Francesco Borgatti

We show how spatially controlled sulfur vacancy engineering enables monolayer MoS2 to act as an electret, storing quasi-permanent electrostatic charge within a single atomic layer and modulating its emission properties. Sulfur vacancies are created by stamp-assisted, electrode-free electrochemical nanolithography, yielding tunable defect densities from 1010 to 1013 cm–2. The vacancy domains act as electron traps, resulting in surface charge density up to 1 μC cm–2, with charge retention exceeding 300 days under ambient conditions. Kelvin probe and electric force microscopies reveal electrostatic patterns replicating the lithographic motif. These domains also define a colocalized exciton-quenching regions in fluorescence microimages. They modulate the exciton fluorescence lifetime recorded at room temperature from tens of nanoseconds to a few hundred picoseconds by enhanced nonradiative exciton deactivation and induce a different balancing between excitons and trion emission via free electron draining from the untreated zones of the crystal.

Through fine defect engineering, we introduce electret functionality into monolayer MoS₂. Sulfur vacancies (Vₛ) are patterned with sub-micrometre resolution, acting as deep electron traps that enable long-lived electrostatic charge storage within a single atomic layer. Using stamp-assisted, electrode-free electrochemical nanolithography, we create vacancy patterns with tunable densities in the 1010-1013 defects/cm2 range. This enables programmable surface charge densities up to 1 µC cm-2, with charge retention exceeding 300 days under ambient conditions. The resulting electret behaviour is directly visualised by Kelvin probe force microscopy and electric force microscopy. The same vacancy-rich domains also act as exciton-quenching regions, generating co-localised electrostatic and optical patterns. This allows tuning of the apparent fluorescence lifetime from 15 ns down to 180 ps. These results establish defect-engineered MoS₂ as the first two-dimensional electret and highlight its potential for nanoscale charge storage and optoelectronic control in two-dimensional materials.

This study highlights the structural, chemical, and magnetic properties of Fe₃O₄/MgCr₂O₄/Fe₃O₄ spinel oxide trilayers and the conditions for preserving the attributes of Fe₃O₄ thin films for potential device applications.

Defects are inherent in transition metal dichalcogenides and significantly affect their chemical and physical properties. In this study, surface defect electrochemical nanopatterning is proposed as a promising method to tune in a controlled manner the electronic and functional properties of defective MoS₂ thin films. Using parallel electrochemical nanolithography, MoS₂ thin films are patterned, creating sulphur vacancy‐rich active zones alternated with defect‐free regions over a centimetre scale area, with sub‐micrometre spatial resolution. The patterned films display tailored optical and electronic properties due to the formation of sulphur vacancy‐rich areas. Moreover, the effectiveness of defect nanopatterning in tuning functional properties is demonstrated by studying the electrocatalytic activity for the hydrogen evolution reaction.

In formulas employed for analysis of organic electronic devices, the relative dielectric constant value of the semiconductor organic films is often assumed rather than measured, even though it is a fundamental parameter for a correct interpretation. This is particularly true for ultrathin films made of discrete molecular layers. In this work, Spectroscopy Ellipsometry and Scanning Capacitance Microscopy were used to study thin films made of N,N′‐bis(n‐octyl)‐x:y,dicyanoperylene‐3,4 : 9,10‐bis(dicarboximide). The relative dielectric constant presents a non‐monotonic trend with thickness: it is equal to 2.1 for one molecular layer, saturating at 3.2 for increasing thickness. This maximum value, equivalent to the bulk one, occurs when the coverage is in between the third to the fourth layer. In this range, the growth switches from a Frank–Van der Merwe (2D growth) to a Volmer‐Weber mode (3D growth); in addition, the molecular configuration assumes a bent/distorted geometry with respect to the initial edge‐on one. These results establish a morphological dependence of the dielectric constant, especially in the vicinity of the substrate interface, that disappears at a certain distance from it.