Random laser ablated tags for anticounterfeiting purposes and towards physically unclonable functions.

Anticounterfeiting tags affixed to products offer a practical solution to combat counterfeiting. To be effective, these tags must be economical, capable of ultrafast production, mass-producible, easy to authenticate, and automatable. We present a universal laser ablation technique that rapidly generates intrinsic, randomly distributed craters (in under a second) on laser-sensitive materials using a nanosecond pulsed infrared laser.

High-κ Dielectric (HfO)/2D Semiconductor (HfSe) Gate Stack for Low-Power Steep-Switching Computing Devices.

Herein, a high-quality gate stack (native HfO formed on 2D HfSe) fabricated via plasma oxidation is reported, realizing an atomically sharp interface with a suppressed interface trap density (D ≈ 5 × 10 cm eV). The chemically converted HfO exhibits dielectric constant, κ ≈ 23, resulting in low gate leakage current (≈10 A cm) at equivalent oxide thickness ≈0.5 nm.

Facet-Dependent Passivation for Efficient Perovskite Solar Cells.

Understanding the interplay between the surface structure and the passivation materials and their effects associated with surface structure modification is of fundamental importance; however, it remains an unsolved problem in the perovskite passivation field. Here, we report a surface passivation principle for efficient perovskite solar cells via a facet-dependent passivation phenomenon. The passivation process selectively occurs on facets, which is observed with various post-treatment materials with different functionality, and the atomic arrangements of the facets determine the alignments of the passivation layers.

Correlation between the Surface Undulation and Luminescence Characteristics in Semi-Polar 112¯2 InGaN/GaN Multi-Quantum Wells.

Surface undulation was formed while growing InGaN/GaN multi-quantum wells on a semi-polar m-plane (1-100) sapphire substrate. Two distinct facets, parallel to 112¯2 and 011¯1, were formed in the embedded multi-quantum wells (MQWs). The structural and luminescence characteristics of the two facets were investigated using transmission electron microscopy equipped with cathodoluminescence.

Measurement of dielectric function and bandgap of germanium telluride using monochromated electron energy-loss spectroscopy.

Using a monochromator in transmission electron microscopy, a low-energy-loss spectrum can provide inter- and intra-band transition information for nanoscale devices with high energy and spatial resolutions. However, some losses, such as Cherenkov radiation, phonon scattering, and surface plasmon resonance superimposed at zero-loss peak, make it asymmetric. These pose limitations to the direct interpretation of optical properties, such as complex dielectric function and bandgap onset in the raw electron energy-loss spectra.

Wafer-Scale Epitaxial Growth of an Atomically Thin Single-Crystal Insulator as a Substrate of Two-Dimensional Material Field-Effect Transistors.

As the electron mobility of two-dimensional (2D) materials is dependent on an insulating substrate, the nonuniform surface charge and morphology of silicon dioxide (SiO) layers degrade the electron mobility of 2D materials. Here, we demonstrate that an atomically thin single-crystal insulating layer of silicon oxynitride (SiON) can be grown epitaxially on a SiC wafer at a wafer scale and find that the electron mobility of graphene field-effect transistors on the SiON layer is 1.5 times higher than that of graphene field-effect transistors on typical SiO films.

Conversion between Metavalent and Covalent Bond in Metastable Superlattices Composed of 2D and 3D Sublayers.

Reversible conversion over multimillion times in bond types between metavalent and covalent bonds becomes one of the most promising bases for universal memory. As the conversions have been found in metastable states, an extended category of crystal structures from stable states via redistribution of vacancies, research on kinetic behavior of the vacancies is highly in demand. However, it remains lacking due to difficulties with experimental analysis.

Observation of the Early Stages of Rapid Solid-Liquid Reaction in Closed Liquid Cell TEM Using Graphene Encapsulation.

In situ liquid cell transmission electron microscopy (TEM) is a very useful tool for investigating dynamic solid–liquid reactions. However, there are challenges to observe the early stages of spontaneous solid–liquid reactions using a closed-type liquid cell system, the most popular and simple liquid cell system. We propose a graphene encapsulation method to overcome this limitation of closed-type liquid cell TEM.

Determination of Dy substitution site in NdDyFeB by HAADF-STEM and illustration of magnetic anisotropy of "g" and "f" sites, before and after substitution.

NdFeB and NdDyFeB (x = 0.25, 0.50) particles were prepared by the modified co-precipitation followed by reduction-diffusion process.

Method of Ga removal from a specimen on a microelectromechanical system-based chip for in-situ transmission electron microscopy.

In-situ transmission electron microscopy (TEM) holders that employ a chip-type specimen stage have been widely utilized in recent years. The specimen on the microelectromechanical system (MEMS)-based chip is commonly prepared by focused ion beam (FIB) milling and ex-situ lift-out (EXLO). However, the FIB-milled thin-foil specimens are inevitably contaminated with Ga ions.

Electroplated Silver-Nickel Core-Shell Nanowire Network Electrodes for Highly Efficient Perovskite Nanoparticle Light-Emitting Diodes.

The low sheet resistance and high optical transparency of silver nanowires (AgNWs) make them a promising candidate for use as the flexible transparent electrode of light-emitting diodes (LEDs). In a perovskite LED (PeLED), however, the AgNW electrode can react with the overlying perovskite material by redox reactions, which limit the electroluminescence efficiency of the PeLED by causing the degradation of and generating defect states in the perovskite material. In this study, we prepared Ag-Ni core-shell NW electrodes using the solution-electroplating technique to realize highly efficient PeLEDs based on colloidal formamidinium lead bromide (FAPbBr) nanoparticles (NPs).

Rapid and mass-producible synthesis of high-crystallinity MoSe nanosheets by ampoule-loaded chemical vapor deposition.

MoSe is an attractive transition-metal dichalcogenide with a two-dimensional layered structure and various attractive properties. Although MoSe is a promising negative electrode material for electrochemical applications, further investigation of MoSe has been limited, mainly by the lack of MoSe mass-production methods. Here, we report a rapid and ultra-high-yield synthesis method of obtaining MoSe nanosheets with high crystallinity and large grains by ampoule-loaded chemical vapor deposition.

Wafer-Scale and Low-Temperature Growth of 1T-WS Film for Efficient and Stable Hydrogen Evolution Reaction.

The metallic 1T phase of WS (1T-WS ), which boosts the charge transfer between the electron source and active edge sites, can be used as an efficient electrocatalyst for the hydrogen evolution reaction (HER). As the semiconductor 2H phase of WS (2H-WS ) is inherently stable, methods for synthesizing 1T-WS are limited and complicated. Herein, a uniform wafer-scale 1T-WS film is prepared using a plasma-enhanced chemical vapor deposition (PE-CVD) system.

Amorphous TaMnO Layer as a Diffusion Barrier for Advanced Copper Interconnects.

An amorphous TaMnO layer with 1.0 nm thickness was studied as an alternative Cu diffusion barrier for advanced interconnect. The thermal and electrical stabilities of the 1.

Characteristics of an Amorphous Carbon Layer as a Diffusion Barrier for an Advanced Copper Interconnect.

The size of the advanced Cu interconnects has been significantly reduced, reaching the current 7.0 nm node technology and below. With the relentless scaling-down of microelectronic devices, the advanced Cu interconnects thus requires an ultrathin and reliable diffusion barrier layer to prevent Cu diffusion into the surrounding dielectric.

Evaluation of ion/electron beam induced deposition for electrical connection using a modern focused ion beam system.

Focused ion beam method, which has excellent capabilities such as local deposition and selective etching, is widely used for micro-electromechanical system (MEMS)-based in situ transmission electron microscopy (TEM) sample fabrication. Among the MEMS chips in which one can apply various external stimuli, the electrical MEMS chips require connection between the TEM sample and the electrodes in MEMS chip, and a connected deposition material with low electrical resistance is required to apply the electrical signal. Therefore, in this study, we introduce an optimized condition by comparing the electrical resistance for C-, Pt-, and W- ion beam induced deposition (IBID) at 30 kV and electron beam induced deposition (EBID) at 1 and 5 kV.

Low angle boundary migration of shot-peened pure nickel investigated by electron channeling contrast imaging and electron backscatter diffraction.

Study on recrystallization of deformed metal is important for practical industrial applications. Most of studies about recrystallization behavior focused on the migration of the high-angle grain boundaries, resulting in lack of information of the kinetics of the low angle grain boundary migration. In this study, we focused on the migration of the low angle grain boundaries during recrystallization process.

Millimeter-Scale Growth of Single-Oriented Graphene on a Palladium Silicide Amorphous Film.

It is widely accepted in condensed matter physics and material science communities that a single-oriented overlayer cannot be grown on an amorphous substrate because the disordered substrate randomizes the orientation of the seeds, leading to polycrystalline grains. In the case of two-dimensional materials such as graphene, the large-scale growth of single-oriented materials on an amorphous substrate has remained unsolved. Here, we demonstrate experimentally that the presence of uniformly oriented graphene seeds facilitates the growth of millimeter-scale single-oriented graphene with 3 × 4 mm on palladium silicide, which is an amorphous thin film, where the uniformly oriented graphene seeds were epitaxially grown.

Investigation of Zirconium Effect on the Corrosion Resistance of Aluminum Alloy Using Electrochemical Methods and Numerical Simulation in an Acidified Synthetic Sea Salt Solution.

Corrosion resistance of Zr that has been added to an Al alloy (U1070) is higher than that of a commercial Al alloy (A1070). A decreasing number and size of Al₃Fe intermetallic particles (IMPs) were observed by electron microprobe analysis and transmission electron microscopy. Based on the numerical corrosion simulation, it was confirmed that decreasing the number and size of IMPs was favorable for improving the corrosion resistance of the Al alloy due to the reduction of the galvanic effect.

Quantification of crystallinity using zero-loss filtered electron diffraction.

The quantity of the crystalline phases present in a nanomaterial is an important parameter that governs the correlation between its properties and microstructure. However, quantification of crystallinity in nanoscale-level applications by conventional methods (Raman spectroscopy and X-ray diffraction) is difficult because of the spatial limitations of sampling. Therefore, we propose a technique that involves using energy-filtered electron diffraction in transmission electron microscopy which offers improved spatial resolution.

Dirac electrons in a dodecagonal graphene quasicrystal.

Quantum states of quasiparticles in solids are dictated by symmetry. We have experimentally demonstrated quantum states of Dirac electrons in a two-dimensional quasicrystal without translational symmetry. A dodecagonal quasicrystalline order was realized by epitaxial growth of twisted bilayer graphene rotated exactly 30°.

Epitaxial-Growth-Induced Junction Welding of Silver Nanowire Network Electrodes.

In this study, we developed a roll-to-roll Ag electroplating process for metallic nanowire electrodes using a galvanostatic mode. Electroplating is a low-cost and facile method for deposition of metal onto a target surface with precise control of both the composition and the thickness. Metallic nanowire networks [silver nanowires (AgNWs) and copper nanowires (CuNWs)] coated onto a polyethylene terephthalate (PET) film were immersed directly in an electroplating bath containing AgNO.