@article {853, title = {The correlation between emission in freshly prepared porous silicon and the carrier density in silicon water}, journal = {Asian Journal of Spectroscopy}, volume = {6}, year = {2002}, author = {Zou, Bingsuo and Wang, Jianping and El-Sayed, Mostafa A} } @article {857, title = {Origin of emission from porous silicon: Temperature-dependence correlation with proton conductivity}, journal = {Physical Review B}, volume = {62}, year = {2000}, pages = {16595}, publisher = {APS}, abstract = {The excitation, emission, and Fourier transform infrared (FTIR) spectra of freshly prepared and aged porous silicon (PS) are examined. The effects of aging and temperature changing on the emission and excitation spectra of fresh and aged PS samples is also studied. Aging in air is found to result in a redshift in the emission spectrum, but a blueshift in the excitation spectrum. Increasing the temperatures leads to a general decrease in the emission intensities of both samples: however, the green emission of fresh sample shows an unusually large and sudden increase in its intensity at the same temperature at which the proton conductivity in the silicon wafer increases. The temperature dependence of the O-H vibration intensity of silicon wafers shows a sudden decrease at that temperature. These results are consistent with a model in which the excitation leads to the formation of exciton in the confined nanostructure, and the formation of electron and hole that are trapped by surface traps, whose nature is dependent on the chemical composition of the surface (and thus its age). These conclusions are confirmed by the results of the FTIR spectra of the two samples, the temperature dependence of the emission, and its correlation with the proton conductivity in the fresh PS.}, doi = {10.1103/PhysRevB.62.16595}, url = {http://link.aps.org/doi/10.1103/PhysRevB.62.16595}, author = {Zou, Bingsuo and Wang, Jianping and Liu, C. and Zhang, J.Z. and El-Sayed, Mostafa A} } @article {1236, title = {Comparison between the polarized Fourier-transform infrared spectra of aged porous silicon and amorphous silicon dioxide films on Si (100) surface}, journal = {Journal of Molecular Structure}, volume = {508}, number = {1-3}, year = {1999}, note = {Wang, JP Zou, BS El-Sayed, MA}, month = {Sep}, pages = {87-96}, abstract = {The s- and p-polarized Fourier transform infrared spectra were measured for an aged porous silicon (PS) film on Si (100) surface. The asymmetric stretching and symmetric stretching modes as well as the bending or rocking mode of the Si-O-Si group are studied. The deconvoluted spectra in Si-O-Si asymmetric stretching frequency region at different polarization directions show two pairs of vibrational modes, and can be assigned to the longitudinal-optic (LO) and transverse-optic (TO) pair of the corresponding vibrational modes. The smaller LO-TO pair splitting, the broader bandwidth, and the lower polarization ratio of the PS vibration bands as compared with those observed in an a-SiO2 film on Si wafer, suggest a less ordered SiO2 structure and a shorter range of coulombic interaction in PS. (C) 1999 Elsevier Science B.V. All rights reserved.}, isbn = {0022-2860}, doi = {10.1016/s0022-2860(99)00003-4}, author = {Wang, Jianping and Zou, Bingsuo and El-Sayed, Mostafa A} } @article {1234, title = {Effect of different capping environments on the optical properties of CdS nanoparticles in reverse micelles}, journal = {International Journal of Quantum Chemistry}, volume = {72}, number = {4}, year = {1999}, note = {Zou, BS Little, RB Wang, JP El-Sayed, MA}, month = {Apr}, pages = {439-450}, abstract = {CdS(E = 2.5 eV) nanoparticles were synthesized in reversed micelles and capped with materials of different band gaps and charge compensation ability: Cd(OH)(2) (4.0 eV), ZnS (3.2 eV), and CdO (2.3 eV). The preparations allowed the examination and comparison of the efficiencies of confinement of the electron and hole by the various capping materials. The absorption and emission spectra of the capped CdS nanoparticles suggest the following: (1) Efficient capping and strong quantum confinement are observed for CdS particles of small size (< 3.8 nm), showing well-resolved photoexcitation spectra; (2) the confinement efficiency improves with capping thickness; (3) although ZnS has smaller band gap than Cd(OH)(2), it was more efficient in surface-charge compensation and it is the best capping agent of the three materials; and (4) the similar band gaps of CdO and CdS resulted spectroscopically in strong mixing between the excited states of these materials. (C) 1999 John Wiley \& Sons, Inc.}, isbn = {0020-7608}, doi = {10.1002/(sici)1097-461x(1999)72:4<439::aid-qua27>3.0.co;2-q}, author = {Zou, Bingsuo and Little, Reginald and Wang, Jianping and El-Sayed, Mostafa A} } @article {1237, title = {Time-resolved Fourier-transform infrared and visible luminescence spectroscopy of photoexcited porous silicon}, journal = {Physical Review B}, volume = {59}, number = {7}, year = {1999}, note = {Wang, JP Song, L Zou, BS El-Sayed, MA}, month = {Feb}, pages = {5026-5031}, abstract = {In order to identify the luminescent centers in aged porous silicon, both the time-resolved vibration spectra in the 750-2000-cm(-1) region and the visible luminescence spectra are studied for the same sample in the 0-440-mu s time domain. Laser excitation gives rise to emission characteristics of the porous silicon as well as strong bleach in the infrared spectrum in the region of the ground-stale silicon-oxygen stretching vibration frequencies at 1100 and 1235 cm(-1). In addition, new transient absorption bands appear in this region as a result of the laser excitation. Three characteristic Lifetimes in the decay of the bleach band at 1235 cm(-1) are observed on the 1-, 10-, and 100-mu s time scale. These are similar to the observed decay times of the photoluminescence from porous silicon. These results suggest that the emitting centers in aged porous silicon are trapped excitation sites in an inhomogeneously defected oxidized silicon surface. [S0163-1829(99)09207-3].}, isbn = {0163-1829}, doi = {10.1103/PhysRevB.59.5026}, author = {Wang, Jianping and Song, Li and Zou, Bingsuo and El-Sayed, Mostafa A} }