We demonstrate that surface-anchored metal-organic frameworks (SURMOFs) are extraordinary well-suited as resists for high-resolution focused electron beam induced processing (FEBIP) techniques. The combination of such powerful lithographic protocols with the huge versatility of MOF materials are investigated in respect to their potential in nanostructures fabrication. The applied FEBIP methods rely on the local decomposition of Fe(CO) and Co(CO)NO as precursors, either by the direct impact of the focused electron beam (electron beam induced deposition, EBID) or through the interaction of the precursor molecules with preirradiated/activated SURMOF areas (electron beam induced surface activation, EBISA). We demonstrate the huge potential of the approach for two different types of MOFs (HKUST-1 and Zn-DPDCPP). Our "surface science" approach to FEBIP, yields well-defined deposits with each investigated precursor/SURMOF combination. Local Auger electron spectroscopy reveals clean iron deposits from Fe(CO); deposits from Co(CO)NO contain cobalt, nitrogen, and oxygen. EBISA experiments were successful with Fe(CO). Remarkably EBISA with Co(CO)NO does not result in deposit formation on both resists, making the process chemically selective. Most importantly we demonstrate the fabrication of "nested-L" test structures with Fe(CO) on HKUST-1 with extremely narrow line widths of partially less than 8 nm, due to reduced electron proximity effects within the MOF-based resists. Considering that the actual diameter of the electron beam was larger than 6 nm, we see a huge potential for significant reduction of the structure sizes. In addition, the role and high potential of loading and transport of the precursor molecules within the porous SURMOF materials is discussed.
Focused electron beam induced deposition (FEBID) is a flexible direct-write method to obtain defined structures with a high lateral resolution. In order to use this technique in application fields such as plasmonics, suitable precursors which allow the deposition of desired materials have to be identified. Well known for its plasmonic properties, silver represents an interesting candidate for FEBID. For this purpose the carboxylate complex silver(I) pentafluoropropionate (AgO2CC2F5) was used for the first time in FEBID and resulted in deposits with high silver content of up to 76 atom %. As verified by TEM investigations, the deposited material is composed of pure silver crystallites in a carbon matrix. It showed good electrical properties and a strong Raman signal enhancement. Interestingly, silver crystal growth presents a strong dependency on electron dose and precursor refreshment.
Carboxylates constitute an extremely promising class of precursor compounds for the electron beam induced deposition of silver. In this work both silver 2,2-dimethylbutyrate and silver pentafluoropropionate were investigated with respect to their dwell-time-dependent deposition behavior and growth characteristics. While silver 2,2-dimethylbutyrate showed a strong depletion in the center of the impinging electron beam profile hindering any vertical growth, silver pentafluoropropionate indicated a pronounced dependency of the deposit height on the dwell time. Truly three-dimensional silver structures could be realized with silver pentafluoropropionate. The pillars were polycrystalline with silver contents of more than 50 atom % and exhibit strong Raman enhancement. This constitutes a promising route towards the direct electron beam writing of three-dimensional plasmonic device parts from the gas phase.
The electron-induced
modification of volatile physisorbed metal–organic
molecules is the key process in focused electron beam induced deposition
(FEBID). In this work, the perfluorinated copper carboxylate [Cu2(μ-O2CC2F5)4], (Cu2(pfp)4), was implemented in FEBID, as
it has the highest metal-to-carbon ratio Cu/C = 1:6 compared to other
Cu precursors used so far. FEBID was obtained within a small temperature
window of 120–130 °C. Transmission electron microscopy
verified the presence of metal(oxide) nanocrystals within a carbonaceous
matrix. The chemical composition analysis revealed the loss of about
80% of ligand material during the electron-induced dissociation. The
copper nanocrystals oxidized within a few minutes in films <80
nm upon exposure to ambient conditions, while they were protected
by a carbon–fluorine-containing matrix in thicker areas of
the deposits. A two-step post-growth annealing procedure with subsequent
oxidizing and reducing atmosphere was used to purify the deposits.
Pure copper crystals were formed in this step.
Highlights
SARS-CoV-2 serological assays have to be interpreted with caution and may need to be optimized to produce reliable results.
we identified significant discrepancies in sensitivity and specificity between compared assays, especially when COVID-19 outpatients were tested.
performance of the compared IgG assays was comparable, when cut-off values were optimized by ROC analysis.
Assays for IgA and IgM demonstrated either a lack of specificity or sensitivity.
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