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In two-dimensional transition metal dichalcogenides, normal strain can modulate electronic band structures, yet leaving the optical selection rules intact. In contrast, a shear strain can perturb the spin-valley locked band structures and possibly induce mixing of the spin subbands which in turn can transfer oscillator strength between spin-allowed bright and spin-forbidden dark excitons. Here, we report a novel scheme to manipulate photoluminescence (PL) in a monolayer WSe2-MoSe2lateral heterostructures, controlled by an external bending method in which strong out-of-plane shear strain (OSS) of up to 5.6% accompanies weak in-plane normal strain up to 0.72%. The spectra revealed a striking dependence on the bending direction that is stagnant in the negative (compressive) strain region and then rapidly changes with increasing positive (tensile) strain. The dependency of the PL signal under tensile bending was represented not only by the large energy shift (>40 meV) of the lowest excited states of both the WSe2and MoSe2monolayers, but also by the tendency to violate the optical selection rules that brightens (darkens) the excitons of the WSe2(MoSe2) side. The analyses on the observed energy shifts and PL intensity changes confirm the different origins in compressive bending compared with tensile bending. The well-established band-anticrossing is identified to be affecting only the compressive deformation region. The spectral changes in the tensile region, on the other hand, originates mainly from the generation of an off-diagonal perturbation to a spin-specific Hamiltonian induced by OSS. The degree of spin-state mixing, which correlates precisely with the spin-flip coefficient of the theoretical model, is further represented by the OSS matrix elements, the spin splitting energy, and the shear deformation potential.

The effective mass approximation (EMA) could be an efficient method for the computational study of semiconductor nanostructures with sizes too large to be handled by first-principles calculations, but the scheme to accurately and reliably introduce EMA parameters for given nanostructures remains to be devised. Herein, we report on an EMA approach based on first-principles-derived data, which enables accurate predictions of the optoelectronic properties of quantum nanostructures. For the CdS/ZnS core/shell quantum rods, for which we recently reported its experimental synthesis, we first carry out density functional theory (DFT) calculations for an infinite nanowire to obtain the nanoscopic dielectric constant, effective mass, and Kohn-Sham potential. The DFT-derived data are then transferred to the finite nanorod cases to set up the EMA equations, from which we estimate the photoluminescence (PL) characteristics. Compared with the corresponding method based on bulk EMA parameters and abrupt potential, we confirm that our EMA approach more accurately describes the PL properties of nanorods. We find that, in agreement with the experimentally observed trends, the optical gap of nanorods is roughly determined by the nanorod diameter and the PL intensity is reduced with increasing the nanorod length. The developed methodology is additionally applied to CdSe nanoplatelets, where reliable experimental data became recently available. Here, we again obtain excellent agreements between calculated and measured optical gap values, confirming the generality of our approach. It is finally shown that the abrupt confinement potential approximation most adversely affects the accuracy of EMA simulations., 14 pages, 6 figures, 3 tables

Seeding promoters facilitate the nucleation and growth of transition metal dichalcogenides in chemical vapor deposition (CVD). However, sophisticated roles of seeding promoter remain unclear. Here, adopting triangular-shaped crystal violet (CV) consisting of nonpolar and polar parts as the seeding promoter, we study the role of seeding promoter for the growth of molybdenum disulfide (MoS2). We systematically control the geometrical configuration of CV on SiO2/Si substrate by changing the solvent polarity and find that it strongly affects the growth of monolayer or multilayer MoS2 domains via CVD. Monolayer MoS2 domains were predominantly grown on randomly lying-down CV configurations on SiO2/Si substrate, whereas multilayer MoS2 domains are synthesized at concentrated polar parts in CV micelle on the substrate. Density functional theory calculations reveal that the initial nucleation step for the MoS2 growth is the adsorption of S on CV and the most favourable S adsorption site is the polar part in CV. Furthermore, it is found that the CV adsorption to SiO2 is mediated by the polar CV part and additionally strengthened in the lying-down CV configuration. Enhancing the thermal stability as well as hindering the re-aggregation of CV at high temperature, the lying down CV configuration allows the predominant growth of monolayer MoS2. This work provides a general framework to understand the growth of MoS2 from aromatic seeding promoters.

In this paper, we report the emulation of synaptic functions such as paired-pulse facilitation (PPF), spike-frequency dependent plasticity (SFDP), and spike-duration dependent plasticity (SDDP) using a solution-processed amorphous indium-gallium-zinc oxide (IGZO) photoelectric synaptic device. Particularly, instead of using electrical stimuli, we used an optical stimuli (light pulse) to modulate the synaptic weight of the IGZO photoelectric synaptic device which is equivalent to the conductance of the IGZO active layer. The time interval between the paired pulses, frequency and the pulse duration of the optical stimuli were controlled to emulate the PPF, SFDP, and SDDP behaviors, respectively. Also, we emulated the Ebbinghaus forgetting curve which is related to the memory retention behavior, as another possible demonstration of the IGZO-based photoelectric synaptic device.

In this study, we show the evolution of nitrogen defects during a sol–gel reaction in flash-lamp-annealed InGaZnO (IGZO) films and their effects on the device characteristics of their thin-film transistors (TFTs). The flash lamp annealing (FLA) of the IGZO TFT for 16 s helps achieve a mobility of approximately 7 cm2 V−1 s−1. However, further extension of the annealing time results only in drastic increases in carrier concentration and off-current. The X-ray photoelectron spectroscopy (XPS) analysis of the N 1s peak unravels the presence of oxygen-vacancy-associated nitrogen defects and their evolution with annealing time, which is possibly responsible for the increase in carrier concentration.

ArF immersion lithography may be the best candidate for sub-60 nm device patterning. However, the polarization effect is the most prominent root cause for the degradation of the image quality in high numerical aperture (NA) immersion lithography as the feature size shrinks. Therefore, it is important to understand the polarization effect in the mask. It is common knowledge that a small mask pattern is considered as the wave guide of transmission light. The induced polarization effect shows the different aspects between the conventional mask and the attenuated phase-shift mask (PSM). In this paper, we considered the effects of polarization state as a function of mask properties. The aerial image depends on the polarization states induced by the mask. We evaluated the performances of the conventional mask and the attenuated PSM by using the Solid-ETM simulation and AIMSTM (Aerial Image Measurement System) tool along with real wafer printing.

Using a three-dimensional local spin-density functional method, we investigate the electronic structure of quasi two-dimensional ellipsoidal quantum dots with elliptical deformation. Changes in the electron addition energy spectra and spin polarization are investigated as a function of the number of electrons and the elliptical deformation on the lateral direction confinement potential, and compared with those of a circular dot which shows a shell structure. Especially, we find that, due to the electron-electron interaction, the anisotropy of an elliptical dot is higher than that of a bare potential by ~1.2 for experimentally realistic potentials.

A stepper motor mechanism activates the azimuth and elevation direction of an X-band downlink antenna-pointing mechanism for effective data transfer from a satellite to a ground station. The stepper motor activation, and an imperfect intermeshed teeth harmonic-drive-gear configuration of the antenna mechanism may induce micro-jitter in the system, which can seriously affect the image quality of high-resolution observation satellites. In this study, to confirm the feasibility of on-orbit micro-jitter isolation of a whole-antenna mechanism assembly, a new type of passive vibration isolation system was proposed and investigated. This proposed system uses a pseudoelastic shape memory alloy compressed mesh washer isolator. The basic characteristics of the isolator were measured by performing static test on the isolator. The effectiveness of the design was also demonstrated via a micro-jitter measurement test, with and without the isolation system.

We report high-performance ink-jet-printed 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TESADT) organic thin-film transistors (OTFTs) facilitated by polymer blending. The film morphology and crystal structure of diF-TESADT films were greatly improved by printing on a predeposited poly(α-methyl styrene) (PαMS) layer possibly due to the confined droplet area and thus increased intermolecular interactions. Additionally, partial dewetting and the formation of irregular film shapes were effectively controlled resulting in uniform and improved device performance in the predeposited blending system. Through a proper optimization of printing parameters such as substrate temperature and processing solvent, diF-TESADT TFTs with an average field-effect mobility of 0.34±0.13 cm2 V-1 s-1 (max 0.64 cm2 V-1 s-1) and subthreshold slope of 0.456±0.090 V decade-1 have been achieved.

Enhanced stability of all solution-processed organic thin-film transistors (OTFTs) has been achieved by replacing metallic electrodes with glycerol-modified poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) polymer electrodes. The modified PEDOT:PSS showed a substantially low electrical resistivity of 6.4×10-3 Ω cm with improved environmental stability and water-resistant characteristics, which are crucial for highly reliable applications. Additionally, the modified PEDOT:PSS electrodes were highly stable under intense mechanical stress, allowing their application to flexible electronics. Particularly, all solution-processed flexible and transparent OTFTs with the modified PEDOT:PSS electrodes showed a field-effect mobility decrease of only 2.7% after a tensile mode mechanical fatigue test, while OTFTs with metallic electrodes showed a mobility decrease of 56.6% under identical test conditions.

We investigated the effects of annealing temperature on the electrical characteristics of solution-processed zinc tin oxide (ZTO) thin-film transistors (TFTs). When the annealing temperature increased from 300 to 500 °C, the threshold voltage of solution-processed ZTO TFTs decreased from 16.89 to -0.23 V owing to the increase in electron concentration in the active layer. The increase in electron concentration is caused by the decrease in Cl atomic concentration. When the annealing temperature increased to 500 °C, the saturation mobility increased from 0.18 to 4.75 cm2·V-1·s-1 and the threshold voltage shift for positive gate bias stress as a reliability characteristic decreased from 5.34 to 2.6 V, because of the decomposition of halide residues such as Cl and the nanocrystallization.

We investigated the effect of annealing treatment and surface morphology on power conversion efficiency (PCE) of organic photovoltaic (OPV) devices. The bulk-heterojunction OPV devices were fabricated by using poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) as a donor and an acceptor material, respectively. Significant changes of surface morphology and grain size were observed by varying annealing temperature, which is possibly due to different diffusion rate of PCBM molecules into the bulk-heterojunction polymer films. From these results, we conclude that differences in surface morphology and grain size are responsible for the significantly different PCE in the OPV devices. Consequently, the PCE is improved from 0.5 to 2.6% combined with the increase of short-circuit current and fill factor by annealing treatment at 150 °C.

We report all solution-processed high-resolution bottom-contact indium-gallium-zinc-oxide (IGZO) thin film transistors (TFTs) using a simple surface patterning and dip-casting process. High-resolution nanoparticulate Ag source/drain electrodes and a sol?gel processed IGZO semiconductor were deposited by a simple dip-casting along with a photoresist-free, non-relief-pattern lithographic process. The deposited Ag and IGZO solution can be steered into the desired hydrophilic areas by a low surface energy self-assembled monolayer, resulting in source/drain electrodes and semiconducting layer, respectively. The all solution-processed bottom-contact IGZO TFTs including a channel length of 10??m typically showed a mobility range 0.05?0.2?cm2?V?1?s?1 with an on/off ratio of more than 106.

We have developed a new technique for fabricating a hole (well) with a diameter of about 1 µm for a microelectrode on the surface of SiO2 (600 nm)/CoSi2 (10 nm)/Si substrate. This process enabled the fabrication of electrode holes while maintaining the original nanolevel flatness (R a∼0.8 nm) of the SiO2 surface. A lipid bilayer was formed by giant vesicle fusion on these microelectrodes. Fluorescence microscope, in situ atomic force microscope and electrical characteristics measurements showed that a single lipid bilayer of sufficiently high resistance (gigaohm seal) was successfully fabricated.

Phase-shifting masks (PSMs) have provided us a breakthrough in the future semiconductor industry by extending lithography further to the submicrometer order. PSMs have been used over the past several years, and their requirements have changed due to the development of semiconductor technology. We investigated high-transmittance attenuated PSMs (HT-Att-PSMs) that satisfy the requirements of 20±5% transmittance and 180° phase shift at the exposure wavelength and less than 40% transmittance at the inspection wavelength. Regarding the wavelength, we targeted the inspection wavelength of 248 nm for ArF laser (exposure wavelength of 193 nm) HT-Att-PSM, and 365 nm for KrF laser (exposure wavelength of 248 nm) HT-Att-PSM. In this study, we developed refractive index-extinction coefficient-thickness (n-k-d) charts showing optimum optical constant ranges for HT-Att-PSM using the matrix method. The simulation was verified by comparing calculated transmittance data with measured ones.