Liquid-Vapor Phase-Change Heat Transfer on Functionalized Nanowired Surfaces and Beyond

Electronic symmetry breaking by charge disproportionation results in multifaceted changes in the electronic, magnetic and optical properties of a material, triggering ferroelectricity, metal/insulator transition and colossal magnetoresistance. Yet, charge disproportionation lacks technological relevance because it occurs only under specific physical conditions of high or low temperature or high pressure. Here we demonstrate a voltage-triggered charge disproportionation in thin molecular films of a metal–organic complex occurring in ambient conditions. This provides a technologically relevant molecular route for simultaneous realization of a ternary memristor and a binary memcapacitor, scalable down to a device area of 60 nm2. Supported by mathematical modelling, our results establish that multiple memristive states can be functionally non-volatile, yet discrete—a combination perceived as theoretically prohibited. Our device could be used as a binary or ternary memristor, a binary memcapacitor or both concomitantly, and unlike the existing ‘continuous state’ memristors, its discrete states are optimal for high-density, ultra-low-energy digital computing. Charge disproportionation in thin molecular films of a metal–organic complex enables the realization of a ternary memristor and binary memcapacitor.

Charge disproportionate molecular redox for discrete memristive and memcapacitive switching

Reversible wettability transition between superhydrophilicity and superhydrophobicity through alternate heating-reheating cycle on laser-ablated brass surface

Brain inspired electronics with organic memristors could offer a functionally promising and cost-effective platform for flexible, wearable, and personalized computing technologies. While there are different material approaches (viz. oxides, nitrides, 2D, organic) to realize memristors, organic materials are characteristically unique, as they could, in principle, offer spatially uniform switching, tunable molecular functionalities, and ultra-low switching energies approaching atto joules that are highly desirable but elusive with other material systems. However, despite a long-standing effort spanning almost 2 decades, the performance and mechanistic understanding in organic memristors are quite far from a translational stage and even a single suitable candidate is yet to emerge. Almost all the reported organic memristors lack reproducibility, endurance, stability, uniformity, scalability, and speed that are needed for an industrial application. In this review, we analyze the root cause of the prolonged failures of organic memory devices and discuss a new family of organic memristors, made of transition metal complexes of redox active organic ligands (RAL), that satisfy and go beyond the requirements specified in the 2015 ITRS roadmap for RRAM devices. These devices exhibit cyclability > 1012, retention of several months, on/off ratio > 103, switching voltage approaching 100 mV, rise time less than 30 ns, and switching energy <1 fJ, offering a quantum leap in organic memristor technology. This could give birth to a new generation of organic memristors that are industrially competitive with ample scopes for functional tunability by molecular engineering, such as variation of the metal center and ligands as well as the counterions. A combination of molecular and device engineering may enable this material system to be an ideal candidate for brain inspired electronics.

An organic approach to low energy memory and brain inspired electronics

Controlling the wetting property of ceramics, which is characterized by their water contact angles (WCAs), is of great interest because of their better thermal and chemical robustness compared with polymer materials. Among many ceramics, rare earth oxides (REOs) have attracted attention because of their high WCA (∼115°). Although several non-wetting mechanisms of REOs have been proposed thus far, the intrinsic mechanism has not been clarified yet due to the lack of information on crystallographic orientation–surface energy (SE)–WCA relationships. Here we report the WCA of (001), (110), and (111) oriented REO epitaxial films, which have different surface energies. We found that the WCA of fresh REO epitaxial film surfaces, which were prepared using a pulsed laser deposition technique, strongly depends on the crystallographic orientations, WCA(111) > WCA(110) > WCA(001), which reflects the differences in surface energy; SE(111) < SE(110) < SE(001). Moreover, we found that the WCA on REOs increases rapidly and converges to about 80° upon exposure to ambient air, regardless of the crystallographic orientation, likely due to surface adsorption of airborne carbon species. The present finding of ‘There is a strong correlation between the crystallographic orientation, wetting property and the surface energy’ is of great importance for the understanding of the wetting properties of ceramics.

Crystallographic orientation–surface energy–wetting property relationships of rare earth oxides

Herein, we report a systematic study of water contact angle (WCA) of rare-earth oxide thin-films. These ultra-smooth and epitaxial thin-films were grown using pulsed laser deposition and then characterized using X-Ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), and atomic force microscopy (AFM). Through both the traditional sessile drop and the novel f–d method, we found that the films were intrinsically hydrophilic (WCA < 10°) just after being removed from the growth chamber, but their WCAs evolved with an exposure to the atmosphere with time to reach their eventual saturation values near 90° (but always stay ‘technically’ hydrophilic). X-Ray photoelectron spectroscopy analysis was used to further investigate qualitatively the nature of hydrocarbon contamination on the freshly prepared as well as the environmentally exposed REO thin-film samples as a function of the exposure time after they were removed from the deposition chamber. A clear correlation between the carbon coverage of the surface and the increase in WCA was observed for all of the rare-earth films, indicating the extrinsic nature of the surface wetting properties of these films and having no relation to the electronic configuration of the rare-earth atoms as proposed by Azimi et al.

Jia Zhunan

Papers

Intrinsic hydrophilic nature of epitaxial thin-film of rare-earth oxide grown by pulsed laser deposition.