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1
Content available remote

Dye Aggregation Influence on Dye Sensitized Solar Cell Performance in Nanocoral ZnO-Based Thin Film Cells Sensitized with N-719 and Rose Bengal Dyes

100%
Borysiewicz M., Chusnutdinow S., Wzorek M., Wojciechowski T.
Acta Physica Polonica A
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2016
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vol. 130
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issue 5
1187-1189
EN
Dye sensitized solar cells were fabricated using ZnO nanostructured photoelectrodes sensitized with N-719 or Rose Bengal dyes. We assessed the device performance as a function of the sensitization time and found a dependence on time for the N-719 and no significant changes for the Rose Bengal. Furthermore, we observe that the structure of the N-719 molecule beneficial for sensitization of TiO₂ may lead to the degradation of the ZnO crystals and a growth of an amorphous shell limiting dye performance in the cells.
2
Content available remote

Ferroelectric Field Effect Transistor Based on Modulation Doped CdTe/CdMgTe Quantum Wells

100%
Kolkovsky V., Wojciechowski T., Wojtowicz T., Karczewski G.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1173-1178
EN
In this work, we observed effects of changing the electron concentration and electron mobility upon the poling of the Cd_{0.96}Zn_{0.04}Te ferroelectric gate deposited on the top of the CdTe-based modulation doped quantum well structure, which are confirmation of the existence of the electrostatic field originating from the ferroelectric material, which can be controlled by an external voltage. The analysis of the data obtained from the Hall effect measurements showed that the electron mobility and carrier concentration decreased by a factor of 2.5 and 1.5, respectively upon the negative poling of the gate with respect to the poled by the positive voltage. Moreover, the electrostatic field, depending on its directions, causes depletion of accumulation of electrons in the 2D channel, i.e., it is a source of the field effect.
3
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Investigation of Porous Zn Growth Mechanism during Zn Reactive Sputter Deposition

88%
Borysiewicz M., Wojciechowski T., Dynowska E., Kamińska E., Piotrowska A.
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vol. 125
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issue 5
1144-1148
EN
Ar-O-Zn plasma discharges created during DC reactive magnetron sputtering of a Zn target and RF reactive magnetron sputtering of a ceramic ZnO target were investigated and compared by means of the Langmuir probe measurements in order to determine the mechanism of growth of porous Zn films during DC-mode Zn reactive sputtering. The power supplied to the magnetrons during the sputtering was kept at 125 W and the plasma was characterised as a function of oxygen content in the sputtering gas mixture, ranging from 0 to 60% for two gas pressures related to porous Zn film deposition, namely 3 mTorr and 5 mTorr. Based on the correlation of plasma properties measurements with scanning electron microscope imaging and X-ray diffraction of the films deposited under selected conditions it was found that the growth of porous, polycrystalline Zn films was governed by high electron density in the plasma combined with a high electron temperature and an increased energy of the ions impinging on the substrate.
4
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Tuning Transparent Supercapacitor Performance by Controlling the Morphology of its ZnO Electrodes

88%
Borysiewicz M., Wzorek M., Ekielski M., Kaczmarski J., Wojciechowski T.
Acta Physica Polonica A
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2017
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vol. 131
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issue 6
1550-1553
EN
Transparent supercapacitors were fabricated using nanostructures ZnO electrodes deposited using reactive magnetron sputtering. By fine tuning the deposition process parameters the electrodes with different morphologies were obtained, from hierarchical through sponge-like to nanocolumnar. The device performance related to the electrode morphology was assessed. It was found that the nanocolumnar electrodes provided best performance both in terms of effective device capacitance (18.3 μF/cm²) and transparency ( ≈ 100% in the visible range). The worst performance, with 80% lower effective capacitance, was obtained in the devices with the sponge-like morphology.
5
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Low Temperature Processing of Nanostructures Based on II-VI Semiconductors Quantum Wells

76%
Majewicz M., Śnieżek D., Wojciechowski T., Baran E., Nowicki P., Wojtowicz T., Wróbel J.
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vol. 126
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issue 5
1174-1176
EN
We report the first results of electron beam lithography processes performed on polymethyl methacrylate (PMMA) and hydrogen silsesquioxane (HSQ) resists, which have been pre-backed in vacuum at T ≤ 90°C. For such low temperature processing the lithographical resolution is reduced as compared to standard procedures, however, the exposure contrast and adhesion to CdTe and HgTe substrates have been sufficient for the fabrication of sub-μ m quantum devices. Furthermore, the new method of electrical microcontact forming is proposed, based on the local melting and annealing of an indium metal layer, performed with the application of accelerated electron beam. The method has been tested for CdTe/CdMgTe quantum wells using the lithography techniques, the exposure parameters have been optimized by inspecting the morphology of annealed metal film via the in situ imaging.
6
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Magnetic Force Microscopy Study of Zn_{1-x}Co_{x}O Nanowires Grown by Rapid Thermal Evaporation

64%
Aleszkiewicz M., Fronc K., Aleszkiewicz P., Zaleszczyk W., Dziawa P., Wojciechowski T., Wojtowicz T., Karczewski G.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
865-867
EN
In this work we studied domain structure of Zn_{1-x}Co_{x}O nanowires which are single arms of tetrapode crystals. The as-grown material exhibits hysteretic behavior even at room temperature as revealed by SQUID mesurements. In order to get insight into the magnetic properties of individual tetrapodes they were dismembered into nanowires of nanometric diameters, deposited on a flat substrate and imaged by magnetic force microscopy. A magnetic interaction between the magnetic force microscopy probe and single nanowires has been detected which confirms that nanometric volume of the material possesses a magnetic moment. The magnetic force microscopy contrast is attractively independent of the tip magnetization direction which indicates that shape anisotropy of nanowires is not strong enough to prevent occurrence of tip-induced magnetic field disturbance.
7
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Spectroscopy of Indirect Excitons in Vertically Stacked CdTe Quantum Dot Structures

64%
Kukliński K., Kłopotowski Ł., Fronc K., Wojnar P., Wojciechowski T., Czapkiewicz M., Kossut J., Karczewski G., Wojtowicz T.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
856-858
EN
We show that by means of an electric field we can tune the energy levels in vertical quantum dot pairs and study transitions related to recombination of direct and indirect excitons. With decreasing the reverse bias, we observe both the blue- and red-shifted indirect exciton transitions. Based on the band profile of our device, we conclude that the former corresponds to the recombination of the electron and hole localized in the top and the bottom dot, respectively and the latter is related to the recombination of the electron and hole localized in the bottom and the top dot, respectively.
8
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Atomic Force Microscopy Study of a Voltage Effect on CdZnTe Crystal Dimensions

64%
Aleszkiewicz P., Wojciechowski T., Fronc K., Kolkovsky V., Janik E., Jakieła R., Mycielski A., Karczewski G., Aleszkiewicz M.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1041-1047
EN
In this work we studied the influence of an external electric voltage on spatial dimensions of CdZnTe mixed crystals. In order to get an absolute magnitude of the sample thickness and to gain insight to the changes of lateral dimension, in quasi-bulk 3 μm thick CdZnTe layers grown by molecular beam epitaxy square craters were formed by ion sputtering in a secondary ion mass spectrometer. The vertical and lateral dimensions of the craters were studied by the atomic force microscopy. The atomic force microscopy measurement revealed that the thickness of the CdZnTe layer increases in a result of applying a single voltage pulse to the sample surface and decreases reversibly after applying reversely biased voltage. The voltage triggering was high enough to switch the conductivity state of the sample i.e., the effect of thickness change is accompanied by the effect of conductivity switching. The thickness change is significant, reaching several percents of the entire layer thickness.
9
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TEM Study of the Structural Properties of Nanowires Based on Cd, Zn, Te grown by MBE on Silicon Substrates

64%
Kaleta A., Kret S., Sanchez A., Bilska M., Kurowska B., Szczepańska A., Płachta J., Wojnar P., Wojciechowski T.
Acta Physica Polonica A
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2017
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vol. 131
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issue 5
1399-1405
EN
In this work we report on the atomic structures, elemental distribution, defects and dislocations of three types of semiconductor nanowires: ZnTe, CdTe, and complex ZnTe/(Cd,Zn)Te core/shell hetero-nanowires grown by a molecular beam epitaxy on (111) Si substrate using a vapor-liquid-solid mechanism. The structural properties and the chemical gradients were measured by transmission electron microscopy methods. The nanowires reveal mainly sphalerite structure, however wurtzite nanowires were also observed.
10
Content available remote

Electronic Properties of Thin HfO_2 Films Fabricated by Atomic Layer Deposition on 4H-SiC

64%
Taube A., Gierałtowska S., Gutt T., Małachowski T., Pasternak I., Wojciechowski T., Rzodkiewicz W., Sawicki M., Piotrowska A.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
696-698
EN
Applicability of thin HfO_2 films as gate dielectric for SiC MOSFET transistor is reported. Layers characterisation was done by means of atomic force microscopy and scanning electron microscopy, spectroscopic ellipsometry and C-V and I-V measurements of MIS structures. High permittivity dielectric layers were deposited using atomic layer deposition. Investigation showed high value of κ = 15 and existence of high density surface states (5 × 10^{12} eV^{-1} cm^{-2}) on HfO_2/SiC interface. High leakage current is caused probably due to low conduction band offset between hafnium oxide and silicon carbide.
11
Content available remote

Magnetic and Structural Study of (ZnTe)/Co Core-Shell Nanowires Grown by Molecular Beam Epitaxy

64%
Misiuna P., Dłużewski P., Wojciechowski T., Lewińska S., Ślawska-Waniewska A., Wawro A., Wiater M., Wojtowicz T., Baczewski L.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
517-519
EN
Arrays of crystalline ZnTe nanowires grown by vapor-liquid-solid mechanism were covered with cobalt in a molecular beam epitaxy system. Magnetic and structural characterization of such core/shell nanowires was performed. Using scanning electron microscopy and transmission electron microscopy it was found that the mean shell thickness of cobalt was about 35% of the nominal deposition thickness. Deposited cobalt had a polycrystalline structure covering the ZnTe nanowires evenly along their length. With the increment of temperature during Co deposition the roughness of the nanowire sidewalls increases. Vibrating sample magnetometry measurements revealed that the magnetization easy-axis direction is perpendicular to the long axis of the nanowires, which is in agreement with theoretical predictions. Oxidation of Co shell does not change the anisotropy direction of such structures, however it increases their coercivity. Exchange bias effect at the interface of cobalt and cobalt oxides suggested by some authors is not responsible for such anisotropy orientation.
12
Content available remote

Defect Structure of High-Temperature-Grown GaMnSb/GaSb

64%
Romanowski P., Bak-Misiuk J., Dynowska E., Domagala J., Sadowski J., Wojciechowski T., Barcz A., Jakiela R., Caliebe W.
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issue 2
341-343
EN
GaMnSb/GaSb(100) layers with embedded MnSb inclusions have been grown at 720 K using MBE technique. This paper presents the investigation of the defect structure of Ga_{1-x}Mn_{x}Sb layers with different content of manganese (up to x = 0.07). X-ray diffraction method using conventional and synchrotron radiation was applied. Dimensions and shapes of inclusions were detected by scanning electron microscopy. Depth profiles of elements were measured using secondary ion mass spectroscopy technique.
13
Content available remote

Terahertz Response of a Point Contact Based on CdTe/CdMgTe Quantum Well in Magnetic Field

52%
Grigelionis I., Białek M., Grynberg M., Czapkiewicz M., Kolkovskiy V., Wiater M., Wojciechowski T., Wróbel J., Wojtowicz T., But D., Knap W., Łusakowski J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1069-1072
EN
A photoresponse at THz frequencies of a quantum point contact fabricated on a CdTe/CdMgTe quantum well was studied at low temperatures as a function of magnetic field. The spectra show a structure which was interpreted as resulting from the cyclotron resonance and magnetoplasmon excitations. The wavelength of the fundamental magnetoplasmon mode was found to be about 2 μm which coincides with one of dimensions of the point contact. We also discuss the possibility of coupling of magnetoplasmon modes to shallow impurity transitions in the quantum well.
14
Content available remote

Physical Properties of ZnCoO Tetrapods and Nanofibers

52%
Gas K., Fronc K., Dziawa P., Knoff W., Wojciechowski T., Zaleszczyk W., Baranowska-Korczyc A., Morhange J., Paszkowicz W., Elbaum D., Karczewski G., Wojtowicz T., Szuszkiewicz W.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
868-870
EN
In this paper the physical properties of two types of Co-doped ZnO nanostructures: tetrapods and nanofibers grown by a rapid thermal evaporation process and prepared by the electrospinning technique, respectively, were investigated and analyzed. Surface morphology of the samples was examined using scanning electron microscopy. X-ray diffraction measurements showed hexagonal wurtzite crystal structure of both types of investigated nanostructures. Both X-ray diffraction and Raman scattering data confirmed high phase purity of the samples. The magnetic properties studied with the use of the SQUID magnetometer confirmed a presence of ferromagnetic order in analyzed nanostructures. The observed photoluminescence spectra exhibited two groups of lines. The first one, in the ultraviolet spectral range, is due to the optical transitions close to ZnO band gap, the second one in the red region is most probably related to the Co^{2+} d-d internal transitions. The influence of native defects on the optical properties is also shown and discussed. All results reported here lead us to the conclusion that in the mixed crystal nanostructures obtained, a fraction of the Zn^{2+} ions is substituted by Co^{2+} ions.
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