Goran Dražič | Jozef Stefan International Postgraduate School (original) (raw)

Papers by Goran Dražič

Research paper thumbnail of Ge quantum dot lattices in Al2O3 multilayers

Journal of Nanoparticle Research, 2013

ABSTRACT In this article, we show how to produce materials consisting of regularly ordered Ge qua... more ABSTRACT In this article, we show how to produce materials consisting of regularly ordered Ge quantum dot lattices in an amorphous alumina matrix with a controllable Ge quantum dot size, shape, spacing, crystalline structure, and degree of regularity in their ordering. The production of such materials is achievable already at room temperature by magnetron sputtering deposition of a (Ge + Al2O3)/Al2O3 multilayer. The materials show photoluminescence in the visible and ultraviolet light range, a size-dependent blue shift of the photoluminescence peak and an enhancement of its intensity by size reduction, indicating the quantum dot origin of the photoluminescence. The materials also exhibit excellent mechanical properties due to the alumina matrix. Their internal structure is shown to be highly resistive to irradiation with energetic particles for a large range of the irradiation parameters.

Research paper thumbnail of Solvothermal synthesis of zinc oxide microspheres

The solvothermal synthesis of ZnO particles from zinc acetylacetonate [Zn(acac) 2 ] in the presen... more The solvothermal synthesis of ZnO particles from zinc acetylacetonate [Zn(acac) 2 ] in the presence of triethanolamine (TEA) and various solvent systems at 170 C is reported. The structural, optical and morphological characteristics of ZnO particles were investigated. It was found that the size and shape of ZnO nanoparticles and the way of their aggregation depend on the mole ratio [TEA]/[Zn(acac) 2 ] and the type of alcohol used as a solvent. Doubling the molar ratio of TEA to Zn(acac) 2 in the presence of ethanol favoured the formation of huge spherical aggregates (>3 mm) assembled from fine and uniform ZnO nanoparticles (~20 nm). The results of present investigation show a strong impact of surface interactions between the formed ZnO nanoparticles and the molecules of solvent and TEA on the way of growth and aggregation, which enables the control of their morphological properties. The results show that TEA serves as a link between primary ZnO nanoparticles to form spherical aggregates with a controllable diameter. The results of X-ray diffraction size-strain analysis indicate the presence of size anisotropy with bigger crystallites in the direction of the c-ax of the zincite lattice compared with the direction perpendicular to the c-ax. The red shift of the absorption edge and reduced band gap energies are clearly visible with the increased sample microsphere size.

Research paper thumbnail of The challenges of 157 nm nanolithography: surface morphology of silicon-based copolymers

Materials Science and Engineering: C, 2003

Lithography at 157 nm using F 2 laser is the next step after 193 nm for ULSI fabrication with dim... more Lithography at 157 nm using F 2 laser is the next step after 193 nm for ULSI fabrication with dimensions below 50nm. However there are problems related to the development of the 157 nm technology, the most important being the design of photoresists with suitable absorption at 157nm and low outgassing. On the other hand high resolution capabilities of resist depend on the surface roughness and its modification following 157nm illumination of the resist. In this communication, a copolymer of ethyl-polyhedral oligomeric silsesquioxane (ethyl-POSS) and tert-butyl methacrylate (TBMA) was evaluated for surface homogeneity, before and after exposure to 157nm at different concentrations of the homo-polymers. Surface roughness depends on the chemical composition of the resist, and AFM images of exposed areas indicate accumulation of matter at the edge of the boundaries between exposed and non-exposed areas. PAPER REFERENCE NUMBER: A480

Research paper thumbnail of Hydrothermal synthesis of alpha-Fe2O3 nanorings with the help of divalent metal cations, Mn2+, Cu2+, Zn2+ and Ni2+

Journal of Molecular Structure, 2011

The morphologies of α-Fe 2O 3 spindles and nanotubes was modified by the addition of divalent met... more The morphologies of α-Fe 2O 3 spindles and nanotubes was modified by the addition of divalent metal cations M 2+ (M = Mn, Cu, Zn, Ni). Divalent metal cations gradually modify the spindle to pseudosphere and the nanotube to nanoring particle morphologies. At a higher concentration of added divalent cations the nanodisc morphology was obtained. The SEM/EDS and TEM/EDX analyses showed that precipitates contained Fe, O and P elements, but none of the precipitates contained divalent metal cations. The XRD patterns of each investigated sample fitted well to pure hematite (α-Fe 2O 3) and there were no other phases observed. The Mössbauer and XRD lines broadened with the addition of divalent metal cations. The mean crystallite sizes were calculated using the Scherrer equation from XRD line broadening of 104 and 110 lines of hematite. With the addition of a Mn 2+ cation the mean crystallite size gradually increased in the a-axis direction. The relative high value of the mean crystallite size in the a-axis direction was found for nanorings modified by a Cu 2+ cation. This high crystal distortion in the a-axis direction upon adding Cu 2+ was explained by a strong Jahn-Teller effect of Cu 2+ that has a tetragonally distorted coordination sphere in an octahedral coordination. Thus, quite opposite to a pure system, the modification by divalent metal cations induced the preferential growth of α-Fe 2O 3 crystals in the a-axis direction. It was suggested that divalent metal cations introduced the defects into the planes parallel to the basal plane (0 0 1) and thus changed the type of hydroxyl groups on hematite planes, which as a consequence switched the preferential growth of the α-Fe 2O 3 along the c-axis to the growth along the a-axis.

Research paper thumbnail of Co nanocrystals in amorphous multilayers–a structure study

Research paper thumbnail of Analytical Electron Microscopy of Advanced Ceramic Materials

Research paper thumbnail of Effects of PbO excess in Pb(Mg1/3Nb2/3)O3–PbTiO3 ceramics: Part I. Sintering and dielectric properties

Journal of Materials Research, 1999

... M. Villegas, JF Fernández, and AC Caballero Electroceramics Department, Instituto de Cerámica... more ... M. Villegas, JF Fernández, and AC Caballero Electroceramics Department, Instituto de Cerámica y Vidrio, CSIC, 28500 Arganda del Rey, Madrid ... transmission electron microscopy (TEM) study of the sintered specimens revealed a core-shell structure in more than 30% of grains. ...

Research paper thumbnail of Cuprous Oxide Nanowires Prepared by an Additive-Free Polyol Process

Crystal Growth & Design, 2007

The polyol method was employed for the first time to synthesize cuprous oxide nanowires using onl... more The polyol method was employed for the first time to synthesize cuprous oxide nanowires using only a precursor of Cu(II) acetate monohydrate and diethylene glycol (DEG). With careful control of the reaction temperature (190°C), the precursor concentration (0.01-0.1 mol/L), and the reaction time (6 h), we prepared Cu 2 O nanowires with a diameter of approximately 20 nm and a length up to 5 µm. The nanowires were characterized by SEM, TEM, XRD, and IR spectroscopy.

Research paper thumbnail of Effect of chloride on the sinterization of Au/CeO2 catalysts

Research paper thumbnail of Photodeposition of Au and Pt on ZnO and TiO2

Studies in Surface Science and Catalysis, 2010

Research paper thumbnail of Gold nanoparticles on ceria supports for the oxidation of carbon monoxide

Research paper thumbnail of Catalytic performance of Au/ZnO nanocatalysts for CO oxidation

Journal of Catalysis, 2010

Research paper thumbnail of Preparation of Au nanoparticles on Ce-Ti-O supports

Studies in Surface Science and Catalysis, 2010

Research paper thumbnail of Titanium dioxide nanoparticle based materials for photocatalytic conversion of water pollutants

Nanocomposites for waste water treatment, 2014

Research paper thumbnail of Influence of aggregates on sintering of MgCrO sub (4)-TiO sub (2) solid solution

Research paper thumbnail of Conditions for formation of germanium quantum dots in amorphous matrices by MeV ions: Comparison with standard thermal annealing

We investigate how MeV ions with different ion-beam parameters (ion type, electronic stopping pow... more We investigate how MeV ions with different ion-beam parameters (ion type, electronic stopping power, and velocity) influence the formation, arrangement, and ordering quality in three types of (Ge + SiO 2 )/SiO 2 multilayer films. The multilayers differ in total thickness, Ge-rich layer thickness, and Ge content. The results show that the most important parameter for structural manipulation with MeV ions is the electronic stopping power S e . Ion velocity is found to be another crucial parameter, while at the same time it can be seen that the multilayer type does not play an important role. The temperature increase within the ion tracks is estimated using the thermal spike model and cluster separation distribution. The structural changes produced by ion beams and estimated temperatures are compared to those obtained by standard thermal annealing. It is concluded that the estimated temperatures within the ion tracks are in excellent agreement with the annealing temperatures and with the structural changes observed in the irradiated multilayers. Furthermore, a characteristic parameter of the temperature profile that presents the model-predicted temperature increase is determined for which the structural changes caused by ion beams are comparable to those achieved by standard annealing.

Research paper thumbnail of Effects of PbO excess in Pb (Mg~ 1~/~ 3Nb~ 2~/~ 3O~ 3-PbTiO~ 3 ceramics: Part II. Microstructure development

JOURNAL OF …, 1999

... M. Villegas, JF Fernández, and AC Caballero Electroceramics Department, Instituto de Cerámica... more ... M. Villegas, JF Fernández, and AC Caballero Electroceramics Department, Instituto de Cerámica y Vidrio, CSIC, 28500 Arganda del Rey, Madrid ... transmission electron microscopy (TEM) study of the sintered specimens revealed a core-shell structure in more than 30% of grains. ...

Research paper thumbnail of Evaluation of activation characteristics of silicon carbide in a fusion spectrum

… Nuclear Energy for New …, 2008

... 25 0.0E+00 3.0E+06 6.0E+06 9.0E+06 1.2E+07 1.5E+07 1.8E+07 neutron energy [eV] relative sp ec... more ... 25 0.0E+00 3.0E+06 6.0E+06 9.0E+06 1.2E+07 1.5E+07 1.8E+07 neutron energy [eV] relative sp ectru m [leth arg y scale] ... 1202-1205. [2] MJ Loughlin, RA Forrest, “Comprehensive activation calculations of reference materials for near term reactor concepts”, Fusion Eng. Des. ...

Research paper thumbnail of Preparation of alumina ceramics from aqueous suspensions employing the hydrolysis of aluminum nitride

Journal of Materials Research, 2002

ABSTRACT This paper summarizes the effects of selected processing parameters on the behavior of a... more ABSTRACT This paper summarizes the effects of selected processing parameters on the behavior of aqueous alumina suspensions during hydrolysis-assisted solidification and on the properties of the green and sintered parts prepared by this technique. Measurements of the changes in viscosity, the pH, and the impedance of aqueous suspensions with time were performed to evaluate the process. Using impedance spectroscopy, the effects of the addition of AlN, the solids content in the ceramic suspension, and the effect of the solidification temperature on the progress of solidification were followed. It was demonstrated that the solidification temperature significantly affects not only the solidification rate but also the properties of the green and sintered parts. A transmission electron microscopy analysis of dry green parts revealed that the host ceramic particles are bound by a predominantly amorphous AlOOH phase, which results in a high strength for the green parts.

Research paper thumbnail of Synthesis of magnetic iron oxide nanoparticles for biomedical applications

Magnetic iron oxide nanoparticles have been synthesized by an hydrothermal method using three dif... more Magnetic iron oxide nanoparticles have been synthesized by an hydrothermal method using three different iron precursors. The yield of synthesis was determined for all samples and found to be dependent on the iron precursor, solution pH and reaction time. The ...

Research paper thumbnail of Ge quantum dot lattices in Al2O3 multilayers

Journal of Nanoparticle Research, 2013

ABSTRACT In this article, we show how to produce materials consisting of regularly ordered Ge qua... more ABSTRACT In this article, we show how to produce materials consisting of regularly ordered Ge quantum dot lattices in an amorphous alumina matrix with a controllable Ge quantum dot size, shape, spacing, crystalline structure, and degree of regularity in their ordering. The production of such materials is achievable already at room temperature by magnetron sputtering deposition of a (Ge + Al2O3)/Al2O3 multilayer. The materials show photoluminescence in the visible and ultraviolet light range, a size-dependent blue shift of the photoluminescence peak and an enhancement of its intensity by size reduction, indicating the quantum dot origin of the photoluminescence. The materials also exhibit excellent mechanical properties due to the alumina matrix. Their internal structure is shown to be highly resistive to irradiation with energetic particles for a large range of the irradiation parameters.

Research paper thumbnail of Solvothermal synthesis of zinc oxide microspheres

The solvothermal synthesis of ZnO particles from zinc acetylacetonate [Zn(acac) 2 ] in the presen... more The solvothermal synthesis of ZnO particles from zinc acetylacetonate [Zn(acac) 2 ] in the presence of triethanolamine (TEA) and various solvent systems at 170 C is reported. The structural, optical and morphological characteristics of ZnO particles were investigated. It was found that the size and shape of ZnO nanoparticles and the way of their aggregation depend on the mole ratio [TEA]/[Zn(acac) 2 ] and the type of alcohol used as a solvent. Doubling the molar ratio of TEA to Zn(acac) 2 in the presence of ethanol favoured the formation of huge spherical aggregates (>3 mm) assembled from fine and uniform ZnO nanoparticles (~20 nm). The results of present investigation show a strong impact of surface interactions between the formed ZnO nanoparticles and the molecules of solvent and TEA on the way of growth and aggregation, which enables the control of their morphological properties. The results show that TEA serves as a link between primary ZnO nanoparticles to form spherical aggregates with a controllable diameter. The results of X-ray diffraction size-strain analysis indicate the presence of size anisotropy with bigger crystallites in the direction of the c-ax of the zincite lattice compared with the direction perpendicular to the c-ax. The red shift of the absorption edge and reduced band gap energies are clearly visible with the increased sample microsphere size.

Research paper thumbnail of The challenges of 157 nm nanolithography: surface morphology of silicon-based copolymers

Materials Science and Engineering: C, 2003

Lithography at 157 nm using F 2 laser is the next step after 193 nm for ULSI fabrication with dim... more Lithography at 157 nm using F 2 laser is the next step after 193 nm for ULSI fabrication with dimensions below 50nm. However there are problems related to the development of the 157 nm technology, the most important being the design of photoresists with suitable absorption at 157nm and low outgassing. On the other hand high resolution capabilities of resist depend on the surface roughness and its modification following 157nm illumination of the resist. In this communication, a copolymer of ethyl-polyhedral oligomeric silsesquioxane (ethyl-POSS) and tert-butyl methacrylate (TBMA) was evaluated for surface homogeneity, before and after exposure to 157nm at different concentrations of the homo-polymers. Surface roughness depends on the chemical composition of the resist, and AFM images of exposed areas indicate accumulation of matter at the edge of the boundaries between exposed and non-exposed areas. PAPER REFERENCE NUMBER: A480

Research paper thumbnail of Hydrothermal synthesis of alpha-Fe2O3 nanorings with the help of divalent metal cations, Mn2+, Cu2+, Zn2+ and Ni2+

Journal of Molecular Structure, 2011

The morphologies of α-Fe 2O 3 spindles and nanotubes was modified by the addition of divalent met... more The morphologies of α-Fe 2O 3 spindles and nanotubes was modified by the addition of divalent metal cations M 2+ (M = Mn, Cu, Zn, Ni). Divalent metal cations gradually modify the spindle to pseudosphere and the nanotube to nanoring particle morphologies. At a higher concentration of added divalent cations the nanodisc morphology was obtained. The SEM/EDS and TEM/EDX analyses showed that precipitates contained Fe, O and P elements, but none of the precipitates contained divalent metal cations. The XRD patterns of each investigated sample fitted well to pure hematite (α-Fe 2O 3) and there were no other phases observed. The Mössbauer and XRD lines broadened with the addition of divalent metal cations. The mean crystallite sizes were calculated using the Scherrer equation from XRD line broadening of 104 and 110 lines of hematite. With the addition of a Mn 2+ cation the mean crystallite size gradually increased in the a-axis direction. The relative high value of the mean crystallite size in the a-axis direction was found for nanorings modified by a Cu 2+ cation. This high crystal distortion in the a-axis direction upon adding Cu 2+ was explained by a strong Jahn-Teller effect of Cu 2+ that has a tetragonally distorted coordination sphere in an octahedral coordination. Thus, quite opposite to a pure system, the modification by divalent metal cations induced the preferential growth of α-Fe 2O 3 crystals in the a-axis direction. It was suggested that divalent metal cations introduced the defects into the planes parallel to the basal plane (0 0 1) and thus changed the type of hydroxyl groups on hematite planes, which as a consequence switched the preferential growth of the α-Fe 2O 3 along the c-axis to the growth along the a-axis.

Research paper thumbnail of Co nanocrystals in amorphous multilayers–a structure study

Research paper thumbnail of Analytical Electron Microscopy of Advanced Ceramic Materials

Research paper thumbnail of Effects of PbO excess in Pb(Mg1/3Nb2/3)O3–PbTiO3 ceramics: Part I. Sintering and dielectric properties

Journal of Materials Research, 1999

... M. Villegas, JF Fernández, and AC Caballero Electroceramics Department, Instituto de Cerámica... more ... M. Villegas, JF Fernández, and AC Caballero Electroceramics Department, Instituto de Cerámica y Vidrio, CSIC, 28500 Arganda del Rey, Madrid ... transmission electron microscopy (TEM) study of the sintered specimens revealed a core-shell structure in more than 30% of grains. ...

Research paper thumbnail of Cuprous Oxide Nanowires Prepared by an Additive-Free Polyol Process

Crystal Growth & Design, 2007

The polyol method was employed for the first time to synthesize cuprous oxide nanowires using onl... more The polyol method was employed for the first time to synthesize cuprous oxide nanowires using only a precursor of Cu(II) acetate monohydrate and diethylene glycol (DEG). With careful control of the reaction temperature (190°C), the precursor concentration (0.01-0.1 mol/L), and the reaction time (6 h), we prepared Cu 2 O nanowires with a diameter of approximately 20 nm and a length up to 5 µm. The nanowires were characterized by SEM, TEM, XRD, and IR spectroscopy.

Research paper thumbnail of Effect of chloride on the sinterization of Au/CeO2 catalysts

Research paper thumbnail of Photodeposition of Au and Pt on ZnO and TiO2

Studies in Surface Science and Catalysis, 2010

Research paper thumbnail of Gold nanoparticles on ceria supports for the oxidation of carbon monoxide

Research paper thumbnail of Catalytic performance of Au/ZnO nanocatalysts for CO oxidation

Journal of Catalysis, 2010

Research paper thumbnail of Preparation of Au nanoparticles on Ce-Ti-O supports

Studies in Surface Science and Catalysis, 2010

Research paper thumbnail of Titanium dioxide nanoparticle based materials for photocatalytic conversion of water pollutants

Nanocomposites for waste water treatment, 2014

Research paper thumbnail of Influence of aggregates on sintering of MgCrO sub (4)-TiO sub (2) solid solution

Research paper thumbnail of Conditions for formation of germanium quantum dots in amorphous matrices by MeV ions: Comparison with standard thermal annealing

We investigate how MeV ions with different ion-beam parameters (ion type, electronic stopping pow... more We investigate how MeV ions with different ion-beam parameters (ion type, electronic stopping power, and velocity) influence the formation, arrangement, and ordering quality in three types of (Ge + SiO 2 )/SiO 2 multilayer films. The multilayers differ in total thickness, Ge-rich layer thickness, and Ge content. The results show that the most important parameter for structural manipulation with MeV ions is the electronic stopping power S e . Ion velocity is found to be another crucial parameter, while at the same time it can be seen that the multilayer type does not play an important role. The temperature increase within the ion tracks is estimated using the thermal spike model and cluster separation distribution. The structural changes produced by ion beams and estimated temperatures are compared to those obtained by standard thermal annealing. It is concluded that the estimated temperatures within the ion tracks are in excellent agreement with the annealing temperatures and with the structural changes observed in the irradiated multilayers. Furthermore, a characteristic parameter of the temperature profile that presents the model-predicted temperature increase is determined for which the structural changes caused by ion beams are comparable to those achieved by standard annealing.

Research paper thumbnail of Effects of PbO excess in Pb (Mg~ 1~/~ 3Nb~ 2~/~ 3O~ 3-PbTiO~ 3 ceramics: Part II. Microstructure development

JOURNAL OF …, 1999

... M. Villegas, JF Fernández, and AC Caballero Electroceramics Department, Instituto de Cerámica... more ... M. Villegas, JF Fernández, and AC Caballero Electroceramics Department, Instituto de Cerámica y Vidrio, CSIC, 28500 Arganda del Rey, Madrid ... transmission electron microscopy (TEM) study of the sintered specimens revealed a core-shell structure in more than 30% of grains. ...

Research paper thumbnail of Evaluation of activation characteristics of silicon carbide in a fusion spectrum

… Nuclear Energy for New …, 2008

... 25 0.0E+00 3.0E+06 6.0E+06 9.0E+06 1.2E+07 1.5E+07 1.8E+07 neutron energy [eV] relative sp ec... more ... 25 0.0E+00 3.0E+06 6.0E+06 9.0E+06 1.2E+07 1.5E+07 1.8E+07 neutron energy [eV] relative sp ectru m [leth arg y scale] ... 1202-1205. [2] MJ Loughlin, RA Forrest, “Comprehensive activation calculations of reference materials for near term reactor concepts”, Fusion Eng. Des. ...

Research paper thumbnail of Preparation of alumina ceramics from aqueous suspensions employing the hydrolysis of aluminum nitride

Journal of Materials Research, 2002

ABSTRACT This paper summarizes the effects of selected processing parameters on the behavior of a... more ABSTRACT This paper summarizes the effects of selected processing parameters on the behavior of aqueous alumina suspensions during hydrolysis-assisted solidification and on the properties of the green and sintered parts prepared by this technique. Measurements of the changes in viscosity, the pH, and the impedance of aqueous suspensions with time were performed to evaluate the process. Using impedance spectroscopy, the effects of the addition of AlN, the solids content in the ceramic suspension, and the effect of the solidification temperature on the progress of solidification were followed. It was demonstrated that the solidification temperature significantly affects not only the solidification rate but also the properties of the green and sintered parts. A transmission electron microscopy analysis of dry green parts revealed that the host ceramic particles are bound by a predominantly amorphous AlOOH phase, which results in a high strength for the green parts.

Research paper thumbnail of Synthesis of magnetic iron oxide nanoparticles for biomedical applications

Magnetic iron oxide nanoparticles have been synthesized by an hydrothermal method using three dif... more Magnetic iron oxide nanoparticles have been synthesized by an hydrothermal method using three different iron precursors. The yield of synthesis was determined for all samples and found to be dependent on the iron precursor, solution pH and reaction time. The ...