Study On The Structure And Properties Of Silicon Clusters Based On Density Functional Theory

Silicon core approximants terminated with hydrogen,hydroxyl and methyl termination were investigated by density-functional-theory calculations within B3LYP hybrid functional formalism using 6-31G?d?Gaussian type molecular-orbital basis set.Optimized geometric structures including bond lengths and bond angles for all clusters were obtained.The related chemical and physical properties of the steady state structure of the cluster system were investigated.This work provides a solid theoretical basis for the surface functionalization of silicon core approximants using as liquid,or particle sensing by using microring resonator.The main research is shown as follows:Si=O double bond on the surface of silicon core approximants is obtained by study of the density of state,natural bond orbital,HOMO-LUMO orbital analysis and engergy gap of silicon clusters.All data show the Si=O double bond is found to be the most probable surface structures of the silicon cluster exposed to the atmosphere of H₂O,O₂and CH₃CH₂OH gases.Considering the deviations of electronic structures from monotonic behavior as a function of size of silicon core approximants with different terminations which do not possess a very high symmetry,proper sizes of cluster are chosen in the calculations so as to reduce the computation times.The data of average binding energy of silicon cluster show that the value of average binding energy of silicon cluster with Si=O double bond smaller than others,e.g.E_SiO?-9.78eV?<E_SiOH?-4.77eV?<E_SiCH3?-3.78eV?<E_SiH?-3.66eV?.The data of E_gap of silicon cluster with SiO double bond have the lowest value,e.g.E_gap^SiO?3.64eV?<E_gap^SiOH?6.50eV?<E_gap^SiCH3?7.39eV?<E_gap^SiH?7.76eV?,that reveal Si=O double bond is found to be the most probable surface structures of silicon core approximants when they are under the irradiation of light.The data of HOMO energy show that the silicon cluster with Si=O double bond have largest value,e.g.E^SiO_HOMO?-6.98eV?>E_HOMO^SiOH?-7.13eV?>E_HOMO^SiCH3?-7.46eV?>E^SiH_HOMO?-7.78eV?.The higher HOMO energy indicates that the cluster is highly active,active silicon core approximants have fluorescence emission when exposed in.This provides theoretical support for the structure that may exist on the surfaces of the approximants under illuminating radiation.At the same time,the dipole moment of the cluster is calculated.The silicon cluster with Si=O double bond have largest dipole moment,which compatible with result of average binding energy of silicon cluster.We also used the same method to investigate the silicon clusters terminated by different functional groups,and they were also discussed.At the same time,the silicon clusters with this surface structure were applied to the bonding of specific molecular or clusters,and it is possible to detect specific molecules.So on the other hand,we further study the sensing of whispering-gallery-modes in a microring resonator coated with a fluorescent high-refractive-index film consisted of the silicon cluster.It is probably used to detect specific molecules and modeled using finite-difference time-domain method.A short pulse with ultrawide bandwidth in the high-index film spans the circumference of the ring.The spectra of the high-index film and the pulse propagation in time domain were simulated.The results indicate redshifts of the resonance wavelengths with an increasing refractive index inside the ring.A sensitivity of 28.5 nm/RIU is found for the index of1.48.Considering the effects of scattering and absorption of a single object adhered to the inner surface of the microring,an obvious splitting or broadening of resonance modes is found for sensing.For single particles with a radius of 3?m,the mode splitting is increased with increasing number of particles from one to nine.The estimation of the size of the particles is also studied based on the mode splitting of the optical field in the ring depends on the scattering of the particles.This work reveals the potential applications of whispering-gallery-modes in a microring resonator coated with a fluorescent high-index film for sensing one or multiple objects and eVen a single molecule.