Hydrogen Ion Beams from Nanostructured Gas Field Ion Sources

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div class="title">Hydrogen Ion Beams from Nanostructured Gas Field Ion Sources - Volume 22 Issue S3 - Hironori Moritani, Radovan Urban, Mark Salomons, Robert Wolkow, Jason Pitters

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We show that a thermally stable Ir / W <111> single-atom tip is a very good point ion source for rare gases (He, Ar) and reactive gases ( H <sub>2</sub> , O <sub>2</sub> ). The ion beams are emitted from the topmost atom with a very small opening angle (≪1°) and, most importantly, they exhibit high brightness. In addition, the ion currents are very stable. These good properties together with the long lifetime of the tip and the reliable tip preparation method make this tip especially suitable for applications in gas field ion source focused ion beam systems.
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In this report we present a straightforward new technique for fabricating nanotips. This approach is based on spatially controlling the reaction of nitrogen gas with the surface atoms of a tungsten tip in a field ion microscope (FIM). Confining this field-assisted etching reaction to the shank has enabled us to produce single-atom tips with an apex radius far sharper than the nominal 10 nm radius of curvature tips we start with. Tip sharpening is evidenced in several ways. The FIM imaging voltage drops dramatically from, typically, 4.4 to 1.6 kV. Nanotip formation is also evident from the increase in the FIM magnification and the decrease in the apex area, which are monitored throughout the experiment. A subsequent field evaporation allows the nanotip to be sequentially deconstructed to further describe the extraordinary sharp tip that was formed. We also demonstrate the utility of these nanotips for the scanning tunneling microscope.
Mass-spectroscopical analysis of the ions produced at a point emitter with dynamic supply of hydrogen at room temperature or in modified field ion microscopes at 78° and 20°K showed the abundant occurrence of H3+ besides H+ and H2+ observed earlier by Inghram and Gomer. The triatomic molecule ion is formed only in the narrow range of field strength near best image conditions. The mechanism of H3+ formation under the extreme field conditions is uncertain. Field ion-microscopic observation shows H3+ only over single protruding surface atoms, which might act as sites for deactivation of an intermediate state, or simply provide a region of locally enhanced field to allow quick field ionization of short-lived H3.
Through the use of tin (Sn) based solder balls and patterned laser lift-off technique, a metal substrate technology was proposed for the fabrication of vertical-structured metal substrate GaN-based light-emitting diodes (VM-LEDs). Advantages including reserving the merits of metallic substrate and simplifying the fabrication processes of vertical-structured GaN-based LEDs were demonstrated. As compared to conventional sapphire substrate GaN-based LEDs, the fabricated VM-LEDs with an emission area of 620×620 μm2 show an increase in light output power about 145.36% at 350 mA with a significant decrease in forward voltage from 4.51 to 3.46 V.
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