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Binary and ternary transition metal dichalcogenide (TMD) heterostructures, MSe2 and MSeS (where M = Mo or W), are investigated as future building blocks for high‐performance device applications with a tailorable electronic bandgap. For light‐emitting device applications, investigating the decay time of the material is a prerequisite. Herein, time‐resolved photoluminescence (TRPL) of binary and ternary TMD heterostructures is measured. A tri‐exponential function is adopted to fit the TRPL data. Short, medium, and long decay times are <50 ps, ≈400 ps, and >400 ps, respectively. Except for monolayer MoSe2 and MoSeS, only two PL decay time components are observed with a large contribution from short decay time photocarriers (>80%). Bilayer TMDs exhibit a much shorter PL decay time, which could be attributed to the indirect nature of excitons and different dielectric environments, compared with that of monolayer TMDs. Using the center‐of‐mass (CM) method, a PL decay time map is successfully obtained for binary and ternary TMD heterostructures. This allows the qualitative visualization of the decay time distribution within the heterostructure or among other materials. This technique could be applied to assess the decay time of materials used in high‐performance light‐emitting devices. [ABSTRACT FROM AUTHOR]

Augmenting contact lenses with sensing capabilities requires incorporating multiple functionalities within a diminutive device. Inspired by multifunctional biophotonic nanostructures of glasswing butterflies, a nanostructured scleral lens with enhanced optical, bactericidal, and sensing capabilities is reported. When used in conjunction with a smartphone‐integrated Raman spectrometer, the feasibility of point‐of‐care applications is demonstrated. The bioinspired nanostructures made on parylene films are mounted on the anterior and posterior side of a scleral lens to create a nanostructured lens. Compared to unstructured parylene, nanostructured parylene minimizes glare by 4.3‐fold at large viewing angles up to 80o. When mounted on a scleral lens, the nanostructures block 2.8‐fold more ultraviolet (UVA) light while offering 1.1‐fold improved transmission in the visible regime. Furthermore, the nanostructures exhibit potent bactericidal activity against Escherichia coli, killing 89% of tested bacteria within 4 h. The same nanostructures, when gold‐coated, are used to perform rapid label‐free multiplex detection of lysozyme and lactoferrin, the protein biomarkers of the chronic dry eye disease, in whole human tears using drop‐coating deposition Raman spectroscopy. The detection of both proteins in whole human tear samples from different subjects using the nanostructured lens produced excellent correlation with commercial enzyme‐based assays while simultaneously displaying a 1.5‐fold lower standard deviation. [ABSTRACT FROM AUTHOR]

The Raman tensors of the three modes at ∼55, ∼80, and ∼160 cm−1 for the non-van der Waals layered material Bi2O2Se, which were assigned to Eu, Eg, and A1g, respectively, were experimentally investigated. Two modes at ∼55 and ∼80 cm−1, which were not observable in perfect crystal Bi2O2Se in the backscattering configuration, owing to the Raman selection rule, were activated by defects. These two modes exhibit strong polarization dependence at line defects and the excitation energy; thus, their Raman polarizability tensors exhibit strong dependence on the defect morphology and geometric characteristics of Bi2O2Se. The results of this study confirm that the Raman tensors of nanocrystalline structures can be modulated by defects. [ABSTRACT FROM AUTHOR]

Three p‐type thermoelectric (TE) polymers based on the indacenodithiophene moiety substituted with bis(alkylsulfanyl)methylene side‐chains (IDTS) are synthesized. The TE characteristics of IDTS‐based donor–donor' (D–D′) type PIDTSDTTT and donor–acceptor (D–A) type polymers, PIDTSBT and PIDTS2FBT are investigated. Remarkably higher electrical conductivity (σ = ≈1000 S cm−1) and power factor (PF = ≈120 μW m−1 K−2) by doping with AuCl3 are measured for PIDTSDTTT compared to D–A type polymers. The higher σ of PIDTSDTTT originates from its higher carrier concentration compared to those of PIDTSBT and PIDTS2FBT. Moreover, the facile polaron‐to‐bipolaron transition is measured, and the charge carriers are calculated to be more stable with extended delocalization in PIDTSDTTT compared to D–A polymers. The significantly higher doping stability in PIDTSDTTT can be explained in terms of the higher conduction band of bipolarons than the valence band of O2 and H2O, which blocks the facile reduction of bipolarons in air. The energetic structures of doped polaron and bipolaron states, as well as pristine TE polymers, must be carefully considered to realize efficient and stable p‐type thermoelectric polymers, where a D–D′ type structure with further enhanced carrier mobility can be considered as a potential molecular framework. [ABSTRACT FROM AUTHOR]

Static and low frequency noise (LFN) characterizations in two-dimensional (2D) N-type random network thin film transistors (RN-TFTs) based on single-walled carbon nanotubes were presented. For the electrical parameter extraction, the Y-function method was used to suppress the series resistance (Rsd) influence. The gate-to-channel capacitance (Cgc) was directly measured by the split capacitance-to-voltage method and compared to 2D metal-plate capacitance model (C2D). In addition, to account for the percolation-dominated 2D RN-TFTs, a numerical percolation simulation was performed. LFN measurements were also carried out and the results were well interpreted by the carrier number and correlated mobility fluctuation model. Finally, one-dimensional (1D) cylindrical analytical capacitance based model (C1D) was suggested and applied to provide better consistency between all electrical parameters based on experimental and simulation results. [ABSTRACT FROM AUTHOR]

While aluminum nitride (AlN) is at the heart of next-generation optoelectronic applications, the growth of highly crystalline AlN remains a challenge. We investigated the formation of nanovoids (NVs) in AlN crystals and the concomitant effect on the structural and optoelectronic characteristics of AlN crystal layers. Surface treatment with a H3PO4 acid solution etched the initial AlN layer and as-deposited template to introduce NVs between the initial and subsequent AlN layers, and at the interfaces between the epitaxial layers and substrate during AlN regrowth. This approach suppressed the propagation of threading dislocations to the surface, thus promoting the growth of highly crystalline AlN materials. Raman spectroscopy analysis revealed that the residual stresses in AlN films were relaxed by the formation of nanovoids. UV-visible spectrometer analysis confirmed that the regrown AlN had an optical bandgap of 6.08 eV and could be suitable for use in a solar-blind UV photodetector. Furthermore, a metal–semiconductor–metal (MSM) photodetector fabricated on AlN crystals regrown on a template, acid-etched with nanovoids, showed improved photoresponse characteristics and solid solar-blind UV photodetector capability, compared to a MSM fabricated on AlN crystals regrown on an untreated template. We expect that our research will support and promote further development of group-III nitride materials and optoelectronic devices with excellent structural properties. [ABSTRACT FROM AUTHOR]

The nanoscale tribological characteristics of atomic-layered niobium diselenide (NbSe2) were investigated using atomic force microscopy (AFM). Two-dimensional NbSe2 atomic layers were produced on a weakly-adherent silicon wafer using two different methods: (1) mechanical exfoliation and (2) controlled synthesis via chemical vapor deposition. Using an AFM cantilever tip, a normal force was applied on the NbSe2 atomic-scale thin films in order to measure friction force. The as-synthesized NbSe2 thin films exhibited atomic lattice stick-slip friction, with the thinnest sheets showing a sliding length-dependent increase in static friction. This tendency is attributed to the increased susceptibility of the thinner chemically-synthesized NbSe2 sheets toward out-of-plane elastic deformation. [ABSTRACT FROM AUTHOR]

Graphene/carbon nanotube (CNT) junction barrier height was investigated using all-carbon field-effect transistor structure with graphene and single-walled CNT (SWCNT) network as source (S)/drain (D)/gate electrodes and as channel, respectively. SWCNT network channel was formed by dielectricphoresis process at the prepatterned graphene S/D electrodes. By analyzing the measured current–voltage characteristics by the diode circuit model, the Schottky barrier height at the graphene and CNT junction was found to be approximately 0.5 eV. [ABSTRACT FROM AUTHOR]

Functional nanocomposites comprising of biomaterials and non-biomaterials are one of the main subjects of recent research due to their wide range of potential applications. Here, we demonstrate that the porous DNA hydrogel (Dgel) can be an excellent template for combining carbon nanotubes (CNTs) and polyaniline (PANI) resulting in high performance supercapacitor electrodes. These hybrid supercapacitors have been constructed by electrostatic deposition of conductive CNTs on DNA hydrogel followed by coating of PANI pseudocapacitor. Performances of supercapacitors in terms of specific capacitance, cycling stability, power density, and energy density have been systematically investigated. The specific capacitance of these DNA hydrogel based supercapacitors has reached up to 146.4 F g−1 with a power density of 23.3 kW kg−1 and an energy density of 13.0 Wh kg−1 in acidic media which is higher than commercially available products. In addition, the cytotoxicity of our supercapacitors was evaluated in vitro in cell culture media during the charge–discharge processes. In both human and mouse skin cell culture media, our devices exhibited zero cytotoxicity. Our novel biological hybrid electrodes can be a platform towards biocompatible and implantable energy storage devices for in vivo applications. [ABSTRACT FROM AUTHOR]

Single-crystalline GaN-based light-emitting diodes (s-LEDs) on crystalline sapphire wafers can provide point-like light sources with high conversion efficiency and long working lifetimes. Recently, s-LEDs on silicon wafers have been developed in efforts to overcome the size limitations of the sapphire substrate. However, to create larger, cheaper and efficient flat light sources, the fabrication of high-performance s-LEDs on amorphous glass substrates would be required, which remains a scientific challenge. Here, we report the fabrication of nearly single-crystalline GaN on amorphous glass substrates, in the form of pyramid arrays. This is achieved by high-temperature, predominant GaN growth on a site-confined nucleation layer with preferential polycrystalline morphology through local hetero-epitaxy. InGaN/GaN multiple-quantum wells formed on the GaN pyramid arrays exhibit a high internal quantum efficiency of 52%. LED arrays fabricated using these GaN pyramid arrays demonstrate reliable and stable area-type electroluminescent emission with a luminance of 600 cd m?2. [ABSTRACT FROM AUTHOR]

ZnO nanoparticles were grown on single-walled carbon nanotubes (SWNTs) by atomic layer deposition using diethylzinc (DEZ) and water. The athors discuss that, because of chemical inertness of nanotubes to DEZ and water molecules, such nanoparticles are not likely to grow on the wall of clean and perfect nanotubes. Rather, the growth of ZnO nanoparticles should be attributed to imperfection of nanotubes, such as defects and carbonaceous impurities. Lifetime of field emission from SWNTs with the ZnO nanoparticles is 2.5 times longer than that from the as-grown nanotubes. It is thought that the protection of the defects or impurities by ZnO nanoparticles mainly contributed to the improvement of the field emission lifetime from SWNTs. [ABSTRACT FROM AUTHOR]

Spectral discrimination by animal visions such as human, bird, and butterfly is numerically compared by angular analysis of photo‐response (PR) which will be recorded at photo‐receptors. Hyperspectral imaging system is utilized to simulate various animal vision. Bird vision is acute to discriminate colors among different vegetables due to its evenly spaced and narrow spectral responsivity of photo‐receptors compared to that of human. Butterfly vision is excellent in discriminating red tomato ripening due to the exclusive photo‐receptors detecting only over 600 nm. Even real and fake fruits in the same perceived color for human is discriminated by bird vision. Artificial vision with finely resolved polychromatic artificial cone cells are demonstrated surpassing human vision using visible multispectral camera. This provides insights on designing novel bio‐inspired vision system. [ABSTRACT FROM AUTHOR]

Photoresponse on the silicon nanowire (SiNW) and organic semiconductor interfaces embedding an insulating barrier is understood by a photogating effect associated with charge separations. Still elusive one is when the thickness of organic semiconductor is decreased down to a few molecular layers, where the photoresponse can be strongly altered by the spatial confinement of photoinduced carriers. In this work, the photoresponse modulation of SiNW field‐effect transistors coated with an ultrathin organic semiconductor poly(3‐hexylthiophene) (P3HT) is reported, where the P3HT layer thickness is changed by an order of magnitude. In the absence of laser illumination, the P3HT interface on SiNW slightly decreases the SiNW channel current, irrespective of the P3HT thickness. Upon the laser illumination, the thick case of P3HT layers (≈100 nm) supports the dissociation of photoinduced electrons and holes, hence the photogating effect largely decreases the SiNW channel current. When the P3HT layer thickness is decreased down to the P3HT hole diffusion length (≈8.5 nm), the photoinduced P3HT holes screen out the P3HT interface states, effectively increasing the SiNW channel current up to the intrinsic level. The method of engineering the organic semiconductor thickness suggests a complementary optoelectronic operation, verifying the controllable photoresponse within a compact nanodevice. For the modern nanoscale electronics, the increased surface‐to‐volume ratio renders that the device performance becomes more dependent on the surrounding environmental conditions such as organics incorporated. In this work, the authors show that the photoresponse of such nanodevices can be significantly altered when polymers poly(3‐hexylthiophene) with different thicknesses are integrated with the current state‐of‐the‐art silicon nanowire field‐effect transistors. [ABSTRACT FROM AUTHOR]

The patterning of colloidal quantum dots with nanometer resolution is essential for their application in photonics and plasmonics. Several patterning approaches, such as the use of polymer composites, molecular lock-and-key methods, inkjet printing and microcontact printing of quantum dots have been recently developed. Herein, we present a simple method of patterning colloidal quantum dots for photonic nanostructures such as straight lines, rings and dot patterns either on transparent or metallic substrates. Sub-10 nm width of the patterned line could be achieved with a well-defined sidewall profile. Using this method, we demonstrate a surface plasmon launcher from a quantum dot cluster in the visible spectrum. [ABSTRACT FROM AUTHOR]

Imaging spectral information of materials and analysis of its properties have become an intriguing tool for consumer electronics used for food inspection, beauty care, etc. Those sensory physical quantities are difficult to quantify. Hyperspectral imaging cameras, which capture the figure and spectral information simultaneously, can be a good candidate for nondestructive remote sensing. In this study, with the aid of a hyperspectral imaging system (HIS) and machine learning (ML) techniques, meat freshness is converted into a measurable physical quantity, i.e., the freshness index (FI). Herein, the FI is defined as meat fluorescence, which has a strong correlation with the bacterial density. Combined with ML techniques, hyperspectral data are processed more efficiently. By employing linear discriminant and quadratic component analyses, the FI can be estimated from its decision boundary after hyperspectral data are obtained in an unknown freshness state. We demonstrate that the HIS integrated with ML performs as the artificial eye and brain, which is advanced machine vision for consumer electronics, including refrigerators and smartphones. Advanced sensing versatility utilized by computational sensing systems allows hyper-personalization and hyper-customization of human life.

Atomic-layered materials, such as high-quality bismuth oxychalcogenides, which are composed of oppositely charged alternate layers grown using chemical vapor deposition, have attracted considerable attention. Their physical properties are well-suited for high-speed, low-power-consumption optoelectronic devices, and the rapid determination of their crystallographic characteristics is crucial for scalability and integration. In this study, we introduce how the crystallographic structure and quality of such materials can be projected through Raman spectroscopy analysis. Frequency modes at ∼55, ∼78, ∼360, and ∼434 cm -1 were detected, bearing out theoretical calculations from the literature. The low-frequency modes positioned at 55 and 78 cm -1 were activated by structural defects, such as grain boundaries and O-rich edges in the Bi 2 O 2 Se crystals, accompanied by sensitivity to the excitation energy. Furthermore, the line defects at ∼55 cm -1 exhibited a strong 2-fold polarization dependence, similar to graphene/graphite edges. Our results can help illuminate the mechanism for activating the Raman-active mode from the infrared active mode by defects, as well as the electronic structures of these two-dimensional layered materials. We also suggest that the nanoscale width line defects in Bi 2 O 2 Se can be visualized using Raman spectroscopy.

Artificial synaptic platforms are promising for next-generation semiconductor computing devices; however, state-of-the-art optoelectronic approaches remain challenging, owing to their unstable charge trap states and limited integration. We demonstrate wide-band-gap (WBG) III-V materials for photoelectronic neural networks. Our experimental analysis shows that the enhanced crystallinity of WBG synapses promotes better synaptic characteristics, such as effective multilevel states, a wider dynamic range, and linearity, allowing the better power consumption, training, and recognition accuracy of artificial neural networks. Furthermore, light-frequency-dependent memory characteristics suggest that artificial optoelectronic synapses with improved crystallinity support the transition from short-term potentiation to long-term potentiation, implying a clear emulation of the psychological multistorage model. This is attributed to the charge trapping in deep-level states and suppresses fast decay and nonradiative recombination in shallow traps. We believe that the fingerprints of these WBG synaptic characteristics provide an effective strategy for establishing an artificial optoelectronic synaptic architecture for innovative neuromorphic computing.

The enhanced growth of Cu oxides underneath graphene grown on a Cu substrate has been of great interest to many groups. In this work, the strain and doping status of graphene, based on the gradual growth of Cu oxides from underneath, were systematically studied using time evolution Raman spectroscopy. The compressive strain to graphene, due to the thermal expansion coefficient difference between graphene and the Cu substrate, was almost released by the nonuniform Cu 2 O growth; however, slight tensile strain was exerted. This induced p-doping in the graphene with a carrier density up to 1.7 × 10 13 cm -2 when it was exposed to air for up to 30 days. With longer exposure to ambient conditions (>1 year), we observed that graphene/Cu 2 O hybrid structures significantly slow down the oxidation compared to that using a bare Cu substrate. The thickness of the CuO layer on the bare Cu substrate was increased to approximately 270 nm. These findings were confirmed through white light interference measurements and scanning electron microscopy.

The metal/graphene interface has been one of the most important research topics with regard to charge screening, charge transfer, contact resistance, and solar cells. Chemical bond formation of metal and graphene can be deduced from the defect induced D-band and its second-order mode, 2D band, measured by Raman spectroscopy, as a simple and nondestructive method. However, a phonon mode located at ∼1350 cm -1 , which is normally known as the defect-induced D-band, is intriguing for graphene deposited with noble metals (Ag, Au, and Cu). We observe anomalous K-point phonons in nonreactive noble metal/graphene heterostructures. The intensity ratio of the midfrequency mode at ∼1350 cm -1 over G-band (∼1590 cm -1 ) exhibits nonlinear but resonant behavior with the excitation laser wavelength, and more importantly, the phonon frequency-laser energy dispersion is ∼10-17 cm -1 eV -1 , which is much less than the conventional range. These phonon modes of graphene at nonzero phonon wave vector (q ≠ 0) around K points are activated by localized surface plasmon resonance and not by the defects due to chemical bond formation of metal/graphene. This hypothesis is supported by density functional theory (DFT) calculations for noble metals and Cr along with the measured contact resistances.

The ability of metasurfaces to manipulate light at the subwavelength scale offers unprecedented functionalities for passive and active lasing devices. However, applications of metasurfaces to optical devices are rare due to fabrication difficulties. Here, we present quantum dot light emitting diodes (QDLEDs) with a metasurface-integrated metal electrode and demonstrate microscopically controlled LED emission. By incorporating slot-groove antennas into the metal electrode, we show that LED emission from randomly polarized QD sources can be polarized and directed at will. Utilizing the relation between polarization and emission direction, we also demonstrate microscopic LED beam splitting through the selective choice of polarization.

Rapid progress in two-dimensional (2D) crystalline materials has recently enabled a range of device possibilities. These possibilities may be further expanded through the development of advanced 2D glass materials. Zachariasen carbon monolayer, a novel amorphous 2D carbon allotrope, was successfully synthesized on germanium surface. The one-atom-thick continuous amorphous layer, in which the in-plane carbon network was fully sp 2 -hybridized, was achieved at high temperatures (>900°C) and a controlled growth rate. We verified that the charge carriers within the Zachariasen carbon monolayer are strongly localized to display Anderson insulating behavior and a large negative magnetoresistance. This new 2D glass also exhibited a unique ability as an atom-thick interface layer, allowing the deposition of an atomically flat dielectric film. It can be adopted in conventional semiconductor and display processing or used in the fabrication of flexible devices consisting of thin inorganic layers.