Despite the remarkable advances in mitigating ice formation and accretion, however, no engineered anti-icing surfaces today can durably prevent frost formation, droplet freezing, and ice accretion in an economical and ecofriendly way. Herein, sustainable and low-cost electrolyte hydrogel (EH) surfaces are developed by infusing salted water into a hydrogel matrix for avoiding icing. The EH surfaces can both prevent ice/frost formation for an extremely long time and reduce ice adhesion strength to ultralow value (Pa-level) at a tunable temperature window down to −48.4 °C. Furthermore, ice can self-remove from the tilted EH surface within 10 s at −10 °C by self-gravity. As demonstrated by both molecular dynamic simulations and experiments, these extreme performances are attributed to the diffusion of ions to the interface between EH and ice. The sustainable anti-icing properties of EH can be maintained by replenishing in real-time with available ion sources, indicating the promising applications in offshore platforms and ships.

performance substrates for surface-enhanced Raman spectroscopy, with high enhancement factors of up to 3 × 10 8 relative to thin gold films. The methods described here extend the range of metallic nanostructures that can be fabricated over large areas, and are likely to find many applications in molecular electronics, plasmonics, and biosensing.

Metallic nanogaps with metal-metal separations of less than 10 nm have many applications in nanoscale photonics and electronics. However, their fabrication remains a considerable challenge, especially for applications that require patterning of nanoscale features over macroscopic length-scales. Here, some of the most promising techniques for nanogap fabrication are evaluated, covering established technologies such as photolithography, electron-beam lithography (EBL), and focused ion beam (FIB) milling, plus a number of newer methods that use novel electrochemical and mechanical means to effect the patterning. The physical principles behind each method are reviewed and their strengths and limitations for nanogap patterning in terms of resolution, fidelity, speed, ease of implementation, versatility, and scalability to large substrate sizes are discussed.

Squeezing light into nanometer-sized metallic nanogaps can generate extremely high near-field intensities, resulting in dramatically enhanced absorption, emission, and Raman scattering of target molecules embedded within the gaps. However, the scarcity of low-cost, high-throughput, and reproducible nanogap fabrication methods offering precise control over the gap size is a continuing obstacle to practical applications. Using a combination of molecular self-assembly, colloidal nanosphere lithography, and physical peeling, we report here a high-throughput method for fabricating large-area arrays of triangular nanogaps that allow the gap width to be tuned from ∼10 to ∼3 nm. The nanogap arrays function as high-performance substrates for surface-enhanced Raman spectroscopy (SERS), with measured enhancement factors as high as 10 8 relative to a thin gold film. Using the nanogap arrays, methylene blue dye molecules can be detected at concentrations as low as 1 pM, while adenine biomolecules can be detected down to 100 pM. We further show that it is possible to achieve sensitive SERS detection on binary-metal nanogap arrays containing gold and platinum, potentially extending SERS detection to the investigation of reactive species at platinum-based catalytic and electrochemical surfaces.

others are limited to the patterning of a single metal, and consequently cannot be applied to the fabrication of asymmetric nanoscale devices such as rectifiers and ambipolar devices that require the use of closely spaced dissimilar metal electrodes.Beesley et al. recently reported an alternative method for fabricating arrays of high aspect-ratio asymmetric nanogap electrodes, which exploits the ability of selected self-assembled monolayers (SAMs) to attach conformally to a prepatterned metal layer and thereby weaken adhesion to a subsequently deposited metal film. [24] The method-referred to as adhesion lithography or "a-lith"-has the advantage of involving only a few simple processing steps that can be carried out at room temperature under ambient conditions, using inexpensive equipment. Adhesion lithography provides a rapid route to highly aligned, electrically isolated, asymmetric electrodes separated on the nanometer length scale, and has been successfully applied to a broad range of nanogap devices, including light-emitting diodes, [25] optical sensors, [26] high frequency (>20 MHz) Schottky diodes, [27,28] field effect transistors, [29,30] and memristors. [30,31] The main processing steps in the usual a-lith procedure are summarized in Figure 1. A thin (≈50 nm) metal film (M1) is deposited on a substrate, and selectively patterned to expose the underlying substrate in regions where a second metal will subsequently be deposited (Figure 1a). An alkyl-containing metallophilic SAM is conformally attached to all exposed surfaces of M1, with the alkyl chains facing outwards from the metal surface ( Figure 1b). Next, a second metal film (M2) is uniformly deposited over the full area of the substrate (Figure 1c). Owing to the presence of the SAM, the adhesion of M2 to M1 is much weaker than its adhesion to the substrate. In consequence, if an adhesive tape or film is applied uniformly to the surface of M2 (Figure 1d) and then pulled away (Figure 1e-(i)), M2 will detach from the regions above M1 and remain only in those areas where M2 is in direct contact with the substrate. Hence, at the end of the procedure the two metals will sit in a complementary arrangement, side-by-side on the substrate, separated in the limiting case by just the length of the SAM-a few nanometers or less. The SAM may subsequently be removed by UV/ozone or oxygen plasma treatment, leaving an unfilled gap between the two electrodes (Figure 1f).In practice, the reported electrode spacings achieved with adhesion lithography have been substantially higher than the SAM length, typically lying in the 15-100 nm size range, depending on how the peeling step is carried out. (Factors such Adhesion lithography ("a-lith") is a simple method for forming nanoscale gaps between dissimilar metals. In its usual form, a metal is patterned on a substrate, and conformally coated with an alkyl-functionalized self-assembled monolayer, rendering it nonadhesive to other metals; a second metal is then deposited uniformly over the full area of the substrate; finall...