Wyniki wyszukiwania - Biblioteka Nauki

1

Exchange Integrals in Hg_{0.95}Mn_{0.05}Se Obtained by the Wave Shape Analysis of Shubnikov-de Haas Oscillations

100%

Dybko K. , Kossut J.

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nr 4

697-700

EN

The Shubnikov-de Haas oscillations were measured in Hg_{0.95}Mn_{0.05}Se at liquid helium temperatures, in magnetic fields up to 13 tesla. The analysis of the experimental data was performed by means of the wave shape method. The dependence of effective g-factor of the conduction electrons and difference Dingle temperature on magnetic field was determined. Non-zero difference Dingle temperature is a clear evidence of spin dependent scattering in this material. The sp-d exchange constants consistent with extracted spin splitting and difference Dingle temperature, α = -0.39 ± 0.06 eV, β = 0.95 ± 0.07 eV, are in good agreement with the values obtained from magnetooptics.

2

Electron-Electron Interaction Effects in Quantum Hall Regime of GaN/AlGaN Heterostructures

61%

Siekacz M. , Dybko K. , Maude D. , Potemski M. , Knap W. , Skierbiszewski C.

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nr 2

269-273

EN

We measured the activation of resistivity at quantum Hall minima in high mobility two-dimensional electron gas confined at AlGaN/GaN interface. The effective g-factor and effective mass was deduced. The electron-electron interactions modify both quantities compared to their bare band values. It is found that the influence of interactions is much more pronounced onto g-factor than effective mass. The relative spin susceptibility was also calculated and compared with available theories. The best agreement was found with the ideal two-dimensional gas model in random phase approximation.

3

New materials for thermoelectric generators based on PbTe-MnTe and PbTe-CdTe semiconductor alloys and nanocomposites

61%

Story T. , Dybko K. , Dziawa P. , Mycielski A. , Szczerbakow A. , Szot M.

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2011

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nr 6

64-69

EN

New trends in the field of thermoelectrics are discussed for PbTe-based semiconductor thermoelectric materials exhibiting density of states engineering effects strongly enhancing thermoelectric power (PbMnTe) and spontaneous formation of nano-scale two-phase crystal structures (PbTeCdTe) – technologically scalable realization of electron crystal - phonon glass concept of new thermoelectric materials.

4

Selected Properties of Lattice Dynamics of HgSe and β-HgS

51%

Szuszkiewicz W. , Dybko K. , Dynowska E. , Górecka J. , Witkowska B. , Hennion B. , Jouanne M. , Julien C.

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nr 5

1029-1032

EN

Optical phonon dispersion for β-HgS was measured by the neutron scattering for the first time. The results confirmed theoretically predicted anomalous behavior of phonon modes in this material, resulting probably from high ionicity of mercury sulphide and large difference of Hg and S atomic mass. Influence of the isotopic effects on the TO-phonon mode for HgSe and HgS is analyzed. The possible observation of such effects in IR reflectivity spectra taken for HgSe at low temperature is discussed.

5

Structure Dependent Conductivity of Ultrathin ZnO Films

51%

Snigurenko D. , Kopalko K. , Krajewski T. , Łuka G. , Gierałtowska S. , Witkowski B. , Godlewski M. , Dybko K. , Paszkowicz W. , Guziewicz E.

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nr 6

1042-1044

EN

Zinc oxide films dedicated for hybrid organic/inorganic devices have been studied. The films were grown at low temperature (100°C, 130C and 200°C) required for deposition on thermally unstable organic substrates. ZnO layers were obtained in atomic layer deposition processes with very short purging times in order to shift a structure of the films from polycrystalline towards amorphous one. The correlation between atomic layer deposition growth parameters, a structural quality and electrical properties of ZnO films was determined.

6

Electrostatic Gates for GaN/AlGaN Quantum Point Contacts

51%

Czapkiewicz M. , Cywiński G. , Dybko K. , Siekacz M. , Wolny P. , Gierałtowska S. , Guziewicz E. , Skierbiszewski C. , Wróbel J.

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nr 6

1026-1028

EN

We report on AlGaN/GaN quantum point contacts fabricated by using e-beam lithography and dry ion etching. The tunable nano-constrictions are defined by the integration of side and top gates in a single device. In this configuration, the planar gates are located on the both sides of a quantum channel and the metallic top gates, which cover the active region, are separated from the substrate by an insulating and passivating layers of HfO_2 or Al_2O_3/HfO_2 composite. The properties of devices have been tested at T = 4.2 K. For side gates we have obtained a very small surface leakage current I_g< 10^{-11} A at gate voltages |V_g| < 2 V, however, it is not enough to close the quantum channel. With top gates we have been able to reach the pinch-off voltage at V_g = - 3.5 V at a cost of I_g ≈ 10^{-6} A, which has been identified as a bulk leakage current.

7

Multifunctional La_{0.7}Sr_{0.3}MnO_3-YBa_2Cu_3O_7 Heterostructures

51%

Przyslupski P. , Dybko K. , Tsarou A. , Werner-Malento K. , Sawicki M. , Laviano F. , Gozzellino L. , Mezzetti E.

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nr 1

15-22

EN

Complex perovskite oxides exhibit a rich spectrum of functional responses such as: superconductivity, magnetism etc. Combination of different oxides in multilayered structures increases the number of physical responses. Heterogeneous oxide structures represent a new class of nanostructures. They consist of ferromagnetic La_{0.67}Sr_{0.33}MnO_3 (F-LSMO) manganite and superconducting YBa_2Cu_3O_7 (Sc-YBCO) cuprate. The interaction between the two order parameters gives rise to new physical effects. In this review we will discuss various physical effects obtained in the bilayer and trilayer heterostructures. For example, the LSMO/YBCO bilayer structures are used to study the mechanism of magnetic pinning. The other possibility is the fabrication of spin valve-like structures LSMO/YBCO/LSMO. The spin dependent transport in trilayer structure was studied taking into account crossed Andreev reflection and electron co-tunneling processes.

8

Experimental and Theoretical Analysis οf PbTe-CdTe Solid Solution Grown by Physical Vapour Transport Method

41%

Szot M. , Szczerbakow A. , Dybko K. , Kowalczyk L. , Smajek E. , Domukhovski V. , Łusakowska E. , Dziawa P. , Mycielski A. , Story T. , Bukała M. , Galicka M. , Sankowski P. , Buczko R. , Kacman P.

Acta Physica Polonica A

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2009

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tom 116

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nr 5

959-961

EN

Bulk monocrystals of Pb_{1-x}Cd_{x}Te, with the Cd content x up to 0.11, were grown by physical vapour transport method. The structural, electrical and optical properties of these ternary crystals were studied experimentally and theoretically. All investigated samples exhibit rock-salt structure and high crystal quality, which was confirmed by X-ray rocking curve width parameter of about 100 arcsec. The decrease of the lattice parameter with increasing Cd content x was found experimentally, in agreement with ab initio calculations. The band structures of Pb_{1-x}Cd_{x}Te mixed crystals for x values up to 0.2 were calculated using tight binding approach. The calculated band gap in the L-point increases with the Cd content in qualitative agreement with photoluminescence measurements in the infrared. For all studied Pb_{1-x}Cd_{x}Te samples, the Hall effect and electrical conductivity measurements, performed in the temperature range from 4 to 300 K, revealed p-type conductivity.

9

Ferromagnetic Transition in Ge_{1-x}Mn_{x}Te Layers

41%

Knoff W. , Domukhovski V. , Dybko K. , Dziawa P. , Jakieła R. , Łusakowska E. , Reszka A. , Świątek K. , Taliashvili B. , Story T. , Szałowski K. , Balcerzak T.

Acta Physica Polonica A

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2009

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tom 116

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nr 5

904-906

EN

Ferromagnetic transition temperature in thin layers of diluted magnetic (semimagnetic) semiconductor Ge_{1-x}Mn_{x}Te was studied experimentally by SQUID magnetometry method and analyzed theoretically for a model Ising-type diluted magnetic system with Ruderman-Kittel-Kasuya-Yosida indirect exchange interaction. The key features of the experimentally observed dependence of the Curie temperature on Mn content (x ≤ 0.12) and conducting hole concentration p = (1-10) × 10^{21} cm^{-3} were reproduced theoretically for realistic valence band and crystal lattice parameters of p-Ge_{1-x}Mn_{x}Te taking into account short carrier mean free path encountered in this material and Ruderman-Kittel-Kasuya-Yosida mechanism with both delta-like and diffused character of spatial dependence of the exchange coupling between magnetic ions and free carriers.