Využití pozitronia na studium rozdělení velikostí nanoskopických volných objemů v černých kovech

• Název práce v češtině: Využití pozitronia na studium rozdělení velikostí nanoskopických volných objemů v černých kovech
• Název v anglickém jazyce: Use of positronium for study of size distribution of free volumes in black metals
• Klíčová slova: pozitronium|černé kovy|mikroporozita
• Klíčová slova anglicky: positronium|black metals|microporosity
• Akademický rok vypsání: 2023/2024
• Typ práce: disertační práce
• Ústav: Katedra fyziky nízkých teplot (32-KFNT)
• Vedoucí / školitel: prof. Mgr. Jakub Čížek, Ph.D.
• Konzultanti: RNDr. Petr Hruška, Ph.D.

Zásady pro vypracování

1. Prostudování odborné literatury o černých kovech a jejich mikrostruktuře
2. Seznámení se s metodou měření mikroskopické porozity pomocí pozitronia
3. Příprava tenkých vrstev černých kovů
4. Charakterizace mikrostruktury a absorpce světla v připravených vrstvách černých kovů
5. Výzkum mikroskopické porozity v přiravených tenkých vrstvách černých kovů pomocí pozitroia.
6. Analýza výsledků a určení rozdělení velikostí volných objemů v černých kovech
7. Vytvoření fyzikálního modelu růstu černých kovů
8. Sepsání disertační práce

Seznam odborné literatury

P.Hautojärvi: Positrons in Solids, Topics in Current Physics, Springer-Verlag, Berlin (1979)
J. Cizek, Mater. Sci. Technol. 34 (2018) 577.
A.H. Pfund, Rev. Sci. lnstrum. 1 (1930) 397.
M. Novotný et al., Cent. Eur. J. Phys. 7 (2009) 327.
A.Y. Vorobyev, C. Guo, Advances in Mechanical Engineering 2 (2010) 452749.
T.V. Teperik et al., Nature Photonics 2 (2008) 299.
P. Strimer et al., Infrared Physics 21 (1981) 37.
A.B. Christiansen, et al. Sci. Rep. 5 (2015) 10563.
S. Gu, et al., Biosensors and Bioelectronics 55 (2014) 106.
D.W. Gidley et al., Annu. Rev. Mater. Res. 36 (2006) 49.
A. Seeger, F. Banhart, Phys. Stat. Sol. A 102 (1987) 171.
C.H. Hodges, M.J. Stott, Phys. Rev. B 7 (1973) 73.
M. Eldrup et al, Chem. Phys. 63 (1981) 51.
A.C.L. Jones et al., Phys. Rev. Lett. 117 (2016) 216402.

Předběžná náplň práce v anglickém jazyce

Thermal evaporation or magnetron sputtering of metals in carefully adjusted low pressure (in the range of 100 Pa) of a non-interacting gas enables deposition of porous structures known as black metals [1]. Contrary to normal metals with highly reflective surface black metal films appear completely dark since light incident on the black metal surface is absorbed in multiple reflections in fractal-like structure of percolated micro-cavities with various sizes. Because of these unique structural features black metals absorb light in the visible to infrared spectral region [2]. The physical mechanism leading to formation of such peculiar porous structure is not completely understood yet.
Black metal films are promising for many applications including camouflage, engraving, marking [3] as well as optoelectronic, imaging, electrochemical sensing and solar cells [4-6]. Utilization of black metals in sensors profits from the fact that surface area of black metals is much higher than the geometrical surface area, e.g. 60 m2/g for black Pd [7].
The structure of micro-cavities (morphology and size distribution) is crucial for performance of black metals absorbers and sensors. The morphology and size distribution of micro-cavities can be modified by variation of the deposition process (sputtering rate, inert gas pressure, substrate temperature etc.) and also by subsequent surface treatment by pulsed laser. A key process governing the interaction of laser radiation with matter and consequently induced surface modifications is the absorption of laser energy by an irradiated material, which depends on laser parameters (i.e. wavelength, pulse duration, fluence), material properties and atmosphere. Preparation of black metal films with well defined porous structure tailored for specific applications requires reliable non-destructive characterization of pore size distribution providing necessary feedback to the preparation procedure.
Positronium (Ps), i.e. hydrogen-like bound state of electron and positron, is an excellent probe of micro-cavities in porous materials and enables non-destructive determination of their size distribution [8]. Inside conventional dense metals Ps does not form since any bound state of positron and electron is quickly destroyed by the screening of conduction electrons [9]. However, in porous metals a thermalized positron escaping from a metal through inner surface into a cavity may form Ps by picking an electron on the surface [10].
The purpose of the proposed Ph.D. work is the determination of size distribution of micro-cavities in black Au, Al and Pd films employing positron annihilation spectroscopy. The size distributions of micro-cavities will be determined from measured lifetimes of ortho-Ps pick-off annihilation using the Tao-Eldrup model [11]. The size distribution determined this way will be linked with deposition parameters of the black metal thin films and parameters of subsequent laser treatment. As a result the influence of the deposition and laser treatment parameters on the morphology and size distribution of black metal films will be elucidated. The research will be performed in the laboratory of positron annihilation spectroscopy at the Department of Low-Temperature Physics and at the Helmholtz Zentrum Dresden-Rossendorf (Germany). This planned research will enable preparation of black film layers with micro-cavities tailored for specific demands of various applications, e.g. gas sensors, light absorbers etc. Moreover, the planed research will help to clarify the fundamental problem of the physical mechanism of black metal growth as well as the mechanism of Ps formation on a metal surface [12].

References
[1] A.H. Pfund, Rev. Sci. lnstrum. 1 (1930) 397.
[2] M. Novotný et al., Cent. Eur. J. Phys. 7 (2009) 327.
[3] A.Y. Vorobyev, C. Guo, Advances in Mechanical Engineering 2 (2010) 452749.
[4] T.V. Teperik et al., Nature Photonics 2 (2008) 299.
[5] P. Strimer et al., Infrared Physics 21 (1981) 37.
[6] A.B. Christiansen, et al. Sci. Rep. 5 (2015) 10563.
[7] S. Gu, et al., Biosensors and Bioelectronics 55 (2014) 106.
[8] D.W. Gidley et al., Annu. Rev. Mater. Res. 36 (2006) 49.
[9] A. Seeger, F. Banhart, Phys. Stat. Sol. A 102 (1987) 171.
[10] C.H. Hodges, M.J. Stott, Phys. Rev. B 7 (1973) 73.
[11] M. Eldrup et al, Chem. Phys. 63 (1981) 51.
[12] A.C.L. Jones et al., Phys. Rev. Lett. 117 (2016) 216402.