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1

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

Pressure-Dependent Coupling of the ^{3}A_{2}(F) and ^{1}T_{2}(D) States of Ni^{2+} in ZnS and ZnSe

100%

Wasik D., Baj M., Liro Z.

Acta Physica Polonica A

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1991

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vol. 79

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issue 2-3

319-322

EN

We have investigated two close-lying ^{3}A_{2}(F) and ^{1}T_{2}(D) states of Ni^{2+} impurity in ZnS and ZnSe. These states are strongly coupled to each other via the spin-orbit interaction and therefore, small variations of their energies induced by pressure have significantly changed absorption spectra related to them. In order to give a good interpretation to the experimental results we took into account the interaction between both states, their coupling to the lattice vibrations and the pressure-dependent separation between them.

3

Hydrostatic Pressure Study of MBE CdMnTe Doped with Bromine

88%

Szczytko J., Wasik D., Przybytek J., Baj M., Waag A.

Acta Physica Polonica A

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1995

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vol. 88

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issue 5

933-936

EN

We present Hall effect and resistivity measurements as a function of pressure performed on MBE-grown Cd_{1-x}Mn_{x}Te (with x = 0.14) layer (1 μm) doped with bromine. The experimental data were analysed using positive and negative U model of the Br centres. We found that both models could reproduce the experimental points, but in the case of positive U model - only under assumption that the sample was completely uncompensated.

4

MnAs Nanocrystals Embedded in GaAs

76%

Kwiatkowski A., Wasik D., Kamińska M., Twardowski A., Dłużewski P., Borysiuk J., Sadowski J.

Acta Physica Polonica A

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2008

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vol. 114

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issue 5

1207-1211

EN

Magnetic properties of MnAs nanocrystals embedded in GaAs are analyzed in the frame of phenomenological model proposed by Sasaki for ferritin superparamagnets. Our calculations explain qualitatively experimental data of magnetization versus temperature, obtained according to zero-field-cooled and field-cooled protocols. They show dynamics of magnetization of MnAs nanocrystals in range of temperature from 10 K to 320 K. There is transition from state in which very slow dynamics is observed (frozen state) to state in which dynamics is fast (quasi-superparamagnetic state).

5

76%

Kwiatkowski A., Borysiuk J., Bożek R., Wasik D., Kamińska M., Sadowski J., Twardowski A.

Acta Physica Polonica A

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2006

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vol. 110

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issue 2

233-236

EN

We report on cross-sectional transmission electron microscopy and magnetic force microscopy studies performed on self-organized MnAs nanoclusters embedded in GaAs. It was found that 10÷20 nm large MnAs ferromagnetic nanocrystals were formed during rapid thermal annealing of Ga_{1-x}Mn_xAs layers at 600ºC, leading to magnetic contrasts in magnetic force microscopy images.

6

Influence of Epitaxial Strain on Magnetic Anisotropy in (Ga,Mn)As

76%

Juszyński P., Wasik D., Gryglas-Borysiewicz M., Przybytek J., Szczytko J., Twardowski A., Sadowski J.

Acta Physica Polonica A

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2012

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vol. 122

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issue 6

1004-1006

EN

Two (Ga,Mn)As samples having different magnetic anisotropy (one with in-plane easy axis and another one with out-of-plane easy axis) were studied by means of magnetotransport experiments. Anisotropy field B_{A} was determined for both samples as a function of temperature. For the sample having in-plane easy axis, an inversion of the direction of planar Hall effect hysteresis was observed upon increase of temperature. This result was simulated using the Stoner-Wohlfarth model.

7

Highly Compensated GaAs Crystal Obtained by Molecular CO Doping

76%

Bożek R., Korona K., Nowak G., Wasik D., Słupiński T., Kaczor P.

Acta Physica Polonica A

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1993

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vol. 84

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issue 4

669-672

EN

GaAs:C crystal was grown by liquid encapsulated Czochralski technique with large partial pressure of CO in ambient atmosphere p_{CO}/p_{tot} = 0.2 and investigated using near and infrared absorption, photoluminescence, photoconductivity, photo-induced current transient spectroscopy and photo-Hall measurements. High resistivity of the crystal was found in electrical measurements (10^{7} Ω cm, the Fermi level at 0.67 eV below conduction band at 300 K). Local vibrational mode revealed increased concentration of carbon acceptor and presence of oxygen related complexes. Photoluminescence spectra were dominated by two bands with peak energies at 1.49 eV and 0.8 eV. The near band gap emission shifts with excitation intensity up to 4 meV/decade. In photocurrent spectrum a strong photoionization band with E = 0.55 eV is observed.

8

Spatial Correlations of Donor Charges in MBE CdTe

64%

Suski T., Wiśniewski P., Litwin-Staszewska E., Wasik D., Przybytek J., Baj M., Karczewski G., Wojtowicz T., Zakrzewski A., Kossut J.

Acta Physica Polonica A

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1995

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vol. 88

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issue 5

929-932

EN

We present experimental evidence that at high pressures indium donors in CdTe localize electrons in spatially correlated manner. We have studied Hall mobility, μ_{H}, as a function of electron concentration, n_{H}, at T=77 K. Changes of n_{H} have been achieved by two methods. High pressure freeze-out of electrons onto localized states of In-donors leads to the mobility enhancement with respect to the situation when n_{H} has been modified by means of a subsequent annealing of the sample. As a result, depending on the degree of spatial correlations in the impurity charges arrangement, different values of μ_{H} correspond to the same value of n_{H}. The variation of mobility with electron concentration suggests that the localized state of In-donor represents likely negatively charged DX state.

9

Phase Analysis of Magnetic Inclusions in Nanomaterials Based on Multiwall Carbon Nanotubes

64%

Brzózka K., Krajewski M., Małolepszy A., Stobiński L., Szumiata T., Górka B., Gawroński M., Wasik D.

Acta Physica Polonica A

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2017

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vol. 131

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issue 4

863-865

EN

Functionalized multiwall carbon nanotubes as well as nanocomposite based on that material covered by nanoparticles composed of iron oxides were the subject of investigations. In order to identify all iron-bearing phases including those reported on the base of previous X-ray diffraction measurements, the transmission Mössbauer spectroscopy was utilized. The experiments were carried out both at room temperature and also at low temperatures. It was stated that in the investigated nanotubes some impurities were present, originating from the catalyst remains, in form of Fe-C and α -Fe nanoparticles. The Mössbauer spectra collected for the nanocomposite showed a complex shape characteristic of temperature relaxations. The following subspectra related to iron-based phases were identified: sextet attributed to hematite, with hyperfine magnetic field reduced due to the temperature relaxations, sextet corresponding to iron carbide as well as two doublets linked to superparamagnetic hematite and ferrihydrites.

10

Infrared Spectroscopy of GaAs Doped with Mn

64%

Rutkowska A., Wasik D., Witowski A., Sadowski M., Orłowski W., Strzelecka G., Hruban A., Kamińska M., Twardowski A., Potemski M.

Acta Physica Polonica A

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2005

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vol. 108

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issue 5

845-849

EN

We found that the fine structure related to Lyman spectra of [Mn^{2+}(d^5) + a hole] centers in GaAs was present only for samples with low Mn concentration. Such samples, at low temperature, did not show any hopping conductance within Mn impurity band. Magnetooptical measurements revealed that magnetic field induced splitting of the Lyman optical transitions was larger than Zeeman splitting observed for typical shallow acceptors in GaAs, like Be, Zn, and C. This experimental result proved that in the case of Mn acceptor impurity, the exchange coupling of a hole and the S = 5/2 Mn^{2+}(d^5) core could not be neglected, which was in accordance with the [Mn^{2+}(d^5) + a hole] model of the neutral Mn center in GaAs.

11

Magnetoluminescence Studies of GaN:Fe

64%

Niedźwiadek A., Wysmołek A., Wasik D., Potemski M., Szczytko J., Kamińska M., Twardowski A., Łucznik B., Pastuszka B., Grzegory I.

Acta Physica Polonica A

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2007

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vol. 112

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issue 2

177-182

EN

We report on magneto-optical studies on iron doped GaN crystals grown using hydride vapor phase epitaxy method on bulk GaN substrate. The investigated samples showed an intensive 1.3 eV luminescence band, characteristic of Fe^{3+}(d^5) center in GaN. A high quality of the investigated samples allowed us to observe a well-resolved fine structure of intracenter transitions between ^4T_1(G) and ^6A_1(S) states, consisting of four sharp no-phonon lines. All the observed no-phonon lines showed pronounced splittings in magnetic field. From the analysis of the magneto-optical data, the structure of split ^4T_1(G) multiplet in the magnetic field applied along c-axis of GaN crystals was established.

12

Fabrication and Physical Properties of SiC-GaAs Nano-Composites

64%

Kalisz G., Grzanka E., Wasik D., Świderska-Środa A., Gierlotka S., Borysiuk J., Kamińska M., Twardowski A., Pałosz B.

Acta Physica Polonica A

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2005

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vol. 108

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issue 4

717-721

EN

Nano-composites consisting of primary phase of hard nanocrystalline SiC matrix and the secondary nanocrystalline semiconductor (GaAs) phase were obtained by high-pressure zone infiltration. The synthesis process occurs in three stages: (i) at room temperature the nanopowder of SiC is compacted along with GaAs under high pressure up to 8 GPa, (ii) the temperature is increased above the melting point of GaAs up to 1600~K and, the pores are being filled with liquid, (iii) upon cooling GaAs nanocrystallites grow in the pores. Synthesis of nano-composites was performed using a toroid-type high-pressure apparatus (IHPP of the Polish Academy of Sciences, Warsaw) and six-anvil cubic press (MAX-80 at HASYLAB, Hamburg). X-ray diffraction studies were performed using a laboratory D5000 Siemens diffractometer. Phase composition, grain size, and macrostrains present in the synthesized materials were examined. Microstructure of the composites was characterized using scanning electron microscopy and high resolution transmission electron microscopy. Far-infrared reflectivity measurements were used to determine built-in strain.

13

Formation of Mn-Related Defect Band in InP

52%

Macieja B., Korona K., Piersa M., Witowski A., Wasik D., Wysmołek A., Strzelecka G., Hruban A., Surma B., Palczewska M., Kamińska M., Twardowski A.

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EN

Electron paramagnetic resonance, optical absorption, luminescence and electrical studies of InP highly doped with Mn were performed. Electron paramagnetic resonance revealed presence of manganese in Mn^{2+}(d^5) configuration. In optical absorption, systematic reduction of InP band gap was observed with increase in Mn content. This was correlated with increase in photoionization-type absorption band starting at 0.2 eV. Time-resolved photoluminescence measurements showed decrease in photoexcited carrier lifetime and shortening of donor-acceptor pair recombination time with increase in Mn content. Moreover, photoluminescence band was shifted to lower energies, similarly to optical band gap. In electrical transport two mechanisms of conductivity were observed. Valence band transport dominated at higher temperatures, above 160 K, and activation energy of free-hole concentration was determined as about 0.20 eV. At lower temperatures hopping conductivity, clearly related to Mn defect band, was present. All these results were consistent with assumption of creation of Mn-related defect-band at 0.2 eV above InP valence band. It was found that Mn centers responsible for this band were in configurations of either d^5 or d^5 plus a hole localized about 7Å around corresponding Mn core.

Refine search results

Influence of Iron Nanowires Oxidation on Their Semiconducting Properties

Pressure-Dependent Coupling of the ^{3}A_{2}(F) and ^{1}T_{2}(D) States of Ni^{2+} in ZnS and ZnSe

Hydrostatic Pressure Study of MBE CdMnTe Doped with Bromine

MnAs Nanocrystals Embedded in GaAs

Influence of Epitaxial Strain on Magnetic Anisotropy in (Ga,Mn)As

Highly Compensated GaAs Crystal Obtained by Molecular CO Doping

Spatial Correlations of Donor Charges in MBE CdTe

Phase Analysis of Magnetic Inclusions in Nanomaterials Based on Multiwall Carbon Nanotubes

Infrared Spectroscopy of GaAs Doped with Mn

Magnetoluminescence Studies of GaN:Fe

Fabrication and Physical Properties of SiC-GaAs Nano-Composites

Formation of Mn-Related Defect Band in InP