Atomistic Simulations of P(NDI2OD-T2) Morphologies: From Single Chain to Condensed Phases

We investigate theoretically the structure, crystallinity, and solubility of a high-mobility n-type semiconducting copolymer, P(NDI2OD-T2), and we propose a set of new force field parameters. The force field is reparametrized against density functional theory (DFT) calculations, with the aim to reproduce the correct torsional angles that govern the polymer chain flexibility and morphology. We simulate P(NDI2OD-T2) oligomers in different environments, namely, in vacuo, in the bulk phase, and in liquid toluene and chloronaphthalene solution. The choice of these solvents is motivated by the fact that they induce different kinds of molecular preaggregates during the casting procedures, resulting in variable device performances. Our results are in good agreement with the available experimental data; the polymer bulk structure, in which the chains are quite planar, is correcly reproduced, yet the isolated chains are flexible enough to fold in vacuo. We also calculate the solubility of P(NDI2OD-T2) in toluene and chloronaphthalene, predicting a much better solubility of the polymer in the latter, also in accordance to experimental observations. Different morphologies and dynamics of the oligomers in the two solvents have been observed. The proposed parameters make it possible to obtain the description of P(NDI2OD-T2) in different environments and can serve as a basis for extensive studies of this polymer semiconductor, such as, for example, the dynamics of aggregation in solvent

Light Ion Accelerating Line (L3IA): Test Experiment at ILIL-PW

The construction of a novel Laser driven Light Ions Acceleration Line(L3IA) is progressing rapidly towards the operation, following the recent upgrade of the ILIL-PW laser facility. The Line was designed following the pilot experimental activity carried out earlier at the same facility to define design parameters and to identify main components including target control and diagnostic equipment, also in combination with the numerical simulations for the optimization of laser and target parameters. A preliminary set of data was acquired following the successful commissioning of the laser system >100 TW upgrade. Data include output from a range of different ion detectors and optical diagnostics installed for qualification of the laser-target interaction. An overview of the results is given along with a description of the relevant upgraded laser facility and features.Comment: 6 pages, 7 figures, 18 references, presented at the EAAC 201

Mapping Orientational Order of Charge-Probed Domains in a Semiconducting Polymer

Structure–property relationships are of fundamental importance to develop quantitative models describing charge transport in organic semiconductor based electronic devices, which are among the best candidates for future portable and lightweight electronic applications. While microstructural investigations, such as those based on X-rays, electron microscopy, or polarized optical probes, provide necessary information for the rationalization of transport in macromolecular solids, a general model predicting how charge accommodates within structural maps is not yet available. Therefore, techniques capable of directly monitoring how charge is distributed when injected into a polymer film and how it correlates to structural domains can help fill this gap. Supported by density functional theory calculations, here we show that polarized charge modulation microscopy (p-CMM) can unambiguously and selectively map the orientational order of the only conjugated segments that are probed by mobile charge in the few nanometer thick accumulation layer of a high-mobility polymer-based field-effect transistor . Depending on the specific solvent-induced microstructure within the accumulation layer, we show that p-CMM can image charge-probed domains that extend from submicrometer to tens of micrometers size, with markedly different degrees of alignment. Wider and more ordered p-CMM domains are associated with improved carrier mobility, as extracted from device characteristics. This observation evidences the unprecedented opportunity to correlate, directly in a working device, electronic properties with structural information on those conjugated segments involved in charge transport at the buried semiconductor–dielectric interface of a field-effect device

Low-frequency modes in the Raman spectrum of sp-sp2 nanostructured carbon

A novel form of amorphous carbon with sp-sp2 hybridization has been recently produced by supersonic cluster beam deposition showing the presence in the film of both polyynic and cumulenic species [L. Ravagnan et al. Phys. Rev. Lett. 98, 216103 (2007)]. Here we present a in situ Raman characterization of the low frequency vibrational region (400-800 cm-1) of sp-sp2 films at different temperatures. We report the presence of two peaks at 450 cm-1 and 720 cm-1. The lower frequency peak shows an evolution with the variation of the sp content and it can be attributed, with the support of density functional theory (DFT) simulations, to bending modes of sp linear structures. The peak at 720 cm-1 does not vary with the sp content and it can be attributed to a feature in the vibrational density of states activated by the disorder of the sp2 phase.Comment: 15 pages, 5 figures, 1 tabl

Time-stability of a Single-crystal Diamond Detector for fast neutron beam diagnostic under alpha and neutron irradiation

Single-crystal Diamond Detectors (SDDs), due to their good charge carrier transport properties, low leakage and therefore good energy resolution, are good candidates for fast neutron measurement on pulsed spallation sources and fusion plasma experiments. Moreover, diamonds are known to be resistant to neutron irradiation. Nevertheless, measurements show transient effects during irradiation with ionizing particles, as the alpha particle calibration sources. The decrease of the detector counting rate of a counting chain and the pulse height are interpreted as due to a charge trapping inside the detector, which modifies the drift electric field. These instabilities are strongly dependent on the specific type of the interaction. Measurements have been carried out with both alpha particles in the laboratory and neutrons at the ISIS neutron spallation source. We show that these polarization effects are not permanent: the detector performances can be restored by simply inverting the detector bias high voltage. Prime Novelty Statement The measurements described in the paper were performed in order to study the polarization effect in Single-crystal Diamond Detector. This effect was observed under alpha particle and neutron irradiation. With the Transient Current Technique an interpretation of the effect is given

Ban the burn: the trans-local campaign against ocean incineration, 1983–1988

Ocean incineration, i.e., the thermal destruction of toxic substances in ships outfitted with high-temperature combustion chambers, promised to solve the age-old problem of hazardous waste disposal. This method was perfected throughout the 1970s and commercialized in the early 1980s, only to be abandoned by the end of that decade. My paper charts the rise and fall of ocean incineration and explains its decline. I argue that local and transnational protests formed the main constraint on ocean incineration. My research, combining social and environmental history, shows how a trans-local coalition challenged uneven socio-ecological developments through a successful “Ban the Burn” campaign.Cities, Migration and Global Interdependenc

Human Rights vs. Human Life: The US-Soviet Bottom-Line

In 1977 an incident occurred in a tiny fisherman village located in the south-eastern corner of Italy, which resonated in both Washington and Moscow. That kind of linkages in history, combining the micro and macro levels of analysis simultaneously, is what inspires me the most as a historian and what makes me feel so much at home at EUR’s history department. An overarching, comprehensive view of history, one that intertwines the local and global together, helps me in the exploration of the global repercussions that a plethora of apparently marginal events recurrently had throughout the cold war.History and International Relation

Efficient calculation of electronic coupling integrals with the dimer projection method via a density matrix tight-binding potential

Designing organic semiconductors for practical applications in organic solar cells, organic field-effect transistors, and organic light-emitting diodes requires understanding charge transfer mechanisms across different length and time scales. The underlying electron transfer mechanisms can be efficiently explored using semiempirical quantum mechanical (SQM) methods. The dimer projection (DIPRO) method combined with the recently introduced non-self-consistent density matrix tight-binding potential (PTB) [Grimme et al., J. Chem. Phys. 158, 124111 (2023)] is used in this study to evaluate charge transfer integrals important for understanding charge transport mechanisms. PTB, parameterized for the entire Periodic Table up to Z = 86, incorporates approximate non-local exchange, allowing for efficient and accurate calculations for large hetero-organic compounds. Benchmarking against established databases, such as Blumberger's HAB sets, or our newly introduced JAB69 set and comparing with high-level reference data from omega B97X-D4 calculations confirm that DIPRO@PTB consistently performs well among the tested SQM approaches for calculating coupling integrals. DIPRO@PTB yields reasonably accurate results at low computational cost, making it suitable for screening purposes and applications to large systems, such as metal-organic frameworks and cyanine-based molecular aggregates further discussed in this work

π-Conjugation and End Group Effects in Long Cumulenes: Raman Spectroscopy and DFT Calculations

We have investigated the structure and spectroscopic properties of cumulenic carbon chains, focusing on the peculiar π-conjugation properties and end-group effects that influence their behavior. With support from Density Functional Theory (DFT) calculations, we have analyzed the IR and Raman spectra of cumulenes characterized by different end-capping groups and we have related them to the bond length alternation (BLA) pattern and local spectroscopic parameters associated with the CC bonds along the sp-carbon chain. For cumulenes we observe a breakdown of the correlation existing in polyynes among frequencies, Raman intensities of the Ʀ line (longitudinal CC stretching modes), and BLA. While the low Ʀ line frequency and equalized CC bonds would indicate the “metallic” character of cumulenic species, we obtain an unusually strong Raman intensity, which is typical of bond-alternated (semiconductive) structures. DFT calculations reveal that this is a consequence of π-electron conjugation, which markedly extends from the sp-carbon chain to the aryl rings belonging to the end groups. These findings suggest the existence of a strong electronic, vibrational and structural coupling between sp-carbon chains and sp2-carbon species, which could play a key role in nanostructured sp/sp2-hybrid carbon materials (e.g., linear carbon chains coupled to graphene domains). Within this context, Raman spectroscopy is a valuable tool for the detailed characterization of the molecular properties of this kind of materials

Guiding Charge Transport in Semiconducting Carbon Nanotube Networks by Local Optical Switching

Photoswitchable, ambipolar field-effect transistors (FETs) are fabricated with dense networks of polymer-sorted, semiconducting single-walled carbon nanotubes (SWCNTs) in top-gate geometry with photochromic molecules mixed in the polymer matrix of the gate dielectric. Both hole and electron transport are strongly affected by the presence of spiropyran and its photoisomer merocyanine. A strong and persistent reduction of charge carrier mobilities and thus drain currents upon UV illumination (photoisomerization) and its recovery by annealing give these SWCNT transistors the basic properties of optical memory devices. Temperature-dependent mobility measurements and density functional theory calculations indicate scattering of charge carriers by the large dipoles of the merocyanine molecules and electron trapping by protonated merocyanine as the underlying mechanism. The direct dependence of carrier mobility on UV exposure is employed to pattern high- and low-resistance areas within the FET channel and thus to guide charge transport through the nanotube network along predefined paths with micrometer resolution. Near-infrared electroluminescence imaging enables the direct visualization of such patterned current pathways with good contrast. Elaborate mobility and thus current density patterns can be created by local optical switching, visualized and erased again by reverse isomerization through heating