The accurate characterization of buried electronic structures in solution-processed bulk heterojunctions (BHJs) remains challenging due to surface phase separation and spectral overlap between donor and acceptor components. In this study, a depth-resolved analytical methodology is demonstrated by integrating ultraviolet photoelectron spectroscopy (UPS) with argon gas cluster ion beam (Ar-GCIB) sputtering. This approach enables evaluation of the depth-dependent electronic structure and relative energy-level alignment in spin-coated P3HT:PCBM71 BHJ films with varying compositions (3:1, 1:1, and 1:3 by weight). Surface-sensitive UPS and reflection electron energy loss spectroscopy (REELS) reveal that the as-prepared BHJ films exhibit a P3HT-enriched surface, resulting in electronic structures dominated by the donor component. Upon controlled Ar-GCIB sputtering, the contribution of PCBM71 increases, enabling separation of donor and acceptor electronic states. By applying a linear combination analysis to the valence band spectra, the HOMO levels of P3HT and PCBM71 are extracted as a function of sputtering time. Notwithstanding the potential for modifications in polymeric materials induced by sputtering, the extracted HOMO offsets remain consistent (1.13–1.20 eV) across varying compositions and sputtering conditions, thereby indicating the preservation of the relative donor–acceptor energy-level alignment. This work demonstrates a practical methodology for probing buried electronic structures in complex BHJ systems that are not accessible by conventional surface-sensitive techniques.

Molybdenum disulfide (MoS₂), as a representative two-dimensional (2D) transition metal dichalcogenide, has attracted significant interest for next-generation electronic and optoelectronic devices. However, conventional lithography and etching processes often involve harsh chemicals or plasma treatments that introduce defects and residues, thereby limiting the reliable fabrication of MoS₂-based devices. Here, we demonstrate a two-step scanning probe lithography approach for the controlled etching of mechanically exfoliated MoS₂ flakes onto a silicon substrate. Contact mode atomic force microscopy (AFM) with a diamond-coated tip was used to perform mechanical etching under high-force conditions. The debris generated from the etching process was effectively removed by the subsequent cleaning step, which employed a mild-force contact mode operation. By this careful two-step etching process, a reliable contamination-free etching of a 2D MoS2 flake was successfully carried out. Additionally, the contaminated diamond-coated AFM tip, which can be damaged during repeated etching processes, can be repaired with a simple oxygen plasma treatment. This approach can be applied to other 2D materials, including graphene, and provides a new direction for the nanofabrication of 2D materials in next-generation electronic devices.

Hybrid organic-inorganic perovskites exhibit rich structural dynamics that govern their stability and optoelectronic performance. Here we map the temperature-composition phase behavior of dimethylammonium lead mixed halides, DMAPbBr3-xClx with x = 0, 0.5, 1.5, 2, 2.5 and 3, by combining temperature-dependent powder Xray diffraction, Raman and Brillouin spectroscopy, dielectric spectroscopy and differential scanning calorimetry. All compositions undergo a first-order transition between an orthorhombic (P212121) low-temperature phase and a hexagonal (P63/mmc) high-temperature phase. The transition temperature increases monotonically with Cl content at 251, 256, 265, 283, 306, and 318 K for x = 0, 0.5, 1.5, 2, 2.5, and 3, respectively. Distinct experimental signatures include: (i) abrupt hardening/softening anomalies of low-frequency Raman modes (down to 10 cm-1) associated with octahedral twists and Pb-X stretching; (ii) softening of the longitudinal acoustic phonon mode and a discontinuous jump at transition temperatures in the Brillouin spectra, evidencing elastic modulus renormalization; (iii) step-like increases in the real part of the dielectric permittivity (epsilon 1), reflecting increased DMA reorientational polarizability and (iv) sharp DSC endotherms that quantify latent heat and confirm the first-order character. We integrate these datasets to develop a temperature-composition phase diagram for DMAPbBr3-xClx and clarify how halide substitution stiffens the lattice and strengthens hydrogen-bond network to tune the transition temperature. The results provide mechanistic insight into cation-framework coupling in DMA-based perovskites and valuable insights for optimizing their structural properties to enhance device performance.

We present a comprehensive spectroscopic and computational investigation of the mixed-halide hybrid perovskite system DMAPbBr3-xClx (x = 0, 0.8, 1.6, 1.9, 2.5, 3), revealing unprecedented insights into halide-mediated structural dynamics. Through advanced antisolvent vapor-assisted crystallization, we synthesized high-quality single crystals for comprehensive characterization via complementary Brillouin, Raman, and Fourier-transform infrared (FTIR) spectroscopy techniques. Our room-temperature Brillouin analysis uncovers a pronounced composition-driven symmetry transformation from hexagonal (P63/mmc) to orthorhombic (P212121) between x = 1.9 and 2.5, marked by an abrupt enhancement in longitudinal acoustic phonon frequency. Systematic Raman and FTIR investigations demonstrate definitive correlations between halide substitution and dimethylammonium cation vibrational signatures, elucidating critical relationships between halide mass, bond strength, and hydrogen bonding interactions. Remarkably, temperature-dependent Raman spectroscopy reveals anomalous phonon hardening with increasing temperature-a phenomenon we attribute to quartic anharmonicity within the face-sharing PbX6 octahedral framework. The distinctive redshift behavior of the nu(CNC) mode provides compelling evidence of thermal weakening in cation-framework coupling mechanisms. These discoveries establish fundamental structure-property relationships in DMA-based halide perovskites and demonstrate the strategic potential of halide substitution for precise engineering of vibrational and elastic properties in next-generation low-symmetry hybrid perovskite systems.

GPR119 has emerged as a promising target for treating type 2 diabetes and associated obesity, as its stimulation induces the secretion of glucagon-like peptide-1 and glucose-dependent insulinotropic peptide in the intestinal tract as well as the glucose-dependent release of insulin in pancreatic β-cells. We describe the design and synthesis of novel GPR119 agonists containing a 1,4-disubstituted cyclohexene scaffold. Compound 21b displayed nanomolar potency (EC50 = 3.8 nM) for hGPR119 activation and demonstrated a hypoglycemic efficacy of 17.0% in an oral glucose tolerance test. The hypoglycemic effect of compound 21b, compared to sitagliptin, a DPP-4 inhibitor, showed the relatively higher efficacy in both FATZO and db/db mice. Additionally, compound 21b exhibited a significant reduction in body weight in a female diet-induced obese rat model, comparable to that of metformin. Furthermore, in vivo pharmacokinetic experiments revealed that compound 21b is a potential candidate for the treatment of type 2 diabetes and obesity.

The power output of piezoelectric sensors based on nanowires (NWs) is governed by various factors, but largely depends on the alignment of the NWs. However, aligning the NWs has proved to be difficult. We successfully developed self-powered and flexible piezoelectric motion sensors (PMSs) with InN NWs as a response medium. The device performance was maximized by spatially controlling the alignment of the InN NWs by applying a magnetic field, which was the first step in the development of the NW-PMSs. The output voltage of the PMS with the InN NWs aligned along the bending direction was measured to be 3.05 V, which was a significant improvement of 2.44 times compared to that with randomly-distributed NWs. A systematic analysis of the extent to which the performance of the PMSs depend on the device parameters, such as the length of the NWs, bending frequency, operation time (up to 30 days), relative humidity, and bending cycle, indicates that the device performance is sufficient for real-life applications. For example, attachment of the self-powered PMSs to human joints such as the finger, wrist, elbow, and knee revealed that these motion sensors are highly effective, thereby indicating the possibility of detecting the various motions of the human body. The self-powered PMSs developed in this work are expected to contribute to rehabilitation, disease prevention, and human-machine interaction.

As an effective method to fabricate a large-area cross-sectional sample for lithium-ion battery electrodes, we perform in-plane polishing of LiNi0.8Co0.15Al0.05O2 (NCA) cathode samples and obtain a large cross-sectional area with a diameter of 1.5 mm. The polished cross-sections of NCA cathode particles are sufficiently flat to perform the atomic force microscopy (AFM) measurements on each cathode particle. Following AFM-based Kelvin probe force microscopy and scanning spreading resistance microscopy measurements, an identical in-plane polished NCA sample is assembled into a coin cell for the charge and discharge processes. After 90 charge/discharge cycles, the in-plane-polished sample is successfully disassembled from the coin cell without causing critical damage. In addition, a microcrack structure, which is a typical degradation feature of the cycles of NCA particles, is observed for the identical in-plane polished NCA sample. This indicates that the in-plane polishing method is effective for investigating identical NCA electrode samples before and after the charge/discharge process. Furthermore, the in-plane polishing method can be successfully applied to the large-area polishing of a Si-based anode which is a mixture of Si carbon complexes and graphite particles. This study presents a novel methodology for analyzing the degradation of lithium-ion battery electrode materials.

Lithium is a promising anode material for advanced batteries because of its high capacity and low redox potential. However, its practical use is hindered by nonuniform Li deposition and dendrite formation, leading to safety concerns in Li metal batteries. Our study shows that Ag-based materials enhance the uniformity of Li deposition on Ag-modified Li (AgLi) surfaces, thereby addressing these key challenges. This improvement is due to the strong affinity of Ag for Li, which promotes uniform deposition and dissolution. Additionally, the AgLi surface demonstrated an improved cycling stability, which is crucial for long-term battery reliability. Emphasizing our analytical approach, we utilized comprehensive techniques such as Kelvin probe force microscopy (KPFM) and electrochemical atomic force microscopy (EC-AFM) to locally analyze the electrical properties and unravel the Li deposition/dissolution mechanisms. KPFM analysis provided crucial insights into surface potential variations, while EC-AFM highlighted topographical changes during the Li deposition and dissolution processes, contributing significantly to the development of safer and more efficient Li metal batteries.

One of the most critical points in the study of LIB-related materials is the extremely high reactivity of Li. In addition to pure Li metal, many Li-containing materials employed in LIBs are highly reactive under ambient conditions. Therefore, they should be stored and treated in an inert environment, such as vacuum chambers and gloveboxes filled with inert gases. In particular, most pristine cathode materials contain Li and are more reactive in air than pristine anode materials are. For instance, various impurities, mostly Li2CO3, are grown on the surface of pristine NCA (LiNixCoyAlzO2, x + y + z = 1) materials. The precise characterization of these ambient-induced surface impurities is critical for understanding the intrinsic properties of these cathode materials. In this study, we directly image and characterize ambient-induced surface impurities formed on the surface of high-Ni NCA (LiNi0.8Co0.15Al0.05O2) materials using Kelvin probe force microscopy (KPFM) and scanning spreading resistance microscopy (SSRM). The ambient-induced surface impurities show clearly distinguishable work functions and resistance features compared with the pristine NCA surface. In particular, it is confirmed that the resistance of ambient-induced impurities is significantly higher than that of pristine NCA materials, which can deteriorate the performance of LIB cells. This study provides direction for the fabrication, storage, and processing of LIB cathode materials.

Light absorption and emission phenomena are attractive topics in a wide range of research fields, because they can be applied to the development of optoelectronic devices.Nanoscale measurement tools with light illumination are important for investigating optoelectronic properties.In this study, we design and fabricate a bottom-illumination-type compact light illumination module with a laser diode.The module is successfully installed and operated in a commercial atomic force microscope (AFM) instrument.Using this module, we can locally illuminate a MoS 2 flake from the bottom and perform AFM measurements to reveal its thickness and size.In addition, photoconductive AFM (pc-AFM) can be conducted by measuring the current between the metallic tip and the sample in the dark and under illumination.The most important advantage of our light illumination module is that we can illuminate a specific sample area locally without illuminating the rest of the sample area.This module can be used for pc-AFM or Kelvin probe force microscopy study under illumination for various optoelectronic materials or devices.

Multiwalled carbon nanotube (MWCNT) forests have extremely large surface areas and high catalytic activity. To use them as alternative materials for Pt/fluorine-doped tin oxide (FTO) conventional counter electrodes (CEs) in dye-sensitized solar cells (DSSCs), a unique Ru metal layer, prepared with 600-cycle atomic layer deposition, was employed. The best Ru-coated MWCNT forest (Ru/MWCNT) CE performance was achieved by examining the experimental conditions for the MWCNT forests, including deposition processes, catalyst thicknesses and synthesis time. The results revealed that 20μm-thick MWCNT forests with numerous defects/disordered sites exhibit excellent CE performance. In practice, Ru/MWCNT CEs prepared under optimal synthesis conditions show low charge transfer resistance (Rct of approximately 2.5 ohm) and series resistance (Rs of approximately 14 ohm) that are even better than those for Pt/FTO CEs (Rct=6.36 ohm and Rs=16.4 ohm). Owing to these excellent Rct and Rs values, dye-sensitized solar cells with optimized Ru/MWCNT CEs showed better performance than those containing Pt/FTO CEs. Finally, post-heat treatment of Ru/MWCNT CEs increased the cell efficiency of the DSSCs.

Quantum dots possess exceptional optoelectronic properties, such as narrow bandwidth, controllable wavelength, and compatibility with solution-based processing. However, for efficient and stable operation in electroluminescence mode, several issues require resolution. Particularly, as device dimensions decrease, a higher electric field may be applied through next-generation quantum dot light-emitting diode (QLED) devices, which could further degrade the device. In this study, we conduct a systematic analysis of the degradation phenomena of a QLED device induced by a high electric field, using scanning probe microscopy (SPM) and transmission electron microscopy (TEM). We apply a local high electric field to the surface of a QLED device using an atomic force microscopy (AFM) tip, and we investigate changes in morphology and work function in the Kelvin probe force microscopy mode. After the SPM experiments, we perform TEM measurements on the same degraded sample area affected by the electric field of the AFM tip. The results indicate that a QLED device could be mechanically degraded by a high electric field, and work function changes significantly in degraded areas. In addition, the TEM measurements reveal that In ions migrate from the indium tin oxide (ITO) bottom electrode to the top of the QLED device. The ITO bottom electrode also deforms significantly, which could induce work function variation. The systematic approach adopted in this study can provide a suitable methodology for investigating the degradation phenomena of various optoelectronic devices.

One of the most critical points in the study of LIB-related materials is the extremely high reactivity of Li. In addition to pure Li metal, many Li-containing materials employed in LIBs are highly reactive under ambient conditions. Therefore, they should be stored and treated in an inert environment, such as vacuum chambers and gloveboxes filled with inert gases. In particular, most pristine cathode materials contain Li and are more reactive in air than pristine anode materials are. For instance, various impurities, mostly Li2CO3, are grown on the surface of pristine NCA (LiNixCoyAlzO2, x+y+z=1) materials. The precise characterization of these ambient-induced surface impurities is critical for understanding the intrinsic properties of these cathode materials. In this study, we directly image and characterize ambient-induced surface impurities formed on the surface of high-Ni NCA (LiNi0.8Co0.15Al0.05O2) materials using Kelvin probe force microscopy (KPFM) and scanning spreading resistance microscopy (SSRM). The ambient-induced surface impurities show clearly distinguishable work functions and resistance features compared with the pristine NCA surface. In particular, it is confirmed that the resistance of ambient-induced impurities is significantly higher than that of pristine NCA materials, which can deteriorate the performance of LIB cells. This study provides direction for the fabrication, storage, and processing of LIB cathode materials.

To apply and utilize high-performance batteries in actual devices, achieving stable cycle operation during the charging and discharging process is the main key. In particular, keeping the stability of anodes without performance degradation as Li inserts and extracts is critical. Here, we report a straightforward and effective method for forming the stable Li ionic conductive layers in silicon-carbon composite anode, which can be practically applicable for anode production. Stable layers of lithium metasilicate, known as a good Li ionic conductor, were successfully fabricated on Si nanoparticles within silicon-carbon composite by simply mixing lithium oxide nanoparticles with a coar tar pitch carbon source during high-temperature carbonization process of the composite particles. From electrochemical measurements applied to various types of cell manufactured by conventional production process, a cell with selectively coated anodes and conventional LiNixMnyCozO2 cathode show a significantly higher performance stability and an excellent fast charging characteristics. This study presents a straightforward and effective method to increase the stability of silicon-carbon composite anode materials at low cost for commercial production of high-performance lithium ion battery.

A high energy density is an essential requirement for commercial lithium-ion batteries (LIBs) in electric vehicles (EVs) because it directly affects driving range. In addition, the fast charging performance of LIBs, which determines the charging time, is critical in the EV industry. A common approach to enhance the energy density of LIBs is to increase the active material loading by increasing the electrode thickness. However, there is limited scope for increasing the thickness of LIB electrodes in fast charging operations because the power density characteristics of LIB cells are degraded with increasing electrode thickness. Here, we estimate the lithium concentration distribution within thick LIB cathodes after charging/discharging by studying the work function distribution within the thick electrodes using Kelvin probe force microscopy (KPFM). First, to determine the relationship between the work function and lithium content in LIB cathodes, we measure the work function of thin LiNi0.88Co0.09Al0.03O2 (NCA) electrodes under various state-of-charge (SOC) conditions. From these measurements, it is demonstrated that the work function of the NCA electrodes is proportional to the SOC. The results suggest that the work function measurements obtained using KPFM can be used to estimate the Li concentration of NCA electrodes. Next, we perform depth-dependent KPFM measurements in thick NCA samples, which can provide depth profiles of the work function depending on the C-rate conditions. The work function shows a monotonic increase along the depth direction of the thick NCA cathodes, implying a depth-dependent inhomogeneous distribution of lithium concentrations.

Quantum dots (QDs) have outstanding optoelectronic properties. However, several issues need to be resolved for efficient and stable operation in electroluminescence mode. In particular, as device dimensions become smaller, a higher electric field can be applied through the device which may induce further degradation of the device. In this study, we perform a systematic analysis of the degradation phenomena of a quantum dot light-emitting diode (QLED) device induced by a high electric field, using scanning probe microscopy (SPM) and transmission electron microscopy (TEM). A local high electric field is applied using an atomic force microscopy (AFM) tip on the surface of a QLED device, and the changes in morphology and work function are investigated in the Kelvin probe force microscopy (KPFM) mode. After the SPM experiments, TEM measurements are performed on the identical sample area degraded by the electric field of the AFM tip. The results demonstrate that a QLED device could be mechanically degraded by a high electric field and the work function changes significantly in the degraded areas. In addition, the TEM measurements illustrates that the In ions migrate from the indium tin oxide (ITO) bottom electrode to the top of the QLED device.

Graphene nanoribbon, which is the one-dimensional form of graphene, is an attractive nano structure for next generation electronic devices. Herein, we studied the electronic properties of pseudo-GNRs in large-scale graphene sheets grown on Ge(110) using low temperature scanning tunneling microscopy (STM) and spectroscopy (STS). Based on our STM results, the pseudo-GNRs are aligned in the <112> direction of the Ge surface; the alignment of the pseudo-GNRs is controlled by the surface reconstruction of Ge(110) substrate, which can be an important merit in terms of the mass fabrication. Bandgap energies ranging from ∼0.12 to ∼0.3 eV were measured via STS on pseudo-GNRs in graphene/Ge(110), while the surrounding graphene area outside the pseudo-GNR growth region shows the typical electronic structure of graphene, verifying the spontaneous formation of metallic-semiconducting-metallic junction nanostructure. This study unveils the geometric and electronic properties of pseudo-GNRs in graphene/Ge(110), providing essential information for the realization of next-generation nanoelectronic devices.

The polymerization of graphitic carbon nitride (g-C3N4) into large single crystals has been particularly challenging. This study presents a quick and simple method to grow high quality two-dimensional graphitic carbon nitride nanosheets with a large domain size (up to 40 mu m) on copper (Cu) foils. The chemical vapor deposition (CVD) method was used with melamine (C3H6N6) as the source. Electron backscatter diffraction (EBSD) revealed that graphitic carbon nitride prefers a Cu(111) surface to a Cu(211) surface, which is consistent with the theoretical calculations. Moreover, it was demonstrated that the carrier gas is critical for the growth of graphitic carbon nitride. The use of noble Ar gas is recommended because it has a weaker etching effect compared to that of the more commonly used hydrogen (H-2) gas. Furthermore, CVD-grown high-quality graphitic carbon nitride films can be easily transferred onto other substrates for various applications, such as photodetectors or metal-free photocatalysts. (C) 2021 Published by Elsevier B.V.

Metal halide perovskite solar cells (PSCs) have been considered to be one of the most promising next-generation energy harvesters over the past decades due to remarkably rapid improvement of power conversion efficiency in photovoltaics. However, energy harvesters based on the solar energy source have an intrinsic environment limitation for indoor applications. A feasible solution to the limitation is to add non-solar energy harvesting functions to the solar energy harvesters. Here, the piezoelectric properties of two types of metal halide PSCs are investigated, the 3D only and the 3D/2D structure, showing PCEs of 21.3% and 23.2%, respectively. Piezo-response force microscopy and synchrotron-based X-ray diffraction demonstrate that both types of PSC sample have piezoelectricity. Remarkably, the 3D/2D structure has considerably higher piezoelectric amplitude than the 3D-only. The deep level transient spectroscopy results reveal that the enhancement in the piezoelectricity of the 3D/2D structure originates from Pb-Br defects. This study unravels the role of defects in the piezoelectricity of metal halide PSCs and provides a direction to develop the multi-function energy harvesters based on the PSCs.

Transition metal dichalcogenides (TMDs) have been widely studied as attractive two-dimensional (2D) materials. In particular, specific TMD materials have attracted increasing attention because of their intriguing features as 2D topological insulators (TIs), which have a metallic edge state and bulk band gap. To realize next-generation devices that employ the metallic edge states of 2D TI materials, precise patterning of the edges is essential. In this study, we demonstrate a simple nanopatterning technique for 1 T'-MoTe2, which is known to be a 2D TI material, using atomic force microscopy (AFM)-based scanning probe lithography (SPL). Our AFM-based SPL method entails delicately scratching a few-layer 1 T'-MoTe2 sample while applying an electric field using a conductive AFM tip. The proposed method enables nanoscale lines, holes, and letters to be reliably patterned on the 1 T'-MoTe2 sample. This study results in the development of a clean method that is compatible with existing mass-production facilities to fabricate various TMD materials for realizing next-generation electronic devices and for studying the underlying physics of these materials.