Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSynthesis of tunable $SnS-TaS_2$ nanoscale superlattices
119
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Nanoscale superlattices represent a compelling platform for designed materials as the specific identity and spatial arrangement of constituent layers can lead to tunable properties. A number of kinetically-stabilized layered chalcogenide nanocomposites have taken inspiration from misfit compounds, a thermodynamically stable class of materials formed of van der Waals-bonded (vdW) layers. This class of vdW heterostructure superlattices have been reported in telluride and selenide chemistries, but have not yet been extended to sulfides. Here we present $SnS-TaS_2$ nanoscale superlattices with tunable layer architecture. Thin films are prepared from layered amorphous precursors and deposited to mimic the targeted superlattice; subsequent low temperature annealing activates self-assembly into designed nanocomposites. Structure and composition for materials are investigated that span stacking sequences between $[(SnS)_{1+delta}]_3(TaS_2)_1$ and $(SnS)_7(TaS_2)_1$ using x-ray diffraction, x-ray fluorescence, and transmission electron microscopy. A graded deposition approach is implemented to stabilize heterostructures of multiple stacking sequences with a single preparation. Precise control over the architecture of such nanoscale superlattices is a critical path towards controlling the properties of quantum materials and constituent devices.
rate research
Read More
The origin of the functional properties of complex oxide superlattices can be resolved using time-resolved synchrotron x-ray diffraction into contributions from the component layers making up the repeating unit. The CaTiO3 layers of a CaTiO3/BaTiO3 superlattice have a piezoelectric response to an applied electric field, consistent with a large continuous polarization throughout the superlattice. The overall piezoelectric coefficient at large strains, 54 pm/V, agrees with first-principles predictions in which a tetragonal symmetry is imposed on the superlattice by the SrTiO3 substrate.
As the length-scales of materials decrease, heterogeneities associated with interfaces approach the importance of the surrounding materials. Emergent electronic and magnetic interface properties in superlattices have been studied extensively by both experiments and theory. $^{1-6}$ However, the presence of interfacial vibrations that impact phonon-mediated responses, like thermal conductivity $^{7,8}$, has only been inferred in experiments indirectly. While it is accepted that intrinsic phonons change near boundaries $^{9,10}$, the physical mechanisms and length-scales through which interfacial effects influence materials remain unclear. Herein, we demonstrate the localized vibrational response associated with the interfaces in SrTiO$_3$-CaTiO$_3$ superlattices by combining advanced scanning transmission electron microscopy imaging and spectroscopy and density-functional-theory calculations. Symmetries atypical of either constituent material are observed within a few atomic planes near the interface. The local symmetries create local phonon modes that determine the global response of the superlattice once the spacing of the interfaces approaches the phonon spatial extent. The results provide direct visualization and quantification, illustrating the progression of the local symmetries and interface vibrations as they come to determine the vibrational response of an entire superlattice; stated differently, the progression from a material with interfaces, to a material dominated by interfaces, to a material of interfaces as the period decreases. Direct observation of such local atomic and vibrational phenomena demonstrates that their spatial extent needs to be quantified to understand macroscopic behavior. Tailoring interfaces, and knowing their local vibrational response, provides a means of pursuing designer solids having emergent infrared and thermal responses.
We propose a tunable electronic band gap and zero-energy modes in periodic heterosubstrate-induced graphene superlattices. Interestingly, there is an approximate linear relation between the band gap and the proportion of inhomogeneous substrate (i.e., percentages of different components) in the proposed superlattice, and the effect of structural disorder on the relation is discussed. In inhomogeneous substrate with equal widths, zero-energy states emerge in the form of Dirac points by using asymmetric potentials, and the positions of Dirac points are addressed analytically. Further, the Dirac point exists at $mathbf{k}=mathbf{0}$ only for specific potentials; every time it appears, the group velocity vanishes in $k_y$ direction and the resonance occurs. For general cases that inhomogeneous substrate with unequal widths, a part of zero-energy states are described analytically, and differently, they are not always Dirac points. Our prediction may be realized on the heterosubstrate such as SiO$_2$/BN type.
Skyrmions are localized magnetic spin textures whose stability has been shown theoretically to depend on material parameters including bulk Dresselhaus spin orbit coupling (SOC), interfacial Rashba SOC, and magnetic anisotropy. Here, we establish the growth of a new class of artificial skyrmion materials, namely B20 superlattices, where these parameters could be systematically tuned. Specifically, we report the successful growth of B20 superlattices comprised of single crystal thin films of FeGe, MnGe, and CrGe on Si(111) substrates. Thin films and superlattices are grown by molecular beam epitaxy and are characterized through a combination of reflection high energy electron diffraction, x-ray diffraction, and cross-sectional scanning transmission electron microscopy (STEM). X-ray energy dispersive spectroscopy (XEDS) distinguishes layers by elemental mapping and indicates good interface quality with relatively low levels of intermixing in the [CrGe/MnGe/FeGe] superlattice. This demonstration of epitaxial, single-crystalline B20 superlattices is a significant advance toward tunable skyrmion systems for fundamental scientific studies and applications in magnetic storage and logic.
We investigate analytically the anisotropic dielectric properties of single crystal {alpha}-SnS near the fundamental absorption edge by considering atomic orbitals. Most striking is the excitonic feature in the armchair- (b-) axis direction, which is particularly prominent at low temperatures. To determine the origin of this anisotropy, we perform first-principles calculations using the GW0 Bethe-Salpeter equation (BSE) including the electron-hole interaction. The results show that the anisotropic dielectric characteristics are a direct result of the natural anisotropy of p orbitals. In particular, this dominant excitonic feature originates from the py orbital at the saddle point in the {Gamma}-Y region.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
