Université de Fribourg

Preferential out-of-plane conduction and quasi-one-dimensional electronic states in layered 1T-TaS 2

Martino, E. ; Pisoni, A. ; Ćirić, L. ; Arakcheeva, A. ; Berger, H. ; Akrap, Ana ; Putzke, C. ; Moll, P. J. W. ; Batistić, I. ; Tutiš, E. ; Forró, László ; Semeniuk, K.

In: npj 2D Materials and Applications, 2020, vol. 4, no. 1, p. 1–9

Layered transition metal dichalcogenides (TMDs) are commonly classified as quasi-two-dimensional materials, meaning that their electronic structure closely resembles that of an individual layer, which results in resistivity anisotropies reaching thousands. Here, we show that this rule does not hold for 1T-TaS2—a compound with the richest phase diagram among TMDs. Although the onset of ...

Université de Fribourg

Mahan excitons in room-temperature methylammonium lead bromide perovskites

Palmieri, Tania ; Baldini, Edoardo ; Steinhoff, Alexander ; Akrap, Ana ; Kollár, Márton ; Horváth, Endre ; Forró, László ; Jahnke, Frank ; Chergui, Majed

In: Nature Communications, 2020, vol. 11, no. 1, p. 850

In a seminal paper, Mahan predicted that excitonic bound states can still exist in a semiconductor at electron-hole densities above the insulator-to-metal Mott transition. However, no clear evidence for this exotic quasiparticle, dubbed Mahan exciton, exists to date at room temperature. In this work, we combine ultrafast broadband optical spectroscopy and advanced many-body calculations to...

Université de Fribourg

Persistent antiferromagnetic order in heavily overdoped Ca1-x La x FeAs2

Martino, Edoardo ; Bachmann, Maja D ; Rossi, Lidia ; Modic, Kimberly A ; Zivkovic, Ivica ; Rønnow, Henrik M ; Moll, Philip J W ; Akrap, Ana ; Forró, László ; Katrych, Sergiy

In: Journal of Physics: Condensed Matter, 2019, vol. 31, no. 48, p. 485705

In the Ca1−x La x FeAs2 (1 1 2) family of pnictide superconductors, we have investigated a highly overdoped composition (x = 0.56), prepared by a high-pressure, high-temperature synthesis. Magnetic measurements show an antiferromagnetic transition at T N = 120 K, well above the one at lower doping (0.15 < x < 0.27).Below the onset of long-range...

Université de Fribourg

Accounting for inertia effects to access the high-frequency microrheology of viscoelastic fluids

Domínguez-García, P. ; Cardinaux, Frédéric ; Bertseva, Elena ; Forró, László ; Scheffold, Frank ; Jeney, Sylvia

In: Physical Review E, 2014, vol. 90, no. 6, p. 060301

We study the Brownian motion of microbeads immersed in water and in a viscoelastic wormlike micelles solution by optical trapping interferometry and diffusing wave spectroscopy. Through the mean-square displacement obtained from both techniques, we deduce the mechanical properties of the fluids at high frequencies by explicitly accounting for inertia effects of the particle and the surrounding...

Université de Fribourg

Multi-functional magnetic photoluminescent photocatalytic polystyrene-based micro- and nano-fibers Obtained by electrospinning

Schaer, Michel ; Crittin, Mireille ; Kasmi, Lamia ; Pierzchala, Katarzyna ; Calderone, Caroline ; Digigow, Reinaldo G. ; Fink, Alke ; Forró, László ; Sienkiewicz, Andrzej

In: Fibers, 2014, vol. 2, no. 1, p. 75–91

This work reports on the implementation of electrospinning (ES) as a facile route to encapsulate nano-engineered materials in a polystyrene (PS) matrix. We applied ES to co-encapsulate two kinds of nanoparticles, i.e., upconversion nanophosphors (UCNPs) and superparamagnetic iron oxide nanoparticles (SPIONs), in polystyrene (PS)-based micro- and nano-fibers (PSFs). This approach made it...

Université de Fribourg

Evaluation of the toxicity of graphene derivatives on cells of the lung luminal surface

Horváth, Lenke ; Magrez, Arnaud ; Burghard, Marko ; Kern, Klaus ; Forró, László ; Schwaller, Beat

In: Carbon, 2013, vol. 64, p. 45–60

Graphene-based nanomaterials are expected to have a profound impact on a broad range of applications. However, studies devoted to investigating the putative adverse health effects of these nanomaterials are hugely underrepresented in the current scientific literature. We have investigated the in vitro short-term cellular toxicity associated with graphene derivatives (GD): graphene oxide and...

Université de Fribourg

Cellular toxicity of TiO₂-based nanofilaments

Magrez, Arnaud ; Horvth, Lenke ; Smajda, Rita ; Salicio, Valérie ; Pasquier, Nathalie ; Forró, László ; Schwaller, Beat

In: ACS Nano, 2009, vol. 3, no. 8, p. 2274–2280

At present, nanofilaments are not exclusively based on carbon atoms but can be produced from many inorganic materials in the form of nanotubes and nanowires. It is essential to systematically assess the acute toxicity of these newly synthesized materials since it cannot be predicted from the known toxicity of the same material in another form. Here, the cellular toxicity of TiO₂-based...