Thickness-dependent patterning of MoS2 sheets with well-oriented triangular pits by heating in air

Patterning ultrathin MoS2 layers with regular edges or controllable shapes is appealing since the properties of MoS2 sheets are sensitive to the edge structures. In this work, we have introduced a simple, effective and well-controlled technique to etch layered MoS2 sheets with well-oriented equilateral triangular pits by simply heating the samples in air. The anisotropic oxidative etching is greatly affected by the surrounding temperature and the number of MoS2 layers, whereby the pit sizes increase with the increase of surrounding temperature and the number of MoS2 layers. First-principles computations have been performed to explain the formation mechanism of the triangular pits. This technique offers an alternative avenue to engineering the structure of MoS2 sheets.

Thickness-dependent wrinkling of PDMS films for programmable mechanochromic responses

We report a remarkable thickness-dependent wrinkling behavior of oxygen plasma-treated polydimethylsiloxane(PDMS)flms,in which an energy barrier separates the wrinkling mechanics into two regimes.For thick films,the film wrinkles with a constant periodicity which can be precisely predicted by the classic nonlinear finite mechanics.Reducing the film thickness below 1 mm leads to nonuniform wrinkles with an increasing periodicity which gives rise to random scattering and transparency changes under mechanical strains.By tuning the flm thickness,we were able to control both the quality and size of the periodic wrinkles and further design mechanochromic devices featuring briliant structural colors and programmable colorimetric responses.This work sheds light on the fundamental understanding of the wrinkling mechanics of bilayer systems and their intriguing mechanochromic applications.

Thickness-dependent morphologies of Ag on n-layer MoS2 and its surface-enhanced Raman scattering

The size and density of Ag nanoparticles on n-layer MoS2 exhibit thickness- dependent behavior. The size and density of these particles increased and decreased, respectively, with increasing layer number （n） of n-layer MoS2. Furthermore, the surface-enhanced Raman scattering （SERS） of Ag on this substrate was observed. The enhancement factor of this scattering varied with the thickness of MoS2. The mechanisms governing the aforementioned thickness dependences are proposed and discussed.

Thickness-Dependent Microstructure and its Effect on Anisotropic Mechanical Properties of Duplex Stainless Steel 2205 Multi-pass Welded Joints

In this study,the thickness-dependent microstructural characteristics of duplex stainless steel 2205 multi-pass welded joints were first investigated by the combination of optical microscope and electron back-scattered diffraction observation.Subsequently,a series of tensile tests of miniature samples cut from different passes and directions were performed to analyze the thickness-dependent and anisotropic mechanical properties.The results demonstrate that the microstructure changed with the welded passes,i.e.,a large number of grain boundary austenite,Widmanstätten austenite and a small number of tiny intragranular austenite existed at the surface passes,while a mass of intragranular austenite were found at the middle passes.Meanwhile,the Kurdjumov–Sachs orientation relationship was widespread at the welded zone.In addition,the yield and tensile strengths of the middle passes were greater than that of the surface passes due to the grain-boundary strengthening by tiny intragranular austenite.Furthermore,due to the existence of Kurdjumov–Sachs orientation relationship,the longitudinal yield and tensile strength were greater than transverse values,particularly for the middle passes.

Thickness-dependent and strain-tunable magnetism in twodimensional van der Waals VSe_(2)

Two-dimensional(2D)van der Waals(vdW)magnetic materials with reduced dimensionality often exhibit unexpected properties compared to their bulk counterparts.In particular,the mechanical flexibility of 2D structure,enhanced ferromagnetism at reduced layer thickness,as well as robust perpendicular magnetic anisotropy are quite appealing for constructing novel spintronic devices.The vdW vanadium diselenide(VSe_(2))is an attractive material whose bulk is paramagnetic while monolayer is ferromagnetic with a Curie temperature(Tc)above room temperature.To explore its possible device applications,a detailed investigation on the thickness-dependent magnetism and strain modulation behavior of VSe_(2)is highly demanded.In this article,the VSe_(2)nanoflakes were controllably prepared via chemical vapor deposition(CVD)method.The few-layer single VSe_(2)nanoflakes were found to exhibit magnetic domain structures at room temperature.Ambient magnetic force microscopy(MFM)phase images reveal a clear thickness-dependent magnetism and the MFM phase contrast is traceable for the nanoflakes of layer thickness below~6 nm.Moreover,applying strain is found efficient in modulating the magnetic moment and coercive field of 2D VSe_(2)at room temperature.These results are helpful for understanding the ferromagnetism of high temperature 2D magnets and for constructing novel straintronic devices or flexible spintronic devices.

Optimal parameter space for stabilizing the ferroelectric phase of Hf_(0.5)Zr_(0.5)O_(2) thin films under strain and electric fields

Hafnia-based ferroelectric materials, like Hf_(0.5)Zr_(0.5)O_(2)(HZO), have received tremendous attention owing to their potentials for building ultra-thin ferroelectric devices. The orthorhombic(O)-phase of HZO is ferroelectric but metastable in its bulk form under ambient conditions, which poses a considerable challenge to maintaining the operation performance of HZO-based ferroelectric devices. Here, we theoretically addressed this issue that provides parameter spaces for stabilizing the O-phase of HZO thin-films under various conditions. Three mechanisms were found to be capable of lowering the relative energy of the O-phase, namely, more significant surface-bulk portion of(111) surfaces, compressive c-axis strain,and positive electric fields. Considering these mechanisms, we plotted two ternary phase diagrams for HZO thin-films where the strain was applied along the in-plane uniaxial and biaxial, respectively. These diagrams indicate the O-phase could be stabilized by solely shrinking the film-thickness below 12.26 nm, ascribed to its lower surface energies. All these results shed considerable light on designing more robust and higher-performance ferroelectric devices.

Multi-carrier transport in ZrTe_5 film

Single-layered zirconium pentatelluride （ZrTes） has been predicted to be a large-gap two-dimensional （2D） topolog- ical insulator, which has attracted particular attention in topological phase transitions and potential device applications. Herein, we investigated the transport properties in ZrTe5 films as a function of thickness, ranging from a few nm to several hundred nm. We determined that the temperature of the resistivity anomaly peak （Tp） tends to increase as the thickness decreases. Moreover, at a critical thickness of ~ 40 rim, the dominating carriers in the films change from n-type to p-type. A comprehensive investigation of Shubnikov-de Hass （SdH） oscillations and Hall resistance at variable temperatures revealed a multi-carrier transport tendency in the thin films. We determined the carrier densities and mobilities of two majority car- riers using the simplified two-carrier model. The electron carriers can be attributed to the Dirac band with a non-trivial Berry phase ~, while the hole carriers may originate from surface chemical reaction or unintentional doping during the microfabrication process. It is necessary to encapsulate the ZrTe5 film in an inert or vacuum environment to potentially achieve a substantial improvement in device quality.

Unprecedently low thermal conductivity of unique tellurium nanoribbons

Tellurene,probably one of the most promising two-dimensional(2D)system in the thermoelectric materials,displays ultra-low thermal conductivity.However,a linear thickness-dependent thermal conductivity of unique tellurium nanoribbons in this study reveals that unprecedently low thermal conductivity can be achieved via well-defined nanostructures of low-dimensional tellurium instead of pursuing dimension-reduced 2D tellurene.For thinnest tellurium nanoribbon with thickness of 144 nm,the thermal conductivity is only∼1.88±0.22 W·m^(−1)·K^(−1) at room temperature.It’s a dramatic decrease(45%),compared with the well-annealed high-purity bulk tellurium.To be more specific,an expected thermal conductivity of tellurium nanoribbons is even lower than that of 2D tellurene,as a result of strong phonon-surface scattering.We have faith in low-dimensional tellurium in which the thermoelectric performance could realize further breakthrough.