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Comprehensive Measurements of the Volume-phase Holographic Gratings for the Dark Energy Spectroscopic Instrument
摘要： The Dark Energy Spectroscopic Instrument (DESI) is a Stage IV ground-based dark energy experiment that will be employed on the Mayall 4 m Telescope to study the expansion history of the universe. In the era of massively multiplexed fiber-fed spectrographs, DESI will push the boundaries of fiber spectroscopy with a design capable of taking 5000 simultaneous spectra over 360 to 980 nm. The instrument utilizes a suite of three-channel spectrographs, where volume-phase holographic (VPH) gratings provide dispersions. Thirty-six VPH gratings were produced and their performances were evaluated at the Lawrence Berkeley National Laboratory. We present the design and the evaluation tests for the production run of the VPH gratings, verifying the incidence angle, area-weighted efficiency, and wavefront errors (WFEs). We also present the specialized test set-up developed on-site to assess the grating performances. Measurements of the VPH gratings show high consistency in area-weighted efficiency to within an rms of 2% for the red and near-infrared and 6.2% for the blue gratings. Measured WFEs also showed high consistency per bandpass. Comprehensive evaluations show that the VPH gratings meet DESI performance requirements and have been approved for integration.
关键词： dark energy,techniques: spectroscopic,instrumentation: spectrographs
更新于2025-09-04 15:30:14
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Physical Properties of Pure and Nano Ag Doped Liquid Crystalline Compounds Containing 1,3,4-Oxadizole Unit
摘要： Dielectric properties and other physical properties such as electrical conductivity (AC) and relaxation time or activation energy have been studied for two systems pure LC [V]6,6, [V]7,6, [V]8,6, [V]6,7, [V]7,7 and [V]8,7 and their doped with silver nanoparticles. The results show the increasing in real dielectric permittivity ? with increasing length terminal chain. So the real dielectric permittivity increasing with raising temperature. To compare between the values of (400) Hz and (4000) Hz we observe these values at the low frequency are larger than that in high frequency. Generally, one can see that the doping of Ag nano particles effectively reduced the permittivity of the LC materials with its large electric dipole moment. The electrical conductivity σ value for pure LC samples in general increases with increasing temperature. So we observed increasing of electrical conductivity values at high frequency. The time scale is discussed in terms of the Arrhenius plot. Generally, with increasing the temperature the time period that spends by molecules at the transition state will increase. The activation energy Ea values show the increase in the activation energy to the doped systems.
关键词： Dielectric permittivity,Doped liquid crystals,Liquid crystals,Relaxation time,Electrical conductivity,Activation energy,Silver nanoparticles
更新于2025-09-04 15:30:14
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Enhancement of a Nanoscale Novel Esaki Tunneling Diode Source TFET (ETDS-TFET) for Low-Voltage Operations
摘要： This paper presents a novel nanoscale tunnel FET consisting of an Esaki tunneling diode in the source region. A unique part of the source region is replaced by a heavily doped N-type silicon material establishing a tunneling diode inside the source region. Also, the gate metal is deliberately extended into the source region in order to more couple the created tunneling diode inside the source region. In the result of this new configuration, the band energy bending occurs inside the source region and also the potential barrier will be modified in the channel region thus increasing the ratio of ION to IOFF (ION/IOFF) and reducing the leakage current and ambipolar current for the proposed structure. The proposed structure has been compared with the conventional TFET and PNPN-TFET structure in terms of the ION/IOFF, Leakage current, ambipolar current, drain-source conductance, short channel effects, source-drain capacitance and minimum noise figure showing a performance superiority with respect to other structures under the study.
关键词： Tunnel FET,Band energy,Potential barrier,Esaki tunneling diode
更新于2025-09-04 15:30:14
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Internal Energy Distribution of Secondary Ions Under Argon and Bismuth Cluster Bombardments: “Soft” Versus “Hard” Desorption–Ionization Process
摘要： The emission/ionization process under massive argon cluster bombardment was investigated by measuring the internal energy distributions of a series of benzylpyridinium ions. Argon clusters with kinetic energies between 10 and 20 keV and cluster sizes ranging from 500 to 10,000 were used to establish the influence of their size, energy, and velocity on the internal energy distribution of the secondary ions. It is shown that the internal energy distribution of secondary ions principally depends on the energy per atom or the velocity of the cluster ion beam (E/n ∝ v2). Under low energy per atom (E/n ? 10 eV), the mean internal energy and fragmentation yield increase rapidly with the incident energy of individual constituents. Beyond 10 eV/atom impact (up to 40 eV/atom), the internal energy reaches a plateau and remains constant. Results were compared with those generated from bismuth cluster impacts for which the mean internal energies correspond well to the plateau values for argon clusters. However, a significant difference was found between argon and bismuth clusters concerning the damage or disappearance + impact cross section. A 20 times smaller disappearance cross section was measured under 20 keV Ar2000 + bombardment, thus quantitatively showing the low damage effect of large argon clusters compared to 25 keV Bi5 for almost the same molecular ion yield.
关键词： Bismuth cluster,Argon cluster,Internal energy,TOF-SIMS,Benzylpyridinium ion
更新于2025-09-04 15:30:14
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Synthesis, structural characterization and photophysical properties of 7-cyanohexahelicene
摘要： 7-Cyanoexahelicene has been prepared in racemic form through a short photochemical synthetic approach and its enantiomeric separation was studied and allowed to obtain (P)- and (M)-enantiomers in 100% ee and > 98.5% ee, respectively. The optical rotatory dispersion and electronic circular dichroism (ECD) spectra of the resolved ones were measured. Other optical properties such as UV and photoluminescence as well as the electrochemical behavior were also examined in solutions.
关键词： Optical resolution,Chirality,Couplings,Photophysical properties,gap energy,Helicenes,Photooxidation
更新于2025-09-04 15:30:14
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Nucleation-Limited Ferroelectric Orthorhombic Phase Formation in Hf <sub/>0.5</sub> Zr <sub/>0.5</sub> O <sub/>2</sub> Thin Films
摘要： Various possibilities have been proposed as the cause of the doped- or undoped-HfO2 thin film materials showing unusual ferroelectricity. These assumptions are based on empirical results, yet finding the origin of the unprecedented ferroelectricity within HfO2 has suffered from a serious gap between its theoretical calculation, mostly based on thermodynamic approach and the actual experimental results. To fill the gap, this study proposes to consider the kinetic energy, providing the evidence of the kinetic energy barrier upon a phase transformation from the tetragonal phase to the monoclinic phase affected by the TiN top electrode (capping layer). 10 nm thick Hf0.5Zr0.5O2 thin films are deposited and annealed with or without the TiN capping layer with subsequent annealing at different time and temperature. Arrhenius plot is constructed to obtain the activation energy for the tetragonal-to-monoclinic phase transformation by calculating the amount of the transformed phase using X-ray diffraction pattern. Johnson–Mehl–Avrami and nucleation-limited transformation models are utilized to describe the characteristic nucleation and growth time and calculate the activation energy for the monoclinic phase transformation of the Hf0.5Zr0.5O2 thin film. Both models demonstrate that the TiN capping layer provides a kinetic energy barrier for tetragonal-to-monoclinic phase transformation and enhances the ferroelectric property.
关键词： ferroelectric thin films,hafnium zirconium oxide,activation energy,nucleation-limited transformation,nucleation and growth transformation kinetics
更新于2025-09-04 15:30:14
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Solar-charged pseudocapacitors: Simultaneous conversion and storage of solar energy in ZnO@NiO nanorod arrays
摘要： In this paper, bias-free solar-driven pseudocapacitors based on ZnO@NiO nanorod arrays had been reported, which enable the synergistic coupling of light harvesting and electrochemical storage within one single electrode. When solar-charging, ZnO/NiO PN junction served as a driving force to separate the excitons and induce electron-injection through the interface to counter electrode forming charging bias. At this bias, the OH- trapped by photoexcited holes can make redox reaction with NiO and produce electrons. As expected, under a 1-sun illumination and no external electric bias, this ZnO/NiO composite exhibits a good specific capacitance of 44.5 F g?1 at current densities of 0.5 A g?1 as well as a good cycling performance (99% capacity retention after 50 cycles). Additionally, the capacitance equation was derived to account for the boosted capacitance as the increased solar-charging time. These findings here suggest the potential of further developing light-induced electrical energy storage and release on demand by a one-component light-charged capacitors.
关键词： solar energy conversion,ZnO@NiO nanorod arrays,photo-capacitor,pseudocapacitance
更新于2025-09-04 15:30:14
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Effect of an underdamped vibration with both diagonal and off‐diagonal exciton–phonon interactions on excitation energy transfer
摘要： A numerically exact approach, named as the hierarchical stochastic Schr?dinger equation, is employed to investigate the resonant vibration-assisted excitation energy transfer in a dimer system, where an underdamped vibration with both diagonal and off-diagonal exciton–phonon interactions is incorporated. From a large parameter space over the site-energy difference, excitonic coupling, and reorganization energy, it is found that the promotion effect of the underdamped vibration is significant only when the excitonic coupling is smaller than the site-energy difference. Under the circumstance, there is an optimal strength ratio between diagonal and off-diagonal exciton–phonon interactions for the resonant vibration-assisted excitation energy transfer as the site-energy difference is greater than the reorganization energy, whereas in the opposite situation the most efficient energy transfer occurs as the exciton–phonon interaction is totally off-diagonal.
关键词： underdamped vibration,energy transfer,exciton–phonon interaction,non-Condon effect
更新于2025-09-04 15:30:14
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Stored energy release in neutron irradiated silicon carbide
摘要： The purpose of this investigation is to experimentally quantify the stored energy release upon thermal annealing of previously irradiated high-purity silicon carbide (SiC.) Samples of highly-faulted poly-crystalline CVD b-SiC and single crystal 6HeSiC were irradiated in a mixed spectrum ?ssion reactor near 60 (cid:1)C in a ?uence range from 5 (cid:3) 1023 to 2 (cid:3) 1026 n/m2 (E > 0.1 MeV), or about 0.05e20 dpa, in order to quantify the stored energy release and correlate the release to the observed microscopic swelling, lattice dilation, and microstructure as observed through TEM. Within the ?uence of this study the crystalline material was observed to swell to a remarkable extent, achieving 8.13% dilation, and then cross a threshold dose for amorphization at approximately 1 (cid:3) 1025 n/m2 (E > 0.1 MeV) Once amorphized the material attains an as-amorphized swelling of 11.7% at this irradiation condition. Coincident with the extraordinary swelling obtained for the crystalline SiC, an equally impressive stored energy release of greater than 2500 J/g at the critical threshold for amorphization is inferred. As expected, following amorphization the stored energy in the structure diminishes, measured to be approximately 590 J/g. Generally, the ?ndings of stored energy are consistent with existing theory, though the amount of stored energy given the large observed crystalline strain is remarkable. The overall conclusion of this work ?nds comparable stored energy in SiC to that of nuclear graphite, and similar to graphite, a stored energy release in excess of its speci?c heat in some irradiation conditions.
关键词： Neutron irradiation,Amorphization,Silicon carbide,Swelling,Stored energy
更新于2025-09-04 15:30:14
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[Springer Theses] The Electronic Transitions of Molecular Oxygen || Temperature Effects on the Lifetime of O2(a1Δg)
摘要： The non-radiative deactivation of O2(a1(cid:2)g) and O2(b1(cid:3) + g) by solvent molecules has been a topic of intense and extensive research for almost half a century. The seminal interest derived in part from an unusually large effect of solvent and solvent deuteration on the lifetime of O2(a1(cid:2)g). The lifetime of O2(a1(cid:2)g), τ (cid:2), varies by 5 orders of magnitude in different solvents, and differences between H/D-isotopologues of the same solvent often exceed a factor of 20. The early reports on the subject were based on indirect probe-based measurements of τ (cid:2). Therefore, the interpretations were often misguided and afforded considerable controversy. With the advent of fast near-IR sensitive detectors in the late 1970s, it became possible to detect O2(a1(cid:2)g) phosphorescence with time-resolution. This facilitated the recording of an increasingly accurate set of data, which in turn, led to the development of ever more sophisticated theories. This effort culminated in the 1990’s with the development of an empirical model of electronic-to-vibrational (e-to-v) energy transfer. This model, which by now is widely accepted, focusses on the solvent as a “vibrational energy sink” that accept the excitation energy of O2(a1(cid:2)g) and O2(b1(cid:3) + g). In particular, the model accounts nicely for H/D solvent isotope effects on τ (cid:2) that are signi?cantly different from those observed on τ (cid:3). Nevertheless, as we shall see in the present chapter, it still has some important limitations.
关键词： electronic-to-vibrational energy transfer,solvent molecules,temperature effects,O2(a1(cid:2)g),non-radiative deactivation
更新于2025-09-04 15:30:14