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Papers by Mihai Anastasescu

Journal of Optoelectronics and Advanced Materials, 2009

Vacuum thermal evaporated (AsSe)1-x(AgI)x films with different compositions (x = 5, 15, 20 and 30... more Vacuum thermal evaporated (AsSe)1-x(AgI)x films with different compositions (x = 5, 15, 20 and 30 mol %) have been studied by spectroscopic ellipsometry and atomic-force microscopy. The ellipsometric results have shown that the optical constants and optical band gap energy values vary with increasing AgI content in the films. Additional XRD measurements revealed that the films are amorphous with more ordered structures at larger x values. AFM images visualized that randomly distributed hillocks emerged from the smooth film surface yielding an rms roughness of 0.6-1.0 nm with a tendency to increase with increasing AgI content.

Materials Science and Engineering: B, 2021

Abstract Structural and functional changes induced by TiO2 addition to spherical zinc selenide to... more Abstract Structural and functional changes induced by TiO2 addition to spherical zinc selenide together with lysozyme adsorption lead to valuable bioinorganic catalysts with enhanced activity. Spherical zinc selenide and its composite with TiO2 were obtained by hydrothermal method and subsequently modified by lysozyme adsorption. Morphological, structural and functional characteristics of zinc selenide based materials (ZnSe, TiO2-ZnSe) and their hybrids with lysozyme (Lys/ZnSe, Lys/TiO2-ZnSe) were investigated. TiO2 addition to ZnSe results in significant changes of surface composition, electrochemical behavior and lysozyme retention capacity. The lysozyme modified ZnSe and TiO2-ZnSe surfaces doubles the biocatalysts efficiency for 4-Methylumbelliferyl β-D-N,N′,N″-triacetylchitotrioside hydrolysis reaction compared to free lysozyme.

Chemical Physics, 2021

Abstract The use of porphyrinic compounds for photodynamic therapy (PDT) in cancer is well docume... more Abstract The use of porphyrinic compounds for photodynamic therapy (PDT) in cancer is well documented, but the aggregation tendency in physiologically-relevant media impedes on their medical use. The present study argues for the use of atomic force microscopy (AFM) for the evaluation of the aggregation tendency in terms of topography, self-similarity (fractal behavior) and textural properties of some promising A3B-type porphyrinic compounds, previously described by our group. It was found that the samples are isotropic and rough enough to favor cell adhesion. Despite having different aggregation tendencies, the P and Zn(II)P compounds (5 µM) were similarly incorporated into tumour cells (HT-29 human colon carcinoma and U-87 MG human glioblastoma), as demonstrated by flow cytometry data. Results suggest that there might be an aggregation, “window” that does not impede on the interaction of the investigated porphyrins with tumor cells.

Optical Materials, 2021

Abstract The aim of this paper is to prepare multi-layered ITO thin films by a low cost and envir... more Abstract The aim of this paper is to prepare multi-layered ITO thin films by a low cost and environmental-friendly method for different applications (optoelectronics, sensors, etc.). ITO films with 15 layers were obtained by successive depositions using the sol-gel & dip-coating method on three different substrates: glass, SiO2/glass and SiO2/Si. Comparative structural, morphological and optical characterization were performed by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), Cross Section Transmission Electron Microscopy (XTEM) coupled with Selected Area Electron Diffraction (SAED), Infrared Spectroscopic Ellipsometry (IRSE) and Raman spectroscopy analyses. The optical constants (refractive index n and extinction coefficient k) were determined in a large spectral range (300-27500 cm−1) by spectroscopic ellipsometry (SE). The thicknesses determined by SE were confirmed by HRTEM (High Resolution TEM) measurements which also presents in detail the textural properties of the ITO films at nanometric level. A comparison between IRSE and Raman analysis in the infrared active region was presented.

Applied Surface Science, 2020

This paper reports the comparative study of piezoelectric nanostructures deposited on metallic fl... more This paper reports the comparative study of piezoelectric nanostructures deposited on metallic flexible substrate versus rigid substrates as a new architecture for energy harvesters. Rigid metallic substrates are multi-layered types of Pt/Ti/SiO 2 /Si or Au/Ti/SiO 2 /Si while Ti foil is a flexible metallic substrate. The active piezo-layer consisted of a vertical ZnO nanowires (ZnO NWs) array grown by the hydrothermal method at low temperature, on a previously deposited crystalline seed (nucleation) sol-gel layer and covered with a layer of polymethylmethacrylate (PMMA). The new obtained nanostructures have been characterized in different stages of preparation by X-Ray Diffraction, Scanning and Transmission Electron Microscopy, Atomic Force Microscopy, Spectroscopic Ellipsometry. The piezoelectric performance of PMMA/(ZnO NWs)/Ti structures was evaluated by measuring the d 33 coefficient. Results show that ZnO nanowires have successfully grown on the flexible substrates with a piezoelectric coefficient four times greater than on rigid substrates. By improving vertical integration of ZnO NWs on flexible metallic substrate, PMMA/(ZnO NWs)/Ti affordable nanostructures open the way towards integration in wireless or defence technologies and in wearable or implantable biomedical systems as efficient harvester.

Journal of Physics: Conference Series, 2020

We report a study of p-Si(100) surface layers modified by plasma immersion ion implantation (PIII... more We report a study of p-Si(100) surface layers modified by plasma immersion ion implantation (PIII) and dry oxidation. This is expected to allow one to engineer near-surface layers with different thicknesses and levels of amorphization. Hydrogen ions were introduced into a shallow near-surface Si region through PIII with energy of 2 keV and doses ranging from 1013 ion/cm2 to 1015 ion/cm2. The implanted Si surface was subjected to oxidation in dry oxygen atmosphere at temperatures ranging from 700 °C to 800 °C. The optical and structural properties of the modified Si layers were studied in detail by spectroscopic ellipsometry (SE) in the IR spectral range of 300 – 4000 cm−1. The surface morphology was examined by atomic force microscopy (AFM) imaging at different scales and by fractal analysis. Through decomposition of the main Si-O bands into Gaussian peaks, different Si oxidation states were identified, suggesting non-stoichiometric oxide layer composition.

Dyes and Pigments, 2019

The study reports a series of results obtained by synthesis, spectral and morphological analysis ... more The study reports a series of results obtained by synthesis, spectral and morphological analysis of new tetrapyrrolic structures: 5-(4-hydroxy-3-methoxyphenyl)-10,15,20-tris-(4-carboxymethylphenyl) porphyrin (P1.2), Zn(II)-5-(4-hydroxy-3methoxyphenyl)-10,15,20-tris-(4-carboxymethylphenyl) porphyrin (Zn(II)1.2) and Cu(II)-5-(4-hydroxy-3-methoxyphenyl)-10,15,20-tris-(4-carboxymethylphenyl) porphyrin (Cu(II)1.2), as potential candidates for theranostics. Porphyrins were obtained by microwave synthesis under solvent-free conditions and characterized by elemental analysis, FT-IR, UV-Vis and NMR spectroscopies. The absorption properties of the synthetized compounds were studied in different solvents (ethanol, polyethylene glycol 200, dimethylsulfoxide, dichloromethane, chloroform). The spectral profile of the new porphyrins was completed by studying the fluorescence emission and singlet oxygen formation quantum yields. P1.2 and Zn(II)1.2 exhibit fluorescence while for Cu(II)1.2 the fluorescence emission is negligible. P1.2 and Zn(II)1.2 exhibited photodynamic therapy (PDT) acceptable values of singlet oxygen generation. In the case of Cu(II)1.2 this parameter is reduced ca. 5 times. For powdered samples of P1.2 adsorbed onto powdered PEG a detailed study was performed correlating the fluorescence emission intensity with sample absorption to determine the concentration range where aggregation does not occur. Fluorescence emission quantum yields and lifetimes were determined for all samples under study to determine the useful range of concentrations for PDT use. Atomic force microscope (AFM) studies were also made, which exhibit the aggregate species formation for high loadings of the porphyrin P1.2 adsorbed onto specific surfaces.

Materials Science in Semiconductor Processing, 2017

Titania films doped with low amount of vanadium were deposited on different substrates (microscop... more Titania films doped with low amount of vanadium were deposited on different substrates (microscope glass, microscope glass covered with SiO 2 barrier layer, and silicon wafer with a thermally grown layer of SiO 2) by dip coating from solutions prepared by sol-gel and microwave (MW) assisted sol-gel syntheses. The selected molar composition was 99.95:0.05 which corresponds to 0.03 at% of V. The films were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray diffraction (XRD) and Spectroscopic Ellipsometry (SE). The deposited films thermally treated at 450°C, presented homogeneous and continuous nanostructured surfaces and good adherence to the substrates used. All samples crystallized in anatase phase and have good optical properties. The highest transmission value was obtained for the V-doped TiO 2 films (T > 90%) deposited from solutions prepared by microwaves assisted sol-gel method. Based on the obtained results it was concluded that the method of preparation has higher influence on the properties of the resulted films than the substrates used.

Journal of Thermal Analysis and Calorimetry, 2017

In order to establish the influence of the preparation method on thermal behaviour of gels obtain... more In order to establish the influence of the preparation method on thermal behaviour of gels obtained by the sol–gel and microwave-assisted sol–gel methods, a comparative thermal analysis study was conducted by the thermogravimetric and differential thermal analysis (TG/DTG/DTA) and evolved gas analysis (EGA) on TiO2 and V2O5-doped TiO2 gels, where TiO2:V2O5 molar ratio was set to 99.95:0.05 and 98.0:2.0. In contrast to TiO2 gels, for which the thermal behaviour was not significantly influenced by the preparation method, the microwave-irradiated binary samples showed a more complex and prolonged decomposition compared to their non-irradiated counterparts. This observation was correlated with influence of microwaves in enhancing the reaction rate between the Ti and V reagents leading to formation of more complex compositions of gels. Based on TG/DTG/DTA results, the temperatures of 300 and 450 °C were chosen for the processing of powders in air. All samples thermally treated at 300 and 450 °C crystallized in a single anatase phase except the TiO2:V2O5 with a molar ratio 99.95:0.05, obtained by microwave-assisted sol–gel method that contains also small amount of rutile phase. At 550 °C all samples contain mixture of anatase and rutile phases.

Journal of Sol-Gel Science and Technology, 2016

In the present work, TiO2 and V-doped TiO2 films with TiO2/V2O5 molar ratios 98:2 and 99.95:0.05 ... more In the present work, TiO2 and V-doped TiO2 films with TiO2/V2O5 molar ratios 98:2 and 99.95:0.05 were prepared by sol–gel and microwave (MW) assisted sol–gel syntheses. The reagents used were tetraethyl orthotitanate, vanadyl acetylacetonate and ethanol as solvent. The solutions were prepared either by stirring for 2 h at room temperature or by exposing them for 5 min to microwaves at 300 W in an oven operated at frequency of 2.45 GHz. The deposition of the films was realized by dip-coating on microscope glass substrate. The multilayer films were obtained by successive deposition. The first benefit of using MW-assisted sol–gel preparation was the essentially increased stability of the resulted solution against gelling, behavior that is of great interest for multilayer depositions. A comprehensive structural, morphological and optical characterization of the obtained films was realized. Differences between the films obtained by the two types of preparation routes are reflected in a more compact and continuous structure with very low roughness, increased thickness and higher refractive index as well as increased transmission when MW-assisted sol–gel method was used.Graphical Abstract

Applied Surface Science, 2017

Aluminum Nitride (AlN) thin films were synthesized on Si (100) wafers at 450 • C by pulsed laser ... more Aluminum Nitride (AlN) thin films were synthesized on Si (100) wafers at 450 • C by pulsed laser deposition. A polycrystalline AlN target was multipulsed irradiated in a nitrogen ambient, at different laser pulse repetition rate. Grazing Incidence X-Ray Diffraction and Atomic Force Microscopy analyses evidenced nanocrystallites with a hexagonal lattice in the amorphous AlN matrix. The thickness and optical constants of the layers were determined by infrared spectroscopic ellipsometry. The optical properties were studied by Fourier Transform Infrared reflectance spectroscopy in polarised oblique incidence radiation. Berreman effect was observed around the longitudinal phonon modes of the crystalline AlN component. Angular dependence of the A 1 LO mode frequency was analysed and connected to the orientation of the particles' optical axis to the substrate surface normal. The role of the laser pulse frequency on the layers' properties is discussed on this basis.

Materials Science in Semiconductor Processing, 2016

Abstract Nb doped titania (TiO 2 :Nb) multilayered films (1–10 layers) with anatase structure wer... more Abstract Nb doped titania (TiO 2 :Nb) multilayered films (1–10 layers) with anatase structure were obtained by the low-cost sol–gel and dipping method on microscope glass substrates, followed by thermal treatment at 450 °C for 1 h. After each layer deposition, an intermediate annealing step was performed at 300 °C for 30 min. Doping TiO 2 sol–gel films with a low amount of Nb (0.8 at%) allows obtaining an improved CO sensor able to operate under environmental atmosphere (air). It was found that the sensor sensitivity is less dependent on the film thickness but is significantly influenced by Nb doping at the optimal working temperature of 400 °C. Good recovery characteristics were obtained for a wide CO detection range, between 0 and 2000 ppm. The gas-sensing behavior of the films was correlated with the structural, chemical and morphological properties of the multi-layered structures.

Applied Surface Science, 2016

We report on multi-stage pulsed laser deposition of aluminum nitride (AlN) on Si (1 0 0) wafers, ... more We report on multi-stage pulsed laser deposition of aluminum nitride (AlN) on Si (1 0 0) wafers, at different temperatures. The first stage of deposition was carried out at 800 • C, the optimum temperature for AlN crystallization. In the second stage, the deposition was conducted at lower temperatures (room temperature, 350 • C or 450 • C), in ambient Nitrogen, at 0.1 Pa. The synthesized structures were analyzed by grazing incidence X-ray diffraction (GIXRD), transmission electron microscopy (TEM), atomic force microscopy and spectroscopic ellipsometry (SE). GIXRD measurements indicated that the two-stage deposited AlN samples exhibited a randomly oriented wurtzite structure with nanosized crystallites. The peaks were shifted to larger angles, indicative for smaller inter-planar distances. Remarkably, TEM images demonstrated that the high-temperature AlN "seed" layers (800 • C) promoted the growth of poly-crystalline AlN structures at lower deposition temperatures. When increasing the deposition temperature, the surface roughness of the samples exhibited values in the range of 0.4-2.3 nm. SE analyses showed structures which yield band gap values within the range of 4.0-5.7 eV. A correlation between the results of singleand multi-stage AlN depositions was observed.

Applied Surface Science, 2015

By codoping with a donor-acceptor pair through a two-step chemical method we have succeed to obta... more By codoping with a donor-acceptor pair through a two-step chemical method we have succeed to obtain p-type ZnO thin films on glass. Firstly, a thin undoped ZnO seed layer was deposited by sol-gel method followed by the deposition of InN codoped ZnO film obtained through the hydrothermal technique. The influence of post-deposition annealing temperature (100 • C, 300 • C and 500 • C) on the samples was investigated from a structural, chemical, morphological and optoelectrical point of view. X-ray diffractometry (XRD), infrared ellipsometry and X-ray photoelectron spectroscopy (XPS) analyses have confirmed the codoped nature of the ZnO thin films. The XRD pattern analysis has established the films have wurtzite nanocrystalline structure, the crystallite sizes varying between 10 nm and 13 nm with the annealing temperature. Continuous and homogenous films with nanorods surface morphology has been obtained, as visualized by scanning electron microscopy measurements. Hall Effect measurements have established that all samples, regardless of annealing temperature, showed p-type conduction due to the successful incorporation of nitrogen in the film, with the highest carrier concentration registered at 500 • C. This is in good correlation with the nitrogen content in the films as revealed from XPS. In all samples, the XPS depth profiling has shown a nitrogen gradient with higher elemental concentration at the surface.

Journal of Physics: Conference Series, 2014

The surface morphology of p-Si(100) wafers after RF plasma immersion (PII) H + ion implantation i... more The surface morphology of p-Si(100) wafers after RF plasma immersion (PII) H + ion implantation into a shallow Si surface layer and after subsequent thermal oxidation was studied by atomic-force microscopic (AFM) imaging. After PII implantation of hydrogen ions with an energy of 2 keV and fluences ranging from 10 13 cm-2 to 10 15 cm-2 , the Si wafers were oxidized in dry O 2 at temperatures ranging from 700 o C to 800 o C. From the analysis of the AFM images, the surface amplitude parameters were evaluated and considered in terms of the technological conditions. The amplitude parameters showed a clear dependence on the H + dose and the oxidation temperature, with the tendency of increasing with the increase of both the H + ion fluence and the oxidation temperature. The implantation causes surface roughening, changing the RMS roughness value from 0.15 nm (typical for a polished Si(100) surface) to the highest value 0.6 nm for the H + fluence of 10 15 ions/cm 2. Oxidation of the H + implanted Si region, as the oxide is growing inward into Si, levels away the pits created by implants and results in a smoother surface, although keeping the RMS values larger than 0.2 nm.

2007 International Semiconductor Conference, 2007

Titanium oxynitride thin films were deposited by sol-gel method on quartz substrate in an attempt... more Titanium oxynitride thin films were deposited by sol-gel method on quartz substrate in an attempt to study the microstructural and optical properties of TiOxNy films deposited by sol-gel method. For this purpose, X-ray diffraction (XRD), atomic force microscopy (AFM), and spectroscopic ellipsometry (SE) investigations were performed. Examining the surface morphology and grain sizes of the films, complex nanostructured surfaces, with

Journal of Physics: Conference Series, 2014

Preliminary results of the studies of electrical properties of ZnO films, codoped with donor and ... more Preliminary results of the studies of electrical properties of ZnO films, codoped with donor and acceptor pair In-N are reported. The films were grown on Si substrates by chemical route procedures involving a sol-gel followed by hydrothermal treatment at 500?C. For electrical characterization, current-voltage and capacitance-voltage measurements were conducted on MIS structures with embedded ZnO(In,N) films. The estimated doping concentration in the studied films is higher than 1?1016 cm?3 corresponding to a semiconductor with good conductivity. However, the obtained large values of the differential specific resistivity (? = 3.2?105 ?cm) suggest that the nitrogen acceptors in these films are compensated by some kind of donor-type defects.

2006 International Semiconductor Conference, 2006

SnO2 thin films have been deposited on glass from Sn (II)-2-ethylhexanoate precursor using the di... more SnO2 thin films have been deposited on glass from Sn (II)-2-ethylhexanoate precursor using the dip-coating sol-gel method. Based on spectroscopic ellipsometry (SE) measurements optical and structural properties of the SnO2 films have been obtained. It was found that the concentration of tin oxide sols used for deposition strongly influences the thickness and the optical properties of the film, such as

Thin Solid Films, 2007

A comparative study of the sol–gel films prepared in the SiO2–P2O5 system starting with triethylp... more A comparative study of the sol–gel films prepared in the SiO2–P2O5 system starting with triethylphosphate, triethylphosphite and phosphoric acid as P precursors was performed. The work addresses basic aspects of physics, chemistry, and engineering of oxide films for applications in microelectronics, sensing, nano-photonics, and optoelectronics by establishing the influence of different precursors on the composition, structure and optical properties of

physica status solidi c, 2008

1 National Institute of Research and Development for Optoelectronics-INOE 2000, Atomistilor Str. ... more 1 National Institute of Research and Development for Optoelectronics-INOE 2000, Atomistilor Str. 1, PO Box MG - 5, 77125 Magurele, Romania 2 University “Politehnica” Timisoara, Pta. Victoriei nr. 2, 300006 Timisoara, Romania 3 Institute of Physical Chemistry “IGMurgulescu”, Spl. ...

Journal of Optoelectronics and Advanced Materials, 2009

Vacuum thermal evaporated (AsSe)1-x(AgI)x films with different compositions (x = 5, 15, 20 and 30... more Vacuum thermal evaporated (AsSe)1-x(AgI)x films with different compositions (x = 5, 15, 20 and 30 mol %) have been studied by spectroscopic ellipsometry and atomic-force microscopy. The ellipsometric results have shown that the optical constants and optical band gap energy values vary with increasing AgI content in the films. Additional XRD measurements revealed that the films are amorphous with more ordered structures at larger x values. AFM images visualized that randomly distributed hillocks emerged from the smooth film surface yielding an rms roughness of 0.6-1.0 nm with a tendency to increase with increasing AgI content.

Materials Science and Engineering: B, 2021

Abstract Structural and functional changes induced by TiO2 addition to spherical zinc selenide to... more Abstract Structural and functional changes induced by TiO2 addition to spherical zinc selenide together with lysozyme adsorption lead to valuable bioinorganic catalysts with enhanced activity. Spherical zinc selenide and its composite with TiO2 were obtained by hydrothermal method and subsequently modified by lysozyme adsorption. Morphological, structural and functional characteristics of zinc selenide based materials (ZnSe, TiO2-ZnSe) and their hybrids with lysozyme (Lys/ZnSe, Lys/TiO2-ZnSe) were investigated. TiO2 addition to ZnSe results in significant changes of surface composition, electrochemical behavior and lysozyme retention capacity. The lysozyme modified ZnSe and TiO2-ZnSe surfaces doubles the biocatalysts efficiency for 4-Methylumbelliferyl β-D-N,N′,N″-triacetylchitotrioside hydrolysis reaction compared to free lysozyme.

Chemical Physics, 2021

Abstract The use of porphyrinic compounds for photodynamic therapy (PDT) in cancer is well docume... more Abstract The use of porphyrinic compounds for photodynamic therapy (PDT) in cancer is well documented, but the aggregation tendency in physiologically-relevant media impedes on their medical use. The present study argues for the use of atomic force microscopy (AFM) for the evaluation of the aggregation tendency in terms of topography, self-similarity (fractal behavior) and textural properties of some promising A3B-type porphyrinic compounds, previously described by our group. It was found that the samples are isotropic and rough enough to favor cell adhesion. Despite having different aggregation tendencies, the P and Zn(II)P compounds (5 µM) were similarly incorporated into tumour cells (HT-29 human colon carcinoma and U-87 MG human glioblastoma), as demonstrated by flow cytometry data. Results suggest that there might be an aggregation, “window” that does not impede on the interaction of the investigated porphyrins with tumor cells.

Optical Materials, 2021

Abstract The aim of this paper is to prepare multi-layered ITO thin films by a low cost and envir... more Abstract The aim of this paper is to prepare multi-layered ITO thin films by a low cost and environmental-friendly method for different applications (optoelectronics, sensors, etc.). ITO films with 15 layers were obtained by successive depositions using the sol-gel & dip-coating method on three different substrates: glass, SiO2/glass and SiO2/Si. Comparative structural, morphological and optical characterization were performed by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), Cross Section Transmission Electron Microscopy (XTEM) coupled with Selected Area Electron Diffraction (SAED), Infrared Spectroscopic Ellipsometry (IRSE) and Raman spectroscopy analyses. The optical constants (refractive index n and extinction coefficient k) were determined in a large spectral range (300-27500 cm−1) by spectroscopic ellipsometry (SE). The thicknesses determined by SE were confirmed by HRTEM (High Resolution TEM) measurements which also presents in detail the textural properties of the ITO films at nanometric level. A comparison between IRSE and Raman analysis in the infrared active region was presented.

Applied Surface Science, 2020

This paper reports the comparative study of piezoelectric nanostructures deposited on metallic fl... more This paper reports the comparative study of piezoelectric nanostructures deposited on metallic flexible substrate versus rigid substrates as a new architecture for energy harvesters. Rigid metallic substrates are multi-layered types of Pt/Ti/SiO 2 /Si or Au/Ti/SiO 2 /Si while Ti foil is a flexible metallic substrate. The active piezo-layer consisted of a vertical ZnO nanowires (ZnO NWs) array grown by the hydrothermal method at low temperature, on a previously deposited crystalline seed (nucleation) sol-gel layer and covered with a layer of polymethylmethacrylate (PMMA). The new obtained nanostructures have been characterized in different stages of preparation by X-Ray Diffraction, Scanning and Transmission Electron Microscopy, Atomic Force Microscopy, Spectroscopic Ellipsometry. The piezoelectric performance of PMMA/(ZnO NWs)/Ti structures was evaluated by measuring the d 33 coefficient. Results show that ZnO nanowires have successfully grown on the flexible substrates with a piezoelectric coefficient four times greater than on rigid substrates. By improving vertical integration of ZnO NWs on flexible metallic substrate, PMMA/(ZnO NWs)/Ti affordable nanostructures open the way towards integration in wireless or defence technologies and in wearable or implantable biomedical systems as efficient harvester.

Journal of Physics: Conference Series, 2020

We report a study of p-Si(100) surface layers modified by plasma immersion ion implantation (PIII... more We report a study of p-Si(100) surface layers modified by plasma immersion ion implantation (PIII) and dry oxidation. This is expected to allow one to engineer near-surface layers with different thicknesses and levels of amorphization. Hydrogen ions were introduced into a shallow near-surface Si region through PIII with energy of 2 keV and doses ranging from 1013 ion/cm2 to 1015 ion/cm2. The implanted Si surface was subjected to oxidation in dry oxygen atmosphere at temperatures ranging from 700 °C to 800 °C. The optical and structural properties of the modified Si layers were studied in detail by spectroscopic ellipsometry (SE) in the IR spectral range of 300 – 4000 cm−1. The surface morphology was examined by atomic force microscopy (AFM) imaging at different scales and by fractal analysis. Through decomposition of the main Si-O bands into Gaussian peaks, different Si oxidation states were identified, suggesting non-stoichiometric oxide layer composition.

Dyes and Pigments, 2019

The study reports a series of results obtained by synthesis, spectral and morphological analysis ... more The study reports a series of results obtained by synthesis, spectral and morphological analysis of new tetrapyrrolic structures: 5-(4-hydroxy-3-methoxyphenyl)-10,15,20-tris-(4-carboxymethylphenyl) porphyrin (P1.2), Zn(II)-5-(4-hydroxy-3methoxyphenyl)-10,15,20-tris-(4-carboxymethylphenyl) porphyrin (Zn(II)1.2) and Cu(II)-5-(4-hydroxy-3-methoxyphenyl)-10,15,20-tris-(4-carboxymethylphenyl) porphyrin (Cu(II)1.2), as potential candidates for theranostics. Porphyrins were obtained by microwave synthesis under solvent-free conditions and characterized by elemental analysis, FT-IR, UV-Vis and NMR spectroscopies. The absorption properties of the synthetized compounds were studied in different solvents (ethanol, polyethylene glycol 200, dimethylsulfoxide, dichloromethane, chloroform). The spectral profile of the new porphyrins was completed by studying the fluorescence emission and singlet oxygen formation quantum yields. P1.2 and Zn(II)1.2 exhibit fluorescence while for Cu(II)1.2 the fluorescence emission is negligible. P1.2 and Zn(II)1.2 exhibited photodynamic therapy (PDT) acceptable values of singlet oxygen generation. In the case of Cu(II)1.2 this parameter is reduced ca. 5 times. For powdered samples of P1.2 adsorbed onto powdered PEG a detailed study was performed correlating the fluorescence emission intensity with sample absorption to determine the concentration range where aggregation does not occur. Fluorescence emission quantum yields and lifetimes were determined for all samples under study to determine the useful range of concentrations for PDT use. Atomic force microscope (AFM) studies were also made, which exhibit the aggregate species formation for high loadings of the porphyrin P1.2 adsorbed onto specific surfaces.

Materials Science in Semiconductor Processing, 2017

Titania films doped with low amount of vanadium were deposited on different substrates (microscop... more Titania films doped with low amount of vanadium were deposited on different substrates (microscope glass, microscope glass covered with SiO 2 barrier layer, and silicon wafer with a thermally grown layer of SiO 2) by dip coating from solutions prepared by sol-gel and microwave (MW) assisted sol-gel syntheses. The selected molar composition was 99.95:0.05 which corresponds to 0.03 at% of V. The films were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray diffraction (XRD) and Spectroscopic Ellipsometry (SE). The deposited films thermally treated at 450°C, presented homogeneous and continuous nanostructured surfaces and good adherence to the substrates used. All samples crystallized in anatase phase and have good optical properties. The highest transmission value was obtained for the V-doped TiO 2 films (T > 90%) deposited from solutions prepared by microwaves assisted sol-gel method. Based on the obtained results it was concluded that the method of preparation has higher influence on the properties of the resulted films than the substrates used.

Journal of Thermal Analysis and Calorimetry, 2017

In order to establish the influence of the preparation method on thermal behaviour of gels obtain... more In order to establish the influence of the preparation method on thermal behaviour of gels obtained by the sol–gel and microwave-assisted sol–gel methods, a comparative thermal analysis study was conducted by the thermogravimetric and differential thermal analysis (TG/DTG/DTA) and evolved gas analysis (EGA) on TiO2 and V2O5-doped TiO2 gels, where TiO2:V2O5 molar ratio was set to 99.95:0.05 and 98.0:2.0. In contrast to TiO2 gels, for which the thermal behaviour was not significantly influenced by the preparation method, the microwave-irradiated binary samples showed a more complex and prolonged decomposition compared to their non-irradiated counterparts. This observation was correlated with influence of microwaves in enhancing the reaction rate between the Ti and V reagents leading to formation of more complex compositions of gels. Based on TG/DTG/DTA results, the temperatures of 300 and 450 °C were chosen for the processing of powders in air. All samples thermally treated at 300 and 450 °C crystallized in a single anatase phase except the TiO2:V2O5 with a molar ratio 99.95:0.05, obtained by microwave-assisted sol–gel method that contains also small amount of rutile phase. At 550 °C all samples contain mixture of anatase and rutile phases.

Journal of Sol-Gel Science and Technology, 2016

In the present work, TiO2 and V-doped TiO2 films with TiO2/V2O5 molar ratios 98:2 and 99.95:0.05 ... more In the present work, TiO2 and V-doped TiO2 films with TiO2/V2O5 molar ratios 98:2 and 99.95:0.05 were prepared by sol–gel and microwave (MW) assisted sol–gel syntheses. The reagents used were tetraethyl orthotitanate, vanadyl acetylacetonate and ethanol as solvent. The solutions were prepared either by stirring for 2 h at room temperature or by exposing them for 5 min to microwaves at 300 W in an oven operated at frequency of 2.45 GHz. The deposition of the films was realized by dip-coating on microscope glass substrate. The multilayer films were obtained by successive deposition. The first benefit of using MW-assisted sol–gel preparation was the essentially increased stability of the resulted solution against gelling, behavior that is of great interest for multilayer depositions. A comprehensive structural, morphological and optical characterization of the obtained films was realized. Differences between the films obtained by the two types of preparation routes are reflected in a more compact and continuous structure with very low roughness, increased thickness and higher refractive index as well as increased transmission when MW-assisted sol–gel method was used.Graphical Abstract

Applied Surface Science, 2017

Aluminum Nitride (AlN) thin films were synthesized on Si (100) wafers at 450 • C by pulsed laser ... more Aluminum Nitride (AlN) thin films were synthesized on Si (100) wafers at 450 • C by pulsed laser deposition. A polycrystalline AlN target was multipulsed irradiated in a nitrogen ambient, at different laser pulse repetition rate. Grazing Incidence X-Ray Diffraction and Atomic Force Microscopy analyses evidenced nanocrystallites with a hexagonal lattice in the amorphous AlN matrix. The thickness and optical constants of the layers were determined by infrared spectroscopic ellipsometry. The optical properties were studied by Fourier Transform Infrared reflectance spectroscopy in polarised oblique incidence radiation. Berreman effect was observed around the longitudinal phonon modes of the crystalline AlN component. Angular dependence of the A 1 LO mode frequency was analysed and connected to the orientation of the particles' optical axis to the substrate surface normal. The role of the laser pulse frequency on the layers' properties is discussed on this basis.

Materials Science in Semiconductor Processing, 2016

Abstract Nb doped titania (TiO 2 :Nb) multilayered films (1–10 layers) with anatase structure wer... more Abstract Nb doped titania (TiO 2 :Nb) multilayered films (1–10 layers) with anatase structure were obtained by the low-cost sol–gel and dipping method on microscope glass substrates, followed by thermal treatment at 450 °C for 1 h. After each layer deposition, an intermediate annealing step was performed at 300 °C for 30 min. Doping TiO 2 sol–gel films with a low amount of Nb (0.8 at%) allows obtaining an improved CO sensor able to operate under environmental atmosphere (air). It was found that the sensor sensitivity is less dependent on the film thickness but is significantly influenced by Nb doping at the optimal working temperature of 400 °C. Good recovery characteristics were obtained for a wide CO detection range, between 0 and 2000 ppm. The gas-sensing behavior of the films was correlated with the structural, chemical and morphological properties of the multi-layered structures.

Applied Surface Science, 2016

We report on multi-stage pulsed laser deposition of aluminum nitride (AlN) on Si (1 0 0) wafers, ... more We report on multi-stage pulsed laser deposition of aluminum nitride (AlN) on Si (1 0 0) wafers, at different temperatures. The first stage of deposition was carried out at 800 • C, the optimum temperature for AlN crystallization. In the second stage, the deposition was conducted at lower temperatures (room temperature, 350 • C or 450 • C), in ambient Nitrogen, at 0.1 Pa. The synthesized structures were analyzed by grazing incidence X-ray diffraction (GIXRD), transmission electron microscopy (TEM), atomic force microscopy and spectroscopic ellipsometry (SE). GIXRD measurements indicated that the two-stage deposited AlN samples exhibited a randomly oriented wurtzite structure with nanosized crystallites. The peaks were shifted to larger angles, indicative for smaller inter-planar distances. Remarkably, TEM images demonstrated that the high-temperature AlN "seed" layers (800 • C) promoted the growth of poly-crystalline AlN structures at lower deposition temperatures. When increasing the deposition temperature, the surface roughness of the samples exhibited values in the range of 0.4-2.3 nm. SE analyses showed structures which yield band gap values within the range of 4.0-5.7 eV. A correlation between the results of singleand multi-stage AlN depositions was observed.

Applied Surface Science, 2015

By codoping with a donor-acceptor pair through a two-step chemical method we have succeed to obta... more By codoping with a donor-acceptor pair through a two-step chemical method we have succeed to obtain p-type ZnO thin films on glass. Firstly, a thin undoped ZnO seed layer was deposited by sol-gel method followed by the deposition of InN codoped ZnO film obtained through the hydrothermal technique. The influence of post-deposition annealing temperature (100 • C, 300 • C and 500 • C) on the samples was investigated from a structural, chemical, morphological and optoelectrical point of view. X-ray diffractometry (XRD), infrared ellipsometry and X-ray photoelectron spectroscopy (XPS) analyses have confirmed the codoped nature of the ZnO thin films. The XRD pattern analysis has established the films have wurtzite nanocrystalline structure, the crystallite sizes varying between 10 nm and 13 nm with the annealing temperature. Continuous and homogenous films with nanorods surface morphology has been obtained, as visualized by scanning electron microscopy measurements. Hall Effect measurements have established that all samples, regardless of annealing temperature, showed p-type conduction due to the successful incorporation of nitrogen in the film, with the highest carrier concentration registered at 500 • C. This is in good correlation with the nitrogen content in the films as revealed from XPS. In all samples, the XPS depth profiling has shown a nitrogen gradient with higher elemental concentration at the surface.

Journal of Physics: Conference Series, 2014

The surface morphology of p-Si(100) wafers after RF plasma immersion (PII) H + ion implantation i... more The surface morphology of p-Si(100) wafers after RF plasma immersion (PII) H + ion implantation into a shallow Si surface layer and after subsequent thermal oxidation was studied by atomic-force microscopic (AFM) imaging. After PII implantation of hydrogen ions with an energy of 2 keV and fluences ranging from 10 13 cm-2 to 10 15 cm-2 , the Si wafers were oxidized in dry O 2 at temperatures ranging from 700 o C to 800 o C. From the analysis of the AFM images, the surface amplitude parameters were evaluated and considered in terms of the technological conditions. The amplitude parameters showed a clear dependence on the H + dose and the oxidation temperature, with the tendency of increasing with the increase of both the H + ion fluence and the oxidation temperature. The implantation causes surface roughening, changing the RMS roughness value from 0.15 nm (typical for a polished Si(100) surface) to the highest value 0.6 nm for the H + fluence of 10 15 ions/cm 2. Oxidation of the H + implanted Si region, as the oxide is growing inward into Si, levels away the pits created by implants and results in a smoother surface, although keeping the RMS values larger than 0.2 nm.

2007 International Semiconductor Conference, 2007

Titanium oxynitride thin films were deposited by sol-gel method on quartz substrate in an attempt... more Titanium oxynitride thin films were deposited by sol-gel method on quartz substrate in an attempt to study the microstructural and optical properties of TiOxNy films deposited by sol-gel method. For this purpose, X-ray diffraction (XRD), atomic force microscopy (AFM), and spectroscopic ellipsometry (SE) investigations were performed. Examining the surface morphology and grain sizes of the films, complex nanostructured surfaces, with

Journal of Physics: Conference Series, 2014

Preliminary results of the studies of electrical properties of ZnO films, codoped with donor and ... more Preliminary results of the studies of electrical properties of ZnO films, codoped with donor and acceptor pair In-N are reported. The films were grown on Si substrates by chemical route procedures involving a sol-gel followed by hydrothermal treatment at 500?C. For electrical characterization, current-voltage and capacitance-voltage measurements were conducted on MIS structures with embedded ZnO(In,N) films. The estimated doping concentration in the studied films is higher than 1?1016 cm?3 corresponding to a semiconductor with good conductivity. However, the obtained large values of the differential specific resistivity (? = 3.2?105 ?cm) suggest that the nitrogen acceptors in these films are compensated by some kind of donor-type defects.

2006 International Semiconductor Conference, 2006

SnO2 thin films have been deposited on glass from Sn (II)-2-ethylhexanoate precursor using the di... more SnO2 thin films have been deposited on glass from Sn (II)-2-ethylhexanoate precursor using the dip-coating sol-gel method. Based on spectroscopic ellipsometry (SE) measurements optical and structural properties of the SnO2 films have been obtained. It was found that the concentration of tin oxide sols used for deposition strongly influences the thickness and the optical properties of the film, such as

Thin Solid Films, 2007

A comparative study of the sol–gel films prepared in the SiO2–P2O5 system starting with triethylp... more A comparative study of the sol–gel films prepared in the SiO2–P2O5 system starting with triethylphosphate, triethylphosphite and phosphoric acid as P precursors was performed. The work addresses basic aspects of physics, chemistry, and engineering of oxide films for applications in microelectronics, sensing, nano-photonics, and optoelectronics by establishing the influence of different precursors on the composition, structure and optical properties of

physica status solidi c, 2008

1 National Institute of Research and Development for Optoelectronics-INOE 2000, Atomistilor Str. ... more 1 National Institute of Research and Development for Optoelectronics-INOE 2000, Atomistilor Str. 1, PO Box MG - 5, 77125 Magurele, Romania 2 University “Politehnica” Timisoara, Pta. Victoriei nr. 2, 300006 Timisoara, Romania 3 Institute of Physical Chemistry “IGMurgulescu”, Spl. ...