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You can read my Ph. D. thesis here:

  • UW REPOSITORY

8.11.23

My Ph. D. Thesis

For a long time in the industry of electronics, the goal of increasing the efficiency of a device was as important as decreasing its size. The ultimate limit of miniaturization in semiconductor technology is a single atom device. However, for any potential application of a given system, it is necessary to have a fundamental understanding of its various parameters and phenomena occurring therein.

Zero-dimensional semiconductor nanostructures doped with single magnetic ions, which are the subject of this thesis, are the simplest experimental system that enables optical investigations of a single atom in the solid state. In this work I discuss three examples of magnetic dopants, that can be embedded in single quantum dots, while two of them (Vanadium and Nickel) were never explored thus far. The investigated samples were manufactured by the Molecular Beam Epitaxy method and were optically characterized in spectroscopic and magnetospectroscopic measurements.

For the case of CdTe quantum dots with single Vanadium dopants a theoretical model is presented, that explains experimentally observed phenomena. Furthermore, the determination of Vanadium dopant spin equal to 1/2 shows that this system could be a solid state realization of a qubit.

The investigation of CdTe quantum dots doped with single Nickel ions showed their tendency to temporal variations of their charge state. Solving this issue required the development of a method of manufacturing electrical contacts for the studied samples. The application of an external electric field to the quantum dots allowed not only for the stabilization of their charge state but also opened up new possibilities for experimental studies.

In particular, the electrical contacting of epitaxially grown samples was utilized in order to further investigate an already partially explored system of CdSe quantum dots doped with single Iron ions. One of the most important outcomes was the first known observation of X-- and XX- states in these quantum dots.


Link to the repository HERE.

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17.5.23

Article: Coherent imaging and dynamics of excitons in MoSe2 monolayers epitaxially grown on hexagonal boron nitride

MoSe2 AFM

The technology of preparing heterostructures made of semiconducting transition metal dichalcogenides (TMDs) is based on the exfoliation of thin films from van der Waals bulk crystals. While the nonscalability of the exfoliation top-down approach is not an issue in the fundamental research, for which the proof-of-principle demonstrations are essential, it is a major roadblock on the academia-industry pathway of this field. In order to merge these novel materials with the semiconductor microelectronics, strain-free monolayer samples homogeneously covering wafers of a few-inch diameter are required.

Here we present studies of MoSe2 grown by molecular beam epitaxy on the silicon substrate with exfoliated hBN flakes. We performed four-wave-mixing (FWM) imaging and spatially correlated the obtained amplitude of the nonlinear optical response of the studied flakes with the layer thickness obtained from AFM measurements. It allowed us to precisely characterize the signal originating from the epitaxially-grown monolayers with respect to the surface morphology. Furthermore, by measuring the FWM signal in the temporal domain we were able to determine the dephasing dynamics of exciton complexes and ascertained their temperature dependence.

Our results show that these epitaxial monolayers, while opening the prospect of being compatible with the semiconductor optoelectronics industry, display excellent optical response, providing they crystalize on atomically flat surfaces, here provided by hBN flakes. The quality and intensity of the produced signal are comparable with their non-encapsulated counterparts obtained via exfoliation. As such, our findings fortify the viability of the MBE growth method for the production of high-quality TMD monolayers. Furthermore, its inherent versatility opens up alluring new research venues for this particular family of 2D materials. 

Authors: Karolina Ewa Połczyńska, Simon Le Denmat, Takashi Taniguchi, Kenji Watanabe, Marek Potemski, Piotr Kossacki, Wojciech Pacuski and  Jacek Kasprzak

Nanoscale, 2023,15, 6941-6946

Published 21 March 2023

https://doi.org/10.1039/D2NR04844B

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17.5.23

Article: Magnetic ion relaxation time distribution within a quantum well

Authors: Aleksandra Łopion, Aleksander Bogucki, Wiktor Kraśnicki, Karolina Ewa Połczyńska, Wojciech Pacuski, Tomasz Kazimierczuk, Andrzej Golnik, and Piotr Kossacki

Phys. Rev. B 106, 165309 

Published 25 October 2022

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.106.165309



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6.10.22

Welcome week

 

I have the pleasure of introducing my new project - Welcome Week, which is the event for first-year Ph. D. Candidates at the Doctoral Schools University of Warsaw. Program includes:

4.10.2022 at 17:00, Krakowskie Przedmieście street 24, room 200 – integration meeting with catering, bonus: city game for volunteers

6.10.2022 at 15:00, Krakowskie Przedmieście street 24, room 200  – training with Welcome Point (in English), at 16:00 – training with International Relations Office (in English)

10.10.2022 at 18:00, Krakowskie Przedmieście street 24, room 200  – training on laws and obligations of doctoral candidates (in Polish)

11.10.2022 at 18:00, online – training on laws and obligations of doctoral candidates (in English)

12.10.2022 at 15:00, Krakowskie Przedmieście street 24, room 200  – training on research financing (in English)

13.10.2022 in Indeks Bistro & Bar, Krakowskie Przedmieście 24 – pub quiz and revealing the results of the city game

Stay tuned also on facebook. See you there!

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26.9.22

Festival of Science 2022 - MBE lab

festival of science mbe 2022

This year MBE laboratory at the Faculty of Physics University of Warsaw will be hosting Festival of Science 2022. There will be a possibility to visit the laboratory and get to know basic knowledge about epitaxy. Our guests will see how we grow crystals, and how we observe the growth process. Additionally, we will teach them how to break the crystal with the diamond stylus. It will be fun, you can not miss it!

https://festiwal-nauki.fuw.edu.pl/imprezy/epitaksja-czyli-sztuka-otrzymywania-ultraczystych-krysztalow/

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22.2.22

Article: Angle-resolved optically detected magnetic resonance as a tool for strain determination in nanostructures

Authors: Aleksander Bogucki, Mateusz Goryca, Aleksandra Łopion, Wojciech Pacuski, Karolina E. Połczyńska, Jarosław Z. Domagała, Mateusz Tokarczyk, Tomasz Fąs, Andrzej Golnik, and Piotr Kossacki

Physical Review B 105, 075412 

Published 11 February 2022

https://doi.org/10.1103/PhysRevB.105.075412



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22.2.22

Article: Local field effects in ultrafast light–matter interaction measured by pump-probe spectroscopy of monolayer MoSe2

Authors: Aleksander Rodek, Thilo Hahn, Jacek Kasprzak, Tomasz Kazimierczuk, Karol Nogajewski, Karolina Ewa Połczyńska, Kenji Watanabe, Takashi Taniguchi, Tilmann Kuhn, Paweł Machnikowski, Marek Potemski, Daniel Wigger, Piotr Kossacki

Nanophotonics, vol. 10, no. 10, 2021, pp. 2717-2728

https://doi.org/10.1515/nanoph-2021-0194



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Karolina Ewa Połczyńska

K. E. Połczyńska
Ph. D. in Physics. MBE grower. Quantum dot's enthusiast specialized in solotronics.

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Already measured spectrum in 1/cm at the X scale and wonder how much eV is in the maximum of the peak? No more typing on calculator and searching values of constants. SpectroCalc is the fastest way to calculate 1/cm, nm and eV mutually. Quite useful in optical laboratory and while working out spectroscopical data.

Ph. D. thesis

Ph. D. thesis

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Finally, the thesis has been submitted, and all exams have been successfully completed. Now awaiting the reviews... Exciting times as the day of defense approaches this autumn! Fingers crossed for a positive outcome. Enjoy the attached cover below! pic.twitter.com/ByoZmYADjf

— Karolina Połczyńska (@kepolczynska) July 7, 2023

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  • Article: Local field effects in ultrafast light–matter interaction measured by pump-probe spectroscopy of monolayer MoSe2
    Authors: Aleksander Rodek, Thilo Hahn, Jacek Kasprzak, Tomasz Kazimierczuk, Karol Nogajewski, Karolina Ewa Połczyńska, Kenji Watanabe, Takas...
  • Article: Angle-resolved optically detected magnetic resonance as a tool for strain determination in nanostructures
    Authors: Aleksander Bogucki, Mateusz Goryca, Aleksandra Łopion, Wojciech Pacuski, Karolina E. Połczyńska, Jarosław Z. Domagała, Mateusz Toka...

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