An effective method to deposit atomically smooth ultrathin silver (Ag) films by employing a 1 nm copper (Cu) seed layer is reported. The inclusion of the Cu seed layer leads to the deposition of films with extremely low surface roughness (<0.5 nm), while it also reduces the minimum thickness required to obtain a continuous Ag film (percolation thickness) to 3 nm compared to 6 nm without the seed layer. Moreover, the Cu seed layer alters the growth mechanism of the Ag film by providing energetically favorable nucleation sites for the incoming Ag atoms leading to an improved surface morphology and concomitant lower electrical sheet resistance. Optical measurements together with X-ray diffraction and electrical resistivity measurements confirmed that the Ag film undergoes a layer-by-layer growth mode resulting in a smaller grain size. The Cu seeded Ag growth method provides a feasible way to deposit ultrathin Ag films for nanoscale electronic, plasmonic and photonic applications. In addition, as a result of the improved uniformity, the oxidation of the Ag layer is strongly reduced to negligible values.

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Optical surfaces that can repel both water and oil have much potential for applications in a diverse array of technologies including self-cleaning solar panels, anti-icing windows and windshields for automobiles and aircrafts, low-drag surfaces, and antismudge touch screens. By exploiting a hierarchical geometry made of two-tier nanostructures, primary nanopillars of length scale ∼ 100-200 nm superposed with secondary branching nanostructures made of nanoparticles of length scale ∼ 10-30 nm, we have achieved static contact angles of more than 170° and 160° for water and oil, respectively, while the sliding angles were lower than 4°. At the same time, with respect to the initial flat bare glass, the nanotextured surface presented significantly reduced reflection (<0.5%), increased transmission (93.8% average over the 400 to 700 nm wavelength range), and very low scattering values (about 1% haze). To the authors' knowledge, these are the highest optical performances in conjunction with superomniphobicity reported to date in the literature. The primary nanopillars are monolithically integrated in the glass surface using lithography-free metal dewetting followed by reactive ion etching,1 while the smaller and higher surface area branching structure made of secondary nanoparticles are deposited by the NanoSpray2 combustion chemical vapor deposition (CCVD).

The functionalities of a wide range of optical and opto-electronic devices are based on resonance effects and active tuning of the amplitude and wavelength response is often essential. Plasmonic nano-structures are an efficient way to create optical resonances, a prominent example is the extraordinary optical transmission (EOT) through arrays of nano-holes patterned in a metallic film. Tuning of resonances by heating, applying electrical or optical signals has proven to be more elusive, due to the lack of materials that can induce modulation over a broad spectral range and/or at high speeds. Here we show that nano-patterned metals combined with phase change materials (PCMs) can overcome this limitation due to the large change in optical constants which can be induced thermally or on an ultrafast timescale. We demonstrate resonance wavelength shifts as large as 385 nm --an order of magnitude higher than previously reported--by combining properly designed Au EOT nanostructures with Ge2Sb2Te5 (GST). Moreover, we show, through pump-probe measurements, repeatable and reversible, large-amplitude modulations in the resonances, especially at telecommunication wavelengths, over ps time scales and at powers far below those needed to produce a permanent phase transition. Our findings open a pathway to the design of hybrid metal-PCM nanostructures with ultrafast and widely tuneable resonance responses, which hold potential impact on active nanophotonic devices such as tuneable optical filters, smart windows, bio-sensors and reconfigurable memories.* These authors made equal contribution †valerio.pruneri@icfo.eu 2 Nanophotonic devices incorporating metallic elements can support plasmons, which are collective oscillations of conduction band electrons driven by an external electromagnetic field 1 . Plasmons can confine and guide light well below the diffraction limit, and when supported by suitably engineered nanostructures, they enable the design of disruptive devices for a wide range of applications, including perfect lenses . Plasmons also play an important role in the phenomenon of extraordinary optical transmission (EOT) of visible and infrared light through periodic arrays of subwavelength nanoholes drilled in metallic films. The observation of transmission resonances in these arrays is attributed to the resonant interaction between holes mediated by surface plasmons propagating on the film surfaces 7 . More precisely, transmission peaks emerge close to the Wood anomalies 8 and are well explained in terms of geometrical resonances in the periodic lattice 9,10,11 . An important challenge in the design of plasmonic nanostructures is the precise control of their optical responses in order to meet the requirements of specific device applications. This can be accomplished by casting nanostructures with appropriate materials and geometries. However, such an approach is static and limited by material inhomogeneity and fabrication tolerances. More critically, many applications (e.g., optical switching and modulation) ...

Metal nanoparticles have been used for coloring glass since antiquity. Colors are produced by light scattering and absorption associated with plasmon resonances of the particles. Recently, dewetting at high temperature has been demonstrated as a straightforward high-yield/low-cost technique for nanopatterning thin metal films into planar arrays of spherical nanocaps. Here, we show that by simply tuning the contact angle of the metal dewetted nanocaps one can achieve narrow resonances and large tunability compared with traditional approaches such as changing particle size. A vast range of colors is obtained, covering the whole visible spectrum and readily controlled by the choice of film thickness and materials. The small size of the particles results in a mild dependence on incidence illumination angle, whereas their high anisotropy gives rise to strong dichroism. We also show color tuning through 65 simple, low-cost lithography-free surface nanostructuring, 66 which is ideal for industrially scalable applications.