Annihilation Process Research Articles

New Classical Integrable Systems from Generalized TT[over ¯]-Deformations.

We introduce and study a novel class of classical integrable many-body systems obtained by generalized TT[over ¯] deformations of free particles. Deformation terms are bilinears in densities and currents for the continuum of charges counting asymptotic particles of different momenta. In these models, which we dub "semiclassical Bethe systems" for their link with the dynamics of Bethe ansatz wave packets, many-body scattering processes are factorized, and two-body scattering shifts can be set to an almost arbitrary function of momenta. The dynamics is local but inherently different from that of known classical integrable systems. At short scales, the geometry of the deformation is dynamically resolved: either particles are slowed down (more space available), or accelerated via a novel classical particle-pair creation and annihilation process (less space available). The thermodynamics both at finite and infinite volumes is described by the equations of (or akin to) the thermodynamic Bethe ansatz, and at large scales generalized hydrodynamics emerge.

Photoluminescence Measurement of Triplet Sensitizer-Emitter Solution Using a Customized 3D-Printed Sample Holder

This study explores the photoluminescence (PL) measurement of triplet sensitizer-emitter (TSE) solutions using a custom 3D-printed sample holder, within the context of triplet-triplet annihilation based molecular photon upconversion (TTA-UC) systems targeting the Vis-to-UV spectral region. TTA-UC converts low-energy visible photons to higher-energy ultraviolet (UV) photons, holding promise for solar energy harvesting and photonics applications. Two TSE couples, 4CzIPN/TP and 4CzIPN/QP, were investigated, and their upconverted fluorescence spectra showed peaks at 344 nm and 354 nm / 370 nm, respectively, confirming efficient upconversion capabilities. The 3D-printed sample holder facilitated reproducible PL measurements, enabling the calculation of quantum yields (ΦUC). The 4CzIPN/TP and 4CzIPN/QP couples exhibited low quantum yields (0.028% and 0.043%, respectively), suggesting the need for improved deoxygenation methods to enhance the triplet-triplet annihilation process and overall quantum efficiency. Despite modest yields, successful UV upconverted fluorescence observation underscores the feasibility of the Vis-to-UV TTA-UC system. This study provides insights into TTA-UC optimization and demonstrates the utility of the 3D-printed sample holder for affordable and precise PL measurements, paving the way for future advancements in photonics and solar energy applications.

Exploring nanovoids in spinel ceramics using positron–positronium trapping model

The investigation focused on nanovoids (free-volume defects) in spinel MgAl2O4 ceramics, synthesized at various temperatures, both before and after saturation (water-immersion), utilizing the positron annihilation spectroscopy method. The findings were analyzed within the framework of a multi-channel model. It was demonstrated that this model integrates channels capturing positrons by volumetric defects and the decay of ortho-positronium atoms. Within this refined approach, the first component reflects the microstructural characteristics of the spinel structure, the second component corresponds to volumetric defects near grain boundaries, while the third pertains to the “pick-off” process of ortho-positronium annihilation within water-filled nanopores of the ceramics.

Annealing temperature-dependent induced supramolecular chiroptical response of copolymer thin films studied by pump-modulated transient circular dichroism spectroscopy

Copolymer thin films showing induced supramolecular chirality are of considerable interest for optoelectronic applications such as organic light-emitting diodes. Here, we introduce a new helicene-like chiral additive with two octyloxy substituents which displays excellent chiral induction properties in an achiral polyfluorene copolymer, leading to a circular dichroism (CD) response of up to 10,000 mdeg. This chiral inducer also displays very good thermal stability, which enables us to perform an extended study on the induced chiroptical properties of the cholesteric copolymer thin films annealed at different temperatures in the range 140–260 °C. Starting from about 180 °C, a distinct change in the morphology of the CD-active film is observed by CD microscopy, from micrometre-size granular to extended CD-active regions, where the latter ones display skewed distributions of the dissymmetry parameter gabs. Broadband Müller matrix spectroscopy finds a pronounced CD and circular birefringence (CB) response and only weak linear dichroism (LD, LD’) and linear birefringence (LB, LB’). Ultrafast transient CD spectroscopy with randomly polarised excitation reveals a clean mirror-image-type transient response, which shows a second-order decay of the S1 population due to singlet–singlet annihilation processes.

Ultraheavy atomic dark matter freeze-out through rearrangement

Atomic dark matter is usually considered to be produced asymmetrically in the early Universe. In this work, we first propose that the symmetric atomic dark matter can be thermally produced through the freeze-out mechanism. The dominant atom antiatom annihilation channel is the atomic rearrangement. It has a geometrical cross section much larger than that of elementary fermions. After the atomic formation, this annihilation process further depletes dark matter particles and finally freezes out. To give the observed dark matter relic, the dark atoms are naturally ultraheavy, ranging from 106 to 1010 GeV. Published by the American Physical Society 2024

Doubly heavy dibaryons as seen by string theory

We propose the stringy description of the system consisting of two heavy and four light quarks in the case of two light flavors of equal mass. As an application, we consider the three low-lying Born-Oppenheimer potentials as a function of the heavy quark separation. Our analysis shows that the ground state potential is described in terms of both hadroquarkonia and hadronic molecules. A connected string configuration makes the dominant contribution to the potential of an excited state at small separations, and for separations larger than 0.1 fm, it exhibits the diquark-diquark-diquark structure [Qq][Qq][qq]. For better understanding the quark organization inside the system, we introduce several critical separations related to the processes of string reconnection, breaking and junction annihilation. We also discuss the simplest string configurations including the five-string junctions and their implications for the system, in particular the emergence of composite quark objects different from diquarks and the process of junction fusion. Published by the American Physical Society 2024

Tritium release performance of biphasic Li2TiO3–Li4SiO4 ceramic pebbles fabricated by centrifugal granulation method

At present, the biphasic Li2TiO3–Li4SiO4 ceramic pebbles with high lithium content and crushing load have been viewed as promising tritium breeders for maintaining the safety-state operation of the D-T fusion reactor. The tritium release behavior of Li2TiO3–Li4SiO4 ceramic pebbles fabricated by centrifugal granulation method was investigated by using the Thermal Desorption Spectroscopy apparatus at Shizuoka University. It can be found that the Li2TiO3–Li4SiO4 ceramic pebbles show three tritium release peaks, and most of the tritium was released as HTO observed from T-TDS spectra, and the peaks at 581 K and 734 K are mainly due to tritium release from Li2TiO3 in core and shell. The peak at 813 K is mainly deemed as tritium release derived from the Li4SiO4 shell. The content of tritium release from biphasic Li2TiO3–Li4SiO4 ceramic is up to 11.5 MBq g−1, but the amount of gas species (HT) is only 0.126 MBq g−1. Besides, the isothermal heating experiment showed that the tritium release behavior was subject to diffusion process and de-trapping in defect sites. At the same time, the irradiation defects of E′-center, O-related center, and Ti3+ for breeding material can be found by using an ESR device, and the isochronous heating experiments have manifested that the amount of irradiated defect decreases as heating temperature increases, which indicates that the tritium release behavior is closely related to defect annihilation process. Therefore, the advanced Li2TiO3–Li4SiO4 ceramic breeder can be fabricated based on tritium release result, which will be conducive to meet the practical application of breeder in the future.

In Situ TEM Tracking of Disconnection Motion and Atomic Cooperative Reorientation in the Oriented Attachment of Pt Nanoparticles.

The oriented attachment (OA) of nanoparticles (NPs) is an important crystal growth mechanism in many materials. However, a comprehensive understanding of the atomic-scale alignment and attachment processes is still lacking. We conducted in situ atomic resolution studies using high-resolution transmission electron microscopy to reveal how two Pt NPs coalesce into a single particle via OA, which involves the formation of atomic-scale links and a grain boundary (GB) between the NPs, as well as GB migration. Density functional theory calculations showed that the system energy changes as a function of the number of disconnections during the coalescence process. Additionally, the formation and annihilation processes of disconnection are always accompanied by the cooperative reorientation motion of atoms. These results further elucidate the growth mechanism of OA at the atomic scale, providing microscopic insights into OA dynamics and a framework for the development of processing strategies for nanocrystalline materials.

Paired Electrosynthesis at Interdigitated Microband Electrodes: Exploring Diffusion and Reaction Zones in the Absence of a Supporting Electrolyte.

Electrosynthesis traditionally requires dedicated reactor systems and an added electrolyte, although some paired electrosynthesis processes are possible at interdigitated microband electrodes simply immersed in solution and without an intentionally added electrolyte. Here, 1,1'-ferrocenedimethanol oxidation and activated olefin electro-hydrogenation reactions are investigated as model processes at a Pt-Pt interdigitated microband array electrode with 5 μm width and with 5 μm interelectrode gap. Voltammetric responses for electro-hydrogenation are discussed, and product yields are determined in methanol (MeOH) in the presence/absence of an added electrolyte (LiClO4). An isotope effect is observed in CH3OD solvent, leading to olefin monodeuteration linked to a fast EC-type process close to the cathode surface (in the cathode reaction zone) rather than to charge annihilation in the interelectrode zone. A finite element simulation is employed to visualize/discuss reaction zones and to contrast the rate of charge annihilation processes with/without a supporting electrolyte.

Transient Nanoscopy of Exciton Dynamics in 2D Transition Metal Dichalcogenides.

The electronic and optical properties of 2D transition metal dichalcogenides are dominated by strong excitonic resonances. Exciton dynamics plays a critical role in the functionality and performance of many miniaturized 2D optoelectronic devices; however, the measurement of nanoscale excitonic behaviors remains challenging. Here, a near-field transient nanoscopy is reported to probe exciton dynamics beyond the diffraction limit. Exciton recombination and exciton-exciton annihilation processes in monolayer and bilayer MoS2 are studied as the proof-of-concept demonstration. Moreover, with the capability to access local sites, intriguing exciton dynamics near the monolayer-bilayer interface and at the MoS2 nano-wrinkles are resolved. Such nanoscale resolution highlights the potential of this transient nanoscopy for fundamental investigation of exciton physics and further optimization of functional devices.

Impact of Packing Geometry on Excimer Characteristics and Mobility in Perylene Bisimide Polycrystalline Films.

Efficient exciton transport is essential for high-performance optoelectronics. Considerable efforts have been focused on improving the exciton mobility in organic materials. While it is feasible to improve mobility in organic systems by forming well-ordered stacks, the formation of trap states, particularly the lower-lying states referred to as excimers, remains a significant challenge to enhancing mobility. The mobility of excimer excitons intricately depends on the strength of excitonic coupling in terms of Förster-type diffusive exciton transfer processes. Given that the formation and mobility of excimer excitons are highly sensitive to molecular arrangements (packing geometries), conducting comprehensive investigations into the structure-property relationship in organic systems is crucial. In this study, we prepared three types of polycrystalline films of perylene bisimide (PBI) by varying substituents at the imide and bay positions, which allowed us to tailor the properties of excimer excitons and their mobility based on packing geometries and excitonic coupling strengths. By utilizing femtosecond transient absorption spectroscopy, we observed ultrafast excimer formation in the higher coupling regime, while in the lower coupling regime, the transition from Frenkel to excimer excitons occurs with a time constant of 500 fs. Under high pump-fluence, exciton-exciton annihilation processes occur, indicating the diffusion of excimer excitons. Intriguingly, employing a three-dimensional diffusion model, we derived a diffusion constant that is 3000 times greater in the high coupling regime than in the low coupling regime. To investigate the optoelectronic properties in the form of a bulk system, we fabricated n-type organic field effect transistors and obtained 8000 times higher mobility in the high coupling regime. Furthermore, photocurrent measurements enable us to investigate the charge carrier transport by mobile excimer excitons, suggesting a 230-fold improvement in external quantum efficiency with tightly packing PBI molecules compared to the low coupling regime. These findings not only offer valuable insights into optimizing organic materials for optoelectronic devices but also unveil the intriguing potential of exciton migration within excimers.

Superior electron mobility, red electroluminescence with high quantum efficiency from printable room temperature columnar liquid crystalline perylene bisimide

Synthesis of highly fluorescent compounds is currently a critical requirement to facilitate the economical and metal-independent manufacture of organic light-emitting diodes (OLEDs) on a large scale. This study presents a highly soluble, swallow tail based electron deficient perylene bisimide (PBIST) exhibiting room temperature columnar oblique (Colob) liquid crystalline behavior along with a high photoluminescence quantum yield, positioning itself as a promising candidate for efficient OLEDs. Incorporation of swallow tails helped in enhancing the solubility and reduction of the clearing points. This unique tailor-made molecular design with the liquid crystalline phase allowed a demonstration of n-type field effect mobility of 0.008 cm2 V−1s−1 when annealed in the liquid crystalline mesophase range (at 70 °C) which can be exploited in the fabrication of printable electronic devices. Capitalizing on the high charge transport and luminescence attributes of PBIST, a series of devices were fabricated by utilizing PBIST as a single emitter and dispersed at different concentrations of 0.3, 0.5 and 1 wt% in host material CBP. Impressively, doped devices featuring the CBP as a host at a 0.5 wt% PBIST concentration exhibited an external quantum efficiency (EQE) as high as 7 %, accompanied by a luminance of 1787 cd/m2. The high EQE is attributed mainly to the triplet–triplet annihilation (TTA) process. This notable EQE enhancement signifies a substantial stride towards expanding the utility of multifunctional columnar self-assembled materials for the advancement of OLEDs.

Modelling Annihilation Properties of Positronium Confined in Nanoporous Materials: A Review.

Positronium (Ps) is a valuable probe to investigate nanometric or sub-nanometric cavities in non-metallic materials, where Ps can be confined. Accessible experimental measurements concern the lifetime of trapped Ps, which is largely influenced by pick-off processes, depending on the size of the cavity as well as on the density of the electrons belonging to the surface of the host trap. Another relevant physical quantity is the contact density, that is the electron density at the positron position, which is usually found to be well below the vacuum value. Here, we review the principal models that have been formulated to account and explain for these physical properties of confined Ps. Starting with models, treating Ps as a single particle formulated essentially to study pick-off, we go on to describe more refined two-particle models because a two-body model is the simplest approach able to describe any change in the contact density, observed in many materials. Finally, we consider a theory of Ps annihilation in nanometric voids in which the exchange correlations between the electron of Ps and the outer electrons play a fundamental role. This theory is not usually taken into account in the literature, but it has to be considered for a correct theory of pick-off annihilation processes.

String fragmentation of a quark pair with entangled spin states: Application to e+e− annihilation

We present a recursive quantum mechanical model for the fragmentation of a string stretched between a quark and an antiquark with entangled spin states. The quarks are assumed to be produced in the e+e− annihilation process via the exchange of a virtual photon and the correlations between their spin states are described by a joint spin-density matrix. The string fragmentation process is formulated at the amplitude level by using the splitting matrices of the recent string+P30 model of polarized quark fragmentation with pseudoscalar and vector meson emissions and accounts for the systematic propagation of the spin correlations in the fragmentation chain. The model is formulated as a recursive recipe suitable for a Monte Carlo implementation. It reproduces the expected angular correlation, due to the Collins effect, between back-to-back pseudoscalar and/or vector mesons. For the latter, this correlation also involves the momenta of the decay products. We use the model for studying the sign of the Collins asymmetry for back-to-back vector and pseudoscalar mesons. Published by the American Physical Society 2024

Direct observation of room-temperature high-level triplet–triplet annihilation process in 1%rubrene-doped OLEDs with a CzDBA sensitizer

Using the magneto-electroluminescence as a sensitive and fingerprint probing tool, a “hot exciton” channel, named the high-level triplet–triplet annihilation (HL-TTA or T2T2A, T2 + T2 → Sn → S1 → S0 + hv) process from the high-lying triplet (T2) to the lowest singlet states, is observed in 1%rubrene-doped organic light-emitting diodes with a thermally activated delayed fluorescence sensitizer of 9,10-bis(4-(9H-carbazol-9-yl)-2,6-dimethylphenyl)-9,10-diboraanthracene (CzDBA) at room temperature. The addition of a sensitizer simultaneously promotes the Dexter energy transfer channels of host-sensitizer and sensitizer-guest triplets, thereby increasing the amounts of T2 states and inducing the occurrence of the HL-TTA process. Additionally, the HL-TTA enhances with the increase in the bias current and decreases with lowering the working temperature, which is consistent with the current dependence of the conventional low-level TTA (T1T1A, T1 + T1 → S1 + S0) process but contrary to its temperature dependence. More interestingly, the high concentration of CzDBA induces the H-type aggregation of rubrene molecules, promoting the singlet fission process but suppressing the HL-TTA process. These findings enrich the physical understanding of hot exciton channels and provide ideas for the preparation of high-performance devices.

Ground state fully heavy pentaquark production in the pair annihilation process

Ground state fully heavy pentaquark production in the pair annihilation process

Defect Passivation of 2D Semiconductors by Fixating Chemisorbed Oxygen Molecules via h-BN Encapsulations.

Hexagonal boron nitride (h-BN) is a key ingredient for various 2D van der Waals heterostructure devices, but the exact role of h-BN encapsulation in relation to the internal defects of 2D semiconductors remains unclear. Here, it is reported that h-BN encapsulation greatly removes the defect-related gap states by stabilizing the chemisorbed oxygen molecules onto the defects of monolayer WS2 crystals. Electron energy loss spectroscopy (EELS) combined with theoretical analysis clearly confirms that the oxygen molecules are chemisorbed onto the defects of WS2 crystals and are fixated by h-BN encapsulation, with excluding a possibility of oxygen molecules trapped in bubbles or wrinkles formed at the interface between WS2 and h-BN. Optical spectroscopic studies show that h-BN encapsulation prevents the desorption of oxygen molecules over various excitation and ambient conditions, resulting in a greatly lowered and stabilized free electron density in monolayer WS2 crystals. This suppresses the exciton annihilation processes by two orders of magnitude compared to that of bare WS2. Furthermore, the valley polarization becomes robust against the various excitation and ambient conditions in the h-BN encapsulated WS2 crystals.

Boosting Reverse Intersystem Crossing of TADF Emitter through Molecular Geometry Adaptation to Crystalline Host

AbstractRapid reverse intersystem crossing (RISC) is one of the prime concerns for blue thermally activated delayed fluorescence (TADF) emitters, as it reduces triplet exciton population, the root cause of detrimental triplet‐mediated annihilation processes that accelerate device efficiency roll‐off and degradation. This work introduces a new concept to tailor the RISC of TADF emitters through their molecular geometry adaptation to crystalline hosts bearing a similar donor‐acceptor structure. A meticulously designed crystalline host comprising isophthalonitrile acceptor (A) and carbazole‐derived donor (D) units, characterized by nearly orthogonal D‐A arrangement, has been demonstrated to alleviate singlet‐triplet energy gap (ΔEST) of the TADF dopant by forcing it to adopt a more twisted D‐A configuration, as corroborated by X‐ray diffraction (XRD) measurements. The approach not only significantly reduces the RISC activation energy, resulting in a remarkable tenfold boost of the RISC rate (above 107 s−1) and fourfold shortening of delayed FL lifetime (down to 1.5 µs), but also offers the additional benefit of suppressing conformational disorder of TADF dopant, producing a narrower emission bandwidth. The presented concept, based on crystalline host‐driven RISC engineering, is anticipated to have a profound impact on the development of high‐performance, stable blue‐emitting TADF organic light‐emitting diodes (OLEDs).

Production of hypernuclei from antiproton capture within a relativistic transport model

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Ortho-positronium annihilation processes in Y zeolites under different environments by measurements of the energy spectra of the positron annihilation radiation

Measurements of the energy distribution of the positron annihilation radiation in Y zeolites are carried out to elucidate the various ortho-positronium annihilation processes that take place in these microporous materials and relate them to the ortho-positronium lifetime components observed by positron annihilation lifetime spectroscopy in earlier studies. Y zeolites with various Si/Al ratios in the range from 2.6 to 40 are investigated under a controlled atmosphere of N2 gas and after exposure to the atmosphere. The ortho-positronium annihilation modes are characterized by analyzing the γ-ray spectra through the use of the f3γ index, which represents the fraction of 3γ-annihilation, and the S parameter. The proportion of ortho-positronium self-annihilation is found to be no less than 15% in N2 gas, but drastically decreases by the physisorption of water molecules and possibly positronium spin exchange interaction with oxygen in the atmosphere. The presence of water molecules suppresses ortho-positronium intrinsic annihilation and, at the same time, promotes ortho-positronium pick-off annihilation in the pores. Similarly, the S parameter rises due to an increased contribution from para-positronium annihilation and ortho-positronium pick-off annihilation, which is also consistent with the physisorption of water and positronium spin exchange. In conjunction with the previously measured ortho-positronium lifetime components, the specific ortho-positronium annihilation sites and processes in these porous materials under different environments are determined and a complete picture of the ortho-positronium behavior in Y zeolites is obtained.Graphical abstractγ-ray energy spectra of Y zeolites with a Si/Al ratio = 2.6 measured in N2 gas and water-saturated zeolites