Estimation of Young’s Modulus of Graphene by Raman Spectroscopy

The Young’s modulus of graphene is estimated by measuring the strain applied by a pressure difference across graphene membranes using Raman spectroscopy. The strain induced on pressurized graphene balloons can be estimated directly from the peak shift of the Raman G band. By comparing the measured strain with numerical simulation, we obtained the Young’s modulus of graphene. The estimated Young’s modulus values of single- and bilayer graphene are 2.4 ± 0.4 and 2.0 ± 0.5 TPa, respectively

Davydov Splitting and Excitonic Resonance Effects in Raman Spectra of Few-Layer MoSe₂

Raman spectra of few-layer MoSe₂ were measured with eight excitation energies. New peaks that appear only near resonance with various exciton states are analyzed, and the modes are assigned. The resonance profiles of the Raman peaks reflect the joint density of states for optical transitions, but the symmetry of the exciton wave functions leads to selective enhancement of the A_1g mode at the A exciton energy and the shear mode at the C exciton energy. We also find Davydov splitting of <i>intra</i>layer A_1g, E_1g, and A_2u modes due to <i>inter</i>layer interaction for some excitation energies near resonances. Furthermore, by fitting the spectral positions of <i>inter</i>layer shear and breathing modes and Davydov splitting of <i>intra</i>layer modes to a linear chain model, we extract the strength of the <i>inter</i>layer interaction. We find that the second-nearest-neighbor interlayer interaction amounts to about 30% of the nearest-neighbor interaction for both in-plane and out-of-plane vibrations

Additional file 1 of In vivo safety and biodistribution profile of Klotho-enhanced human urine-derived stem cells for clinical application

Additional file 1. Table S1: Antibodies for flow cytometry, western blotting, and immunofluorescence analysis

Ising-Type Magnetic Ordering in Atomically Thin FePS₃

Magnetism in two-dimensional materials is not only of fundamental scientific interest but also a promising candidate for numerous applications. However, studies so far, especially the experimental ones, have been mostly limited to the magnetism arising from defects, vacancies, edges, or chemical dopants which are all extrinsic effects. Here, we report on the observation of <i>intrinsic</i> antiferromagnetic ordering in the two-dimensional limit. By monitoring the Raman peaks that arise from zone folding due to antiferromagnetic ordering at the transition temperature, we demonstrate that FePS₃ exhibits an Ising-type antiferromagnetic ordering down to the monolayer limit, in good agreement with the Onsager solution for two-dimensional order–disorder transition. The transition temperature remains almost independent of the thickness from bulk to the monolayer limit with <i>T</i>_N ∼ 118 K, indicating that the weak interlayer interaction has little effect on the antiferromagnetic ordering

Engineering Optical and Electronic Properties of WS₂ by Varying the Number of Layers

The optical constants, bandgaps, and band alignments of mono-, bi-, and trilayer WS₂ were experimentally measured, and an extraordinarily high dependency on the number of layers was revealed. The refractive indices and extinction coefficients were extracted from the optical-contrast oscillation for various thicknesses of SiO₂ on a Si substrate. The bandgaps of the few-layer WS₂ were both optically and electrically measured, indicating high exciton-binding energies. The Schottky-barrier heights (SBHs) with Au/Cr contact were also extracted, depending on the number of layers (1–28). From an engineering viewpoint, the bandgap can be modulated from 3.49 to 2.71 eV with additional layers. The SBH can also be reduced from 0.37 eV for a monolayer to 0.17 eV for 28 layers. The technique of engineering materials’ properties by modulating the number of layers opens pathways uniquely adaptable to transition-metal dichalcogenides

Probing Evolution of Twist-Angle-Dependent Interlayer Excitons in MoSe₂/WSe₂ van der Waals Heterostructures

Interlayer excitons were observed at the heterojunctions in van der Waals heterostructures (vdW HSs). However, it is not known how the excitonic phenomena are affected by the stacking order. Here, we report twist-angle-dependent interlayer excitons in MoSe₂/WSe₂ vdW HSs based on photoluminescence (PL) and vdW-corrected density functional theory calculations. The PL intensity of the interlayer excitons depends primarily on the twist angle: It is enhanced at coherently stacked angles of 0° and 60° (owing to strong interlayer coupling) but disappears at incoherent intermediate angles. The calculations confirm twist-angle-dependent interlayer coupling: The states at the edges of the valence band exhibit a long tail that stretches over the other layer for coherently stacked angles; however, the states are largely confined in the respective layers for intermediate angles. This interlayer hybridization of the band edge states also correlates with the interlayer separation between MoSe₂ and WSe₂ layers. Furthermore, the interlayer coupling becomes insignificant, irrespective of twist angles, by the incorporation of a hexagonal boron nitride monolayer between MoSe₂ and WSe₂