Deposition of Large Organic Molecules in UHV Conditions, Tomáš Krajňák (supervisor: Jan Čechal), BUT 2019

In this thesis, large organic molecules (DM15N, DM18N, Cu(dbm)2) were deposited. These molecules are cannot be deposited by thermal sublimation due the fact that they decompose at lower temperature than they sublime. The employed molecules to single molecular magnets, which can be potentially used as quantum bites (qubit). The new method of deposition atomic layer injection made by Bihur Crystal company was introduced and tested. The method uses liquid solution with molecules which is driven by argon gas through pulse valve to the sample placed in ultra-high vacuum chamber. During the deposition, droplets of solution are formed on the sample surface. The solvent can be removed by light annealing or by keeping the sample in the vacuum for couple of days. The molecules were investigated by x-ray photoelectron spectroscopy and by scanning electron microscopy to determine fragmentation of the molecules, to study topography of the resultant surface and homogeneity of the deposited layer. We found conditions at which the intact molecules are deposited on the sample surfaces and form molecular nano- and micro- crystals.

Understanding the Image Contrast of Material Boundaries in IR Nanoscopy Reaching 5 nm Spatial Resolution, ACS Photonics, 2018, 5 (8), pp 3372-3378, DOI: 10.1021/acsphotonics.8b00636

Stefan Mastel, Alexander A. Govyadinov, Curdin Maissen, Andrey Chuvilin, Andreas Berger, and Rainer Hillenbrand

Abstract: Scattering-type scanning near-field optical microscopy (s-SNOM) allows for nanoscale-resolved Infrared (IR) and Terahertz (THz) imaging, and thus has manifold applications ranging from materials to biosciences. However, a quantitatively accurate understanding of image contrast formation at materials boundaries, and thus spatial resolution is a surprisingly unexplored terrain. Here we introduce the read/write head of a commercial hard disk drive (HDD) as a most suitable test sample for fundamental studies, given its well-defined sharp material boundaries perpendicular to its ultrasmooth surface. We obtain unprecedented and unexpected insights into the s-SNOM image formation process, free of topography-induced contrasts that often mask and artificially modify the pure near-field optical contrast. Across metal-dielectric boundaries, we observe non-point-symmetric line profiles for both IR and THz illumination, which are fully corroborated by numerical simulations. We explain our findings by a sample-dependent confinement and screening of the near fields at the tip apex, which will be of crucial importance for an accurate understanding and proper interpretation of high-resolution s-SNOM images of nanocomposite materials. We also demonstrate that with ultrasharp tungsten tips the apparent width (resolution) of sharp material boundaries can be reduced to about 5 nm.

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• Corrsponding ORDP dataset: DOI: 10.13140/RG.2.2.19079.65441