Andrei Mardare - Academia.edu (original) (raw)
Papers by Andrei Mardare
The Journal of Physical Chemistry C, Feb 26, 2009
Gold nanoparticles with diameters ranging from 3.2 to 9.7 nm were prepared on an ultrathin anodic... more Gold nanoparticles with diameters ranging from 3.2 to 9.7 nm were prepared on an ultrathin anodic aluminum film by means of molecular beam deposition. Coverages ranging from 17.9% to 48.5% and the subsequent anodic anodization behavior were studied. Further oxide growth does not completely cover the gold nanoparticles but takes place preferentially under the particles with a surprisingly low kinetic hindrance. The gold nanoparticles are electrically isolated from the substrate as demonstrated by the absence of electrocatalytic reactions on the gold surface. A strong surface charge phenomenon is observed, which increases with increasing gold coverage that yields an increase of the capacity up to the minimum potential required for further oxide formation.
The Review of Scientific Instruments, Apr 1, 2009
Automatized microelectrochemical investigations are achieved using a scanning droplet cell. The a... more Automatized microelectrochemical investigations are achieved using a scanning droplet cell. The area reproducibility for a 100 μm oxide spot is found to be better than 1%, a value typically difficult to reach even in macroscopic samples. A systematic change in color appearance is seen for oxide films with a thickness ranging from 14 to 27 nm. Analysis of optical images yields a strictly linear relation between relative transmission and anodization charge and thus allows determination of the oxide thickness with a remarkable precision better than 0.5 nm at an absolute film thickness value that is at least a factor of 20 smaller than the wavelength of light.
Materials Science Forum, 2006
ABSTRACT Three types of bottom electrodes were deposited by RF magnetron sputtering on SiO2/Si su... more ABSTRACT Three types of bottom electrodes were deposited by RF magnetron sputtering on SiO2/Si substrates: LaNiO3 (LNO), Pt/Ti and LNO/Pt/Ti. The effect of different deposition and processing conditions for the LNO films on the ferroelectric properties of sputtered Pb(Zr0.52Ti0.48)O-3 (PZT) capacitors was investigated. The LNO films were either deposited at room temperature and heat-treated in O-2 flow in the furnace at 500 or 600 degrees C or made in situ in the range of 200-500 degrees C. Other deposition parameters under study were the pressure, the RF power and the Ar:O-2 ratio. The resistivity of the LNO films was measured and on some of the films with the lower values, amorphous PZT was deposited and then crystallized in the furnace. X-ray diffraction results show that the PZT films deposited over Pt/Ti had a preferential (100) orientation, while those deposited over LNO made in situ are strongly (100) oriented and the ones deposited over amorphous LNO do not exhibit any preferential orientation. The remanent polarization of the capacitors was around 28 mu C/cm(2) when amorphous LNO or Pt/Ti electrodes were used and around 20 mu C/cm(2) with LNO made in situ. Leakage currents were improved when LNO electrodes made in situ was used; a good ferroelectric fatigue performance of the capacitors when subjected to 10(10) switching cycles was also observed.
Mater Sci Forum, 2006
ABSTRACT A dense ceramic target of BiFeO3 was synthesized by the urea combustion method. X-ray di... more ABSTRACT A dense ceramic target of BiFeO3 was synthesized by the urea combustion method. X-ray diffraction indicates that this target is composed of a mixture of phases, the main one is BiFeO3, but Bi46Fe2O72 and Bi2Fe4O9 are also present in small amounts. The BiFeO3 target was used for depositing thin films on Pt/Ti/SiO2/Si substrates by the laser ablation technique. The depositions were made in oxygen atmosphere at pressures in the range between 5x10(-3) and 2x10(-2) mbar, using a KrF laser. The substrate temperatures were 450 or 500 degrees C and the laser energy, the frequency and the distance between the target and the substrate were kept constant at 125mJ, 10Hz and 4cm, respectively. After a deposition time of 30minutes the thickness of the films was approximately 400nm. Some of the films were heat-treated in situ, in 100mbar O-2 for 30minutes, at the same temperatures used for deposition. X-ray diffraction results show the BiFeO3 phase, as well as some Bi46Fe2O72 and Bi2Fe4O9. The films were crystallized without any preferential orientation, but the ones made at 2x10(-2) mbar and 450 degrees C were partially amorphous. For measuring the ferroelectric hysteresis loops, either All top electrodes were deposited by thermal evaporation or Pt, by sputtering. The distorted shapes of the hysteresis loops obtained indicated that the films exhibit weak ferroelectric properties and high leakage current values.
Journal of the Electrochemical Society, 2015
High throughput screening of photoelectrochemical activity was performed on a WO 3 -CoO thin film... more High throughput screening of photoelectrochemical activity was performed on a WO 3 -CoO thin film combinatorial library using photoelectrochemical scanning droplet cell microscopy. The compositional spread was deposited using co-evaporation of WO 3 and metallic Co followed by thermal oxidation in pure oxygen. The elemental compositional mapping along the library via EDX revealed a total compositional gradient of 29 at%. The microstructure and crystallographic properties were investigated via SEM and XRD. Small cubic grains of WO 3 were identified on the surface for Co contents up to 13 at% while CoO remained amorphous along the entire library in mixture with both cubic and orthorhombic WO 3 . A remarkable peak of photoactivity was identified in a compositional range of 7 to 15 at% Co with current density values in excess of 110 μA cm −2 for an applied potential of 1 V vs. SHE. Surface XPS investigations were used for correlating the bulk and surface composition of the library. In the compositional region corresponding to the maximum photoactivity peak, a constant W/Co atomic ratio was measured on the surface while the corresponding bulk ratio was increasing. This effect could be the result of a mixed contribution from an enhanced electrocatalytic activity for oxygen evolution on the surface and increased bulk radiation absorption.
Electrochimica Acta, Sep 1, 2009
A comprehensive study of the anodic oxide formation on HfTi alloys over the entire range of comp... more A comprehensive study of the anodic oxide formation on HfTi alloys over the entire range of composition was conducted. Combinatorial thin film libraries were prepared by co-sputtering. HRSEM and XRD were used to characterize the thin films and to confirm ...
Automatized microelectrochemical investigations are achieved using a scanning droplet cell. The a... more Automatized microelectrochemical investigations are achieved using a scanning droplet cell. The area reproducibility for a 100 mum oxide spot is found to be better than 1%, a value typically difficult to reach even in macroscopic samples. A systematic change in color appearance is seen for oxide films with a thickness ranging from 14 to 27 nm. Analysis of optical images yields a strictly linear relation between relative transmission and anodization charge and thus allows determination of the oxide thickness with a remarkable precision better than 0.5 nm at an absolute film thickness value that is at least a factor of 20 smaller than the wavelength of light.
Electrochimica Acta, 2015
physica status solidi (a), 2015
Journal of the Electrochemical Society, 2015
Thin Solid Films, 2015
ABSTRACT
physica status solidi (a), 2015
ABSTRACT A CuZn thin film combinatorial library was fabricated using a thermal co-evaporator. Usi... more ABSTRACT A CuZn thin film combinatorial library was fabricated using a thermal co-evaporator. Using scanning electron microscopy (SEM), X-ray fluorescence spectroscopy (XRF) and X-ray diffraction (XRD) microcstructure, composition and crystallographic properties were investigated. Pure brass alloys were evidenced due to solid solution mixing of Cu and Zn. The crystallite size and lattice parameters were calculated and compared with values of pure Cu and α-brass. With the aid of scanning in a wide compositional spread (3.4 at.% Zn to 27 at.% Zn). droplet cell microscopy (SDCM) the thermally evaporated CuZn thin film combinatorial library was screened for electrocatalytic effects on the formaldehyde oxidation. The obtained cyclic voltammograms show the occurrence of the formaldehyde oxidation leading to formic acid. CuZn thin film alloys were examined for their electrocatalytic oxidation of formaldehyde in an aqueous 0.1 M Na2SO4 solution at different pH values using cyclic voltammetry. The highest catalytic effect was obtained at a pH value of 13.0 for a composition of Cu–8.0 at.% Zn.
Materials Science Forum, 2006
Journal of Solid State Electrochemistry, 2016
Aluminium terbium alloys were prepared by simultaneous thermal evaporation resulting in a thin fi... more Aluminium terbium alloys were prepared by simultaneous thermal evaporation resulting in a thin film library covering a 5 to 25 at.% Tb compositional spread. Synchrotron x-ray diffraction (XRD) proves all of the alloys to be amorphous. Scanning electron microscopy (SEM) measurements reveal the structural changes upon increase in Tb content with the formation of small, Tb-rich segregations right before a drastic change in morphology around 25 at.% Tb. Anodic oxides were formed systematically in cyclic voltammograms using scanning droplet cell microscopy. Coulometric analysis revealed a linear thickness over formation potential behaviour with film formation factors ranging from 1.2 nm V(-1) (5 at.% Tb) to 1.6 nm V(-1) (25 % Tb). Electrochemical impedance spectroscopy was performed for each incremental oxidation step resulting in a linear relation between inverse capacity and formation potential with dielectric constants ranging from 8 (5 at.% Tb) to 16 (25 at.% Tb).
Materials Science Forum, 2006
ABSTRACT Three types of bottom electrodes were deposited by RF magnetron sputtering on SiO2/Si su... more ABSTRACT Three types of bottom electrodes were deposited by RF magnetron sputtering on SiO2/Si substrates: LaNiO3 (LNO), Pt/Ti and LNO/Pt/Ti. The effect of different deposition and processing conditions for the LNO films on the ferroelectric properties of sputtered Pb(Zr0.52Ti0.48)O-3 (PZT) capacitors was investigated. The LNO films were either deposited at room temperature and heat-treated in O-2 flow in the furnace at 500 or 600 degrees C or made in situ in the range of 200-500 degrees C. Other deposition parameters under study were the pressure, the RF power and the Ar:O-2 ratio. The resistivity of the LNO films was measured and on some of the films with the lower values, amorphous PZT was deposited and then crystallized in the furnace. X-ray diffraction results show that the PZT films deposited over Pt/Ti had a preferential (100) orientation, while those deposited over LNO made in situ are strongly (100) oriented and the ones deposited over amorphous LNO do not exhibit any preferential orientation. The remanent polarization of the capacitors was around 28 mu C/cm(2) when amorphous LNO or Pt/Ti electrodes were used and around 20 mu C/cm(2) with LNO made in situ. Leakage currents were improved when LNO electrodes made in situ was used; a good ferroelectric fatigue performance of the capacitors when subjected to 10(10) switching cycles was also observed.
physica status solidi (a), 2015
Materials Science Forum, 2006
The Journal of Physical Chemistry C, Feb 26, 2009
Gold nanoparticles with diameters ranging from 3.2 to 9.7 nm were prepared on an ultrathin anodic... more Gold nanoparticles with diameters ranging from 3.2 to 9.7 nm were prepared on an ultrathin anodic aluminum film by means of molecular beam deposition. Coverages ranging from 17.9% to 48.5% and the subsequent anodic anodization behavior were studied. Further oxide growth does not completely cover the gold nanoparticles but takes place preferentially under the particles with a surprisingly low kinetic hindrance. The gold nanoparticles are electrically isolated from the substrate as demonstrated by the absence of electrocatalytic reactions on the gold surface. A strong surface charge phenomenon is observed, which increases with increasing gold coverage that yields an increase of the capacity up to the minimum potential required for further oxide formation.
The Review of Scientific Instruments, Apr 1, 2009
Automatized microelectrochemical investigations are achieved using a scanning droplet cell. The a... more Automatized microelectrochemical investigations are achieved using a scanning droplet cell. The area reproducibility for a 100 μm oxide spot is found to be better than 1%, a value typically difficult to reach even in macroscopic samples. A systematic change in color appearance is seen for oxide films with a thickness ranging from 14 to 27 nm. Analysis of optical images yields a strictly linear relation between relative transmission and anodization charge and thus allows determination of the oxide thickness with a remarkable precision better than 0.5 nm at an absolute film thickness value that is at least a factor of 20 smaller than the wavelength of light.
Materials Science Forum, 2006
ABSTRACT Three types of bottom electrodes were deposited by RF magnetron sputtering on SiO2/Si su... more ABSTRACT Three types of bottom electrodes were deposited by RF magnetron sputtering on SiO2/Si substrates: LaNiO3 (LNO), Pt/Ti and LNO/Pt/Ti. The effect of different deposition and processing conditions for the LNO films on the ferroelectric properties of sputtered Pb(Zr0.52Ti0.48)O-3 (PZT) capacitors was investigated. The LNO films were either deposited at room temperature and heat-treated in O-2 flow in the furnace at 500 or 600 degrees C or made in situ in the range of 200-500 degrees C. Other deposition parameters under study were the pressure, the RF power and the Ar:O-2 ratio. The resistivity of the LNO films was measured and on some of the films with the lower values, amorphous PZT was deposited and then crystallized in the furnace. X-ray diffraction results show that the PZT films deposited over Pt/Ti had a preferential (100) orientation, while those deposited over LNO made in situ are strongly (100) oriented and the ones deposited over amorphous LNO do not exhibit any preferential orientation. The remanent polarization of the capacitors was around 28 mu C/cm(2) when amorphous LNO or Pt/Ti electrodes were used and around 20 mu C/cm(2) with LNO made in situ. Leakage currents were improved when LNO electrodes made in situ was used; a good ferroelectric fatigue performance of the capacitors when subjected to 10(10) switching cycles was also observed.
Mater Sci Forum, 2006
ABSTRACT A dense ceramic target of BiFeO3 was synthesized by the urea combustion method. X-ray di... more ABSTRACT A dense ceramic target of BiFeO3 was synthesized by the urea combustion method. X-ray diffraction indicates that this target is composed of a mixture of phases, the main one is BiFeO3, but Bi46Fe2O72 and Bi2Fe4O9 are also present in small amounts. The BiFeO3 target was used for depositing thin films on Pt/Ti/SiO2/Si substrates by the laser ablation technique. The depositions were made in oxygen atmosphere at pressures in the range between 5x10(-3) and 2x10(-2) mbar, using a KrF laser. The substrate temperatures were 450 or 500 degrees C and the laser energy, the frequency and the distance between the target and the substrate were kept constant at 125mJ, 10Hz and 4cm, respectively. After a deposition time of 30minutes the thickness of the films was approximately 400nm. Some of the films were heat-treated in situ, in 100mbar O-2 for 30minutes, at the same temperatures used for deposition. X-ray diffraction results show the BiFeO3 phase, as well as some Bi46Fe2O72 and Bi2Fe4O9. The films were crystallized without any preferential orientation, but the ones made at 2x10(-2) mbar and 450 degrees C were partially amorphous. For measuring the ferroelectric hysteresis loops, either All top electrodes were deposited by thermal evaporation or Pt, by sputtering. The distorted shapes of the hysteresis loops obtained indicated that the films exhibit weak ferroelectric properties and high leakage current values.
Journal of the Electrochemical Society, 2015
High throughput screening of photoelectrochemical activity was performed on a WO 3 -CoO thin film... more High throughput screening of photoelectrochemical activity was performed on a WO 3 -CoO thin film combinatorial library using photoelectrochemical scanning droplet cell microscopy. The compositional spread was deposited using co-evaporation of WO 3 and metallic Co followed by thermal oxidation in pure oxygen. The elemental compositional mapping along the library via EDX revealed a total compositional gradient of 29 at%. The microstructure and crystallographic properties were investigated via SEM and XRD. Small cubic grains of WO 3 were identified on the surface for Co contents up to 13 at% while CoO remained amorphous along the entire library in mixture with both cubic and orthorhombic WO 3 . A remarkable peak of photoactivity was identified in a compositional range of 7 to 15 at% Co with current density values in excess of 110 μA cm −2 for an applied potential of 1 V vs. SHE. Surface XPS investigations were used for correlating the bulk and surface composition of the library. In the compositional region corresponding to the maximum photoactivity peak, a constant W/Co atomic ratio was measured on the surface while the corresponding bulk ratio was increasing. This effect could be the result of a mixed contribution from an enhanced electrocatalytic activity for oxygen evolution on the surface and increased bulk radiation absorption.
Electrochimica Acta, Sep 1, 2009
A comprehensive study of the anodic oxide formation on HfTi alloys over the entire range of comp... more A comprehensive study of the anodic oxide formation on HfTi alloys over the entire range of composition was conducted. Combinatorial thin film libraries were prepared by co-sputtering. HRSEM and XRD were used to characterize the thin films and to confirm ...
Automatized microelectrochemical investigations are achieved using a scanning droplet cell. The a... more Automatized microelectrochemical investigations are achieved using a scanning droplet cell. The area reproducibility for a 100 mum oxide spot is found to be better than 1%, a value typically difficult to reach even in macroscopic samples. A systematic change in color appearance is seen for oxide films with a thickness ranging from 14 to 27 nm. Analysis of optical images yields a strictly linear relation between relative transmission and anodization charge and thus allows determination of the oxide thickness with a remarkable precision better than 0.5 nm at an absolute film thickness value that is at least a factor of 20 smaller than the wavelength of light.
Electrochimica Acta, 2015
physica status solidi (a), 2015
Journal of the Electrochemical Society, 2015
Thin Solid Films, 2015
ABSTRACT
physica status solidi (a), 2015
ABSTRACT A CuZn thin film combinatorial library was fabricated using a thermal co-evaporator. Usi... more ABSTRACT A CuZn thin film combinatorial library was fabricated using a thermal co-evaporator. Using scanning electron microscopy (SEM), X-ray fluorescence spectroscopy (XRF) and X-ray diffraction (XRD) microcstructure, composition and crystallographic properties were investigated. Pure brass alloys were evidenced due to solid solution mixing of Cu and Zn. The crystallite size and lattice parameters were calculated and compared with values of pure Cu and α-brass. With the aid of scanning in a wide compositional spread (3.4 at.% Zn to 27 at.% Zn). droplet cell microscopy (SDCM) the thermally evaporated CuZn thin film combinatorial library was screened for electrocatalytic effects on the formaldehyde oxidation. The obtained cyclic voltammograms show the occurrence of the formaldehyde oxidation leading to formic acid. CuZn thin film alloys were examined for their electrocatalytic oxidation of formaldehyde in an aqueous 0.1 M Na2SO4 solution at different pH values using cyclic voltammetry. The highest catalytic effect was obtained at a pH value of 13.0 for a composition of Cu–8.0 at.% Zn.
Materials Science Forum, 2006
Journal of Solid State Electrochemistry, 2016
Aluminium terbium alloys were prepared by simultaneous thermal evaporation resulting in a thin fi... more Aluminium terbium alloys were prepared by simultaneous thermal evaporation resulting in a thin film library covering a 5 to 25 at.% Tb compositional spread. Synchrotron x-ray diffraction (XRD) proves all of the alloys to be amorphous. Scanning electron microscopy (SEM) measurements reveal the structural changes upon increase in Tb content with the formation of small, Tb-rich segregations right before a drastic change in morphology around 25 at.% Tb. Anodic oxides were formed systematically in cyclic voltammograms using scanning droplet cell microscopy. Coulometric analysis revealed a linear thickness over formation potential behaviour with film formation factors ranging from 1.2 nm V(-1) (5 at.% Tb) to 1.6 nm V(-1) (25 % Tb). Electrochemical impedance spectroscopy was performed for each incremental oxidation step resulting in a linear relation between inverse capacity and formation potential with dielectric constants ranging from 8 (5 at.% Tb) to 16 (25 at.% Tb).
Materials Science Forum, 2006
ABSTRACT Three types of bottom electrodes were deposited by RF magnetron sputtering on SiO2/Si su... more ABSTRACT Three types of bottom electrodes were deposited by RF magnetron sputtering on SiO2/Si substrates: LaNiO3 (LNO), Pt/Ti and LNO/Pt/Ti. The effect of different deposition and processing conditions for the LNO films on the ferroelectric properties of sputtered Pb(Zr0.52Ti0.48)O-3 (PZT) capacitors was investigated. The LNO films were either deposited at room temperature and heat-treated in O-2 flow in the furnace at 500 or 600 degrees C or made in situ in the range of 200-500 degrees C. Other deposition parameters under study were the pressure, the RF power and the Ar:O-2 ratio. The resistivity of the LNO films was measured and on some of the films with the lower values, amorphous PZT was deposited and then crystallized in the furnace. X-ray diffraction results show that the PZT films deposited over Pt/Ti had a preferential (100) orientation, while those deposited over LNO made in situ are strongly (100) oriented and the ones deposited over amorphous LNO do not exhibit any preferential orientation. The remanent polarization of the capacitors was around 28 mu C/cm(2) when amorphous LNO or Pt/Ti electrodes were used and around 20 mu C/cm(2) with LNO made in situ. Leakage currents were improved when LNO electrodes made in situ was used; a good ferroelectric fatigue performance of the capacitors when subjected to 10(10) switching cycles was also observed.
physica status solidi (a), 2015
Materials Science Forum, 2006