Agnes Gubicza

Electrically conductive metal–organic frameworks (MOFs) and MOF‐like coordination polymers are an emerging class of materials that combine good electrical charge transport with unique properties such as nanoporosity. The combination of different metal nodes and organic linkers allows tailoring MOFs to specific properties and applications in electronics, like selective chemiresistive sensing. The intrinsic crystallinity of MOFs, which usually promotes efficient charge transport, makes them also difficult to integrate into flexible systems, as crystalline MOFs are often brittle. The present study reports on a fast and reliable interfacial synthesis of conductive MOF films composed of two different organic ligands, 2,3,6,7,10,11‐hexahydroxytriphenylene (HHTP) and 7,7,8,8‐tetracyanoquinodimethane (TCNQ), lacking long‐range periodic order while preserving good electrical conductivity of 0.033 S cm⁻¹ at room temperature and chemiresistive response toward ambient changes. The hybrid nature of the discontinuous film is investigated multiparametrically by electron and atomic force microscopy as well as by Raman spectroscopy. This study demonstrates that including different types of MOFs is a good compromise between structural order and conductivity, thus making hybrid framework architectures to a promising active material for chemiresistive sensors without the need for high crystallinity.

An oxygen-free lithographical fabrication method enables room temperature atomic switches terminated by oxygen sensitive metals.

Strongly coupled dye molecules are known to produce narrowband absorption in a large spectral range. Here we exploit this feature to achieve organic photodetectors with ultra-narrow full-width at half-maximum response at low bias voltage.

Providing a chemical control over charge transport through molecular junctions is vital to developing sensing applications at the single‐molecule scale. Quantum‐interference effects that affect the charge transport through molecules offer a unique chance to enhance the chemical control. Here, we investigate how interference effects can be harnessed to optimize the response of single molecule dithienoborepin (DTB) junctions to the specific coordination of a fluoride ion in solution. The single‐molecule conductance of two DTB isomers is measured using scanning tunneling microscopy break‐junction (STM‐BJ) before and after fluoride ion exposure. We find a significant change of conductance before and after the capture of a fluoride ion, the magnitude of which depends on the position of the boron atom in the molecular structure. This single‐molecule sensor exhibits switching ratios of up to four orders of magnitudes, suggesting that the boron–fluoride coordination can lead to quantum‐interference effects. This is confirmed by a quantum chemical characterization, pointing toward a cross‐conjugated path through the molecular structure as the origin of the effect.

The microscopic origins and technological impact of 1/f type current fluctuations in Ag based, filamentary type resistive switching devices have been investigated upon downscaling toward the ultimate single atomic limit. The analysis of the low-frequency current noise spectra revealed that the main electronic noise contribution arises from the resistance fluctuations due to internal dynamical defects of Ag nanofilaments. The resulting 0.01–1% current noise ratio, i.e. the total noise level with respect to the mean value of the current, is found to be universal: its magnitude only depends on the total resistance of the device, irrespective of the materials aspects of the surrounding solid electrolyte and of the specific filament formation procedure. Moreover, the resistance dependence of the current noise ratio also displays the diffusive to ballistic crossover, confirming that stable resistive switching operation utilizing Ag nanofilaments is not compromised even in truly atomic scale junctions by technologically impeding noise levels.

We demonstrate Nb₂O₅ memristive devices with tuneable low-bias resistances and optimized high-bias impedance for high speed neuromorphic operation.

Prevailing models of resistive switching arising from electrochemical formation of conducting filaments across solid state ionic conductors commonly attribute the observed polarity of the voltage-biased switching to the sequence of the active and inert electrodes confining the resistive switching memory cell. Here we demonstrate stable switching behaviour in metallic Ag-Ag₂S-Ag nanojunctions at room temperature exhibiting similar characteristics. Our experimental results and numerical simulations reveal that the polarity of the switchings is solely determined by the geometrical asymmetry of the electrode surfaces. By the lithographical design of a proof of principle device we demonstrate the merits of simplified fabrication of atomic-scale, robust planar Ag₂S memory cells.

Resistive switching in Ag₂S nanojunctions is quantitatively understood by considering the local overheating of the junction volume at finite bias.

The non-exponential dynamics of resistive switchings in Ag₂S memristive nanojunctions provides an ideal basis for non-volatile memory applications.

We demonstrate Ag₂S memristive devices optimized for high speed operation. Andreev reflection spectroscopy reveals highly transparent, atomic scale conducting channels.