Centrum pre nanodiagnostiku materiálov

KUNDRATA, Ivan – FRÖHLICH, Karol – VANČO, Ľubomír – MICUŠÍK, Matej – BACHMANN, Julien

In Beilstein Journal of Nanotechnology. Vol. 10, (2019)

https://doi.org/10.3762/bjnano.10.142

Abstract

Lithiated thin films are necessary for the fabrication of novel solid-state batteries, including the electrodes and solid electrolytes. Physical vapour deposition and chemical vapour deposition can be used to deposit lithiated films. However, the issue of conformality on non-planar substrates with large surface area makes them impractical for nanobatteries the capacity of which scales with surface area. Atomic layer deposition (ALD) avoids these issues and is able to deposit conformal films on 3D substrates. However, ALD is limited in the range of chemical reactions, due to the required volatility of the precursors. Moreover, relatively high temperatures are necessary (above 100 °C), which can be detrimental to electrode layers and substrates, for example to silicon into which the lithium can easily diffuse. In addition, several highly reactive precursors, such as Grignard reagents or n-butyllithium (BuLi) are only usable in solution. In theory, it is possible to use BuLi and water in solution to produce thin films of LiH. This theoretical reaction is self-saturating and, therefore, follows the principles of solution atomic layer deposition (sALD). Therefore, in this work the sALD technique and principles have been employed to experimentally prove the possibility of LiH deposition. The formation of homogeneous air-sensitive thin films, characterized by using ellipsometry, grazing incidence X-ray diffraction (GIXRD), in situ quartz crystal microbalance, and scanning electron microscopy, was observed. Lithium hydride diffraction peaks have been observed in as-deposited films by GIXRD. X-ray photoelectron spectroscopy and Auger spectroscopy analysis show the chemical identity of the decomposing air-sensitive films. Despite the air sensitivity of BuLi and LiH, making many standard measurements difficult, this work establishes the use of sALD to deposit LiH, a material inaccessible to conventional ALD, from precursors and at temperatures not suitable for conventional ALD.

GRANČIČ, B. – PLEVA, Milan – MIKULA, M. – ČAPLOVIČOVÁ, Mária – SATRAPINSKYY, L – ROCH, Tomáš – TRUCHLÝ, M. – SAHUL, Martin – GREGOR, M. – ŠVEC, Peter, Sr. – ZAHORAN, Miroslav – KÚŠ, Peter

In Surface & Coatings Technology. Vol. 367, June (2019)

https://doi.org/10.1016/j.surfcoat.2019.04.017

Abstract

Magnetron co-sputtering from TiB₂ and TaB₂ stoichiometric targets is used to prepare AlB₂-prototype ternary Ti_1-xTa_xB_2±Δ solid solution, with x in the range from 0 to 1. Using this technique, the boron-to-metal ratio (B/Me) varies with the actual Ti and Ta content. The boron-to‑tantalum ratio can be increased by decreasing the TaB₂ target voltage, which has a considerable effect on the coating structure. Coatings with B/Me > 2 reveal highly textured nanocolumnar structure, while the coatings with B/Me < 2 tend to be nanocrystalline (without any preferred crystallite orientation) or amorphous. All the deposited coatings have a hardness higher than 32 GPa. The under-stoichiometric (B/Me < 2) coatings show material pile-up around the cube-corner indent edges, an indication for plastic flow and increased ductility.

BENKOVIČOVÁ, Monika – HOLOS, Ana – NÁDAŽDY, Peter – HALAHOVETS, Yurily – KOTLÁR, Mário – KOLLÁR, Jozef – ŠIFFALOVIČ, Peter – JERGEL, Matej – MAJKOVÁ, Eva – MOSNÁČEK, Jaroslav – IVANČO, Ján

In Physical Chemistry Chemical Physics. Vol. 21, iss. 18 (2019)

Abstract

The ability to control the interparticle distance in self-assembled arrays of nanoparticles plays an important role in a large number of applications, which require tunable electronic and photonic properties. Importantly, practical applications in real devices rely on arrays satisfying more stringent requirements of lateral homogeneity controlled over a large scale. Herein, the interparticle distance in ordered nanoparticle assemblies was controlled by varying the nanoparticle effective size via the molecular chemical nature and chain length of the ligand. Iron oxide nanoparticles (IONPs) were functionalized by three types of ligands, namely (i) a mixture of oleic acid/oleylamine (OA/OAm), (ii) poly(n-butyl acrylate) (PBA) and (iii) polystyrene (PS), while two different molar masses of PBA and PS were used. The polymeric ligands with narrow dispersity and bearing phosphonic chain-end groups were prepared by atom transfer radical polymerization. Functionalization of the IONPs with polymeric ligands was achieved using a ligand exchange method. Both the hydrodynamic diameter and size distribution of the nanoparticles in colloidal solution were determined by dynamic light scattering (DLS). The mean interparticle distances in Langmuir–Schaefer monolayers prepared on solid substrates were assessed by means of the pair correlation function calculated from the atomic force microscopy (AFM) images. Furthermore, the lateral ordering, homogeneity, and interparticle distances averaged over a mesoscopic scale of the ordered monolayers were studied by the grazing-incidence small-angle X-ray scattering (GISAXS) technique. We demonstrate that the (nanoparticle) centre-to-centre distance in the ordered assemblies constituted by the IONPs with the core diameter of about 6 nm can be varied from 7.6 to about 12 nm with the resulting interparticle gap change by a factor of about 4.

Prerna Chauhan, Stanislav Hasenöhrl, Edmund Dobročka, Ľubomír Vančo, Roman Stoklas, Jaroslav Kováč, Peter Šiffalovič, Ján Kuzmík

In Applied Surface Science. Vol.470, (2019)

https://doi.org/10.1016/j.apsusc.2018.10.231

Abstract

Thick (>150nm) InxAl1-xN layers were grown on GaN/sapphire (0001) by organometallic vapor phase epitaxy. Growth temperature of InxAl1-xN layers was reduced from 790 to 730°C, to examine the effects of growth temperature in InxAl1-xN layers grown under H2 carrier gas. Indium incorporation, surface morphology, electrical, and optical properties of InxAl1-xN layers were examined as a function of growth temperature. Increase in In-molar fraction, as determined by high resolution X-ray diffraction, was observed with decreasing growth temperature of InxAl1-xN layers at the expense of surface roughness. Unstrained InxAl1-xN layer was achieved at 730°C under H2 carrier gas with x=0.18. However, InxAl1-xN layer grown under N2 carrier gas at 730°C to study the effects of carrier gas, was observed with two times higher In-molar fraction (x=0.37) and one order lower carrier concentration. This work shows the essential requirement of a multi-characterization approach to establish a connection between structural, electrical, and optical properties to improve our understanding towards InxAl1-xN. Edge threading dislocations density is found to be the most important parameter in deciding the characteristics of an InxAl1-xN layer.

GUARDIA, Laura – SUÁREZ, Loreto – QUEREJETA, Nausika – VRETENÁR, Viliam – KOTRUSZ, Peter – SKÁKALOVÁ, Viera – CENTENO, Teresa A.

In Electrochimica Acta. Vol. 298, iss. 3 (2019)

Abstract

We present a simple and effective alternative which optimizes electrodes based on low-cost carbons for high-performance supercapacitors. The combination with reduced graphene oxide (rGO) greatly improves the operation of microporous carbons easily produced by one-pot activation of grape seeds. The use of composite electrodes with rGO lowers the supercapacitor resistance and enables a much higher rate capability.

The mixture of rGO flakes and particles of a highly porous carbon obtained by KOH activation allows retaining the high capacitance of 260 F g⁻¹ of the standard electrodes at 1 mA cm⁻² in aqueous H₂SO₄ whereas the value at 200 mA cm⁻² is increased by around 2.4 times. Consequently, at high current density, the capacitor assembled with these composites stores eight times more energy and the power density is multiplied by four.

The synergy between rGO and an ultramicroporous carbon produced by CO₂-activation results extremely profitable, the cell assembled with composite electrodes reaching three times more energy and power at 200 mA cm⁻² than the best performance of the standard counterpart.

More importantly, the higher density of the composite electrodes leads to a capacitance of around 200 F cm⁻³ which translates into a remarkable improvement in the supercapacitor operation normalized to volume.