Thierry Tsafack - Academia.edu (original) (raw)
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Materials Today Chemistry
Abstract Instantaneous adhesion between different materials is a requirement for several applicat... more Abstract Instantaneous adhesion between different materials is a requirement for several applications ranging from electronics to biomedicine. Approaches such as surface patterning, chemical cross-linking, surface modification, and chemical synthesis have been adopted to generate temporary adhesion between various materials and surfaces. Because of the lack of curing times, temporary adhesives are instantaneous, a useful property for specific applications that need quick bonding. However, to this day, temporary adhesives have been mainly demonstrated under dry conditions and do not work well in submerged or humid environments. Furthermore, most rely on chemical bonds resulting from strong interactions with the substrate such as acrylate based. This work demonstrates the synthesis of a universal amphibious adhesive solely by combining solid polytetrafluoroethylene (PTFE) and liquid polydimethylsiloxane (PDMS) polymers. While the dipole-dipole interactions are induced by a large electronegativity difference between fluorine atoms in PTFE and hydrogen atoms in PDMS, strong surface wetting allows the proposed adhesive to fully coat both substrates and PTFE particles, thereby maximizing the interfacial chemistry. The two-phase solid–liquid polymer system displays adhesive characteristics applicable both in air and water, and enables joining of a wide range of similar and dissimilar materials (glasses, metals, ceramics, papers, and biomaterials). The adhesive exhibits excellent mechanical properties for the joints between various surfaces as observed in lap shear testing, T-peel testing, and tensile testing. The proposed biocompatible adhesive can also be reused multiple times in different dry and wet environments. Additionally, we have developed a new reactive force field parameterization and used it in our molecular dynamics simulations to validate the adhesive nature of the mixed polymer system with different surfaces. This simple amphibious adhesive could meet the need for a universal glue that performs well with a number of materials for a wide range of conditions.
ACS Applied Materials & Interfaces
Physical Chemistry Chemical Physics
A theoretical and experimental demonstration of a simple mixture of similar polymer systems (PEO ... more A theoretical and experimental demonstration of a simple mixture of similar polymer systems (PEO and PDMS) for increasing cation conductivity can reopen new opportunities for the development of safer and environment-friendly solid-state batteries.
Advanced Materials Interfaces
ACS Applied Materials & Interfaces
Advanced Functional Materials
Computational Materials Science
2008 International Conference on Simulation of Semiconductor Processes and Devices, 2008
The paper addresses the calculation of the band structure for different phases of the chalcogenid... more The paper addresses the calculation of the band structure for different phases of the chalcogenide Ge2Sb2Te5 compound, which is raising considerable interest in view of the applications to the nonvolatile-memory technology. The band structure is necessary for determining the charge- and heat-transport properties of the material. The band diagram of the face-centered cubic phase, which is the most important one
Journal of Applied Physics, 2011
We present a comprehensive computational study on the properties of rock salt-like and hexagonal ... more We present a comprehensive computational study on the properties of rock salt-like and hexagonal chalcogenide Ge 2 Sb 2 Te 5 supported by experimental data. We calculate the electronic structure using density functional theory (DFT); the obtained density of states (DOS) compares favorably with experiments, and is suitable for transport analysis. Optical constants including refractive index and absorption coefficient capture major experimental features, aside from an energy shift owed to an underestimate of the bandgap that is typical of DFT calculations. We also compute the phonon DOS for the hexagonal phase, obtaining a speed of sound and thermal conductivity in good agreement with the experimental lattice contribution. The calculated heat capacity reaches $1.4 Â 10 6 J/(m 3 K) at high temperature, in agreement with experiments, and provides insight into the low-temperature range (<150 K), where data are unavailable.
Journal of Applied Physics, 2009
The most peculiar feature exhibited by the I͑V͒ characteristics of amorphous-chalcogenide materia... more The most peculiar feature exhibited by the I͑V͒ characteristics of amorphous-chalcogenide materials is undoubtedly its S-shaped behavior. This type of characteristics is very important for the technological application, e.g., in the field of nanoscale solid-state memories. In this paper we give a microscopic particle description of the charge transport across a layer of amorphous Ge 2 Sb 2 Te 5 sandwiched between two planar metallic contacts. A transport scheme based on the generalization of the variable-range hopping has been implemented in a current-driven Monte Carlo code. This approach allows one to investigate the aspects of the microscopic picture responsible for the electrical properties of the device. The results are compared with experimental data.
2009 International Conference on Simulation of Semiconductor Processes and Devices, 2009
Chalcogenide GST materials can suitably be exploited for manufacturing phase-change memory device... more Chalcogenide GST materials can suitably be exploited for manufacturing phase-change memory devices. In this paper a transport model for the amorphous phase of GST is investigated, based on the variable-range hopping model. The model is implemented into a Monte Carlo current-driven simulation of a test device made of a layer of amorphous Ge 2Sb2Te5 in contact with two planar metallic electrodes. The mechanisms governing electron transport within the device are discussed in relation to the variation of physical parameters, such as operating current, trap density, and coupling with the electric field inside the device. 978-1-4244-3947-8/09/$25.00 ©2009 IEEE 978-1-4244-3947-8/09/$25.00 ©2009 IEEE
Materials Today Chemistry
Abstract Instantaneous adhesion between different materials is a requirement for several applicat... more Abstract Instantaneous adhesion between different materials is a requirement for several applications ranging from electronics to biomedicine. Approaches such as surface patterning, chemical cross-linking, surface modification, and chemical synthesis have been adopted to generate temporary adhesion between various materials and surfaces. Because of the lack of curing times, temporary adhesives are instantaneous, a useful property for specific applications that need quick bonding. However, to this day, temporary adhesives have been mainly demonstrated under dry conditions and do not work well in submerged or humid environments. Furthermore, most rely on chemical bonds resulting from strong interactions with the substrate such as acrylate based. This work demonstrates the synthesis of a universal amphibious adhesive solely by combining solid polytetrafluoroethylene (PTFE) and liquid polydimethylsiloxane (PDMS) polymers. While the dipole-dipole interactions are induced by a large electronegativity difference between fluorine atoms in PTFE and hydrogen atoms in PDMS, strong surface wetting allows the proposed adhesive to fully coat both substrates and PTFE particles, thereby maximizing the interfacial chemistry. The two-phase solid–liquid polymer system displays adhesive characteristics applicable both in air and water, and enables joining of a wide range of similar and dissimilar materials (glasses, metals, ceramics, papers, and biomaterials). The adhesive exhibits excellent mechanical properties for the joints between various surfaces as observed in lap shear testing, T-peel testing, and tensile testing. The proposed biocompatible adhesive can also be reused multiple times in different dry and wet environments. Additionally, we have developed a new reactive force field parameterization and used it in our molecular dynamics simulations to validate the adhesive nature of the mixed polymer system with different surfaces. This simple amphibious adhesive could meet the need for a universal glue that performs well with a number of materials for a wide range of conditions.
ACS Applied Materials & Interfaces
Physical Chemistry Chemical Physics
A theoretical and experimental demonstration of a simple mixture of similar polymer systems (PEO ... more A theoretical and experimental demonstration of a simple mixture of similar polymer systems (PEO and PDMS) for increasing cation conductivity can reopen new opportunities for the development of safer and environment-friendly solid-state batteries.
Advanced Materials Interfaces
ACS Applied Materials & Interfaces
Advanced Functional Materials
Computational Materials Science
2008 International Conference on Simulation of Semiconductor Processes and Devices, 2008
The paper addresses the calculation of the band structure for different phases of the chalcogenid... more The paper addresses the calculation of the band structure for different phases of the chalcogenide Ge2Sb2Te5 compound, which is raising considerable interest in view of the applications to the nonvolatile-memory technology. The band structure is necessary for determining the charge- and heat-transport properties of the material. The band diagram of the face-centered cubic phase, which is the most important one
Journal of Applied Physics, 2011
We present a comprehensive computational study on the properties of rock salt-like and hexagonal ... more We present a comprehensive computational study on the properties of rock salt-like and hexagonal chalcogenide Ge 2 Sb 2 Te 5 supported by experimental data. We calculate the electronic structure using density functional theory (DFT); the obtained density of states (DOS) compares favorably with experiments, and is suitable for transport analysis. Optical constants including refractive index and absorption coefficient capture major experimental features, aside from an energy shift owed to an underestimate of the bandgap that is typical of DFT calculations. We also compute the phonon DOS for the hexagonal phase, obtaining a speed of sound and thermal conductivity in good agreement with the experimental lattice contribution. The calculated heat capacity reaches $1.4 Â 10 6 J/(m 3 K) at high temperature, in agreement with experiments, and provides insight into the low-temperature range (<150 K), where data are unavailable.
Journal of Applied Physics, 2009
The most peculiar feature exhibited by the I͑V͒ characteristics of amorphous-chalcogenide materia... more The most peculiar feature exhibited by the I͑V͒ characteristics of amorphous-chalcogenide materials is undoubtedly its S-shaped behavior. This type of characteristics is very important for the technological application, e.g., in the field of nanoscale solid-state memories. In this paper we give a microscopic particle description of the charge transport across a layer of amorphous Ge 2 Sb 2 Te 5 sandwiched between two planar metallic contacts. A transport scheme based on the generalization of the variable-range hopping has been implemented in a current-driven Monte Carlo code. This approach allows one to investigate the aspects of the microscopic picture responsible for the electrical properties of the device. The results are compared with experimental data.
2009 International Conference on Simulation of Semiconductor Processes and Devices, 2009
Chalcogenide GST materials can suitably be exploited for manufacturing phase-change memory device... more Chalcogenide GST materials can suitably be exploited for manufacturing phase-change memory devices. In this paper a transport model for the amorphous phase of GST is investigated, based on the variable-range hopping model. The model is implemented into a Monte Carlo current-driven simulation of a test device made of a layer of amorphous Ge 2Sb2Te5 in contact with two planar metallic electrodes. The mechanisms governing electron transport within the device are discussed in relation to the variation of physical parameters, such as operating current, trap density, and coupling with the electric field inside the device. 978-1-4244-3947-8/09/$25.00 ©2009 IEEE 978-1-4244-3947-8/09/$25.00 ©2009 IEEE