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1
Content available remote

Resonant Phonons in Adsorbed Slabs

100%
Dobrzynski L., Akjouj A., Syla B., Djafari-Rouhani B.
Acta Physica Polonica A
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1992
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vol. 81
|
issue 1
85-90
EN
Resonant phonons, sometimes also called leaky waves, are phonons associated with a crystal defect, a surface, an adsorbed layer and whose frequencies fall inside the bulk crystal band. Such resonant phonons were studied experimentally and theoretically before for clean surfaces and for adsorbed monolayers. We present here a study of resonant phonons associated with the adsorption of a slab of L monolayers on a substrate. With the help of a simple atomic model, we obtained a closed form expression giving the variation of the transverse phonon density of states associated with the adsorption of the slab. An application which qualitatively simulates the adsorption of L monolayers of Ge on Si shows the existence of well-defined resonant phonons within the bulk acoustic band of the substrate.
2
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Content available

Time and Frequency Resolved THz Spectroscopy of Micro- and Nano-Systems

100%
Kröll J., Darmo J., Unterrainer K.
Acta Physica Polonica A
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2005
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vol. 107
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issue 1
92-98
EN
Terahertz time-domain spectroscopy is applied to characterize ultra-thin metallic layers and nanoscale composite material - single-wall carbon nanotube mat.
3
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Nonradiative Recombination Processes in (CdTe,CdCrTe)/CdMgTe Quantum Well Structures

63%
Godlewski M., Ivanovi V., Zakrzewski A., Wojtowicz T., Karczewski G., Kossut J., Bergman J., Monemar B.
Acta Physica Polonica A
|
1997
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vol. 92
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issue 4
781-784
EN
Photoluminescence transitions in (CdTe,CdCrTe)/CdMgTe structure grown by molecular beam epitaxy are studied. Photoluminescence investigations show a very strong reduction of the photoluminescence intensity from chromium doped quantum wells. We explain this fact by a very efficient nonradiative recombination in the chromium-doped quantum wells. The present results indicate that the Auger-type energy transfer from excitons to chromium ions is responsible for the photoluminescence deactivation. The efficiency of this process is evaluated.
4
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Enhanced Exciton-Phonon Interaction in Strained ZnCdSe/ZnSe Quantum Well Structures

63%
Godlewski M., Leonardi K., Hommel D.
Acta Physica Polonica A
|
1997
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vol. 92
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issue 4
769-773
EN
Radiative recombination processes in pseudomorphic ZnCdSe/ZnSe structures are compared to those observed in strain-relaxed structures grown on GaAs substrates with thick ZnSe buffer layers. From the temperature dependence of the photoluminescence line width we evaluate the strength of exciton-phonon interaction with acoustic (dominant at lower temperatures) and optical phonons. Stronger exciton-phonon interaction is observed for pseudomorphic structures. Such enhanced exciton-phonon interaction is likely responsible for a faster photoluminescence deactivation at increased temperatures. We also report different exciton properties (photoluminescence intensity, width, strength of exciton-phonon interaction) in quantum well of a given width but in structures grown with different order of quantum wells. More stable photoluminescence (with increasing temperature) is observed for a given quantum well if it is closer to the buffer layer and not to the cap layer.
5
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Study of Thermal Annealing Effect on the Properties of Silver Thin Films Prepared by DC Magnetron Sputtering

51%
Hajakbari F., Ensandoust M.
Acta Physica Polonica A
|
2016
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vol. 129
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issue 4
680-682
EN
Silver nanoparticles have potential applications in fields of nanosicence and technology. In this work, polycrystalline silver (Ag) thin films were deposited on quartz substrates by DC magnetron sputtering method at the same deposition conditions and then, the Ag films were annealed in oxygen atmosphere for 65 min at different annealing temperatures namely 300, 400, 500 and 600°C. The crystal structure of the films was evaluated by X-ray diffraction. The atomic force microscopy and scanning electron microscopy were employed for surface morphological studies of the films. Normal-incidence transmittance over the wavelength range of 200-2500 nm was measured using a spectrophotometer. The results show that the crystallization of the films increases after annealing and that the Ag films without annealing have lowest roughness. Annealing temperature effectively influences the surface morphology of the films. Optical studies reveal that the as-deposited Ag film has metallic behavior with zero transmittance and after annealing, the transmittance increases due to the formation of silver oxide phases in the films.
6
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Structure, Surface Morphology and Optical Properties of Thin Films of ZnS and CdS Grown by Atomic Layer Epitaxy

51%
Szczerbakow A., Godlewski M., Dynowska E., Ivanov V., Świątek K., Goldys E., Phillips M.
Acta Physica Polonica A
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1998
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vol. 94
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issue 3
579-582
EN
In this communication we report successful growth of monocrystalline cubic ZnS and monocrystalline and polycrystalline cubic and wurtzite films of CdS by atomic layer epitaxy. Structural and optical properties of these films are analysed. ZnS (and CdS/ZnS) films grown on GaAs substrate are cubic. Atomic layer epitaxy grown films provide several advantages over ZnS and CdS materials grown by other techniques, especially compared to bulk material, which is grown at higher temperatures. First results for ZnS/CdS/ZnS quantum well structures are also discussed.
7
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The Pressure Influence on the Properties of S-Phase Coatings Deposited by Reactive Magnetron Sputtering

51%
Fryska S., Baranowska J.
Acta Physica Polonica A
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2013
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vol. 123
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issue 5
854-857
EN
Reactive magnetron sputtering of austenitic stainless steel in nitrogen containing atmosphere was used to deposit coatings composed of S-phase. The process was conducted at constant temperature (200°C). The influence of total and partial nitrogen pressure on coating characteristics was investigated. It was observed that both total and nitrogen partial pressures have influence on coating composition and microstructure. Increasing nitrogen content in the S-phase coating can have a beneficial effect on its corrosion characteristics. It was also found that coatings deposited in the ambient of high nitrogen contents are composed of S-phase and the additional high-nitrogen phase, which is of crucial influence on mechanical properties of the coatings. It was also found that partial argon pressure can contribute to the changes in mechanical properties of the coatings.
8
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Study of Ti, V and Their Oxides-Based Thin Films in the Search for Hydrogen Storage Materials

51%
Tarnawski Z., Zakrzewska K., Kim-Ngan N.-T., Krupska M., Sowa S., Drogowska K., Havela L., Balogh A.
Acta Physica Polonica A
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2015
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vol. 128
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issue 3
431-439
EN
Thin film series consisting of Ti, V, TiO₂ and V₂O₅ layer with different layer geometries, sequences and thicknesses have been prepared by the sputtering technique. The hydrogen depth profile of selected films upon hydrogen charging at 1 bar and/or hydrogenation at pressure up to 102 bar was determined by using secondary ion mass spectrometry and nuclear reaction analysis using a N-15 beam. The highest hydrogen storage with a concentration up to 50 at.% was found in the pure Ti and Ti-contained layer, while it amounts to around 30% in the metallic Ti-V-Ni layer. Hydrogen can diffuse through the TiO₂ layer without accumulation, but can be stored in the VO₂ layer in some cases. Hydrogen can remove the preferential Ti orientation in the films and induce a complete transition of V₂O₅ into VO₂ in the films.
9
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Carbon Doped Austenitic Stainless Steel Coatings Obtained by Reactive Magnetron Sputtering

51%
Fryska S., Giza P., Jedrzejewski R., Baranowska J.
Acta Physica Polonica A
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2015
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vol. 128
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issue 5
879-882
EN
The paper presents the results of investigations of carbon doped austenitic stainless steel coatings (carbon S-phase) obtained by the reactive magnetron sputtering in the reactive atmosphere composed of argon and methane as a carbon source. Stainless steel targets were sputtered under different conditions. During the experiments the argon to methane proportion varied within a range 11/2-7/6. The other parameters such as temperature, pressure, sputtering power, etc. were kept constant. The phase composition was determined using the X-ray diffraction. Electron probe microanalysis (energy dispersive spectroscopy and wavelength dispersive spectroscopy) and glow discharge optical emission spectrometry techniques were used to study element composition of the coatings. Microstructure was investigated by scanning electron microscopy. It was found that varying the methane volume in the reactive atmosphere, it is possible to control the lattice parameter of the carbon S-phase.
10
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Barrier Properties of Coated and Laminated Polyolefin Films for Food Packaging

51%
Lazić V., Budinski-Simendić J., Gvozdenović J., Simendić B.
|
|
issue 5
855-858
EN
The food packaging industry demands polymer films possessing a defined barrier against permeation of gases, moisture and flavor. The objective of this study was to assess the differences between the barrier properties of coated and un-coated polyolefine films. Eight types of packaging films are prepared by standard industrial procedure by cast film extrusion processing with chill rollers: biaxially oriented polypropylene (BOPP), BOPP coated by acrylic copolymer, metallized BOPP by aluminum, and low-density polyethylene (LDPE). The influence of lamination and metallization on the gas molecules (CO_{2}, O_{2} and N_{2}) was determined by Lyssy's method. The moisture transparency was assessed according to the gravimetric method. The substantial differences between the barrier properties of the coated and un-coated films were estimated. It was estimated that the lamination process improves the oxygen barrier but not necessarily the moisture barrier, due to the different mechanisms for oxygen and moisture permeability. The obtained barrier properties data were considered from a practical point of view. It was concluded that films based on metallized BOPP has excellent barrier properties and can be used to over wrap food products.
11
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Exciton Dynamics in CdTe/CdMnTe Multiquantum Well Structures Grown by Molecular Beam. Epitaxy on GaAs Substrate

51%
Godlewski M., Koziarska B., Suchocki A., Karczewski G., Wojtowicz T., Kossut J., Bergman J. P., Monemar B.
Acta Physica Polonica A
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1995
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vol. 88
|
issue 5
985-989
EN
The results of picosecond photoluminescence kinetics of four different CdTe/CdMnTe multiquantum well structures grown by MBE on GaAs substrates are presented. The experimental results show that excitons in CdTe quantum wells are strongly localized by potential fluctuations. Photoluminescence decay times of the localized excitons are considerably shorter (about 120 ps) than those reported for free or quasi-free excitons. An influence of Mn in the barriers on exciton properties is demonstrated. For narrow quantum wells as well as for the multiquantum well structure with the highest Mn mole fraction the excitons migrate during their decay to the states with a lower potential energy. Longer decay times are observed for quasi-localized excitons. We show also that for strongly localized excitons the energy transfer between localized and donor bound excitons is less efficient.
12
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Content available

Preparation and Characterization of d.c.-Plated Nanocrystalline Nickel Deposits

51%
Szeptycka B., Derewnicka D.
Acta Physica Polonica A
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2002
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vol. 102
|
issue 2
199-205
EN
The microstructure, microhardness, corrosion, and wear resistance of d.c.-plated Ni electrodeposits prepared from different types of electrolyzing Watts-type baths, without or with organic compounds, ceramic powder - SiC and polymer - polytetrafluoroethylene (PTFE), on Cu substrate, which was subsequently removed from the deposits, were investigated. With the change of the type of bath, the deposit grain size was found to decrease markedly, e.g. deposits with an average grain size of about 50 nm could be produced from a bath containing 45 g/dm^3 Ni^2+ ions, 5 g/dm^3 SiC, and 20 g/dm^3 PTFE. The surface morphology on the bath side of the electrodeposited Ni or Ni-SiC-PTFE foils was characteristic of the type of bath, and its roughness correlated well with the observed grain size. Microhardness and wear resistance increased with decreasing grain size, as expected. On discussing the factors controlling deposit grain size, it is concluded that the Ni^{2+} ion content in the bath and the presence of organic compounds may have a decisive role.
13
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Optical and Electrical Characterization of (002)-Preferentially Oriented n-ZnO/p-Si Heterostructure

51%
Abdallah B., Al-Khawaja S.
|
EN
In this paper, preferentially oriented (002) ZnO thin films have been grown on Si (100) and glass substrates using radio frequency magnetron sputtering. The dependence of the quality of the ZnO thin films at different substrate temperatures on the growth is studied. A ZnO thin film with c-axis-oriented würtzite structure is obtained at a growth temperature from 200 to 400°C. X-ray diffraction shows that the full width at half maximum θ -2θ of (002) ZnO/Si is located at approximately 34.42°, which is used to infer the grain size that is found to be 17 nm to 19.7 nm. The FWHM is 9.5° to 8° in rocking curve mode, from which the crystalline quality has been determined. The texture degree demonstrates the improvement in quality with the increase of substrate temperature, which is best at 400°C. The band gap extracted by UV transmittance spectrum has been identified as 3.2 eV at 400°C. The electrical characteristics via C-V and I-V measurements on the basis of the heterojunction thermal emission model confirm the domination of high-density grain boundary layer existing at the interface. The transport currents indicate to the presence of space-charge-limited current and trap-charge-limited current mechanisms.
14
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Optical Characterization of CdZnSe/ZnSe Multiquantum Well System

51%
Godlewski M., Karpińska K., Bergman J., Monemar B., Kurtz E., Hommel D.
Acta Physica Polonica A
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1995
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vol. 87
|
issue 1
209-212
EN
Optical properties of Cd_{x}Zn_{1-x}Se/ZnSe (x = 0.12) multiquantum well system are discussed. The transient photoluminescence and optically de­tected cyclotron resonance experiments demonstrate a strong contribution of bound exciton emission to the low temperature photoluminescence spec­tra.
15
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Thermal Expansion of Free-Volume in Hexadecane Confined in the Silica Gel Nanopores

51%
Šauša O., Majerník V., Illeková E., Macová E., Berek D.
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vol. 125
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issue 3
798-800
EN
Temperature dependence of the free-volume of voids in hexadecane (HXD) confined in the 3 nm silica gel pores (Develosil-30) was measured by positron annihilation lifetime spectroscopy. Different amount of HXD was filled into the pores of matrix. The anomalous thermal expansion was observed in the partially filled pores with extremely low filling. The thermal expansion coefficient of free-volume voids in this solidified HXD layer has a negative sign at temperatures below 180 K compared to high- or full-filled pores of silica gel. At these temperatures, the positron annihilation lifetime spectroscopy measurements demonstrate the appearance of a new type of the free volume within HXD which has been interpreted as the cracks in the HXD layer on the inner walls of matrix cavities. The differential scanning calorimetry method confirmed that the processes were enacted within pores and not on the outer surfaces of silica gel grains. In the sample with the extremely low filling, only the one HXD solidification/melting effect connected with confined states is manifested.
16
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Garnet Single Crystal as Substrate Material for HTSC Films

51%
Mukhopadhyay P.
Acta Physica Polonica A
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1997
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vol. 92
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issue 1
147-151
EN
The use of high temperature superconductor for device application has made the compatibility of the film and substrate an important issue. Garnets having reasonably low dielectric constant and low dielectric losses can be viable low cost substrate materials for the microwave devices. Garnet single crystals like Gd_{3}Ga_{5}O_{12} (GGG), Y_{3}Ga_{5}O_{12} (YGG), Y_{3}Al_{5}O_{12} (YAG) etc. can be potential HTSC substrate materials for microwave devices. Properties of HTSC films on some of these garnet crystals are compared here.
17
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Influence of Growth Conditions on Optical Properties of ZnCdSe/ZnSe Quantum Wells Grown by Molecular Beam Epitaxy

51%
Godlewski M., Bergman J., Monemar B., Kurtz E., Hommel D.
Acta Physica Polonica A
|
1996
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vol. 90
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issue 4
785-788
EN
The results of investigations of photoluminescence, time-resolved photoluminescence, photoluminescence kinetics and their temperature dependencies are discussed for two types of ZnCdSe/ZnSe multi quantum well structures - for pseudomorphic and for strain relaxed structure. Densities of 2D localized states and averaged localization energies, as seen by excitons, are determined from the photoluminescence kinetics measurements. We show distinct differences between exciton properties in two multi quantum well structures studied.
18
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Phonon Contribution in Thermodynamics οf Nano-Crystalline Films and Wires

45%
Šetrajčić J., Mirjanić D., Vučenović S., Ilić D., Markoski B., Jaćimovski S., Sajfert V., Zorić V.
Acta Physica Polonica A
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2009
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vol. 115
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issue 4
778-782
EN
Spectra of possible phonon states, as well as thermodynamic characteristics of nanocrystals (ultrathin film and quantum wire) of simple cubic crystalline structure are analyzed in this paper, using the method of two-time dependent Green functions. From energy spectra and internal energy of the system the thermal capacitance of these structures in low temperature region is found. The temperature behavior of specific heat is compared to that of corresponding bulk structure. It is shown that at extremely low temperatures thermal capacitance of quantum wire is considerably lower than the thermal capacitance of film as well as the bulk sample. Consequences of this fact are discussed in detail and its influence to thermodynamic properties of materials is estimated.
19
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Characterization of Transparent and Nanocrystalline TiO_{2}:Nd Thin Films Prepared by Magnetron Sputtering

45%
Domaradzki J., Wojcieszak D., Prociow E., Kaczmarek D.
Acta Physica Polonica A
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2009
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vol. 116
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issue S
S-75-S-77
EN
In this work structural and optical properties of TiO_{2} thin films doped with different amount of Nd have been outlined. The result have shown that by quantity of Nd amount in the film dense nanocrystalline or amorphous thin films were obtained.
20
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Comparison of Pure and Doped TiO₂ Thin Films Prepared by Sol-Gel Spin-Coating Method

38%
Çiçek Bezir N., Evcin A., Kayali R., Özen M., Balyaci G.
Acta Physica Polonica A
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2017
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vol. 132
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issue 3
620-624
EN
In this study, using spin-coating sol-gel method we fabricated TiO₂ thin films, doped with different concentrations (1, 2, and 3 mole %) of Ce, Dy, and Eu. Characterization of the prepared samples was performed by means of the X-ray diffraction, scanning electron microscopy, ultraviolet visible absorption, and differential thermal and thermo gravimetric analysis. X-ray diffraction measurements have shown that in Eu and Dy-doped samples crystal structure consists of mixed rutile and the dominant anatase phases, however the Ce doped samples consist of anatase phase only. Scanning electron microscopy images have revealed that while average thin film thickness of the Dy-doped samples decreases with increasing concentration of Dy, the average film thicknesses of samples doped with Ce and Eu increases with increasing concentrations of these dopants. Ultraviolet visible absorption spectroscopy measurements have shown that while absorbances of the samples doped by 1 and 2 mole % of the dopants have nearly similar properties, these properties differ from each other for 3 mole % of the dopants. Finally, differential thermal and thermo gravimetric analyses have shown that the chemical reactions and weight losses of the samples have occurred at the expected temperatures.
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