A scanning tunneling microscopy study of anthraquinone (AQ) on the Au(111) surface shows that the molecules self-assemble into several structures depending on the local surface coverage. At high coverages, a close-packed saturated monolayer is observed, while at low coverages, mobile surface molecules coexist with stable chiral hexamer clusters. At intermediate coverages, a disordered 2D porous network interlinking close-packed islands is observed in contrast to the giant honeycomb networks observed for the same molecule on Cu(111). This difference verifies the predicted extreme sensitivity [J. Wyrick et al., Nano Lett. 11, 2944 (2011)] of the pore network to small changes in the surface electronic structure. Quantitative analysis of the 2D pore network reveals that the areas of the vacancy islands are distributed log-normally. Log-normal distributions are typically associated with the product of random variables (multiplicative noise), and we propose that the distribution of pore sizes for AQ on Au(111) originates from random linear rate constants for molecules to either desorb from the surface or detach from the region of a nucleated pore.

A metallic spin filter is observed at the interface between Alq 3 adsorbates and a Cr(001) surface. It can be changed to a resistive (i.e. gapped) filter by substituting Cr ions to make Crq 3 adsorbates. Spin polarized scanning tunneling microscopy and spectroscopy shows these spin dependent electronic structure changes with single molecule resolution. Density functional theory calculations highlight the structural and electronic differences at the interfaces. For Alq 3 , a charge transfer interaction with the substrate leads to a metallic spin filter. For Crq 3 , direct covalent interactions mix molecular orbitals with the substrate surface state to make two wellseparated interfacial hybrid orbitals.

We report our in-house R&D efforts of designing and developing key integrated photonic devices and technologies for a chip-scale optical oscillator and/or clock. This would provide precision sources to RF-photonic systems. It could also be the basic building block for a photonic technology to provide positioning, navigation, and timing as well as 5G networks. Recently, optical frequency comb (OFC)-based timing systems have been demonstrated for ultra-precision time transfer. Our goal is to develop a semiconductor-based, integrated photonic chip to reduce the size, weight, and power consumption, and cost of these systems. Our approach is to use a self-referenced interferometric locking circuit to provide short-term stabilization to a micro-resonator-based OFC. For long-term stabilization, we use an epsilon-near-zero (ENZ) metamaterial to design an environment-insensitive cavity/resonator, thereby enabling a chipscale optical long-holdover clock. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

We report on the growth and characterization of wavelength-thick indium tin oxide (ITO) films deposited using high power impulse magnetron sputtering (HiPIMS) with post deposition processing to achieve an epsilon near zero (ENZ) property at 1550 nm telecom wavelengths. The goal is to fabricate 1550 nm ENZ films for use as claddings for waveguides, resonators, or high-contrast metastructures in photonic devices operated at telecom wavelengths. We developed a HiPIMS growth and post-annealing process to improve on existing ENZ ITO quality and uniformity. By consecutively annealing the ITO film, the plasma frequency gradually shifts, enabling fine tuning of the ENZ wavelength regime from 1800 to 1500 nm. The films were characterized using spectroscopic ellipsometry, transmission electron microscopy, x-ray diffraction, and energy dispersive x-ray spectroscopy. Our micro-analyses shows that the change in the microstructure resulted in the change in the optical properties of the ITO. These findings allow us to control the ENZ property at the desired wavelength and reduce the absorption loss, which is beneficial for device application.

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