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Papers by Valentin Teodorescu

Research paper thumbnail of The Influence of the Structural and Morphological Properties of WO3 Thin Films Obtained by PLD on the Photoelectrochemical Water-Splitting Reaction Efficiency

Nanomaterials

Due to its physical and chemical properties, the n-type tungsten oxide (WO3) semiconductor is a s... more Due to its physical and chemical properties, the n-type tungsten oxide (WO3) semiconductor is a suitable photoanode for water decomposition reaction. The responses of the photoelectrochemical PEC water-splitting properties as an effect of structural and optical changes of WO3 thin films, as well as the nature of electrolyte solutions, were studied in this work. The WO3 thins films have been obtained by pulsed laser deposition (PLD) on silicon (Si(001)) covered with platinum substrates using three different laser wavelengths. As the XRD (X-ray diffraction) and XTEM (cross-section transmission electron microscopy) analysis shows, the formation of highly crystalline monocline WO3 phase is formed for the film deposited at 1064 nm wavelength and poor crystalline phases with a large ordering anisotropy, characteristic of 2D structures for the films deposited at 355 nm and 193 nm wavelengths, respectively. The photogenerated current densities Jph depend on the laser wavelength, in both alk...

Research paper thumbnail of How morphology determines the charge storage properties of Ge nanocrystals in HfO2

Scripta Materialia, 2016

Abstract The strong correlation between morphology and charge storage properties of HfO 2 /Ge/HfO... more Abstract The strong correlation between morphology and charge storage properties of HfO 2 /Ge/HfO 2 /Si trilayer structures was evidenced. The morphology of structures deposited by magnetron sputtering and electron beam evaporation was tailored by rapid thermal annealing and investigated by transmission electron microscopy, Raman and X-ray photoelectron spectroscopies. The best hysteresis loops (capacitance–voltage characteristics) were obtained for trilayers with high density Ge nanocrystals located in the position of as-deposited Ge layer. The decrease of Ge nanocrystals density narrows the memory window, by spreading Ge atoms into HfO 2 matrix (sputtered trilayers), or by Ge atoms expulsion toward HfO 2 nanocrystals surface (evaporated trilayers).

Research paper thumbnail of Room temperature ammonia sensing with Barium Strontium Titanate under humid air background

Sensors and Actuators B: Chemical, 2015

Research paper thumbnail of Crystalline structure of very hard tungsten carbide thin films obtained by reactive pulsed laser deposition

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1999

... IN Mihailescu, Eniko Gyorgy, G. Marin, M. Popescu, VS Teodorescu, J. Van Landuyt, C. Grivas, ... more ... IN Mihailescu, Eniko Gyorgy, G. Marin, M. Popescu, VS Teodorescu, J. Van Landuyt, C. Grivas, A. Hatziapostolou. Abstract. ... Phys. 58, 1765 (1985). SI Anisimov, D. Bauerle, and BS Luk'yanchuk, “Gas dynamics and film profiles in pulsed-laser deposition of materials,” Phys. Rev. ...

Research paper thumbnail of Laser processing of nanostructures: enhancing functional properties of lead-free perovskite nanostructures through chemical pressure and epitaxial strain

Functional Nanostructured Interfaces for Environmental and Biomedical Applications

Research paper thumbnail of Thermal behavior of Cu-doped TiO2 gels synthesized by the sol-gel method

Revue Roumaine de Chimie

The thermal behavior of Cu-doped TiO2 gels obtained by the sol-gel method was investigated by the... more The thermal behavior of Cu-doped TiO2 gels obtained by the sol-gel method was investigated by thermogravimetric and differential thermal analysis (TG/DTG/DTA) and differential scanning calorimetry (DSC) measurements. The comparative investigation of the structure and morphology of the as-prepared gels and of the nanopowders obtained by annealing them was realized by transmission electron microscopy (TEM), Fourier transmission infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Significant differences were noticed depending on the amount of dopant (0.5 or 2.0 mol % CuO). A higher dopant concentration resulted in a more complex decomposition of the sample. This behavior was associated with the formation of various molecular species in the sol-gel solutions before gelation, determined by the different amount of the dopant used.

Research paper thumbnail of Influence of SiGe Nanocrystallization on Short-Wave Infrared Sensitivity of SiGe–TiO2 Films and Multilayers

The Journal of Physical Chemistry C

Research paper thumbnail of GeSn/SiO2 Multilayers by Magnetron Sputtering Deposition for Short-Wave Infrared Photonics

ACS Applied Materials & Interfaces

Research paper thumbnail of Epitaxial GeSn Obtained by High Power Impulse Magnetron Sputtering and the Heterojunction with Embedded GeSn Nanocrystals for Shortwave Infrared Detection

Research paper thumbnail of Orthorhombic HfO2 with embedded Ge nanoparticles in nonvolatile memories used for the detection of ionizing radiation

Research paper thumbnail of Tryptophan / Dextran70 Based - Fluorescent Silver Nanoparticles: Synthesis and Physicochemical Properties

Research paper thumbnail of Ambiguous Role of Growth-Induced Defects on the Semiconductor-to-Metal Characteristics in Epitaxial VO2/TiO2 Thin Films

ACS Applied Materials & Interfaces

Research paper thumbnail of Spherical cobalt/cobalt oxide - Carbon composite anodes for enhanced lithium-ion storage

Research paper thumbnail of GeSn Nanocrystals in GeSnSiO2 by Magnetron Sputtering for Short-Wave Infrared Detection

ACS Applied Nano Materials

Research paper thumbnail of Networked mesoporous SnO 2 nanostructures templated by Brij ® 35 with enhanced H 2 S selective performance

Microporous and Mesoporous Materials

Research paper thumbnail of Rapid thermal annealing procedure for densification of sol-gel indium tin oxide thin films

Crystal Engineering

In this work, we report on the interest of the rapid thermal annealing (RTA) for densification of... more In this work, we report on the interest of the rapid thermal annealing (RTA) for densification of sol-gel (SG) indium tin oxide (ITO) thin films. The crystalline structure of these ITO films was visualized by transmission electron microscopy (TEM) and corresponding electron diffraction pattern were compared with data from pure In 2 O 3. The average grain size, measured from TEM micrographs, ranges from 5 to 50 nm. The film densification was followed by Rutherford backscattering spectrometry coupled with cross-section TEM observations. A comparison with classical annealing is discussed.

Research paper thumbnail of <title>Continuous Wave Laser Oxidation Of Copper</title>

Industrial Applications of Laser Technology

ABSTRACT

Research paper thumbnail of Sensors based on mesoporous SnO2-CuWO4 with high selective sensitivity to H2S at low operating temperature

Journal of Hazardous Materials, 2017

Development of new sensitive materials by different synthesis routes in order to emphasize the se... more Development of new sensitive materials by different synthesis routes in order to emphasize the sensing properties for hazardous H2S detection is one of a nowadays challenge in the field of gas sensors. In this study we obtained mesoporous SnO2-CuWO4 with selective sensitivity to H2S by an inexpensive synthesis route with low environmental pollution level, using tripropylamine (TPA) as template and polyvinylpyrrolidone (PVP) as dispersant/stabilizer. In order to bring insights about the intrinsic properties, the powders were characterized by means of a variety of complementary techniques such as: X-Ray Diffraction, XRD; Transmission Electron Microscopy, TEM; High Resolution TEM, HRTEM; Raman Spectroscopy, RS; Porosity Analysis by N2 adsorption/desorption, BET; Scanning Electron Microscopy, SEM and X-ray Photoelectron Spectroscopy, XPS. The sensors were fabricated by powders deposition via screen-printing technique onto planar commercial Al2O3 substrates. The sensor signals towards H2S exposure at low operating temperature (100°C) reaches values from 10(5) (for SnWCu600) to 10(6) (for SnWCu800) over the full range of concentrations (5-30ppm). The recovery processes were induced by a short temperature trigger of 500°C. The selective sensitivity was underlined with respect to the H2S, relative to other potential pollutants and relative humidity (10-70% RH).

Research paper thumbnail of In situ transmission electron microscopy study of Ni silicide phases formed on (001) Si active lines

Journal of Applied Physics, Jun 30, 2001

Research paper thumbnail of Influence of Substrate on Hafnium Silicate Metal-Insulator-Metal Capacitors Grown by Atomic Layer Deposition

Research paper thumbnail of The Influence of the Structural and Morphological Properties of WO3 Thin Films Obtained by PLD on the Photoelectrochemical Water-Splitting Reaction Efficiency

Nanomaterials

Due to its physical and chemical properties, the n-type tungsten oxide (WO3) semiconductor is a s... more Due to its physical and chemical properties, the n-type tungsten oxide (WO3) semiconductor is a suitable photoanode for water decomposition reaction. The responses of the photoelectrochemical PEC water-splitting properties as an effect of structural and optical changes of WO3 thin films, as well as the nature of electrolyte solutions, were studied in this work. The WO3 thins films have been obtained by pulsed laser deposition (PLD) on silicon (Si(001)) covered with platinum substrates using three different laser wavelengths. As the XRD (X-ray diffraction) and XTEM (cross-section transmission electron microscopy) analysis shows, the formation of highly crystalline monocline WO3 phase is formed for the film deposited at 1064 nm wavelength and poor crystalline phases with a large ordering anisotropy, characteristic of 2D structures for the films deposited at 355 nm and 193 nm wavelengths, respectively. The photogenerated current densities Jph depend on the laser wavelength, in both alk...

Research paper thumbnail of How morphology determines the charge storage properties of Ge nanocrystals in HfO2

Scripta Materialia, 2016

Abstract The strong correlation between morphology and charge storage properties of HfO 2 /Ge/HfO... more Abstract The strong correlation between morphology and charge storage properties of HfO 2 /Ge/HfO 2 /Si trilayer structures was evidenced. The morphology of structures deposited by magnetron sputtering and electron beam evaporation was tailored by rapid thermal annealing and investigated by transmission electron microscopy, Raman and X-ray photoelectron spectroscopies. The best hysteresis loops (capacitance–voltage characteristics) were obtained for trilayers with high density Ge nanocrystals located in the position of as-deposited Ge layer. The decrease of Ge nanocrystals density narrows the memory window, by spreading Ge atoms into HfO 2 matrix (sputtered trilayers), or by Ge atoms expulsion toward HfO 2 nanocrystals surface (evaporated trilayers).

Research paper thumbnail of Room temperature ammonia sensing with Barium Strontium Titanate under humid air background

Sensors and Actuators B: Chemical, 2015

Research paper thumbnail of Crystalline structure of very hard tungsten carbide thin films obtained by reactive pulsed laser deposition

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1999

... IN Mihailescu, Eniko Gyorgy, G. Marin, M. Popescu, VS Teodorescu, J. Van Landuyt, C. Grivas, ... more ... IN Mihailescu, Eniko Gyorgy, G. Marin, M. Popescu, VS Teodorescu, J. Van Landuyt, C. Grivas, A. Hatziapostolou. Abstract. ... Phys. 58, 1765 (1985). SI Anisimov, D. Bauerle, and BS Luk&amp;amp;#x27;yanchuk, “Gas dynamics and film profiles in pulsed-laser deposition of materials,” Phys. Rev. ...

Research paper thumbnail of Laser processing of nanostructures: enhancing functional properties of lead-free perovskite nanostructures through chemical pressure and epitaxial strain

Functional Nanostructured Interfaces for Environmental and Biomedical Applications

Research paper thumbnail of Thermal behavior of Cu-doped TiO2 gels synthesized by the sol-gel method

Revue Roumaine de Chimie

The thermal behavior of Cu-doped TiO2 gels obtained by the sol-gel method was investigated by the... more The thermal behavior of Cu-doped TiO2 gels obtained by the sol-gel method was investigated by thermogravimetric and differential thermal analysis (TG/DTG/DTA) and differential scanning calorimetry (DSC) measurements. The comparative investigation of the structure and morphology of the as-prepared gels and of the nanopowders obtained by annealing them was realized by transmission electron microscopy (TEM), Fourier transmission infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Significant differences were noticed depending on the amount of dopant (0.5 or 2.0 mol % CuO). A higher dopant concentration resulted in a more complex decomposition of the sample. This behavior was associated with the formation of various molecular species in the sol-gel solutions before gelation, determined by the different amount of the dopant used.

Research paper thumbnail of Influence of SiGe Nanocrystallization on Short-Wave Infrared Sensitivity of SiGe–TiO2 Films and Multilayers

The Journal of Physical Chemistry C

Research paper thumbnail of GeSn/SiO2 Multilayers by Magnetron Sputtering Deposition for Short-Wave Infrared Photonics

ACS Applied Materials & Interfaces

Research paper thumbnail of Epitaxial GeSn Obtained by High Power Impulse Magnetron Sputtering and the Heterojunction with Embedded GeSn Nanocrystals for Shortwave Infrared Detection

Research paper thumbnail of Orthorhombic HfO2 with embedded Ge nanoparticles in nonvolatile memories used for the detection of ionizing radiation

Research paper thumbnail of Tryptophan / Dextran70 Based - Fluorescent Silver Nanoparticles: Synthesis and Physicochemical Properties

Research paper thumbnail of Ambiguous Role of Growth-Induced Defects on the Semiconductor-to-Metal Characteristics in Epitaxial VO2/TiO2 Thin Films

ACS Applied Materials & Interfaces

Research paper thumbnail of Spherical cobalt/cobalt oxide - Carbon composite anodes for enhanced lithium-ion storage

Research paper thumbnail of GeSn Nanocrystals in GeSnSiO2 by Magnetron Sputtering for Short-Wave Infrared Detection

ACS Applied Nano Materials

Research paper thumbnail of Networked mesoporous SnO 2 nanostructures templated by Brij ® 35 with enhanced H 2 S selective performance

Microporous and Mesoporous Materials

Research paper thumbnail of Rapid thermal annealing procedure for densification of sol-gel indium tin oxide thin films

Crystal Engineering

In this work, we report on the interest of the rapid thermal annealing (RTA) for densification of... more In this work, we report on the interest of the rapid thermal annealing (RTA) for densification of sol-gel (SG) indium tin oxide (ITO) thin films. The crystalline structure of these ITO films was visualized by transmission electron microscopy (TEM) and corresponding electron diffraction pattern were compared with data from pure In 2 O 3. The average grain size, measured from TEM micrographs, ranges from 5 to 50 nm. The film densification was followed by Rutherford backscattering spectrometry coupled with cross-section TEM observations. A comparison with classical annealing is discussed.

Research paper thumbnail of <title>Continuous Wave Laser Oxidation Of Copper</title>

Industrial Applications of Laser Technology

ABSTRACT

Research paper thumbnail of Sensors based on mesoporous SnO2-CuWO4 with high selective sensitivity to H2S at low operating temperature

Journal of Hazardous Materials, 2017

Development of new sensitive materials by different synthesis routes in order to emphasize the se... more Development of new sensitive materials by different synthesis routes in order to emphasize the sensing properties for hazardous H2S detection is one of a nowadays challenge in the field of gas sensors. In this study we obtained mesoporous SnO2-CuWO4 with selective sensitivity to H2S by an inexpensive synthesis route with low environmental pollution level, using tripropylamine (TPA) as template and polyvinylpyrrolidone (PVP) as dispersant/stabilizer. In order to bring insights about the intrinsic properties, the powders were characterized by means of a variety of complementary techniques such as: X-Ray Diffraction, XRD; Transmission Electron Microscopy, TEM; High Resolution TEM, HRTEM; Raman Spectroscopy, RS; Porosity Analysis by N2 adsorption/desorption, BET; Scanning Electron Microscopy, SEM and X-ray Photoelectron Spectroscopy, XPS. The sensors were fabricated by powders deposition via screen-printing technique onto planar commercial Al2O3 substrates. The sensor signals towards H2S exposure at low operating temperature (100°C) reaches values from 10(5) (for SnWCu600) to 10(6) (for SnWCu800) over the full range of concentrations (5-30ppm). The recovery processes were induced by a short temperature trigger of 500°C. The selective sensitivity was underlined with respect to the H2S, relative to other potential pollutants and relative humidity (10-70% RH).

Research paper thumbnail of In situ transmission electron microscopy study of Ni silicide phases formed on (001) Si active lines

Journal of Applied Physics, Jun 30, 2001

Research paper thumbnail of Influence of Substrate on Hafnium Silicate Metal-Insulator-Metal Capacitors Grown by Atomic Layer Deposition