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We present a low-loss integrated photonics platform in the visible and near ultraviolet regime. Fully-etched waveguides based on atomic layer deposition (ALD) of aluminum oxide operate in a single transverse mode with <3 dB/cm propagation loss at a wavelength of 371 nm. Ring resonators with intrinsic quality factors exceeding 470,000 are demonstrated at 405 nm, and the thermo optic coefficient of ALD aluminum oxide is estimated to be 2.75 × 10 −5 [RIU/ • C]. Absorption loss is sufficiently low to allow on-resonance operation with intracavity powers up to at least 12.5 mW, limited by available laser power. Experimental and simulated data indicates the propagation loss is dominated by sidewall roughness, suggesting lower loss in the blue and UV is achievable. I. INTRODUCTIONThe success of silicon photonics in telecommunications has lead to the application of nano-scale photonics in a variety of fields including computing, nonlinear optics, quantum information processing, and biochemical sensing 1-5 . Compact device footprints and an ability to leverage the same manufacturing techniques employed in the semiconductor industry are strong incentives both for systems designers and in applications where low cost is necessary. Label-free biosensors, optical interconnects for computers and datacenters, integrated lasers with III-V gain media, and phased arrays consisting of thousands of elements have all been demonstrated using the same basic silicon photonic technology 1,5-8 . However, with a bandgap at 1.1 um, silicon is unsuitable for applications which require visible or ultraviolet light, such as optogenetics 9,10 , protein sensing 11,12 , and atom-based sensing, time-keeping, and information processing [13][14][15][16] . A straightforward way of bypassing this limitation is to use silicon nitride, commonly integrated alongside silicon, which has transparency into the visible. Waveguide platforms based on silicon nitride are quite mature, particularly for red and near infrared (NIR) wavelengths. Less progress has been made for devices operating in the blue and near ultraviolet (UV, NUV). This is predominantly due to the high material absorption (>20 dB/cm) that begins in the low 400 nm wavelength range 17 .The most common alternative to silicon nitride for ultraviolet photonics are the III-V nitride materials, particularly aluminum nitride (AlN) and aluminum-gallium nitride alloys (AlGaN) 18 . AlN has a bandgap corresponding to λ ∼ 200 nm and exhibits second-order nonlinearities, making it attractive for integrated nonlinear optics and electrical tuning of reso-2 nant structures. Early demonstrations of ultraviolet waveguides in AlN suffered extremely high loss (389 dB/cm at a wavelength λ = 450 nm) due to a combination of bulk (polycrystalline) material loss and high sidewall roughness 19 . More recent work using nanocrystalline AlN has brought the loss coefficient down by an order of magnitude (∼50 dB/cm at λ = 405 nm) but in a regime where device size is restricted to sub-centimeter or sub-millimeter lengths when s...

The propagation of roughness from a patterned silicon surface by polymer thin films was measured as a function of film thickness, time, and surface interaction using atomic force microscopy and synchrotron X-ray reflection. In the presence of an interacting surface, the decay length of the surface modulation was much longer than that observed in simple liquids. By measuring the time dependence of the surface corrugation amplitude, we were able to extract a surface diffusion coefficient by applying a modified version of the Mullins theory for surface diffusion in crystalline solids. The measured diffusion coefficients were an order of magnitude smaller than in the bulk, and scaled as 1/M 3/2, in agreement with previous SIMS results. The results are interpreted in terms of surface interactions confining polymer chains over distances larger than the radii of gyration.