DFT/TDDFT study of electronic and optical properties of Surface-passivated Silicon nanocrystals, Sin (n = 20, 24, 26 and 28)

Abstract

Density functional theory and Time-dependent density functional theory (TDDFT)-based calculations were performed on surface-passivated Silicon nanocrystals (SPSNs) of different sizes. The surface passivation was achieved using H, F and Cl atoms. Various properties of the resulting optimized structures Si n H n , Si n H n-1 F and Si n H n-1 Cl (n = 20, 24, 26 and 28) like binding Energy, dipole moment, HOMO-LUMO gap, vibrational IR spectra and absorption wavelengths were determined. Surface passivation studies reveal that all the SPSNs are insulators and TDDFT study performed using two basis sets 6-31G

Quantum Chemical Characterization and Design of Quantum Dots for Sensing Applications

“…In recent years, there has been a number of studies that have used density functional theory (DFT) and time-dependent density functional theory (TDDFT) to study the properties of fluorescent biosensors 28 − 30 including QD-based systems. 31 − 37 It is common to interpret the photophysical behavior of the fluorophores in terms of the molecular orbital diagram based upon the Kohn–Sham orbitals and energies. 38 − 43 A more accurate approach is to calculate the excited states explicitly through TDDFT or higher-level wavefunction-based calculations, which can also provide greater insights into the sensing mechanisms of the fluorescent probes.…”

“… 33 Calculation of emission spectra has been reported for functionalized graphene quantum dots, 35 acetate-functionalized CdSe, 36 or halogen atom-passivated silicon nanocrystals. 37 Dye-sensitized QDs have been studied with TDDFT with the effects of solvent included through polarized continuum solvent models. 54 , 55 Also, studies involving orbital characterization have been performed for ligated QDs, which have included investigation of CT mechanisms.…”

“…In recent years, there has been a number of studies that have used density functional theory (DFT) and time-dependent density functional theory (TDDFT) to study the properties of fluorescent biosensors − including QD-based systems. − It is common to interpret the photophysical behavior of the fluorophores in terms of the molecular orbital diagram based upon the Kohn–Sham orbitals and energies. − A more accurate approach is to calculate the excited states explicitly through TDDFT or higher-level wavefunction-based calculations, which can also provide greater insights into the sensing mechanisms of the fluorescent probes. − Examples of studies of QDs include hydrogenated silicon quantum dots of varying sizes, boronizated and oxidated graphene QDs, and graphene QDs functionalized with various oxygen-containing functional groups . Calculation of emission spectra has been reported for functionalized graphene quantum dots, acetate-functionalized CdSe, or halogen atom-passivated silicon nanocrystals . Dye-sensitized QDs have been studied with TDDFT with the effects of solvent included through polarized continuum solvent models. , Also, studies involving orbital characterization have been performed for ligated QDs, which have included investigation of CT mechanisms. ,, …”

Intriguing properties of unusual silicon nanocrystals

“…The extension of the absorption spectra of Si 19 X 12 and Si 18 GeX 12 clusters up to the IR is assigned to the insertion of the central over-coordinated Si or Ge atoms. The role of endohedral atoms (Si or Ge); i.e., with over-coordinated Si or Ge atoms, on the ability of nanocrystals to absorb in the VIS and IR can be denitively demonstrated when comparing with Si n H nÀ1 M clusters (with M ¼ H, Cl, and F; n ¼ 20, 24, 26, and 28)42 which have no over-coordinated Si atoms and display absorption strictly limited to the UV region. This observation especially holds for the tetrahedral silicon fullerene Si 20 H 20 that has quite the same size of about 1 nm.…”

The effect of oxide shell thickness on the structural, electronic, and optical properties of Si-SiO2 core-shell nano-crystals: A (time dependent)density functional theory study

“…Chopra and Rai have studied the effect of surface passivation of silicon NCs (<1 nm) with hydrogen, fluorine, and chlorine. 24 They have reported that the surface passivation and the cluster size only weakly affect the conductivity of considered NCs. Oxygen as a widely used material in silicon technology is well known for the modification of the optical and electrical properties of silicon NCs.…”