• Controlling the refractive index and third-order nonlinearity of polyimide/Ta2O5 nanolaminates for optical applications

      Färm, Elina; Mehravar, Soroush; Kieu, Khanh; Peyghambarian, Nasser; Ritala, Mikko; Leskelä, Markku; Kemell, Marianna; Univ Arizona, Coll Opt Sci (A V S AMER INST PHYSICS, 2019-11-11)
      In this study, the authors investigated third-order optical nonlinearity in polyimide/Ta2O5 nanolaminates deposited by atomic layer deposition. Third harmonic signal measurements were done with a multiphoton microscope at an excitation wavelength of 1.55 μm, laser pulse duration of 150 fs, and estimated pulse energy of 1.2 nJ. Third-order optical nonlinearity is an essential property in optical signal applications for telecommunication. Transparency at telecommunication wavelengths and a high refractive index are desired for a material. Polyimide is optically transparent, enabling light guidance through the material. The refractive index of the material can be fine-tuned by combining polyimide with a substantially higher refractive index material—in this case, Ta2O5. The layer thicknesses in nanolaminates were varied, and the third harmonic generation was compared to plain polyimide and Ta2O5 reference films. Third harmonic generation in the nanolaminates decreased slightly and refractive index increased with increasing Ta2O5 content. Normalized third-order nonlinear susceptibilities, χ(3), calculated for the nanolaminates were between the values of Ta2O5 and polyimide and increased with increasing polyimide content.
    • Reaction of aqueous ammonium sulfide on SiGe 25%

      Heslop, Stacy L.; Peckler, Lauren; Muscat, Anthony J.; Univ Arizona, Dept Chem & Biochem; Univ Arizona, Dept Chem & Environm Engn (A V S AMER INST PHYSICS, 2017-05)
      SiGe 25% substrates were treated with aqueous solutions of ammonium sulfide with and without added acid to understand the adsorption of sulfur on the surface. X-ray photoelectron spectroscopy showed no sulfide layer was deposited from aqueous (NH4)(2)S alone and instead both Si and Ge oxides formed during immersion in the sulfur solution. The addition of hydrofluoric and hydrochloric acids dropped the pH from 10 to 8 and deposited sulfides, yet increased the oxide coverage on the surface and preferentially formed Ge oxides. The sulfur coverage grew with increasing concentrations of acid in the aqueous (NH4)(2)S. The simultaneous deposition of O and S is suspected to be the result of oxidized sulfur species in solution. Metal-insulator-semiconductor capacitor (MISCAP) devices were fabricated to test the electrical consequences of aqueous ammonium sulfide wet chemistries on SiGe. MISCAPs treated with acidic ammonium sulfide solutions contained fewer interface defects in the valence band region. The defect density (D-it) was on the order of 10(+12) cm(-2) eV(-1). The flat band voltage shift was lower after the acidic ammonium sulfide treatment, despite the presence of surface oxides. Adsorption of S and potentially O improved the stability of the surface and made it less electrically active. (C) 2017 American Vacuum Society.
    • Uranium and arsenic unregulated water issues on Navajo lands

      Ingram, Jani C; Jones, Lindsey; Credo, Jonathan; Rock, Tommy; Univ Arizona, Coll Med, Clin Translat Sci (A V S AMER INST PHYSICS, 2020-03-20)
      The geologic profile of the western United States lends itself to naturally elevated levels of arsenic and uranium in the groundwater and can be aggravated by mining. The Navajo Nation, located in the American Southwest, is the largest contiguous Native American Nation and has over a 100-year legacy of hard rock mining. Concentrations of uranium and arsenic above drinking water standards in unregulated water sources pose various human-health risks to the Navajo Nation due to the lack of public water infrastructure that exists. Although high natural background concentrations may occur in some environments, anthropogenic contamination concerns are especially troublesome for the Navajo Nation, where past uranium mining activity and natural sources affect unregulated water supplies. Community engaged research on uranium and arsenic present in unregulated water wells in the western portion of the Navajo Nation has been a focus of the Ingram laboratory since 2003. These studies have provided important information, particularly for uranium and arsenic, to the communities and the Navajo tribal leaders.