Effect of Passivation on Stability and Electronic Structure of Bulk-like ZnO Clusters

Electronic structure of nearly stoichiometric and nonstoichiometric clusters of ZnO having bulk-like wurtzite geometry passivated with fictitious hydrogen atoms are comparatively analyzed for structural evolution using density functional theory-based electronic structure calculations. A parameter, average binding energy per atomic number (ABE-number), is introduced for better insight of structural evolution. The stability of a cluster is determined by binding energy per atom and ABE-number, whereas structural evolution on the basis of spin-polarized energy spectrum is studied via site projected partial density of states (l-DOS). The overall structural evolution is mapped for bare and passivated ZnO clusters to l-DOS. The study has established a correlation between the stability of clusters and their l-DOS. O-excess and O-surfaced clusters are found to be more stable. The HOMO–LUMO gap varies from 0 to 6.3 eV by tuning the size, composition, and surface termination of the clusters. Present results reported for clusters of sizes up to ∼1 nm can pave a path for formulating strategies for experimental synthesis of ZnO nanoparticles for tuning the HOMO–LUMO gap

Ethylenediamine-Mediated Wurtzite Phase Formation in ZnS

The usual high temperature wurtzite phase of ZnS was successfully obtained at low temperature (170 °C) in the presence of ethylenediamine (EN) as the soft template. X-ray diffraction and Raman spectroscopy analysis confirmed the EN-mediated phase transformation (zinc blende to wurtzite) of ZnS. X-ray photoelectron spectroscopy (XPS) showed that all the samples were sulfur deficient. A high temperature X-ray diffraction (XRD) study showed that ZnS samples, both EN-mediated and without EN, retained their phases except small changes in the unit cell dimension. Besides the EN-mediated phase transition, morphology transformations from nearly spherical shape to nanorods are also observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The coupling between EN molecules with ZnS is confirmed by Fourier transform infrared spectroscopy. A significant reduction in the phase transition temperature of ZnS has been achieved as compared to the bulk transition temperature (1020 °C). Mechanisms of phase transformation have been discussed. The density functional theory (DFT) supports the rod formation and wurtzite structure in the presence of nitrogen-terminated ZnS surface

Ethylenediamine-Mediated Wurtzite Phase Formation in ZnS

The usual high temperature wurtzite phase of ZnS was successfully obtained at low temperature (170 °C) in the presence of ethylenediamine (EN) as the soft template. X-ray diffraction and Raman spectroscopy analysis confirmed the EN-mediated phase transformation (zinc blende to wurtzite) of ZnS. X-ray photoelectron spectroscopy (XPS) showed that all the samples were sulfur deficient. A high temperature X-ray diffraction (XRD) study showed that ZnS samples, both EN-mediated and without EN, retained their phases except small changes in the unit cell dimension. Besides the EN-mediated phase transition, morphology transformations from nearly spherical shape to nanorods are also observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The coupling between EN molecules with ZnS is confirmed by Fourier transform infrared spectroscopy. A significant reduction in the phase transition temperature of ZnS has been achieved as compared to the bulk transition temperature (1020 °C). Mechanisms of phase transformation have been discussed. The density functional theory (DFT) supports the rod formation and wurtzite structure in the presence of nitrogen-terminated ZnS surface

Ethylenediamine-Mediated Wurtzite Phase Formation in ZnS

The usual high temperature wurtzite phase of ZnS was successfully obtained at low temperature (170 °C) in the presence of ethylenediamine (EN) as the soft template. X-ray diffraction and Raman spectroscopy analysis confirmed the EN-mediated phase transformation (zinc blende to wurtzite) of ZnS. X-ray photoelectron spectroscopy (XPS) showed that all the samples were sulfur deficient. A high temperature X-ray diffraction (XRD) study showed that ZnS samples, both EN-mediated and without EN, retained their phases except small changes in the unit cell dimension. Besides the EN-mediated phase transition, morphology transformations from nearly spherical shape to nanorods are also observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The coupling between EN molecules with ZnS is confirmed by Fourier transform infrared spectroscopy. A significant reduction in the phase transition temperature of ZnS has been achieved as compared to the bulk transition temperature (1020 °C). Mechanisms of phase transformation have been discussed. The density functional theory (DFT) supports the rod formation and wurtzite structure in the presence of nitrogen-terminated ZnS surface

Band Gap Bowing at Nanoscale: Investigation of CdS_<i>x</i>Se_1–<i>x</i> Alloy Quantum Dots through Cyclic Voltammetry and Density Functional Theory

The band gap bowing effect in oleic acid-stabilized CdS_<i>x</i>Se_1–<i>x</i> alloy quantum dots (Q-dots) with varying composition has been studied experimentally by means of cyclic voltammetry and theoretically using density functional theory based calculations. Distinct cathodic and anodic peaks observed in the cyclic voltammograms of diffusing quantum dots alloy are attributed to the respective conduction and valence band edges. The quasi-particle gap values determined from voltammetric measurements are compared with interband transition peaks in UV–vis and PL spectra. Electronic structure for alloy Q-dots is determined computationally with projector augmented wave method for a particular size of dots. The band gap bowing is observed predominantly in the conduction band states. The bowing parameter determined experimentally (0.45 eV) has been found to be in good agreement with the one estimated from DFT (0.43 eV)

Electronic Structure of Visible Light-Driven Photocatalyst δ‑Bi₁₁VO₁₉ Nanoparticles Synthesized by Thermal Plasma

Size confinement for tailoring of electronic structures can in principle be explored for enhancement of photocatalytic properties. In the present work, vanadium-doped bismuth oxide nanoparticles, with an average particle size of 36 nm, are synthesized for the first time, using the thermal plasma method, in large scale with high yield to explore for photocatalytic applications. The electronic and crystallographic structures of the sample are studied experimentally and theoretically. Systematic investigations of the electronic structure of the fluorite type cubic phase of Bi₁₁VO₁₉ nanoparticles are reported for the first time. Enhancement is observed in the photocatalytic activity as compared to other delta phases of bismuth vanadate. The valence band is found to comprise mainly of O 2p states, whereas the conduction band arises from V 3d states giving rise to a band gap value of 2.26 eV. Absence of excess O in δ-Bi₂O₃ results in shrinking of the band gap because of O 2p, Bi 6s and 6p states from the surrounding atoms at doping sites. Bi₁₁VO₁₉ nanoparticles show an efficient visible light absorption and exhibit excellent photodegradation properties of methylene blue solution under visible light irradiation