Hydrogen incorporation into materials via proton irradiation is relevant to materials processing in environments ranging from the technological to the astrophysical. For example, technological development needs for nuclear reactor materials have driven significant research in high energy/nucleon proton irradiation at high doses in metals. Low dose proton irradiation may also prove useful as a means of introducing defects and dopants to engineer physical properties of nanomaterials for sensor applications. Of importance in astrophysical environments around stars, including our Sun, recent research by our group has demonstrated the production of radiolytic water and hydroxyl in the surfaces of silicates irradiated by high doses of low energy/nucleon protons. Improved understanding of the fundamental processes underlying proton incorporation and participation in near-surface chemical reactions and in producing structural and optoelectronic changes are thus relevant to interpretation of space weathering effects on airless bodies, to engineering of nanoscale sensors, and to development of shielding materials for space exploration and reactor environments.

Following on the observation of radiolytic water and hydroxyl in proton-irradiated silicate surfaces, we plan to explore proton-irradiation of oxides to better understand how hydrogen is incorporated and the role of ion-induced defects in subsequent chemical reaction and volatile evolution.

The Advanced Electron Microscopy Center is part of the School of Ocean and Earth Science and Technology, and is managed by Dr. Hope Ishii. The Center features electron and ion microscopy instruments for sample analysis, and additional tools and instruments for small sample preparation. The Center boasts a world-class, state-of-the-art aberration-corrected TEM/STEM and FIB (described below), the only instruments of their kind in the state of Hawaii. Together, these tools enable micro- and nano-scale characterization of the chemistry (elemental composition, oxidation states, bonding) and structure (crystalline/amorphous structure, defects, interfaces) that provide the foundation for understanding processing-property relationships in the photocatalytic, battery and high-pressure materials, recycling and water purification, and nanodevice developments (detectors/sensors).

FEI Titan3 G2 60-300 “SuperSTEM”: The Titan is an aberration-corrected (scanning) transmission electron microscope, or TEM/STEM, that has an environmental enclosure for improved noise isolation, as well as a monochromator and dual spherical aberration correctors for the probe and image in. It is aligned for operation at 80, 200 and 300 kV. It is equipped with a high angle annular dark field (HAADF) detector, Gatan Tridiem GIF (Gatan imaging filter) for imaging and spectroscopy and an EDAX Genesis 4000 Si(Li) solid state energy dispersive x-ray spectrometer with ultrathin window. Sub-Ångström spatial resolution and energy resolutions of 100-150 meV at 200 kV and 150-200 meV at 300 kV are routinely achievable. EDX elemental detection limits are down to a few ppm for long count times on robust samples. The TEM/STEM will be applied to assess photovoltaic and battery samples, water purification materials and newly developed high-pressure materials.

Dual beam Helios focused ion beam instrument (FIB): A companion instrument to the Titan (S)TEM, the FEI Helios NanoLab 660 dual-beam Focused Ion Beam (FIB) microscope combines a Schottky field emission secondary electron microscope (SEM) electron column and Tomahawk ion column in the same instrument. The FIB is equipped with a silicon-drift energy dispersive X-ray detector for elemental analyses and a retractable backscatter detector and retractable STEM detector with bright field, dark field and high angle annular dark field segments for imaging in addition to in-column secondary electron detectors. An in situ micromanipulator and C, W and Pt deposition capabilities enable nanometer-scale deposition and milling for nano-surgery, nano-engineering and TEM sample preparation. The FIB achieves 0.6 nm electron-beam resolution at 15 kV and 4 nm ion-beam resolution at 30 kV. The FIB will be used for sample preparation for TEM/STEM, assessment of material chemistry, texture, and morphology and for nanodevice modifications.

Supporting Equipment: Other equipment in the Center to support materials science research includes a vacuum oven and soft-walled cleanroom with a Zeiss stereomicroscope, Nikon petrographic optical microscope, digital camera and image capture software, and a Leica Ultracut EM UC7 ultramicrotome for embedded sample preparation of thin sections for TEM/STEM analysis.