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DDC: 530 × Subject: Phase separation ×

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Now showing 1 - 3 of 3
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    Site-controlled formation of single Si nanocrystals in a buried SiO2 matrix using ion beam mixing
    (Frankfurt am Main : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2018) Xu, X.; Prüfer, T.; Wolf, D.; Engelmann, H.-J.; Bischoff, L.; Hübner, R.; Heinig, K.-H.; Möller, W.; Facsko, S.; von Borany, J.; Hlawacek, G.
    For future nanoelectronic devices - such as room-temperature single electron transistors - the site-controlled formation of single Si nanocrystals (NCs) is a crucial prerequisite. Here, we report an approach to fabricate single Si NCs via medium-energy Si+ or Ne+ ion beam mixing of Si into a buried SiO2 layer followed by thermally activated phase separation. Binary collision approximation and kinetic Monte Carlo methods are conducted to gain atomistic insight into the influence of relevant experimental parameters on the Si NC formation process. Energy-filtered transmission electron microscopy is performed to obtain quantitative values on the Si NC size and distribution in dependence of the layer stack geometry, ion fluence and thermal budget. Employing a focused Ne+ beam from a helium ion microscope, we demonstrate site-controlled self-assembly of single Si NCs. Line irradiation with a fluence of 3000 Ne+/nm2 and a line width of 4 nm leads to the formation of a chain of Si NCs, and a single NC with 2.2 nm diameter is subsequently isolated and visualized in a few nanometer thin lamella prepared by a focused ion beam (FIB). The Si NC is centered between the SiO2 layers and perpendicular to the incident Ne+ beam.
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    Iron-assisted ion beam patterning of Si(001) in the crystalline regime
    (Bristol : IOP, 2012) Macko, S.; Grenzer, J.; Frost, F.; Engler, M.; Hirsch, D.; Fritzsche, M.; Mücklich, A.; Michely, T.
    We present ion beam erosion experiments on Si(001) with simultaneous sputter co-deposition of steel at 660 K. At this temperature, the sample remains within the crystalline regime during ion exposure and pattern formation takes place by phase separation of Si and iron-silicide. After an ion fluence of F ≈ 5.9×10 21 ions m -2, investigations by atomic force microscopy and scanning electron microscopy identify sponge, segmented wall and pillar patterns with high aspect ratios and heights of up to 200 nm. Grazing incidence x-ray diffraction and transmission electron microscopy reveal the structures to be composed of polycrystalline iron-silicide. The observed pattern formation is compared to that in the range of 140-440K under otherwise identical conditions, where a thin amorphous layer forms due to ion bombardment.
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    Quantitative hyperspectral coherent diffractive imaging spectroscopy of a solid-state phase transition in vanadium dioxide
    (Washington, DC [u.a.] : Assoc., 2021) Johnson, Allan S.; Conesa, Jordi Valls; Vidas, Luciana; Perez-Salinas, Daniel; Günther, Christian M.; Pfau, Bastian; Hallman, Kent A.; Haglund, Richard F.; Eisebitt, Stefan; Wall, Simon
    Solid-state systems can host a variety of thermodynamic phases that can be controlled with magnetic fields, strain, or laser excitation. Many phases that are believed to exhibit exotic properties only exist on the nanoscale, coexisting with other phases that make them challenging to study, as measurements require both nanometer spatial resolution and spectroscopic information, which are not easily accessible with traditional x-ray spectromicroscopy techniques. Here, we use coherent diffractive imaging spectroscopy (CDIS) to acquire quantitative hyperspectral images of the prototypical quantum material vanadium oxide across the vanadium L2,3 and oxygen K x-ray absorption edges with nanometer-scale resolution. We extract the full complex refractive indices of the monoclinic insulating and rutile conducting phases of VO2 from a single sample and find no evidence for correlation-driven phase transitions. CDIS will enable quantitative full-field x-ray spectromicroscopy for studying phase separation in time-resolved experiments and other extreme sample environments where other methods cannot operate.