2020 New's Items

Layer-dependent topological phase in a two-dimensional quasicrystal and approximant

Jeffrey D. Cain
Amin Azizi
Matthias Conrad
Sinead M. Griffin
Alex Zettl
2020

The electronic and topological properties of materials are derived from the interplay between crystalline symmetry and dimensionality. Simultaneously introducing “forbidden” symmetries via quasiperiodic ordering with low dimensionality into a material system promises the emergence of new physical phenomena. Here, we isolate a two-dimensional (2D) chalcogenide quasicrystal and approximant, and investigate their electronic and topological properties. The 2D layers of the materials with a composition close to Ta1.6Te, derived from a layered transition metal...

Solid-State Ionic Rectification in Perovskite Nanowire Heterostructures

Kong Q
Obliger A
Lai M
Gao M
Limmer DT
Yang P
2020

Halide perovskites have attracted increasing research attention with regard to their potential for optoelectronic applications. Because of its low activation energy, ion migration is implicated in the long-term stability and many unusual transport behaviors of halide perovskite devices. However, direct observation and precise control of the ionic transport in halide perovskite crystals remain challenging. Here, we have designed an axial CsPbBr3–CsPbCl3 nanowire heterostructure, in which electric-field-induced halide ion migration...

Onsager Transport Coefficients and Transference Numbers in Polyelectrolyte Solutions and Polymerized Ionic Liquids

Fong KD
Self J
McCloskey BD
Persson KA
2020

Electrolytes featuring negatively charged polymers, such as nonaqueous polyelectrolyte solutions and polymerized ionic liquids, are currently under investigation as potential high cation transference number (t+) electrolytes for lithium-ion batteries. Herein, we use coarse-grained molecular dynamics simulations to characterize the Onsager transport coefficients of polyelectrolyte solutions as a function of chain length and concentration. For all the systems studied, we find that the rigorously computed transference number is substantially lower than that...

Behavior of Protein-Inspired Synthetic Random Heteropolymers

Hilburg SL
Ruan Z
Xu T
Alexander-Katz A
2020

Random heteropolymers (RHPs) are an interesting class of materials useful in many theories and applications. While previous studies typically focused on simplified RHP systems, here we explore a more complex scenario inspired by highly heterogeneous molecules like proteins. Our system consists of four monomers mimicking different classes of amino acids. Using molecular dynamics simulations and small-angle X-ray scattering, we explore dynamical and structural features of these RHPs in solution. Our results show that the RHPs assemble with heterogeneous interfaces reminiscent of...

A charge-density-based general cation insertion algorithm for generating new Li-ion cathode materials

Shen J-X
Horton M
Persson KA
2020

Future lithium (Li) energy storage technologies, in particular solid-state configurations with a Li metal anode, opens up the possibility of using cathode materials that do not necessarily contain Li in its as-made state. To accelerate the discovery and design of such materials, we develop a general, chemically, and structurally agnostic methodology for identifying the optimal Li sites in any crystalline material. For a given crystal structure, we attempt multiple Li insertions at symmetrically in-equivalent positions by analyzing the electronic charge density obtained from first-...

Rationalizing Calcium Electrodeposition Behavior by Quantifying Ethereal Solvation Effects on Ca2+ Coordination in Well-Dissociated Electrolytes

Driscoll DM
Dandu NK
Hahn NT
Seguin TJ
Persson KA
Zavadil KR
Curtiss LA
Balasubramanian M
2020

Ca-ion electrochemical systems have been pushed to the forefront of recent multivalent energy storage advances due to their use of earth-abundant redox materials and their high theoretical specific densities in relation to monovalent or even other more widely explored multivalent-charge carriers. However, significant pitfalls in metal plating and stripping arise from electrolyte decomposition and can be related to the coordination environment around Ca2+ with both the negatively charged anion and the organic–aprotic solvent. Here, we apply multiple...

Thermal stability for Te-based devices

Zhao C
Hurtado L
Javey A
2020
Tellurium (Te) has recently been rediscovered as an attractive semiconducting material for a wide range of electronic and optoelectronic applications. However, thermal instability of Te-based devices has not been investigated and introduces major drawbacks for their practical applications. Toward this goal, this work explores the influence of annealing temperatures on Te transistors and their two failure mechanisms, related to the sublimation of the Te channel and the degradation of the contacts. To overcome these challenges, we fabricated a Te device that is graphene-contacted and SiOx...

Design of higher valency in covalent organic frameworks

Gropp C
Ma T
Hanikel N
Yaghi OM
2020

The valency (connectivity) of building units in covalent organic frameworks (COFs) has been primarily 3 and 4, corresponding to triangles and squares or tetrahedrons, respectively. We report a strategy for making COFs with valency 8 (cubes) and "infinity" (rods). The linker 1,4-boronophenylphosphonic acid-designed to have boron and phosphorus as an isoelectronic combination of carbon-group elements-was condensed into a porous, polycubane structure (BP-COF-1) formulated as (-B4P4O12-)(-C6H4-)4 It was characterized...

Study of MEM Relay Contact Design and Body-Bias Effects on on-State Resistance Stability

Osoba B
Almeida SF
Sikder U
Ye ZA
Hu X
Esatu TK
Liu TK
2020

Body-biased micro-electro-mechanical (MEM) relays previously have been demonstrated to be a promising alternative to transistors for ultra-low voltage digital logic applications. A basic requirement for reliable relay-based circuit operation is suitably low and stable relay ON-state resistance (RON). In this work, the effect of body biasing on RON is investigated for relays of different contact designs. It is found that a single direct contact design not only provides for the smallest hysteresis voltage but also the smallest RON, making it the most suitable for low voltage...

Neutral Exciton Diffusion in Monolayer MoS 2

Uddin SZ
Kim H
Lorenzon M
Yeh M
Lien DH
Barnard ES
Htoon H
Weber-Bargioni A
Javey A
2020

Monolayer transition metal dichalcogenides (TMDCs) are promising materials for next generation optoelectronic devices. The exciton diffusion length is a critical parameter that reflects the quality of exciton transport in monolayer TMDCs and limits the performance of many excitonic devices. Although diffusion lengths of a few hundred nanometers have been reported in the literature for as-exfoliated monolayers, these measurements are convoluted by neutral and charged excitons (trions) that coexist at room temperature due to natural background doping. Untangling the diffusion of...