Explore the vast range of titles available.

Probing novel properties, arising from twisted interfaces, has traditionally relied on the stacking of exfoliated two-dimensional materials and the spontaneous formation of van der Waals bonds. So far, investigations involving intimate covalent or ionic bonds have not been a focus. Yet, we show here that an established technique, involving thermocompressional wafer bonding, works well for creating twisted non-van der Waals interfaces. We have successfully bonded z-cut lithium niobate single crystals to create ferroelectric oxide interfaces with strong polar discontinuities and have mapped the associated emergent interfacial conductivity. In some instances, a dramatic change in microstructure occurs, involving local dipolar switching. A twist-induced collapse in the capability of the system to effec8tively screen interfacial bound charge is implied. Importantly, this only occurs around specific moiré twist angles with sparse coincident lattices and associated short-range aperiodicity. In quasicrystals, aperiodicity is known to induce pseudo-bandgaps and we suspect a similar phenomenon here. Wafer bonding has allowed the synthesis of twisted interfaces which support polar discontinuities in ferroelectric lithium niobate. Two-dimensional sheet conductivity arises but is suppressed when twist angles lead to interfacial lattice aperiodicity.

Building efficient triplet-harvesting layers for photovoltaic applications requires a deep understanding of the microscopic properties of the components involved and their dynamics. Singlet fission is a particularly appealing mechanism as it generates two excitons from a single photon. However, the pathways of the coupled triplets into free species, and their dependence on the intermolecular geometry, has not been fully explored. In this work, we produce highly ordered dilute pentacene films with distinct parallel and herringbone dimers and aggregates. Using electron paramagnetic resonance spectroscopy, we provide compelling evidence for the formation of distinct quintet excitons in ambient conditions, with intrinsically distinctive electronic and kinetic properties. We find that the ability of quintets to separate into free triplets is promoted in the parallel dimers and this provides molecular design rules to control the triplets, favouring either enhanced photovoltaic efficiency (parallel) or strongly bound pairs that could be exploited for logic applications (herringbone). Singlet fission results in the formation of a pair of triplets, known as a quintet. Here, the authors identify long-lived quintets in dilute pentacene films at room temperature, with lifetimes influenced by intermolecular geometry having implications for the design of triplet-harvesting films.

The characteristic relaxation and dephasing times of the electronic spins in thin-film copper phthalocyanine are long enough that this common, low-cost organic semiconductor has potential for both quantum and classical information processing. New materials for spintronics Spintronics devices, which exploit the intrinsic spin of electrons as well as their charge, require precise control and read-out of electron spins. For organic semiconductors to find use in spintronic applications, it is desirable to identify molecules that possess long spin relaxation times. This paper establishes that copper phthalocyanine, a blue pigment commonly used in paints and dyes, appears to satisfy this requirement. It is inexpensive and can be easily processed into a thin-film form of the type used for device fabrication, making it a candidate material system for spin-based quantum information processing and other spintronic applications. Organic semiconductors are studied intensively for applications in electronics and optics 1 , and even spin-based information technology, or spintronics 2 . Fundamental quantities in spintronics are the population relaxation time ( T 1 ) and the phase memory time ( T 2 ): T 1 measures the lifetime of a classical bit, in this case embodied by a spin oriented either parallel or antiparallel to an external magnetic field, and T 2 measures the corresponding lifetime of a quantum bit, encoded in the phase of the quantum state. Here we establish that these times are surprisingly long for a common, low-cost and chemically modifiable organic semiconductor, the blue pigment copper phthalocyanine 3 , in easily processed thin-film form of the type used for device fabrication. At 5 K, a temperature reachable using inexpensive closed-cycle refrigerators, T 1 and T 2 are respectively 59 ms and 2.6 μs, and at 80 K, which is just above the boiling point of liquid nitrogen, they are respectively 10 μs and 1 μs, demonstrating that the performance of thin-film copper phthalocyanine is superior to that of single-molecule magnets over the same temperature range 4 . T 2 is more than two orders of magnitude greater than the duration of the spin manipulation pulses, which suggests that copper phthalocyanine holds promise for quantum information processing, and the long T 1 indicates possibilities for medium-term storage of classical bits in all-organic devices on plastic substrates.

Chiral π -conjugated molecules bring new functionality to technological applications and represent an exciting, rapidly expanding area of research. Their functional properties, such as the absorption and emission of circularly polarized light or the transport of spin-polarized electrons, are highly anisotropic. As a result, the orientation of chiral molecules critically determines the functionality and efficiency of chiral devices. Here we present a strategy to control the orientation of a small chiral molecule (2,2′-dicyano[6]helicene) by the use of organic and inorganic templating layers. Such templating layers can either force 2,2′-dicyano[6]helicene to adopt a face-on orientation and self-assemble into upright supramolecular columns oriented with their helical axis perpendicular to the substrate, or an edge-on orientation with parallel-lying supramolecular columns. Through such control, we show that low- and high-energy chiroptical responses can be independently ‘turned on’ or ‘turned off’. The templating methodologies described here provide a simple way to engineer orientational control and, by association, anisotropic functional properties of chiral molecular systems for a range of emerging technologies. The properties of chiral conjugated molecules, such as the absorption and/or emission of circularly polarized light or electron transport, are highly anisotropic. Now it has been shown that templating layers can control the orientation and anisotropic properties of small chiral molecules in bulk thin films useful for a range of emerging technologies.

The viability of dilute magnetic semiconductors in applications is linked to the strength of the magnetic couplings, and room temperature operation is still elusive in standard inorganic systems. Molecular semiconductors are emerging as an alternative due to their long spin-relaxation times and ease of processing, but, with the notable exception of vanadium-tetracyanoethylene, magnetic transition temperatures remain well below the boiling point of liquid nitrogen. Here we show that thin films and powders of the molecular semiconductor cobalt phthalocyanine exhibit strong antiferromagnetic coupling, with an exchange energy reaching 100 K. This interaction is up to two orders of magnitude larger than in related phthalocyanines and can be obtained on flexible plastic substrates, under conditions compatible with routine organic electronic device fabrication. Ab initio calculations show that coupling is achieved via superexchange between the singly occupied a 1g ( ) orbitals. By reaching the key milestone of magnetic coupling above 77 K, these results establish quantum spin chains as a potentially useable feature of molecular films. Molecular semiconductors are promising candidates for spintronics applications but they often suffer from low magnetic transition temperatures, usually below the boiling point of liquid nitrogen. Here, the authors observe high-temperature antiferromagnetism in cobalt phthalocyanine films and powders.

We report on a new approach for the fabrication of ferromagnetic molecular thin films. Co-evaporated films of manganese phthalocyanine (MnPc) and tetracyanoquinodimethane (TCNQ) have been produced by organic molecular beam deposition (OMBD) on rigid (glass, silicon) and flexible (Kapton) substrates kept at room temperature. The MnPc:TCNQ films are found to be entirely amorphous due to the size mismatch of the molecules. However, by annealing while covering the samples highly crystalline MnPc films in the β-polymorph can be obtained at 60 °C lower than when starting with pure MnPc films. The resulting films exhibit substantial coercivity (13 mT) at 2 K and a Curie temperature of 11.5 K.

Molecular layers show antiferromagnetic ordering up to room temperature and are able to exchange bias a ferromagnetic electrode, demonstrating that molecules could be much more than a simple vehicle for transporting spin. Gruber and colleagues show that a molecular film can control the interaction and induce exchange bias.

Inorganic semiconductors based on heavy pnictogen cations (Sb and Bi ) have gained significant attention as potential nontoxic and stable alternatives to lead-halide perovskites for solar cell applications. A limitation of these novel materials, which is being increasingly commonly found, is carrier localization, which substantially reduces mobilities and diffusion lengths. Herein, CuSbSe is investigated and discovered to have delocalized free carriers, as shown through optical pump terahertz probe spectroscopy and temperature-dependent mobility measurements. Using a combination of theory and experiment, the critical enabling factors are found to be: 1) having a layered structure, which allows distortions to the unit cell during the propagation of an acoustic wave to be relaxed in the interlayer gaps, with minimal changes in bond length, thus limiting deformation potentials; 2) favourable quasi-bonding interactions across the interlayer gap giving rise to higher electronic dimensionality; 3) Born effective charges not being anomalously high, which, combined with the small bandgap ( 1.2 eV), result in a low ionic contribution to the dielectric constant compared to the electronic contribution, thus reducing the strength of Fröhlich coupling. These insights can drive forward the rational discovery of perovskite-inspired materials that can avoid carrier localization.

Molecular layers show antiferromagnetic ordering up to room temperature and are able to exchange bias a ferromagnetic electrode, demonstrating that molecules could be much more than a simple vehicle for transporting spin.