The observed branching ratios for B→KЈ decays are much larger than factorization predictions in the standard model ͑SM͒. Many proposals have been made to reconcile the data and theoretical predictions. In this paper we study these decays within the SM using flavor SU͑3͒ symmetry. Treating the singlet 1 and octet ( Ϯ,0 ,K Ϯ ,K 0 ,K 0 , 8 ) pseudoscalar mesons as a nonet multiplet, we find that if small annihilation amplitudes are neglected only 11 hadronic parameters are needed to describe B→ PP decays where P can be one of the , K, and Ј mesons. We find that existing data are consistent with the SM. We also predict several measurable branching ratios and CP asymmetries for B→K()(Ј), (Ј)(Ј) decays. Experiments in the near future can provide important tests for the standard model with flavor symmetry.

A two-dimensional photonic crystal with a large full band gap has been designed, fabricated, and characterized. The photonic crystal design was based on a calculation using inverse iteration with multigrid acceleration. The fabrication of the photonic crystal on silicon was realized by the processes of electron-beam lithography and inductively coupled plasma reactive ion etching. It was found that the hexagonal array of circular columns and rods has an optimal full photonic band gap. In addition, we show that a larger extraction of light from our designed photonic crystal can be obtained when compared with the frequently used photonic crystals reported previously. Our designed PC structure therefore should be very useful for creating highly efficient optoelectronic devices.

This study of the optoelectronic properties of blue light-emitting diodes under direct current stress. It is found that the electroluminescence intensity increases with duration of stress, and the efficiency droop curves illustrated that the peak-efficiency and the peak-efficiency-current increases and decreases, respectively. We hypothesize that these behaviors mainly result from the increased internal quantum efficiency.

The combination of electron beam lithography and electrochemical deposition has been employed to fabricate well-controlled submicrometer-scale CdSe pillars. The formation of the wurtzite crystal structure of CdSe pillars has been confirmed by x-ray diffraction and Raman spectra. Quite interestingly, we found that the intensity of micro-photoluminescence can be greatly enhanced at the specially designed two-dimensional photonic crystals (PCs) based on Maxwell’s equations. This peculiar phenomenon can be explained quite well in terms of the effects of PCs. PCs can provide a photonic bandgap for the emission in the lateral dimensions so that the emission of CdSe pillars cannot propagate in the lateral plane and can only propagate upward with respect to PCs. Besides, PCs can also provide a pathway for the phase match between guided modes and radiation modes to avoid total internal reflection. Thus, the detected PL intensity normal to the lateral plane can be greatly enhanced.

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