- Bucharest, Bucuresti, Romania
We report on the fabrication of dye-sensitized solar cells with a TiO2 buffer layer between the transparent conductive oxide substrate and the mesoporous TiO2 film, in order to improve the photovoltaic conversion efficiency of the device.... more
We report on the fabrication of dye-sensitized solar cells with a TiO2 buffer layer between the transparent conductive oxide substrate and the mesoporous TiO2 film, in order to improve the photovoltaic conversion efficiency of the device. The buffer layer was fabricated by pulsed laser deposition whereas the mesoporous film by the doctor blade method, using TiO2 paste obtained by the sol–gel technique. The buffer layer was deposited in either oxygen (10 Pa and 50 Pa) or argon (10 Pa and 50 Pa) onto transparent conducting oxide glass kept at room temperature. The cross-section scanning electron microscopy image showed differences in layer morphology and thickness, depending on the deposition conditions. Transmission electron microscopy studies of the TiO2 buffer layers indicated that films consisted of grains with typical diameters of 10 nm to 30 nm. We found that the photovoltaic conversion efficiencies, determined under standard air mass 1.5 global (AM 1.5G) conditions, of the sola...
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Abstract Composite silk fibroin–poly(3-hydroxybutyric-acid-co-3-hydroxyvaleric-acid) (SF–PHBV) biodegradable coatings were grown by Matrix Assisted Pulsed Laser Evaporation on titanium substrates. Their physico-chemical properties and... more
Abstract Composite silk fibroin–poly(3-hydroxybutyric-acid-co-3-hydroxyvaleric-acid) (SF–PHBV) biodegradable coatings were grown by Matrix Assisted Pulsed Laser Evaporation on titanium substrates. Their physico-chemical properties and particularly the degradation behavior in simulated body fluid at 37 °C were studied as first step of applicability in local controlled release for tissue regeneration applications. SF and PHBV, natural biopolymers with excellent biocompatibility, but different biodegradability and tensile strength properties, were combined in a composite to improve their properties as coatings for biomedical uses. FTIR analyses showed the stoichiometric transfer from targets to coatings by the presence in the spectra of the main absorption maxima characteristic of both polymers. XRD investigations confirmed the FTIR results showing differences in crystallization behavior with respect to the SF and PHBV content. Contact angle values obtained through wettability measurements indicated the MAPLE deposited coatings were highly hydrophilic; surfaces turning hydrophobic with the increase of the PHBV component. Degradation assays proved that higher PHBV contents resulted in enhanced resistance and a slower degradation rate of composite coatings in SBF. Distinct drug-release schemes could be obtained by adjusting the SF:PHBV ratio to controllably tuning the coatings degradation rate, from rapid-release formulas, where SF predominates, to prolonged sustained ones, for larger PHBV content.
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Ultraviolet photons of KrF-laser (λ = 248 nm) based on reactive pulsed laser deposition (RPLD) were used for the synthesis of chromium oxides (Cr3-XO3-Y), iron oxides (Fe2O3-X) 2D structures and Fe2O3-X/Cr3-XO3-Y 2D heterostructure with... more
Ultraviolet photons of KrF-laser (λ = 248 nm) based on reactive pulsed laser deposition (RPLD) were used for the synthesis of chromium oxides (Cr3-XO3-Y), iron oxides (Fe2O3-X) 2D structures and Fe2O3-X/Cr3-XO3-Y 2D heterostructure with variable stoichiometry, electrical properties and thickness. 2D structures' depositions were carried out on <100>Si substrate at its temperature change in the range of 293-800 K. XRD analysis showed the evidence of these structures deposited on substrate had polycrystalline phases' content. All 2D structures and heterostructures demonstrated semiconductor temperature behaviour with variable band gap (Eg) less than 1.0 eV, depending on substrate temperature, oxygen pressure in the reactor and structure thickness. Thickness of all kinds' deposits (55-75 nm) depended on oxygen pressure, substrate temperature and the number of laser pulses. The optimum oxygen pressure and substrate temperature were found when thermo electromotive force coefficient (Seebeck coefficient, S) was high as 3.0-8.0 mV/K for Cr3-XO3-Y and for Fe2O3-X 2D structures, accordingly, in the range (280-330) K. The highest S coefficient obtained for 4 layered Fe2O3-X/Cr3-XO3-Y 2D heterostructures was about 15 mV/K in the range (280-330) K. This made these 2D structures and 2D heterostructures, synthesized by UV photons using RPLD method, an exceptionally strong candidate for effective thermo sensors operating at moderate temperature.
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Ultraviolet photons of KrF-laser (λ = 248 nm) were used for the synthesis of nanometric chromium oxide films with variable thickness, stoichiometry and electrical properties. The synthesis was based on reactive pulsed laser deposition... more
Ultraviolet photons of KrF-laser (λ = 248 nm) were used for the synthesis of nanometric chromium oxide films with variable thickness, stoichiometry and electrical properties. The synthesis was based on reactive pulsed laser deposition (RPLD). Film deposition was carried out on <100>Si substrate in the range 293-800 K. XRD analysis showed evidence of films deposited on Si substrate had polycrystalline structure. All films demonstrated semiconductor temperature behaviour with variable band gap (E g) less than 1.0 eV, depending on substrate temperature, oxygen pressure in the reactor and film thickness. Film thickness (55-200 nm) depended on oxygen pressure, substrate temperature and the number of laser pulses. It was found out the optimum oxygen pressure and substrate temperature when thermo electromotive force coefficient (Seebeck coefficient, S) was high as 3.0-8.0 mV/K and, accordingly, the thermoelectric figure of merit (ZT) was high as 0.23-5.0 in the range 280-330 K. This ...
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Calcium phosphates (CaPs) are the most widely used bone substitutes in tissue engineering due to their similarity with the inorganic bone composition and excellent biocompatibility. Because of their poor mechanical properties CaPs are... more
Calcium phosphates (CaPs) are the most widely used bone substitutes in tissue engineering due to their similarity with the inorganic bone composition and excellent biocompatibility. Because of their poor mechanical properties CaPs are frequently deposited as coatings ...
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ABSTRACT ZrC thin films were grown on (100) Si substrates by the pulsed laser deposition (PLD) technique using a high-repetition rate excimer laser working at 40 Hz. The substrate temperature during depositions was set at 300 °C and the... more
ABSTRACT ZrC thin films were grown on (100) Si substrates by the pulsed laser deposition (PLD) technique using a high-repetition rate excimer laser working at 40 Hz. The substrate temperature during depositions was set at 300 °C and the cooling rate was 5 °C/min. X-ray diffraction investigations showed that the films were crystalline. Films deposited under residual vacuum or 2 × 10− 3 Pa of CH4 atmosphere exhibited a (200)-axis texture, while those deposited under 2 × 10− 2 Pa of CH4 atmosphere were found to be equiaxed. The surface elemental composition of as-deposited films, analyzed by Auger electron spectroscopy (AES), showed the usual high oxygen contamination of carbides. Once the topmost − 3–5 nm region was removed, the oxygen concentration rapidly decreased, being around 3–4% only in bulk. Scanning electron microscopy (SEM) investigations showed a smooth, featureless surface morphology, corroborating the roughness values below 1 nm (rms) obtained from simulations of the X-ray reflectivity (XRR) curves. From the same simulations we also estimated films mass density values of around 6.32–6.57 g/cm3 and thicknesses that correspond to a deposition rate of around 8.25 nm/min. Nanoindentation results showed a hardness of 27.6 GPa and a reduced modulus of 228 GPa for the best quality ZrC films deposited under an atmosphere of 2 × 10− 3 Pa CH4.
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Research Interests: Engineering, Materials Science, PHOTOELECTRON SPECTROSCOPY, ITO - Tin doped Indium Oxide, Pulsed Laser Deposition, and 10 moreThin Film, Physical sciences, Electronic Structure, CHEMICAL SCIENCES, Phase Transformation, Binding Energy, X Ray Photoelectron Spectroscopy, Energy Levels, Conversion Efficiency, and Tin Oxide
The aim of this study was to obtain biomimetic inorganicorganic thin films as coatings for metallic medical implants. These contain hydroxyapatite, the inorganic component of the bony tissues, and a natural biopolymer silk fibroin ... more
The aim of this study was to obtain biomimetic inorganicorganic thin films as coatings for metallic medical implants. These contain hydroxyapatite, the inorganic component of the bony tissues, and a natural biopolymer silk fibroin added in view to induce the surface ...
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Al(2) O(3) substrates with controlled porosity were manufactured from nanosized powders obtained by plasma processing. It was observed that when increasing the sintering temperature the overall porosity was decreasing, but the pores got... more
Al(2) O(3) substrates with controlled porosity were manufactured from nanosized powders obtained by plasma processing. It was observed that when increasing the sintering temperature the overall porosity was decreasing, but the pores got larger. In a second step, Ce stabilized ZrO(2) doped hydroxyapatite coatings were pulsed laser deposited onto the Al(2) O(3) substrates. It was shown that the surface morphology, consisting of aggregates and particulates in micrometric range, was altered by the substrate porosity and interface properties, respectively. TEM studies evidenced that Ce stabilized ZrO(2) doped HA particulates ranged from 10 to 50 nm, strongly depending on the Al(2) O(3) porosity. The coatings consisted of HA nanocrystals embedded in an amorphous matrix quite similar to the bone structure. These findings were congruent with the increased biocompatibility and bioactivity of these layers confirmed by enhanced growing and proliferation of human mesenchymal stem cells.
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... II. PKTien, R.Ulrich, and RJMartin, MODES OF PROPAGATING LIGHT WAVES IN THIN DEPOSITED SEMICONDUCTOR FILMS, Appl. Phys. Lett. ... Actuators B 30, 77 (1996). J.Waswa, J.Irudayaraj, and C.DebRoy, LWT 40, 187 (2007). Electronic mail:... more
... II. PKTien, R.Ulrich, and RJMartin, MODES OF PROPAGATING LIGHT WAVES IN THIN DEPOSITED SEMICONDUCTOR FILMS, Appl. Phys. Lett. ... Actuators B 30, 77 (1996). J.Waswa, J.Irudayaraj, and C.DebRoy, LWT 40, 187 (2007). Electronic mail: ion.mihailescu@inflpr.ro. ...
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ABSTRACT Very thin TiN and ZrN films (&lt;500 nm) were grown on (1 0 0) Si substrates at temperatures up to 500 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser under residual vacuum or various mixtures of... more
ABSTRACT Very thin TiN and ZrN films (&lt;500 nm) were grown on (1 0 0) Si substrates at temperatures up to 500 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser under residual vacuum or various mixtures of CH4 or N2. Auger electron spectroscopy investigations found that films contained a relatively low oxygen concentration, usually below 3.0 at%. Films deposited under residual vacuum or very low N2 pressures (&lt;3 × 10−3 Pa) contained 3–6 at% C atoms in the bulk. This fraction grew to 8–10 at% when the deposition was performed under an atmosphere of 2 × 10−3 Pa CH4. To avoid C atoms incorporation into the bulk a deposition pressure of 10 Pa N2 was required. X-ray photoelectron spectroscopy investigations found that oxygen was mostly bonded in an oxynitride type of compound, while carbon was bonded into a metallic carbide. The presence of C atoms in the chemical composition of the TiN or ZrN improved the measured hardness of the films.
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ABSTRACT ZrC films were grown on (1 0 0) Si substrates by the pulsed laser deposition (PLD) technique using a KrF excimer laser working at 40 Hz. The nominal substrate temperature during depositions was set at 300 °C and the cooling rate... more
ABSTRACT ZrC films were grown on (1 0 0) Si substrates by the pulsed laser deposition (PLD) technique using a KrF excimer laser working at 40 Hz. The nominal substrate temperature during depositions was set at 300 °C and the cooling rate was 5 °C/min. X-ray diffraction investigations showed that films deposited under residual vacuum or under 2 × 10−3 Pa of CH4 atmosphere were crystalline, exhibiting a (2 0 0)-axis texture, while those deposited under 2 × 10−2 Pa of CH4 atmosphere were found to be equiaxed and with smaller grain size. The surface elemental composition of as-deposited films, analyzed by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), showed the usual high oxygen contamination of carbides. Once the topmost 2–4 nm region was removed, the oxygen concentration rapidly decreased, down to around 3–8% only in bulk. Simulations of the X-ray reflectivity (XRR) curves indicated a smooth surface morphology, with roughness values below 1 nm (rms) and films density values of around 6.30–6.45 g/cm3, very close to the bulk density. The growth rate, estimated from thickness measurements by XRR was around 8.25 nm/min. Nanoindentation results showed for the best quality ZrC films a hardness of 27.6 GPa and a reduced modulus of 228 GPa.
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ABSTRACT ZrC/ZrN and ZrC/TiN multilayers were grown on (1 0 0) Si substrates at 300 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser. X-ray diffraction investigations showed that films were crystalline, the... more
ABSTRACT ZrC/ZrN and ZrC/TiN multilayers were grown on (1 0 0) Si substrates at 300 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser. X-ray diffraction investigations showed that films were crystalline, the strain and grain size depending on the nature and pressure of the gas used during deposition. The elemental composition, analyzed by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), showed that films contained a low level of oxygen contamination. Simulations of the X-ray reflectivity (XRR) curves acquired from films indicated a smooth surface morphology, with roughness below 1 nm (rms) and densities very close to bulk values.Nanoindentation results showed that the ZrC/ZrN and ZrC/TiN multilayer samples exhibited hardness values between 30 and 33 GPa, slightly higher than the values of 28–30 GPa measured for pure ZrC, TiN and ZrN films.
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ABSTRACT We synthesized by pulsed laser deposition (Ba,Sr,Y)TiO3 and (Ba,Pb,Y)TiO3 thin films on mechanically polished nickel substrates.The synthesized thin films were analyzed for: crystalline structure by X-ray diffractometry,... more
ABSTRACT We synthesized by pulsed laser deposition (Ba,Sr,Y)TiO3 and (Ba,Pb,Y)TiO3 thin films on mechanically polished nickel substrates.The synthesized thin films were analyzed for: crystalline structure by X-ray diffractometry, morphology and surface topography by atomic force microscopy, optical and scanning electron microscopy, and elemental composition by energy dispersive X-ray spectroscopy and electrical properties by electrical measurements.We have shown that film properties were determined by the dopants, target composition, and deposition parameters (oxygen pressure, substrate temperature and incident laser fluence). All films exhibited a semiconducting behavior, as proved by the decrease of electrical resistance with heating temperature.