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  1. Free, publicly-accessible full text available August 1, 2024
  2. Abstract

    The compact size, scalability, and strongly confined fields in integrated photonic devices enable new functionalities in photonic networking and information processing, both classical and quantum. Gallium phosphide (GaP) is a promising material for active integrated photonics due to its high refractive index, wide bandgap, strong nonlinear properties, and large acousto‐optic figure of merit. This study demonstrates that silicon‐lattice‐matched boron‐doped GaP (BGaP), grown at the 12‐inch wafer scale, provides similar functionalities as GaP. BGaP optical resonators exhibit intrinsic quality factors exceeding 25,000 and 200,000 at visible and telecom wavelengths, respectively. It further demonstrates the electromechanical generation of low‐loss acoustic waves and an integrated acousto‐optic (AO) modulator. High‐resolution spatial and compositional mapping, combined with ab initio calculations, indicate two candidates for the excess optical loss in the visible band: the silicon‐GaP interface and boron dimers. These results demonstrate the promise of the BGaP material platform for the development of scalable AO technologies at telecom and provide potential pathways toward higher performance at shorter wavelengths.

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  3. null (Ed.)
    Abstract Extreme shear deformation is used for several material processing methods and is unavoidable in many engineering applications in which two surfaces are in relative motion against each other while in physical contact. The mechanistic understanding of the microstructural evolution of multi-phase metallic alloys under extreme shear deformation is still in its infancy. Here, we highlight the influence of shear deformation on the microstructural hierarchy and mechanical properties of a binary as-cast Al-4 at.% Si alloy. Shear-deformation-induced grain refinement, multiscale fragmentation of the eutectic Si-lamellae, and metastable solute saturated phases with distinctive defect structures led to a two-fold increase in the flow stresses determined by micropillar compression testing. These results highlight that shear deformation can achieve non-equilibrium microstructures with enhanced mechanical properties in Al–Si alloys. The experimental and computational insights obtained here are especially crucial for developing predictive models for microstructural evolution of metals under extreme shear deformation. 
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  4. Abstract

    The behavior of polar LaMnO3(LMO) thin films deposited epitaxially on nonpolar SrTiO3(001) (STO) is dictated by both the LMO/STO band alignment and the chemistry of the Mn cation. Using in situ X‐ray photoelectron spectroscopy, the valence band offset (VBO) of LMO/STO heterojunctions is directly measured as a function of thickness, and found that the VBO is 2.5 eV for thicker (≥3 u.c.) films. No evidence of a built‐in electric field in LMO films of any thickness is found. Measurements of the Mn valence by MnL‐edge X‐ray absorption spectroscopy and by spatially resolved electron energy loss spectra in scanning transmission electron microscopy images reveal that Mn2+is present at the LMO surface, but not at the LMO/STO interface. These results are corroborated by density functional theory simulations that confirm a VBO of ≈2.5 eV for both ideal and intermixed interfaces. A model is proposed for the behavior of polar/nonpolar LMO/STO heterojunctions in which the polar catastrophe is alleviated by the formation of oxygen vacancies at the LMO surface.

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