Effect of Phenyl-Capping and Dimer Formation on the Electronic States of CdS Nanoparticles by Means of Semiempirical Molecular Orbital Calculations

Abstract

A semiempirical molecular orbital calculation (MOPAC-PM3) was applied to investigate the effects of crystal arrangement, phenyl capping, and dimer formation for CdS nanoparticles. Molecular structures of possible polynuclear cadmium complexes were classified into four categories, zinc blende (ZB) tetrahedron, ZB cuboctahedron, wurtzite (W), and ZB-W mixture, and the last one is found to be the most favorable formation. The first excitation energies for these cluster complexes were calculated as the HOMO-LUMO energy difference and compared with the absorption peak energy reported in the literature. The electronic effect in polynuclear Cd thiophenolate complexes was discussed in terms of the fractionated density of states as an anti-π-bond interaction between the benzene π-orbital and the S 3p-orbitals. The dimer formation did not affect significantly the excited state of the nanoparticle dimer based on the estimation of intramolecular electron interaction.Semiconductor nanoparticles have attracted much interest of researchers in basic science and applied materials. 1 Change in the electronic properties with size confinement is the origin of the unique properties of semiconductor nanoparticles. Investigation of the electronic structure of nanoparticles is possible by means of quantum chemical methods, explicitly using the molecular presentation. Since the chemical structure of polynuclear metal complex is clearly presented, it is a suitable model to investigate the electronic states of semiconductor nanoparticles. Some molecular orbital (MO) approaches to understand the electronic state of inorganic semiconductor nanoparticles have been reported so far, by using extend Hueckel, 2 CNDO/ 2, 3 CNDO/S, 4 and ab initio 5 methods for CdS nanocrystals. The extend Hueckel approach to Cd x S y clusters of zinc blende structure, where x e 20 and y e 35, has showed the decrease in HOMO-LUMO energy difference. 2 The CNDO/2 method is used to investigate surface defects of CdS nanocrystal with 221 Cd atoms. 3 Calculation of the oscillator strength of CdS nanoparticles has been tried by means of the CNDO/S method. 4 Ab initio calculation for a CdS cluster of tetrahedral symmetry up to Cd 13 sulfide clusters allowed us to compare the bond length to the experimental values. 5 All reported MO calculations were performed for clusters with terminating hydrogen or without other atoms. However, real nano lusters are often capped with organic molecules, which may induce some effect on the electronic states of nanoparticles. For CdSe clusters containing ligand molecules, a density functional theory (DFT) approach to the synthesized clusters displayed the effect encountered in the transition from molecules to the solid state. 6 Since we are much interested in the interaction of inorganic CdS surface and capped organic molecules, 7 we applied a semiempirical MO method, PM3 in the MOPAC series, to investigate the electronic interaction between organic molecules and CdS particles. In this report, at first we applied this calculation method to...

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“…Size-quantized semiconductor nanoparticles have been promising materials for applications such as multicolored fluorescent markers for biological analysis and optoelectronics devices. − Cadmium selenide (CdSe) nanoparticles have been intensively investigated because their band gap emission can be tuned in the whole visible region depending on their particle size. ,, Various methods for the synthesis of CdSe nanoparticles have been reported, and it has been shown that particle size was varied by reaction conditions, such as reaction temperature and time. In most cases, crystal growth in hot organic solvents must be monitored during the progression of the reaction, and difficult techniques have therefore been required for controlling the size of nanoparticles formed. ,,,, …”

“…Size-quantized semiconductor nanoparticles have been promising materials for applications such as multicolored fluorescent markers for biological analysis and optoelectronics devices. [1][2][3][4][5][6][7][8][9][10] Cadmium selenide (CdSe) nanoparticles have been intensively investigated because their band gap emission can be tuned in the whole visible region depending on their particle size. 1,4,6 Various methods for the synthesis of CdSe nanoparticles have been reported, and it has been shown that particle size was varied by reaction conditions, such as reaction temperature and time.…”

Atomistic theory and simulation of the morphology and structure of ionic nanoparticles

“…Densityfunctional tight binding (DFTB) is one such method that has been applied to the study of nanomaterials. [56][57][58] Semi-empirical quantum mechanical methods, such as MNDO-based techniques, are also applicable in many cases, such as CdS nanoparticles and their capping, 59,60 which have also been studied using DFTB. 61 An alternative to reducing the complexity of the Hamiltonian by explicit simplification is to apply some degree of localisation to the matrix elements in order to lead to linear-scaling construction.…”

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