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Journal ArticleDOI: 10.1088/0957-4484/14/7/320

Size dependence of optical properties in solution-grown Pb1?xFexS nanoparticle films

01 Jul 2003-Nanotechnology (IOP Publishing)-Vol. 14, Iss: 7, pp 809-812
Abstract: The optical band gap (Eg) of Pb1−xFexS solution-grown nanoparticle films was varied from 2.65 to 2.22 eV with an increase in iron concentration 0.25 ≤ x ≤ 0.75 in films grown at fixed pH and temperature by the chemical bath deposition method. The presence of excitonic structure in the ternary Pb1−xFexS for x ≥ 0.50 suggests increasing binding energy with increase in iron concentration in the films. A shift of excitonic peak towards higher energy with an increase in iron concentration is also observed.

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Topics: Chemical bath deposition (61%), Binding energy (59%), Band gap (56%) ...read more
Citations
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Journal ArticleDOI: 10.1016/J.JALLCOM.2010.01.135
Abstract: In this paper, we report on the modification of optical band gap of PbS nanostructured films over a wide spectral range (∼475–1000 nm) due to in situ Cd-doping and size confinement The films investigated in this study are grown by chemical bath deposition (CBD) at different temperatures and the doping was conducted for a fixed impurity concentration The PbS films grown under optimal deposition conditions are found to crystallize in face centered cubic (fcc) structure with an average crystallite size in the range of 22–27 nm The estimated optical band gap was in the range of 122–142 eV, for films grown at different temperatures Doping was found to influence the film growth and results in a reduction of crystallite size (down to 9 nm) Consequently, quantum size effect becomes pronounced in the Cd-doped PbS films, which lead to a significant enhancement in the optical band gap (up to 261 eV) X-ray photoelectron spectroscopy analysis confirms the substitutional doping of Cd into PbS lattice Band gap modification due to quantum confinement and formation of ternary PbCdS are addressed

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Topics: Band gap (61%), Chemical bath deposition (57%), Thin film (53%) ...read more

64 Citations


Journal ArticleDOI: 10.1016/J.IJHYDENE.2010.04.057
Abstract: Alkali-earth metaniobate compounds, ANb 2 O 6 (A = Ca, Sr, Ba), were prepared by the conventional solid-state reaction route and their electronic band structures and photocatalytic activities were investigated The prepared powders were characterized using X-ray diffraction (XRD), field-emission electron microscopy (FE-SEM), UV–vis diffuse reflectance spectroscopy, and fluorescence spectroscopy It was found that the particle sizes (∼1 μm) and BET surface areas (∼1 m 2 /g) of the metaniobate compounds were nearly identical From the electronic band structure calculations, however, the band-gap energies of these metaniobate compounds were found to be in the order of CaNb 2 O 6 > SrNb 2 O 6 > BaNb 2 O 6 These calculated band-gap energies were consistent with those estimated from the UV–vis diffuse reflectance spectra Moreover, the conduction-band edge (reduction potential) of SrNb 2 O 6 calculated from the electronegativity data was higher than those of CaNb 2 O 6 and BaNb 2 O 6 The photoluminescence spectra revealed that CaNb 2 O 6 exhibited a strong blue luminescence emission (at 300K), while no obvious emissions were observed in either SrNb 2 O 6 or BaNb 2 O 6 The luminescence behaviors of these metaniobate compounds and their band structure variations originating from their crystal structures play an important role in their photocatalytic activity for the evolution of H 2 from pure water SrNb 2 O 6 , which has a higher conduction-band edge potential than the other compounds, exhibited higher photocatalytic activity

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59 Citations


Open accessJournal ArticleDOI: 10.3762/BJNANO.3.50
A. Begum1, Amir Hussain, Atowar RahmanInstitutions (1)
Abstract: Nanocrystalline lead selenide (PbSe) thin films were prepared on glass substrates by a chemical bath deposition method, using sodium selenosulfate (Na2SeSO3) as a source of Se2− ions, and lead acetate as a source of Pb2+ ions. Trisodium citrate (TSC) was used as a complexing agent. PbSe films were prepared at various deposition temperatures while the pH value was kept fixed at 11, and the effect on the resulting film properties was studied by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and optical absorption studies. The structural parameters, such as the lattice constant (a), crystallite size (D), dislocation density (ρ) and microstrain (e) were evaluated from the XRD spectra. It was found that average crystallite size, as calculated from Scherrer’s formula, increased from 23 to 33 nm as the deposition temperature was varied from 303 to 343 K. The dislocation density and microstrain were found to vary inversely with the crystallite size, whereas the lattice constant was found to increase with an increase in crystallite size. The optical absorption spectra of the nanocrystalline PbSe films showed a blue shift, and the optical band gap (Eg) was found to increase from 1.96 to 2.10 eV with the decrease in crystallite size.

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Topics: Nanocrystalline material (67%), Chemical bath deposition (59%), Crystallite (57%) ...read more

54 Citations


Journal ArticleDOI: 10.1016/J.VACUUM.2005.08.021
10 Mar 2006-Vacuum
Abstract: Deposition of polycrystalline copper (I) selenide thin films onto glass substrates at relatively low temperature (95 °C) have been carried out by chemical route using optimized preparative conditions. The XRD pattern confirmed the formation of copper (I) selenide semiconducting films with orthorhombic structure. A direct-type transition with band gap energy of 1.73 eV was reported from optical absorption studies. p-Type behavior confirmed from sign of thermally induced voltage (thermo-emf), which may find interesting applications in hetero-junction solar cells as an absorber layer.

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Topics: Copper indium gallium selenide solar cells (67%), Selenide (65%), Thin film (58%) ...read more

40 Citations


Journal ArticleDOI: 10.1016/J.ELECTACTA.2013.03.044
Abstract: PbS thin films were deposited on transparent conducting substrates by pulse electrodeposition. Stoichiometric and highly adherent films were obtained by optimizing the deposition parameters such as pulse duration, deposition and dissolution potentials. Structural properties of the films were studied using XRD, and HRTEM techniques. The film consists of nanocrystals with size in the range 2–20 nm. Using atomic resolution images an atomic model with cuboctahedral morphology was proposed for the PbS crystals. The stability of the PbS nanoparticles was attributed to the surface configuration of Pb and S atoms causing low surface energy. SEM and AFM surface analysis indicated a uniform and void free surface with agglomerations of crystals with an average size in the order of 250 nm. Appearance of the 2LO mode in the Raman spectra revealed good crystalline quality of the film, and the characteristic bands were assigned in agreement with the mineral galena. The XPS spectrum in the binding energy region of sulfur shows the presence of S in 2 different environments; S 2p3/2 at 160.4 eV which is due to the sulfur in sulfide (PbS), and a second peak at higher binding energy of 161.64 eV which can be due to Pb–S–O and the Pb 4f 7/2 peak at binding energy 138 eV indicate the presence of traces of PbO. However, Raman and XRD analysis showed no evidence of PbO and PbSO 3 . From the transmittance spectrum the band gap of the film was estimated as 0.74 eV. The resistivity of the film was 2 × 10 4 ohm-cm and the films were photosensitive.

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Topics: Thin film (56%), Lead sulfide (55%), Surface energy (54%) ...read more

36 Citations


References
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Journal ArticleDOI: 10.1063/1.453325
Abstract: The transition of PbS from molecular to bulk form has been observed in polymer films. As the particle size decreases the band gap shifts to the blue and eventually approaches the transition energy of the first allowed excited state, X→A, of a PbS molecule. Discrete absorption bands also appear. The electron‐hole‐in‐a‐box model with effective mass approximation cannot explain the observed size dependence. We have developed two theoretical models, both including the effect of band nonparabolicity, that successfully explain the observed size dependence down to about 25 A.

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Topics: Band gap (55%), Electronic band structure (52%), Excited state (50%)

772 Citations



Open accessJournal ArticleDOI: 10.1103/PHYSREVB.36.4215
15 Sep 1987-Physical Review B
Abstract: Optical band gaps, ${E}_{g}$, up to 0.5 eV higher than in single-crystal samples, are observed for chemically deposited films of CdSe and explained in terms of a quantum-size effect, whereby the electrons are localized in individual crystallites. The increase in ${E}_{g}$ depends strongly on deposition temperature, with the greatest increase obtained at the lowest temperature. Annealing at temperatures above the deposition temperature causes a decrease in ${E}_{g}$; this decrease is stronger at higher annealing temperature. Structural studies of the as-deposited layers showed them to be composed of microcrystalline, cubic CdSe, and electron microscopy resolved them into individual crystallites of typically 40--80-A\r{} diameter, depending on deposition temperature. This is the first example reported of a three-dimensional quantum-size effect in a film.

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Topics: Cadmium selenide (55%), Band gap (54%), Annealing (metallurgy) (53%) ...read more

279 Citations


Journal ArticleDOI: 10.1063/1.451119
Abstract: Metal selenide clusters have been made and characterized, using the arrested precipitation colloidal technique. A comparison of sulfide and selenide spectra enables observation of the effect of changes in the highest occupied molecular orbitals upon cluster electronic properties. The first and second excited electronic states are both observed as a function of size in ZnSe clusters. The systematic dependence of the spectra lead to assignment of the higher state to a 1S‐type hole based upon the split‐off valence band. It is shown that the energy spectrum of discrete hole states is controlled by the spin‐orbit energy and the isotropic hole mass in small, highly symmetrical clusters. This result contrasts with the heavy hole and light hole states observed for planar confinement. In ≂ 20 A diameter ZnS clusters, there is a strong vibronic temperature dependence in the excited state spectra, while in clusters of smaller gap materials such vibronic effects are very minor. We conjecture that lifetime broadening ...

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Topics: Excited state (56%), Electronic structure (51%), Selenide (51%) ...read more

235 Citations


Journal ArticleDOI: 10.1103/PHYSREVB.41.6079
15 Mar 1990-Physical Review B
Abstract: The lowest excited electronic state of small CdSe crystallites is calculated within a tight-binding approximation. Two types of crystal shape and a spatially varying dielectric constant are considered. The results are found to compare favorably to recent experiments.

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Topics: Excited state (59%), Electronic structure (55%), Electron hole (54%) ...read more

137 Citations


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