Archive for March 2016

5 papers will be presented at the materials research society

ACTAlab will be presenting 5 papers at MRS 2016, Phoenix Arizona. The abstracts are listed below.

 

Design of Functional Chalcogenide Materials for Electronics, Photonics, and Data Storage
Janne Kalikka; Xilin Zhou; Yuhan Quek; Giacommo Nannicini; Robert Simpson

We propose an new approach to the design of functional chalcogenide materials.  Our approach synergistically exploits both Edisonian and bottom up design approaches. Our materials discovery program employs both compuational-based Genetic algorithm-led materials optimisation and combinatorial composition-spread materials screening methods. As a proof-of-concept our methods are applied to Sb2Te3-GeTe phase-change materials. We show through experiment and simulation that our approach to materials design can accelerate the optimisation and discovery of new superlattices of van der Waals bonded 2-D chalcogenide crystal superlattices.

 

Strain Engineered Interfacial Phase Change Materials: Diffusive Atomic Switches in 2D

Xilin Zhou; Janne Kalikka; Eric Dilcher; Ju Li; Simon Wall; Robert E. Simpson

Sb2Te3 – GeTe van der Waals (vdW) heterostructures represent the state of the art in phase change memory material technology. Energy efficient data storage is achieved by confining the phase transition to the interface between the two layers, consequently the entropic losses that are associated with the reversible amorphous-crystalline phase transition in conventional Ge-Sb-Te alloys are suppressed. Accordingly these ‘interfacial phase change memory’ (iPCM) heterostructures present a viable route to lower the energy consumption of data storage devices. The full potential of phase change materials extends beyond their current application in data storage. Indeed, the iPCM structure, which is composed from the topological insulator Sb2Te3, provides a path toward switchable spintronic devices, whilst conventional phase change alloys are finding a new lease of life in tuneable photonics. We show that the iPCM switching mechanism entails pre-melting of a 0.5 nm thick two–dimensional GeTe crystal plane, and the energy required for the premelt–switching is lowered by applying biaxial strain. We theoretically and experimentally demonstrate that the GeTe 2D crystal strain is dictated by the Sb2Te3 layer thickness and consequently the switching energy is readily decreased by simply increasing the thickness of the Sb2Te3 layers of the heterostructure. Finally we lay the foundation for a generalisable approach to the design of switchable vdW heterostructures by identifying four critical rules for the heterostructure superlattice design.

 

Strain Engineered Diffusive Atomic Switching in Chalcogenide Heterostructure Superlattices  

Janne Kalikka; Xilin Zhou; Ju Li; Simon Wall; Eric Dilcher; Robert Simpson

Strain engineering is an emerging route for designing materials with specific properties or functions, such as tuneable band gap, carrier mobility, chemical reactivity, and diffusivity. In this presentation we show how strain can be used to control atomic diffusion in van der Waals (vdW) heterostructures of two dimensional (2D) crystals. We use strain to increase the diffusivity of Ge and Te atoms that are confined to 0.5 nm thick 2D planes within an Sb2Te3–GeTe vdW superlattice. The thickness ratio of the 2D crystal layers dictates the strain in the GeTe. We use this effect to substantially lower the energy required for atomic switching. By identifying four critical rules for the superlattice configuration, we lay the foundation for a generalisable approach to the design of switchable vdW heterostructures. As Sb2Te3–GeTe is a topological insulator, we envision that these rules may enable new methods to control spin and topological properties of materials in reversible and energy efficient ways.