Active Carboxylic Acid-Terminated Alkanethiol Self-Assembled Monolayers on Gold Bead Electrodes for Immobilization of Cytochromes c

It is extremely difficult to immobilize cytochrome c (cyt c) on carboxylic acid-terminated alkanethiol self-assembled monolayers (HOOC-SAM) on gold bead electrodes prepared in a hydrogen flame. We found that simple pretreatment of a HOOC-SAM/gold bead electrode by potential cycling in buffer solution in the range ±300 mV prior to immobilization of the protein facilitated stable cyt c binding to HOOC-SAMs. The stability of cyt c on the HOOC-SAMs is independent of the topology of the gold surface

Dynamical simulations of an electronically induced solid-solid phase transformation in tungsten

The rearrangement of a material's electron density during laser irradiation leads to modified nonthermal forces on the atoms that may lead to coherent atomic motions and structural phase transformation on very short time scales. We present ab initio molecular dynamics simulations of a martensitic solid-solid phase transformation in tungsten under conditions of strong electronic excitation. The transformation is ultrafast, taking just over a picosecond, and follows the tetragonal Bain path. To examine whether a solid-solid bcc-fcc phase transformation could occur during laser irradiation, we use two-temperature molecular dynamics (2T-MD) simulations with a specially developed potential dependent on the electronic temperature. Our simulations show that the occurrence of the solid-solid phase transformation is in competition with ultrafast nonthermally assisted melting with the strength of the electron-phonon coupling determining the lifetime of the new solid phase. In tungsten the melting transition is predicted to occur too rapidly for the fcc phase to be detectable during laser irradiation

Surface exciton formation on InP(110)-(1x1) studied by time- and angle-resolved photoemission spectroscopy

Physical Review B. 2023, 107 (7), P.075304-1-075304-1

Ultrafast dynamics of photoinjected electrons at the nonthermal regime in the intra-Γ-valley relaxation in InP studied by time- and angle-resolved photoemission spectroscopy

Physical Review B. 2022, 106 (12), P.125204-1-125204-1

Ultrafast relaxation dynamics of highly excited hot electrons in silicon

International audienceUltrafast relaxation dynamics of hot electrons with excess energies exceeding 1 eV in Si is studied using time-resolved photoemission spectroscopy and ab initio calculations. Experimentally, the photoemission peaks from hot electrons excited in bulk electronic states along the Γ−L and Γ−X directions with excess energy (Eex) 1.1–3.2 eV with respect to the conduction band minimum are identified, and the time constants that characterize the decay of transient populations are determined. The decay time, which is 30±3fs at Eex=3.0eV and increases to 115±5fs at Eex=1.1eV, has the same scaling with Eex irrespective of the location of hot electrons in the Brillouin zone. The calculations show that the momentum scattering time due to electron-phonon coupling is shorter than 10 fs for Eex larger than 1.5 eV, being too short to be measured. The combination of theoretical and experimental results reveals that hot electrons with high excess energy in Si are transformed into hot-electron ensembles quasiequilibrated only in momentum space by the ultrafast momentum scattering, and that the experimentally determined time constant of population decay corresponds to the energy relaxation taking place as a whole on a time scale ten times longer than that of the momentum relaxation. The detailed methodology of the analysis of experimental data which we provide in this work, as well as our conclusions which concern the relaxation dynamics of electrons with Eex exceeding 1 eV in Si, can be applied to interpret hot-carrier relaxation phenomena in a wide range of semiconducting materials

Dynamics of Highly Excited Electrons in 3D and 2D Semiconductors: Theory and Experiments

International audienceThe rapid development of the computational methods based on density functional theory, on the one hand, and of the time-energy-and momentum-resolved spectroscopy, on the other hand, allows today an unprecedently detailed insight into the processes governing hot electron relaxation dynamics, and, in particular, into the role of the electron-phonon coupling [1]. Recently, we have developed a computational method, based on density functional theory and on interpolation of the electron-phonon matrix elements in Wannier space, for the calculation of the electron-phonon coupling in polar materials [2]. This method allowed us to successfully interpret the dynamics of hot electron relaxation in bulk GaAs, in excellent agreement with time-and angle-resolved photoemission experiments. We have demonstrated, for the relaxation of hot carriers in GaAs, the existence of two distinct relaxation regimes, one related with the momentum, and the other with energy relaxation [3]. Interestingly, the energy relaxation times become faster at lower energies [4]. In this work, we will present our new results, both experimental and theoretical, on hot electron relaxation in silicon. Numerous additional experiments were performed with respect to the work of [5], and a new interpretation of the measured relaxation times is provided, based on our ab initio calculations and on the concept of hot electron ensembles proposed recently in [3]. Moreover, we will present our recent results, both experimental and theoretical, on the hot electron relaxation and cooling in InSe. InSe is a quasi-2D material which was shown recently to have potential interest for optoelectronics [6]. In this work, we will discuss our new results on the relaxation and cooling dynamics in doped InSe

Formation of hot-electron ensembles quasiequilibrated in momentum space by ultrafast momentum scattering of highly excited hot electrons photoinjected into the Gamma valley of GaAs

We study ultrafast scattering dynamics of hot electrons photoinjected with high excess energies in the Gamma valley of the conduction band of GaAs, using time- and angle-resolved photoemission spectroscopy and ab initio calculations. At ultrafast rates of the order of 10 fs, the packets in the Gamma valley are transformed into hot-electron ensembles (HEEs) quasiequilibrated in momentum space but not in energy space. The energy relaxation of the HEEs takes place as a whole on a longer time scale with rates dependent only on the excess energy, irrespective of the momenta of hot electrons. Both momentum scattering and energy relaxation are ruled by the electron-phonon interaction