Dilute suspensions of repulsive particles exhibit a Newtonian response to flow that can be accurately predicted by the particle volume fraction and the viscosity of the suspending fluid. However, such a description fails when the particles are weakly attractive. In a simple shear flow, suspensions of attractive particles exhibit complex, anisotropic microstructures and flow instabilities that are poorly understood and plague industrial processes. One such phenomenon, the formation of log-rolling flocs, which is ubiquitously observed in suspensions of attractive particles that are sheared while confined between parallel plates, is an exemplar of this phenomenology. Combining experiments and discrete element simulations, we demonstrate that this shear-induced structuring is driven by hydrodynamic coupling between the flocs and the confining boundaries. Clusters of particles trigger the formation of viscous eddies that are spaced periodically and whose centers act as stable regions where particles aggregate to form flocs spanning the vorticity direction. Simulation results for the wavelength of the periodic pattern of stripes formed by the logs and for the log diameter are in quantitative agreement with experimental observations on both colloidal and noncolloidal suspensions. Numerical and experimental results are successfully combined by means of rescaling in terms of a Mason number that describes the strength of the shear flow relative to the rupture force between contacting particles in the flocs. The introduction of this dimensionless group leads to a universal stability diagram for the log-rolling structures and allows for application of shear-induced structuring as a tool for assembling and patterning suspensions of attractive particles.

Carbyne and linear carbon structures based on sp-hybridization are attractive targets as the ultimate one-dimensional system (i.e., one-atom in diameter) featuring wide tunability of optical and electronic properties. Two possible structures exist for sp-carbon atomic wires: (a) the polyynes with alternated single-triple bonds and (b) the cumulenes with contiguous double bonds. Theoretical studies predict semiconducting behavior for polyynes, while cumulenes are expected to be metallic. Very limited experimental work, however, has been directed toward investigating the electronic properties of these structures, mostly at the single-molecule or monolayer level. However, sp-carbon atomic wires hold great potential for solution-processed thinfilm electronics, an avenue not exploited to date. Herein, we report the first field-effect transistor (FET) fabricated employing cumulenic sp-carbon atomic wires as a semiconductor material. Our proof-of-concept FET device is easily fabricated by solution drop casting and paves the way for exploiting sp-carbon atomic wires as active electronic materials.

Hybrid quantum wells are electronic structures were charge carriers are confined along stacked inorganic planes, separated by insulating organic moieties. 2D quantum confined hybrid materials are of great interest from...

Silver benzeneselenolate [AgSePh]∞ is a coordination polymer that hosts a hybrid quantum well structure. The recent advancements in the study of its tightly bound excitons (~300 meV) and photoconductive properties makes it an interesting representative of a material platform that is an environmentally stable alternative to 2D metal halide perovskites in terms of optoelectronic properties. To this aim, several challenges are to be addressed, among which the lack of control over the metal-organic reaction process in the reported synthesis of the [AgSePh]∞ nanocrystal film (NC). This issue contributed to cast doubts over the origin of its intra-bandgap electronic states. In this article we study all the steps to obtain phase pure [AgSePh]∞ NC films, from thin silver films through its oxidation and reaction via a chemical vapor-solid with benzeneselenol, by means of UV-vis, XRD, SEM, and AFM. Raman and FTIR spectroscopy are also employed to provide vibrational peaks assignment, for the first time on this polymer. Our analysis supports an acid-base reaction scheme based on an acid attacking the metal oxide precursor, generating water as byproduct of the polymeric synthesis, speeding up the reaction by solvating the PhSeH. The reaction readily goes to completion within 30 min in a supersaturated PhSeH / N2 atmosphere at 90 °C. Our analysis suggests the absence of precursor's leftovers or oxidized species that could contribute to the intra-gap states. By tuning the reaction parameters, we gained control on film morphology to obtain substrate-parallel oriented micro-crystals showing different excitonic absorption intensities. Finally, centimeters size high quality [AgSePh]∞ NC films could be obtained, enabling exploitation of their optoelectronic properties, such as UV photodetection, in largearea applications.

Understanding thermal transport in 2D materials and especially in graphene is a key challenge for the design of heat management and energy conversion devices. The high sensitivity of measured transport properties to structural defects, ripples and vacancies is of crucial importance in these materials. Using a first principle based approach combined with an exact treatment of the disorder, we address the impact of vacancies on phonon lifetimes and thermal transport in graphene. We find that perturbation theory fails completely and overestimates phonon lifetimes by almost two orders of magnitude. Whilst, in defected graphene, LA and TA modes remain well defined, the ZA modes become marginal. In the long wavelength limit, the ZA dispersion changes from quadratic to linear and the scattering rate is found proportional to the phonon energy, in contrast to the quadratic scaling often assumed. The impact on thermal transport, calculated beyond the relaxation time approximation and including first principle phonon-phonon scattering rates as reported recently for pristine graphene, reveals spectacular effects even for extremely low vacancy concentrations.

has boosted the field of large-area flexible and printed electronics. These advances have enabled a plethora of applications such as organic light-emitting diodes, [1,2] organic photovoltaics, [3,4] organic thermoelectrics, [5,6] organic field-effect transistors (OFETs), [7][8][9][10] organic (bio)sensors, [11][12][13] and neuromorphic devices. [14,15] In this context, organic field-effect transistors (OFETs) are not only relevant for their direct technological application, but they also represent an ideal test-bed to investigate thin-film electrical properties. Organic semiconductors are typically classified in two main families, namely conjugated polymers and small molecules. The former, polymers, are particularly appealing as a result of their solution processability, and OFETs with charge mobility above the standard for hydrogenated amorphous silicon (0.5-1 cm 2 V −1 s −1 ) have been extensively reported. [16] The latter, small molecules, are prone to arrange in ordered molecular crystals, and through several years of chemical tailoring and fine tuning of the films processing, small-molecule OFETs with field-effect mobility >10 cm 2 V −1 s −1 have been achieved. [17][18][19] The chemical root of the π-conjugation of these materials is associated with the sp 2 -hybridization of carbon atoms in their backbone. This peculiar trait is also common to Solution-processed, large-area, and flexible electronics largely relies on the excellent electronic properties of sp 2 -hybridized carbon molecules, either in the form of π-conjugated small molecules and polymers or graphene and carbon nanotubes. Carbon with sp-hybridization, the foundation of the elusive allotrope carbyne, offers vast opportunities for functionalized molecules in the form of linear carbon atomic wires (CAWs), with intriguing and even superior predicted electronic properties. While CAWs represent a vibrant field of research, to date, they have only been applied sparingly to molecular devices. The recent observation of the field-effect in microcrystalline cumulenes suggests their potential applications in solution-processed thin-film transistors but concerns surrounding the stability and electronic performance have precluded developments in this direction. In the present study, ideal field-effect characteristics are demonstrated for solution-processed thin films of tetraphenyl[3]cumulene, the shortest semiconducting CAW. Films are deposited through a scalable, large-area, meniscus-coating technique, providing transistors with hole mobilities in excess of 0.1 cm 2 V −1 s −1 , as well as promising operational stability under dark conditions. These results offer a solid foundation for the exploitation of a vast class of molecular semiconductors for organic electronics based on sp-hybridized carbon systems and create a previously unexplored paradigm.

Quantum transport and thermoelectric properties of single layered transition metal dichalchogenide MoS₂.

Engineering the molecular structure of conjugated polymers is key to advance the field of organic electronics. In this work, we synthesized a molecularly encapsulated version of the naphthalene diimide bithiophene co-polymer PNDIT2, which is among the most popular high charge mobility organic semiconductors in n-type field-effect transistors, and non-fullerene acceptors in organic photovoltaic blends. The encapsulating macrocycles shield the bithiophene units, while leaving the naphthalene diimide units available for intermolecular interactions. With respect to PNDIT2, the encapsulated counterpart displays increased backbone planarity. Molecular encapsulation prevents pre-aggregation of the polymer chains in common organic solvents, while it permits π-stacking in the solid-state and promotes thin film crystallinity through an intermolecular-lock mechanism. Consequently, n-type semiconducting behavior is retained in field-effect transistors, although charge mobility is lower than in PNDIT2, due to the absence of the fibrillar microstructure that originates from pre-aggregation in solution. Hence, molecularly encapsulating conjugated polymers represents a promising chemical strategy in order to tune molecular interaction in solution and the backbone conformation, and to consequently control the nanomorphology of casted films, without altering the electronic structure of the core polymer.