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Fourfold exchange anisotropy has recently been discovered in bilayers consisting of a ferromagnetic (FM) layer exchange-coupling with an epitaxial antiferromagnetic (AF) layer. The chemical ordering of the AF layer plays an important role in the interfacial exchange coupling of AF/FM bilayers. Herein, we studied the thickness dependence of the chemical ordering and fourfold exchange anisotropy of FeRh/CoFe bilayers before and after the AF–FM phase transition of FeRh. The chemical ordering parameter of FeRh obtained by x-ray diffraction increases with thickness due to the decrease in the proportion of low-order interfaces, which results in an increase in the magnetic phase transition temperature and a decrease in the phase transition width, residual magnetization in the AF state, and lattice constant. After the occurrence of the AF–FM phase transition, the fourfold exchange anisotropy observed in the CoFe layer by magneto-optical Kerr effect changes from the FeRh〈110〉 to 〈100〉 directions, indicating the orientation change in the cubic magnetocrystalline anisotropy of FeRh. The fourfold exchange anisotropy measured by ferromagnetic resonance continues to increase with the FeRh thickness, indicating an effective thickness by far larger than that of chemically disordered AF systems. The FeRh/FM exchange coupling is highly dependent on chemical ordering, not only on the low-order surface of a few nanometers but also on the high-order interior extending to a depth of tens of nanometers.

Among the families of transition metal dichalcogenides (TMDs), Pd-based TMDs have been one of the less explored materials. In this study, we investigate the electronic properties of PdX2 (X = S, Se, or Te) bulk and thin films. The analysis of structural stability shows that the bulk and thin film (1 to 5 layers) structures of PdS2 exhibit pyrite, while PdTe2 exhibits 1T. Furthermore, PdSe2 exhibits pyrite in bulk and thin films down to the bilayer. Most surprisingly, PdSe2 monolayer transits to 1T phase. For the electronic properties of the stable bulk configurations, pyrite PdS2 and PdSe2, and 1T PdTe2, demonstrate semi-metallic features. For monolayer, on the other hand, the stable pyrite PdS2 and 1T PdSe2 monolayers are insulating with band gaps of 1.399 eV and 0.778 eV, respectively, while 1T PdTe2 monolayer remains to be semi-metallic. The band structures of all the materials demonstrate a decreasing or closing of indirect band gap with increasing thickness. Moreover, the stable monolayer band structures of PdS2 and PdSe2 exhibit flat bands and diverging density of states near the Fermi level, indicating the presence of van Hove singularity. Our results show the sensitivity and tunability of the electronic properties of PdX2 for various potential applications.

Several current topics are introduced in this review, with particular attention to highly proton-conductive polymer thin films with organized structure and molecularly oriented structure. Organized structure and molecularly oriented structure are anticipated as more promising approaches than conventional less-molecular-ordered structure to elucidate mechanisms of high proton conduction and control proton conduction. This review introduces related polymer materials and molecular design using lyotropic liquid crystals and hydrogen bond networks for high proton conduction. It also outlines the use of substrate surfaces and external fields, such as pressure and centrifugal force, for organizing structures and molecularly oriented structures.

The friction properties of graphene at the microscale are important for its application as a solid lubricant in micro-/nano-electromechanical system components. In this work, the friction properties of graphene under the action of a 5-μm-diameter microsphere probe are investigated using atomic force microscopy. A special phenomenon was found that the friction coefficient changed from positive to negative during the unloading process on different thicknesses of graphene. The applied normal load corresponding to the turning point of friction coefficient was not subject to the variation of the unloading range but increased with the increment of graphene thickness. Different stick–slip behaviors were observed, demonstrating the main reason for the above frictional characteristics is out-of-plane deformation. The anomalous friction between the contact interface of the microsphere probe and the graphene discussed broadens new horizons for the frictional properties of graphene.

Ultrathin solid slabs often have properties different from those of the bulk phase. This effect can be observed both in traditional three-dimensional materials and in van der Waals (vdW) solids in the few monolayer limit. In the present work, the band gap variation of the CdTe slabs, induced by their thickness, was studied by the density functional theory (DFT) method for the sphalerite (zinc-blende) phase and for the recently proposed inverted phase. The sphalerite phase has the Te–Cd–Te–Cd atomic plane sequence, while in the inverted phase Cd atoms are sandwiched by Te planes forming vdW blocks with the sequence Te–Cd–Cd–Te. Based on these building blocks, a bulk vdW CdTe crystal was built, whose thermodynamical stability was verified by DFT calculations. Band structures and partial densities of states for sphalerite and inverted phases were calculated. It was demonstrated for both phases that using slabs with a thickness of one to several monolayers for sphalerite phase (vdW blocks for inverted phase), structures with band gaps varying in a wide range can be obtained. The presented results allow us to argue that ultrathin CdTe can be a promising electronic material.

In this study, an ordered Ag/TiO2/Ni nanopillar arrays hybrid substrate was designed, and the charge transfer (CT) process at the metal–semiconductor and substrate–molecule interface was investigated based on the surface-enhanced Raman scattering (SERS) spectra of 4-Aminothiophenol (PATP) absorbed on the composite system. The surface plasmon resonance (SPR) absorption of Ag changes due to the regulation of TiO2 thickness, which leads to different degrees of CT enhancement in the system. The CT degree of SERS spectra obtained at different excitation wavelengths was calculated to study the contribution of CT enhancement to SERS, and a TiO2 thickness-dependent CT enhancement mechanism was proposed. Furthermore, Ag/TiO2/Ni nanopillar arrays possessed favorable detection ability and uniformity, which has potential as a SERS-active substrate.

Since the experiments found that two-dimensional (2D) materials such as single-layer MoS2 can withstand up to 20% strain, strain-modulated magnetism has gradually become an emerging research field. However, applying strain alone is difficult to modulate the magnetism of single-layer pristine MoS2, but applying strain combined with other tuning techniques such as introducing defects makes it easier to produce and alter the magnetism in MoS2. Here, we summarize the recent progress of strain-dependent magnetism in MoS2. First, we review the progress in theoretical study. Then, we compare the experimental methods of applying strain and their effects on magnetism. Specifically, we emphasize the roles played by web buckles, which induce biaxial tensile strain conveniently. Despite some progress, the study of strain-dependent MoS2 magnetism is still in its infancy, and a few potential directions for future research are discussed at the end. Overall, a broad and in-depth understanding of strain-tunable magnetism is very necessary, which will further drive the development of spintronics, straintronics, and flexible electronics.

Background At certain temperatures and strain rates, low carbon steels, as well as some aluminum and magnesium-based alloys, exhibit plastic flow instability at the onset of their respective yield points, known as the Lüders phenomena. Such phenomenon is recognized by a distinct yield point and subsequent plateau on the stress-strain curve, and takes the form of a band when full-field tensile strain contours are observed experimentally. Objective This paper aims to investigate the specimen thickness dependence of the Lüders effect in AISI 1524 hot-rolled steel alloy. Sixteen samples were cut from hot-rolled plates and uniaxial testing in conjunction with digital image correlation were performed to gain insight and quantify the Lüders band’s spatial characteristics during the extent of the plateau. More specifically, 1 mm, 2 mm, 3 mm, and 4 mm thick flat specimens of mild steel were tested under identical conditions, most notably strain rate, in order to isolate and understand the effect of specimen thickness. Results Results revealed that both the Lüders band width and velocity depend on the specimen thickness. An increase in specimen thickness resulted in an increase in Lüders band width, and an increase in Lüders band velocity on 1524 steel alloy. Moreover, the angle at which the Lüders band appeared on the front surface of the specimen with respect to the different thicknesses revealed the 3D nature of the band’s formation. Conclusions The obtained results and observations suggested a 3D nature of the band’s formation in AISI 1524; whereby nucleation takes place at the core of the material before propagating in the thickness direction towards the structure’s surface. Moreover, it was concluded that the Lüders band special features, width and velocity is dependent on a structure’s thickness.

The defects into the hexagonal network of a sp2-hybridized carbon atom have been demonstrated to have a significant influence on intrinsic properties of graphene systems. In this paper, we presented a study of temperature-dependent Raman spectra of G peak and D’ band at low temperatures from 78 to 318 K in defective monolayer to few-layer graphene induced by ion C+ bombardment under the determination of vacancy uniformity. Defects lead to the increase of the negative temperature coefficient of G peak, with a value almost identical to that of D’ band. However, the variation of frequency and linewidth of G peak with layer number is contrary to D’ band. It derives from the related electron-phonon interaction in G and D’ phonon in the disorder-induced Raman scattering process. Our results are helpful to understand the mechanism of temperature-dependent phonons in graphene-based materials and provide valuable information on thermal properties of defects for the application of graphene-based devices.