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Gotthard Seifert - One of the best experts on this subject based on the ideXlab platform.
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Optical Properties of Cadmium Sulfide Clusters
The Journal of Physical Chemistry B, 2003Co-Authors: Jan-ole Joswig, Gotthard Seifert, Thomas A. Niehaus, Michael SpringborgAbstract:Using a time-dependent extension of a density-functional tight-binding method, we have calculated the excitation spectra of stoichiometric Cadmium Sulfide clusters up to 144 atoms. The spectra show a strong dependency of the lowest unoccupied molecular orbitals on the structural properties of the clusters, especially on the number of single-bonded surface atoms. Furthermore, we calculated the single-particle energy eigenvalues for a number of clusters up to 440 atoms without structural relaxation. Here, with increasing cluster size the gap between highest occupied and lowest unoccupied molecular orbitals (HOMO/LUMO gap) is decreasing asymptotically toward the bulk band gap of Cadmium Sulfide for clusters with no single-bonded surface atoms and tending to a zero gap for clusters with a large number of single-bonded surface Cadmium atoms. The latter is caused by low-lying Cadmium 5s states.
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Structural and Electronic Properties of Cadmium Sulfide Clusters
The Journal of Physical Chemistry B, 2000Co-Authors: Jan-ole Joswig, Michael Springborg, Gotthard SeifertAbstract:Crystalline Cadmium Sulfide is a semiconductor for which the wurtzite and zinc blende structures are energetically almost degenerate. Due to quantum-confinement effects, it is possible to tune the optical properties of finite Cadmium Sulfide clusters by varying their size. Here, we report results of a theoretical study devoted to the properties of stoichiometric CdnSn clusters as a function of their size n. We have optimized the structure, whereby our initial structures are spherical parts of either of the two crystal structures, and we have studied systems with up to almost 200 atoms. The calculations were performed by using a simplified LCAO-DFT-LDA scheme. The results include the structure, electronic energy levels (in particular the frontier orbitals HOMO and LUMO), and stability as a function of size. The results allow for a unique definition of a surface region. The Mulliken populations indicate that the bonds within this region are more ionic than in the bulk. Furthermore, whereas the HOMO is deloc...
Michael Springborg - One of the best experts on this subject based on the ideXlab platform.
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Optical Properties of Cadmium Sulfide Clusters
The Journal of Physical Chemistry B, 2003Co-Authors: Jan-ole Joswig, Gotthard Seifert, Thomas A. Niehaus, Michael SpringborgAbstract:Using a time-dependent extension of a density-functional tight-binding method, we have calculated the excitation spectra of stoichiometric Cadmium Sulfide clusters up to 144 atoms. The spectra show a strong dependency of the lowest unoccupied molecular orbitals on the structural properties of the clusters, especially on the number of single-bonded surface atoms. Furthermore, we calculated the single-particle energy eigenvalues for a number of clusters up to 440 atoms without structural relaxation. Here, with increasing cluster size the gap between highest occupied and lowest unoccupied molecular orbitals (HOMO/LUMO gap) is decreasing asymptotically toward the bulk band gap of Cadmium Sulfide for clusters with no single-bonded surface atoms and tending to a zero gap for clusters with a large number of single-bonded surface Cadmium atoms. The latter is caused by low-lying Cadmium 5s states.
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Structural and Electronic Properties of Cadmium Sulfide Clusters
The Journal of Physical Chemistry B, 2000Co-Authors: Jan-ole Joswig, Michael Springborg, Gotthard SeifertAbstract:Crystalline Cadmium Sulfide is a semiconductor for which the wurtzite and zinc blende structures are energetically almost degenerate. Due to quantum-confinement effects, it is possible to tune the optical properties of finite Cadmium Sulfide clusters by varying their size. Here, we report results of a theoretical study devoted to the properties of stoichiometric CdnSn clusters as a function of their size n. We have optimized the structure, whereby our initial structures are spherical parts of either of the two crystal structures, and we have studied systems with up to almost 200 atoms. The calculations were performed by using a simplified LCAO-DFT-LDA scheme. The results include the structure, electronic energy levels (in particular the frontier orbitals HOMO and LUMO), and stability as a function of size. The results allow for a unique definition of a surface region. The Mulliken populations indicate that the bonds within this region are more ionic than in the bulk. Furthermore, whereas the HOMO is deloc...
Jan-ole Joswig - One of the best experts on this subject based on the ideXlab platform.
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Optical Properties of Cadmium Sulfide Clusters
The Journal of Physical Chemistry B, 2003Co-Authors: Jan-ole Joswig, Gotthard Seifert, Thomas A. Niehaus, Michael SpringborgAbstract:Using a time-dependent extension of a density-functional tight-binding method, we have calculated the excitation spectra of stoichiometric Cadmium Sulfide clusters up to 144 atoms. The spectra show a strong dependency of the lowest unoccupied molecular orbitals on the structural properties of the clusters, especially on the number of single-bonded surface atoms. Furthermore, we calculated the single-particle energy eigenvalues for a number of clusters up to 440 atoms without structural relaxation. Here, with increasing cluster size the gap between highest occupied and lowest unoccupied molecular orbitals (HOMO/LUMO gap) is decreasing asymptotically toward the bulk band gap of Cadmium Sulfide for clusters with no single-bonded surface atoms and tending to a zero gap for clusters with a large number of single-bonded surface Cadmium atoms. The latter is caused by low-lying Cadmium 5s states.
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Structural and Electronic Properties of Cadmium Sulfide Clusters
The Journal of Physical Chemistry B, 2000Co-Authors: Jan-ole Joswig, Michael Springborg, Gotthard SeifertAbstract:Crystalline Cadmium Sulfide is a semiconductor for which the wurtzite and zinc blende structures are energetically almost degenerate. Due to quantum-confinement effects, it is possible to tune the optical properties of finite Cadmium Sulfide clusters by varying their size. Here, we report results of a theoretical study devoted to the properties of stoichiometric CdnSn clusters as a function of their size n. We have optimized the structure, whereby our initial structures are spherical parts of either of the two crystal structures, and we have studied systems with up to almost 200 atoms. The calculations were performed by using a simplified LCAO-DFT-LDA scheme. The results include the structure, electronic energy levels (in particular the frontier orbitals HOMO and LUMO), and stability as a function of size. The results allow for a unique definition of a surface region. The Mulliken populations indicate that the bonds within this region are more ionic than in the bulk. Furthermore, whereas the HOMO is deloc...
Qiang Ye - One of the best experts on this subject based on the ideXlab platform.
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γ-Radiation synthesis of silver–polystyrene and Cadmium Sulfide–polystyrene nanocomposite microspheres
Materials Letters, 2003Co-Authors: Dazhen Wu, Zhicheng Zhang, Xuewu Ge, Yuhong Huang, Qiang YeAbstract:Abstract Silver–polystyrene and Cadmium Sulfide–polystyrene nanocomposite microspheres were fabricated by γ-ray irradiation. Dispersion polymerization induced by γ-ray irradiation was exploited to prepare monodispersed polystyrene microspheres. Silver (Ag) and Cadmium Sulfide (CdS) nanoparticles were generated on the polystyrene microsphere surface via subsequent reduction of Ag+ by γ-ray irradiation, as well as by precipitation reaction of Cd2+ and S2−, which was released from the decomposition of Na2S2O3 upon γ-ray irradiation. The products were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. The TEM images demonstrate that well-dispersed silver (∼11 nm) and Cadmium Sulfide nanoparticles (∼23 nm) were attached to the surface of polystyrene microspheres (∼380 nm).
A. S. K. Sinha - One of the best experts on this subject based on the ideXlab platform.
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Activity of Cadmium Sulfide Photocatalysts for Hydrogen Production from Water: Role of Support
Industrial & Engineering Chemistry Research, 1999Co-Authors: Manjit K. Arora, Shail Upadhyay, Namita Sahu, A. S. K. SinhaAbstract:Alumina-supported Cadmium Sulfide photocatalysts for reduction of water to hydrogen were prepared by different techniques and characterized. The band gap, the dispersion of Cadmium Sulfide, and the contact between Cadmium Sulfide and alumina are affected by the preparation technique. Those preparation techniques that promote better dispersion of Cadmium Sulfide and give rise to a chemical interaction between Cadmium Sulfide and alumina impart a superior activity to the catalyst. The chemical interaction leads to decoration of Cadmium Sulfide surface by alumina which results in an intimate contact between them. Catalyst prepared by coprecipitation shows the intimate contact but has a poor dispersion of Cadmium Sulfide, whereas impregnation of alumina hydrogel results in a catalyst having both intimate contact between alumina and Cadmium Sulfide and better dispersion of Cadmium Sulfide; consequently, this results in enhanced activity.
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Active Cadmium Sulfide Photocatalysts for Hydrogen Production from Water
Industrial & Engineering Chemistry Research, 1998Co-Authors: Manjit K. Arora, A. S. K. Sinha, Shail UpadhyayAbstract:Cadmium Sulfide photocatalysts for H2 production from water using visible light were prepared by different techniques, i.e., liquid−liquid, gas−liquid, and solid−liquid reactions. The crystallite size and distribution, band gap, and stoichiometric composition of Cadmium Sulfide and consequently the activity were affected by the preparation technique. The activity of Cadmium Sulfide showed a strong correlation with its semiconducting (n- or p-type) behavior. Cadmium Sulfide that was prepared by gas−solid reaction had excess interstitial Cadmium ions in the lattice, which had been attributed to its n-type semiconductor behavior and superior activity. The n-type behavior of Cadmium Sulfide has been correlated to its stoichiometry.
