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Papers by stephane kenmoe

This interview is with Stéphane Kenmoe, who is not only a promising young researcher, but also an... more This interview is with Stéphane Kenmoe, who is not only a promising young researcher, but also an outstanding and active science communicator – worldwide.

Physical Chemistry Chemical Physics, 2017

arXiv (Cornell University), Oct 29, 2022

We present the status of the research in the field of atomic and molecular physics in Africa as w... more We present the status of the research in the field of atomic and molecular physics in Africa as well as some challenges hindering the efforts being made by the African scientists. We further report the discussions and progress of the African Strategy for Fundamental and Applied Physics (ASFAP) working group on Atomic and Molecular physics with the view of providing the continent research direction for next decade.

Research Square (Research Square), Nov 5, 2021

We used Density Functional Theory (DFT) calculations to investigate the structural, electronic, m... more We used Density Functional Theory (DFT) calculations to investigate the structural, electronic, magnetic, mechanical and thermodynamic properties of CoYSb (Y = Cr, Mo and W) compounds. These are XYZ type half-Heusler alloys, which also exist in the face centred cubic MgAgAs-type structure and conform to F43m space group. We computed these properties in three different atomic arrangements known as Type-I, Type-II and Type-III phases. In all these phases, the alloys were found to be in the ferromagnetic state. Furthermore, the calculated electronic band structure and the total electronic density of states indicated a metallic behaviour in CoWSb, nearly half-metallic in CoMoSb and half-metallic in CoCrSb, with a minority-spin band gap of 0.81 eV. Furthermore, the calculated mechanical properties predicted an anisotropic behaviour of these alloys in their stable phase. Finally, due to its high Debye temperature value, CoCrSb shows stronger covalent bonding than CoMoSb and CoWSb, respectively.

Journal of Chemical Physics, Dec 10, 2018

For rational design and improvement of electronic and optical properties of water-splitting photo... more For rational design and improvement of electronic and optical properties of water-splitting photocatalysts, the ability to control the band edge positions relative to the water redox potentials and the photoresponse as a function of environmental conditions is essential. We combine ab initio molecular dynamics simulations with ab initio many-body theoretical calculations to predict the bandgap and band edge energies, as well as the absorption spectrum of pristine and N- and S-doped TiO2 nanotubes using the DFT+U and G0W0 approaches. Both levels of theory show similar trends, and N+S-codoping appears to be the optimal system for photocatalytic water splitting both in dry and humid conditions. However, the effect is rather moderate. Compared to DFT+U, the enhanced many-body effects in the G0W0 calculations push the absolute energies of the band edges to higher values and yield increased quasi-particle bandgaps in better agreement with experiment. In dry and humid conditions, the electronic bandgap for all systems is found to be in the range of 6.0–6.2 eV with a redshift from electronic gap to optical gap. The absorption spectra show an optical anisotropy and different absorption thresholds for different light polarizations.

The interaction of 2-propanol with Co 3 O 4 (001) was studied by vibrational sum frequency spectr... more The interaction of 2-propanol with Co 3 O 4 (001) was studied by vibrational sum frequency spectroscopy (vSFS) and by ab initio molecular dynamics (AIMD) simulations of 2-propanol dissolved in a water film to gain insight at the molecular level into the pathways of catalytic oxidation. The experimental study has been performed under near ambient condition, where the presence of water vapor is unavoidable, resulting in a water film on the sample and thereby allowing us to mimic the solution-water interface. Both experiment and theory conclude that 2-propanol adsorbs molecularly. The lack of dissociation is attributed to the adsorption geometry of 2-propanol in which the O-H bond does not point towards the surface. Furthermore, the copresent water not only competitively adsorbs on the surface but also inhibits 2-propanol deprotonation. The 1 calculations reveal that the presence of water deactivates the lattice oxygen, thereby reducing the surface activity. This finding sheds light on the multifaceted role of water at the interface for the electrochemical oxidation of 2-propanol in aqueous solution as recently reported. 1 At higher temperatures 2-propanol remains molecularly adsorbed on Co 3 O 4 (001) until it desorbs with increasing surface temperature.

arXiv (Cornell University), Apr 4, 2022

The African School of Fundamental Physics and Applications, also known as the African School of P... more The African School of Fundamental Physics and Applications, also known as the African School of Physics (ASP), was initiated in 2010, as a three-week biennial event, to offer additional training in fundamental and applied physics to African students with a minimum of three-year university education. Since its inception, ASP has grown to be much more than a school. ASP has become a series of activities and events with directed ethos towards physics as an engine for development in Africa. One such activity of ASP is the African Conference on Fundamental and Applied Physics (ACP). The first edition of ACP took place during the 2018 edition of ASP at the University of Namibia in Windhoek. In this paper, we report on the second edition of ACP, organized on March 7-11, 2022, as a virtual event.

Journal of Chemical Physics, 2018

Physical Chemistry Chemical Physics, 2017

The Journal of Chemical Physics

The interaction of 2-propanol with Co3O4(001) was studied by vibrational sum frequency spectrosco... more The interaction of 2-propanol with Co3O4(001) was studied by vibrational sum frequency spectroscopy and ab initio molecular dynamics simulations of 2-propanol dissolved in a water film to gain an insight, at the molecular level, into the pathways of catalytic oxidation. The experimental study has been performed under near ambient conditions, where the presence of water vapor is unavoidable, resulting in a water film on the sample and, thereby, allowing us to mimic the solution–water interface. Both experiment and theory conclude that 2-propanol adsorbs molecularly. The lack of dissociation is attributed to the adsorption geometry of 2-propanol in which the O–H bond does not point toward the surface. Furthermore, the copresent water not only competitively adsorbs on the surface but also inhibits 2-propanol deprotonation. The calculations reveal that the presence of water deactivates the lattice oxygen, thereby reducing the surface activity. This finding sheds light on the multifacete...

Physical Chemistry Chemical Physics

We present a thermodynamically stable tetramethylammonium lead iodide perovskite with GW0 and GW ... more We present a thermodynamically stable tetramethylammonium lead iodide perovskite with GW0 and GW bandgaps of 2.63 eV and 2.83 eV. At 293.15 K, an SLME efficiency between 7% and 12% was reported between 0.01 μm and 100 μm absorber thicknesses.

Solids, 2022

We used density functional theory (DFT) calculations to investigate the structural, electronic, m... more We used density functional theory (DFT) calculations to investigate the structural, electronic, magnetic, mechanical, and thermodynamic properties of CoYSb (Y = Cr, Mo and W) compounds. These are XYZ type half-Heusler alloys, which also exist in the face centred cubic MgAgAs-type structure and conform to F4¯3m space group. We computed these properties in three different atomic arrangements known as Type-I, Type-II, and Type-III phases. In all these phases, the alloys were found to be in the ferromagnetic state. Furthermore, the calculated electronic band structure and the total electronic density of states indicated a metallic behavior in CoWSb, nearly half-metallic behavior in CoMoSb, and half-metallic behavior in CoCrSb, with a minority-spin band gap of 0.81 eV. Furthermore, the calculated mechanical properties predicted an anisotropic behavior of these alloys in their stable phase. Finally, due to its high Debye temperature value, CoCrSb shows stronger covalent bonding than CoMoS...

Applied Surface Science Advances

Ab initio molecular dynamics simulations of a single hydrated 2-propanol molecule were performed ... more Ab initio molecular dynamics simulations of a single hydrated 2-propanol molecule were performed to study the role of temperature, surface structure and electrochemical environment for the oxidation of 2-propanol to acetone at the Co 3 O 4 (001)/H 2 O interface. On the A-terminated and B-terminated surfaces, which differ in the relative number of Co 2+ and Co 3+ ions at the surface, 2-propanol adsorbs molecularly on the Co 2+ and Co 3+ sites, respectively. In both cases, no C-H bond cleavage is observed at room temperature. However, under oxidative conditions, which are modeled here by partial dehydrogenation of the mixed hydroxyl/water adsorbate layer, dehydrogenation of the alcoholic OH group is observed on both surface terminations. As a result, adsorbed 2-propanolate is formed. The reaction on the less hydroxylated Bterminated surface further proceeds with C-H bond cleavage at the 2-carbon 1 atom. The oxidation product acetone remains adsorbed on the Co 3+ site during the simulation period of approximately 20 ps. Both deprotonation steps are aided by the presence of the adsorbed hydroxyl groups in the vicinity of the adsorbed alcohol molecule, because both hydrogen atoms from the reactand molecule are transferred as protons to form adsorbed water molecules. Different from the case of the partially dehydrogenated environment, raising the system temperature from 300 to 450 K, which can be considered a simple model for high temperature thermal catalysis, does not lead to oxidation via C-H dehydrogenation of the 2-propanol molecule.

Crystals

The ab initio method is used to calculate the electronic, elastic, lattice-dynamic, and thermoele... more The ab initio method is used to calculate the electronic, elastic, lattice-dynamic, and thermoelectric properties of the semimetal Half-Heusler compound HfIrAs. Density Functional Theory within Generalized Gradient Approximation is used to carry out calculations of lattice parameters, band structure, electronic density of states, phonon band structure, phonon density of states, elastic moduli, specific heat at constant volume, the Seebeck coefficient, electrical conductivity, the power factor, and the dimensionless figure of merit. The electronic band structure reveals that the compound is semimetal. The phonon dispersion shows that HfIrAs is dynamically stable. The projected phonon density of states, which shows the contribution of each constituent atom at every frequency level, is also reported. The ratio of bulk modulus to shear modulus is 2.89; i.e., the material is ductile, and it satisfies stability criteria. The thermoelectric properties of this compound at different temperat...

The density functional theory was used to explore the structural, electronic, dynamical, and ther... more The density functional theory was used to explore the structural, electronic, dynamical, and thermoelectric properties of a VIrSi Half-Heulser (HH) alloy. The minimum lattice constant of 5.69 ( ̊A) was obtained for VIrSi alloy. Besides, the band structure and the projected density of states for this HH alloy were calculated, and the gap between the valence and conduction bands was noted to be 0.2 eV. Also, the quasi-harmonic approximation was used to predict the dynamical stability of the VIrSi HH alloy. At 300 K, the Seebeck Coefficient of 370 and -270 μV.K−1., respectively, was achieved for the p and n-type doping. From the power factor result, the highest peak of 18 X 1011W/cm.K2 is obtained in the n-type doping. The Figure of Merit (ZT) result revealed that VIrSi alloy possesses a high ZT at room temperature, which would make VIrSi alloy applicable for thermoelectric performance.

We use theoretical X-ray absorption near-edge spectroscopy (XANES) to investigate the electronic ... more We use theoretical X-ray absorption near-edge spectroscopy (XANES) to investigate the electronic structure of the active sites during 2-propanol oxidation to acetone on the Co3O4 (001) surface in humid conditions. In the gas phase, the O K-edge spectra of 2-propanol and acetone as well that of 2-propoxide considered as reaction intermediate, present no pre-edge peaks. Upon 2-propanol adsorption at the Co site of Co3O4 (001) surface, the O K-edge spectrum presents a distinct peak preceded by a bumb in the pre-edge region, both due to dipole transitions from O 1s to 2p states hybridized with Co 3d empty states. The formation of 2- propoxide leads to two distinct pre-edge peaks due to the increase of 3d empty states. A further increment of these pre-edge peaks is observed when acetone is formed and is rather ascribed to the new contributions of carbon 2p empty states in the transitions occurring in the pre-edge region. The changes observed in the pre-edge peak along the oxidation were ...

This interview is with Stéphane Kenmoe, who is not only a promising young researcher, but also an... more This interview is with Stéphane Kenmoe, who is not only a promising young researcher, but also an outstanding and active science communicator – worldwide.

Physical Chemistry Chemical Physics, 2017

arXiv (Cornell University), Oct 29, 2022

We present the status of the research in the field of atomic and molecular physics in Africa as w... more We present the status of the research in the field of atomic and molecular physics in Africa as well as some challenges hindering the efforts being made by the African scientists. We further report the discussions and progress of the African Strategy for Fundamental and Applied Physics (ASFAP) working group on Atomic and Molecular physics with the view of providing the continent research direction for next decade.

Research Square (Research Square), Nov 5, 2021

We used Density Functional Theory (DFT) calculations to investigate the structural, electronic, m... more We used Density Functional Theory (DFT) calculations to investigate the structural, electronic, magnetic, mechanical and thermodynamic properties of CoYSb (Y = Cr, Mo and W) compounds. These are XYZ type half-Heusler alloys, which also exist in the face centred cubic MgAgAs-type structure and conform to F43m space group. We computed these properties in three different atomic arrangements known as Type-I, Type-II and Type-III phases. In all these phases, the alloys were found to be in the ferromagnetic state. Furthermore, the calculated electronic band structure and the total electronic density of states indicated a metallic behaviour in CoWSb, nearly half-metallic in CoMoSb and half-metallic in CoCrSb, with a minority-spin band gap of 0.81 eV. Furthermore, the calculated mechanical properties predicted an anisotropic behaviour of these alloys in their stable phase. Finally, due to its high Debye temperature value, CoCrSb shows stronger covalent bonding than CoMoSb and CoWSb, respectively.

Journal of Chemical Physics, Dec 10, 2018

For rational design and improvement of electronic and optical properties of water-splitting photo... more For rational design and improvement of electronic and optical properties of water-splitting photocatalysts, the ability to control the band edge positions relative to the water redox potentials and the photoresponse as a function of environmental conditions is essential. We combine ab initio molecular dynamics simulations with ab initio many-body theoretical calculations to predict the bandgap and band edge energies, as well as the absorption spectrum of pristine and N- and S-doped TiO2 nanotubes using the DFT+U and G0W0 approaches. Both levels of theory show similar trends, and N+S-codoping appears to be the optimal system for photocatalytic water splitting both in dry and humid conditions. However, the effect is rather moderate. Compared to DFT+U, the enhanced many-body effects in the G0W0 calculations push the absolute energies of the band edges to higher values and yield increased quasi-particle bandgaps in better agreement with experiment. In dry and humid conditions, the electronic bandgap for all systems is found to be in the range of 6.0–6.2 eV with a redshift from electronic gap to optical gap. The absorption spectra show an optical anisotropy and different absorption thresholds for different light polarizations.

The interaction of 2-propanol with Co 3 O 4 (001) was studied by vibrational sum frequency spectr... more The interaction of 2-propanol with Co 3 O 4 (001) was studied by vibrational sum frequency spectroscopy (vSFS) and by ab initio molecular dynamics (AIMD) simulations of 2-propanol dissolved in a water film to gain insight at the molecular level into the pathways of catalytic oxidation. The experimental study has been performed under near ambient condition, where the presence of water vapor is unavoidable, resulting in a water film on the sample and thereby allowing us to mimic the solution-water interface. Both experiment and theory conclude that 2-propanol adsorbs molecularly. The lack of dissociation is attributed to the adsorption geometry of 2-propanol in which the O-H bond does not point towards the surface. Furthermore, the copresent water not only competitively adsorbs on the surface but also inhibits 2-propanol deprotonation. The 1 calculations reveal that the presence of water deactivates the lattice oxygen, thereby reducing the surface activity. This finding sheds light on the multifaceted role of water at the interface for the electrochemical oxidation of 2-propanol in aqueous solution as recently reported. 1 At higher temperatures 2-propanol remains molecularly adsorbed on Co 3 O 4 (001) until it desorbs with increasing surface temperature.

arXiv (Cornell University), Apr 4, 2022

The African School of Fundamental Physics and Applications, also known as the African School of P... more The African School of Fundamental Physics and Applications, also known as the African School of Physics (ASP), was initiated in 2010, as a three-week biennial event, to offer additional training in fundamental and applied physics to African students with a minimum of three-year university education. Since its inception, ASP has grown to be much more than a school. ASP has become a series of activities and events with directed ethos towards physics as an engine for development in Africa. One such activity of ASP is the African Conference on Fundamental and Applied Physics (ACP). The first edition of ACP took place during the 2018 edition of ASP at the University of Namibia in Windhoek. In this paper, we report on the second edition of ACP, organized on March 7-11, 2022, as a virtual event.

Journal of Chemical Physics, 2018

Physical Chemistry Chemical Physics, 2017

The Journal of Chemical Physics

The interaction of 2-propanol with Co3O4(001) was studied by vibrational sum frequency spectrosco... more The interaction of 2-propanol with Co3O4(001) was studied by vibrational sum frequency spectroscopy and ab initio molecular dynamics simulations of 2-propanol dissolved in a water film to gain an insight, at the molecular level, into the pathways of catalytic oxidation. The experimental study has been performed under near ambient conditions, where the presence of water vapor is unavoidable, resulting in a water film on the sample and, thereby, allowing us to mimic the solution–water interface. Both experiment and theory conclude that 2-propanol adsorbs molecularly. The lack of dissociation is attributed to the adsorption geometry of 2-propanol in which the O–H bond does not point toward the surface. Furthermore, the copresent water not only competitively adsorbs on the surface but also inhibits 2-propanol deprotonation. The calculations reveal that the presence of water deactivates the lattice oxygen, thereby reducing the surface activity. This finding sheds light on the multifacete...

Physical Chemistry Chemical Physics

We present a thermodynamically stable tetramethylammonium lead iodide perovskite with GW0 and GW ... more We present a thermodynamically stable tetramethylammonium lead iodide perovskite with GW0 and GW bandgaps of 2.63 eV and 2.83 eV. At 293.15 K, an SLME efficiency between 7% and 12% was reported between 0.01 μm and 100 μm absorber thicknesses.

Solids, 2022

We used density functional theory (DFT) calculations to investigate the structural, electronic, m... more We used density functional theory (DFT) calculations to investigate the structural, electronic, magnetic, mechanical, and thermodynamic properties of CoYSb (Y = Cr, Mo and W) compounds. These are XYZ type half-Heusler alloys, which also exist in the face centred cubic MgAgAs-type structure and conform to F4¯3m space group. We computed these properties in three different atomic arrangements known as Type-I, Type-II, and Type-III phases. In all these phases, the alloys were found to be in the ferromagnetic state. Furthermore, the calculated electronic band structure and the total electronic density of states indicated a metallic behavior in CoWSb, nearly half-metallic behavior in CoMoSb, and half-metallic behavior in CoCrSb, with a minority-spin band gap of 0.81 eV. Furthermore, the calculated mechanical properties predicted an anisotropic behavior of these alloys in their stable phase. Finally, due to its high Debye temperature value, CoCrSb shows stronger covalent bonding than CoMoS...

Applied Surface Science Advances

Ab initio molecular dynamics simulations of a single hydrated 2-propanol molecule were performed ... more Ab initio molecular dynamics simulations of a single hydrated 2-propanol molecule were performed to study the role of temperature, surface structure and electrochemical environment for the oxidation of 2-propanol to acetone at the Co 3 O 4 (001)/H 2 O interface. On the A-terminated and B-terminated surfaces, which differ in the relative number of Co 2+ and Co 3+ ions at the surface, 2-propanol adsorbs molecularly on the Co 2+ and Co 3+ sites, respectively. In both cases, no C-H bond cleavage is observed at room temperature. However, under oxidative conditions, which are modeled here by partial dehydrogenation of the mixed hydroxyl/water adsorbate layer, dehydrogenation of the alcoholic OH group is observed on both surface terminations. As a result, adsorbed 2-propanolate is formed. The reaction on the less hydroxylated Bterminated surface further proceeds with C-H bond cleavage at the 2-carbon 1 atom. The oxidation product acetone remains adsorbed on the Co 3+ site during the simulation period of approximately 20 ps. Both deprotonation steps are aided by the presence of the adsorbed hydroxyl groups in the vicinity of the adsorbed alcohol molecule, because both hydrogen atoms from the reactand molecule are transferred as protons to form adsorbed water molecules. Different from the case of the partially dehydrogenated environment, raising the system temperature from 300 to 450 K, which can be considered a simple model for high temperature thermal catalysis, does not lead to oxidation via C-H dehydrogenation of the 2-propanol molecule.

Crystals

The ab initio method is used to calculate the electronic, elastic, lattice-dynamic, and thermoele... more The ab initio method is used to calculate the electronic, elastic, lattice-dynamic, and thermoelectric properties of the semimetal Half-Heusler compound HfIrAs. Density Functional Theory within Generalized Gradient Approximation is used to carry out calculations of lattice parameters, band structure, electronic density of states, phonon band structure, phonon density of states, elastic moduli, specific heat at constant volume, the Seebeck coefficient, electrical conductivity, the power factor, and the dimensionless figure of merit. The electronic band structure reveals that the compound is semimetal. The phonon dispersion shows that HfIrAs is dynamically stable. The projected phonon density of states, which shows the contribution of each constituent atom at every frequency level, is also reported. The ratio of bulk modulus to shear modulus is 2.89; i.e., the material is ductile, and it satisfies stability criteria. The thermoelectric properties of this compound at different temperat...

The density functional theory was used to explore the structural, electronic, dynamical, and ther... more The density functional theory was used to explore the structural, electronic, dynamical, and thermoelectric properties of a VIrSi Half-Heulser (HH) alloy. The minimum lattice constant of 5.69 ( ̊A) was obtained for VIrSi alloy. Besides, the band structure and the projected density of states for this HH alloy were calculated, and the gap between the valence and conduction bands was noted to be 0.2 eV. Also, the quasi-harmonic approximation was used to predict the dynamical stability of the VIrSi HH alloy. At 300 K, the Seebeck Coefficient of 370 and -270 μV.K−1., respectively, was achieved for the p and n-type doping. From the power factor result, the highest peak of 18 X 1011W/cm.K2 is obtained in the n-type doping. The Figure of Merit (ZT) result revealed that VIrSi alloy possesses a high ZT at room temperature, which would make VIrSi alloy applicable for thermoelectric performance.

We use theoretical X-ray absorption near-edge spectroscopy (XANES) to investigate the electronic ... more We use theoretical X-ray absorption near-edge spectroscopy (XANES) to investigate the electronic structure of the active sites during 2-propanol oxidation to acetone on the Co3O4 (001) surface in humid conditions. In the gas phase, the O K-edge spectra of 2-propanol and acetone as well that of 2-propoxide considered as reaction intermediate, present no pre-edge peaks. Upon 2-propanol adsorption at the Co site of Co3O4 (001) surface, the O K-edge spectrum presents a distinct peak preceded by a bumb in the pre-edge region, both due to dipole transitions from O 1s to 2p states hybridized with Co 3d empty states. The formation of 2- propoxide leads to two distinct pre-edge peaks due to the increase of 3d empty states. A further increment of these pre-edge peaks is observed when acetone is formed and is rather ascribed to the new contributions of carbon 2p empty states in the transitions occurring in the pre-edge region. The changes observed in the pre-edge peak along the oxidation were ...