Jožef Stefan Institute

About: Jožef Stefan Institute is a facility organization based out in Ljubljana, Slovenia. It is known for research contribution in the topics: Liquid crystal & Dielectric. The organization has 3828 authors who have published 12614 publications receiving 291025 citations.

Charge Photogeneration in Few-Layer MoS2

Abstract: The 2D semiconductor MoS2 in its mono- and few-layer form is expected to have a significant exciton binding energy of several 100 meV, suggesting excitons as the primary photoexcited species. Nevertheless, even single layers show a strong photovoltaic effect and work as the active material in high sensitivity photodetectors, thus indicating efficient charge carrier photogeneration. Here, modulation spectroscopy in the sub-ps and ms time scales is used to study the photoexcitation dynamics in few-layer MoS2. The results suggest that the primary photoexcitations are excitons that efficiently dissociate into charges with a characteristic time of 700 fs. Based on these findings, simple suggestions for the design of efficient MoS2 photovoltaic and photodetector devices are made.

Mobile Domain Walls as a Bridge between Nanoscale Conductivity and Macroscopic Electromechanical Response

Abstract: The interfaces in complex oxides present unique properties exploitable in nanoscale devices. Recent studies on ferroelectric BiFeO3, BaTiO3, and Pb(Zr, Ti) O-3 have revealed an unusually high electric conductivity of the domain walls (DWs), adding another degree of freedom for controlling the local properties of these materials. While most of the investigations are focused on thin films for nanoscale applications, many practical devices, including piezoelectric sensors, actuators, and transducers, rely on the macroscopic properties of bulk polycrystalline materials where the average effect of local properties should be small. It is shown that in polycrystalline BiFeO3 the local domain-wall conductivity interferes with the dynamics of the DWs within the grains, resulting in an unexpectedly large effect on the macroscopic piezoelectric response. The results thus bridge the local conductivity and the macroscopic piezoelectricity via domain-wall dynamics, revealing that the domain-wall conductivity must be considered when interpreting and controlling macroscopic electromechanical properties.

Two-dimensional Ising model criticality in a three-dimensional uniaxial relaxor ferroelectric with frozen polar nanoregions.

Abstract: The charge-disordered three-dimensional uniaxial relaxor ferroelectric ${\mathrm{Sr}}_{061}{\mathrm{Ba}}_{039}{\mathrm{Nb}}_{2}{\mathrm{O}}_{6}$ splits up into metastable polar nanoregions and paraelectric interfaces upon cooling from above ${T}_{c}$ The frozen polar nanoregions are verified by piezoresponse force microscopy, respond domainlike to dynamic light scattering and dielectric excitation, reveal nonergodicity at $Tg{T}_{c}$ via global aging, and coalesce into polar nanodomains below ${T}_{c}$ Contrastingly, the percolating system of unperturbed interfaces becomes ferroelectric with two-dimensional Ising-model-like critical exponents $\ensuremath{\alpha}=0$, $\ensuremath{\beta}=1/8$, and $\ensuremath{\gamma}=7/4$, as corroborated by ac calorimetry, second harmonic generation, and susceptometry, respectively

Acidic pH as a physiological regulator of human cathepsin L activity.

Abstract: Human cysteine protease cathepsin L was inactivated at acid pH by a first-order process. The inactivation rate decreased with increasing concentrations of a small synthetic substrate, suggesting that substrates stabilize the active conformation. The substrate-independent inactivation rate constant increased with organic solvent content of the buffer, consistent with internal hydrophobic interactions, disrupted by the organic solvent, also stabilizing the enzyme. Circular dichroism showed that the inactivation is accompanied by large structural changes, a decrease in α-helix content being especially pronounced. The high activation energy of the reaction at pH 3.0 (200 kJ·mol−1) supported such a major conformational change occurring. The acid inactivation of cathepsin L was irreversible, consistent with the propeptide being needed for proper folding of the enzyme. Aspartic protease cathepsin D was shown to cleave denatured, but not active cathepsin L, suggesting a potential mechanism for in-vivo regulation and turnover of cathepsin L inside lysosomes.