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Organic thermoelectric materials are promising for wearable heating and cooling devices, as well as near-room-temperature energy generation, due to their nontoxicity, abundance, low cost, and flexibility. However, their primary challenge preventing widespread use is their reduced figure of merit (zT) caused by low electrical conductivity. This study presents a method to enhance the thermoelectric performance of solution-processable organic materials through confined crystallization using the lithographically controlled wetting (LCW) technique. Using PEDOT as a benchmark, we demonstrate that controlled crystallization at the nanoscale improves electrical conductivity by optimizing chain packing and grain morphology. Structural characterizations reveal the formation of a highly compact PEDOT arrangement, achieved through a combination of confined crystallization and DMSO post-treatment, leading to a 4-fold increase in the power factor compared to spin-coated films. This approach also reduces the thermal conductivity dependence on electrical conductivity, improving the zT by up to 260%. The LCW technique, compatible with large-area and flexible substrates, offers a simple, green, and low-cost method to boost the performance of organic thermoelectrics, advancing the potential for sustainable energy solutions and advanced organic electronic devices.

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., (© 2024 The Author(s). Small Methods published by Wiley‐VCH GmbH.)

GaN nanowires (NWs) grown by molecular beam epitaxy on Ti films sputtered on Al 2 O 3 are studied by X-ray diffraction (XRD) and grazing-incidence small-angle X-ray scattering (GISAXS). XRD, performed both in symmetric Bragg reflection mode and at grazing incidence, reveals Ti, TiN, Ti 3 O, Ti 3 Al and Ga 2 O 3 crystallites with in-plane and out-of-plane lattice parameters intermediate between those of Al 2 O 3 and GaN. These topotaxial crystallites in the Ti film, formed as a result of interfacial reactions and N exposure, possess little misorientation with respect to Al 2 O 3 . As a result, GaN NWs grow on the top TiN layer, possessing a high degree of epitaxial orientation with respect to the substrate. The measured GISAXS intensity distributions are modelled by the Monte Carlo method, taking into account the orientational distributions of NWs, the variety of their cross-sectional shapes and sizes, and the roughness of their side facets. The cross-sectional size distributions of the NWs and the relative fractions of the {1100} and {1120} side facets are determined., (© Vladimir M. Kaganer et al. 2023.)

Methylammonium lead tribromide (MAPbBr 3 ) perovskite single crystals demonstrate to be excellent direct X-ray and gamma-ray detectors with outstanding sensitivity and low limit of detection. Despite this, thorough studies on the photophysical effects of exposure to high doses of ionizing radiation on this material are still lacking. In this work, we present our findings regarding the effects of controlled X-ray irradiation on the optoelectronic properties of MAPbBr 3 single crystals. Irradiation is carried out in air with an imaging X-ray tube, simulating real-life application in a medical facility. By means of surface photovoltage spectroscopy, we find that X-ray exposure quenches free excitons in the material and introduces new bound excitonic species. Despite this drastic effect, the crystals recover after 1 week of storage in dark and low humidity conditions. By means of X-ray photoelectron spectroscopy, we find that the origin of the new bound excitonic species is the formation of bromine vacancies, leading to local changes in the dielectric response of the material. The recovery effect is attributed to vacancy filling by atmospheric oxygen and water.

In this study, the structure and morphology, as well as time, ultraviolet radiation, and humidity stability of thin films based on newly developed 1D (PRSH)PbX 3 (X = Br, I) pseudo-perovskite materials, containing 1D chains of face-sharing haloplumbate octahedra, are investigated. All films are strongly crystalline already at room temperature, and annealing does not promote further crystallization or film reorganization. The film microstructure is found to be strongly influenced by the anion type and, to a lesser extent, by the DMF/DMSO solvent volume ratio used during film deposition by spin-coating. Comparison of specular X-ray diffraction and complementary grazing incidence X-ray diffraction analysis indicates that the use of DMF/DMSO mixed solvents promotes the strengthening of a dominant 100 or 210 texturing, as compared the case of pure DMF, and that the haloplumbate chains always lie in a plane parallel to the substrate. Under specific DMF/DMSO solvent volume ratios, the prepared films are found to be highly stable in time (up to seven months under fluxing N 2 and in the dark) and to highly moist conditions (up to 25 days at 78% relative humidity). Furthermore, for representative (PRSH)PbX 3 films, resistance against ultraviolet exposure (λ = 380 nm) is investigated, showing complete stability after irradiation for up to 15 h at a power density of 600 mW/cm 2 . These results make such thin films interesting for highly stable perovskite-based (opto)electronic devices.

Paper is the ideal substrate for the development of flexible and environmentally sustainable ubiquitous electronic systems, which, combined with two-dimensional materials, could be exploited in many Internet-of-Things applications, ranging from wearable electronics to smart packaging. Here we report high-performance MoS 2 field-effect transistors on paper fabricated with a "channel array" approach, combining the advantages of two large-area techniques: chemical vapor deposition and inkjet-printing. The first allows the pre-deposition of a pattern of MoS 2 ; the second, the printing of dielectric layers, contacts, and connections to complete transistors and circuits fabrication. Average I ON /I OFF of 8 × 10 3 (up to 5 × 10 4 ) and mobility of 5.5 cm 2 V -1 s -1 (up to 26 cm 2 V -1 s -1 ) are obtained. Fully functional integrated circuits of digital and analog building blocks, such as logic gates and current mirrors, are demonstrated, highlighting the potential of this approach for ubiquitous electronics on paper.

We report room temperature Hall mobility measurements, low temperature magnetoresistance analysis and low-frequency noise characterization of inkjet-printed graphene films on fused quartz and SiO 2 /Si substrates. We found that thermal annealing in vacuum at 450 °C is a necessary step in order to stabilize the Hall voltage across the devices, allowing their electrical characterization. The printed films present a minimum sheet resistance of 23.3 Ω sq -1 after annealing, and are n-type doped, with carrier concentrations in the low 10 20 cm -3 range. The charge carrier mobility is found to increase with increasing film thickness, reaching a maximum value of 33 cm 2 V -1 s -1 for a 480 nm-thick film printed on SiO 2 /Si. Low-frequency noise characterization shows a 1/f noise behavior and a Hooge parameter in the range of 0.1-1. These results represent the first in-depth electrical and noise characterization of transport in inkjet-printed graphene films, able to provide physical insights on the mechanisms at play.

We demonstrate an all-epitaxial and scalable growth approach to fabricate single-crystalline GaN nanowires on graphene by plasma-assisted molecular beam epitaxy. As substrate, we explore several types of epitaxial graphene layer structures synthesized on SiC. The different structures differ mainly in their total number of graphene layers. Because graphene is found to be etched under active N exposure, the direct growth of GaN nanowires on graphene is only achieved on multilayer graphene structures. The analysis of the nanowire ensembles prepared on multilayer graphene by Raman spectroscopy and transmission electron microscopy reveals the presence of graphene underneath as well as in between nanowires, as desired for the use of this material as contact layer in nanowire-based devices. The nanowires nucleate preferentially at step edges, are vertical, well aligned, epitaxial, and of comparable structural quality as similar structures fabricated on conventional substrates.