Ionel Stavarache

Ionel Stavarache
The National Institute of Materials Physics · Laboratory of Nanoscale Condensed Matter

PhD

About

84
Publications
11,125
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634
Citations
Citations since 2017
33 Research Items
396 Citations
2017201820192020202120222023020406080
2017201820192020202120222023020406080
2017201820192020202120222023020406080
2017201820192020202120222023020406080

Publications

Publications (84)
Article
Full-text available
Lately, there is a growing interest in organic photovoltaic (OPV) cells due to the organic materials’ properties and compatibility with various types of substrates. However, their efficiencies are low relative to the silicon ones; therefore, other ways (i.e., electrode micron/nanostructuring, synthesis of new organic materials, use of additives) to...
Article
Full-text available
The high-k-based MOS-like capacitors are a promising approach for the domain of non-volatile memory devices, which currently is limited by SiO2 technology and cannot face the rapid downsizing of the electronic device trend. In this paper, we prepare MOS-like trilayer memory structures based on high-k ZrO2 by magnetron sputtering, with a 5% and a 10...
Article
Full-text available
"Nanocrystalline Si and Ge are ofhigh interestfor integrated Si photonics related to light emission, opticul sensors, photodetectors, solar energy harvesting and conversion devices, and also forfloating gate non-volatile memories (NVMs). In this review, we have focused on nanocrystalline porous Si (nc-PS) with extension to Si nanodots, and Ge nanoc...
Article
Full-text available
Cu 2 ZnSnS 4 (CZTS) is regarded as one of the emerging materials for next-generation thin film solar cells. However, its synthesis is complex, and obtaining a single-phase CZTS thin film is difficult. This work reports the elaboration of Cu 2 ZnSnS 4 thin films by a sequential magnetron sputtering deposition of Cu 2 SnS 3 (CTS) and ZnS as stacked f...
Preprint
Full-text available
Nanocrystalline Si and Ge are of high interest for integrated Si photonics related to light emission, optical sensors, photodetectors, solar energy harvesting and conversion devices, and also for floating gate non-volatile memories (NVMs). In this review, we have focused on nanocrystalline porous Si (nc-PS) with extension to Si nanodots, and Ge nan...
Article
Amorphous metal chalcogenides have good switching properties for resistive memories, but have low thermal stability. In this work, the response to rapid thermal stress, as high as 550 °C, of amorphous Cu-GeSe, Ag-GeSe, Cu-GeTe, Ag-GeTe thin films, is investigated. Metal-GeTe films, which are amorphous up to 280 °C, are the most stable. Metal-GeSe f...
Article
Full-text available
In this work, amorphous tin oxide thin films were deposited by non-reactive radio frequency magnetron sputtering. A ceramic \({\text{SnO}}_2\) target was used, while different working pressures were employed. The target to substrate distance was fixed to 17 cm, and the substrate was not intentionally heated. The properties of \({\text{SnO}}_2\) (th...
Poster
Full-text available
Development of floating gate (FG) non-volatile memories (NVMs) based on nanocrystals (NCs) is of great importance for the continuous increasing requirements for highly efficient data storage. NCs by tuning of their size, density & interface quality with embedding oxide make possible the adjusting of device parameters. These NVMs use FG of either me...
Article
In this paper, we report studies on Al2O3/Ge/Al2O3 trilayer memory structures deposited by magnetron sputtering at room temperature on p-Si substrates coated with 3 nm SiO2. The changes of the structure, morphology and memory properties induced by rapid thermal annealing (RTA) in a broad temperature range 550–900 °C have been carefully investigated...
Article
Full-text available
One of the key elements in assessing traffic safety on the roads is the detection of asphalt conditions. In this paper, we propose an optical sensor based on GeSi nanocrystals embedded in SiO2 matrix that discriminates between different slippery road conditions (wet and icy asphalt and asphalt covered with dirty ice) in respect to dry asphalt. The...
Article
Full-text available
Films of SiGe nanocrystals (NCs) in oxide have the advantage of tuning the energy band gap by adjusting SiGe NCs composition and size. In this study, SiGe-SiO2 amorphous films were deposited by magnetron sputtering on Si substrate followed by rapid thermal annealing at 700, 800 and 1000 °C. We investigated films with Si:Ge:SiO2 compositions of 25:2...
Conference Paper
Films of amorphous Ge nanoparticles in Si3N4 on heated Si and quartz substrates at 300°C were obtained by co-sputtering Ge, and Si3 N4 . The films structure and photo-electrical behaviour were studied through transmission electron microscopy and, current- voltage and spectral photo-current investigations, respectively. The spectral photo-current we...
Article
Full-text available
Multilayer structures comprising of SiO 2 /SiGe/SiO 2 and containing SiGe nanoparticles were obtained by depositing SiO 2 layers using reactive direct current magnetron sputtering (dcMS), whereas, Si and Ge were co-sputtered using dcMS and high-power impulse magnetron sputtering (HiPIMS). The as-grown structures subsequently underwent rapid thermal...
Article
Trilayer memory capacitors of control HfO<sub>2</sub>/ floating gate of Ge nanoparticles in HfO<sub>2</sub> / tunnel HfO<sub>2</sub> /Si substrate deposited by magnetron sputtering and subsequently annealed are investigated for the first time for applications in radiation dosimetry. In the floating gate (FG), amorphous Ge nanoparticles (NPs) are a...
Article
Full-text available
In this work, rapid thermal annealing (RTA) was applied to indium tin oxide (ITO) films in ambient atmosphere, resulting in significant improvements of the quality of the ITO films that are commonly used as conductive transparent electrodes for photovoltaic structures. Starting from a single sintered target (purity 99.95%), ITO thin films of predef...
Article
Full-text available
In this work we prepared films of amorphous germanium nanoparticles embedded in SiO2 deposited by magnetron sputtering on Si and quartz heated substrates at 300, 400 and 500 °C. Structure, morphology, optical, electrical and photoconduction properties of all films were investigated. The Ge concentration in the depth of the films is strongly depende...
Poster
Full-text available
We deal with new solutions for fabricating new advanced materials based on SiGeSn nanocrystals (NCs) in oxides with targeted photoconductive (PHC) and non-volatile memory (NVM) properties, using environmentally friendly and cost-effective technologies and raw materials with impact on wide range domains of applications as environment, biomedicine, f...
Article
Detection in short-wave infrared (SWIR) has become a very stringent technology requirement for developing fields like hyperspectral imaging or climate changes. In a market dominated by III-V materials, GeSn, a Si compatible semiconductor, has the advantage of cost efficiency and inerrability by using the mature Si technology. Despite the recent pro...
Conference Paper
Trilayer MOS capacitors gate HfO2 /floating gate of Ge nanocrystals in HfO2 /tunnel HfO2 /Si substrate were prepared in the aim to be used for the detection of ionizing radiation. Magnetron sputtering and rapid thermal annealing were used for their fabrication. Capacitance-voltage measurements showed that Ge nanocrystals are the most important char...
Article
Full-text available
Arrays of magnetic Ni–Cu alloy nanowires with different compositions were prepared by a template-replication technique using electrochemical deposition into polycarbonate nanoporous membranes. Photolithography was employed for obtaining interdigitated metallic electrode systems of Ti/Au onto SiO2/Si substrates and subsequent electron beam lithograp...
Data
Additional experimental data.
Conference Paper
Full-text available
The photosensing properties related to the structure of GeSi/TiO2 multilayers prepared under different conditions are studied. TiO2 cap/(GeSi/TiO2)2 multilayers (ML) were deposited by magnetron sputtering (MS) and annealed by rapid thermal annealing. Trilayers of TiO2 cap/GeSi/TiO2 (TL) were also deposited using reactive high power impulse MS (HiPI...
Article
Lowering the temperature of crystallization by deposition of thin films on a heated substrate represents the easiest way to find new means to develop and improve new working devices based on nanocrystals embedded in thin films. The improvements are strongly related with the increasing of operation speed, substantially decreasing the energy consumpt...
Article
Nanocomposites have been obtained by dispersing various amounts of vapor grown carbon nanofibers within isotactic polypropylene. Thermal investigations done by differential scanning calorimetry and dynamic mechanical analysis revealed the effect of the vapor grown carbon nanofibers on the melting, crystallization, α, and β relaxations. Direct curre...
Article
Using a fast and eco-friendly deposition method, ITO thin films with different thicknesses (0.5 μm–0.7 μm) were deposited on glass substrates by radio frequency magnetron sputtering technique. A comparative analysis of these oxide films was then carried out. AFM investigations showed that the deposited films were smooth, uniform and having a surfac...
Chapter
XTEM observations revealing high diffusivity and Ge segregation in UV laser pulse annealed SiGeO and GeTiO amorphous films V.S. Teodorescu1, A.V. Maraloiu1, A. Kuncser1, C. Ghica1, M.L. Ciurea1, A.M. Lepadatu1, I. Stavarache1, D.N. Scarisoreanu2, M. Dinescu2, M-G. Blanchin3 1National Institute of Materials Physics, 077125, Bucharest-Magurele, Roman...
Article
Thin films of chalcogenide, Cu(In,Ga)Se2 have been obtained using a single quaternary target by radio frequency magnetron sputtering method, with thickness in the range 750 nm to 1200 nm. X-ray photoelectron spectroscopy investigations showed, that the composition of Cu(In,Ga)Se2 thin films was very similar to that of the used target CuIn0.75Ga0.25...
Article
Full-text available
Obtaining high-quality materials, based on nanocrystals, at low temperatures is one of the current challenges for opening new paths in improving and developing functional devices in nanoscale electronics and optoelectronics. Here we report a detailed investigation of the optimization of parameters for the in situ synthesis of thin films with high G...
Article
Full-text available
This paper presents some investigations of the effect of nanopatterning on the properties of aluminum layer deposited by sputtering. UV-Nanoimprint Lithography technique has been used for the realization of a 2D array of nanostructures (pillars) in aluminum film characterized by cylindrical shape and the following structural parameters: diameter be...
Article
Full-text available
Heterostructures based on zinc phthalocyanine (ZnPc), magnesium phthalocyanine (MgPc) and 5,10,15,20-tetra(4-pyrydil)21H,23H-porphine (TPyP) were deposited on ITO flexible substrates by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. Organic heterostructures containing (TPyP/ZnPc(MgPc)) stacked or (ZnPc(MgPc):TPyP) mixed layers were cha...
Article
The article presents the fabrication and characterization of NV (non-volatile) memory devices based on SiO2/Ge/SiO2 trilayer structures on Si wafers. The trilayer structures were obtained by using the magnetron sputtering method for the deposition of gate SiO2 and intermediate Ge layers and the rapid thermal oxidation for the growth of tunnel SiO2...
Article
Full-text available
Laser pulse processing of surfaces and thin films is a useful tool for amorphous thin films crystallization, surface nanostructuring, phase transformation and modification of physical properties of thin films. Here we show the effects of nanostructuring produced at the surface and under the surface of amorphous GeTiO films through laser pulses usin...
Article
Full-text available
Heterostructures with layers from small molecules organic compounds were deposited on ITO/glass substrate by thermal vacuum evaporation (TVE) technique. Structural, optical and morphological investigations were carried out on the realised layers (zinc phthalocyanine-ZnPc, fullerene-C60 and 1,4,5,8-naphthalene-tetracarboxylic dianhydride-NTCDA). The...
Article
GeSi-based nanostructures show unique properties which make them suitable for integrated circuit technology. The strong interest is to enhance their electronic properties in order to improve the device performance. In order to obtain fundamental knowledge on the electrical transport taking place in GeSi nanostructures we have investigated the effec...
Article
The structure of GeSiO films resulted from deposition and annealing conditions draws their electrical behaviour. GeSiO films prepared either by magnetron sputtering or sol-gel method and subsequently annealed are formed of Ge nanocrystals and/or amorphous Ge nanoparticles embedded in amorphous SiO2 matrix. Firstly, the size effect which is the main...
Article
The GeTiO2 amorphous films were deposited by magnetron sputtering and subsequently annealed at 400, 550, 600 and 700 degrees C for nanostructuring. The structure of annealed films was investigated by X-ray diffraction and transmission electron microscopy. The transmittance spectra of all annealed GeTiO2 films were measured and simulated by using Br...
Article
GeSi nanostructured films were obtained by cosputtering from two Ge and Si targets and subsequent annealing in furnace in N2 for 5 h at 700, 800 and 900 °C, with the aim to show the correlation between electrical properties and crystalline structure of the films. The as-deposited films are amorphous, have a Ge:Si composition of 55:45 and 185 nm thi...
Chapter
Quantum well solar cells with p-i-n structure are presented. The physical processes in multiple quantum well solar cells, the materials commonly used for photovoltaic applications, and technological aspects are analyzed. The quantum confinement effect produces resonant energy levels located in the valence and conduction bands of well layers. In add...
Article
Ge-SiO2 films with high Ge/Si atomic ratio of about 1.86 were obtained by co-sputtering of Ge and SiO2 targets and subsequently annealed at different temperatures between 600 and 1000 °C in a conventional furnace in order to show how the annealing process influences the film morphology concerning the Ge nanocrystal and/or amorphous nanoparticle for...
Conference Paper
This paper analyses and discusses the effect of Ge/Si atomic ratio and annealing temperature on the conduction mechanisms governing the electrical behavior of Ge-SiO2 films containing Ge nanoparticles embedded in amorphous SiO2 matrix. For this, the experimental conductance-temperature curves are modeled in correlation with the microstructure findi...
Article
Full-text available
Amorphous Ge/SiO2 multilayer structures deposited by magnetron sputtering have been annealed at different temperatures between 650 and 800 °C for obtaining Ge nanocrystals in oxide matrix. The properties of the annealed structures were investigated by transmission electron microscopy, Raman spectroscopy, and low temperature photoluminescence. The G...
Article
Nanocomposites have been obtained by dispersing vapor grown carbon nanofibers (VGCNF) within isotactic polypropylene (iPP) via melt mixing. VGCNFs were purified and disentangled before blending with iPP. The mixing was performed by using HAAKE Rheomix, at 180 ^oC and 65 rpm for 9 minutes followed by an additional mixing at 90 rpm for 5 minutes (sam...
Chapter
Quantum well solar cells with p-i-n structure are presented. The physical processes in multiple quantum well solar cells, the materials commonly used for photovoltaic applications, and technological aspects are analyzed. The quantum confinement effect produces resonant energy levels located in the valence and conduction bands of well layers. In add...
Article
We report the presence of a fast Ge diffusion effect produced during laser crystallization of Si0.45Ge0.55 films deposited by magnetron sputtering on Si(100) substrates. The laser irradiation was performed using the 266 nm wavelength radiation of the Nd-YAG laser. After the irradiation with 10 laser pulses at a fluence of 30 mJ/cm2 the top part of...
Article
This paper presents a detailed transmission electron microscopy (TEM) study of GeSiO films with Ge nanoparticles. The films with 2.5 μm thickness were deposited by magnetron sputtering and subsequently annealed in H2 at 2 atm and 500 °C for 2 h for nanostructuring. After H2 annealing, the majority of the resulted Ge nanoparticles are amorphous, les...
Article
The effects of 5 Multiplication-Sign 10{sup 11} cm{sup -26+}I{sup 127} ions of 28 MeV kinetic energy on high resistivity (100) Si were studied. The profile of primary defects was simulated. The defects produced by irradiation which act as traps were investigated. Thermally stimulated current measurements without externally applied bias were used, a...
Conference Paper
In this paper we continue the previous investigations on nanostructured GexSi1-x films. The films were deposited by magnetron sputtering and annealed in N2 atmosphere at 700 °C. Their structure was investigated and correlated with the electrical behavior. For this, conventional and high-resolution transmission electron microscopy together with sele...
Conference Paper
Full-text available
This paper reports on the conduction mechanisms in amorphous SiO2 films with embedded Ge nanoparticles. For this, measurements of current-temperature and current-voltage were employed and correlated with the microstructure results obtained from transmission electron microscopy (TEM). TEM images reveal that our films contain big Ge nanoparticles wit...
Conference Paper
Full-text available
N-type P-doped silicon single crystals with resistivity higher than 8000 Ωcm were irradiated with 127I6+ ions of 28 MeV kinetic energy. The penetration of the ions through the target and the processes of energy loss were simulated using the CTRIM Monte Carlo code, and point defect production was calculated in the frame of our diffusion-reaction mod...
Article
Full-text available
The films containing Ge nanoparticles embedded in SiO2 matrix were prepared by RF magnetron sputtering and subsequently by thermal annealing. Their structure was investigated by conventional transmission electron microscopy and high resolution transmission electron microscopy together with energy-dispersive X-ray spectroscopy. The electrical behavi...
Article
Full-text available
The long time degradation produced by particles and ions in crystalline materials used for devices to work in space, or for detectors in HEP and astroparticles, is characterised by the non-ionising energy loss, which is calculated in the frame of an analytical model. The transient phenomena as short time degradation are characterised by the time an...
Conference Paper
GeSiO nanostructures obtained by using two different preparation methods, sol-gel and magnetron-sputtering were studied. They are formed from Ge nanoparticles dispersed in amorphous matrix, with different morphology depending on the preparation method. Electrical investigations (current-voltage and current-temperature measurements) were performed a...
Conference Paper
This paper presents the preparation and investigation of structure and electrical properties of nanostructures consisting of Si1-xGex nanocrystals. Nanostructures were prepared by RF magnetron sputtering, followed by thermal annealing. X-ray diffraction, TEM, high resolution TEM and SAED measurements were performed. Current-voltage and current-temp...
Article
The trap parameters of defects in Si/CaF2 multilayered structures were determined from the analysis of optical charging spectroscopy measurements. Two kinds of maxima were observed. Some of them were rather broad, corresponding to "normal" traps, while the others, very sharp, were attributed to stress-induced traps. A procedure of optimal linear sm...
Article
Full-text available
Percolation phenomena are investigated and discussed in three kinds of nanostructures: first two are nanocrystalline silicon-based systems, Si nanodots embedded in amorphous SiO2 matrix and porous silicon formed by an oxidized nanowire network, and the third consisting of a multi-walled carbon nanotube network embedded in amorphous SiN. The current...
Article
The quantum efficiency of the absorption on quantum confinement levels is investigated. This is achieved by modeling the electron confinement in a spherical quantum dot (QD). The confinement levels are calculated using both infinite and finite rectangular quantum wells. The spectral internal quantum efficiency is evaluated within both the models, b...
Article
Full-text available
The electrical behavior of multi-walled carbon nanotube network embedded in amorphous silicon nitride is studied by measuring the voltage and temperature dependences of the current. The microstructure of the network is investigated by cross-sectional transmission electron microscopy. The multi-walled carbon nanotube network has an uniform spatial e...
Article
Electrical and photoconductive properties of films consisting of amorphous Ge nanoparticles uniformly distributed in amorphous SiO 2 were studied. These films were prepared by sol-gel method and treated by rapid thermal annealing technique. Measurements of current-voltage and conductance-temperature characteristics, spectral and bias dependences of...
Conference Paper
The thermal spike model which takes into account both ionization and nuclear energy loss processes of the projectile as distinct electronic and atomic heat sources is used to describe transient processes induced by ions in silicon. The time and space dependencies of the lattice and electron temperatures near the projectile trajectory are calculated...
Conference Paper
GeSiO nanosystems were obtained using two different preparation methods, sol-gel and magnetron-sputtering. Transmission electron microscopy measurements were performed to investigate the films structure. Amorphous and crystalline Ge dots embedded in amorphous silicon dioxide were observed. The Ge concentration in the GeSiO films was by Energy-dispe...
Conference Paper
The temperature dependence of the capture coefficients in trapping phenomena is investigated. It is proved that, besides the dependence induced by the thermal velocity of the carriers, the stress-induced traps at the interfaces of the multi-layered structures present a supplementary temperature dependence. This dependence is found to be of Gaussian...
Article
Full-text available
The influence of the shape of silicon quantum dots embedded in an amorphous silica matrix on the quantum confinement energy levels, as well as that of the Si / SiO <sub>2</sub> potential barrier, are studied. The energy levels are computed using both the infinite and finite rectangular quantum well models for spherical quantum dots and the infinite...
Article
Transmission electron microscopy and X-ray photoelectron spectroscopy analyses are performed to investigate Ge nanoparticles embedded in an amorphous SiO2 matrix. GeSiO thin films are prepared by two methods, sol–gel and radio frequency magnetron sputtering. After the deposition, the sol–gel films are annealed in either N2 (at 1atm and 800°C) or H2...
Conference Paper
Full-text available
This paper presents the investigation of electrical properties of carbon nanotubes (CNT). A sandwich configuration, quartz substrate/Cr/Al/CNT (partially immersed in SiN)/Cr/Al was investigated. The CNT are mainly oriented parallel with the electrodes. Current - voltage characteristics were taken at 20 K and room temperature and a current - tempera...