FORTH Institute of Electronic Structure and Laser

Fluorescent organic light-emitting diodes (OLEDs) still face major obstacles to combining high efficiency with solution processability and energy-sustainable operation. In this work, a tetra-carboxyphenyl porphyrin–nitrogen carbon dots (TCPP-NCDots) derivative is introduced as a solution-processable electron transport layer (ETL) in OLEDs based on a green–yellow emissive polymer. The structural, optical, and electronic properties of the TCPP-NCDots ETL are comprehensively characterised by ultraviolet–visible absorption spectroscopy, steady-state photoluminescence, Fourier-transform infrared spectroscopy, atomic force microscopy, and cyclic voltammetry. These studies reveal a synergistic effect of porphyrin functionalisation on the carbon dots, which improves electron injection and transport toward the emissive layer. At an optimum concentration of 1 mg mL−1, the TCPP-NCDots ETL yields a 21.6% enhancement in external quantum efficiency compared with the reference device without an ETL, while simultaneously suppressing efficiency roll-off. The optimised devices also maintain stable operation under ambient conditions, highlighting TCPP-NCDots as a promising, sustainable ETL platform for next-generation fluorescent OLEDs.

We propose an efficient protocol to realize multi-qubit gates in arrays of neutral atoms. The atoms encode qubits in the long-lived hyperfine sublevels of the ground electronic state. To realize the gate, we apply a global laser pulse to transfer the atoms to a Rydberg state with strong blockade interaction that suppresses simultaneous excitation of neighboring atoms arranged in a star-graph configuration. The number of Rydberg excitations, and thereby the parity of the resulting state, depends on the multiqubit input state. Upon changing the sign of the interaction and de-exciting the atoms with an identical laser pulse, the system acquires a geometric phase that depends only on the parity of the excited state, while the dynamical phase is completely canceled. Using single qubit rotations, this transformation can be converted to the C k Z or C k NOT quantum gate for k + 1 atoms. We also present extensions of the scheme to implement quantum gates between distant atomic qubits connected by a quantum bus consisting of a chain of atoms.

Thermodynamics-basedmodels predict the structure of polymer-graftednanoparticles (PGNs) as well as their assembly behavior based on geometricparameters such as particle size, degree of polymerization, and densityof grafted chains. The role of microscopic polymer dynamics, suchas the mobility of repeat units in the melt state, in the evolutionof the structure and properties remains unknown. Brillouin light spectroscopy(BLS), due to its capability to concurrently discern the local andglobal elastic properties of PGN assemblies, enables the probing ofmicroscopic processes, such as brush interdigitation, sensitive tothe annealing of the assembly. For poly­(methyl methacrylate) (PMMA)-graftedsilica (SiO2) PGNs in the dry powder state and annealedabove the glass transition temperature, BLS revealed fully reversiblelocal elasticity, indicative of limited interdigitation between adjacentPGNs. This contrasts with polystyrene (PS)–SiO2 analogsthat displayed ready (and irreversible) fusion of brush layers duringannealing. The retardation of brush interdigitation in PMMA-graftedsystems is surprising, given the similar thermomechanical propertiesof both polymers, and is rationalized as the consequence of higherfriction between PMMA repeats compared to PS. Microscopic dynamicsthus has a profound impact on the kinetic path of structure (and property)evolution and thus should be considered during the processing of PGNsinto functional hybrid materials.

This study investigates amorphous anodized porous TiO2 (a-TiO2) as a substrate for iridium-based oxygen evolution catalysts. The substrates were prepared via anodization of Ti foil in a glycerol-based solution for 15 min @ 60 V. Nickel was subsequently electrodeposited to act both as a conductive and sacrificial layer for the galvanic deposition of iridium from an Ir(IV) chloro-complex solution. Electrochemical anodization resulted in a uniform IrOx layer on the a-TiO2 substrate, featuring Ir aggregates ~250 nm in size and an Ir:Ni atomic ratio of ca. 7, as determined by EDS analysis. The quantity of Ni determined by ICP-MS bulk analysis indicated that Ni resided also within the porous matrix. Varying the Ni deposition charge density (qNi) revealed that an intermediate loading (1463 mC cm−2) provided the best balance between Ir accessibility during the galvanic replacement step and electronic continuity. The optimized IrOx/Ir-Ni/a-TiO2 electrode achieved excellent OER performance (η = 344 mV @ 10 mA cm−2; 1.68 mA μgIr−1 @ η = 300 mV) at an ultra-low Ir loading of 2.15 μgIr cm−2 and demonstrated good short-term stability, with only a 20 mV potential increase over 4 h of continuous operation at 5.5 mA cm−2. Overall, this strategy offers a scalable pathway for producing efficient OER electrodes with minimal noble metal loading.

Constraining the origin of the nanohertz gravitational-wave background necessitates precise noise modelling to avoid parameter estimation biases. In this work, we find the inferred properties of the putative gravitational wave background in the second data release of the European Pulsar Timing Array to be in better agreement with theoretical expectations under the improved noise model. In particular, our improved noise models show consistency of the background’s strain spectral index with the value of −2/3, favoring the population of supermassive black hole binaries as the origin of the background. Our results further suggest that the observed gravitational wave emission is the dominant source of the binary energy loss, with no evidence of environmental effects or eccentric orbits. At the reference gravitational wave frequency of yr−1, we also find a lower power-law strain amplitude of the background than in previous data analyses. This mitigates some of the tensions of the strain amplitude with the expected number density and mass scale of binaries discussed in the literature. Our analysis demonstrates the importance of accurate modelling of radio pulsar pulse profile variations, hierarchical properties of noise across pulsars, as well as noise model averaging, when inferring properties of the gravitational wave background.