Design of the Threshold-Controllable Memristor Emulator Based on NDR Characteristics.

Due to the high manufacturing cost of memristors, an equivalent emulator has been employed as one of the mainstream approaches of memristor research. A threshold-type memristor emulator based on negative differential resistance (NDR) characteristics is proposed, with the core part being the R-HBT network composed of transistors. The advantage of the NDR-based memristor emulator is the controllable threshold, where the state of the memristor can be changed by setting the control voltage, which makes the memristor circuit design more flexible. The operation frequency of the memristor emulator is about 250 kHz. The experimental results prove the feasibility and correctness of the threshold-controllable memristor emulator circuit.

Optically Guided Pyroelectric Manipulation of Water Droplet on a Superhydrophobic Surface.

Controlled droplet manipulation by light has tremendous technological potential. We report here a method based on photothermally induced pyroelectric effects that enables manipulation and maneuvering of a water droplet on a superhydrophobic surface fabricated on lithium tantalite (LiTaO3). In particular, we demonstrate that the pyroelectric charge distribution has an essential role in this process. Evenly distributed charges promote a rapid hydrophobic to hydrophilic transition featuring a very large water contact angle (WCA) change of ∼76.5° in air. This process becomes fully reversible in silicone oil. In contrast, the localized charge distribution induced by guided laser illumination leads to very different and versatile functionalities, including droplet shape control and motion manipulation. The influence of a saline solution is also investigated and compared to the deionized water droplet. The focusing effect of the water droplet, a phenomenon that widely exists in nature, is particularly of interest. Simple tuning of the laser incident angle results in droplet deformation, jetting, splitting, and guided motion. Potential applications, such as droplet pinning and transfer, are presented. This approach offers a wide range of versatile functionalities and ready controllability, including contactless, electrodeless, and precise spatial and fast temporal control, with tremendous potential for applications requiring remote droplet control.

Multimode Nonlinear Coupling Induced by Internal Resonance in a Microcantilever Resonator.

Coupled resonators represent a generic model for many physical systems. In this context, a microcantilever is a multimode resonator clamped at one end, and it finds extensive application in high-precision metrology and is expected to be of great potential use in emerging quantum technologies. Here, we explore the microcantilever as a flexible platform for realizing multimode nonlinear interactions. Multimode nonlinear coupling is achieved by (1:2) internal resonance (IR) and parametric excitation with efficient coherent energy transfer. Specifically, we demonstrate abundant tunable parametric behaviors via frequency and voltage sweeps; these behaviors include mode veering, degenerate four-wave mixing (D4WM) with satellite resonances, partial amplitude suppression, acoustic frequency comb (AFC) generation, mechanically induced transparency (MIT), and normal-mode splitting. The experiments depict a new scheme for manipulating multimode microresonators with IR and parametric excitation.

Optically Induced Rapid Wetting Transition on Zn-Polar and O-Polar Zinc Oxide.

The design and fabrication of surfaces that support rapid wetting transition remain technologically challenging. Here, we examine the effects of optical illumination on the wetting behaviors of zinc oxide (ZnO) single crystals. We find that ultraviolet irradiation above the band gap energy promotes a rapid wetting transition, characterized by sliding of the water droplet, within a few seconds. Notably, the transition for Zn-polar (0001) ZnO surfaces is even faster than that for O-polar (0001̅) ZnO surfaces. We confirmed that process is dependent on power, surface polarity, and solution pH and reversible through illumination by near-infrared light, which restores the water contact angle back to its initial value. Surface chemical analysis revealed that the instantaneous photocatalytic formation of surface-terminated hydroxyl (-OH) groups is responsible for the observed rapid wetting transition. Density functional theory calculations with the inclusion of onsite Coulomb interactions revealed that both the Zn-polar and O-polar surfaces can be easily covered with -OH groups through the adsorption of -OH groups or hydrogen atoms, respectively. This study develops a route to fabricate optically active and controllable microfluidic devices that support rapid wetting transitions for water droplet manipulation.