmon-based sensing devices. A low-index dielectric is necessary for the sensing medium to support a highly-penetrating surface plasmon evanescent field that extends well into the dielectric medium. The air-like refractive index, n, of an aerogel substrate provides another dimension for ultralow-index plasmonic devices. In this paper, we experimentally observed an angular surface plasmon resonance dip at 74° with the ultralow-index aerogel substrate, as was expected from theory. We also demonstrated the comparatively high-sensitivity surface plasmon resonance wavelength, λ, while the change in Δλ/Δn with different substrates was studied in detail. A 740 nm-period metal grating was imprinted on aerogel (n = 1.08) and polydimethylsiloxane (PDMS; n = 1.4) substrates. The ultraviolet–visible–near-infrared spectra were observed in the reflection mode on the grating, resulting in sensitivities of 740.2 and 655.9 nm/RIU for the aerogel and PDMS substrates, respectively. Numerical simulations were performed to understand the near-field of the surface plasmon, which demonstrated resonances well correlated with the experimentally observed results. The near-field due to excitation of the surface plasmon polaritons is observed to be more confined and to penetrate deeper into the sensing medium when a low-index substrate is used.

Broadband light absorbers are essential components for a variety of applications, including energy harvesting and optoelectronic devices. Thus, the development of a versatile absorbing structure that is applicable in various operating environments is required. In this study, a material-versatile ultrabroadband absorber consisting of metal-coated self-aggregated Al2O3 nanowire bundles with multiscale funnel structures is fabricated. A high absorptance of ∼0.9 over the AM 1.5G spectrum (300–2500 nm) is realized for absorbers with a range of metal coatings, including Al, W, and titanium nitride (TiN). We demonstrate that the plasmonic nanofocusing and index-matching effects of the funnel structure result in strong ultrabroadband absorption for the various metal coatings, even though the coating materials have different optical properties. As an example of applicability in an operating environment, in the evaluation of the thermal-oxidation resistance, the Al-coated solar absorber exhibits superior performanc...

Optical metamaterials with an artificial subwavelength structure offer new approaches to implement advanced optical devices. However, some of the biggest challenges associated with the development of metamaterials in the visible spectrum are the high costs and slow production speeds of the nanofabrication processes. Here, we demonstrate a macroscale (>35 mm) transformation-optics wave bender (293 mm2) and Luneburg lens (855 mm2) in the broadband white-light visible wavelength range using the concept of elasto-optic metamaterials that combines optics and solid mechanics. Our metamaterials consist of mesoscopically homogeneous chunks of bulk aerogels with superior, broadband optical transparency across the visible spectrum and an adjustable, stress-tuneable refractive index ranging from 1.43 down to nearly the free space index (∼1.074). The experimental results show that broadband light can be controlled and redirected in a volume of >105λ × 105λ × 103λ, which enables natural light to be processed directly by metamaterial-based optical devices without any additional coupling components., Large-scale graded-index metamaterial devices are difficult to fabricate owing to limitations of typical micro- and nanofabrication approaches. Here, Shin et al. demonstrate millimetre-scale transformation elements based on elasto-optic metamaterials made from aerogels.

Direct graphene growth on semiconductor substrates is an important goal for successful integration of graphene with the existing semiconductor technology. We test the feasibility of this goal by using molecular beam epitaxy on various semiconductor substrates: group IV (Si, SiC), group III–V (GaAs, GaN, InP), and group II–VI (ZnSe, ZnO). Graphitic carbon has been formed on most substrates except Si. In general, the crystallinities of carbon layers are better on substrates of hexagonal symmetry than those on cubic substrates. The flatness of graphitic carbon grown by molecular beam epitaxy is noticeable, which may help the integration with semiconductor structures.

Recently, Lee et al. [S.W. Lee, H.S. Kim, K.Y. Yoo, Improvement of Lee and Lee's authenticated key agreement scheme, Appl. Math. Comput., in press] showed that Lee-Lee password-based authenticated key agreement scheme [N.Y. Lee, M.F. Lee, Further improvement on the modified authenticated key agreement scheme, Appl. Math. Comput. 157 (2004) 729-733] is vulnerable to an off-line dictionary attack and proposed an improved scheme. In this paper, we show that Lee et al.'s scheme is not only incomplete, i.e., two parties establishing a session key may not share a common session key, but also still vulnerable to an off-line dictionary attack, i.e., an adversary can confirm the correctness of a guessed-password by checking if the scheme's flows are in a domain (for example, whether a flow is in GF(n) or not). A main reason causing these security breaches is that the scheme's flows are constructed by using two different types of group operations. Finally, we suggest a simple counter-measure to overcome the problems. gest a simple counter-measure to overcome the problems.

It has been elucidated that the responses to light by the human eye influence not only color and brightness recognition but also physiological aspects such as hormones. Melatonin, which affects human circadian rhythms, is sensitive to the blue wavelength region of light. We have investigated the spectroscopic effects of light from virtual reality (VR) and augmented reality (AR) display devices on nonvisual characteristics by means of an analysis of the spectral power distribution (SPD). The circadian illuminance and melatonin suppression value were introduced as representative figures of merits for spectroscopically evaluating nonvisual characteristics. A VR/AR-like custom-made instrument was used to study how the SPD of the display light source affects nonvisual characteristics. Moreover, using multilayer thin-film filters, optimal conditions for minimizing the change of the visual color characteristics of the display while reducing the influence on the non-visual characteristics are also discussed. For the AR device, we found that its spectrum was mostly affected by external light rather than by the spectrum of the AR display itself.

Passive film formation on a chromium surface was studied by three-parameter ellipsometry as the film was formed by anodic polarization in citrate buffer solutions. The thickness and the optical constants of the film were obtained from automatic measurements as functions of time of anodic polarization, from subsecond to 60 s range. The thickness of the passive film increased rapidly within a few seconds, during which both the real and imaginary parts of the complex refractive index of the film changed. These film properties approached near stationary-state values after about 20 s. The stationary-state film thickness increased linearly with the potential of the chromium electrode and depended on pH of the electrolyte, whereas the optical constants did not show significant dependence on these factors. The passive film appeared to be a homogeneous single near-dielectric film, possibly of a composition close to Cr{sub 2}O{sub 3}. No indication of a transformation of the film was observed during the early stages of passivation.

To guarantee secure communication in wireless sensor networks, secret keys should be securely established between sensor nodes. Recently, a simple key distribution scheme has been proposed for pair-wise key establishment in sensor networks by Anderson, Chan, and Perrig. They defined a practical attack model for non-critical commodity sensor networks. Unfortunately, the scheme is vulnerable under their attack model. In this paper, we describe the vulnerability in their scheme and propose a modified one. Our scheme is secure under their attack model and the security of our scheme is proved. Furthermore, our scheme does not require additional communication overhead nor additional infrastructure to load potential keys into sensor nodes.

A prototype field emission display device was fabricated using copper nanowires as emitters. The copper nanowires were grown by chemical vapor deposition without any catalyst or template, which were analyzed by electron microscopy to show a five-fold twinned structure with a pentagonal pyramid tip. The electron diffraction pattern disclosed that the twin boundaries were mismatched irregularly. The anisotropic growth of the copper nanowires in gas phase could be attributed to the passivation of the {100} side planes by the phosphite molecules dissociated from the precursor. Field emission characteristics of the nanowires were measured.