Calculated Charge Distributions Research Articles

Solar-Driven Conversion of CO2 to C2 Products by the 3d Transition Metal Intercalates of Layered Lead Iodides.

Photocatalytic CO2 reduction to high-value-added C2+ products presents significant challenges, which is attributed to the slow kinetics of multi-e- CO2 photoreduction and the high thermodynamic barrier for C-C coupling. Incorporating redox-active Co2+/Ni2+ cations into lead halide photocatalysts has high potentials to improve carrier transport and introduce charge polarized bimetallic sites, addressing the kinetic and thermodynamic issues, respectively. In this study, a coordination-driven synthetic strategy is developed to introduce 3d transition metals into the interlamellar region of layered organolead iodides with atomic precision. The resultant bimetallic halide hybrids exhibit selective photoreduction of CO2 to C2H5OH using H2O vapor at the evolution rates of 24.9-31.4µmol g-1h-1 and high selectivity of 89.5-93.6%, while pristine layered lead iodide yields only C1 products. Band structure calculations and photoluminescence studies indicate that the interlayer Co2+/Ni2+ species greatly contribute to the frontier orbitals and enhance exciton dissociation into free carriers, facilitating carrier transport between adjacent lead iodide layers. In addition, Bader charge distribution calculations and in situ experimental spectroscopic studies reveal that the asymmetric Ni-O-Pb bimetallic catalytic sites exhibit intrinsic charge polarization, promoting C-C coupling and leading to the formation of the key *OC-CHO intermediate.

Seasonal charge distributions of submicron atmospheric particles in Yokohama, Japan

Charge distribution measurements are required to understand the spatiotemporal distribution of the number concentrations of submicron atmospheric particles that affect radiative forcing and particle deposition in human airways. The number concentrations of non-charged and charged particles within the 0.3–0.5 μm diameter (D) range were measured at Keio University in Yokohama, Japan, from June 2022 to January 2023 by combining a parallel-pate particle separator and optical particle counters to investigate critical parameters controlling the charging state of submicron atmospheric particles. The measurement uncertainties in the average charge number per particle (pave) and the standard deviation (1σ), derived from the charge distribution of the submicron particles, were within 15%. The monthly median values of 1σ increased in summer and decreased in winter and correlated with the water vapor amount and wind speed. The 1σ values in summer and winter, derived from the seasonally averaged charge distributions of particles, were close to those from the theoretically calculated charge distribution of particles within 0.387–0.5 μm D range and with D = 0.3 μm, respectively, suggesting that the observed particle charge distributions approached the stationary charge distribution for the effective D. In summer, the frequent transport of water molecules and ions from the Pacific Ocean causes efficient collisions between multiple ions and submicron particles with a larger effective D, which may expand the charge distribution of particles. The polarity ratio, the concentration of positively charged particles relative to that of negatively charged particles, was almost unity, indicating the well-balanced charge polarity of the submicron atmospheric particles. The polarity ratio and pave changed significantly during lightning events, indicating that the atmospheric particle charge balance broke. Our findings show that the charge distribution of submicron atmospheric particles can be partly controlled by meteorological parameters (e.g., absolute humidity) and the microphysical properties of the particles.

Detailed modeling of odd–even staggering in fission-fragment charge distributions

During the last 10 years or so the Brownian shape-motion (BSM) model has been used in numerous calculations of fission-fragment mass and charge distributions with encouraging agreement with experimental measurements. In this model the structure obtained in the fission-fragment distributions is entirely a consequence of the structures in the calculated five-dimensional (5D) potential-energy surfaces. The potential-energy model until recently did not accommodate the influence of the emerging fragment properties on the calculated potential energy. Therefore there were no odd-even effects in the calculated fission-fragment distributions. Recent extensions of the potential-energy model allow properties of the nascent fragments to be included in the potential-energy model. Application of the BSM model to execute random walks on these more detailed potential-energy surfaces led to calculated fission-fragment yields that exhibited odd-even effects, which “by eye” indicated reasonable agreement with experimental data. The present work goes a step further with a quantitative comparison between experimental and theoretical results based on the global and local odd-even staggering observables. Theoretical calculations and experimental observations both show that pairing effects and enhancement of two-nucleon relative to one-nucleon transfer in heavy-ion collisions decrease with excitation energy and implementing a damping of these quantities with excitation energy leads to improved agreement with experiment. Characteristic variations of the local staggering with charge split seen in the experimental data are also present in the calculated results.

What triggers the coupling of proton transfer and electron transfer at the active site of nitrogenase?

In converting N2 to NH3 the enzyme nitrogenase utilises 8 electrons and 8 protons in the complete catalytic cycle. The source of the electrons is an Fe4S4 reductase protein (Fe-protein) which temporarily docks with the MoFe-protein that contains the catalytic active cofactor, FeMo-co, and an electron transfer cluster called the P cluster. The overall mechanism involves 8 repetitions of a cycle in which reduced Fe-protein docks with the MoFe-protein, one electron transfers to the P-cluster, and then to FeMo-co, followed by dissociation of the two proteins and re-reduction of the Fe-protein. Protons are supplied serially to FeMo-co by a Grotthuss proton translocation mechanism from the protein surface along a conserved chain of water molecules (a proton wire) that terminates near S atoms of the FeMo-co cluster [CFe7S9Mo(homocitrate)] where the multiple steps of the chemical conversions are effected. It is assumed that the chemical mechanisms use proton-coupled electron-transfer (PCET) and that H atoms (e- + H+) are involved in each of the hydrogenation steps. However there is neither evidence for, or mechanism proposed, for this coupling. Here I report calculations of cluster charge distribution upon electron addition, revealing that the added negative charge is on the S atoms of FeMo-co, which thereby become more basic, and able to trigger proton transfer from H3O+ waiting at the near end of the proton wire. This mechanism is supported by calculations of the dynamics of the proton transfer step, in which the barrier is reduced by ca. 3.5 kcal mol-1 and the product stabilised by ca. 7 kcal mol-1 upon electron addition. H tunneling is probable in this step. In nitrogenase it is electron transfer that triggers proton transfer.

Mechanistic studies of HF/BF3-catalyzed anthracene polymerization to prepare mesophase pitch.

The mesophase pitch prepared by acid catalytic method typically had the advantages of low softening point and high solubility. To fully understand the mechanism of acid-catalyzed reactions and gain a deeper understanding of the microstructure of mesophase pitch, this article studied the mechanism of hydrofluoride/boron trifluoride (HF/BF3)-catalyzed anthracene using molecular simulation methods. The results showed that there might be two types of carbocations present in the system: classical and non-classical carbocations, and five reactions might occur, protonation reaction, chain elongation reaction, intramolecular cyclization reaction, deprotonation reaction, and dehydrogenation reaction. Classical carbocations acted as reactive intermediates in the chain elongation reaction and intramolecular cyclization reaction. When anthracene occurred chain elongation reactions with carbocations to form polymers, the generation of the tetramer required lager energy barriers than that of the dimer and trimer. The stiffness and flatness of molecules could be increased via intramolecular cyclization reactions. The polymers of anthracene might also occurred dehydrogenation reactions when the non-classical carbocations played the role of reactive intermediates. The dehydrogenation reactions required large energy barriers, which might be the reason for the product having a high aliphatic hydrogen content. The Materials Studio (MS) 2020 software was used to complete the simulation. The atomic charge distribution calculation and the structure optimization of molecules were carried out using the B3LYP functional and DNP basis. The DFT-D (TS) dispersion corrections were added to calculate the dispersion interaction between aromatic molecules. The complete LST/QST method was used to search the transition states and calculate the reaction energy barrier.

(Invited) Towards GaN Passivation: Identification of GaN Surface/Interface States

GaN has been emerging as the next technological semiconductor after silicon and has already secured its superiority in the niche of power electronics with a rapidly growing interest since the advent of electric vehicles. To enable GaN to concur more microelectronic applications, one major barrier has yet to be surpassed. Rather limited control has so far been achieved over the density of GaN interface states. To achieve it, native and process-induced surface states need to be fully identified. Photoluminescence (PL) has been the most commonly used method in the study of GaN defects, and it typically shows a wide sub-bandgap peak centered at 2.2 eV that has been called the yellow luminescence (YL) band. Despite 30 years of studies, the debate as to whether this is a bulk or surface defect has not been settled. Present deep level characterization methods have not provided clear enough evidence. Theoretical studies attempted to associate this luminescence with various bulk defects, e.g., Ga-vacancies, O or O-C complexes,[1] while various optical spectroscopy studies, point to a surface origin.[2]Here, we report results of using an optical spectroscopy method based on surface photovoltage before and after a mild anneal in vacuum. The method is capable of showing the energy distribution of charge density trapped in surface states and thus of monitoring changes thereof. Using the method in air on untreated GaN reveals two peaks over the same ranges of the yellow and blue peaks observed by PL. After a mild anneal at 170 C for 24 hrs in vacuum, the “yellow” charge density peak was absent. Exposure to air was then observed to fully restore the “yellow” charge density peak. This observation clearly points to the involvement of an airborne molecule, a constituent of air, as the source for charge in the yellow-luminescence-related state. If this deep level were a bulk defect, it would not be able to interact with air. This observed interaction with air thus provides a first direct evidence that the yellow luminescence-related defect is a surface state. Experiments of controlled exposure to the various air constituents to identify the related airborne molecule are currently ongoing. The same method is now used in a search for passivation method for this surface state.The method we use is based on the following model. Illumination using sub-band gap photon energies excites electrons from the surface states over the surface potential barrier, consequently, reducing the surface band bending, and this change is observed as photovoltage (Fig. 1). We have already shown how this photovoltage can be used for calculation of the surface charge distribution in GaN HEMT.[3] In the case of bulk crystal, the model is slightly different, and a quantitative relation may be obtained between the measured photovoltage and the surface state charge distribution. Quantitative calculation requires knowledge of the surface band bending in equilibrium, which may not always be reliably obtained. However, when the spectrum is acquired using low photon flux, assuring the change in the band bending is small compared with the equilibrium band bending the surface charge density is practically relative to the derivative of the photovoltage, and thus, qualitative distribution may be obtained.[4]Figure 2 exemplifies the use of the model presented here to obtain a qualitative charge density spectrum. It shows surface charge density obtained using the model from the photovoltage spectrum shown as inset.This method is then used in Fig. 3 to compare three spectra of the same sample: In air (red), in vacuum (green) - the yellow peak is slightly reduced, and after heating up to 450 K for 24 h in vacuum (blue) - the yellow peak is practically gone.These results suggest that the charge in the yellow-luminescence-related state is contributed by a non-inert constituent of air, and this interaction may not be possible unless this state is a surface state. In the talk, preliminary results on the chemical identity of this air constituent will be presented.[1] Van de Walle et al., Microscopic origins of surface states on nitride surfaces, J. Appl. Phys. 101, 081704 (2007).[2] Shalish et al., Yellow luminescence and related deep levels in unintentionally doped GaN films, Phys. Rev. B 59, 9748 (1999).[3] Turkulets et el., Surface states in AlGaN/GaN high electron mobility transistors: Quantitative energetic profiles and dynamics of the surface Fermi level, Appl. Phys. Lett. 115, 023502 (2019).[4] Turkulets et al. The GaN(0001) yellow-luminescence-related surface state and its interaction with air. Surfaces and Interfaces 38, 102834 (2023). Figure 1

Computational simulation on the study of Tacrolimus and its improved dermal retention using Poly(Ԑ-caprolactone) nanocapsules

Tacrolimus (TAC) is a drug from natural origin that can be used for topical application to control autoimmune skin diseases such as atopic dermatitis, psoriasis, and vitiligo. Computational simulation based on quantum mechanics theory by solving Schrödinger Equation for n-body problem may allow the theoretical calculation of drug geometry, charge distribution and dipole moment, electronic levels and molecular orbitals, electronic transitions, and vibrational transitions. Additionally, the development of novel nanotechnology-based delivery systems containing TAC can be an approach for reducing the dose applied topically, increasing dermal retention, and reducing the reported side effects due to the controlled release pattern. Firstly, this paper was devoted to obtaining the molecular, electronic, and vibrational data for TAC by using five semi-empirical (SE) methods and one Density Functional Theory (DFT) method in order to expand the knowledge about the drug properties by computational simulation. Then, this study was carried out to prepare TAC-loaded poly(ԑ-caprolactone) nanocapsules by interfacial polymer deposition following solvent displacement and investigate the in vitro drug permeation using the Franz diffusion cell and the photoacoustic spectroscopy. Computational simulations were compared in the three schemes SE/SE, SE/DFT, and DFT/DFT, where the first method represented the procedure used for geometry optimization and the second one was performed to extract electronic and vibrational properties. Computational data showed correspondence with TAC geometry description and electronic properties, with few differences in HOMO – LUMO gap (Δ) and dipole values. The SE/DFT and DFT/DFT methods presented a better drug description for the UV–Vis, Infrared, and Raman spectra with low deviation from experimental values. Franz cell model demonstrated that TAC was more delivered across the Strat-M® membrane from the solution than the drug-loaded poly(ԑ-caprolactone) nanocapsules. Photoacoustic spectroscopy assay revealed that these nanocapsules remained more retained into the Strat-M® membranes, which is desirable for the topical application.

High-Pressure and High-Temperature Dion-Jacobson Layered Perovskite Polymorphs of KWO3 F.

Two new Dion-Jacobson layered perovskite polymorphs of the known oxyfluoride compound KWO3 F are reported. A high-pressure modification was synthesized using a multianvil setup and subsequently transformed into a high-temperature phase at ∼311 °C. The crystal structures of both polymorphs were determined by use of single-crystal X-ray diffraction and are described in detail herein. Differential thermal analyses and thermogravimetric analyses were carried out to further investigate the phase transition characteristics. Bond valence (BV) and charge distribution (CHARDI) calculations confirm the occupancy of mixed O|F anion positions, and Rietveld refinements as well as MAPLE calculations support the structure models.

Inducing Nucleophilic Reactivity at Beryllium with an Aluminyl Ligand.

The reactions of anionic aluminium or gallium nucleophiles {K[E(NON)]}2 (E = Al, 1; Ga, 2; NON = 4,5-bis(2,6-diisopropylanilido)-2,7-ditert-butyl-9,9-dimethylxanthene) with beryllocene (BeCp2) led to the displacement of one cyclopentadienyl ligand at beryllium and the formation of compounds containing Be-Al or Be-Ga bonds (NON)EBeCp (E = Al, 3; Ga, 4). The Be-Al bond in the beryllium-aluminyl complex [2.310(4) Å] is much shorter than that found in the small number of previous examples [2.368(2) to 2.432(6) Å], and quantum chemical calculations suggest the existence of a non-nuclear attractor (NNA) for the Be-Al interaction. This represents the first example of a NNA for a heteroatomic interaction in an isolated molecular complex. As a result of this unusual electronic structure and the similarity in the Pauling electronegativities of beryllium and aluminium, the charge at the beryllium center (+1.39) in 3 is calculated to be less positive than that of the aluminium center (+1.88). This calculated charge distribution suggests the possibility for nucleophilic behavior at beryllium and correlates with the observed reactivity of the beryllium-aluminyl complex with N,N'-diisopropylcarbodiimide─the electrophilic carbon center of the carbodiimide undergoes nucleophilic attack by beryllium, thereby yielding a beryllium-diaminocarbene complex.

Theoretical Base of Pseudo Chemical Potential (PCP) Method

Pseudo chemical potential (PCP) method is a novel one based on the thermodynamic formalization, and the purpose of this work is to clarify theoretical base of PCP method and to perfect PCP method into a novel method for molecular calculation. Therefore, it is very important to clarify validity of thermodynamic formalization that becomes principle and methodology of this method for achievement of its purpose. The thermodynamic formalization in molecular calculation is to achieve molecular calculation by using principle and methodology of thermodynamics. In order to apply the method of thermodynamic formalization in molecular calculation, it must be clarified that molecule (atom) electron system, computational object of PCP method, can be considered to be “thermodynamic system”. In this paper, we have clarified the temperature zero limit (TZL) state of a finite temperature thermal equilibrium system, as physical base of the pseudo chemical potential (PCP) method, having thermodynamic properties and therefore being the research object of thermodynamic formalism. Furthermore, we have proved an existence of energy minimization principle, as the theoretical base of PCP method, and from it derived the variation equation and defined the electron charge distribution equation, and on the basis of it analyzed theoretically the electronegativity equalization principle. Resultantly, herein we have demonstrated theoretical validity of PCP method, as a novel method for calculation of molecular energies and charge distributions.

Fine structure of the charge density wave in bulk VTe2

Vanadium ditelluride (VTe2) has been intensively explored to understand the charge density wave (CDW) phase and its connection to magnetic properties. Here, we conduct a systematic study to understand the fine structure of CDW via scanning tunneling microscopy (STM) combined with density functional theory (DFT) calculations. STM topograph at 79 K shows that a CDW phase in VTe2 has a stripe modulation with 3 × 1 periodicity, following the double zigzag chain of distorted Te lattices. Interestingly, the 3 × 1 CDW modulation undergoes contrast inversion between filled and empty state topographs. Atomistic features and contrast changes of CDW observed in STM are clearly reproduced in our DFT simulation images. Charge distribution calculation indicates that the spatial extension and density of Te 5p orbitals have strong variations with filled and empty states, explaining the fine structure of 3 × 1 CDW in VTe2. Our finding provides an inspiring insight to further research on the less explored electronic structure of VTe2.

Regioselective rearrangement reactions of naphthyl naphthylmethyl ethers by using Lewis acids or UV light irradiation

Reaction of 1-naphthyl naphthylmethyl ethers 1 and 2 with Lewis acids (BF3-Et2O or Et2AlCl) in CH2Cl2 produced rearranged products of the naphthylmethyl group to the 2- and 7-positions of the naphthalene, whereas rearrangement of 2-naphthyl ethers 3 and 4 proceeded to the 1-position. When benzene solution of compound 1 was irradiated, rearrangement to the 4-position proceeded, whereas rearrangement of 2 proceeded to the 2- and 4-positions. Photoinduced rearrangement of 3 and 4 proceeded to the 1-position as in the reaction using Lewis acids. In the reaction with Lewis acids, ion pair consists of Lewis acid-coordinated naphthoxy anions and naphthylmethyl cations, and in the photoreaction, radical pair generated by homolytic cleavage of the C-O bond, are proposed to be intermediates. Calculations of the negative charge distribution and the spin density of the intermediates showed that the regioselectivity of the reactions can be explained by the charge density and spin density of each fragment, steric hindrance, and solvent cage effect.

Co3O4 and CuBi2O4 Hybrid Nanostructures for Efficient Nonenzymatic Glucose Detection in Human Blood and Serum Samples with Mechanistic Insights

AbstractIn this report, CuBi2O4/Co3O4 has been used for the electrochemical detection of glucose. Herein, CuBi2O4 nanorods and Co3O4 has been hybridized with CuBi2O4 to form CuBi2O4/Co3O4 nanocomposite hydrothermally. CuBi2O4 and CuBi2O4/Co3O4 electrodes are fabricated by using drop casting method. Structural, morphological studies of CuBi2O4/Co3O4 and electrochemical characterizations pertaining to its performance in comparison to CuBi2O4 for electrochemical detection of glucose are performed and discussed elaborately. The detailed mechanism involved in the electrochemical detection of glucose is proposed. The electrode has shown the sensitivity of 49 μA mM−1 cm−2 with a limit of detection (LOD) of 0.136 μM. DFT calculations are performed on the optimized molecules involved in the electrochemical detection of glucose confirming CuBi2O4/Co3O4 acting as electron donor while glucose as electron acceptor. Further, natural bond orbital (NBO) for charge distribution calculations and ESP mappings for the optimized molecules are performed to understand nucleophilic/electrophilic positions. This study reveals that CuBi2O4 and its modifications are promising materials for the electrochemical detection of glucose. Further, the role of Co3O4 in improving the sensitivity and electrochemical performance for detection of glucose has been discussed.

Electronic Structure and Solvation Effects from Core and Valence Photoelectron Spectroscopy of Serum Albumin.

X-ray photoelectron spectroscopy of bovine serum albumin (BSA) in a liquid jet is used to investigate the electronic structure of a solvated protein, yielding insight into charge transfer mechanisms in biological systems in their natural environment. No structural damage was observed in BSA following X-ray photoelectron spectroscopy in a liquid jet sample environment. Carbon and nitrogen atoms in different chemical environments were resolved in the X-ray photoelectron spectra of both solid and solvated BSA. The calculations of charge distributions demonstrate the difficulty of assigning chemical contributions in complex systems in an aqueous environment. The high-resolution X-ray core electron spectra recorded are unchanged upon solvation. A comparison of the valence bands of BSA in both phases is also presented. These bands display a higher sensitivity to solvation effects. The ionization energy of the solvated BSA is determined at 5.7 ± 0.3 eV. Experimental results are compared with theoretical calculations to distinguish the contributions of various molecular components to the electronic structure. This comparison points towards the role of water in hole delocalization in proteins.

Charge Distribution and Bond Valence Sum Analysis of Sulfosalts—The ECoN21 Computer Program

The charge distribution (CD) and the bond valence sum (BVS) methods are used to calculate the charges assignable to atomic positions in crystal structures, based on the distribution of bond lengths. Discrepancies between calculated and formal charges may point to errors in the determination of atomic coordinates, in the initial allocation of oxidation numbers, occupancies, or site populations. Unlike the BVS method, which has been frequently used for the validation and interpretation of sulfosalt crystal structures, the CD method has been scarcely and limitedly employed for this group of minerals. In this paper, the applicability of the CD method to sulfosalts is practically tested for the first time. The calculation is made using ECoN21—a novel software tool designed for CD, BVS, and general coordination geometry analysis of crystal structures. The program addresses normal valence compounds with distorted homoligand or heteroligand polyhedra in both cation- and anion-centered descriptions. The program is also able to calculate a comprehensive set of parameters describing the internal and external distortion of coordination polyhedra. The paper presents the background of the CD, BVS, and coordination geometry calculations, as well as several case studies focusing on various applications of these methods to sulfosalts.

A numerical method for quantitatively analyzing the space charge effect of Self-Powered Neutron Detector

In this study, a numerical method that can quantitatively analyze the space charge effect of Self-Powered Neutron Detector (SPND) was proposed and successfully applied to SPNDSignal toolkit. By simulating the charge accumulation in SPND’s insulator, the space charge distribution in the insulator under the specified radiation field and detector parameters were obtained. The obtained electric field can be imported into SPNDSignal to construct a real electric field in the insulator, which makes the numerical response calculation model for SPND more real. The feasibility of this method was demonstrated by a calculation for Ag SPND’s space charge distribution and detector response. Moreover, the effect of this method on response calculation of SPND utilized in reactor core was verified by performing the space charge distribution calculation and response calculation for Rh SPND used in VVER assembly, and the results show a good agreement with reference data.

Crystal growth, structure elucidation and CHARDI/BVS investigations of β-KCoFe(PO4)2.

Single crystals of β-KCoFe(PO4)2, potassium cobalt(II) iron(III) bis-(ortho-phosphate), were grown from the melt under atmospheric conditions. This phosphate crystallizes isotypically with KZnFe(PO4)2 in space group C2/c, adopting a zeolite-ABW type of structure. The structure of the present phosphate is distinguished by an occupational disorder of the two transition-metal sites with ratios Fe:Co of 0.5725:0.4275 for the first and 0.4275:0.5725 for the second site. In the crystal structure, PO4 and (Co,Fe)O4 tetra-hedra are linked through vertices to form elliptical rings with the sequence DDDDUUUU of up (U) and down (D) pointing vertices. Each eight-membered ring is surrounded by four other rings of the same type, delimiting inter-stices with rectangular shape. This arrangement leads to the formation of [(Co/Fe)(PO4)]- ∞ sheets parallel to (001). Stacking of the sheets into a three-dimensional framework results in the formation of two types of channels. The first one is occupied by potassium cations, whereas the second one remains vacant. Calculations of bond-valence sums and charge distribution were used to confirm the structure model.

Electron energy-loss spectroscopy investigation of multipolar behavior in Al nanostructure as a function of surface coating with PVP and oxidation

The inherent, self-limiting oxidation characteristics of Aluminum (Al) nanospheres and nanocubes of similar dimensions (100 nm edge length) are illustrated utilizing the MATLAB based boundary element method (MNPBEM17) optical and electron energy loss spectroscopy (EELS) simulations. Such model systems conveniently establish not only the distinct dipolar and multi-polar plasmonic resonance behaviors with reference to their respective passivated ligand PVP as well as their self-limiting surface conformal/non-conformal oxide layers, demonstrating the vital fact that Al nanostructures could be a suitable substitution of conventional noble metals, especially for UV-plasmonic applications. In the case of Al nanocubes, both oxidation processes were found to be strongly site-selective (edges, corners and faces), whereas a differential variation is observed in Al nanospheres from the center to the surface, effectively corroborated through the simultaneous correlation of optical spectra with the spatially and energetically resolved EELS maps. Moreover, the robust contribution from dark plasmon resonances was also confirmed in the EELS data along with the induced surface charge distribution calculations, further substantiating their strong dependence on the surrounding dielectric environment concerning their oxide passivation as well. Thus, our present results demonstrate a better understanding of the spatial coherence of the plasmonic behavior with reference to the passivated ligand and (non)-conformal oxidation processes of Al nanostructures, in general, thereby providing a fundamental understanding of the plasmon physics necessary to improve the design and optimization of new nanostructures for nanophotonic, nanoantenna and sensing applications.

A reliability study of the PMMA/Al/UV5 bilayer process for ultra-short T shape gates

With the advance of communication technique toward terahertz regime, large scale manufacturing of InP based high electron mobility transistors in InAlAs/InGaAs heterojunctions with ultra-short T shape gates below 30 nm is urgently needed. Despite the reported success over two decades ago of replicating high quality T shape gates by the bilayer of PMMA/UV resists, sandwiched by a thin Al layer, it still has not been applied in industry owing to the low yield caused by the instability of the process. This paper concentrates on the reliability study of the process, trying to trace the failure origin by simulating the electron beam lithography including e-beam exposure and developing for such a T shape gate, based on the Monte Carlo algorithm. Systematic calculations of the spatial charge distributions in the bilayer were carried out and the result enables us to discover that the UV5 scum formed on the top of the PMMA should be responsible for the failure in the process, causing the reliability problem. Electron beam lithography for ultra-short T shape gates by the PMMA/UV5 bilayer was carried out to test the success yield. The effect of the buried Al layer in the bilayer on the T shape profile was also theoretically studied. Using the optimized dose window, the success yield as high as 85–94% has been achieved and 15 nm T shape gates have been successfully replicated.

Structure and electronic properties of LnScO3 compounds: A GGA + U calculation

The lattice parameters, bond lengths, bond angles (octahedra tilt angles), Goldschmidt tolerance factor, density of states and electronic band structure of rare-earth scandates LnScO3 (Ln = Eu, La, Nd, Pr, Sm and Tb) in orthorhombic structure have been investigated in the generalized gradient approximation (GGA) + U method with the on-site Coulomb interaction parameter Ueff varying from 1 to 10 eV. The lattice constants, octahedra tilt angles (except for (Eu,Tb)ScO3 compounds), mean 〈Sc-O〉 and 〈Ln-O〉 bond lengths increased almost linearly with effective U parameter values. However, the tolerance factor has decreased (except for (Eu,Tb)ScO3 compounds). Density of states and electronic band structure computations show that LnScO3 compounds are insulator materials and have direct electronic band gap. The electronic band gap of the compounds first increases and then decreases with increasing Ueff. (GGA) + U calculation shows a strong hybridization between Sc-3d and O-2p states. Rare-earth (Ln)-5d states contribute somewhat to this hybridization. The electronic charge distribution and (P)DOS calculation results show that the bonding behavior of LnScO3 compound is a combination of covalent and ionic nature. Our results show that the structural and electronic properties are affected by the application of the Hubbard U term in GGA calculations and the computed lattice constants, bond distances and octahedra tilt angles deviate more from the experimental values. On the other hand, it was observed that the electronic band gap approached the experimental values at the optimal Ueff values determined for the compounds.