Year: 2020

Polarization dependent photoluminescence and optical anisotropy in CuPtB-ordered dilute GaAs1-xBi xalloys

Posted on by Viliam Vretenár

PAULAUSKAS, Tadas – ACEECHAVIČIUS, Bronislovas – KARPUS, Vytautas – JOČIONIS, Lukas – TUMĖNAS, Saulius – DEVENSON, Jan – PAČ̌EBUTAS, Vaidas – STANIONYTE, Sandra – STRAZDIENE, Viktorija – GEIAUTIS, Andrejus – ČAPLOVIČOVÁ, Mária – VRETENÁR, Viliam – WALLS, Michael G. – KROTKUS, Arunas

In Journal of Applied Physics. Vol. 128, iss. 19 (2020)

https://doi.org/10.1063/5.0030091

The GaAs1–xBix semiconductor alloy allows one to achieve large bandgap reduction and enhanced spin–orbit splitting energy at dilute Bi quantities. The bismide is currently being developed for near- to mid-infrared lasers, multi-junction solar cells, and photodetectors. In this structure–property relationship study of GaAsBi alloys, we report polarization dependent photoluminescence that reaches a polarization ratio up to 2.4 at room temperature. Polarization dependence is also presented using transmittance spectra, birefringence, and linear dichroism. The optical anisotropy observations agree with the predictions of point symmetry reduction in the CuPtB-type ordered GaAsBi phase. The structural ordering is investigated experimentally from the atomic scale in molecular-beam epitaxy (MBE) grown samples on exact and miscut (001) GaAs substrates, as well as on (001) Ge. The latter sample is composed of anti-phase domains in which the ordering axes are rotated by 90° angles. Since the conditions stabilizing the CuPtB ordered phase fall within the typical MBE growth regime of dilute bismides, the optical anisotropy in GaAsBi alloys is expected to be ubiquitous. These findings are important for the future development of GaAsBi-based optoelectronics and also provide new means to analyze structurally complex bismide alloys.

Dehydroaromatization of methane over Mo/ZSM-5 zeolites: influence of aluminum distribution in the crystals

Posted on by Mária Čaplovičová

HORŇÁČEK, Michal – HUDEC, Pavol – JORÍK, Vladimír – ČAPLOVIČOVÁ, Mária – ČAPLOVIČ, Ľubomír – KALIŇÁK, Michal – SMIEŠKOVÁ, Agáta

https://doi.org/10.1007/s11144-020-01887-5

Abstract

Mo/ZSM-5 type catalysts based on two ZSM-5 zeolites with comparable crystal morphology, shape and size, Si/Al in bulk (22–23), acidity and amount of Mo (~ 4.7 wt.%) but having a different (homogeneous and non-homogeneous) Al distribution in particles and different acid sites type distribution were investigated in methane dehydroaromatization. From the results follows that Mo is associated with both BAS and LAS in the samples with almost homogenous Al distribution (MoZSM-5/AH). In the case of both samples with non-homogenous Al distribution (MoZSM-5/BH and MoZSM-5/BNH4) Mo preferably associates with BAS. Evidently lower activity and selectivity of Mo/ZSM-5/AH catalyst in methane transformation compared with Mo/ZSM-5/BH we attribute to the fact that from Mo species which interact with Lewis acid sites in sample ZSM-5/AH less active carburized species are formed as from the Mo associated with Brønsted sites in sample ZSM-5/BH.

Ag-modified LiMn2O4 cathode for lithium-ion batteries: Coating functionalization

Posted on by Mario Kotlár

ABBAS, Somia M. – HASHEM, Ahmed M. – ABDEL-GHANY, Ashraf E. – ISMAIL, Eman H. – KOTLÁR, Mário – WINTER, Martin – LI, Jie – JULIEN, Christian M.

In Energies [Open access]. Vol. 13, iss. 19 (2020)

https://doi.org/10.3390/en13195194

Abstract

In this work, the properties of silver-modified LiMn2O4 cathode materials are revisited. We study the influence of calcination atmosphere on the properties of the Ag-coated LiMn2O4 (Ag/LMO) and highlight the silver oxidation. The effect of the heat treatment in vacuum is compared with that in air by the characterization of the structure, specific surface area, Li transport properties and electrochemical performance of Ag/LMO composites. Surface analyses (XPS and Raman spectroscopy) show that the nature of the coating (~3 wt.%) differs with the calcination atmosphere: Ag/LMO(v) calcined in vacuum displays Ag nanospheres and minor AgO content on its surface (specific surface area of 4.1 m2 g−1), while Ag/LMO(a) treated in air is mainly covered by the AgO insulating phase (specific surface area of 0.6 m2 g−1). Electrochemical experiments emphasize that ~3 wt.% Ag coating is effective to minimize the drawbacks of the spinel LiMn2O4 (Mn dissolution, cycling instability, etc.). The Ag/LMO(v) electrode shows high capacity retention, good cyclability at C/2 rate and capacity fade of 0.06% per cycle (in 60 cycles).

Toward BaSi2/Si Heterojunction Thin-Film Solar Cells: Insights into Heterointerface Investigation, Barium Depletion, and Silicide-Mediated Silicon Crystallization

Posted on by Lubomír Vančo

TIAN, Yilei – MONTES, Ana Rita Bento – VANČO, Ľubomír – ČAPLOVIČOVÁ, Mária – VOGRINČIČ, Peter – SUTTA, Pavol – SATRAPINSKYY, Leonid – ZEMAN, Miro – ISABELLA, Olindo

In Advanced Materials Interfaces. Vol. 7, iss. 19 (2020)

https://doi.org/10.1002/admi.202000887

Abstract

The knowledge of the structural and compositional details of Si/BaSi2/Si heterostructure annealed at high temperature is a prerequisite for BaSi2 application in heterojunction thin-film solar cells. For this purpose, Si/BaSi2/Si heterostructures deposited by magnetron sputtering with different Si layer thickness are submitted to systematic structural and compositional characterizations. Results reveal a BaSi2/Si heterointerfacial variation caused by surface oxidation and Ba diffusion at the high temperature. Its effects on the optical and electrical properties of Si/BaSi2/Si heterostructure are presented. The outcomes of this work can be extended to BaSi2 deposited by other techniques, and generate substantial advantages in BaSi2 development ranging from improvement on material qualities and eventual deployment in thin-film solar cells.

Collapse Mechanism in Few-Layer MoS2 Langmuir Films

Posted on by Mario Kotlár

BODÍK, Michal – DEMYDENKO, Maksym – SHABELNYK, Tetiana – HALAHOVETS, Yuriy – KOTLÁR, Mário – KOSTIUK, Dmytro – SHAJI, Ashin – BRUNOVÁ, Alica – VEIS, Pavel – JERGEL, Matej – MAJKOVÁ, Eva – ŠIFFALOVIČ, Peter

In Journal of Physical Chemistry C. Vol. 124, iss. 29 (2020)

https://doi.org/10.1021/acs.jpcc.0c02365

Abstract

Recent advances in the liquid-phase exfoliation enabled large-scale production of two-dimensional (2D) materials, including few-layer graphene and transition metal dichalcogenides. The exfoliated flakes of 2D materials allow cost-effective deposition of continuous films for various applications ranging from optoelectronics to lubrication technology. The self-assembly of 2D materials on water subphase and subsequent transfer of such a Langmuir film onto a solid substrate offers an unprecedented layer quality in terms of spatial homogeneity as it proceeds in thermodynamic equilibrium. However, while the formation of conventional organic molecular Langmuir films has been widely studied, the application of the Langmuir technique to rigid inorganic 2D materials is still rather unexplored. Here, we study the underlying mechanism behind the formation and collapse at the critical surface pressure of the Langmuir film composed of few-layer MoS2 flakes. The in situ wide-angle X-ray scattering measured in real time and other supportive techniques applied ex situ after the film transfer onto a Si/SiO2 substrate were employed. We identify all principal compression stages up to the Langmuir monolayer collapse and beyond, relying on the texture, surface pressure, and elastic modulus temporal evolution. The results obtained and the conclusions drawn can be extended to a large family of the inorganic Langmuir films of other 2D materials to optimize the deposition process for envisaged application.

Atomic-Resolution EDX, HAADF, and EELS Study of GaAs1-xBix Alloys

Posted on by Viliam Vretenár

PAULAUSKAS, Tadas – PACEBUTAS, Vaidas – BUTKUTE, Renata – ČECHAVIČIUS, Bronislovas – NAUJOKAITIS, Arnas – KAMARAUSKAS, Mindaugas – SKAPAS, Martynas – DEVENSON, Jan – ČAPLOVIČOVÁ, Mária – VRETENÁR, Viliam – LIU, Xiaoyan – KOCIAK, Mathieu – KROTKUS, Arunas

In Nanoscale Research Letters. Vol. 15, iss. 1 (2020)

https://doi.org/10.1186/s11671-020-03349-2

Abstract

The distribution of alloyed atoms in semiconductors often deviates from a random distribution which can have significant effects on the properties of the materials. In this study, scanning transmission electron microscopy techniques are employed to analyze the distribution of Bi in several distinctly MBE grown GaAs1−xBix alloys. Statistical quantification of atomic-resolution HAADF images, as well as numerical simulations, are employed to interpret the contrast from Bi-containing columns at atomically abrupt (001) GaAs-GaAsBi interface and the onset of CuPt-type ordering. Using monochromated EELS mapping, bulk plasmon energy red-shifts are examined in a sample exhibiting phase-separated domains. This suggests a simple method to investigate local GaAsBi unit-cell volume expansions and to complement standard X-ray-based lattice-strain measurements. Also, a single-variant CuPt-ordered GaAsBi sample grown on an offcut substrate is characterized with atomic scale compositional EDX mappings, and the order parameter is estimated. Finally, a GaAsBi alloy with a vertical Bi composition modulation is synthesized using a low substrate rotation rate. Atomically, resolved EDX and HAADF imaging shows that the usual CuPt-type ordering is further modulated along the [001] growth axis with a period of three lattice constants. These distinct GaAsBi samples exemplify the variety of Bi distributions that can be achieved in this alloy, shedding light on the incorporation mechanisms of Bi atoms and ways to further develop Bi-containing III-V semiconductors.

Green synthesis of stable nanocolloids of monodisperse silver and gold nanoparticles using natural polyphenols from fruits of Sambucus nigra L

Posted on by Mária Čaplovičová

MARIYCHUK, Ruslan – PORUBSKÁ, Jana – OSTAFIN, Marek – ČAPLOVIČOVÁ, Mária – ELIÁŠOVÁ, Adriana

In Applied Nanoscience. Vol. 10, iss. 12 (2020)

https://doi.org/10.1007/s13204-020-01324-y

Abstract

In the present work, we report, for the first time, the production of stable nanocolloids of highly monodisperse silver and gold nanoparticles (AgNPs and AuNPs) using phytosynthesis approach. With the aim to eliminate misinterpretations associated with the use of usually applied crude plant extracts, the presented study was focused on the use of polyphenolic fraction isolated from elderberry fruits (Sambucus nigra L.) for the synthesis. Obtained AgNPs and AuNP were characterized by UV–Vis and FTIR spectroscopy, DLS and TEM. We observed unexpectedly high capability of the natural polyphenols not only to form monodisperse nanoparticles but also to stabilise the concentrated nanocolloids (539 mg/L AgNPs and 739 mg/L AuNPs) for at least two years. Moreover, AgNPs showed strong antibacterial properties against pathogenic bacterial strains Staphylococcus aureus and Escherichia coli (inhibited after 15 min and totally stopped growth after 3 and 5 h at 3.125 mg/L concentration).

Ni-mediated reactions in nanocrystalline diamond on Si substrates: the role of the oxide barrier

Posted on by Mária Čaplovičová

TULIČ, Semir – WAITZ, Thomas – ROMANYUK, Oleksandr – VARGA, Marián – ČAPLOVIČOVÁ, Mária – HABLER, Gerlinde – VRETENÁR, Viliam – KOTLÁR, Mário – KROMKA, Alexander – REZEK, Bohuslav – SKÁKALOVÁ, Viera

In RSC Advances. Vol. 10, iss. 14 (2020)

https://doi.org/10.1039/D0RA00809E

Abstract

Nanocrystalline diamond (NCD) films grown on Si substrates by microwave plasma enhanced chemical vapor deposition (MWPECVD) were subjected to Ni-mediated graphitization to cover them with a conductive layer. Results of transmission electron microscopy including electron energy-loss spectroscopy of cross-sectional samples demonstrate that the oxide layer on Si substrates (∼5 nm native SiO2) has been damaged by microwave plasma during the early stage of NCD growth. During the heat treatment for graphitizing the NCD layer, the permeability or absence of the oxide barrier allow Ni nanoparticles to diffuse into the Si substrate and cause additional solid-state reactions producing pyramidal crystals of NiSi2 and SiC nanocrystals. The latter are found impinged into the NiSi2 pyramids but only when the interfacial oxide layer is absent, replaced by amorphous SiC. The complex phase morphology of the samples is also reflected in the temperature dependence of electrical conductivity, where multiple pathways of the electronic transport dominate in different temperature regions. We present models explaining the observed cascade of solid-state reactions and resulting electronic transport properties of such heterostructures.

A bioconjugated MoS2 based nanoplatform with increased binding efficiency to cancer cells

Posted on by Mario Kotlár

KÁLOSI, Anna – LABUDOVÁ, Martina – ANNUŠOVÁ, Adriana – BENKOVIČOVÁ, Monika – BODÍK, Michal – KOLLÁR, Jozef – KOTLÁR, Mário – KASAK, Peter – JERGEL, Matej – PASTOREKOVÁ, Sylvia – ŠIFFALOVIČ, Peter – MAJKOVÁ, Eva

In Biomaterials Science. Vol. 8, iss. 7 (2020)

https://doi.org/10.1039/C9BM01975H

Abstract

We evaluate the application of surfactant-free liquid-phase exfoliated MoS2 nanosheets as a nanoplatform for a cancer detection and treatment system equipped with an antibody–antigen based recognition element. Employing antigen–antibody binding, we increased the probability of the endocytosis of MoS2 nanosheets into CAIX expressing cells by 30%. The nanosheets are functionalized with a specific antibody M75, which forms an antigen–antibody complex with CAIX. The bioconjugation of MoS2 nanosheets involves biocompatible components with low cytotoxicity, verified in the tested cell lines by fluorescence-based cell viability assay. The cellular internalization is quantified by flow cytometry, while the internalization is confirmed by label-free confocal Raman imaging. Raman measurements show increased lysosomal activity in the proximity of the internalized nanoplatforms.

GaAs1-xBix growth on Ge: anti-phase domains, ordering, and exciton localization

Posted on by Mario Kotlár

PAULAUSKAS, Tadas – PACEBUTAS, Vaidas – GEIZUTIS, Andrejus – STANIONYTE, Sandra – DUDUTIENE, Evelina – SKAPAS, Martynas – NAUJOKAITIS, Arnas – STRAZDIENE, Viktorija – CECHAVICIUS, Bronislovas – ČAPLOVIČOVÁ, Mária – VRETENÁR, Viliam – JAKIELA, Rafal – KROTKUS, Arunas

In Scientific Reports. Vol. 10, iss. 1 (2020)

https://doi.org/10.1038/s41598-020-58812-y

Abstract

The dilute bismide alloy GaAs1-xBix has drawn significant attention from researchers interested in its fundamental properties and the potential for infrared optoelectronics applications. To extend the study of bismides, molecular-beam heteroepitaxy of nominally 1.0 eV bandgap bismide on Ge substrates is comprehensively investigated. Analysis of atomic-resolution anti-phase domain (APD) images in the direct-epitaxy revealed a high-density of Ga vacancies and a reduced Bi content at their boundaries. This likely played a key role in the preferential dissolution of Bi atoms from the APD interiors and Bi spiking in Ge during thermal annealing. Introduction of GaAs buffer on offcut Ge largely suppressed the formation of APDs, producing high-quality bismide with single-variant CuPtB-type ordered domains as large as 200 nm. Atomic-resolution X-ray imaging showed that 2-dimensional Bi-rich (111) planes contain up to x = 9% Bi. The anomalously early onset of localization found in the temperature-dependent photoluminescence suggests enhanced interactions among Bi states, as compared to non-ordered samples. Growth of large-domain single-variant ordered GaAs1-xBix films provides new prospects for detailed analysis of the structural modulation effects and may allow to further tailor properties of this alloy for optoelectronic applications.