Letteratura scientifica selezionata sul tema "Proton-Induced QFS"

We present the results of time-resolved photoluminescence (TRPL) and optically detected microwave resonance (ODMR) spectroscopy investigations of semiconductor quantum dots and quantum wells. The ODMR spectra of InAs/GaAs QDs were detected via modulation of the total intensity of the QDs emission induced by 95 GHz microwave excitation and exciton fine structure was studied. Very long life times (up to 10 ns) of photoexcited carriers were observed in this system using TRPL at low temperatures and excitation intensities promising higher responsitivity of such QDs for quantum dot infrared photodetector development. The effects of proton and alpha particles irradiation on carrier dynamics were investigated on different InGaAs/GaAs, InAlAs/AlGaAs and GaAs/AlGaAs QD and QW systems. The obtained results demonstrated that carrier lifetimes in the QDs are much less affected by proton irradiation than that in QWs. A strong influence of irradiation on the PL intensity was observed in multiple QWs after high-energy alpha particles irradiation.

The light-emission efficiency of InAs/GaAs quantum dots (QDs) affected by proton implantation and subsequent annealing is investigated. The photoluminesce (PL) intensity is determined by the carrier capture time and non-radiative center (NRC) lifetime. The intermixing-induced carrier capture enhancement and the implantation-induced NRC generation mutually compete, so there exists a critical implantation dose (). When is less than , the intermixing is the main effect and the PL intensity increases with . On the other hand, when is larger than , the implantation damage is so large that the intensity decreases with the dose. The higher the annealing temperature is, the larger becomes.

While light-emitting nanostructures composed of group-IV materials fulfil the mandatory compatibility with CMOS-fabrication methods, factors such as the structural stability of the nanostructures upon thermal annealing, and the ensuing photoluminescence (PL) emission properties, are of key relevance. In addition, the possibility of improving the PL efficiency by suitable post-growth treatments, such as hydrogen irradiation, is important too. We address these issues for self-assembled Ge quantum dots (QDs) that are co-implanted with Ge ions during their epitaxial growth. The presence of defects introduced by the impinging Ge ions results in pronounced PL-emission at telecom wavelengths up to room temperature (RT) and above. This approach allows us to overcome the severe limitations of light generation in the indirect-band-gap group-IV materials. By performing in-situ annealing, we demonstrate a high PL-stability of the defect-enhanced QD (DEQD) system against thermal treatment up to 600 °C for at least 2 h, even though the Ge QDs are structurally affected by Si/Ge intermixing via bulk diffusion. The latter, in turn, allows for emission tuning of the DEQDs over the entire telecom wavelength range from 1.3 µm to 1.55 µm. Two quenching mechanisms for light-emission are discussed; first, luminescence quenching at high PL recording temperatures, associated with the thermal escape of holes to the surrounding wetting layer; and second, annealing-induced PL-quenching at annealing temperatures >650 °C, which is associated with a migration of the defect complex out of the QD. We show that low-energy ex-situ proton irradiation into the Si matrix further improves the light emission properties of the DEQDs, whereas proton irradiation-related optically active G-centers do not affect the room temperature luminescence properties of DEQDs.

Nano-micelles are self-assembling colloidal dispersions applied to enhance the anticancer efficacy of chemotherapeutic agents. In this study, the conjugate of quarternized chitosan and vanillin imine (QCS-Vani imine) was synthesized using the reaction of a Schiff base characterized by proton-NMR (1HNMR), UV-Vis spectroscopy, and FT-IR. The critical micelle concentration (CMC), particle size, and zeta potential of the resulting product were determined. The QCS-Vani imine conjugate was used as a carrier for the development of curcumin-loaded nano-micelles, and their entrapment efficiency (%EE), drug-loading capacity (%LC) and in vitro release were investigated using HPLC analysis. Moreover, the nano-micelles containing curcumin were combined with various concentrations of cisplatin and evaluated for a possible anticancer synergistic effect. The anticancer activity was evaluated against lung cancer A549 and mouse fibroblast L929 cell lines. The percent yield (%) of the QCS-Vani imine conjugate was 93.18%. The curcumin-loaded QCS-Vani imine nano-micelles were characterized and found to have a spherical shape (by TEM) with size < 200 nm (by DLS) with high %EE up to 67.61% and %LC up to 6.15 ± 0.41%. The loaded lyophilized powder of the nano-micelles was more stable at 4 °C than at room temperature during 120 days of storage. pH-sensitive release properties were observed to have a higher curcumin release at pH 5.5 (cancer environment) than at pH 7.4 (systemic environment). Curcumin-loaded QCS-Vani imine nano-micelles showed higher cytotoxicity and selectivity toward lung cancer A549 cell lines and exhibited lower toxicity toward the normal cell (H9C2) than pure curcumin. Moreover, the curcumin-loaded QCS-Vani imine nano-micelles exhibited an enhanced property of inducing cell cycle arrest during the S-phase against A549 cells and showed prominently induced apoptosis in lung cancer cells compared to that with curcumin. The co-treatment of cisplatin with curcumin-loaded QCS-Vani imine nano-micelles presented an enhanced anticancer effect, showing 8.66 ± 0.88 μM as the IC50 value, in comparison to the treatment with cisplatin alone (14.22 ± 1.01 μM). These findings suggest that the developed QCS-Vani imine nano-micelle is a potential drug delivery system and could be a promising approach for treating lung cancer in combination with cisplatin.

AbstractSelf-assembled quantum dots (QDs) have attracted significant attention because of their potential applications in novel semiconductor devices. In this work, we investigated radiation effects induced by 1.0 MeV proton ion beams on InAs self-assembled quantum dots. In particular, we emphasized the effects of lattice environments of QDs on their luminescence emission after ion beam irradiation. Photoluminescence (PL) spectroscopy was used to characterize the optical properties of QDs subjected to proton irradiation and post-irradiation annealing. Compared to the single-layer QDs grown in GaAs films, the QDs embedded in an AlAs/GaAs superlattice exhibited much higher PL degradation resistance to proton beam bombardment, e.g., at the highest dose (1.0×1014 cm−2) used in this work, a difference of ~ 20-fold in PL intensity was found between the QDs configured in these two different lattice structures. After thermal annealing of irradiated QD samples, ion beam enhanced blueshift of PL was observed to be much more pronounced for the single-layer QDs. We discuss mechanisms that may result in the differences in optical response to ion beams between QDs with different lattice surroundings.

AbstractEffective electron supply to produce ammonia in photoelectrochemical nitrogen reduction reaction (PEC NRR) remains challenging due to the sluggish multiple proton‐coupled electron transfer and unfavorable carrier recombination. Herein, InP quantum dots decorated with sulfur ligands (InP QDs‐S2−) bound to MIL‐100(Fe) as a benchmark catalyst for PEC NRR is reported. It is found that MIL‐100(Fe) can combined with InP QDs‐S2− via Fe─S bonds as bridge to facilitate the electron transfer by experimental results. The formation of Fe─S bonds can facilitate electron transfer from inorganic S2− ligands of InP QDs to the Fe metal sites of MIL‐100(Fe) within 52 ps, ensuring a more efficient electron transfer and electron‐hole separation confirmed by the time‐resolved spectroscopy. More importantly, the process of photo‐induced carrier transfer can be traced by in situ attenuated total reflection surface‐enhanced infrared tests, certifying that the effective electron transfer can promote N≡N dissociation and N2 hydrogenation. As a result, InP QDs‐S2−/MIL‐100(Fe) exhibits prominent performance with an outstanding NH3 yield of 0.58 µmol cm−2 h−1 (3.09 times higher than that of MIL‐100(Fe)). This work reveals an important ultrafast dynamic mechanism for PEC NRR in QDs modified metal‐organic frameworks, providing a new guideline for the rational design of efficient MOFs photocathodes.

AbstractPhotocatalytic hydrogen evolution coupled with organic oxidation reaction is a promising alternative to water splitting, where the efficiency is limited due to the weak correlation between charge separation and surface redox reactions. Here, employing nickel phthalocyanine (NiPc) for hole extraction, NiPc‐modified carbon dots (CDs) are combined with Cu–In–Zn–S quantum dots (CIZS QDs) toward a profound understanding of electron/hole extraction and surface proton generation and reduction. The optimal hydrogen evolution rate reaches 4.10 mmol g−1 h−1 for CIZS/NiPc–CDs with l‐ascorbic acid for hole consumption, 8.10 times to that of CIZS QDs, which is further promoted to 11.12 mmol g−1 h−1 under electron/hole coextraction with Ni2+ introduction. For benzyl‐alcohol‐oxidation‐coupled H2 evolution, this strategy shows a more dramatic activity enhancement (19.54 times), which is also appliable to methanol‐ or furfuryl‐alcohol‐oxidation coupling systems with state‐of‐the‐art activities. Transient photovoltage spectroscopy and apparent kinetics analysis indicate, for the first time, a light‐induced electrocatalysis effect consistent with the Volmer–Heyrovsky process, which establishes a quasiquantitative basis for balancing charge extraction and surface reactions.

Les systèmes à plusieurs corps composés de fermions sont courants dans la nature, tels que les supraconducteurs à haute température, les liquides de Fermi, les noyaux atomiques, la matière de quarks et les étoiles à neutrons. La complexité des interactions entre les particules rend difficile la résolution des équations de la dynamique des particules dans ces systèmes quantiques. Pour simplifier, on modélise souvent ces systèmes en utilisant des particules indépendantes dans un potentiel de champ moyen effectif. Cependant, les interactions résiduelles révèlent des corrélations significatives qui affectent l’occupation des états en dessous et au-dessus du niveau de Fermi. Les noyaux atomiques, avec leurs interactions à courte portée, sont particulièrement intéressants. La physique des corrélations à courte portée (SRC) découle des interactions à courte distance et se manifeste sous la forme de paires de nucléons. Les paires SRC ont une impulsion relative élevée et une impulsion de leur centre de masse faible par rapport à l’impulsion de Fermi (kF = 250 MeV/c). Ces paires forment des fluctuations temporaires de haute densité, limitées par l’interaction nucléon-nucléon répulsive à des distances inférieures à environ 1 fm. La plupart des connaissances sur les SRC proviennent d’expériences de diffusion d’électrons et de protons. Les études indiquent qu’environ 20% des nucléons liés occupent cette région à haute impulsion. La première preuve expérimentale des SRC a été apportée par la mesure d’une queue à haute impulsion dans les distributions d’impulsions des protons lors d’expériences de diffusion d’électrons. Pour étudier les SRC dans les noyaux riches en neutrons, nous avons utilisé des réactions de Quasi-Free Scattering (QFS) en cinématique inverse, avec des faisceaux d’ions radioactifs sur une cible de protons à l’installation R3B de GSI en Allemagne. Cette méthode a permis d’étudier les propriétés des SRC, y compris les rapports de paires np/pp et les distributions d’impulsion, en se concentrant sur les noyaux 12C et 16C avec une énergie de faisceau de 1,25 GeV/u. Les principaux objectifs étaient de développer une méthodologie pour différencier les réactions de diffusion sur des paires SRC des réactions sur un proton suivies par des interactions finales (FSI) et d’étendre les études des SRC aux noyaux riches en neutrons, en particulier les noyaux exotiques comme 16C. L’analyse consistait à identifier les événements SRC produits via les réactions 12C(p, 2pN)A-2 et 16C(p, 2pN)A-2. Des rapports de paires np/pp inférieurs aux prédictions du Generalized Contact Formalism et aux résultats expérimentaux antérieurs ont été extraits, suggérant une interférence des FSI et des effets de champ moyen. Des difficultés sont apparues pour isoler les événements SRC, et nous avons supposé que la section efficace pour la rupture de paires SRC pourrait être réduite à l’énergie de 1,25 GeV/u. De plus, la résolution limitée en impulsion a réduit notre capacité à séparer les événements SRC des autres canaux concurrents, indiquant la nécessité d’améliorer le système de détection. Les faibles statistiques utilisables et les limites d’acceptance de l’équipement expérimental ne nous ont pas permis de réaliser une mesure exclusive des SRC, mais ont fourni des informations essentielles pour améliorer les études futures à R3B. Cette recherche constitue une étape fondamentale dans l’étude des SRC en cinématique inverse. Malgré les difficultés, la méthodologie développée fournit des informations importantes pour mieux identifier la physique des SRC. Les futures expériences devraient envisager des énergies de faisceau plus élevées ou de meilleures techniques de détection pour mieux isoler les événements SRC
Many-body systems composed of fermions are common in nature, such as high-temperature superconductors, Fermi liquids, atomic nuclei, quark matter, and neutron stars. The complexity of interactions between particles makes it difficult to solve the equations governing particle dynamics in these quantum systems. To simplify, these systems are often modeled using independent particles in an effective mean-field potential. However, residual interactions reveal significant correlations that affect the occupation of states below and above the Fermi level. Atomic nuclei, with their short-range interactions, are particularly interesting. The physics of short-range correlations (SRC) arises from short-distance interactions and manifests as nucleon pairs. SRC pairs have a high relative momentum and a low center-of-mass momentum compared to the Fermi momentum (kF = 250 MeV/c). These pairs form temporary high-density fluctuations, limited by the highly repulsive nucleon-nucleon interaction at distances less than about 1 fm. Most of our knowledge about SRC comes from electron and proton scattering experiments. Studies indicate that about 20% of bound nucleons occupy this high-momentum region. The first experimental evidence of SRC was provided by measuring a high-momentum tail in the proton momentum distributions during electron scattering experiments. To study SRC in neutron-rich nuclei, we used Quasi-Free Scattering (QFS) reactions in inverse kinematics, with radioactive ion beams on a proton target at the R3B facility of the GSI accelerator in Germany. This method allowed us to study SRC properties, including np/pp pair ratios and momentum distributions, focusing on the 12C and 16C nuclei with a beam energy of 1.25 GeV/u. The main objectives were to develop a methodology to differentiate between scattering reactions on SRC pairs and reactions on a proton followed by final-state interactions (FSI) and to extend SRC studies to neutron-rich nuclei, particularly exotic nuclei like 16C. The analysis involved identifying SRC events produced via 12C(p, 2pN)A-2 and 16C(p, 2pN)A-2 reactions. We extracted np/pp pair ratios lower than the predictions of the Generalized Contact Formalism and previous experimental results, suggesting interference from FSI and mean-field effects. Difficulties arose in isolating SRC events, and we hypothesized that the cross-section for SRC pair breaking might be reduced at the 1.25 GeV/u beam energy. Additionally, limited momentum resolution reduced our ability to separate SRC events from other competing channels, indicating the need to improve the detection system. The limited usable statistics and acceptance limits of the experimental setup did not allow us to achieve exclusive SRC measurements but provided essential information for improving future studies at R3B. This research constitutes a fundamental step in studying SRC using inverse kinematics. Despite the difficulties, the developed methodology provides important information to better identify SRC physics. Future experiments should consider higher beam energies or better detection techniques to better isolate SRC events