Phase-change Janus particles with switchable dual properties

Abstract

We developed switchable Janus particles (JPs) fabricated by coating one hemisphere of silica microspheres with a phase-change film. We used the chalcogenide GeSbTe (GST), which exhibits a reversible phase change between a metal-like crystalline phase (c-GST) and a dielectric-like amorphous phase (a-GST). As a driving force for self-propelling the JPs, a perpendicular alternating current electric field was applied; the frequency dependence of the motion of an individual JP and that of inter-JP interaction were investigated. At lower frequencies (2–20 kHz), a-GST JPs were propelled with their silica side facing forward, which is similar to the behavior of Au–silica JPs propelled by the well-known induced-charge electrophoresis mechanism, whereas c-GST JPs were immobile because they adhered to the indium tin oxide substrate. At higher frequencies (50–300 kHz), both a-GST and c-GST JPs were propelled with their GST side facing forward and a substantial difference in inter-JP interaction was observed: repulsive collision for c-GST JPs but attractive stacking for a-GST JPs.

Aggregation of self-propelled particles with sensitivity to local order

“…Recent advances in living active matter have found that modifications in individual behavior through the sensing of local densities lead to the formation of regions of orientational disorder and aggregations [52][53][54][55]. Similar observations have been made in experiments with active colloidal systems employing different methods to program the particle motion, like optical feedback loops and field modulations [55][56][57]. Therefore, the observed macroscopic behavior in our model could be relevant, for example, to active colloids with setups allowing the particles to sense and respond to the average orientation of neighbors [58], to the design and control of robot swarms [6,59], and, in general, to systems exhibiting both polar order and MIPS-related behavior [34,60,61].…”

Aggregation of self-propelled particles with sensitivity to local order

“…Recent advances in living active matter have found that modifications in individual behaviour through the sensing of local densities lead to the formation of regions of orientational disorder and aggregations [52][53][54][55]. Simiobservations are made in experiments with active colloidal systems employing different methods to program the particle motion, like optical feedback loops and field modulations [55][56][57]. Therefore, the observed macroscopic behaviour in our model could be of relevance, for example, to active colloids with setups allowing the particles to sense and respond to the average orientation of neighbours [58], to the design and control of robot swarms [6,59], and in general, to systems exhibiting both polar order and MIPS-related behaviour [34,60,61].…”

Enabling Active Nanotechnologies by Phase Transition: From Electronics, Photonics to Thermotics

“…More recently, both Samsung and Intel have commercialized electronic memory devices that are based on the same family of PCMs, namely those along the Sb 2 Te 3 –GeTe pseudobinary compositional tie-line. Beyond data storage, the enormous property contrast exhibited by PCMs has been used to adjust the resonant frequency of optical metamaterial filters − and microring waveguides; , achieve homeostasis by controlling surface emmisivity, create low energy reflective displays, perform arithmatic, control the transmission of GHz, surface plasmon polariton (SPP), and optical waves, − modulate surface phonons, and control the movement of microparticles. , …”

“…Beyond data storage, the enormous property contrast exhibited by PCMs has been used to adjust the resonant frequency of optical metamaterial filters 61−63 and microring waveguides; 64,65 achieve homeostasis by controlling surface emmisivity, 66 create low energy reflective displays, 67 perform arithmatic, 68 control the transmission of GHz, surface plasmon polariton (SPP), and optical waves, 69−71 modulate surface phonons, and control the movement of microparticles. 72,73 Many properties need to be considered when designing or selecting PCMs for nanodevices, such as contrasts of physical properties between two states, the minimum refractive index, optical loss at the operation wavelength, archive stability, switching speed, switching power and energy, fabrication precision, multilevel ability, and write−erase cyclability. Currently, no single PCM composition is well-suited to programming all conceivable nanodevices.…”