Cristian Ursu | Petru Poni Institute of Macromolecular Chemistry Iasi Romania (original) (raw)

Papers by Cristian Ursu

Research paper thumbnail of Diagnostics of plasma plume produced by laser ablation using ICCD imaging and transient electrical probe technique

Journal of Physics: …, 2010

The dynamics of transient plasmas generated by high-fluence nanosecond laser ablation has been in... more The dynamics of transient plasmas generated by high-fluence nanosecond laser ablation has been investigated by means of fast ICCD imaging and electrical probes in transient regime. Measurements have been carried out on plasmas produced in vacuum by a pulsed Excimer laser irradiating stainless steel targets. Two plasma expansion velocities were estimated, one from probe measurements and another from recorded ICCD images. Electron plasma temperature ...

Research paper thumbnail of Comparative Study on Three-Dimensional Morphological Changes of Polyimide Films Exposed to Oxygen Plasma and Pulsed Uv-Laser

The ability to pattern polyimides at different length scales has generated considerable interest ... more The ability to pattern polyimides at different length scales has generated considerable interest in various research fields. In this context, a comparative study of the three-dimensional morphological changes induced on aromatic polyimide films, by RF O2 plasma and pulsed UV-laser exposure is presented. The plasma treatment affects the polymer surface, generating new chemical groups and appearance of granular morphological structures. Instead, for both UV-laser exposure conditions, the surface was characterized by cone-like structures. Depending on the desired application, a convenient surface treatment can be applied to the polyimide films to meet all the requirements regarding morphology, roughness and orientation.

Research paper thumbnail of Excimer Laser-Induced Surface Modification of Poly ( Ethylene Terephthalate )

The effects on chemical and physical properties of biaxial stretched poly(ethylene terephthalate)... more The effects on chemical and physical properties of biaxial stretched poly(ethylene terephthalate) (PET) as a result of KrF (248 nm) and XeCl (308 nm) laser irradiation were investigated. Below ablation threshold, roughening of the surface was detected, with the formation of periodic surface structures for 308 nm irradiation, while above the ablation threshold, dendrites or granular protuberances superimpose the densely-packed nap structures. The changes in surface properties were investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The obtained results suggest that the texture types originate from different contribution rates of photothermal and photochemical mechanisms.

Research paper thumbnail of Physico-chemical Insights on Tuning the Morphology of a Photosensitive Polyimide by UV Laser Irradiation

An aromatic photosensitive polyimide is prepared from 3,3',4,4'-benzophenone tetracarboxy... more An aromatic photosensitive polyimide is prepared from 3,3',4,4'-benzophenone tetracarboxylic dianhydride and 4,4'-diaminodiphenyl methane and its structuring ability upon UV-laser exposure is investigated. Surface modification is performed at two laser fluences, i.e. 89 and 244 mJ/cm2, and different number of pulses. The changes of the surface morphology, induced by the employed patterning technique, are examined. According to atomic force microscopy data cone-like structures are formed and their appearance mechanism is analyzed taking into account the laser irradiation conditions. Surface wettability tests reveal an intensification of hydrophobic character, which may be ascribed to the formation of a thin carbon-enriched layer at the polyimide surface.

Research paper thumbnail of Energy Deposition on the surface of Hall Effect Thrusters for satellites - Simulation by laser beam

Research paper thumbnail of Laser-BNSiO2 Ceramics Interaction: simulation of the energy deposition on dielectric wall surfaces in Hall thrusters

The dielectric wall surfaces of the annular chamber which are used in Hall Effect Thrusters (HET)... more The dielectric wall surfaces of the annular chamber which are used in Hall Effect Thrusters (HET) to limit the plasma discharge play an important role but yet completely not understood and controlled. In order to investigate the effect of an energy flux on the wall we performed tests with a nanosecond pulsed laser to simulate the energy deposition on BNSiO2 (usual dielectric material for HETs). The tests have been carried out with the second harmonic (532 nm) of a Q-switched (10 ns) Nd:YAG laser focused on the samples placed in a vacuum chamber (10-6 Torr). The energy/pulse range explored has been 5 – 320 mJ, leading to fluences of 1 – 1000 J/cm2. The modifications induced by laser irradiation on the BNSiO2 targets have been analysed by profilometry and scanning electron microscopy. The plasma created by laser ablation has also been characterized by optical and spectral methods. The present paper presents preliminary results of these combined investigations.

Research paper thumbnail of XML I/O, Document Format Support, Annotation Schema and Automated Evaluation in a General Architecture for Text Engineering

Abstract: This technical report discusses a number of areas in Software Architecture forLanguage ... more Abstract: This technical report discusses a number of areas in Software Architecture forLanguage Engineering (SALE, [CFB94, Cun94, Cun99, Cun00]) and specificallythe General Architecture for Text Engineering [CGW95, CHGW97,CGHW99, MCB00, BBR00, Cun02]:

Research paper thumbnail of Laser energy deposition on the chamber surface of the PPS100-ML Hall effect thruster : experiment and simulation

Research paper thumbnail of Formation mechanisms of carbon dimer in excimer laser produced plasma

The European Physical Journal D

Research paper thumbnail of Formation mechanisms of carbon dimer in excimer laser produced plasma

The European Physical Journal D

Research paper thumbnail of Diagnostics of plasma plume produced by laser ablation using ICCD imaging and transient electrical probe technique

Journal of Physics: Conference Series, 2010

... ICCD imaging and transient electrical probe technique I Mihaila, C Ursu, A Gegiuc and G Popa ... more ... ICCD imaging and transient electrical probe technique I Mihaila, C Ursu, A Gegiuc and G Popa Department of Physics, Faculty of Physics, “Alexandru Ioan Cuza” University, 700506, Iasi, Romania E-mail: ghpopa@uaic.ro Abstract. ...

Research paper thumbnail of Synthesis and Characterization of Co-Substituted Ferrite Nanocomposites

Ieee Transactions on Magnetics, 2013

Fe O (where x is 0, 0.25, 0.50, 0.75, 1) nanoparticles (NPs) by a wet chemical method using carbo... more Fe O (where x is 0, 0.25, 0.50, 0.75, 1) nanoparticles (NPs) by a wet chemical method using carboxymethyl cellulose (CMC) solution as surfactant. Their structure and magnetic properties were evaluated by X-ray diffraction (XRD), Fourier-Transform Infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). The gas and humidity sensing properties of the samples were also investigated. Powder X-ray diffraction analysis demonstrated the formation of face-centered cubic structure for all the samples. The average crystallite size and lattice parameters have been calculated by Rietveld refinement. The FTIR spectra of NPs confirm the presence of CMC functional groups and stretching bands attributed to the intrinsic vibrations of tetrahedral and octahedral sites of spinel ferrite. The magnetization curves of the nanocomposites at room temperature demonstrated saturation magnetizations from 21 emu/g to 58 emu/g and coercivity values between 130 Oe and 835 Oe. As not many studies have been published on this topic, the gas sensing properties of Ni-substituted Co ferrites have been evaluated. The measurements revealed that Co Ni Fe O is the most sensitive to acetone vapors.

Research paper thumbnail of Energy Deposition on the surface of Hall Effect Thrusters for satellites - Simulation by laser beam

Research paper thumbnail of Physico-chemical Insights on Tuning the Morphology of a Photosensitive Polyimide by UV Laser Irradiation

Research paper thumbnail of Alternative Route for Obtaining <formula formulatype="inline"><tex Notation="TeX">${\rm NiFe}_{2}{\rm O}_{4}$</tex> </formula> Thin Films by Pulsed Laser Deposition

IEEE Transactions on Magnetics, 2000

ABSTRACT Ferrites in thin film form are usually obtained by pulsed laser deposition (PLD). This m... more ABSTRACT Ferrites in thin film form are usually obtained by pulsed laser deposition (PLD). This method can induce the presence of secondary phases, a problem which requires an annealing process. The study aimed at finding a PLD based method through which, in further studies, ferrites with a controllable phase composition can be obtained. Therefore, we obtained ferrite thin films in oxygen atmosphere and in high vacuum. Raman spectroscopy measurements for the samples obtained in high vacuum revealed the formation of magnetite. Instead of annealing, we irradiated these samples with an excimer laser (λ=308nm), at various frequencies, for certain amount of pulses. The Raman spectra revealed the formation of the nickel ferrite phase, as well as the presence of residual magnetite phase.

Research paper thumbnail of Functional silsesquioxane-based hierarchical assemblies for antibacterial/antifungal coatings

J Mater Chem B, Jan 21, 2015

ABSTRACT The paper reports the first study on functional silsesquioxane-based hierarchical assemb... more ABSTRACT The paper reports the first study on functional silsesquioxane-based hierarchical assemblies containing an ordered distribution of silver nanoparticles with a high amount of {111} facets, obtained through sol-gel reaction, intended for antibacterial/antifungal coatings.

Research paper thumbnail of Energy Deposition on the surface of Hall Effect Thrusters for satellites - Simulation by laser beam

Research paper thumbnail of Laser energy deposition on the chamber surface of the PPS100-ML Hall effect thruster : experiment and simulation

Research paper thumbnail of Full silicone interpenetrating bi-networks with different organic groups attached to the silicon atoms

Research paper thumbnail of Characterization of doped TiO2 thin films obtained by pulsed laser deposition

N-doped TiO2 thin films were synthesized by pulsed laser deposition using a TiO2 target in nitrog... more N-doped TiO2 thin films were synthesized by pulsed laser deposition using a TiO2 target in nitrogen atmosphere and glass slides substrates heated at 250 C. The samples were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, ellipsometry and contact angle measurements. The root mean square roughness is increasing with the increase of pulses number. Even if increased surface roughness is known to intensify the hydrophilic behavior of TiO2, the samples do not present the photoinduced superhydrophilic conversion process. The optical constants values are suggesting that the PLD technique is suitable to obtain thin films for optical coatings.

Research paper thumbnail of Diagnostics of plasma plume produced by laser ablation using ICCD imaging and transient electrical probe technique

Journal of Physics: …, 2010

The dynamics of transient plasmas generated by high-fluence nanosecond laser ablation has been in... more The dynamics of transient plasmas generated by high-fluence nanosecond laser ablation has been investigated by means of fast ICCD imaging and electrical probes in transient regime. Measurements have been carried out on plasmas produced in vacuum by a pulsed Excimer laser irradiating stainless steel targets. Two plasma expansion velocities were estimated, one from probe measurements and another from recorded ICCD images. Electron plasma temperature ...

Research paper thumbnail of Comparative Study on Three-Dimensional Morphological Changes of Polyimide Films Exposed to Oxygen Plasma and Pulsed Uv-Laser

The ability to pattern polyimides at different length scales has generated considerable interest ... more The ability to pattern polyimides at different length scales has generated considerable interest in various research fields. In this context, a comparative study of the three-dimensional morphological changes induced on aromatic polyimide films, by RF O2 plasma and pulsed UV-laser exposure is presented. The plasma treatment affects the polymer surface, generating new chemical groups and appearance of granular morphological structures. Instead, for both UV-laser exposure conditions, the surface was characterized by cone-like structures. Depending on the desired application, a convenient surface treatment can be applied to the polyimide films to meet all the requirements regarding morphology, roughness and orientation.

Research paper thumbnail of Excimer Laser-Induced Surface Modification of Poly ( Ethylene Terephthalate )

The effects on chemical and physical properties of biaxial stretched poly(ethylene terephthalate)... more The effects on chemical and physical properties of biaxial stretched poly(ethylene terephthalate) (PET) as a result of KrF (248 nm) and XeCl (308 nm) laser irradiation were investigated. Below ablation threshold, roughening of the surface was detected, with the formation of periodic surface structures for 308 nm irradiation, while above the ablation threshold, dendrites or granular protuberances superimpose the densely-packed nap structures. The changes in surface properties were investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The obtained results suggest that the texture types originate from different contribution rates of photothermal and photochemical mechanisms.

Research paper thumbnail of Physico-chemical Insights on Tuning the Morphology of a Photosensitive Polyimide by UV Laser Irradiation

An aromatic photosensitive polyimide is prepared from 3,3',4,4'-benzophenone tetracarboxy... more An aromatic photosensitive polyimide is prepared from 3,3',4,4'-benzophenone tetracarboxylic dianhydride and 4,4'-diaminodiphenyl methane and its structuring ability upon UV-laser exposure is investigated. Surface modification is performed at two laser fluences, i.e. 89 and 244 mJ/cm2, and different number of pulses. The changes of the surface morphology, induced by the employed patterning technique, are examined. According to atomic force microscopy data cone-like structures are formed and their appearance mechanism is analyzed taking into account the laser irradiation conditions. Surface wettability tests reveal an intensification of hydrophobic character, which may be ascribed to the formation of a thin carbon-enriched layer at the polyimide surface.

Research paper thumbnail of Energy Deposition on the surface of Hall Effect Thrusters for satellites - Simulation by laser beam

Research paper thumbnail of Laser-BNSiO2 Ceramics Interaction: simulation of the energy deposition on dielectric wall surfaces in Hall thrusters

The dielectric wall surfaces of the annular chamber which are used in Hall Effect Thrusters (HET)... more The dielectric wall surfaces of the annular chamber which are used in Hall Effect Thrusters (HET) to limit the plasma discharge play an important role but yet completely not understood and controlled. In order to investigate the effect of an energy flux on the wall we performed tests with a nanosecond pulsed laser to simulate the energy deposition on BNSiO2 (usual dielectric material for HETs). The tests have been carried out with the second harmonic (532 nm) of a Q-switched (10 ns) Nd:YAG laser focused on the samples placed in a vacuum chamber (10-6 Torr). The energy/pulse range explored has been 5 – 320 mJ, leading to fluences of 1 – 1000 J/cm2. The modifications induced by laser irradiation on the BNSiO2 targets have been analysed by profilometry and scanning electron microscopy. The plasma created by laser ablation has also been characterized by optical and spectral methods. The present paper presents preliminary results of these combined investigations.

Research paper thumbnail of XML I/O, Document Format Support, Annotation Schema and Automated Evaluation in a General Architecture for Text Engineering

Abstract: This technical report discusses a number of areas in Software Architecture forLanguage ... more Abstract: This technical report discusses a number of areas in Software Architecture forLanguage Engineering (SALE, [CFB94, Cun94, Cun99, Cun00]) and specificallythe General Architecture for Text Engineering [CGW95, CHGW97,CGHW99, MCB00, BBR00, Cun02]:

Research paper thumbnail of Laser energy deposition on the chamber surface of the PPS100-ML Hall effect thruster : experiment and simulation

Research paper thumbnail of Formation mechanisms of carbon dimer in excimer laser produced plasma

The European Physical Journal D

Research paper thumbnail of Formation mechanisms of carbon dimer in excimer laser produced plasma

The European Physical Journal D

Research paper thumbnail of Diagnostics of plasma plume produced by laser ablation using ICCD imaging and transient electrical probe technique

Journal of Physics: Conference Series, 2010

... ICCD imaging and transient electrical probe technique I Mihaila, C Ursu, A Gegiuc and G Popa ... more ... ICCD imaging and transient electrical probe technique I Mihaila, C Ursu, A Gegiuc and G Popa Department of Physics, Faculty of Physics, “Alexandru Ioan Cuza” University, 700506, Iasi, Romania E-mail: ghpopa@uaic.ro Abstract. ...

Research paper thumbnail of Synthesis and Characterization of Co-Substituted Ferrite Nanocomposites

Ieee Transactions on Magnetics, 2013

Fe O (where x is 0, 0.25, 0.50, 0.75, 1) nanoparticles (NPs) by a wet chemical method using carbo... more Fe O (where x is 0, 0.25, 0.50, 0.75, 1) nanoparticles (NPs) by a wet chemical method using carboxymethyl cellulose (CMC) solution as surfactant. Their structure and magnetic properties were evaluated by X-ray diffraction (XRD), Fourier-Transform Infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). The gas and humidity sensing properties of the samples were also investigated. Powder X-ray diffraction analysis demonstrated the formation of face-centered cubic structure for all the samples. The average crystallite size and lattice parameters have been calculated by Rietveld refinement. The FTIR spectra of NPs confirm the presence of CMC functional groups and stretching bands attributed to the intrinsic vibrations of tetrahedral and octahedral sites of spinel ferrite. The magnetization curves of the nanocomposites at room temperature demonstrated saturation magnetizations from 21 emu/g to 58 emu/g and coercivity values between 130 Oe and 835 Oe. As not many studies have been published on this topic, the gas sensing properties of Ni-substituted Co ferrites have been evaluated. The measurements revealed that Co Ni Fe O is the most sensitive to acetone vapors.

Research paper thumbnail of Energy Deposition on the surface of Hall Effect Thrusters for satellites - Simulation by laser beam

Research paper thumbnail of Physico-chemical Insights on Tuning the Morphology of a Photosensitive Polyimide by UV Laser Irradiation

Research paper thumbnail of Alternative Route for Obtaining <formula formulatype="inline"><tex Notation="TeX">${\rm NiFe}_{2}{\rm O}_{4}$</tex> </formula> Thin Films by Pulsed Laser Deposition

IEEE Transactions on Magnetics, 2000

ABSTRACT Ferrites in thin film form are usually obtained by pulsed laser deposition (PLD). This m... more ABSTRACT Ferrites in thin film form are usually obtained by pulsed laser deposition (PLD). This method can induce the presence of secondary phases, a problem which requires an annealing process. The study aimed at finding a PLD based method through which, in further studies, ferrites with a controllable phase composition can be obtained. Therefore, we obtained ferrite thin films in oxygen atmosphere and in high vacuum. Raman spectroscopy measurements for the samples obtained in high vacuum revealed the formation of magnetite. Instead of annealing, we irradiated these samples with an excimer laser (λ=308nm), at various frequencies, for certain amount of pulses. The Raman spectra revealed the formation of the nickel ferrite phase, as well as the presence of residual magnetite phase.

Research paper thumbnail of Functional silsesquioxane-based hierarchical assemblies for antibacterial/antifungal coatings

J Mater Chem B, Jan 21, 2015

ABSTRACT The paper reports the first study on functional silsesquioxane-based hierarchical assemb... more ABSTRACT The paper reports the first study on functional silsesquioxane-based hierarchical assemblies containing an ordered distribution of silver nanoparticles with a high amount of {111} facets, obtained through sol-gel reaction, intended for antibacterial/antifungal coatings.

Research paper thumbnail of Energy Deposition on the surface of Hall Effect Thrusters for satellites - Simulation by laser beam

Research paper thumbnail of Laser energy deposition on the chamber surface of the PPS100-ML Hall effect thruster : experiment and simulation

Research paper thumbnail of Full silicone interpenetrating bi-networks with different organic groups attached to the silicon atoms

Research paper thumbnail of Characterization of doped TiO2 thin films obtained by pulsed laser deposition

N-doped TiO2 thin films were synthesized by pulsed laser deposition using a TiO2 target in nitrog... more N-doped TiO2 thin films were synthesized by pulsed laser deposition using a TiO2 target in nitrogen atmosphere and glass slides substrates heated at 250 C. The samples were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, ellipsometry and contact angle measurements. The root mean square roughness is increasing with the increase of pulses number. Even if increased surface roughness is known to intensify the hydrophilic behavior of TiO2, the samples do not present the photoinduced superhydrophilic conversion process. The optical constants values are suggesting that the PLD technique is suitable to obtain thin films for optical coatings.