Surface and interface optical phonon modes and electron-phonon interaction in a multi-shell spherical system

Within the framework of the dielectric continuum model, interface optical(IO) and surface optical(SO) phonon modes and the Fr?hlich electron-IO (SO) phonon interaction Hamiltonian in a multi-shell spherical system were derived and studied. Numerical calculation on CdS/HgS/H₂O and CdS/HgS/CdS/H₂O spherical systems have been performed. Results reveal that there are two IO modes and one SO mode for the CdS/HgS/H₂O system, one SO mode and four IO modes whose frequencies approach the IO phonon frequencies of the single CdS/HgS heterostructure with the increasing of the quantum number l for CdS/HgS/CdS/H₂O. It also showed that smaller l and SO phonon compared with IO phonon, have more significant contribution to the electron-IO (SO) phonon interaction. Received 16 October 2001 and Received in final form 23 January 2002 Published online 25 June 2002     

Electron-phonon interaction in spherical multilayer nanoheterostructures

The complete hamiltonian of an electron-phonon system in the second quantization representation for a complex spherical nanoheterostructure with an arbitrary number of semiconducting layers is obtained in a polarized continuum model for bounded volume and interface phonons. The energy of the electron ground state is calculated using the experimentally realized CdS/HgS/H₂O system as an example. The cause of the nonmonotonic dependence of the shift in the electron ground state on the HgS thickness is established as due to the interaction with bounded phonons. Fiz. Tverd. Tela (St. Petersburg) 39, 1109–1113 (June 1997)     

Optical and IR study of CdS nanoparticles dispersed in a new confined p-phenylenevinylene

In the present study we have synthesized CdS semiconducting quantum dots by reverse micelle method using dodecanthiol (C₁₂H₂₆S) as the capping agent. The synthetic medium consists of a quaternary water/Sodium dodecyl sulfate (SDS)/buta-1-ol/hexane microemulsion. The size of the particles was controlled by changing the molar ratio W=[H₂O]/[SdS], where [H₂O] and [SdS] are the molar concentrations in hexane of water and SdS respectively. The CdS nanoparticles were embedded in a new PPV derivate named Fluorinated Bisphenol A P-phenylenevinylene (BPAF-PPV). Fourier transform infrared spectroscopy (FT-IR) showed a strong interaction of thiol groups with CdS nanoparticles. Blue shift of the optical absorption onset is observed due to quantum size effect. The band gap and particle sizes of the nanoparticles were deduced from optical absorption spectra and the use of an effective mass approximation (EMA) model. Photoluminescence spectroscopy evidenced a charge transfer process via the interface between BPAF-PPV/CdS nanoparticles.     

CdS/HgS/CdS球状纳米系统高能级斯塔克线度效应

研究了在层间作用和电场作用下球状纳米系统的电子能量和波函数.以CdS/HgS/CdS球状纳米系统为例,讨论了层间作用、电场和样品线度对高能级斯塔克效应以及谱线频率和强度的影响.结果表明：CdS/HgS/CdS球状纳米系统在外电场作用下发生斯塔克效应的能级分裂规律与氢原子类似,但能级位移量不同.谱线频移与电场强度的平方成正比,多数谱线的频移随线度增大而减小,少数谱线的频移则相反;而层间作用引起谱线的频移随线度增大而减小.除少数谱线外,多数谱线的相对强度随线度增大而减小,层间作用不会改变相对强度随线度的变化趋 关键词： CdS/HgS/CdS球状纳米系统 斯塔克效应 谱线频率 谱线强度     

Electronic spectrum in a quantum double CdS/β-HgS/H2O cylindrical wire

The electronic spectrum in a cylindrical CdS/β-HgS semiconductor heterosystem of the quantum wire type located in an H₂O dielectric medium is investigated. In the energy interval where the levels of both potential wells merge, there is a repulsion effect on the levels (a “bottleneck” effect). The nonmonotonic dependence of the electron and hole spectra on the thickness of the β-HgS film means that in experiments there is an instability of the energy position of the exciton lines in a certain frequency range. Chernovits State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 79–85, May, 1997.     

A photoelectron spectroscopic investigation of the interaction between H2O and oxygen on Ag(110)

The adsorption and reaction of H₂O with adsorbed oxygen atoms on Ag(110) was examined by UPS. In agreement with previous EELS results, H₂O formed multilayers of ice upon adsorption at 140 K. The ice layers could be easily distinguished from monolayer coverages of chemisorbed H₂O (present above 160 K) by UPS. The ice layers produced (1) strong attenuation of the emission from the Ag d-bands, (2) a nearly 2 eV shift of H₂O valence levels to higher binding energy and (3) strong attenuation of emission from the H₂O 3a₁ orbital. H₂O was observed to react stoichiometrically with O(a) above 250 K to produce a pure layer of adsorbed hydroxyl species. The UPS spectra for these species exhibited features at ?5.8 and ?8.7 eV, as well as strong features above the d-bands. These spectra were compared with those for OH(a) on other surfaces, and the difficulties of identifying OH by UPS due to contamination by excess H₂O are discussed.     

Absorptionsspektrum des Ce3+-Ions und Schwingungsspektrum im CeCl3·7H2O und CeCl3·7D2O

The absorption spectra of CeCl₃·7 H₂O, LaCl₃·7 H₂O, CeCl₃·7 D₂O and LaCl₃·7 D₂O have been measured at low temperatures in the region of the 4 f→4 f infrared transitions. The energy levels of the Ce³⁺-ion in these compounds have been derived. The infrared phonon transitions have also been determined from the reflection spectra of these crystals measured in the region between 4000 cm^?1 and 50 cm^?1. Some of the energy levels of the Ce³⁺-ions in the deuterated crystals are shifted for about 10 wavenumbers against those in CeCl₃·7 H₂O. These shifts are probably due to an interaction of the electronic levels with resonant phonon-states in one or the other of the two compounds.     

HgS/CdS/HgS球状纳米系统电子的能量与寿命以及概率分布

建立了HgS/CdS/ HgS球状纳米系统物理模型和电子状态满足的方程.应用S矩阵理论，探讨了 s态电子的能量和寿命以及概率分布随势垒和势阱宽度的变化规律.结果表明：电子能量和寿 命随垒势宽度增大而增大；电子能量随阱宽增大而减小，而寿命随阱宽增大而增大；层间相 互作用对结果有重要影响. 关键词： 球状纳米系统 电子能量和寿命 电子概率分布 势垒势阱宽度     

Interface Optical Phonon Modes and Frohlich Electron-Phonon Interaction Hamiltonian in a Multi-shell Spherical Nanoheterosystem

Under dielectric continuum approximation, interface optical (IO) phonon modes and the Frohlich electron-IO phonon interaction Hamiltonian in a multi-shell spherical nanoheterosystem were derived and studied. Numericalcalculations on three-layer and four-layer CdS/HgS spherical nanoheterosystems have been performed. Results revealthat there are four IO phonon modes for the three-layer system and six IO phonon modes for the four-layer system.On each interface, there are two IO phonon modes, the frequency of one is between WTO,CdS and WLO,CdS, and that ofthe other is between WTO,HgS and WLO,HgS. With the increasing of quantum number l, the frequency of each IO modeapproaches one of the two frequency values of the single CdS/HgS heterostructure, and the potential for each IO modeis more and more localized at a certain interface, furthermore, the coupling between the electron-lO phonons becomes weaker.     

The Dynamic Resistance of CdS/CdSe/ZnS Co-Sensitized TiO2 Solar Cells

Quantum dots' sensitized solar cells (QDSSCs) can create the high-performance and low-cost photovoltaic in the future. In this study, we synthesized the film of TiO₂/CdS/CdSe/ZnS photoanodes by successive ionic layer adsorption reaction (SILAR) method. The absorption spectra, photoluminescent spectra and electrochemical impedance spectra (EIS) of the film TiO₂/CdS/CdSe/ZnS photoanodes show that the structure of energy levels in the conduction band (CB) of photoanode materials CdS, CdSe, and ZnS quantum dots (QDs) can absorb a great number of photons in each region and inject stimulated electrons quickly into the conduction band (CB) of TiO₂. Furthermore, we also studied the influence of the SILAR cycles on the dynamic resistance, the lifetime of electrons in QDSSCs through Nyquist and Bode.     

Hydrothermal preparation and characterization of Cd0.9Mn0.1S nanorods

Cd_0.9Mn_0.1S semiconductor nanorods were successfully prepared by the hydrothermal reaction of CdCl₂·2.5H₂O and MnCl₂·5H₂O with (NH₄)₂S in aqueous solution. Atomic absorption spectrometry (AAS) and energy dispersive spectroscopy (EDS) were used to determine the Mn contents of these complex nanorods. The samples were characterized by scanning electron microscopy (SEM-EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis absorption spectra, photoluminescence (PL) and compared with the undoped CdS nanorods. The results showed that nanostructured multiplex compounds with high aspect ratio were obtained via hydrothermal method. The products showed almost totally rod-like morphology with approximately identical diameter about 20 nm and the maximal length up to 200 nm.     

Photoluminescence and optical characterization of CdS nanoparticles prepared by solid-state method at low temperature

The photoluminescence (PL) and optical properties of CdS nanoparticles prepared by the solid-state method at low temperature have been discussed. The effects of NaCl and anionic surfactant SDBS (sodium dodecylbenzene sulfonate) on the luminescent properties of CdS nanophosphors prepared using this method, without the inert gas or the H₂S environment, were studied separately. The synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM), and energy dispersive X-ray spectroscopy (EDAX). UV–VIS absorption and PL spectra were also studied. XRD studies confirmed the single-phase formation of CdS nanoparticles. TEM micrograph revealed the formation of nearly spherical nanoparticles with a diameter of 2.5 nm. The PL emission for the CdS shows the main peak at 560 nm with a shoulder at 624 nm, with an increase in the PL intensity after the addition of SDBS. The effect of Mn doping on PL intensity has also been investigated. The PL spectra show that the emission intensity decreases as the dopant concentration increases.     

Ab Initio Study on Structures and Vibrational Spectra of M+(H2O)Ar2 (M = Cu,Au)

Previous investigations have shown that it is difficult to acquire the infrared (IR) spectra of M⁺(H₂O) (M?=?Cu, Au) using a single IR photon by attaching an Ar atom to M⁺(H₂O). To explore whether the IR spectra can be obtained using the two Ar atoms tagging method, the geometrical structures, IR spectra and interaction energies are investigated in detail by ab initio electronic structure calculations for M⁺(H₂O)Ar₂ (M?=?Cu, Au) complexes. Two conceivable isomeric structures are found, which result from different binding sites for two Ar atoms. CCSD(T) calculations predict that two Ar atoms are most likely to attach to Cu⁺ for the Cu⁺(H₂O)Ar₂ complex, while the Au⁺(H₂O)Ar₂ complex prefers the isomer in which one Ar atom attaches to an H atom of the H₂O molecule and the other one is bound to Au⁺. Moreover, the calculated binding energies of the second Ar atom are smaller than the IR photon energy, and so it is possible to obtain the IR spectra for both Cu and Au species. The changes in the spectra caused by the attachment of Ar atoms to M⁺(H₂O) are discussed.     

The assignment of quantum numbers in the theoretical spectra of the H2 16O, H2 17O, and H2 18O molecules calculated by variational methods in the region 0–26000 cm−1

Quantum numbers have been assigned in the theoretical spectra of three isotopologues of the water molecule: H₂ ¹⁶O, H₂ ¹⁷O, and H₂ ¹⁸O. The spectra were calculated by variational methods in the region 0–26000 cm^?1 at a temperature of 296 K. For each molecule, the quantum numbers are assigned to more than 28000 levels. The quantum numbers are assigned to 216766, 210679, and 211073 spectral lines of the H₂ ¹⁶O, H₂ ¹⁷O, H₂ ¹⁸O molecules, respectively. The theoretical spectra with the assigned quantum numbers are available in the Internet.     

Adsorption and decomposition of H2O on a K-covered Pt(111) surface

The adsorption of H₂O on clean and K-covered Pt(111) was investigated by utilizing Auger, X-ray and ultra-violet photoemission spectroscopies. The adsorption on Pt(111) at 100–150 K was purely molecular (ice formation) in agreement with previous work. No dissociation of this adsorbed H₂O was noted on heating to higher temperatures. On the other hand, adsorption of H₂O on Pt(111) + K leads to dissociation and to the formation of OH species which were characterized by a work function increase, an O 1s binding energy of 530.9 eV and UPS peaks at 4.7 and 8.7 eV below the Fermi level. The amount of OH formed was proportional to the K coverage for θ_K > 0.06 whereas no OH could be detected for θ? 0.06. Dissociation of H₂O occurred already at T = 100 K, with a sequential appearance of O 1s peaks at 531 and 533 eV representing OH and adsorbed H₂O, respectively. At room temperature and above only the OH species was observed. Annealing of the surface covered with coadsorbed K/OH indicated the high stability of this OH species which could be detected spectroscopically up to 570 K. The adsorption energy of H₂O coadsorbed with K and OH on Pt(111) is increased relative to that of H₂O on Pt. The work function due to this adsorbed H₂O increases whereas it decreases for H₂O on Pt(111). The energy shifts of valence and O1s core levels of H₂O on Pt + K as deduced from a comparison of gas phase and adsorbate spectra are 2.8–4.2 eV compared to ≈ 1.3–2.3 eV for H₂O on Pt (111). This increased relaxation energy shift suggests a charge transfer screening process for H₂O on Pt + K possibly involving the unoccupied 4a₁ orbital of H₂O. The occurrence of this mode of screening would be consistent with the higher adsorption energy of H₂O on Pt + K and with its high propensity to dissociate into OH and H.     

Mixed-solvothermal synthesis of CdS micro/nanostructures and their optical properties

Several novel cadmium sulfide (CdS) micro/nanostructures, including cauliflower-like microspheres, football-like microspheres, tower-like microrods, and dendrites were controllably prepared via an oxalic acid-assisted solvothermal route using ethylene glycol (EG) and H₂O as pure and mixed solvents with different S sources. The as-prepared products were characterized by X-ray powder diffraction (XRD), scanning electronic microscope (SEM) and UV-vis spectrophotometer (UV). It was found that CdS micro/nanostructures can be selectively obtained by varying the composition of solvent, concentration of oxalic acid, and sulfur sources. UV-vis absorption spectra reveal that their absorption properties are shape-dependent. The possible formation process of the CdS micro/nanostructures was briefly discussed. This route provides a facile way to tune the morphologies of CdS over a wide range.     

Effect of CdS nanoparticles on fluorescence from Sm doped SiO2 glass

Sm³⁺ doped CdS nanoparticles have been prepared by sol-gel method. The effect of annealing temperatures and doping concentrations of CdS on the photoluminescence spectra of Sm³⁺ were studied. From the measurement of its optical absorption, three phenomenological Judd-Ofelt intensity parameters (Ω₂, Ω₄, and Ω₆) have been computed and used to parameterize the radiative properties. The influences of CdS on Sm³⁺ ions were studied by fluorescence spectroscopy. The fluorescence spectra revealed that the emission intensity of samarium increased considerably in the presence of CdS nanoparticles. The evaluation of radiative properties of Sm³⁺ containing CdS showed that the ⁴G_5/2→⁶H_7/2 transition in silica matrix had the potential to be a laser transition.     

Enhanced Oxidation Stability of Quasi Core-Shell Alloyed CdSeS Quantum Dots Prepared Through Aqueous Microwave Synthesis Technique

Quasi core shell alloyed CdSeS quantum dots (QDs) have been prepared through a facile aqueous-phase route employing microwave irradiation technique. The optical spectroscopy and structure characterization evidenced the quasi core shell alloyed structures of CdSeS QDs. The X-ray diffraction patterns of the obtained CdSeS QDs displayed peak positions very close to those of bulk cubic CdS crystal structures and the result of X-ray photoelectron spectroscopy data re-confirmed the thick CdS shell on the CdSe core. The TEM images and HRTEM images of the CdSeS QDs ascertained the well-defined spherical particles and a relatively narrow size distribution. On the basis, the stability of the obtained QDs in an oxidative environment was also discussed using etching reaction by H₂O₂. The experiments result showed the as-prepared QDs present high tolerance towards H₂O₂, obviously superior to the commonly used CdTe QDs and core-shell CdTe/CdS QDs, which was attributed to the unique quasi core-shell CdSeS crystal structure and the small lattice mismatch between CdSe and CdS semiconductor materials. This assay provided insight to obtain high stable crystal structured semiconductor nanocrystals in the design and synthesis process.     

Surface chemistry of Zn3P3 single crystals studied by XPS

X-ray photoemission spectroscopy (XPS) has been used to study the surface reaction of Zn₃P₂ single crystals.The spectra of crystals exposed to H₂, O₂, CO₂, O₂+H₂O or CO₂+H₂O during a four week period were compared to the spectra of as-grown or in UHV scraped samples. For samples contaminated with the wet gases O₂+H₂O and CO₂+H₂O additional phosphorus core levels together with a shift of the zinc core levels were observed. For crystals exposed to atmosphere during several months no phosphorus could be detected on the gasgrown surface, whereas the stochiometry of Zn₃P₂ was maintained within the bulk. Crystals with scraped surfaces showed no moisture sensitivity. No surface contamination was also detected for Zn₃P₂ crystals deposited with up to 1000 L H₂O or exposed to atmosphere during 30 min.     

Water line parameters for weak lines in the range 9000-12 700 cm

A total of 7923 transitions previously derived from long pathlength, Fourier transform spectra of pure water vapor (Schermaul et al., J. Mol. Spectrosc. 211 (2002) 169) have been refitted and reanalyzed using a newly calculated variational linelist. Of these, 6600 lines are weaker than 1 × 10⁻²⁴ cm/molecule, for which reliable intensities are obtained. These weak lines include 1082 lines, largely due to H₂¹⁶O, which have not been previously observed. A total of 7156 lines were assigned resulting in 329 new energy levels for H₂¹⁶O spread over 32 vibrational levels. Estimates are also given for the band origins of the (022), (140), and (051) vibrational states.