Conduction Band States Research Articles

Ultrafast Electron Dynamics at the P‐rich Indium Phosphide/TiO2 Interface

AbstractThe current efficiency records for generating green hydrogen via solar water splitting are held by indium phosphide (InP)‐based photo‐absorbers, protected by TiO2 layers grown through atomic layer deposition (ALD). InP is also a leading material for photonic integrated circuits and computing, where ultrafast near‐surface behavior is key. A previous study described electronic pathways at the phosphorus‐rich (P‐rich) surface of p‐doped InP(100) using time‐resolved two‐photon photoemission (tr‐2PPE) spectroscopy. Here, the intricate electron pathways of the P‐rich InP surface modified with ALD‐deposited TiO2 are explored. Photoexcited bulk InP electrons migrate through a bulk‐to‐surface transition cluster of states and surface states and inject into the TiO2 conduction band (CB). Energy levels and occupation dynamics of CB states in P‐rich InP and TiO2 adlayers are observed, with discrete states preserved up to 10 nm TiO2 deposition. Thermalization lifetimes of excited electrons > 0.8 eV above the InP conduction band minimum (CBM) are preserved for layer thicknesses up to 2.5 nm. Annealing at 300 °C to achieve crystalline TiO2 reconstructions destroys interfacial states, affecting charge transfer. These observations enable innovative engineering of the P‐rich InP/TiO2 heterointerface, opening new possibilities for studying hot‐carrier extraction, adsorbate effects, surface plasmons, and improving photovoltaic and PEC water‐splitting devices.

Structural, optoelectronic, and magnetic properties of Q‑carbon studied by hybrid density functional theory ab initio calculations and experiment

This work presents a theoretical study of the structural, optoelectronic, and magnetic properties of Q‑carbon, utilizing hybrid functionals within density functional theory (DFT) ab initio calculations. Moreover, experiments were conducted to measure structural parameters, dielectric functions, and magnetic properties, using various techniques. From the DFT simulations, structural, electronic, and optical properties have been simulated. The band gap energy was calculated using a hybrid approach, which combine HSE functional with different values of exact Hartree-Fock (HF) exchange (α). We propose a theoretical investigation of cubic and quasi-cubic forms of Q‑carbon. Our findings indicate that a non-cubic Q‑carbon cell is energetically more stable and possesses higher cell mass density and bulk modulus compared to a cubic cell. Calculations indicated that Q‑carbon exhibits semiconductor behavior; an indirect band gap of 3.10 eV and a direct band gap of about 3.4 eV was obtained for α = 0.44, in good agreement with experimental values. The density of states analysis allowed us to identify the p orbital of sp2 hybridized atoms as being prevalent on the top of the valence band and in the lowest energy conduction band states. Magnetic moment values of 0.37 μB and 0.41μB was found in two sp2 bonded C atoms, in accordance with the experimental observation. Several optical properties were calculated. The theoretical findings are compatible with the experimental results shown here and available in the literature, with excellent agreement found between the calculated optical band gap and that obtained from absorption measurements.

Fe-N Co-Doped BiVO4 Photoanode with Record Photocurrent for Water Oxidation.

Bismuth vanadate ranks among the most promising photoanodes for photoelectrochemical water splitting. Nonetheless, slow charge separation and transportare key barriers to its photoefficiency. Here, we present a co-doping strategy that significantly improves the charge separation performance of BVO. Under standard one sun illumination, the Fe-N co-doped BVO photoanode (Fe-N-BVO) by N-coordinated Fe precursor reaches a record photocurrent density of 7.01 mA cm-2 at 1.23 V vs RHE after modified a surface co-catalyst. By contrast, much lower photocurrent density is obtained for the N-doped and Fe-doped BVO with separated N and Fe precursors. The detailed characterizations show that the high activity of the Fe-N-BVO is attributed to the enhanced photo-induced bulk charge separation and the accelerated surface water oxidation kinetics. XPS, EXAFS and DFT calculations clearly show that, instead of formation of deep trapping state in the individually doped BVO, the co-doping of Fe-N into BVO generates Fe-based electronic states just below the bottom of conduction band and N-derived states just above the top of valence band. Such modulations in electronic structure enable the efficient trap of the electrons and holes to enhance the separation of photo-induced carriers, but hinder the charge recombination originated from the deep trapping sites.

Role of local structure in the optical and electronic properties of oxygen vacancies in different crystal phases of Ga2O3

We investigate the structural, electronic, and optical properties of oxygen vacancies (VO) in crystalline α, β, and ε−Ga2O3 using density functional theory (DFT) calculations with the PBE0-TC-LRC functional. Our results reveal that the charge transition levels (CTLs) associated with VO exhibit significant variations depending on the crystal phase and the coordination environment of surrounding atoms. In particular, VOs surrounded by tetrahedral Ga atoms (T-Ga) exhibit deeper CTLs compared to those surrounded by octahedral Ga atoms (O-Ga). We also observe distinct atomic relaxations, with larger displacements of T-Ga atoms compared to O-Ga atoms in the vicinity of VOs. Using linear-response time-dependent DFT, we investigate the optical transitions of VO and identify two distinct types of transitions: defect state to conduction band state and valence band to defect state. These results can be used to better understand the optical properties of VO defects in Ga2O3 films. Published by the American Physical Society 2024

Inorganic/organic sublattice roles in band edge photodynamics of isoelectronically substituted hybrid semiconductors

Zero-dimensional organic–inorganic hybrid metal halides are unique semiconductors with fruitful physical properties. Usually, only the inorganic polyhedrons dominate the band edge electronic and photophysical properties of such hybrid semiconductors, whereas the organic components mainly act as structure-stabilizing units. Herein, we study the electronic structures and photodynamics of isoelectronically Br-substituted (I) zero-dimensional organic–inorganic copper halide semiconductors (C9H14N)3Cu3(BrxI1−x)6. They are composed of both inorganic [Cu3(BrxI1−x)6]3− units and organic C9H14N+ skeletons. It is surprising to find that unlike usual organic–inorganic metal halides, although the heavily isoelectronic substitution of halogen atoms in the (C9H14N)3Cu3I6 crystal leads to significant shrinkage of the lattice, it does not remarkably alter the bandgap and luminescence peak owing to the site-projected density of states as revealed by the density functional theory calculation. The inorganic units dominate the valence band edge quantum states, whereas the organic skeletons dominate the conduction-band edge states. However, the isoelectronic substitution significantly lowers the symmetry of the crystal, and as a result, the quantum transition probability at the band edge increases first and decreases then with increasing concentration of substituting bromine atoms. The (C9H14N)3Cu3(BrxI1−x)6 crystals exhibit dual-band luminescence with large Stokes shift and near-unity quantum yield. It arises from the excitons trapped by two kinds of centers. The critical participation of the organic skeletons in the electronic structures and band edge photodynamics refresh our knowledge of their roles in the hybrid semiconductors.

Electronic structures, thermal properties and molecular dynamics of CsGdCl3 and CsNdCl3 perovskite crystals by first-principles calculations

Lanthanide-based perovskite crystals have been characterized for proposing material design guidelines of perovskite solar cell with stability of photovoltaic performance. The purpose of this study is to characterize band structures, phonon dispersions, molecular dynamics, electronic and thermal conductivities of CsGdCl3 and CsNdCl3 perovskite crystals by first-principles calculation analysis. The CsGdCl3 and CsNdCl3 crystals had wide distributions of 5d orbital of Gd3+ ion, 5d and 4f orbitals of Nd2+ ion near conduction band state as n-type semiconductive behavior. The phonon dispersions and thermal conductivities indicate effects of acoustic phonon on carrier scattering. The CsGdCl3 crystal suppressed carrier scattering as elastic behavior, improving electron diffusion and dynamic stability. The CsNdCl3 crystals expected to cause carrier scattering with acoustic phonon and molecular dynamics. The CsGdCl3 crystal have the superior potential of the performance as semiconductor characteristics equivalent to the performance of the CsPbCl3 crystal.

Beyond Cation Disorder: Site Symmetry‐Tuned Optoelectronic Properties of the Ternary Nitride Photoabsorber ZrTaN3

AbstractTernary nitrides are rapidly emerging as promising compounds for optoelectronic and energy conversion applications, yet comparatively little of this vast composition space has been explored. Furthermore, the crystal structures of these compounds can exhibit a significant amount of disorder, the consequences of which are not yet well understood. Here, the deposition of bixbyite‐type ZrTaN3 thin films is demonstrated by reactive magnetron co‐sputtering and observed semiconducting character, with a strong optical absorption onset at 1.8 eV and significant photoactivity, with prospective application as functional photoanodes. It is found that Wyckoff‐site occupancy of cations is a critical factor in determining these beneficial optoelectronic properties. First‐principles calculations show that cation disorder leads to minor deviations in the total energy but modulates the bandgap by 0.5 eV, changing orbital hybridization of valence and conduction band states. In addition to demonstrating that ZrTaN3 is a promising visible light‐absorbing semiconductor and active photoanode material, the findings provide important insights regarding the role of cation ordering on the electronic structure of ternary semiconductors. In particular, it is shown that not only cation order, but also the cationic Wyckoff site occupancy has a substantial impact on key optoelectronic properties, which can guide future design and synthesis of advanced semiconductors.

Effect of Surface Electron Trapping and Small Polaron Formation on the Photocatalytic Efficiency of Copper(I) and Copper(II) Oxides.

Cu2O, CuO, and mixed phase Cu2O/CuO represent promising candidates for photoelectrochemical H2 evolution due to their strong visible light absorption, earth-abundance, and chemical stability. However, the photoelectrochemical efficiency in these materials remains far below the theoretical limit, largely due to poorly understood surface electron dynamics. These dynamics depend on defect states, such as Cu atom vacancies and phase boundaries, which control electron trapping, charge carrier separation, and recombination. In this work, we study the photoinduced electron and hole dynamics at the surface of various Cu oxides using ultrafast extreme ultraviolet reflection-absorption (XUV-RA) spectroscopy. In Cu2O we find that photoexcitation occurs as electron promotion from primarily Cu 3d valence band to Cu 4s conduction band states compared to O 2p valence band to Cu 4s conduction band states in CuO. In catalysts with a significant concentration of Cu vacancies, we observe fast electron trapping to the Cu 3d defect band occurring in less than 100 fs. In contrast, photoexcited electrons in phase pure CuO do not trap to midgap states; rather these electrons form small polarons within approximately 500 fs. Photoelectrochemical measurements of these catalysts show that Cu vacancy-mediated electron trapping correlates with a significant loss of photocurrent. Together, these results provide a detailed picture of the defect states and associated ultrafast carrier dynamics that govern the photocatalytic efficiency in widely studied Cu2O and CuO photocatalysts.

Possible Wigner states in CrI3 heterostructures with graphene: A tight-binding model perspective

In this study, we present an effective tight-binding model for an accurate description of the lowest energy quadruplet of a conduction band in a ferromagnetic CrX3 monolayer, tuned to the complementary density functional theory simulations. This model, based on a minimum number of chromium orbitals, captures a distinctively flat dispersion in those bands but requires taking into account hoppings beyond nearest neighbors, revealing ligand-mediated electron pathways connecting remote chromium sites. Doping of states in the lowest conduction band of CrX3 requires charge transfer, which, according to recent studies [Tenasini , ; Tseng , ; Cardoso , , can occur in graphene(G)/CrX3 heterostructures. Here, we use the detailed description of the lowest conduction band in CrI3 to show that G/CrI3/G and G/CrI3 are type-II heterostructures where light holes in graphene would coexist with heavy electrons in the magnetic layer, where the latter can be characterized by Wigner-Seitz radius rs∼25−35 (as estimated for hBN-encapsulated structures). Published by the American Physical Society 2024

Hot electron effect in high-order harmonic generation from graphene driven by elliptically polarized light

We studied high-order harmonic generation (HHG) in graphene driven by either linearly or elliptically polarized mid-infrared (MIR) light, and we additionally applied terahertz (THz) pulses to modulate the electron distribution in graphene. The high-harmonic spectrum obtained using linearly polarized MIR light contains only odd-order harmonics. We found that the intensities of the fifth- and seventh-order harmonics are reduced by the modulation with the THz pulses. In addition, we found that the THz-induced reduction of the seventh-order harmonic driven by elliptically polarized MIR light (at ellipticity ε = 0.3) is larger than that of seventh-order harmonic driven by linearly polarized MIR light (ε = 0). The observed behavior can be reproduced by theoretical calculations that consider different electron temperatures (caused by the THz pulses). Furthermore, the observed stronger suppression of HHG driven by elliptically polarized light reveals the following: in the case of elliptically polarized light, the generation of harmonics via interband transitions to conduction-band states that are closer to the Dirac point is more important than in the case of linearly polarized light. In other words, the quantum pathways via interband transitions to low-energy states are the origin of the enhancement of HHG that can be achieved in graphene by using elliptically polarized light.

Probing the Band Splitting near the Γ Point in the van der Waals Magnetic Semiconductor CrSBr.

This study investigates the electronic band structure of chromium sulfur bromide (CrSBr) through comprehensive photoluminescence (PL) characterization. We clearly identify low-temperature optical transitions between two closely adjacent conduction-band states and two different valence-band states. The analysis on the PL data robustly unveils energy splittings, band gaps, and excitonic transitions across different thicknesses of CrSBr, from monolayer to bulk. Temperature-dependent PL measurements elucidate the stability of the band splitting below the Néel temperature, suggesting that magnons coupled with excitons are responsible for the symmetry breaking and brightening of the transitions from the secondary conduction band minimum (CBM2) to the global valence band maximum (VBM1). Collectively, these results not only reveal splitting in both the conduction and valence bands but also highlight a significant advance in our understanding of the interplay between the optical, electronic, and magnetic properties of antiferromagnetic two-dimensional van der Waals crystals.

Optoelectronic and transport properties of Lead-Free halide based Na2AgTlZ6 (Z = Cl, Br, I) double perovskites for energy harvesting applications

The bandgap engineering and deliberate band edge manipulation of perovskites make them potential candidates for the photovoltaic industry. Here we theoretically investigate the structure, density of states, and photovoltaic and thermoelectric characteristics of Na2AgTlZ6 (Z = Cl, Br, I) using WIEN2k code. The incorporation of Br and I at the Cl site caused the increase in lattice constant which leads to the decrease in bulk modulus and Debye temperature. The computed values of Poisson (<0.26) and Pugh (<1.75) ratio verified their brittle nature. The bandgap analysis reveals direct bandgap nature and bandgap value lie in the visible region for parent composition and infrared and far infrared when Cl is replaced with Br and I. The density of state plots uncovers the shifting of energy states in valence and conduction bands towards the Fermi level with the increasing number of electrons in the halogens. The increase in the value of dielectric constant, refractive index, and shifting of peaks towards lower energy value is witnessed with atomic number of halogen atoms. The viability of these compositions for thermoelectric devices is further confirmed when electrical conductivity and Seebeck coefficient dependent Figure of merit and power factor are evaluated in the temperature range of 200–800 K. In addition, the anisotropic nature of studied compositions is explored through the computation of the modulus of elasticity including Young’s modulus, Shear modulus in addition to compressibility, and Poisson’s ratio.

Conduction Band Replicas in a 2D Moiré Semiconductor Heterobilayer.

Stacking monolayer semiconductors creates moiré patterns, leading to correlated and topological electronic phenomena, but measurements of the electronic structure underpinning these phenomena are scarce. Here, we investigate the properties of the conduction band in moiré heterobilayers of WS2/WSe2 using submicrometer angle-resolved photoemission spectroscopy with electrostatic gating. We find that at all twist angles the conduction band edge is the K-point valley of the WS2, with a band gap of 1.58 ± 0.03 eV. From the resolved conduction band dispersion, we deduce an effective mass of 0.15 ± 0.02 me. Additionally, we observe replicas of the conduction band displaced by reciprocal lattice vectors of the moiré superlattice. We argue that the replicas result from the moiré potential modifying the conduction band states rather than final-state diffraction. Interestingly, the replicas display an intensity pattern with reduced 3-fold symmetry, which we show implicates the pseudo vector potential associated with in-plane strain in moiré band formation.

Bifunctional activity and theoretical study of transition metal molybdates for hydrogen and oxygen evolution reaction

Effective, sturdy and cheap electrocatalysts are extremely desirable for water electrolysis. In this work, transition metal molybdates (MMoO4, M = Fe, Co, Ni) with extraordinary oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) in basic electrolyte solution was reported. β-Fe2(MoO4)3 catalyst exhibits better electrocatalytic performance and robustness for both HER and OER compared to NiMoO4 and CoMoO4. Theoretical study (DFT calculation) disclose that the Fe atoms increase the energy states near the Fermi level in β-Fe2(MoO4)3 which makes it more conductive leading to superior OER and HER activity. Compared to CoMoO4 and NiMoO4, β-Fe2(MoO4)3 have well defined multiple Mo 4d orbitals at the conduction band. These are empty states in conduction band, ready to receive the electrons. Further, the computed overpotential values for NiMoO4, CoMoO4, and β-Fe2(MoO4)3 surfaces follow the trend, β-Fe2(MoO4)3 < NiMoO4 < CoMoO4, corroborating with the experimental results.

Unraveling Electron Dynamics in p-type Indium Phosphide (100): A Time-Resolved Two-Photon Photoemission Study.

Renewable ("green") hydrogen production through direct photoelectrochemical (PEC) water splitting is a potential key contributor to the sustainable energy mix of the future. We investigate the potential of indium phosphide (InP) as a reference material among III-V semiconductors for PEC and photovoltaic (PV) applications. The p(2 × 2)/c(4 × 2)-reconstructed phosphorus-terminated p-doped InP(100) (P-rich p-InP) surface is the focus of our investigation. We employ time-resolved two-photon photoemission (tr-2PPE) spectroscopy to study electronic states near the band gap with an emphasis on normally unoccupied conduction band states that are inaccessible through conventional single-photon emission methods. The study shows the complexity of the p-InP electronic band structure and reveals the presence of at least nine distinct states between the valence band edge and vacuum energy, including a valence band state, a surface defect state pinning the Fermi level, six unoccupied surface resonances within the conduction band, as well as a cluster of states about 1.6 eV above the CBM, identified as a bulk-to-surface transition. Furthermore, we determined the decay constants of five of the conduction band states, enabling us to track electron relaxation through the bulk and surface conduction bands. This comprehensive understanding of the electron dynamics in p-InP(100) lays the foundation for further exploration and surface engineering to enhance the properties and applications of p-InP-based III-V-compounds for, e.g., efficient and cost-effective PEC hydrogen production and highly efficient PV cells.

STRUCTURAL, ELECTRONIC AND MAGNETIC PROPERTIES OF VANADIUM DOPED DELAFOSSITE CUGAO2: AN AB INITIO STUDY

Delafossite copper gallium oxide (CuGaO2) is one of the most important copper-based delafossite materials reported. It has variety of applications that include but are not limited to; photo catalysis, dye-sensitized solar cells. However, due to the wide band gap of this material, it appears very attractive as transparent conductive oxide (TCO). Thus, it is very important and applicable in optoelectronic device technologies. In this paper, the structural, electronic and magnetic properties of vanadium (V) doped delafossite CuGaO2 are investigated using first principle study based on density functional theory (DFT) as implemented in the QUANTUM ESPRESSO simulation package. We used Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) exchange-correlation scheme for the undoped and vanadium (V) doped structures. There is no structural transition after the doping. The results indicated that the V doping reduced the band gap of the undoped delafossite CuGaO2 by 0.8 eV. It also contributed more to the conduction band states. However, our results also revealed that the 50 % V doping induced significant changes to the magnetic properties of the undoped CuGaO2. It was found that the undoped CuGaO2 is slightly paramagnetic similar to the same group member CuAlO2, whereas the V doped CuGaO2 system is slightly ferromagnetic. This result is in agreement with previous literature concerning the effect of doping semiconductor material with magnetic metals. Thus, based on our results, V doped CuGaO2 material may be considered as an important candidate for spintronics and other related applications.

Analyzing photoionization cross-sectional modulation in CdSe/CdS core–shell nanodots: Impact of strain and applied electric field

The role of strain in material properties is well-established, serving as a tool for altering atomic positions and defect formation, adjusting electronic structures and lattice vibrations, and influencing phase transitions, physical characteristics, and chemical properties. In this study, we conducted theoretical calculations of the binding energy and photoionization cross section (PCS) within a spherical core/shell quantum dot (CSQD) for the different transitions between the ground state of a donor impurity and the four low-lying conduction band states. During our study, we employed the finite element method to determine the energy levels and wave functions of the system within the effective mass approximation. Subsequently, we investigated the changes in PCS and binding energy while varying shell width under the influence of an applied electric field, considering both cases with and without the effect of strain. The strain effect was incorporated based on Hooke's law, and we developed specific expressions and utilized the continuum linear elasticity mechanical model for a single spherically symmetric shell. The results demonstrate that the strain correction enhances the binding energy of the four low-lying energy levels, leading to a shift of the PCS peaks toward higher energies. Conversely, the application of an external electric field has varying effects depending on the specific transition being considered. We compared our theoretical results with available experimental data and found them to be in good agreement. The pronounced blue-shift and substantial enhancement in magnitude of PCS spectra concerning shell width, electric field, and strain make CSQDs highly promising candidates for applications in adjustable nano-optoelectronic devices.

Terahertz linear/non-linear anomalous Hall conductivity of moiré TMD hetero-nanoribbons as topological valleytronics materials

Twisted moiré van der Waals heterostructures hold promise to provide a robust quantum simulation platform for strongly correlated materials and realize elusive states of matter such as topological states in the laboratory. We demonstrated that the moiré bands of twisted transition metal dichalcogenide (TMD) hetero-nanoribbons exhibit non-trivial topological order due to the tendency of valence and conduction band states in K valleys to form giant band gaps when spin-orbit coupling (SOC) is taken into account. Among the features of twisted WS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}/MoS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document} and WSe2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}/MoSe2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}, we found that the heavy fermions associated with the topological flat bands and the presence of strongly correlated states, enhance anomalous Hall conductivity (AHC) away from the magic angle. By band analysis, we showed that the topmost conduction bands from the ± K-valleys are perfectly flat and carry a spin/valley Chern number. Moreover, we showed that the non-linear anomalous Hall effect in moiré TMD hetero-nanoribbons can be used to manipulate terahertz (THz) radiation. Our findings establish twisted heterostructures of group-VI TMD nanoribbons as a tunable platform for engineering topological valley quantum phases and THz non-linear Hall conductivity.

Electronic, optical and charge transport properties of Zn-porphyrin-C60 MOFs: a combined periodic and cluster modeling.

Density functional theory (DFT) calculations were performed on the 5,15 meso-positions of nine porphyrin-containing MOFs; Zn2(TCPB)-(NMe2-ZnP); (H4TCPB = 1,2,4,5-tetrakis(4-carboxyphenyl)benzene), (NMe2-ZnP = [5,15-bis[(4-pyridyl)-ethynyl]-10,20-bis-(dimethylamine) porphinato]zinc(II)) functionalized with nitrogen-, oxygen-, and sulfur-containing groups to study their effects on the electronic, optical and transport properties of the materials. The properties of these materials have also been investigated by encapsulating fullerene (C60) in their pores (C60@MOFs). The results indicate that the guest C60 in the MOF generates high photoconductivity through efficient porphyrin/fullerene donor-acceptor (D-A) interactions, which are facilitated by oxygen and sulfur functionalities. DFT calculations show that C60 interacts favorably in MOFs due to negative Eint values. Encapsulated C60 molecules modify the electronic band structure, affecting the conduction band and unoccupied states of MOFs corresponding to C60 p orbitals. TD-DFT calculations show that incorporating C60 promotes D-A interactions in MOFs, leading to charge transfer in the near-infrared and visible photoinduced electron transfer (PET) from porphyrins to C60. Nonequilibrium Green's function-based calculations for MOFs with sulfur group, with and without C60, performed using molecular junctions with Au(111)-based electrodes show increased charge transport for the doped MOF. These insights into tuning electronic/optical properties and controlling charge transfer can aid in the design of new visible/near-infrared MOF-based optoelectronic devices.

Unraveling the effect of pressure on structural phase transition, electronic, and optical properties of Hf1-xSixO2 (x = 0, 0.03, 0.06, 0.09): A first-principles investigation

The non-centrosymmetric phase of HfO2 with excellent Si compatibility has great importance in integrated photonic circuits, non-volatile memory, and ferroelectric field effect transistors. We report a theoretical study of pressure-induced phase transition from a centrosymmetric m-HfO2 to non-centrosymmetric o-HfO2 with Si doping. The reported phase transition pressures, i.e. 15, 14, 8, and 8 GPa for x = 0, 0.03, 0.06, and 0.09, respectively, for Hf1-xSixO2 are in excellent agreement with available experimental results. With increasing Si concentrations, the transition pressures reduce significantly, which is explained in terms of bond length and charge transfer. The thermal stability of the obtained o-HfO2 phase is examined via ab-initio molecular dynamics up to its synthesis temperature. The negative formation energy also confirms its thermodynamical stability. Density of states indicates the noticeable appearance of Si states in the lower conduction band and an increase in the extent of hybridization between Hf-5d, O-2p, and Si-2p atomic states. The doping changes the nature of band gap from indirect to direct, concurrently reducing the magnitude. The o-HfO2 shows a low value of static dielectric constant, which results in a smaller refractive index (1.82) and lower reflectivity in the infrared and visible regions.