Phase-change alloys are the functional materials at the heart of an emerging digital-storage technology. The GeTe-Sb₂Te₃ pseudo-binary systems, in particular the composition Ge₂Sb₂Te₅ (GST), are one of a handful of materials which meet the unique requirements of a stable amorphous phase, rapid amorphous-to-crystalline phase transition, and significant contrasts in optical and electrical properties between material states. The properties of GST can be optimized by doping with p-block elements, of which Bi has interesting effects on the crystallization kinetics and electrical properties. A comprehensive simulational study of Bi-doped GST is carried out, looking at trends in behavior and properties as a function of dopant concentration. The results reveal how Bi integrates into the host matrix, and provide insight into its enhancement of the crystallization speed. A straightforward explanation is proposed for the reversal of the charge-carrier sign beyond a critical doping threshold. The effect of Bi on the optical properties of GST is also investigated. The microscopic insight from this study may assist in the future selection of dopants to optimize the phase-change properties of GST, and also of other PCMs, and the general methods employed in this work should be applicable to the study of related materials, for example, doped chalcogenide glasses.

Here, the formation of eutectic Gallium-Indium (EGaIn) liquid-metal microdroplets, both spherical and non-spherical, in microfluidic devices at room temperature is reported. Monodisperse microdroplets were created in an aqueous polyethylene glycol (PEG) solution, in oxygenated and in deoxygenated silicone oil. The volume of the droplets depends on the channel dimensions and flow rates applied, varying between 0.5 and 4 nL. Non-spherical droplets were formed in oxygenated silicone oil due to the instantaneous formation of an oxide layer. These metal “micro-rice” droplets retained their shape and did not spontaneously reflow to form shapes of the lowest interfacial energy on egress from the channel, unlike in aqueous PEG solution and in deoxygenated silicone oil. Liquid-metal droplets with such tunable morphology can potentially be used in MEMS devices for optical and electrical switches, valves and micropumps.

A simple technique is described to functionalize a small library of microcantilever (MC) chips presenting varied headgroups. A generic azide monolayer, bound to the MC surface, can be coupled with various alkynes using efficient "click" chemistry. This method is compatible with many functional groups, and novel headgroups are introduced on the MC surface by means of alkynes synthesized via a one-step reaction. The surface "click" reaction reduces greatly the effort that would be required to synthesize and purify the corresponding functional thiols. This technique represents a convenient complementary tool for Phase-Shifting Interferometric Microscopy (PSIM) read-out that has been developed in our group. The affinity of these surface coatings towards different solvents can be estimated by measuring the deflection of the cantilevers. A proof-of-concept sensor composed of four individual MC chips presenting different headgroups can unambiguously discriminate the fingerprint response of a nerve-gas simulant from other solvent vapors.

A method for fabricating infrared-transmitting waveguides that yields low optical losses and strong confinement of light is presented. The method minimises the number of fabrication steps by exploiting the photosensitivity of arsenic trisulfide glass, using it both as a photoresist and as a waveguiding material. Controlled annealing/remelting of the waveguides minimises scattering due to fluctuations in refractive index at the interface between the waveguide and the surrounding medium, allowing low losses to be realised. Bends and Y-splitter structures have been realised, as well as the longest As₂S₃ serpentine planar waveguides yet reported.