X. Zhou publishes new paper on tuning the properties of GeTe with Oxygen

Today, Xilin Zhou’s paper, which discusses how oxygen doping influences the the local structure of GeTe, has been published in ACS Applied Materials and Interfaces.

Interestingly when oxygen is added into GeTe, the energy required to switch the material in a phase change random access memory cell is lowered, yet counter intuitively the crystallization temperature is increased by O doping. Previously we showed that there is zero change in density for O concentrations of about 5 at.%. We believe that this allows the material to be switched with a lower enthalpy change, hence explaining the energy efficient  memory switching.

The paper is available here: http://pubs.acs.org/doi/abs/10.1021/acsami.6b05071



EPCOS 2016 – 3 papers accepted

Weiling Dong, Jitendra Behera, and Rob Simpson will present three papers at EPCOS 2016 in Cambridge, UK. The conference will be held in September 2016.

The papers are:

  • Wideband visible absorbers by Ge2Sb2Te5 and Al nanogratings, Weiling Dong, Yimei Qiu, Joel K.W. Yang, Robert E. Simpson, and Tun Cao
  • Laser switching of nanostructured phase change materials, Jitendra K. Behera, Xilin Zhou, and Robert E. Simpson
  • Genetic algorithm inspired design of Ge2Sb2Te5 structures, Robert E Simpson, Janne Kalikka, Jitendra K Behera, Giacomo Nannicini and Xilin Zhou 


See you in Cambridge!

ACTAlab welcomes MISTI students

ACTAlab is hosting three visiting students from MIT through the MISTI program.

Kaitlyn Mullin will be researching self organised dispersions of micropartcicles

Kiara Cui will be researching methods to screen chalcogenides for applications in photonics

Nina Anwar will be investigating the threshold switching effect in amorphous chalcogenide thin films.

W. Dong publishes new paper on wide band absorbers in the visible spectrum

Weiling Dong et al. has publsihed a paper in the Journal of Physical Chemistry C which describes how plasmonic nanogratings can be combined with phase change materials to create strong absorption in the visible spectrum. Weiling explained that the simple design of her structure will enable mass production of these super absorbers.

The research was conducted in collaboration with Prof Tun Cao of Dalian University of Technology, China.

ACTAlab is developing tuneable optical filters based on chalcogenides for a wide range of applications from displays to pollution detectors.



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.

Advanced Materials publication

Congratulations to Xilin Zhou et al on their recent publication in Advanced Materials which demonstrates how Sb2Te1 layers can be used to subject GeTe layers to biaxial tensile strain. This strain engineered structural design increases the switching rate of the GeTe layers whilst also decreasing the switching energy. Consequently when these materials are incorporated into random access memory devices the energy required to store data is decreased. If these memory cells are incorporated in to smart phones and laptops, the battery lifetime is expected to increased.


Read all about the work here: DOI: 10.1002/adma.201505865 or download the article here.

Image credit: Adam Simpson