Papers by Kremena Makasheva
HAL (Le Centre pour la Communication Scientifique Directe), Oct 27, 2019
Proper description of the electrical behavior of miniaturized devices requires better understandi... more Proper description of the electrical behavior of miniaturized devices requires better understanding of the breakdown phenomena in microgaps (< 10µm) at atmospheric pressures. In microgaps the breakdown characteristics deviate from those defined by the Paschen's law. It is now well accepted that the departure from Paschen's law is due to the contribution of field electron emission. Apart from the small distance, the presence of protrusions on the cathode surface can largely intensify this phenomenon. In this work, the electric field distribution is simulated in needle-plate configuration in presence of various nanoprotrusions on the cathode surface. The purpose is to find conditions when the nanoprotrusions can initiate field electron emission due to a local enhancement of the electric field. The maximum electric field is determined by the location and the geometry of the nanoprotrusions. Surprisingly, for a semi-circle shape of nanoprotrusions, the maximum electric field does not depend on the size of nanoprotrusions.
Characterization of the ionic silver release from differently coated nanoparticles and from nanostructured surfaces using algae as biosensors
HAL (Le Centre pour la Communication Scientifique Directe), 2017
Biomaterials science, 2024
The interaction of foreign implants with their surrounding environment is significantly influence... more The interaction of foreign implants with their surrounding environment is significantly influenced by the adsorption of proteins on the biomaterial surfaces, playing a role in microbial adhesion. Therefore, understanding protein adsorption on solid surfaces and its effect on microbial adhesion is essential to assess the associated risk of infection. The aim of this study is to evaluate the effect of conditioning by fibronectin (Fn) or bovine serum albumin (BSA) protein layers of silica (SiO 2) surfaces on the adhesion and detachment of two pathogenic microorganisms: Pseudomonas aeruginosa PAO1-Tn7-gfp and Candida albicans CIP 48.72. Experiments are conducted under both static and hydrodynamic conditions using a shear stress flow chamber. Through the use of very low wall shear stresses, the study brings the link between the static and dynamic conditions of microbial adhesion. The results reveal that the microbial adhesion critically depends on: (i) the presence of a protein layer conditioning the SiO 2 surface, (ii) the type of protein and (iii) the protein conformation and organization in the conditioning layer. In addition, a very distinct adhesion behaviour of P. aeruginosa is observed towards the two tested proteins, Fn and BSA. This effect is reinforced by the amount of proteins adsorbed on the surface and their organization in the layer. The results are discussed in the light of atomic force microscopy analysis of the organization and conformation of proteins in the layers after adsorption on the SiO 2 surface, as well as the specificity in bacterial behaviour when interacting with these protein layers. The study also demonstrates the very distinctive behaviours of the prokaryote P. aeruginosa PAO1-Tn7-gfp compared to the eukaryote C. albicans CIP 48.72. This underscores the importance of considering species-specific interactions between the protein conditioning layer and different pathogenic microorganisms, which appear crucial in designing tailored anti-adhesive surfaces.
Frontiers in nanotechnology, Apr 11, 2024
Rational engineering of thin nanocomposite layers, deposited in reactive plasmas, requires knowle... more Rational engineering of thin nanocomposite layers, deposited in reactive plasmas, requires knowledge on the plasma behavior in order to produce multifunctional deposits with tailored properties (structural, optical, electrical, etc.) This work presents an experimental study of nanoparticles synthesized in the plasma gas-phase and their subsequent use as buildingblocks to form layer-by-layer nanostructures. The experiment is performed in a plasma process that successfully combines plasma polymerization of an organosilicon molecular precursor (hexamethyldisiloxane, HMDSO) and sputtering of a metallic (silver) target. Pulsed injection of the precursor is found to promote cyclic nanoparticle formation in Ar/HMDSO reactive plasmas. The plasma electron temperature is found to vary in the range 1.6-2.2 eV as derived from time-resolved optical emission spectroscopy of the plasma energetic conditions. This diagnostic method is also shown to provide a reliable tool for online monitoring of the nanoparticle synthesis process. Two types of layer-by-layer structured nanocomposites can be obtained depending on the type of nanoparticles synthesized: (i) organosilicon nanoparticles of size less than 100 nm in all studied plasma conditions for a large quantity of injected HMDSO and (ii) raspberry-like nanoparticles of size less than 150 nm when the quantity of injected HMDSO is reduced. The organosilicon nanoparticle growth follows a polydimethylsiloxane (PDMS)-like oligomerization scheme in which the R 2-Si(-O) 2 silicon bond tends towards the formation of polymeric structure in a R 3-Si(-O) 1 silicon chemical environment, containing Si-(CH 2)-Si type bridges that are involved in cross-linking. The elemental composition of the raspberrylike nanoparticles is similar to that of the organosilicon nanoparticles,
Charge injection and transport mechanisms occurring at metal/dielectric interface may strongly im... more Charge injection and transport mechanisms occurring at metal/dielectric interface may strongly impact devices performance and reliability. However, these phenomena remain partially understood, mainly due to the lack of adapted characterization tools. In this paper, we propose an investigation of the charging behavior at the Al/SiN x interface using Kelvin Probe Force Microscopy (KPFM). Indeed, KPFM measurements permit to probe space charge density with a sub micrometric resolution. Results presented here emphasize that electrons and holes are injected and trapped close to cathode and anode, respectively. The charge clouds remain stacked to the interface (2-3µm). Moreover, the amount of injected charges increases with the applied bias. The injected electrons and holes follow the same dissipation mechanism in time after bias removal.
HAL (Le Centre pour la Communication Scientifique Directe), Mar 21, 2016
HAL (Le Centre pour la Communication Scientifique Directe), Mar 16, 2015
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Utilisation des courbes de force pour l'étude à l'échelle nanométrique des charges piégées dans les diélectriques en couches minces
HAL (Le Centre pour la Communication Scientifique Directe), Mar 16, 2018
HAL (Le Centre pour la Communication Scientifique Directe), Sep 15, 2019
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Nanotechnology, Nov 21, 2017
To understand the physical phenomena occurring at metal/dielectric interfaces, determination of t... more To understand the physical phenomena occurring at metal/dielectric interfaces, determination of the charge density profile at nanoscale is crucial. To deal with this issue, charges were injected applying a DC voltage on lateral Al-electrodes embedded in a SiN x thin dielectric layer. The surface potential induced by the injected charges was probed by Kelvin probe force microscopy (KPFM). It was found that the KPFM frequency mode is a better adapted method to probe accurately the charge profile. To extract the charge density profile from the surface potential two numerical approaches based on the solution to Poisson's equation for electrostatics were investigated: the second derivative model method, already reported in the literature, and a new 2D method based on the finite element method (FEM). Results highlight that the FEM is more robust to noise or artifacts in the case of a non-flat initial surface potential. Moreover, according to theoretical study the FEM appears to be a good candidate for determining charge density in dielectric films with thicknesses in the range from 10 nm to 10 μm. By applying this method, the charge density profile was determined at nanoscale, highlighting that the charge cloud remains close to the interface.
Nanotechnology, May 9, 2016
Charge injection and retention in thin dielectric layers remain critical issues for the reliabili... more Charge injection and retention in thin dielectric layers remain critical issues for the reliability of many electronic devices because of their association to a large number of failure mechanisms. To overcome this drawback a deep understanding of the mechanisms leading to charge injection close to the injection area is highly demanded. Even though the charge injection is extensively studied and reported in the literature to characterize the charge storage capability of dielectric materials, questions about charge injection mechanisms when using Atomic Force Microscopy (AFM) remain open. In this paper, a thorough study of charge injection by using AFM in thin plasma processed amorphous silicon oxynitride layers with properties close to that of thermal silica layers is presented. The study considers the impact of applied voltage polarity, work function of the AFM tip coating and tip curvature radius. A simple theoretical model was developed and used to analyze the obtained experimental results. The electric field distribution is computed as a function of tip geometry. The obtained experimental results highlight that after injection in the dielectric layer the charge lateral spreading is mainly controlled by the radial electric field component independently on the carrier polarity. The injected charge density is influenced by the nature of electrode metal coating (work function) and its geometry (tip curvature radius). The electron injection is mainly ruled by the Schottky injection barrier through field electron emission mechanism enhanced by thermionic electron emission. The hole injection mechanism seems to differ from the electron one in the dependence on the work function of the metal coating. Based on the performed analysis, it is suggested that for hole injection by AFM, pinning of the metal Fermi level with the metal-induced gap states in the studied silicon oxynitride layers starts playing a role in the injection mechanisms.
Ion Beam Synthesis of multifunctional metallic nanoparticles embedded in dielectrics
HAL (Le Centre pour la Communication Scientifique Directe), 2017
Investigating the impact of C/O on dust formation in cold plasma reactors
HAL (Le Centre pour la Communication Scientifique Directe), 2016
Carbon-rich cosmic dust analogues obtained in cold plasmas with hexamethyldisiloxane as precursor
HAL (Le Centre pour la Communication Scientifique Directe), 2015
Probing the impact of the C/O ratio and metals on the properties of dust particles in a cold plasma reactor
HAL (Le Centre pour la Communication Scientifique Directe), 2018
Fabrication and characterization of silicon nanocrystals in silicon nitride matrix: study of the interface states and structure
HAL (Le Centre pour la Communication Scientifique Directe), 2013
Time resolved investigation of dynamical dusty argon plasmas with pulsed injection of HMDSO
HAL (Le Centre pour la Communication Scientifique Directe), 2018
Attempt to catch the C/O transition in dust formation in cold plasma experiments
HAL (Le Centre pour la Communication Scientifique Directe), 2018
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Papers by Kremena Makasheva