Continuous Droplet-Actuating Platforms via an Electric Field Gradient: Electrowetting and Liquid Dielectrophoresis.

This work develops a technology for actuating droplets of any size without the requirement for high voltages or active control systems, which are typically found in competitive systems. The droplet actuation relies on two microelectrodes separated by a variable gap distance to generate an electrostatic gradient. The physical mechanism for the droplet motion is a combination of liquid dielectrophoresis and electrowetting. Investigating the system behavior as a function of the driving frequency identified the relative contribution of these two mechanisms and the optimum operating conditions. A fixed signal frequency of 0.5 kHz actuated various liquids and contaminants. Droplet actuation was demonstrated on several platforms, including linear, radial-symmetric, and bilateral-symmetric droplet motion. The electrode designs are scalable and can be fabricated on a flexible and optically transparent substrate: these key advancements will enable consumer applications that were previously inaccessible. A self-cleaning platform was also tested under laboratory conditions and on the road. This technology has significant potential in microfluidics and self-cleaning platforms, for example, in the automotive sector to clean body parts, camera covers, and sensors.

Computer Aided Patterning Design for Self-Assembled Microsphere Lithography (SA-MSL).

In this paper, we use a finite difference time domain solver to simulate the near field optical properties of self-assembled microsphere arrays when exposed to an incoherent light source. Such arrays are typically used for microsphere lithography where each sphere acts as a ball lens, focusing ultraviolet light into an underlying photoresist layer. It is well known that arrays of circular features can be patterned using this technique. However, here, our simulations show that additional nanometer scale features can be introduced to the pattern by optimising the sphere dimensions and exposure conditions. These features are shown to arise from the contact points between the microspheres which produce paths for light leakage. For hexagonally close packed arrays, the six points of contact lead to star shapes in the photoresist. These star shapes have subfeature sizes comparable to the current achievable resolution of low-cost fabrication techniques.

Measurement of femtometre-scale atomic displacements by X-ray absorption spectroscopy.

The frequencies of extended X-ray absorption fine-structure (EXAFS) measurements, which are oscillations occurring on the high-energy side of an X-ray absorption edge, can be used to identify interatomic distances in materials. We have used a dispersive X-ray spectrometer, which has no moving components, to make rapid measurements with minimal energy drift of the difference in EXAFS from the Fe K edge in an iron-cobalt thin film undergoing periodic strain through magnetostriction. We show that magnetostriction can be detected by differential X-ray absorption. The magnitude of the recorded signal relative to the noise shows a sensitivity to mean differential atomic motion of one femtometre: a factor of 100 times more sensitive than that normally available.

Magnetic domain-wall dynamics in a submicrometre ferromagnetic structure.

As fabrication technology pushes the dimensions of ferromagnetic structures into the nanoscale, understanding the magnetization processes of these structures is of fundamental interest, and key to future applications in hard disk drives, magnetic random access memory and other 'spintronic' devices. Measurements on elongated magnetic nanostructures highlighted the importance of nucleation and propagation of a magnetic boundary, or domain wall, between opposing magnetic domains in the magnetization reversal process. Domain-wall propagation in confined structures is of basic interest and critical to the performance of a recently demonstrated magnetic logic scheme for spintronics. A previous study of a 500-nm-wide NiFe structure obtained very low domain-wall mobility in a three-layer device. Here we report room-temperature measurements of the propagation velocity of a domain wall in a single-layer planar Ni80Fe20 ferromagnetic nanowire 200 nm wide. The wall velocities are extremely high and, importantly, the intrinsic wall mobility is close to that in continuous films, indicating that lateral confinement does not significantly affect the gyromagnetic spin damping parameter to the extreme extent previously suggested. Consequently the prospects for high-speed domain-wall motion in future nanoscale spintronic devices are excellent.