Seznam abstraktů 2022: POSTEROVÁ SEKCE E

We present the surface lifetime characterization of the textured silicon surface for application in solar cells. The measurement by the Sinton WCT-120 PL lifetime tester is compared with the simulation by the Silvaco TCAD software to get possible values of the surface recombination velocity. The n-type silicon textured surface wafers were used as the substrate. In the first experiment, the carrier lifetime was measured and simulated after chemical cleaning of the surface. The second experiment was done after deposition of aluminium oxide by the Atomic Layer Deposition on the textured surface. The thermal method was used with TMA as a precursor. The two-dimensional TCAD calculation was realized on the silicon structure with textured surface. The surface profile was determined by the AFM measurement. Two electrodes were placed on both sides of the structure to calculate the current flow generated by the light pulse. The real Sinton optical source spectrum was approximated by the five beams in the range 690 - 830 nm with different intensities. The current decrease connected with the decay of the optical intensity was simulated. The comparison of experimental results with the TCAD simulation gives the possibility to distinguish between the bulk carrier lifetime and surface recombination velocity. The coincidence of the measured and simulated graphs by fitting the simulation parameters results in the realistic value of the surface recombination velocity. It can be used for the classification of the silicon surface passivation influence on the solar cells’ efficiency.

The interaction of polar molecules with an external electric field provides a tool for manipulating molecular structure. And this is also the case for polar polymers, which can undergo complex structural changes due to the external electric field. The study of such changes in the polymer structure is of great importance, for example, for the technology of electrospinning. The microscopic changes caused by the electric field influence both the quality of the electrospinning process and the properties of the resulting materials. The effect of electric field on the structure of polymer chains can be studied experimentally, theoretically or by methods of molecular modeling. In previous molecular modeling studies [1, 2], special attention was paid to modeling the dynamics of the initial stages of the process of electrospinning of polymer solutions. In this contribution, our recent molecular dynamics simulation study [3] is extended by including short ethylene glycol oligomers. In an effort to explain the results of work [3], molecular dynamics simulations are carried out to study the structure of mono-, di-, tetra- and octaethylene glycol in water and methanol. An attempt was made to study the geometry of individual monomer units and dipolar behavior of the oligomer chain. The field-induced structural changes of the oligomer molecules in both solvents are monitored and used to infer what might be responsible for the solvent specific, field-induced anisotropy of a polymer coil reported previously [3].
REFERENCES: [1] Nezbeda, I., J. Jirsák, F. Moučka a W. Smith: Application of molecular simulations: Insight into liquid bridging and jetting phenomena. Condensed Matter Physics, 18(1):13602:1-10, 2015.; [2] Jirsák, J., P. Pokorný, P. Holec a Š. Dědičová: A Molecular-Level Picture of Electrospinning. Water, 12(9):2577:1-31, 2020.; [3] Dědičová, Š., J. Dočkal, F. Moučka a J. Jirsák: Molecular dynamics simulation study of the effect of a strong electric field on the structure of a poly(oxyethylene) chain in explicit solvents. Journal of Molecular Liquids, 338(2):116622, 2021.

Biomedical applications of nanomaterials depend on the size and morphology of nanoparticles and their biocompatibility. However, the armory of trusted protocols usually includes reducing agents, including sodium borohydride, methoxy polyethylene glycol, potassium tartrate, etc., and capping agents, including sodium dodecyl benzyl sulfate, polyvinylpyrrolidone, etc., which are usually toxic. The unavoidable presence of toxic compounds in nanocolloid systems limits the use of nanoparticles for biological systems.
This study aims to synthesize non-spherical gold nanoparticles using plant extracts and characterize their properties for biomedical applications.
Gold nanoparticles were obtained through the direct interaction of Au3+ cations with aqueous (water-ethanol) extracts of selected plants (juniper, elderberry, goldenrod, and peppermint) under different synthesis conditions. Ultraviolet and visible spectroscopic measurements confirmed the response of the obtained Au nanocolloid solutions to near-infrared radiation. This response opens the prospect of using the obtained nanoparticles in nanomedicine for antitumor therapy, targeted drug transport, diagnostics or drug delivery systems. The position of the maximum near-infrared radiation can be adjusted by the synthesis conditions (extract composition, concentration, reagent ratio, pH, and temperature). Infrared spectroscopy shows the conversion of polyphenolic compounds to carboxyl compounds, which probably play the role of effective capping agents. Transmission electron microscopy and atomic force microscopy showed the formation of a mixture of circum-spherical Au nanoparticles and non-spherical Au nanoparticles: nanotriangles with sizes from 20 nm and nanohexagons with sizes > 100 nm.

We present a multi-methodological analysis of the influence of the thermal vibrations on the Mössbauer effect. Our study is focused on β-phase of tin for which we have our own Mössbauer measurements of the Mössbauer factor as a function of temperature. We have employed atomic-scale numerical results in the form of mean square displacements of atoms determined by quantum-mechanical calculations as the input for a theoretical analysis of Mössbauer effect. The dependence of Mössbauer factor was modeled using continuum-level thermodynamic modeling based on the quasi-harmonic approximation. The resulting temperature dependence of Mössbauer factor as obtained from our approach agrees with our experimental data similarly well as the results based on classical Debye model. Importantly, we show that the latter simplistic model of thermal vibrations of solids can be replaced by exact state-of-the-art quantum-mechanical calculations of phonons. We expect a better agreement between our theoretical results and experimental data if an improved pseudopotential for quantum-mechanical calculations of Sn is available. Importantly, while both Debye and our approach slightly deviate from the experiment data, our suggested methodology bears promises for future improvement if an improved potential for Sn is available. The prospect of further improvement is hardly expected in the case of classical over-simplified Debye model that has been mostly used so far. (for detail see Friák et al., Computational Materials Science 215 (2022) 111780).

Hydrogels are three-dimensional networks of physically or chemically interconnected polymers that can absorb and retain a large amount of water in their internal structure. Hydrogels can be used in a wide range of medical applications (e.g., wound dressings, controlled drug release, scaffolds for tissue engineering). The application potential of hydrogels is defined by the combination of their crucial material properties (e.g., stiffness, mechanical strength, transport properties). These properties are primarily based on the morphology of the internal structure. Accurate analysis of the ultrastructure of hydrogels is important for understanding the parameters affecting the functionality of hydrogels, nevertheless, still represents a methodologically demanding task. Therefore, this work was focused on the optimization and testing of methods suitable for the analysis of the nanostructure of hydrogel materials with a focus on determining the pore size.
Conventional porosimetry methods (e.g., DSC thermoporometry), direct visualization methods (SEM, cryo-SEM, and AFM) as well as rheology and turbidimetry were chosen as methods for structural analysis. Hydrogels based on polyvinyl alcohol (PVA) were chosen as representative hydrogel systems for testing these methods. The results obtained by the individual methods were compared. Based on the results of this work, the usability and benefits of the individual methods were discussed concerning the sample preparation, time, and financial demands, and also in terms of compliance of pore sizes with the range of sizes declared for PVA hydrogels.

Iron(III) oxide exists in four stable crystalline polymorphs, α-, β-, γ- and ε-Fe2O3, whereas each of these phases has its specific crystal structure and hence also physical features. Specifically, ε-Fe2O3 is a rare iron(III) oxide phase. ε-Fe2O3 is still hard to synthesize as a single-phase. Moreover, due to the thermodynamic reasons, it can be synthesized only in the nanosized form. ε-Fe2O3 exhibits a high coercivity at room temperature, coupled magnetoelectric features and ferromagnetic resonance in microwave domain. For these reasons, it is widely regarded as an intriguing material for magnetic storage media and spintronic devices and as a suppressant of unwanted electromagnetic interference in signal transmissions. This contribution presents a method to synthesize pure ε-Fe2O3 nanoparticles and ε-Fe2O3 nanoparticles doped with Sc atoms, employing a sol-gel synthetic protocol. For determination of the structure and composition, X-ray powder diffraction, electron microscopy techniques, 57Fe Mössbauer spectroscopy, and magnetization measurements were used. REFERENCES: [1] J. Tuček, R. Zbořil, A. Namai, S. Ohkoshi, Chem. Mater. 2010, 22, 24, 6483-6505 (2010).; [2] J. Jin, S. Ohkoshi, K. Hashimoto, Adv. Mater. 2004, 16, No. 1, January 5 (2004).; [3] M.Gich, M. Popovici, D. Nižňanský, A. Roig, C. Savii, L.Casas, E. Molins, K. Zaveta, C. Enache, J. Sort, S. de Brion, G. Chouteau, J. Nogués, Chem. Mater. 16, 5542-5548 (2004).; [4] Michaela Polášková, Ondřej Malina, Jiří Tuček, Petr Jakubec; Nanoscale, 14, 5501-5513 (2022).

In the past 20 years, the wet chemical oxidation process has been used for Si wafer passivation by tunnel oxide in solar cell technology such as TOPCon or POLO. The key idea of our technology approach is to study different wet oxidation recipes such as HNO3, DI-Water (the water resistivity must be 18.2MΩcm), and H2SO4 by using the programmable robotized wet bench with different etching recipes. Additionally to oxide passivation, the Aluminum oxide (Al2O3) layer providing a positive fixed charge is deposited by using Atomic Layer Deposition (ALD). The n-type Si /wafers with orientation <1 0 0> have a thickness of 140µcm and base resistivity of 3.5Ω-cm with pyramids featuring surface orientation <1 1 1> are used as substrate. The wafers are cleaned using the standard RCA cleaning process, the removal of the native oxide is done by hydrofluoric acid HF or ammonium fluoride NH4F. The lifetime is measured by the contactless photoconductance method using Sinton WCT-120 PL measurement equipment. It is observed that the lifetime after the RCA+HF method shows a higher lifetime than the lifetime obtained after the ALD process. The carrier lifetime of the wafers is above 1ms while the measured value is in the orders of lower magnitude. This means that the lifetime is dominated by surface recombination velocity. Like this quick feedback on the quality of electronic passivation is provided and the technological parameters can be effectively optimized.

Continued miniaturization, motivated by market pressure for the development of small devices, requires a deeper understanding of the preparation and application of structures based on low-dimensional systems, e.g. two-dimensional materials. One such material is graphene, a monoatomic layer of carbon atoms ordered in a hexagonal lattice. A key step in using graphene is its transfer from a metal (copper) catalyst to the desired substrate. However, this process influences its physical properties through contamination or mechanical stress, which can be measured by several techniques. In this work, optimal conditions for the large-area ellipsometric contrast micrography and Brewster angle microscopy visualization of contamination on monolayer graphene from the transfer process were found. These samples were also locally characterized by atomic force microscopy and micro-Raman spectroscopy mapping. To support the obtained results, the electrical measurements were done. Namely, we have conducted transfer (field-effect) and output performance of the prepared devices to address the doping level, along with a four-point and transfer length measurement to address the effects of the electrodes doping and sheet resistance of the prepared layers.

The Langmuir-Blodgett method in combination with vertical deposition provides a simple way to prepare ordered monolayers of nanoparticles on substrates with an area of ​​up to tens of square centimeters. These monolayers can be used as a starting point for the preparation of other interesting nanomaterials with applications in optics, nanophotonics, sensorics and other areas. The basic preparation steps are deposition of nanoparticles on the water surface, compression of the layer using movable barriers into a close packed arrangement and transfer of the monolayer to the substrate through vertical deposition. Optimizing individual process steps for a given material and size of nanoparticles is key to achieving the required properties of the prepared monolayers.

The depth distribution of implanted nitrogen determines structural changes, especially in the formation of new phases. The new phases strongly influence surface properties such as hardness, wear resistance, and corrosion resistance. Computational and experimental simulations of the influence of the contaminating carbon layer on the depth distribution of nitrogen in the titanium alloy were performed. Carbon contamination of the surface with different thicknesses and its effects on the concentration profile was simulated. It has been proven that the ion energy distribution changes with the thickness of the layer after passing through the layer. The influence of the layer density and its impact on the displacement of the experimental depth profiles was demonstrated. With a combination of experimental and theoretical approaches, the physical phenomena involved in the deformation of concentration profiles were explained.

Boron or phosphorous can significantly control the electronic properties of diamond (10.1016/j.tsf.2010.05.031, 10.1002/ijch.199800005). Here, boron doped diamond (BDD) thin films are well-established and comprehensively studied and tested for sensing applications (10.1021/jacs.9b11183, 10.1007/978-1-4615-2257-7_7). However, the B concentration is crucial for particular applications and so, several techniques are used to quantify its amount within the films including secondary ion mass spectrometry, X-ray photoelectron spectroscopy (XPS), electron energy-loss spectroscopy, neutron depth profiling, etc.
In this work, we focus on the boron content quantification by RF-Glow Discharge-Optical Emission Spectroscopy (GD-OES) operated in advanced modes: (a) the ultrafast sputtering operation, (b) the differential interferometric profiling, and (c) the quantitative depth profile and thickness evaluation in GD of microcrystalline intrinsic and BDD (10.1039/C7JA00146K). More significantly, we have applied nuclear reaction analysis and XPS with depth profiling to support the results. Furthermore, the electrical measurement shows clear evidence of increased conductivity with increasing the boron content in the growth mixture. Raman spectra reveal the sharp diamond peak at 1333 cm-1, with minor defects (D peak) at 1350 cm-1, along with the trans-polyacetylene peak. All the samples reveals microcrystalline nature, as confirmed by SEM and AFM. We believe that our findings contribute to state-of-the-art and the application of advanced analytic techniques built-in features of a GD-OES in the characterization of intrinsic and BDD films.

Polyethylene (PE) is one of the simplest and well-known polymeric material with widely used. Linear low-density polyethylene (LLDPE) is a synthetic polymer most commonly used in food packaging or plastic bag production. The aim of this study was to examine the influence of the rice husks content and mTiO2 on the thermal properties of linear low densitiy polyethylene (LLDPE)/rice husks (RH)/mTiO2 biocomposite. Rice husk (RH) is one of the major agricultural residues produced as a byproduct during the rice milling process and it can be widely used due to its properties. The incorporation of RH into polymer matrices provides advantageous characteristics, such as biodegradability, light weight, toughness, and resistance to weathering. In addition to rice husks, rutile (mTiO2) was added, which is one of the most famous fillers due to its excellent properties such as stability and resistance to high temperatures. LLDPE/RH/mTiO2 biocomposites were prepared by mixing RH in content of 10, 20, 30, 40 and 50 wt % of RH and 5 wt % of mTiO2 in the neat LLDPE in a Brabender mixer. By DSC techniques phase transitions, TGA technique the thermal stability while by DMA technique viscoelastic properties of the LLDPE/RH/mTiO2 biocomposites were obtained with the respect of RH content and addition of mTiO2. According to DSC results for LLDPE/RH/mTiO2 biocomposites changes in the melting (Tm) and crystallisation (Tc) temperature indicated that there was some degree of interaction between LLDPE, RH and mTiO2. The TGA results show that the LLDPE is more thermally stable with addition of mTiO2. The viscoelastic properties were improved with addition of mTiO2.

Research investigating the interface between bacteria cells and nanomaterials requires a multi-faceted approach to fully elucidate the mechanism of interaction. A range of techniques are often used to analyse the same sample, but it is not always possible to do so under the same conditions which can make it difficult to reanalyse specific regions of interest. Here, we describe a procedure for preparing a multi-component sample containing bacteria and chitosan-coated hydrogenated nanodiamonds decorated with silver nanoparticles for correlative microscopy, specifically AFM in SEM (NenoVision). Standard microbiological culture techniques were used to grow Escherichia coli (E. coli), with or without cell surface appendages, which acted as the biological component of the sample. The nanocomposite was composed of hydrogenated nanodiamond particle core coated with chitosan before in-situ synthesis of silver nanoparticles on the nanodiamond/chitosan surface. Such nanocomposites have positive zeta potential so they are electrostatically attracted to the bacteria cell walls. Equal volumes of bacteria and nanocomposites are then combined in liquid before a substrate with a TEM reference grid is submerged in the suspension to collect bacteria-diamond-metal nanocomposite complexes. For correlation analyses, the location of the specific region of interest is identified via the reference grid. On such composite samples, 3D topographical images as well as local mechanical properties of the composite samples are acquired by using atomic force microscopy (AFM) detection regimes. The images are correlated with SEM secondary electron images (able to see also inside the cells) and back-scattered electrons (BSE) to detect the silver nanoparticles. Raman spectroscopy mapping is also used for the compositional analysis. We discuss various composite preparation parameters as well as measurement parameters with view to their impact on the ex-situ and in-situ correlative analysis and possible life science applications.

Scanning probe microscopy has significant speed limitations when compared to other microscopic methods, either optical or electron beam based. This is a problem when using the method for industrial purposes, such as searching for sample defects in the semiconductor industry.
A way to overcome this is the use of adaptive sampling instead of measuring in a raster pattern. In this contribution we present our experience with using Gaussian processes for planning the scanning strategy. Performance examples are demonstrated on simulated SPM data and on real measurements on wide bandgap semiconductor samples.

In this contribution we present a novel low cost Digital Signal Processor (DSP) designed for creating custom built Scanning Probe Microscope (SPM) setups. We show that using a low cost FPGA board coupled with a set of high bit depth AD and DA converters a versatile tool for building SPM systems can be created. Performance examples are demonstrated on various custom built systems, including high accuracy metrology SPM where the benefits of the novel controller when controlling the parasitic angular motion can be shown. The practical aspects related with interfacing to the DSP and running different types of SPM experiments will be discussed as well.

Surface Enhanced Raman Spectroscopy (SERS) is an important method for characterization of different materials and chemical analytes at low concentrations. The Raman signal with the plasmonic amplification is strongly dependent on the surface nanostructure. The filter paper could be used as the substrate for the chemical analysis of organic materials. We investigated the influence of different TiO2 thicknesses deposited on the ashless filter paper surface on the signal efficiency. TiO2 is hydrophilic and biocompatible. High-surface area TiO2 on the filter paper will help create 3D heterostructure to collect more analyte molecules. We used Sentech SI 500 thermal Atomic Layer Deposition (ALD) System with 10, 20, and 50 growth cycles and the TTIP precursor. Surface structure was investigated by Atomic Force Microscopy (AFM). The silver (Ag) colloid solution was dropped on the filter paper before standard R6G biomarker solutions were deposited. The Raman signal measured by In Via Renishaw spectrometer was compared for the different samples. TiO2 ALD-20 cycle gave the highest enhancement factor (~2.3 X 105) compared to other ALD-coated samples. Interestingly, the TiO2 ALD coating generally results in an enhancement factor more than 20 times higher than the reference sample (namely filter paper without the ALD coating). SERS mapping results suggest the uniformity and reliability of SERS measurements across a large area (40 x 40 um2). The finding paves a new direction for preparing simple, flexible, and biocompatible SERS substrates, which could be readily applied in detecting various biomolecular or organic analytes.

Implanting titanium with nitrogen ions changes (improves) its hardness and tribological properties. In order to understand how these properties are influenced, it is important to determine the nitrogen depth distribution, which can be significantly affected by ion channeling effect. To predict this effect, atomistic molecular dynamics (MD) simulations can be used. In this work, we analyzed the nitrogen channeling in titanium target by MD for 4 target surface orientations, different target temperatures (300 - 1155 K), and within low ion energies (500 - 4000 eV). Additionally, we determined the critical angles for which the channeling effects are suppressed.