U. Cvelbar - Academia.edu (original) (raw)

Papers by U. Cvelbar

HAL (Le Centre pour la Communication Scientifique Directe), 2009

Journal of Alloys and Compounds

Materials Chemistry and Physics, 2021

Abstract Properties of substoichiometric tungsten oxide (WO3-x) semiconducting nanomaterials in d... more Abstract Properties of substoichiometric tungsten oxide (WO3-x) semiconducting nanomaterials in diverse applications are morphology-dependent. However, it remains challenging to control morphology and structure of WO3-x nanomaterials. Here, we report the solvothermal synthesis of WO3-x nanostructures with different morphologies in tungsten hexachloride-ethanol solution through adjusting the filling fraction of ethanol in autoclave. The structural and morphological conversion mechanisms are related to the changes in the viscosity and Brownian motion caused by the concentration of tungsten hexachloride in ethanol. The studies on the photoluminescence (PL) properties reveal that the WO3-x nanostructures emit ultraviolet, blue, green and red emissions. The PL emissions are attributed to the recombination between the electron occupying the resonant defect state in the conduction band and the hole in the valence band and the transitions between the conduction and valence bands as well as the transition between the oxygen vacancy states. The enhancement of PL intensity is related to the increase of oxygen vacancies and the phonon suppression during the PL emission as well as the nanocavity structure. Furthermore, the potential applications in the catalysis fields are discussed. These results provide a new technique to control the structure of WO3-x nanomaterials and contribute to the development of next-generation PL emission nanodevices based on vacancy- and structure-engineered WO3 materials and the rational design of catalytic materials.

Materials Science and Engineering: B, 2020

Substoichiometric tungsten oxide (WO x , 2 < x < 3) nanomaterials are important nanoscale semicon... more Substoichiometric tungsten oxide (WO x , 2 < x < 3) nanomaterials are important nanoscale semiconductor materials with broad applications in optoelectronic devices; however a controllable modification of their physical properties remains challenging task. Here, we report an alternative green synthesis of hybrid nanostructures composed by WO x and ZnWO 4 phases in ethanol via a solvothermal process using ZnO and WCl 6 as the precursors. The results indicate that the formation of ZnWO 4 leads to the structural conversion of WO x from nanorods to nanoparticles due to the effect of ZnWO 4 on the side growth of WO x nanostructures. Moreover, the surface morphology tailored by ZnWO 4 and crystalline phase transformation induce different photoluminescence (PL) emission from pure WO x nanostructures and WO x /ZnWO 4 hybrid nanostructures due to the increased number of oxygen vacancies.

ECS Meeting Abstracts, 2012

not Available.

Journal of Physics D: Applied Physics, 2019

Exploring the fast synthesis of Zn-doped MoO3-x nanostructures in a N2 environment by the hot fil... more Exploring the fast synthesis of Zn-doped MoO3-x nanostructures in a N2 environment by the hot filament chemical vapour deposition using a mixture of Zn and MoO3 powders is reported, whereas targeted transformation of nanomaterials is done via Zn addition in MoO3 powder. During this process, MoO3-x nanostructures convert from nanoparticles to nanofilms. The structural conversion of MoO3-x nanostructures is the results of the predominant diffusion of MoO3-x and MoO3 molecules along the substrate surface caused by reduced evaporation of MoO3 due to the melting of Zn particles. At room temperature, the pure and Zn-doped MoO3-x nanostructures generate the photoluminescence (PL) emission in the ultraviolet to infrared range, while the PL emission in the visible range has a great change at low temperature. The PL emission is related to the bandgap transition, Mo5+ d-d transition, intervalence charge transfer transition, and transition between the intermediate and valence bands. Furthermore, the PL emission of MoO3-x nanostructures is enhanced by Zn doping. The strong PL emission from Zn-doped MoO3-x nanostructures compared to pure MoO3-x nanostructures results from the increase of oxygen vacancies caused by the Zn incorporation. The enhancement of PL emission at low temperature compared to room temperature is due to the increase of vacancy concentration, weak lattice vibration and relaxation of polarons. Our present results could be used to control the structures of MoO3-x nanomaterials and impact the development of optoelectronic devices based on MoO3 nanomaterials, such as organic solar cells, photovolatic devices and light-emitting diodes.

Plasma Processes and Polymers, 2018

This white paper considers the future of plasma science and technology related to plastics and te... more This white paper considers the future of plasma science and technology related to plastics and textiles, summarizing existing efforts and the current state-of-art for major topics related to plasma processing techniques. It draws on the frontier of plasma technologies in order to see beyond and identify the grand challenges which we face in the following 5 to 10 years. To progress and move the frontier forward, the paper highlights the major enabling technologies and topics related to the design of surfaces, coatings and materials with non-equilibrium plasmas. The aim is to progress the field of plastics and textile production using advanced plasma processing as the key enabling technology which is environmentally friendly, cost-efficient, and offers high-speed processing. Current industrial challenges and societal needs are identified to steer future technological development in this area.

RSC Advances, 2015

The high sensitivity in response, selectivity and reversibility was achieved on a carbon nanowall... more The high sensitivity in response, selectivity and reversibility was achieved on a carbon nanowall-based sensor for the vapor detection of volatile organic compounds, which were tested by an electrical resistance method during adsorption and desorption cycles.

Biointerphases, 2015

Energy deficiency, global poverty, chronic hunger, chronic diseases, and environment conservation... more Energy deficiency, global poverty, chronic hunger, chronic diseases, and environment conservation are among the major problems threatening the whole mankind. Nanostructure-based technologies could be a possible solution. Such techniques are now used for the production of many vitally important products including cultured and fermented food, antibiotics, various medicines, and biofuels. On the other hand, the nanostructure-based technologies still demonstrate low efficiency and controllability, and thus still are not capable to decisively address the global problems. Furthermore, future technologies should ensure lowest possible environmental impact by implementing green production principles. One of the most promising approaches to address these challenges are the sophisticatedly engineered biointerfaces. Here, the authors briefly evaluate the potential of the plasma-based techniques for the fabrication of complex biointerfaces. The authors consider mainly the atmospheric and inductively coupled plasma environments and show several examples of the artificial plasma-created biointerfaces, which can be used for the biotechnological and medical processes, as well as for the drug delivery devices, fluidised bed bioreactors, catalytic reactors, and others. A special attention is paid to the plasma-based treatment and processing of the biointerfaces formed by arrays of carbon nanotubes and graphene flakes.

Materials Science Forum, 2009

Pulse modulated double hollow cathode RF plasma jet system with two separate independent nozzles ... more Pulse modulated double hollow cathode RF plasma jet system with two separate independent nozzles made of BaTiO3 (BTO) and SrTiO3 (STO) was used for deposition of BSTO thin films on Si and on multi-layer Si/SiO2/TiO2/Pt substrates. Dielectric properties of BSTO layers strongly depend on ratio composition expressed by parameter x = Ba/(Ba+Sr) and on accuracy in presence of other elements. Space resolved optical emission spectroscopy (OES) was used mainly for monitoring of concentration of particles sputtered from the hollow cathode and for feedback correction of power supplied in both nozzles because applied power was responsible for sputtering speed of Ba and Sr particles. Main attention was focused on relation between ratio of spectral intensity of Ba, Ba+, Sr and Sr+ lines close to substrate and ratio of Ba and Sr concentration in the deposited film. 2D map of emission lines intensity distribution for Ba, Ba+, Sr, Sr+, Ti, Ar, and Ar+ for double hollow cathode plasma jet system wit...

Plasma Chemistry and Plasma Processing, 2007

Density of neutral oxygen atoms in the ground state has been measured during treatment of wool fa... more Density of neutral oxygen atoms in the ground state has been measured during treatment of wool fabric samples. Samples were placed in an afterglow reactor with a volume of about 5 l, which was pumped with a two stage rotary pump with the nominal pumping speed of 28 m 3 /h. The source of the oxygen atoms was a microwave discharge operating in the surfatron mode at 2.45 GHz and adjustable output power up to 300 W. The density of O-atoms in the afterglow chamber was measured with a fiber-optics catalytic probe. For the empty reactor, the O density depended on discharge parameters and was between 0.8 and 2.8 • 10 21 m À3 at 40 and 50 Pa respectively. During the treatment of wool, the O density depended largely on the exposure time. For untreated samples, the O density was below the detection limit of the probe, while prolonged treatment allowed for recovering the O density. The recovery always occurred after having submitted wool samples to the dose of the order of 10 23 atoms/m 2. The results were explained by oxidation of the thin lipid layer on the surface of the wool fibres.

Journal of Applied Physics, 2005

We determined the density of neutral nitrogen atoms in an Ar-N2 postglow using a fiber-optics cat... more We determined the density of neutral nitrogen atoms in an Ar-N2 postglow using a fiber-optics catalytic probe. The probe, which had a catalyst made of nitrided iron, was calibrated with a NO titration. The recombination coefficient for the heterogeneous recombination of N atoms on the nitrided iron surface was determined by comparing the probe signal with the NO titration. Within

IEEE Transactions on Plasma Science, 2008

Inductively coupled RF oxygen plasma generated by inductive coil wrapped around a linear glass tu... more Inductively coupled RF oxygen plasma generated by inductive coil wrapped around a linear glass tube is studied. Images of plasma properties in the linear reactor are presented. Plasma diagnostics was performed by spatially resolved optical emission spectroscopy.

IEEE Transactions on Plasma Science, 2011

IEEE Transactions on Plasma Science, 2014

EPL (Europhysics Letters), 2013

A microplasma generated between a stainless-steel capillary and water surface in ambient air with... more A microplasma generated between a stainless-steel capillary and water surface in ambient air with flowing argon as working gas appears as a bright spot at the tube orifice and expands to form a larger footprint on the water surface, and the dimensions of the bell-shaped microplasma are all below 1 mm. The electron density of the microplasma is estimated to be ranging from 5.32 × 10 9 cm −3 to 2.02 × 10 14 cm −3 for the different operating conditions, which is desirable for generating abundant amounts of reactive species. A computational technique is adopted to fit the experimental emission from the N2 second positive system with simulation results. It is concluded that the vibrational temperature (more than 2000 K) is more than twice the gas temperature (more than 800 K), which indicates the non-equilibrium state of the microplasma. Both temperatures showed dependence on the discharge parameters (i.e., gas flow and discharge current). Such a plasma device could be arranged in arrays for applications utilizing plasmainduced liquid chemistry.

Chemical Engineering Journal, 2021

Abstract Hybrid graphene-based nanostructures are considered promising materials for energy stora... more Abstract Hybrid graphene-based nanostructures are considered promising materials for energy storage applications. However, the synthesis of high-quality hybrid graphene nanostructures at high yields is challenging. In the present work we propose a novel, single-step microwave plasma-enabled approach to synthetize customizable hybrid graphene-based nanostructures at high-yield while preserving their quality. Hybrid N-graphene (nitrogen-doped graphene) metal-based nanostructures, for instance, can be produced at a rate of ∼ 19 mg/min. The high energy density region of a microwave plasma provides sufficient energy and “building particles” fluxes towards the low-energy density plasma afterglow for the processes of assembly and growth of N-graphene sheets. Simultaneously, a controlled jet of metal-oxide(-sulfide) microparticles is sprayed into the plasma afterglow region where they bind to N-graphene sheets. Methane/methylamine are used as carbon and nitrogen precursors, combined with micron-sized MnO2 and oxy-MnS particles to synthesize the hybrid structures. As a result, nano-sized (∼10–30 nm) MnOx particles decorated N-graphene (4.6 at. N%) and oxidized metal sulfide anchored N-graphene sheets (3.1 at. N%) are produced at atmospheric conditions. High structural quality and distribution of metal-based nanostructures on N-graphene sheets are revealed using transmission and scanning electron microscopes and other advanced spectroscopic techniques. Finally, an electrode for supercapacitor based on the N-graphene-metal-oxide(sulfide) hybrid nanostructures is developed with promising specific capacitances (∼273 F.g−1 at 0.5 A.g−1). The described chemically engineered process is one of the fastest approaches reported for designing the high-quality hybrid nanostructures produced at a high-yield, and as such, is expected to provide a high impact on the design of electrode materials for sustainable energy storage systems.

Nanotechnology, 2022

Manganese-doped ceria nanoparticles were prepared by hydrothermal synthesis and the prepared samp... more Manganese-doped ceria nanoparticles were prepared by hydrothermal synthesis and the prepared samples were thermally treated at 500 °C for 2 h. The samples were investigated using x-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive x-ray spectroscopy (EDS), N2 adsorption and x-ray photoelectron spectroscopy (XPS). XRD revealed that nanocrystalline ceria is the main phase in all samples, while a romanechite-like phase (Na2Mn5O10) appears in the sample doped with 30% of Mn. TEM coupled with EDS exposed the presence of the same phase in the sample doped with 20% Mn. While ceria particles have spherical morphology and particle size ranging from 4.3 to 9.2 nm, the rare crystals of the romanechite-like phase adopt a tubular morphology with a length of at least 1 μm. However, the decrease in the ceria lattice constant and the EDS spectra of the ceria nanoparticles clearly indicate that a substantial amount of manganese entered the ceria crys...