List of Abstracts 2021: SESSION E - ADVANCED METHODS OF PREPARATION AND CHARACTERIZATION OF NANOMATERIALS

Exploration of fundamental photophysical phenomena at the level of individual quantum objects requires highly specialized optical spectroscopy with subnanometer, single-photon capabilities. Thanks to recent progress in light microscopy with scanning probes, excited states of molecules and their interaction can now be investigated at the nanoscale with unprecedented detail. Precise injection of charge carriers1 into molecules leads to formation of charged states and transient excited states - the excitons. The photons produced by decay of these states carry information about energies, charges, transient dipoles and temporal evolution of the studied systems. Using an optical path to collect photons from the nanocavity between the tip and sample in a cryogenic scanning probe microscope, it is possible to tackle some photophysical phenomena occurring in organic dyes.
In this contribution, I will present our investigation that focused on the local Coulombic effects of the ionic substrate on single Copper-phthalocyanines (CuPc),2 electrofluorochromism of Zinc-phthalocyanine (ZnPc), and describe a new phase fluorometry scheme, that combines radio-frequency-modulation of the picocavity with time-resolved single photon detection.3,4 With this method, exciton lifetimes could be determined and the evolution of the system could be tracked down to the picosecond range. Finally, I will show recent data on quantum entanglement of excitons in small molecular clusters of perylene tetracarboxylic dianhydride (PTCDA).
REFERENCES: [1] Charge carrier injection electroluminescence with CO functionalized tips on single molecular emitters. J Doležal, P Merino, J Redondo, L Ondič, A Cahlík and M Švec, Nano letters 19 (12), 8605-861, 2019.; [2] Mechano-Optical Switching of a Single Molecule with Doublet Emission. J Doležal, P Mutombo, D Nachtigallová, P Jelínek, P Merino and M Švec, ACS Nano 14 (7), 8931-8938, 2020.; [3] Constant amplitude driving of a radio frequency excited plasmonic tunnel junction. J Doležal, P Merino and M Švec, Applied Physics Letters 118 (19), 193301, 2021.; [4] Exciton-Trion Conversion Dynamics in a Single Molecule. J Doležal, S Canola, P Merino and M Švec, ACS Nano 15, 7694-7699, 2021.

Constant amplitude bias modulation over a broad range of microwave frequencies is a prerequisite for application in high-resolution spectroscopic techniques in a tunnel junction, e.g., electron spin resonance spectroscopy or optically detected paramagnetic resonance. Here, we present an optical method for determining the frequency-dependent magnitude of the transfer function of a dedicated high-frequency line integrated with a scanning probe microscope. The method relies on determining the energy cutoff of the plasmonic electroluminescence spectrum, which is linked to the energies of the electrons inelastically tunneling across the junction. We develop an easy-to-implement procedure for effective compensation of a radio frequency line and determination of the transfer function magnitude in the GHz range. We compare our method with conventional fully electronic calibration and find a perfect agreement. We further demonstrate calibration of driving amplitude in radio frequency phase fluorometry for the measurement of exciton lifetimes.

Ti3C2 MXene films find their use in many applications, for example, as a catalyst for chemical reactions, optical coatings for lasers, electrodes for solar cells and LEDs. Dangling titanium bonds in 2D Ti3C2 MXene flakes are terminated by functional groups: oxygen, fluorine, and hydroxide. Water molecules can be found on the surface and in between the MXene flakes in multilayered MXene films, because MXene is hydrophilic. When MXene films are placed in a vacuum, the atoms and molecules are desorbed from the film surface. Within this work, we analyzed the effect of ultraviolet radiation on the photodesorption of atoms and molecules from the surface of the MXene films, as well as the effect of UV radiation on the conductivity of the films. The residual gas analysis was used under vacuum 10-5 - 5·10-7 Pa from 0 to 200 atomic mass units. The conductivity of the films was measured by a two-probe method. The samples were cooled to -180°C with liquid nitrogen. After this, samples were heated at a rate 57°C·min-1 to 300°C to measure the thermally stimulated desorption of atoms and molecules, and the thermally stimulated emission of electrons. MXene films were deposited by the interface method on the glass substrates. The conductivity of the MXene films has a complex behavior. This consists of a combination of the metallic conductivity of the MXene flakes and a semiconductor component, that arises from the oxidation of the MXene flakes and the transformation of the MXene into titanium oxide. At low temperatures, the dominant factor in the resistance is the contribution from titanium oxide, which decreases with temperature increasing. However, as temperature increases the contribution from the resistance associated with metal MXene flakes increases. Various effects of irradiation on the photodesorption of oxygen, fluorine, and hydroxide have been established. Irradiation leads to an increase in the desorption of oxygen and hydroxide from the MXene films, while a decrease was observed for fluorine.

Interest in organic photovoltaics (OPVs) has increased in recent decades as they are less costly, easy to prepare on large and flexible surfaces, and less hazardous to the environment compared to its inorganic counterparts. Significant progress has been made in overcoming the performance limiting factors of OPVs such as short exciton diffusion and lifetime, low carrier mobility, and high energy level offset requirement between donor and acceptor material to efficiently dissociate excitons into free charges. In this work, we present the possibilities of conducting correlative microscopy characterization study on OPV sample using four different methods namely Atomic Force Microscopy (AFM), Kelvin Probe Force Microscopy (KPFM) in the dark and under illumination, Confocal Raman and Photoluminescence Microscopies coupled with spectrometer. The sample used in this work is a P3HT:PCBM film made by spin-coating the mixed solution with 1:08 ratio. The first results show that the film quite uniform with topological variation of about 30 nm. The surface potential increases at the grain boundaries and decreases at the grains. The photovoltaic voltage (PV) at the grain boundaries is higher than the PV at the grains. Furthermore, both photoluminescence (PL) and Raman maps show that there are significant local intensity variations. We found that the results of all four methods are consistent and could provide detailed information about optical and physicochemical properties of the sample. The work was supported by the project CZ.02.1.01/0.0/15_003/0000464 - Centre of Advanced Photovoltaics.

Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are two of the most used, complementary techniques for surface analysis at the nanoscale. Integrating a compact AFM into SEM brings new possibilities for true correlative microscopy and advanced multi-modal sample characterization in various fields, such as Material science, Nanotechnology, Semiconductors, or Life science.
Correlative Probe and Electron Microscopy (CPEM) represents a hardware correlative technology, enabling simultaneous acquisition of SEM and AFM data, and seamless correlation into one 3D image. The strength lies in a combination of AFM modes (3D topography, electrical, mechanical, and magnetic measurements) and SEM capabilities (fast imaging with wide resolution range, chemical analysis, surface modification). CPEM technique can be applied using LiteScope 2.0, produced by NenoVision, ensuring the data are collected in the same coordinate system and with identical pixel size, resulting in 3D complex multi-channel sample characterization.
Above mentioned advantages can be demonstrated on correlative in-situ analysis of LiNiO2 cathode material used in rechargeable batteries. Since the powdered cathode material is prone to rapid oxidation upon air exposure, it needs to be analyzed in-situ by the AFM-in-SEM approach. The SEM combined with the EDX technique provided fast navigation of the AFM probe on the sample, information of elemental composition, and material contrast. The AFM LiteScope was used to measure the sample topography and conductive mapping to characterize the changes in the cathode after charge/discharge cycling. Lastly, the correlated CPEM image combines AFM topography and electrical properties with SEM material contrast and provides straightforward data interpretation.

Plasma-polymerized SiOxCyHz coatings modifying surface properties of metal substrates, plastics, etc., are very perspective materials for wide range of industrial applications. In the present study, a low-pressure RF capacitively coupled discharge in a mixture of trimethylsilyl acetate (TMSA) monomer with different carrier gases (O2, Ar, CH4) was used to prepare organosilicon thin films. This study compares properties of resulting thin films (chemical composition, mechanical properties, wettability, and surface structure). The present work focuses primarily on the investigation of the relationships between the resulting properties of prepared coatings and the discharge parameters.

Zinc oxide nanoparticles have been synthesised using non-thermal atmospheric pressure plasma (ZnO-NTP). We investigated the behaviour of these ligand-free and defect-free particles as a colloid suspension using different solvents, from deionised water to physiological saline and microbial culture broth. We also explored the antibacterial effect of ZnO-NTP in liquid using model microorganisms (E. coli) and standardised protocols with and without white light illumination. The white light source was chosen based upon overlapping spectral output and UV-vis absorbance profile of ZnO-NTP (i.e. between 400-500 nm). We found that the zeta potential of ZnO-NTP became more negative after exposure to microbial broth relative to water, from -12.6 mV to -24.6 mV, which suggests increased colloid stability. However, we observed rapid primary particle agglomeration in all liquid types regardless of pre-treatment by high power sonication. Scanning electron microscopy images revealed large agglomerates of ZnO-NTP interacting with the surface of bacteria cells, ranging in size from 200 nm up to 20 µm. Minimum inhibitory concentration was 128-256 µg/mL regardless of illumination. Growth kinetics of E. coli exposed to 10 and 100 µg/mL ZnO-NTP were similar to that of unexposed bacteria cells using reverse spin bioreactors, and there was no significant difference in viable cell concentration after 24h exposure relative to untreated control irrespective of sample illumination. ACKNOWLEDGEMENTS: The presented work was supported financially by the project GACR 19-02858J.

Contact mode, tapping mode and even contact non-resonant AFM mode (i.e. PFQNM from Bruker, Jumping mode™ from NT-MDT, Fast Force Mapping Mode™ from Oxford Instruments etc.) can often cause movement of highly mobile molecules on the surface. The reason is tip-to-sample contacts when even small force (20 pN) is sufficient to cause movement of molecules, such as helicene-based macrocycles on HOPG surface. Due to this reason AFM achieved a sub-molecular resolution in air on 3 nm helicene-based racemates but not on enantiomers yet.
Therefore, we introduce here novel robust non-contact non-resonant Atomic Force Microscopy method (patent application PCT/CZ2021/050076) for measurements in air (or other environments), which uses the attractive interaction between the tip and the surface to stop the tip approach before the tip touches the surface. During tip-to-sample distance variations the tip approach stops after reaching one of four criteria based on cantilever deflection. Mostly the tip approach stops after reaching negative setpoint value, thus avoiding direct tip-surface contact.
We also show that the tip-to-sample distance variations can be used in mechanically oscillating STM mode (patent application PCT/CZ2021/050077). In this manner the constant current and constant height maps can be obtained during a single image scan of hyperspectral current vs. distance data. Moreover, two additional new channels corresponding to true Local Density of States (LDOS) topography and tunneling barrier height can be created based on the same hyperspectral dataset. Maximal tunnelling current is set for a feedback loop adjusting average tip-to-sample distance.
Both methods can be in principle implemented only via software modification on all commercial SPM machines.
ACKNOWLEDGEMENTS: This work is a part of a wider study focused on correlative microscopic analyses of properties of macromolecules on surfaces of semiconductor and 2D materials. This research is supported by the OPVVV project CZ.02.1.01/0.0/0.0/16_019/0000778 (CAAS).

Dental enamel has the highest hardness and durability in the human body due to its apatite based nanocomposite structure. During the characterization of the enamel, electron diffraction is a tool with unpaired locality, which provides information to relate the structure with mechanical properties. In this work we describe a standardization and evaluation procedure, which allows to enhance the precision of detection and measurement of diffraction rings in polycrystalline specimens. The most important limiting factors are the specimen height, the illumination conditions and lens distortions causing ellipticity of rings. The ideal calibration specimen to compensate for the ellipticity is composed of nanocrystalline grains and produce narrow diffraction rings. In many cases the nanocrystalline apatite specimens themselves are suitable for this purpose, but we also applied specific calibration specimens, which provide reliable means for calibration independent of the structure (grain size, texture, etc…) of the actual specimen. Lattice spacing measurement with 0.1% precision provides a basis for more exact texture determination in nanocrystalline apatite of enamel.

Recently, a novel multi-beam SEM (MSEM) technology for imaging of very large sample areas has been developed by ZEISS. The MultiSEM family features 61 or even 91 electron beams scanning in parallel, resulting in an imaging throughput of up to 2 TeraPixels per hour [s. ref.] is now achievable, therefore enabling extremely large-scale imaging experiments in 2D and 3D.
Here, we present a unique advancement enabling correlative microscopy, which uses a centralized software platform to pull together data from light-, electron-, Ion-, SIMS and X-Ray Microscopy (XRM). Beyond just correlating the various datasets, the approach allows data from one technique to be used to drive the hardware in another technique, facilitating easy transfer of information between the suite of available microscopes and the operator.
The presentation will give an overview of the current state of the technology, its potential application space and the challenges in data handling imposed by the enormously increased data rate.
REFERENCE: [1] Ref. : Crosby K, Eberle AL, Zeidler D (2016) Multi-beam SEM Technology for High Throughput Imaging. MRS Advances, 1 (26):1915-1920.

Nanomaterials are considered a key resource with high potential for broad application. So far, only a few nanomaterials, in particular metal oxide nanoparticles from gas phase synthesis, have been used on a large scale. Advanced applications often require colloidal nanoparticles with defined properties. Their production is more complex, they have a poor shelf life, and distributors demand high prices. The conditions for innovative application research must be improved by easier access to colloidal nanoparticles.
A compact and fully-automatic benchtop machine has been developed for quick, easy and reliable production of colloidal nanoparticles. The machine uses the method of laser synthesis of colloids. Laser radiation of high intensity enables the breakdown of almost any solid into nanoparticles. In addition, different dispersants and stabilizers can be used. An almost infinite range of colloids becomes available with one machine.
We provide an insight into the operation of the machine and report in particular on the high performance efficiency of the laser-based synthesis. Furthermore, we highlight benefits of using the device in R&D and report innovative applications of colloidal nanoparticles made possible by the technology.

This work includes the synthesis of AgCuNi nanoparticles (NPs) by the hot-injection thermal decomposition method in three different morphologies by applying various copper precursors. Prepared NPs have been characterised with a focus on their size, shape, optical and thermal properties. The morphology of NPs was evaluated using scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy. Nickel always formed the outer shell of NPs, while the morphology of the AgCu core has been varied. Thermal properties of AgCuNi nanoparticles were measured by different scanning calorimetry. Nickel shell figures as a solid capping agent to avoid aggregation of AgCu core. The effect of AgCu morphology core on the thermal properties has been clearly demonstrated and melting point depression of the AgCu system has been noticed Theoretical phase diagram of AgCu NPs, calculated by CALPHAD method has been satisfactorily verified.
ACKNOWLEDGMENTS: The work has been financially supported by the Czech Science Foundation under the project GA17-15405S, GJ20-03636Y, and by the Institutional project of Masaryk University MUNI/A/1375/2018.
CIISB research infrastructure project LM2015043 funded by MEYS CR is gratefully acknowledged for the financial support of the measurements at the CF Cryo-electron Microscopy and Tomography.