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Simplification and experimental investigation of geometrical surface smoothness model for multi-track laser cladding processes
摘要： The formation of large area parts requires construction of multi-track laser cladding layers which are significantly influenced by the overlapping coefficient. The geometrical model of optimal overlap ratio to obtain least surface fluctuation of multi-track claddings is derived into a simpler form in terms of the aspect ratio of single-track clads. The error analysis further demonstrates the effectiveness of these models. Multi-track single layer claddings are fabricated at a series of overlap ratios under two process conditions. The surface states of cladding layers are then evaluated by two types of smoothness definitions with two fitting methods to study the optimal overlap ratios. The results show that the experimental optimum conditions identified by two methods are slightly different from each other. The theoretical prediction is in good agreement with the experimental one when the aspect ratio is great enough to support the model assumptions.
关键词： Laser cladding,Multi-track clads,Overlap ratio,Geometrical model,Surface smoothness
更新于2025-11-28 14:24:20
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Excimer based FRET between non-FRET pair flourophores aided by the aromatic moiety of anionic surfactants: An experimental observation
摘要： A new FRET pair has been reported based on the apperance of excimeric emission and hence significant spectral overlap between an otherwise non-FRET pair fluorophores viz pyrene and rhodamine 6G in the anionic sodiumdodecylbenzenesulfonate (SDBS) micellar system. The occurence of FRET based on such modulation of spectral overlap integral has not been dealt with in detail in comparison to the other FRET parameters like distance between the fluorophores and orientation. Due to the presence of benzene ring in the SDBS micellar system the formation of excimers is augemented due to the π?π interactions between the pyrene molecules and the benzene units of the surfactants. The excimeric pyrene has a bathochromically shifted peak which overlaps with the absorption peak of rhodamine 6G thereby giving rise to energy transfer as FRET between these otherwise non-FRET pair molecules. The efficiency of FRET between the pyrene and rhodamine 6G can be modulated by the degree of spectral overlap between the excimeric peak of pyrene and the absorption peak of rhodamime6g. All the experiments were carried in the Sodiumdodecylsulfate (SDS) micellar system also, which unlike SDBS does not possess any benzene unit, in order to compare the results of excimer formation as well the FRET process.
关键词： rhodamine 6G,Pyrene,overlap integral,Excimer,FRET
更新于2025-11-19 16:46:39
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Suppressed Triplet Exciton Diffusion Due to Small Orbital Overlap as a Key Design Factor for Ultralong-Lived Room-Temperature Phosphorescence in Molecular Crystals
摘要： Persistent room-temperature phosphorescence (RTP) under ambient conditions is attracting attention due to its strong potential for applications in bioimaging, sensing, or optical recording. Molecular packing leading to a rigid crystalline structure that minimizes nonradiative pathways from triplet state is often investigated for efficient RTP. However, for complex conjugated systems a key strategy to suppress the nonradiative deactivation is not found yet. Here, the origin of small rates of a nonradiative decay process from triplet states of conjugated molecular crystals showing RTP is reported. Optical microscopy analysis showed that, despite a favorable molecular stacking, an aromatic crystal with strong RTP is characterized by small diffusion length and small values of the diffusion coefficient of triplet excitons. Quantum chemical calculations reveal a large overlap between the lowest unoccupied molecular orbitals but very small overlap between the highest occupied molecular orbitals (HOMOs). Inefficient electron exchange caused by the small overlap of HOMOs prevents triplet excitons from diffusing over long distances and consequently from quenching at defect sites inside the crystal or at the crystal surface. These results will allow design of comprehensive molecular structures to obtain molecular solids with more efficient RTP.
关键词： suppressed nonradiative rate,persistent room-temperature phosphorescence,triplet exciton diffusion,molecular orbital overlap,fluorescence microscopy
更新于2025-09-23 15:23:52
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A comparative study on single-laser and multi-laser selective laser melting AlSi10Mg: defects, microstructure and mechanical properties
摘要： AlSi10Mg samples fabricated by using a multi-laser beam selective laser melting system have been studied in this paper. The relative density, defects, microstructure and mechanical properties of the isolated and overlap samples are investigated. It is found that the width and depth of the melt pools in overlap area are larger than that in isolated area, which leads to an obvious boundary between the overlap area and isolated area. Moreover, a few small pores are found in the melt pools along the overlap boundary. The isolated and overlap area in as-built samples have similar microstructure, microhardness and tensile strengths. The morphology and distribution of Si changed into particles from continuous dendrite after annealing treatment. However, it did not cause the grains to grow up. The microhardness and tensile strengths have little difference due to almost the same grain size. The slight difference in strength and elongation of isolated and overlap samples are supposed to be caused by small pores. It can be concluded that the microstructure significantly influences the microhardness and strengths of the AlSi10Mg samples, while the small pores have limited influences. There are a few smooth surfaces on the fractures of both isolated and overlap samples, which turn out to be the melt pool boundaries, indicating that the cracks mainly propagate along the melt pool boundaries.
关键词： Defects,Microstructure,Mechanical properties,Multi-laser beam,Overlap area
更新于2025-09-23 15:23:52
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Conformational Transitions of Polymer Chains in Solutions Characterized by Fluorescence Resonance Energy Transfer
摘要： The critical overlap concentration C* is an important concept in polymer solutions and is defined as the boundary between dilute and semidilute regimes. In this study, the chain conformational changes of polystyrene (PS) with both high (Mn = 200,000 Da) and low (Mn = 13,000 Da) molecular weights in cis-decalin were compared by intrachain fluorescence resonance energy transfer (FRET). The random labeling of donor and acceptor chromophores strategy was employed for long PS chains, whereas chain-end labeling was used for short PS chains. By monitoring the spectroscopic intensity ratio between acceptor and donor, the concentration dependence on chain conformation from dilute to semidilute solutions was determined. Both long and short chains exhibit a conformational transition concentration, above which the polymer chains begin to collapse with concentration significantly. Interestingly, for randomly labeled polymer long chains, such concentration is consistent with C* determined from the viscosity result, below which only slight conformational change of polymer chain takes place. However, for the chain-end labeled short chain, the conformational transition concentration takes place earlier than C*, below which no significant polymer conformation change is observed.
关键词： viscosity,conformational transition,polymer solution,critical overlap concentration,fluorescence
更新于2025-09-23 15:23:52
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Methods for obtaining characteristic γ-ray net peak count from interlaced overlap peak in HPGe γ-ray spectrometer system
摘要： For a characteristic c-ray with interlaced overlap peak, and the case where its reliable and credible net count cannot be obtained using the current high-purity germanium (HPGe) multichannel c-ray spectrum software, two new methods are proposed herein to obtain the c-ray net peak count from the interlaced overlap peak in the HPGe c-ray spectrometer system, of which one is the symmetric conversion method based on Gaussian distribution and the other is where the energy average value of two close c-rays is regarded as the c-ray energy. The experimental results indicate that the two methods mentioned above are reliable and credible. This study is signi?cant for the development of better c-ray spectrum processing software for measuring complex c-ray spectra concerning the nuclear reaction cross section, neutron activation analysis, and analysis of transuranium elements, using an HPGe detector.
关键词： High-purity germanium (HPGe) c-ray spectrometer system,Peak count,Interlaced overlap peak
更新于2025-09-23 15:22:29
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Impact of Stokes Shift on the Performance of Near-Infrared Harvesting Transparent Luminescent Solar Concentrators
摘要： Visibly transparent luminescent solar concentrators (TLSC) have the potential to turn existing infrastructures into net-zero-energy buildings. However, the reabsorption loss currently limits the device performance and scalability. This loss is typically defined by the Stokes shift between the absorption and emission spectra of luminophores. In this work, the Stokes shifts (SS) of near-infrared selective-harvesting cyanines are altered by substitution of the central methine carbon with dialkylamines. We demonstrate varying SS with values over 80 nm and ideal infrared-visible absorption cutoffs. The corresponding TLSC with such modification shows a power conversion efficiency (PCE) of 0.4% for a >25 cm2 device area with excellent visible transparency >80% and up to 0.6% PCE over smaller areas. However, experiments and simulations show that it is not the Stokes shift that is critical, but the total degree of overlap that depends on the shape of the absorption tails. We show with a series of SS-modulated cyanine dyes that the SS is not necessarily correlated to improvements in performance or scalability. Accordingly, we define a new parameter, the overlap integral, to sensitively correlate reabsorption losses in any LSC. In deriving this parameter, new approaches to improve the scalability and performance are discussed to fully optimize TLSC designs to enhance commercialization efforts.
关键词： transparent luminescent solar concentrators,overlap integral,reabsorption loss,Stokes shift,near-infrared harvesting
更新于2025-09-23 15:21:01
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Impact of t-butyl group on the singlet-triplet energy gap via weak orbital overlap of [1,2,5]-thiadiazolo[3,4-C]pyridine based TADF emitters: Structural modification
摘要： We theoretically investigated the combination of D-A and D-spacer (phenyl ring) -A with an electron donating alkyl (t-butyl) group. The strategy of twisting the geometry of the molecule with the alkyl substituents exclusion of strong electron withdrawing or donating groups leads to gain efficient deep blue-blue TADF emitter through maintaining the band gap while the reduction of singlet-triplet energy gap (EST). The t-butyl group strongly twisted the conformation of molecules by the steric hindrance resulted in weak HOMO and LUMO overlap (IH/L) and efficient spatial separation of HOMO and LUMO (rH/L) in the S0 state. In contrast, designed molecules S1 state own large HOMO and LUMO overlap of excited singlet state (IS) and inefficient spatial separation of HOMO and LUMO. The computed results indicated that introducing alkyl group into the phenyl ring of the acceptor of the designed molecules cannot affect the ΔEST. The ΔEST is mainly related to the IH/L, which can be adjusted by tuning the orbital IH/L. The large modular orbital overlap at S1 and T1 excited states resulted large ΔEST occurs in the range of 0.38 to 0.59eV whose dominant contribution switches from charge transfer (CT) to local excitation (LE). Our studied results reiterate (10.1038/srep10923) that modular orbital overlap of IS, HOMO and LUMO overlap of excited triplet state IT, spatial separation of HOMO and LUMO in the excited singlet state (rS) and spatial separation of HOMO and LUMO in the excited triplet state (rT) are the essential factors to determine ΔEST when inconsistencies between ΔEST and IH/L. Increasing the dihedral angle between D and A from molecule 1-4 (9-12), decrease the transition dipole moment which lowering the oscillator strength. When changing the connection position between D and A, molecules 5-8, the oscillator strength reduced to half with respect to molecules 1-4 and 9-12. The present work provides a theoretical understanding of the impact of alkyl substituents on the overlap of HOMO-LUMO resulting to tuning the ΔEST, as well as its influence on the oscillator strength may be a reliable idea to design efficient TADF emitters.
关键词： [1,2,5]-thiadiazolo[3,4-C]pyridine,HOMO-LUMO orbital overlap,fluorescence radiative decay rate,TADF,singlet-triplet energy gap
更新于2025-09-23 15:21:01
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Radiation Hardness Comparison of CMOS Image Sensor Technologies at High Total Ionizing Dose Levels
摘要： The impact of the manufacturing process on the radiation induced degradation effects observed in CMOS image sensors at the MGy total ionizing dose levels is investigated. Moreover, the vulnerability of the partially pinned photodiodes at moderate to high total ionizing doses is evaluated for the first time to our knowledge. It is shown that the 3T standard partially pinned photodiode has the lowest dark current before irradiation, but its dark current increases to ~1 pA at 10 kGy(SiO2). Beyond 10 kGy(SiO2), the pixel functionality is lost. The comparison between several CIS technologies points out that the manufacturing process impacts the two main radiation induced degradations: the threshold voltage shift of the readout chain MOSFETs and the dark current increase. For all the tested technologies, 1.8V MOSFETs exhibit the lower threshold voltage shift and the N MOSFETs are the most radiation tolerant. Among all the tested devices, 1.8V sensors achieve the best dark current performance. Several radiation-hard-by-design solutions are evaluated at MGy level to improve further the understanding of CIS radiation hardening at extreme total ionizing dose.
关键词： Gate Overlap,Radiation Effects,Drain,CMOS Image sensors,Partially Pinned Photodiode,Dark Current,TID,Threshold shift,RHBD
更新于2025-09-23 15:21:01
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Replica Symmetry Breaking in a Weakly Scattering Optofluidic Random Laser
摘要： We report the observation of replica symmetry breaking (RSB) in a weakly scattering optofluidic random laser (ORL). Coherent random lasing is indicated by the presence of narrow peaks rising out of the spectral background. This coherence helps to identify a random laser threshold, which is expected to be gradual with weak scattering. We find that lasing action initiated using optical pulsed pumping coincides with the onset of both RSB and Lévy flight statistics. However, the transition from the photonic paramagnetic to photonic glass phase is more subtle in that the Parisi overlap function broadens instead of completely changing shape. This subtlety is balanced by an accompanying result of identical experimental conditions giving rise to lasing or no lasing depending on the shot. Additional statistical calculations and investigations into the fundamental physical mechanisms present in the ORL support this conclusion. Using simple numerical models, we study the critical spectral properties required for RSB to occur, as indicated by the Parisi overlap function. The simplicity of the models helps demonstrate the sensitive nature of this tool and the necessity of additional verification of the physical mechanisms present in the experiment.
关键词： replica symmetry breaking,Lévy flight statistics,Parisi overlap function,optofluidic random laser,mode competition
更新于2025-09-23 15:19:57