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1
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Influence of Iron Nanowires Oxidation on Their Semiconducting Properties

100%
Krajewski M., Gołasa K., Wasik D.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1a
A-135-A-137
EN
The main aim of this work was to study the impact of thermal annealing on the structure of iron oxide shell covering iron nanowires in relation to their semiconducting properties. Studied nanomaterial has been produced via a simple chemical reduction in an external magnetic field and then it has been thermally-treated at 400°C, 600°C and also 800°C in a slightly oxidizing argon atmosphere. Annealed iron nanowires have been characterized by means of the Raman spectroscopy and photoluminescence in order to study the structure of iron oxide shell and its influence on semiconducting properties of the whole nanostructure. According to obtained experimental results, the composition of iron oxide shell covering the studied nanomaterial is changing with annealing temperature. The thermal treatment at 400°C leads to oxidation of iron coming from the core of nanomaterial and formation of a mixture of Fe₃O₄ and α -Fe₂O₃ on the surfaces of nanowires, while annealing at higher temperatures results in further oxidation of iron as well as the phase transformation of previously created Fe₃O₄ into the most thermodynamically stable form of iron oxide at ambient conditions - α -Fe₂O₃. This oxide has a major impact on the semiconducting properties of studied nanomaterial. Thereby, the measurements of photoluminescence enabled to estimate the bandgap of bulk and surface layer at about 1.8 eV and 2.1 eV, respectively.
2
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Fine Structure of Neutral Excitons in Single GaAlAs Quantum Dots

88%
Molas M., Gołasa K., Piętka B., Potemski M., Babiński A.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
988-990
EN
Optical anisotropy of neutral excitons in GaAlAs/AlAs quantum dots is investigated. Low-temperature polarization-sensitive photoluminescence measurements of single quantum dots are performed. It is found that neutral excitons (X) in the quantum dots exhibit a fine structure splitting. The fine structure splitting ranges from 10 μeV to 100 μeV and correlates with the X energy. The polarization axis of the fine structure splitting is well oriented along [110] crystallographic direction of a substrate. The orientation is attributed to the elongation of GaAlAs/AlAs quantum dots in the [110] direction of the substrate.
3
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Confocal Microscope Studies of MoS_{2} Layer Thickness

88%
Grzeszczyk M., Gołasa K., Piętka B., Babiński A., Szczytko J.
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vol. 126
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issue 5
1207-1208
EN
We have been studying micro-luminescence of various exfoliated MoS_{2} flakes using a confocal microscope. A crucial issue is to determine thickness of the investigated layer. The common way - using atomic force microscopy, electron microscopy or the Raman spectroscopy - requires moving the sample out from the confocal microscope experimental setup and looking for a particular exfoliated flake hidden among thousands of others. In order to preliminarily determine thickness of investigated layers we have performed a study on optical reflectivity and compared the results with the Raman spectroscopy investigations. In this way we were able to calibrate our experimental setup. Optical measurements are much faster than the Raman spectroscopy and can give a good estimation of MoS_{2} thickness.
4
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The Fine Structure of a Triexciton in Single InAs/GaAs Quantum Dots

76%
Molas M., Gołasa K., Furman M., Lapointe J., Wasilewski Z., Potemski M., Babiński A.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
991-993
EN
Results of experimental study of multiexcitonic emission related to the p-shell of single self-assembled InAs/GaAs quantum dots are presented. Optical properties of a first emission line to appear from the p-shell of a strongly excited quantum dots are investigated using low-temperature polarization-sensitive micro-photoluminescence measurements. The emission line is attributed to the recombination of a complex of three electrons and holes confined in a dot (neutral triexciton), 3X. It is found that the emission consists of two linearly polarized components and the fine structure splitting is larger than the respective splitting of a neutral exciton. The optical anisotropy of the 3X emission is related to the anisotropy of the quantum dot localizing potential. The axis of the 3X optical anisotropy changes from dot to dot covering broad range within ± 50 degrees with respect to the axis defined by the optical anisotropy of a neutral exciton (X). Possible origin of the deviation is discussed.
5
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The Effect of Substrate on Vibrational Properties of Single-Layer MoS₂

76%
Gołasa K., Molas M., Nogajewski K., Grzeszczyk M., Zinkiewicz M., Potemski M., Babiński A.
Acta Physica Polonica A
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2016
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vol. 130
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issue 5
1172-1175
EN
We report on the Raman scattering from single-layer molybdenum disulfide (MoS₂) deposited on various substrates: Si/SiO₂, hexagonal boron nitride (h-BN), sapphire, as well as suspended. Room temperature Raman scattering spectra are investigated under both resonant (632.8 nm) and non-resonant (514.5 nm) excitations. A rather weak influence of the substrate on the Raman scattering signal is observed. The most pronounced, although still small, is the effect of h-BN, which manifests itself in the change of energy positions of the E' and A'₁ Raman modes of single-layer MoS₂. We interpret this modification as originating from van der Waals interaction between the MoS₂ and h-BN layers.
6
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Raman Spectroscopy of Shear Modes in a Few-Layer MoS₂

76%
Gołasa K., Grzeszczyk M., Zinkiewicz M., Nogajewski K., Potemski M., Wysmołek A., Babiński A.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1a
A-132-A-134
EN
We study low frequency vibrational modes in atomically thin molybdenum disulfide (MoS₂) by means of the Raman scattering spectroscopy. A shear mode related to rigid interlayer vibrations is identified. Its energy evolution with the increasing number of layers is well described using a linear chain model with only nearest neighbor interactions. The resulting force constant (Kₓ = 2.7 × 10¹⁹ N/m³) corresponds well to the previously published data.
7
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MBE Growth and Characterization of a III-V Distributed Bragg Reflectors and InAs Quantum Dots

64%
Rousset J., Słupinski T., Jakubczyk T., Kobak J., Stawicki P., Gołasa K., Babinski A., Nawrocki M., Pacuski W.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
984-987
EN
We describe the realization and characterization of a distributed Bragg reflectors and InAs quantum dots grown by molecular beam epitaxy. The distributed Bragg reflectors are based on a stack of eight or twenty pairs of GaAs and AlAs layers with a stopband centered at about E_0=1.24 eV (λ_0=1000 nm). The whole structures exhibit a reflectivity coefficient above 90%. The growth rate was monitored in situ by measurement of the oscillations of the thermal emission intensity. The investigations conducted on the InAs quantum dots grown on GaAs show photoluminescence around E=1.25 eV (λ=990 nm). The combination of these two elements results in the realization of a microcavity containing InAs quantum dots and surrounded by 20 pairs of distributed Bragg reflectors.
8
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Structural and Optical Properties of Boron Nitride Grown by MOVPE

64%
Dąbrowska A., Pakuła K., Bożek R., Rousset J., Ziółkowska D., Gołasa K., Korona K., Wysmołek A., Stępniewski R.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1a
A-129-A-131
EN
Boron nitride layers were grown on sapphire substrate by metal organic vapor phase epitaxy system that was originally designed for growth of GaN. Structures were characterized by scanning electron microscopy, atomic force microscopy, the Raman spectroscopy, absorption and time resolved photoluminescence. Presented results confirm successful deposition of BN layers and gives information about basic properties of the material. The Raman line at 1370 cm^{-1} and absorption edges at 5.6-5.9 eV were observed which is related to hexagonal phase.
9
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Optical Properties of Molybdenum Disulfide (MoS_2)

64%
Gołasa K., Grzeszczyk M., Korona K., Bożek R., Binder J., Szczytko J., Wysmołek A., Babiński A.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
849-851
EN
Research of a monolayer and a bulk MoS_2 is reported. The room temperature Raman spectra of the natural MoS_2 crystals for the both resonant (632.8 nm) and the non-resonant (532 nm) excitation are presented. The apparent differences observed in the spectra from the bulk and the one monolayer MoS_2 are discussed. In particular, the feature due to a first order scattering involving the LA(M) phonon in the resonance Raman spectrum of the one monolayer MoS_2 was observed and explained in terms of the disorder in the natural crystal. The disorder is also documented by the line-shape of the room-temperature photoluminescence spectra observed from both the bulk and the one monolayer MoS_2.
10
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Properties of Excitons in Quantum Dots with a Weak Confinement

52%
Gołasa K., Molas M., Goryca M., Kazimierczuk T., Smoleński T., Koperski M., Golnik A., Kossacki P., Potemski M., Wasilewski Z., Babiński A.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
781-784
EN
Statistical properties of neutral excitons, biexcitons and trions confined to natural quantum dots formed in the InAs/GaAs wetting layer are reported. The correlation of the trion binding energy and the biexciton binding energy was found. Magnetospectroscopic measurements of the excitons revealed also the correlation of excitonic effective g^* factor of an exciton with the biexciton binding energy. The qualitative picture of the effect of quantum confinement on the observed correlations is presented.
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