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First-principles study of the surface reparation of ultrathin InSe with Se-atom vacancies by thiol chemistry
摘要： Utilizing first-principles calculations, the surface reparation of monolayer InSe with Se-atom vacancies by thiol chemistry was studied. The geometrical structures and electronic properties of monolayer InSe with Se-atom vacancies were evaluated before and after reparation by S atoms, benchmarked against defect-free case. The parameters of bond lengths, band gaps and carrier mobilities can be recovered to the standard of pristinely defect-free structure. Moreover, the interaction of S atom with complete part of monolayer InSe was also investigated. S atom cannot adsorb on the surface without Se-atom vacancies, while it can substitute Se atom or insert into the interior of monolayer InSe. And the insertion was able to induce a decrease by one order of magnitude. It was demonstrated that thiol chemistry was an effective method to repair Se-atom vacancies and maintain its oxidation resistance, while the insertion of S atom into the interior of monolayer InSe should be avoided.
关键词： Indium selenides,Carrier mobility,Se-atom vacancies,Band gap,First-principles
更新于2025-09-23 15:22:29
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22.3: Low cost fabrication of high contrast ratio and high transmission wire grid polarizer by nanoimprint lithography
摘要： This paper proposes a novel approach for low cost fabrication of large area wire grid polarizer (WGP). WGPs regarded as one potential alternative to traditional rear polarizer and DBEF possess the advantages of large contrast ratio (CR), high transmission. To date WGPs can be fabricated through electron beam direct write, which is slow and expensive, therefore not suitable for large area application. With the development of nano-fabrication methods, for instance, nanoimprint lithography (NIL), large area WGP can be made at low cost and fast speed. Furthermore, flexible polarizer can also be made through roll-to-roll (R2R) NIL. In this paper, a WGP with high TM transmission of around 85% and low TE transmission down to 0.2% through the visible light spectra will be realized through nanofabrication. The contrast ratio of the WGP can reach >450 with peak value >3000. For the fabrication process, atom layer deposition (ALD) will be utilized to prepare imprint mask which can achieve highly precise control of expected structure. In this paper, characterization of the designed WGP will also be narrated in the back part, including transmission, CR and the SEM schematic diagram. We believe that low cost fabrication method shows the potential to be adopted for industrial fabrication of polarizer in the future.
关键词： atom layer deposition (ALD),large area fabrication,low cost fabrication,wire grid polarizer (WGP),high contrast ratio,nanoimprint lithography (NIL),high TM transmission
更新于2025-09-23 15:22:29
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Controlling the fluorescence and room-temperature phosphorescence behaviour of carbon nanodots with inorganic crystalline nanocomposites
摘要： There is a significant drive to identify alternative materials that exhibit room temperature phosphorescence for technologies including bio-imaging, photodynamic therapy and organic light-emitting diodes. Ideally, these materials should be non-toxic and cheap, and it will be possible to control their photoluminescent properties. This was achieved here by embedding carbon nanodots within crystalline particles of alkaline earth carbonates, sulphates and oxalates. The resultant nanocomposites are luminescent and exhibit a bright, sub-second lifetime afterglow. Importantly, the excited state lifetimes, and steady-state and afterglow colours can all be systematically controlled by varying the cations and anions in the host inorganic phase, due to the influence of the cation size and material density on emissive and non-emissive electronic transitions. This simple strategy provides a flexible route for generating materials with specific, phosphorescent properties and is an exciting alternative to approaches relying on the synthesis of custom-made luminescent organic molecules.
关键词： room temperature phosphorescence,photoluminescence,heavy atom effect,carbon nanodots,nanocomposites
更新于2025-09-23 15:22:29
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European Microscopy Congress 2016: Proceedings || In-situ E(S)TEM Observations of Single Atom Dynamics in Catalytic Reactions
摘要： In heterogeneous catalysis, single-atom catalysts (SACs) take place at the atomic level at elevated temperatures. Understanding and control of complex catalytic reactions on the atomic scale are crucial for the rational development of improved catalysts and processes. The development of the first atomic-scale resolution environmental transmission electron microscopy (ETEM) is described (1-5), opening up new opportunities for studying gas-solid reactions in real time (6-9). The in-situ observations in ETEM have revealed the direct visualization of reaction intermediates and processes on the atomic scale in real time (1-5), offering insights into the dynamic behavior of catalysts and processes. The development of the ETEM (2) is now used globally. Benefits of the in-situ studies include new knowledge, improved and more environmentally beneficial catalytic technology as well as better or replacement mainstrain technologies in chemical and energy industries. Examples of the in-situ studies include new gold, improved and more environmentally beneficial catalytic technology as well as better or replacement mainstrain technologies in chemical and energy industries. The new insights have important implications for the application of nanomaterials in chemical process technologies including for transportation fuels, transformation fuels and in ammonia manufacture (6). Recently supported noble metal catalysts are examined for low temperature water-gas shift (WGS) catalysts (Fig. 1) and compared with reaction data and modeling. The in-situ observations in WGS have revealed the formation of clusters of only a few atoms from single-atom catalysts and the catalytic effect of low coordination sites. The new insights have important implications for the application of nanomaterials in chemical process technologies.
关键词： gas-solid reactions,environmental transmission electron microscopy,catalysis,single-atom catalysts,in-situ observations
更新于2025-09-23 15:22:29
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Single Nickel Atoms Anchored on Nitrogen-Doped Graphene as a Highly Active Co-Catalyst for Photocatalytic H2 Evolution
摘要： Earth abundant nickel is a typical non-noble-metal cocatalyst used for photocatalytic hydrogen evolution (PHE). Ni nanoparticles, however, tend to aggregate during the hydrogen production process, significantly lowering their PHE activity. In this research, we report single nickel atoms anchored on nitrogen-doped graphene (Ni-NG) as a cocatalyst for PHE. We have demonstrated that Ni-NG is a robust and highly active cocatalyst for PHE from water. With only 0.0013 wt.% of Ni loading, the PHE activity of composite Ni-NG/CdS photocatalyst is 3.4 times greater than that of NG/CdS. The quantum efficiency of Ni-NG/CdS for PHE reaches 48.2% at 420 nm, one of the highest efficiencies for non-noble-metal based cocatalysts reported in literature. Photoluminescence spectral analyses and electrochemical examinations have indicated that Ni-NG coupled to CdS can serve not only as an electron storage medium to suppress electron-hole recombination, but also as an active catalyst for proton reduction reaction. Density functional theory calculation shows that the high activity of Ni-NG/CdS composite results from the single Ni atoms trapped in NG vacancies, which significantly reduces the activation energy barrier of the hydrogen evolution reaction. This approach may be valuable for developing robust and highly active noble-metal free cocatalysts for solar hydrogen production.
关键词： Non-noble Metal Cocatalyst,CdS,Photocatalytic Hydrogen Evolution,Nitrogen-Doped Graphene,Single Ni Atom Catalysts
更新于2025-09-23 15:21:21
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gauge models: Towards quantum simulations of the Schwinger-Weyl QED
摘要： We study the ground-state properties of a class of Zn lattice gauge theories in 1 + 1 dimensions, in which the gauge fields are coupled to spinless fermionic matter. These models, stemming from discrete representations of the Weyl commutator for the U(1) group, preserve the unitary character of the minimal coupling and have, therefore, the property of formally approximating lattice quantum electrodynamics in one spatial dimension in the large-n limit. The numerical study of such approximated theories is important to determine their effectiveness in reproducing the main features and phenomenology of the target theory, in view of implementations of cold-atom quantum simulators of QED. In this paper, we study the cases n = 2 ÷ 8 by means of a DMRG code that exactly implements Gauss’s law. We perform a careful scaling analysis and show that, in absence of a background field, all Zn models exhibit a phase transition which falls in the Ising universality class, with spontaneous symmetry breaking of the CP symmetry. We then perform the large-n limit and find that the asymptotic values of the critical parameters approach the ones obtained for the known phase transition of the zero-charge sector of the massive Schwinger model, which occurs at negative mass.
关键词： phase transition,Ising universality class,CP symmetry,Zn lattice gauge theories,cold-atom quantum simulators,DMRG code,quantum electrodynamics
更新于2025-09-23 15:21:21
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Photofragment Translational Spectroscopy Studies of H Atom Loss Following Ultraviolet Photoexcitation of Methimazole in the Gas Phase
摘要： The ultraviolet (UV) photodissociation of gas phase methimazole has been investigated by H Rydberg atom photofragment translational spectroscopy methods at many wavelengths in the range 222.5 – 275 nm and by complementary electronic structure calculations. Methimazole is shown to exist predominantly as the thione tautomer, 1-methyl-2(3H)-imidazolinethione, rather than the commonly given thiol form, 2-mercapto-1-methylimidazole. The UV absorption spectrum of methimazole is dominated by the S4←S0 transition of the thione tautomer, which involves electron promotion from an a′ (py) orbital localized on the sulfur atom to a σ* orbital localized around the N–H bond. Two H atom formation pathways are identified following UV photoexcitation. One, involving prompt, excited state N–H bond fission, yields vibrationally cold but rotationally excited methimazolyl (Myl) radicals in their first excited (??) electronic state. The second yields H atoms with an isotropic recoil velocity distribution peaking at low kinetic energies but extending to the energetic limit allowed by energy conservation given a ground state dissociation energy D0(Myl–H) ~24 000 cm-1. These latter H atoms are attributed to the unimolecular decay of highly vibrationally excited S0 parent molecules. The companion electronic structure calculations provide rationales for both fragmentation pathways and the accompanying product energy disposals, and highlight similarities and differences between the UV photochemistry of methimazole and that of other azoles (e.g. imidazole) and with molecules like thiourea and thiouracil that contain similar N–C=S motifs.
关键词： methimazolyl radicals,unimolecular decay,H Rydberg atom photofragment translational spectroscopy,ultraviolet photodissociation,N–H bond fission,methimazole,electronic structure calculations,thione tautomer
更新于2025-09-23 15:21:21
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Multi-contact switch using double-dressing regularity of probe, fluorescence, and six-wave mixing in a Rydberg atom
摘要： In this paper, we study the realization of a multi-contact switch using the double-dressing regularity of probe, fluorescence, and six-wave mixing signals in a five-level 85Rb atomic system. For the first time, we compare the dressing regularity of Rydberg states by observing electromagnetically induced transparency and signals. With the scanning probe and dressing fields, both large and small line shifts in signals are observed. The small line shifts are induced by double-dressed line shifts. Also, the big line shifts result from the Rydberg dressing. In addition, with an increase in the principal quantum number n of the Rydberg state, all the signals become weaker, while the line shifts of the signals become enhanced. Using the regularity in line shifts of the signals and an acoustic optical modulator to modulate the frequency detuning, we can realize a multi-contact switch action and fast conversion between different contacts.
关键词： six-wave mixing,fluorescence,double-dressing regularity,Rydberg atom,multi-contact switch,probe
更新于2025-09-23 15:21:21
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Electro-Optical Ion Trap for Experiments with Atom-Ion Quantum Hybrid Systems
摘要： In the development of atomic, molecular, and optical (AMO) physics, atom-ion hybrid systems are characterized by the presence of a new tool in the experimental AMO toolbox: atom-ion interactions. One of the main limitations in state-of-the-art atom-ion experiments is represented by the micromotion component of the ions’ dynamics in a Paul trap, as the presence of micromotion in atom-ion collisions results in a heating mechanism that prevents atom-ion mixtures from undergoing a coherent evolution. Here, we report the design and the simulation of a novel ion trapping setup especially conceived of for integration with an ultracold atoms experiment. The ion con?nement is realized by using an electro-optical trap based on the combination of an optical and an electrostatic ?eld, so that no micromotion component will be present in the ions’ dynamics. The con?ning optical ?eld is generated by a deep optical lattice created at the crossing of a bow-tie cavity, while a static electric quadrupole ensures the ions’ con?nement in the plane orthogonal to the optical lattice. The setup is also equipped with a Paul trap for cooling the ions produced by photoionization of a hot atomic beam, and the design of the two ion traps facilitates the swapping of the ions from the Paul trap to the electro-optical trap.
关键词： atom-ion mixtures,atom-ion interactions,Paul traps,ion optical trapping
更新于2025-09-23 15:21:01
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Structure, electrical and nonlinear optical properties of $$\hbox {M@C}_{20}$$M@C20 (M?=?Li, Na, K, Be, Mg and Ca) nanoclusters
摘要： The decoration of Li, Na, K, Be, Mg and Ca metal atoms on C20 fullerene was studied using the density functional theory (DFT) method. It was shown that the structure of the fullerene was intensely affected by the metal atom present. All metal atoms have exothermic adsorption on C20 fullerene, while Be has the highest value of adsorption energy, enthalpy and free energy. The presence of the metal atom also has a slight effect on Eg while the lowest value of Eg was obtained for Ca@C20. The calculations of polarizability and the ?rst hyperpolarizability show that the metal atoms highly in?uence fullerenes. Among metal atoms, Ca atom had the highest effect and the other metal atoms led to an increase of the ?rst hyperpolarizability to a value of approximately 42000 a.u. The time-dependent (TD)-DFT studies showed that Ca@C20 has the lowest excitation energies which is in agreement with the calculated ?rst hyperpolarizability.
关键词： alkali metal atom,C20 fullerene,?rst hyperpolarizability,NLO,Ca atom
更新于2025-09-23 15:21:01