Data for EMSL Project 51271 from March 2021
Explore the source record for details and available documents.
Novikova, Irina↗
Engineering topics
Chen, Peng
Publications and source records attributed to Chen, Peng.
Data for EMSL Project 51271 from March 2021
Explore the source record for details and available documents.
Novikova, Irina↗
Coherent Electronic Band Structure of TiTe 2 /TiSe 2 Moiré Bilayer
Here, a van der Waals bonded moiré bilayer formed by sequential growth of TiSe 2 and TiTe 2 monolayers exhibits emergent electronic structure as evidenced by angle-resolved photoemission band mapping. The two monolayers adopt the same lattice orientation but incommensurate lattice constants. Despite the lack of translational symmetry, sharp dispersive bands are observed. The dispersion relations appear distinct from those for the component monolayers alone. Theoretical calculations illustrate the formation of composite bands by coherent electronic coupling despite the weak interlayer bonding, which leads to band renormalization and energy shifts.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Optimal design of acoustic metamaterial cloaks under uncertainty
In this work, we consider the problem of optimal design of an acoustic cloak under uncertainty and develop scalable approximation and optimization methods to solve this problem. The design variable is taken as an infinite-dimensional spatially-varying field that represents the material property, while an additive infinite-dimensional random field represents the variability of the material property or the manufacturing error. Discretization of this optimal design problem results in high-dimensional design variables and uncertain parameters. To solve this problem, we develop a computational approach based on a Taylor approximation and an approximate Newton method for optimization, which is based on a Hessian derived at the mean of the random field. We show our approach is scalable with respect to the dimension of both the design variables and uncertain parameters, in the sense that the necessary number of acoustic wave propagations is essentially independent of these dimensions, for numerical experiments with up to one million design variables and half a million uncertain parameters. Additionally, we demonstrate that, using our computational approach, an optimal design of the acoustic cloak that is robust to material uncertainty is achieved in a tractable manner. The optimal design under uncertainty problem is posed and solved for the classical circular obstacle surrounded by a ring-shaped cloaking region, subjected to both a single-direction single-frequency incident wave and multiple-direction multiple-frequency incident waves. Finally, we apply the method to a deterministic large-scale optimal cloaking problem with complex geometry, to demonstrate that the approximate Newton method’s Hessian computation is viable for large, complex problems.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Purely Cubic Spin Splittings with Persistent Spin Textures
Purely cubic spin splittings in the band structure of bulk insulators have not been extensively investigated yet despite the fact that they may pave the way for novel spin-orbitronic applications and can also result in a variety of promising spin phenomena. By symmetry analysis and first-principles simulations, we report symmetry-enforced purely cubic spin splittings (SEPCSS) that can even lead to persistent spin textures. In particular, these SEPCSS can be thought to be complementary to the cubic Rashba and cubic Dresselhaus types of spin splittings. Strikingly, the presently discovered SEPCSS are expected to exist in the large family of materials crystallizing in the $\bar{6}m2$ and $\bar{6}$ point groups, including the Ge 3 Pb 5 O 11 , Pb 7 Br 2 F 12 , and Pb 7 Cl 2 F 12 compounds.
36 MATERIALS SCIENCE↗
Charge Instability in Single-Layer TiTe 2 Mediated by van der Waals Bonding to Substrates
Single layers of transition metal dichalcogenides are of interest for emergent properties; an often-neglected issue is substrate effects. Here, our experiments show that the charge density wave in a single-layer TiTe 2 grown on PtTe 2 films is strongly suppressed by increasing the PtTe 2 substrate thickness. Given that the interfacial bonding remains of the weak incommensurate van der Waals type, the observed changes are correlated with a thickness-dependent metallicity transformation in the PtTe 2 substrate. The results illustrate the crucial role of the substrate in single-layer physics.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Large spin splittings due to the orbital degree of freedom and spin textures in a ferroelectric nitride perovskite
First-principles simulations are conducted to predict that ferroelectric nitride perovskite LaWN 3 not only exhibits large spin splittings (2.7 eV Å) but also possesses unique spin textures for some of its conduction levels. Such spin splittings around the Γ and L points cannot be interpreted as a typical mixture of Rashba or Dresselhaus configurations but rather require the development of four-band $\textit{k ∙ p}$ models with high-order terms. We further identify that, for some bands, spin splittings can be greatly contributed by the pure orbital degree of freedom (PODF), a unique character of our four-band Hamiltonian compared to the traditional two-band version. The concept of PODF-enhanced spin splittings paves a way for designing materials with large spin splittings. Moreover, the energy levels possessing such large splittings and complex spin textures can be brought close to the conduction-band minimum by applying epitaxial strain.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Improper ferroelectricity in 134-type $AA_3'B_4\text{O}_{12}$ perovskites
The 134-type $\textit{A}$-site ordered LaMn 3 Cr 4 O 12 , that belongs to the family of $AA_3'B_4\text{O}_{12}$ perovskites, with cubic structure and magnetically driven improper polarization is puzzling because the conventional mechanisms leading to the creation of polarization in type-II multiferroics do not apply. By symmetry analysis and first-principles simulations in this work, we discover an original and previously overlooked energetic term that naturally explains the origin of improper polarization in LaMn 3 Cr 4 O 12 . In addition, we demonstrate the existence of three other energetic invariants in $AA_3'B_4\text{O}_{12}$ perovskites, for which other physical quantities (such as oxygen tiltings or shear strain) mediate the interaction between $\textit{G}$-type antiferromagnetic vectors to create and even enhance improper polarization.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Massive Suppression of Proximity Pairing in Topological ( Bi 1 - x Sb x ) 2 Te 3 Films on Niobium
Interfacing bulk conducting topological Bi 2 Se 3 films with s-wave superconductors initiates strong superconducting order in the nontrivial surface states. Yet, bulk insulating topological (Bi 1-x Sb x ) 2 Te 3 films on bulk Nb instead exhibit a giant attenuation of surface superconductivity, even for films only two-layers thick. This massive suppression of proximity pairing is shown by ultrahigh-resolution band mappings and by contrasting quantified superconducting gaps with those of heavily n-doped topological Bi 2 Se 3 /Nb. The results underscore the limitations of using superconducting proximity effects to realize topological superconductivity in nearly intrinsic systems.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Exploring Plasmonic Photocatalysis via Single-Molecule Reaction Imaging
Plasmonic photocatalysis has emerged as a new frontier in heterogeneous catalysis due to its promise in harvesting light to drive reactions. Yet many mechanistic aspects remain to be unambiguously defined. Using single-molecule fluorescence imaging, Li et al. studied a fluorogenic and plasmon-enhanced reaction, amplex red oxidation, on single Au nanorods at subturnover resolution and under operando conditions. Both the rate-determining step and its activation energy were identified from the multiple elemental reactions. Here, the results provide insights into the mechanism of plasmonic photocatalysis that may help the rational design of heterogeneous catalysts.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Switchable encapsulation of polysulfides in the transition between sulfur and lithium sulfide
Encapsulation strategies are widely used for alleviating dissolution and diffusion of polysulfides, but they experience nonrecoverable structural failure arising from the repetitive severe volume change during lithium-sulfur battery cycling. Here we report a methodology to construct an electrochemically recoverable protective layer of polysulfides using an electrolyte additive. The additive nitrogen-doped carbon dots maintain their “dissolved” status in the electrolyte at the full charge state, and some of them function as active sites for lithium sulfide growth at the full discharge state. When polysulfides are present amid the transition between sulfur and lithium sulfide, nitrogen-doped carbon dots become highly reactive with polysulfides to form a solid and recoverable polysulfide-encapsulating layer. This design skilfully avoids structural failure and efficiently suppresses polysulfide shuttling. The sulfur cathode delivers a high reversible capacity of 891 mAh g -1 at 0.5 C with 99.5% coulombic efficiency and cycling stability up to 1000 cycles at 2 C.
25 ENERGY STORAGE↗
Graphene-assisted spontaneous relaxation towards dislocation-free heteroepitaxy
While conventional homoepitaxy forms high-quality epitaxial layers, the limited set of material systems for commercially available wafers restricts the range of materials that can be grown homoepitaxially. At the same time, conventional heteroepitaxy of lattice-mismatched systems produces dislocations above a critical strain energy to release the accumulated strain energy as the film thickness increases. The formation of dislocations, which severely degrade electronic/photonic device performances, is fundamentally unavoidable in highly lattice-mismatched epitaxy. Herein, we introduce a unique mechanism of relaxing misfit strain in heteroepitaxial films that can enable effective lattice engineering. We have observed that heteroepitaxy on graphene-coated substrates allows for spontaneous relaxation of misfit strain owing to the slippery graphene surface while achieving single-crystalline films by reading the atomic potential from the substrate. This spontaneous relaxation technique could transform the monolithic integration of largely lattice-mismatched systems by covering a wide range of the misfit spectrum to enhance and broaden the functionality of semiconductor devices for advanced electronics and photonics.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Two-dimensional numerical simulation of sediment transport using improved critical shear stress methods
Not Available
Feng, Zhiyong↗
Unexpected Giant Microwave Conductivity in a Nominally Silent BiFeO 3 Domain Wall
Nanoelectronic devices based on ferroelectric domain walls (DWs), such as memories, transistors, and rectifiers, have been shown in recent years. Practical high-speed electronics, on the other hand, usually demand operation frequencies in the gigahertz (GHz) regime, where the effect of dipolar oscillation is important. Herein, an unexpected giant GHz conductivity on the order of 10 3 S m -1 is observed in certain BiFeO 3 DWs, which is about 100 000 times greater than the carrier-induced direct current (dc) conductivity of the same walls. Surprisingly, the nominal configuration of the DWs precludes the alternating current (ac) conduction under an excitation electric field perpendicular to the surface. Theoretical analysis reflects that the inclined DWs are stressed asymmetrically near the film surface, whereas the vertical walls in a control sample are not. The resultant imbalanced polarization profile can then couple to the out-of-plane microwave fields and induce power dissipation, which is confirmed by the phase-field modeling. Since the contributions from mobile-carrier conduction and bound-charge oscillation to the ac conductivity are equivalent in a microwave circuit, the research on local structural dynamics may open a new avenue to implement DW nano-devices for radio-frequency applications.
36 MATERIALS SCIENCE↗
Optical sensor employing a refractive index engineered metal oxide material
An optical sensor device includes an optical waveguide portion having a core, the core having a first refractive index, and a functional material layer coupled to the optical fiber portion, the functional material layer being made of a metal oxide material, the functional material layer being structured to have a second refractive index, the second refractive index being less than the first refractive index. The functional material layer may be a nanostructure material comprising the metal oxide material with a plurality of holes or voids formed therein such that the functional material layer is caused to have the second refractive index.
36 MATERIALS SCIENCE↗