Polaron spin dynamics in high-mobility polymeric semiconductors

Polymeric semiconductors exhibit exceptionally long spin lifetimes, and recently observed micrometre spin diffusion lengths in conjugated polymers demonstrate the potential for organic spintronics devices. Weak spin–orbit and hyperfine interactions lie at the origin of their long spin lifetimes, but the coupling mechanism of a spin to its environment remains elusive. Here, we present a systematic study of polaron spin lifetimes in field-effect transistors with high-mobility conjugated polymers as an active layer. We demonstrate how spin relaxation is governed by the charges’ hopping motion at low temperatures, whereas an Elliott–Yafet-like relaxation due to a transient localization of the carrier wavefunctions is responsible for spin relaxation at high temperatures. In this regime, charge, spin and structural dynamics are intimately related and depend sensitively on the local conformation of polymer backbones and the crystalline packing of the polymer chains.* ERC Synergy grant SC2 (no. 610115) * Alexander von Humboldt Foundation * Transregional Collaborative Research Center (SFB/TRR) 173 SPIN+X * Winton Programme for the Physics of Sustainability * Engineering and Physical Sciences Research Council (EPSRC) * Excellence Initiative by the Graduate School Materials Science in Mainz (GSC 266) * European Commission/Région Wallonne (FEDER–BIORGEL project), the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds National de la Recherche Scientifique (FRS-FNRS) under grant no. 2.5020.11 * Tier-1 supercomputer of the Fédération Wallonie-Bruxelles, infrastructure funded by the Walloon Region under grant agreement n111754

A general approach for hysteresis-free, operationally stable metal halide perovskite field-effect transistors.

Despite sustained research, application of lead halide perovskites in field-effect transistors (FETs) has substantial concerns in terms of operational instabilities and hysteresis effects which are linked to its ionic nature. Here, we investigate the mechanism behind these instabilities and demonstrate an effective route to suppress them to realize high-performance perovskite FETs with low hysteresis, high threshold voltage stability (ΔVt 1 cm2/V·s at room temperature. We show that multiple cation incorporation using strain-relieving cations like Cs and cations such as Rb, which act as passivation/crystallization modifying agents, is an effective strategy for reducing vacancy concentration and ion migration in perovskite FETs. Furthermore, we demonstrate that treatment of perovskite films with positive azeotrope solvents that act as Lewis bases (acids) enables a further reduction in defect density and substantial improvement in performance and stability of n-type (p-type) perovskite devices

Conforming nanoparticle sheets to surfaces with Gaussian curvature

Nanoparticle monolayer sheets are ultrathin inorganic–organic hybrid materials that combine highly controllable optical and electrical properties with mechanical flexibility and remarkable strength. Like other thin sheets, their low bending rigidity allows them to easily roll into or conform to cylindrical geometries. Nanoparticle monolayers not only can bend, but also cope with strain through local particle rearrangement and plastic deformation. This means that, unlike thin sheets such as paper or graphene, nanoparticle sheets can much more easily conform to surfaces with complex topography characterized by non-zero Gaussian curvature, like spherical caps or saddles. Here, we investigate the limits of nanoparticle monolayers’ ability to conform to substrates with Gaussian curvature by stamping nanoparticle sheets onto lattices of larger polystyrene spheres. Tuning the local Gaussian curvature by increasing the size of the substrate spheres, we find that the stamped sheet morphology evolves through three characteristic stages: from full substrate coverage, where the sheet extends over the interstices in the lattice, to coverage in the form of caps that conform tightly to the top portion of each sphere and fracture at larger polar angles, to caps that exhibit radial folds. Through analysis of the nanoparticle positions, obtained from scanning electron micrographs, we extract the local strain tensor and track the onset of strain-induced dislocations in the particle arrangement. By considering the interplay of energies for elastic and plastic deformations and adhesion, we construct arguments that capture the observed changes in sheet morphology as Gaussian curvature is tuned over two orders of magnitude

Desenvolvimento e aplicação de método para avaliação da qualidade de termocicladores

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências da Saúde, Programa de Pós-Graduação em Farmácia, Florianópolis, 2017.A técnica da Reação em Cadeia da Polimerase (PCR), que utiliza equipamentos termocicladores para sua execução, vem sendo amplamente utilizada em laboratórios e é um método acurado se realizado de forma criteriosa. Considerando a importância do desempenho dos termocicladores para a execução da técnica, este estudo pretende contribuir para a garantia da qualidade e confiança dos resultados obtidos por técnicas de PCR. Assim, os objetivos deste estudo foram verificar a homogeneidade térmica do bloco térmico do termociclador, a temperatura e a duração efetivamente executadas em cada ciclo da reação, bem como avaliar a eficiência de amplificação dos termocicladores por meio de uma PCR-controle, e avaliar a relação entre o desempenho dos termocicladores e suas condições de uso. A avaliação da temperatura foi realizada por meio de um protocolo de verificação da temperatura estática e por meio de um protocolo que mimetiza os ciclos térmicos de uma PCR, utilizando-se micro-termopares. A maioria dos termocicladores verificados apresentou algum tipo de distorção no seu perfil de temperatura, demonstrando perfil curvo ou com overshooting. Variações significativas de temperatura entre as posições verificadas nos blocos térmicos também foram observadas. As temperaturas efetivamente executadas desviaram pelo menos 0,5°C das programadas em todas as etapas avaliadas. A duração efetiva das etapas foi consideravelmente diminuída, chegando a não haver um platô na temperatura programada em alguns casos. Tais alterações não foram desprezíveis, pois resultaram em falhas nos resultados da PCR-controle pela maioria dos termocicladores. Portanto, não há posições melhores ou piores no bloco térmico, há termociclador com funcionamento adequado ou inadequado. Por fim, ressalta-se a importância de os usuários realizarem a verificação da qualidade dos seus termocicladores a fim de conhecerem melhor o desempenho dos equipamentos, contribuindo para maior reprodutibilidade das PCR principalmente nos laboratórios que utilizam diferentes modelos de termocicladores.Abstract : Polymerase Chain Reaction (PCR) has been widely used in clinical laboratories and in scientific research, being considered a well-established technique if carefully performed. Thermocyclers are essential equipments for PCR execution, which must show good performance. Considering the importance of thermocycler quality control, this research aims to contribute to quality assurance and reliability of the results obtained through PCR. In order to evaluate the quality of thermocyclers at UFSC laboratories, the research aimed to verify the thermal homogeneity in the thermal block, the temperature and duration obtained for each reaction cycle, as well as to evaluate the thermocycler amplification efficiency by means of a PCR control and the relationship between thermocycler performance and its maintenance conditions. Temperature evaluation was done using a protocol for verification of static temperature and another protocol that mimics PCR cycles, all of them using micro thermocouples. Most of the thermocyclers verified presented some type of distortion in their temperature profile, showing a curved profile or overshooting. Significant temperature variations among the positions verified in the thermal blocks were also observed. The effective temperatures deviated at least 0.5°C from those programmed in all stages evaluated. The actual duration of the stages was considerably reduced, not even reading a stable plateau at the programed temperature in some cases. Such changes were not negligible, as they resulted in flaws in the control-PCR in the majority of the thermocyclers. Finally, it is emphasized the importance of users to verify the quality of their thermocyclers in order to know the performance of the equipment, contributing to a greater reproducibility of the PCR, especially among the laboratories that use different models of thermocyclers

Spin relaxation of electron and hole polarons in ambipolar conjugated polymers.

The charge-transport properties of conjugated polymers have been studied extensively for opto-electronic device applications. Some polymer semiconductors not only support the ambipolar transport of electrons and holes, but do so with comparable carrier mobilities. This opens the possibility of gaining deeper insight into the charge-transport physics of these complex materials via comparison between electron and hole dynamics while keeping other factors, such as polymer microstructure, equal. Here, we use field-induced electron spin resonance spectroscopy to compare the spin relaxation behavior of electron and hole polarons in three ambipolar conjugated polymers. Our experiments show unique relaxation regimes as a function of temperature for electrons and holes, whereby at lower temperatures electrons relax slower than holes, but at higher temperatures, in the so-called spin-shuttling regime, the trend is reversed. On the basis of theoretical simulations, we attribute this to differences in the delocalization of electron and hole wavefunctions and show that spin relaxation in the spin shuttling regimes provides a sensitive probe of the intimate coupling between charge and structural dynamics

Room Temperature Optically and Magnetically Active Edges in Phosphorene Nanoribbons

Nanoribbons - nanometer wide strips of a two-dimensional material - are a unique system in condensed matter physics. They combine the exotic electronic structures of low-dimensional materials with an enhanced number of exposed edges, where phenomena including ultralong spin coherence times, quantum confinement and topologically protected states can emerge. An exciting prospect for this new material concept is the potential for both a tunable semiconducting electronic structure and magnetism along the nanoribbon edge. This combination of magnetism and semiconducting properties is the first step in unlocking spin-based electronics such as non-volatile transistors, a route to low-energy computing, and has thus far typically only been observed in doped semiconductor systems and/or at low temperatures. Here, we report the magnetic and semiconducting properties of phosphorene nanoribbons (PNRs). Static (SQUID) and dynamic (EPR) magnetization probes demonstrate that at room temperature, films of PNRs exhibit macroscopic magnetic properties, arising from their edge, with internal fields of ~ 250 to 800 mT. In solution, a giant magnetic anisotropy enables the alignment of PNRs at modest sub-1T fields. By leveraging this alignment effect, we discover that upon photoexcitation, energy is rapidly funneled to a dark-exciton state that is localized to the magnetic edge and coupled to a symmetry-forbidden edge phonon mode. Our results establish PNRs as a unique candidate system for studying the interplay of magnetism and semiconducting ground states at room temperature and provide a stepping-stone towards using low-dimensional nanomaterials in quantum electronics.Comment: 18 pages, 4 figure

Financial incentives to improve adherence to anti-psychotic maintenance medication in non-adherent patients - a cluster randomised controlled trial (FIAT)

Background Various interventions have been tested to achieve adherence to anti-psychotic maintenance medication in non-adherent patients with psychotic disorders, and there is no consistent evidence for the effectiveness of any established intervention. The effectiveness of financial incentives in improving adherence to a range of treatments has been demonstrated; no randomised controlled trial however has tested the use of financial incentives to achieve medication adherence for patients with psychotic disorders living in the community. Methods/Design In a cluster randomised controlled trial, 34 mental health teams caring for difficult to engage patients in the community will be randomly allocated to either the intervention group, where patients will be offered a financial incentive for each anti-psychotic depot medication they receive over a 12 month period, or the control group, where all patients will receive treatment as usual. We will recruit 136 patients with psychotic disorders who use these services and who have problems adhering to antipsychotic depot medication, although all conventional methods to achieve adherence have been tried. The primary outcome will be adherence levels, and secondary outcomes are global clinical improvement, number of voluntary and involuntary hospital admissions, number of attempted and completed suicides, incidents of physical violence, number of police arrests, number of days spent in work/training/education, subjective quality of life and satisfaction with medication. We will also establish the cost effectiveness of offering financial incentives. Discussion The study aims to provide new evidence on the effectiveness and cost effectiveness of offering financial incentives to patients with psychotic disorders to adhere to antipsychotic maintenance medication. If financial incentives improve adherence and lead to better health and social outcomes, they may be recommended as one option to improve the treatment of non-adherent patients with psychotic disorders. Trial Registration Current controlled trials ISRCTN77769281

Lawson criterion for ignition exceeded in an inertial fusion experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion