Low-energy Band Research Articles

Saturation Thickness of Stacked SiO2 in Atomic-layer-deposited Al2O3 Gate on 4H-SiC

Abstract High-k materials as an alternative dielectric layer for SiC power devices have the potential to reduce interfacial state defects and improve MOS channel conduction capability. Besides, under identical conditions of gate oxide thickness and gate voltage, the high-k dielectric enables a greater charge accumulation in the channel region, resulting in a larger number of free electrons available for conduction. However, the lower energy band gap of high-k materials leads to significant leakage currents at the interface with SiC, which greatly affects device reliability. By inserting a layer of SiO2 between the high-k material and SiC, the interfacial barrier can be effectively widened and hence the leakage current will be reduced. In this study, the optimal thickness of the intercalated SiO2 was determined by investigating and analyzing the gate dielectric breakdown voltage and interfacial defects of a dielectric stack composed by atomic-layer-deposited Al2O3 layer and thermally nitride SiO2. Current-voltage and high-frequency capacitance-voltage measurements were performed on metal-oxide-semiconductor test structures with 35 nm thick Al2O3 stacked on 1-, 2-, 3-, 6-, or 9 nm thick nitride SiO2. Measurement results indicate that the current conducted through the oxides was affected by the thickness of the nitride oxide and the applied electric field. Finally, a saturation thickness of stacked SiO2 that contributed to dielectric breakdown and interfacial band offsets was identified. The findings in this paper provides guideline for the SiC gate dielectric stack design with the breakdown strength and the interfacial state defects considered.

Towards halide treatment on CdS thin films for solar cell applications: An evolution to ion size impact on segregation and grain boundaries passivation

In this study, an impact of halide ion size on the physical properties of 200 nm thin thermally evaporated CdS films is explored. The ex-situ halide treatment is performed using 0.2 M solutions of halide compounds viz. CdCl2, CdI2, MgF2, MgCl2 and MgI2 separately and subsequently air annealing at 200 °C. A detailed grain growth mechanism in CdS films based upon nature and size of cations and anions to the treatment species is deeply discussed. The recrystallization responsible for modulation in structural, optical, topographical, photoluminescence, electrical, morphological and compositional properties of CdS films is explored via formation of different complexes. The XRD patterns reveal formation of polycrystalline CdS thin films having mixture of cubic (with space group F4̅ 3 m) and hexagonal phases with (220) cubic preferential orientation. Different crystallographic constants are calculated and discussed where the crystallite size is varied from 34 nm to 48 nm with treatment. Surface topographical study indicates that surface roughness is altered with the halide treatment and observed maximum for MgCl2 treated CdS thin films. The pristine and halide treated CdS thin films show Ohmic nature owing to linear current-voltage behavior. Optical study demonstrates that MgI2 treated films have higher transmittance and lower absorbance and energy band gap is measured out in 2.04–2.48 eV range. PL spectra of CdS films reveal a strong red emission band appeared at ∼685 nm corresponding to Sulfur vacancies (VS) and possible A centers (XS+VCd2−)−. FESEM exploration reveals grain growth with probable activation where maximum grain size is obtained for MgF2 treated films. The EDS patterns confirm deposition of CdS films and also integration of F, Cl, I and Mg in the associated treated CdS films. The investigated findings reveal that size of halide ions plays a decisive role in modification of the physical properties of CdS thin films which could be implicated as optical window to CdTe and CIGS based photovoltaic devices.

Thermal decomposition of trimethylindium and indium trisguanidinate precursors for InN growth: An abinitio and kinetic modeling study.

Indium nitride (InN) is an interesting material for future electronic and photonic-related applications, as it combines high electron mobility and low-energy band gap for photoabsorption or emission-driven processes. In this context, atomic layer deposition techniques have been previously employed for InN growth at low temperatures (typically <350 °C), reportedly yielding crystals with high quality and purity. In general, this technique is assumed to not involve any gas phase reactions as a result from the time-resolved insertion of volatile molecular sources into the gas chamber. Nonetheless, such temperatures could still favor the precursor decomposition in the gas phase during the In half-cycle, therefore altering the molecular species that undergoes physisorption and, ultimately, driving the reaction mechanism to pursue other pathways. Thence, we herein evaluate the thermal decomposition of relevant In precursors in the gas phase, namely, trimethylindium (TMI) and tris(N,N'-diisopropyl-2-dimethylamido-guanidinato) indium (III) (ITG), by means of thermodynamic and kinetic modeling. According to the results, at T = 593K, TMI should exhibit partial decomposition of ∼8% after 400s to first generate methylindium and ethane (C2H6), a percentage that increases to ∼34% after 1h of exposure inside the gas chamber. Therefore, this precursor should be present in an intact form to undergo physisorption during the In half-cycle of the deposition (<10s). On the other hand, the ITG decomposition starts already at the temperatures used in the bubbler, in which it slowly decomposes as it is evaporated during the deposition process. At T = 300 °C, the decomposition is a fast process that reaches 90% completeness after 1s and where equilibrium, at which almost no ITG remains, is achieved before 10s. In this case, the decomposition pathway is likely to occur via elimination of the carbodiimide ligand. Ultimately, these results should contribute for a better understanding of the reaction mechanism involved in the InN growth from these precursors.

Current- and Field-Induced Topology in Twisted Nodal Superconductors.

We show that interlayer current induces topological superconductivity in twisted bilayers of nodal superconductors. A bulk gap opens and achieves its maximum near a "magic" twist angle θ_{MA}. Chiral edge modes lead to a quantized thermal Hall effect at low temperatures. Furthermore, we show that an in-plane magnetic field creates a periodic lattice of topological domains with edge modes forming low-energy bands. We predict their signatures in scanning tunneling microscopy. Estimates for candidate materials indicate that twist angles θ∼θ_{MA} are optimal for observing the predicted effects.

Dominant Two-Dimensional Electron-Phonon Interactions in the Bulk Dirac Semimetal Na3Bi.

Bulk Dirac semimetals (DSMs) exhibit unconventional transport properties and phase transitions due to their peculiar low-energy band structure, yet the electronic interactions governing nonequilibrium phenomena in DSMs are not fully understood. Here we show that electron-phonon (e-ph) interactions in a prototypical bulk DSM, Na3Bi, are predominantly two-dimensional (2D). Our first-principles calculations reveal a 2D optical phonon with strong e-ph interactions associated with in-plane vibrations of Na atoms. We show that this 2D mode governs e-ph scattering and charge transport in Na3Bi and induces a dynamical phase transition to a Weyl semimetal. Our work advances the quantitative analysis of electron interactions in Na3Bi and reveals a dominant low-dimensional interaction in a bulk Dirac semimetal.

Anthracene-bridged sensitizers for environmentally compatible dye-sensitized solar cells: In silico modelling and prediction

Advancement in solar cells has gained the attention of researchers due to increasing demand and renewable energy sources. Modeling of electron absorbers and donors has been performed extensively for the development of efficient solar cells. In this regard, efforts are being made for designing effective units for the active layer of solar cells. In this study, CXC22 was utilized as a reference in which acetylenic anthracene acted as a π bridge and infrastructure was D-π-A. We theoretically designed four novel dye-sensitized solar cells JU1-JU4 by utilizing reference molecules to improve the photovoltaic and optoelectronic properties. All designed molecules differ from R by donor moiety modifications. Different approaches were done to R and all molecules to explore different analyses like binding energies, excitation energies, dipole moment, TDM (transition density matrix), PDOS (partial density of states), absorption maxima, and charge transfer analysis. For the evaluation of results, we used the DFT technique and the findings demonstrated that the JU3 molecule showed a better redshift absorption value (761 nm) as compared to all other molecules due to the presence of anthracene in the donor moiety which lengthens the conjugation. JU3 was proven to be the best candidate among all due to improved excitation energy (1.69), low energy band gap (1.93), higher λmax value, and improved electron and hole energy values leading toward higher power conversion efficiency. All the other theoretically formed molecules exhibited comparable outcomes as compared to a reference. As a result, this work revealed the potential of organic dyes with anthracene bridges for indoor optoelectronic applications. These unique systems are effective contributors to the development of high-performance solar cells. Thus, we provided efficient systems to the experimentalists for the future development of solar cells.

One-dimensional flat bands and Dirac cones in narrow zigzag dice lattice ribbons

We show that four narrow zigzag dice lattice ribbons, which have the minimal widths among their separate categories, constitute a unique collection of systems to study physics related to one-dimensional Dirac cones and flat bands. In zero magnetic field, all three combinations, including only Dirac cones, only flat bands, coexisting Dirac cones and flat bands, are realized in the low-energy band structures of one or two of the four ribbons. In particular, we identify flat bands and Dirac cones corresponding to the edge states of wide ribbons. In a perpendicular magnetic field that gives half a flux quantum per elementary rhombus, two of the four minimal ribbons have fully pinched spectrum, and dynamical evolutions from initially localized wave packets always lead to compact Aharonov-Bohm (AB) cages. The experimental realizations of these narrow zigzag dice lattice ribbons, and the opportunities of exploring novel single-body and many-body physics therein are discussed.

Measurements of spin and orbital parameters in Cen X-3 by Insight-HXMT

We present a detailed temporal analysis for the eclipsing high-mass X-ray binary system Cen X-3 using the Insight-HXMT data in 2018 and 2020. Three consecutive and high statistic observations among data are used for the precise timing analysis. The pulse profiles are revealed to vary with energy and time. The pulse profiles for the 2018 observations showed a double peak in the low energy bands below 10 keV and evolved to a single peak in higher energies without the correlation between pulse fraction and flux, and profiles in low energies changed with time. But the pulse profile for the 2020 observation only showed a broad single-peaked pulse in all energy bands with a positive relation between pulse fraction and flux, which may indicate the transition of the emission patterns from a mixture of a pencil and a fan beam to a dominated pencil-like beam. With performing a binary orbital fitting of spin periods, we obtain an accurate value for the spin period and the orbital parameters. The intrinsic spin period of the neutron star is found to be 4.79920±0.00006 s at MJD 58852.697, with the orbital period determined at Porb=2.08695634±0.00000001 day, and its decay rate of -(1.7832 ± 0.0001) × 10−6 yr−1 for the binary.

Unravelling optical and X-ray properties of the disc-dominated intermediate polar IGR J15094-6649

ABSTRACT We present analyses of an Intermediate Polar, IGR J15094-6649, based on the archival optical data obtained from the Transiting Exoplanet Survey Satellite (TESS) and X-ray data obtained from the Suzaku, NuSTAR, and Neil Gehrels Swift Observatory (Swift). Present analysis confirms and refines the previously reported spin period of IGR J15094-6649 as 809.49584 ± 0.00075 s. Clear evidence of a beat period of 841.67376 ± 0.00082 s is found during the long-term TESS optical observations, which was not evident in the earlier studies. The dominance of X-ray and optical spin pulse unveils the disc-fed dominance accretion, however, the presence of an additional beat frequency indicates that part of the accreting material also flows along the magnetic field lines. The energy-dependent spin pulsations in the low (&amp;lt;10 keV) energy band are due to the photoelectric absorption in the accretion flow. However, the complex absorbers may be responsible to produce low amplitude spin modulations via Compton scattering in the hard (&amp;gt;10 keV) energy band and indicate that the height of the X-ray emitting region may be negligible. The observed double-humped X-ray profiles with a pronounced dip are indicative of the photoelectric absorption in the intervening accretion stream. Analysis of the X-ray spectra reveals the complexity of the X-ray emission, being composed of multitemperature plasma components with a soft excess, reflection, and suffers from strong absorption.

Tuning the Emission of a Nonconventional Aggregation-Induced Emission Polymer via Silicon-Bridged Twisted Intramolecular Charge Transfer for Targeted Delivery and Visualized Drug Release.

The design of tunable luminescent biomaterials with large Stokes shifts is usually pursued by a twisted intramolecular charge transfer (TICT) effect with switchable emission colors in response to various external stimuli. However, such a strategy is usually realized in conjugated molecules containing benzene or its derivatives and consequently suffers from poor biocompatibility. In this work, a hyperbranched polysiloxane (HBPSi)-based non-conjugated fluorescent polymer with TICT and aggregation-induced emission (AIE) features is developed, and its luminescent properties, fluorescence mechanism, and potential applications are investigated. Initially, the non-conjugated HBPSi exhibits remarkable AIE characteristics due to the formation of through-space conjugation. With the introduction of the sulfur atom, a non-conjugated D-A type AIE material, HBPSi-Cys, that exhibits a dual-state emission with a large Stokes shift of 213 nm, is obtained. The correlation of the lower-energy emission band with solvent polarity suggests the existence of the TICT state. TICT and AIE characteristics direct different properties of HBPSi-Cys, with TICT regulating solvatochromic emission wavelengths and AIE manipulating the emission intensity with a compensation effect. Density functional theory calculations reveal that the non-conjugated D-A structure in HBPSi-Cys was formed across the silicon bridge, with auxochromic sulfhydryl groups and adjacent amide groups as acceptor units and amine and hydroxyl groups as donor units. Additionally, the AIE-active HBPSi could be utilized as a fluorescent probe for the analysis of metal ions. After grafting the AS1411 aptamer to HBPSi-Cys as the recognition motif, HBPSi-Apt possesses excellent targeted bioimaging, drug loading, pH/GSH dual-responsive drug release, and visualized drug delivery performance. This work provides a new way to design functional AIE polymers with tunable optical properties, and the synthesized HBPSi-Cys shows great potential as a smart fluorescent biomaterial.

Signatures of Electric Field and Layer Separation Effects on the Spin-Valley Physics of MoSe2/WSe2 Heterobilayers: From Energy Bands to Dipolar Excitons.

Multilayered van der Waals heterostructures based on transition metal dichalcogenides are suitable platforms on which to study interlayer (dipolar) excitons, in which electrons and holes are localized in different layers. Interestingly, these excitonic complexes exhibit pronounced valley Zeeman signatures, but how their spin-valley physics can be further altered due to external parameters-such as electric field and interlayer separation-remains largely unexplored. Here, we perform a systematic analysis of the spin-valley physics in MoSe2/WSe2 heterobilayers under the influence of an external electric field and changes of the interlayer separation. In particular, we analyze the spin (Sz) and orbital (Lz) degrees of freedom, and the symmetry properties of the relevant band edges (at K, Q, and Γ points) of high-symmetry stackings at 0° (R-type) and 60° (H-type) angles-the important building blocks present in moiré or atomically reconstructed structures. We reveal distinct hybridization signatures on the spin and the orbital degrees of freedom of low-energy bands, due to the wave function mixing between the layers, which are stacking-dependent, and can be further modified by electric field and interlayer distance variation. We find that H-type stackings favor large changes in the g-factors as a function of the electric field, e.g., from -5 to 3 in the valence bands of the Hhh stacking, because of the opposite orientation of Sz and Lz of the individual monolayers. For the low-energy dipolar excitons (direct and indirect in k-space), we quantify the electric dipole moments and polarizabilities, reflecting the layer delocalization of the constituent bands. Furthermore, our results show that direct dipolar excitons carry a robust valley Zeeman effect nearly independent of the electric field, but tunable by the interlayer distance, which can be rendered experimentally accessible via applied external pressure. For the momentum-indirect dipolar excitons, our symmetry analysis indicates that phonon-mediated optical processes can easily take place. In particular, for the indirect excitons with conduction bands at the Q point for H-type stackings, we find marked variations of the valley Zeeman (∼4) as a function of the electric field, which notably stands out from the other dipolar exciton species. Our analysis suggests that stronger signatures of the coupled spin-valley physics are favored in H-type stackings, which can be experimentally investigated in samples with twist angle close to 60°. In summary, our study provides fundamental microscopic insights into the spin-valley physics of van der Waals heterostructures, which are relevant to understanding the valley Zeeman splitting of dipolar excitonic complexes, and also intralayer excitons.

Silver(I) Coordination Polymer Ligated by Bipyrazole Me4bpzH2, [Ag(X)(Me4bpzH2)] (X = CF3CO2− and CF3SO3−, Me4bpzH2 = 3,3′,5,5′-Tetramethyl-4,4′-bipyrazole): Anion Dependent Structures and Photoluminescence Properties

Coordination polymers of transition metal ions are fascinating and important to coordination chemistry. One of the ligands known to form particularly interesting coordination polymers is 3,3',5,5'-tetramethyl-4,4'-bipyrazole (Me4bpzH2). Group 11 metal(I) ion coordination polymers, other than those of copper(I), are relatively easy to handle because of their low reactivity towards dioxygen and moisture. However, the known silver(I) coordination polymers often have poor solubility in common solvents and so cannot be easily analyzed in solution. By using a tetramethyl substituted bipyrazole ligand, we have synthesized more soluble silver(I) complexes that contain the trifluoromethyl group in the coordinated ions CF3CO2- and CF3SO3- in [Ag(CF3CO2)(Me4bpzH2)] and [Ag(CF3SO3)(Me4bpzH2)]. We determined both structures by single-crystal X-ray analysis at low temperatures and compared them in detail. Moreover, we investigated the solution behavior of these coordination polymers by 1H-NMR, IR, Raman, UV-Vis spectroscopies, and their low-temperature, solid-state photoluminescence. The high-energy band at ~330 nm corresponded to ligand-centered (bipyrazole) fluorescence, and the low-energy band at ~400 nm to ligand-centered phosphorescence resulting from the heavy atom effect.

Nonlinear Landau-Zener tunneling under higher-order dispersion

We studied nonlinear Landau-Zener tunneling under the effect of higher-order dispersion, transformed the Gross-Pitaevskii (GP) equation with higher-order dispersion terms into a nonlinear two-energy level form using a two-mode approximation, and comprehensively analyzed the loop structure of the lowest-energy band and the nonlinear Landau-Zener tunneling. The results show that, when third-order dispersion coefficient is not zero, there is a spatial inversion symmetry breaking of the energy band structure and unbalanced Landau-Zener tunneling. By analyzing the fixed point's nature of the classical Hamiltonian, we obtain a law for the variation of the loop structure and adiabatic tunneling probability with the dispersion coefficient, consistent with our numerical analysis results. In addition, we analyzed the real-time evolution of solitons with transverse bias and observed the tunneling phenomenon. Consistent with our analysis, the adjustment of the dispersion term can effectively control optical tunneling, which provides an alternative idea for optical switching.

Designing and theoretical study of benzocarbazole-based D-π-D type small molecules donor for organic solar cells

Seven new molecules (S1–S7) of D-π-D type have been designed for organic photovoltaic applications. The DFT and TD-DFT methods were used to investigate the effect of different central bridge groups on the geometric, optoelectronic, and charge transport properties of the constructed molecules. Among them, S4 and S6 have the lowest energy band gap and a red shift in the absorption spectra, revealing the perfect relationship between the central bridge and the strong electron withdrawal character through extended conjugation. Similarly, S6 explored the lowest reorganization energy (RE) value for electron and hole revealing its enhanced charge transition, also shows better ICT characteristics with its highest NLO properties. Compound S4 showed the smallest value of ΔEL−L and Eb, and the highest Voc due to its low HOMO, which improves the photocurrent density of the devices. Thus, the results suggest that bridge modification is a practical strategy to improve the efficiency of OSCs.

Synthesis, crystal structures and biological activities of halogeno-(O-alkylphenylcarbamothioate)bis(triarylphosphine)copper(I) complexes

The aim of this work was to synthesize and characterize a new series of copper(I) complexes with thiocarbamate ligands and to evaluate their biological activity. Treatment of CuX salts (X = Cl, Br, I) with O-alkyl N-phenylcarbamothioates in the presence of two equivalents of PAr3 (Ar = Ph, p-C6H4OMe) affords a series of mononuclear thione complexes [(Ar3P)2Cu{ROC(=S)N(H)Ph}X)] C1-C10. According to X-ray diffraction analyses, all complexes adopt a distorted tetrahedral geometry and feature intramolecular NH···Hal bonding, giving rise to six-membered cycles. Like in the case of the literature-known chloro‑compounds C1 and C2 (d(NH···Cl) ∼ 2.29 Å), the bromo‑derivatives C3–C6 exhibit strong NH···Hal distances varying from 2.48 to 2.63 Å. This intramolecular bonding, which is weaker for the iodo complexes C7-C10 (∼ 2.75 Å), has also been studied by Hirshfeld surface analysis of C1, C3, C4 and C6. The crystal structure of two 1D-polymeric intermediates occurring during the synthesis of C7 and C9, namely [{Cu(μ2-I)2Cu}(μ2-L)2]nCP1 and CP2, has also been elucidated. The complexes display weak luminescence in solution centered on the triarylphosphine ligands. In contrast, in the solid state a high-energy band around 350–450 nm centered on the thioamidate and triarylphosphine ligands is observed, along with a second low energy band typical for MLCT/XLCT states around 450–550 nm. The screening of the biological activity of these complexes reveals the absence of any significant antibacterial capacity. However, the presence of an antioxidant activity with a maximum activity for complexes C3 and C4 has been evidenced using the colorimetric DDPH method. This has been probed in vivo on Wistar rats for the preservation of hepatocytes integrity after liver hypothermic conservation (4 °C) for 24 h in Krebs solution with normal cellular state by addition of [(Ph3P)2Cu{EtOC(=S)N(HPHh}I] C8.

Chiral Decomposition of Twisted Graphene Multilayers with Arbitrary Stacking.

We formulate the chiral decomposition rules that govern the electronic structure of a broad family of twisted N + M multilayer graphene configurations that combine arbitrary stacking order and a mutual twist. We show that at the magic angle in the chiral limit the low-energy bands of such systems are composed of chiral pseudospin doublets that are energetically entangled with two flat bands per valley induced by the moiré superlattice potential. The analytic construction is supported by explicit numerical calculations based on realistic parametrization. We further show that vertical displacement fields can open energy gaps between the pseudospin doublets and the two flat bands, such that the flat bands may carry nonzero valley Chern numbers. These results provide guidelines for the rational design of topological and correlated states in generic twisted graphene multilayers.

Up-Conversion Photoluminescence in Thulia and Ytterbia Co-Doped Yttria-Stabilized Zirconia Single Crystals

ZrO2 is an attractive host matrix for luminescence material because of its excellent physical properties, such as low phonon energy and wide band gap. In this work, the highly transparent Tm2O3 and Yb2O3 co-doped yttria stabilized zirconia (YSZ) (abbreviated as Yb/Tm: YSZ) single crystals were grown by the optical floating zone method. The Yb/Tm: YSZ samples were stabilized in the cubic phase at room temperature when Yb3+ and Tm3+ replaced Y3+. The influence of Yb3+ co-doping on the up-conversion luminescence properties of the crystals was systematically studied. A total of 0.5 mol% Tm2O3 and 2.0 mol% Yb2O3 co-activated YSZ single crystal (abbreviated as 2.0Yb/Tm: YSZ) has the maximum luminous intensity. There were seven absorption peaks located at around 358, 460, 679, 783.3, 850–1000, 1200, and 1721.5 nm that were observed in the absorption spectrum of the 2.0Yb/Tm: YSZ single crystal. There were three up-conversion peaks at around 488, 658 and 800 nm that were observed when the Yb/Tm: YSZ samples were excitated at 980 nm. The fluorescence lifetime of Tm3+ for the 1G4→3H6 transition of the 2.0Yb/Tm: YSZ sample is 7.716 ms as excited with a 980 nm laser. In addition, the oscillator strength parameters Ωλ (λ = 2, 4 and 6) of this sample were derived by the Judd–Ofelt theory to evaluate the laser performance of the host materials. The ratio Ω4/Ω6 of this sample is 0.80, implying its excellent laser output. Therefore, the 2.0Yb/Tm: YSZ single crystal is a considerable potential material for laser and luminescence applications.

Photodissociation study of CO2 on the formation of state-correlated CO(X1Σ+, v) with O(3P2) photoproducts in the low energy band centered at 148 nm.

The spin-forbidden O(3P2) + CO(X1Σ+, v) channel formed from the photodissociation of CO2 in the low energy band centered at 148nm is investigated by using the time-sliced velocity-mapped ion imaging technique. The vibrational-resolved images of the O(3P2) photoproducts measured in the photolysis wavelength range of 144.62-150.45nm are analyzed to give the total kinetic energy releases (TKER) spectra, CO(X1Σ+) vibrational state distributions, and anisotropy parameters (β). The TKER spectra reveal the formation of correlated CO(X1Σ+) with well resolved v = 0-10 (or 11) vibrational bands. Several high vibrational bands that were observed in the low TKER region for each studied photolysis wavelength exhibit a bimodal structure. The CO(X1Σ+, v) vibrational distributions all present inverted characteristics, and the most populated vibrational state changes from a low vibrational state to a relatively higher vibrational state with a change in the photolysis wavelength from 150.45 to 144.62nm. However, the vibrational-state specific β-values for different photolysis wavelengths present a similar variation trend. The measured β-values show a significant bulge at the higher vibrational levels, in addition to the overall slow decreasing trend. The observed bimodal structures with mutational β-values for the high vibrational excited state CO(1Σ+) photoproducts suggest the existence of more than one nonadiabatic pathway with different anisotropies in the formation of O(3P2) + CO(X1Σ+, v) photoproducts across the low energy band.

Study on the Effects of Protective Layer on the Electron and Hole Transmission of Cadmium Sulfide (CdS) Photocatalyst Based on a Simple Quantum Mechanical Model

Cadmium Sulfide (CdS) is a photocatalyst material with a low energy band gap, which exhibits a potential application for the visible light spectrum. However, the serious photo-corrosion of CdS inhibits its wide applications. To prevent photo-corrosion, one can coat the CdS surface coated with an insulating material. The addition of this insulating layer will produce a barrier potential on the surface of the CdS thereby blocking the transmission of electrons and holes. If the thickness of this protective layer is thin enough the electron and hole can be transmitted by the quantum tunneling effect. Using a simple quantum mechanical model, the phenomena of electron and hole transmission through potential barriers due to the presence of a protective layer on the CdS surface can be analyzed. Based on this model, the effects of variations in thickness and type of protective layer on the performance of CdS photocatalyst materials are studied by calculating the transmission coefficient and injection efficiency values. The protective coatings used in this study were Aluminum Oxide (Al2O3), Hafnium Dioxide (HfO2), and Silicon Dioxide (SiO2). The results show that transmission decreases as the thickness of the protective increases. Among the three types of protective coatings used, HfO2 material has the potential to be used because it has the best injection efficiency value.

Exploration of photovoltaic behavior of fused triphenylamine moiety as core donor with modified acceptors: Star-shaped D-[formula omitted]-A conjugated systems

Fullerene-free organic chromophores have drawn considerable attention as successful photonic devices for organic solar cells. So, a series of novel non-fullerene-based donor molecules (HBTD2–HBTD9) were fabricated via structural modification of the terminal acceptor groups from HBTR1. In order to achieve the photovoltaic, photophysical, and electronic behavior of fore-said compounds, density functional theory/time-dependent density functional theory (DFT/TD-DFT) based analyses were accomplished at B3LYP functional along with 6-311G(d,p) basis set. The optical and electrical characteristics of the derivatives were compared with HBTR1 architecture. All designed molecules exhibited a lower EHOMO-ELUMO band gap (2.183–4.106 eV) with a red shift in absorbance compared to the reference compound (4.179 eV). All derivatives (HBTD2–HBTD9), except HBTD3, showed a greater exciton dissociation rate due to low binding energy (Eb = −0.337 to 1.400 eV) when compared with HBTR1 (Eb = 1.401 eV). Interestingly, HBTD9 manifested to be the prime candidate for non-fullerene organic solar cells (NF–OSCs) owing to the lowest energy band gap, large mobility of charges, and least value of binding energy while holding an excellent redshift value compared to all the designed chromophores. This study revealed that these chromophores would be potential competitors in manufacturing effective optoelectronic materials.