Mechanism of Bragg Diffraction-Assisted Light Extraction in GaN-based Light-Emitting Diodes Based on a Self-Consistent Model

By introducing the distribution of the light energy density in GaN-based light-emitting diode (LED),theLED model based on the incoherent regime and the light extraction efficiency are investigated.The energy density asa function of the angle of incidence is calculated to demonstrate the mechanism of the light extraction.The deviationbetween the tendencies of the transmissivity of the output layer and the extraction efficiency is also demonstrated.

Solution Fabrication of a Superconducting MgB2 Coated Conductor on Stainless Steel

We report the solution fabrication of a MgB2 coated conductor on a stainless steel substrate.The precursor solution of Mg(BH_(4))^(2) diethyl ether is initially synthesized by refluxing the milled mixture of NaBH4 and MgCl_(2) in diethyl ether.Then the Mg(BH4)2 diethyl ether is spin coated on a stainless steel substrate and annealed in Mg vapor,which yields a homogeneous MgB_(2) coated conductor.X-ray diffraction indicates that the grown MgB_(2) coated conductor is polycrystalline.It has a superconducting transition temperature of 34-37K.The slope of the upper critical field HC_(2) increases with decreasing temperature,and the extrapolated value of Hc2 (0)reaches ~28 T.The critical current density estimated by the Bean model is JC (25K,0 T)~1 06 A.cm^(-2).These parameters indicate that the solution method is potentially able to produce MgB_(2) coated conductors that can satisfy application purposes.

A Continuous Model for Molecular Vibrations in C_(60)

A continuous model for molecular vibration in C_(60) is developed which presents a physical picture easy to understand.The molecular vibration modes are expanded by vector spherical harmonics.With the choice of suitable parameters,the calculated frequencies are fit the experimental values very well.In combination with the pseudopotential model for the valence electrons in C60,the interaction between the electron and intramolecular phonon in solid C_(60) can be analysed and calculated based on our model.

Laser Induced Light-Force Interaction in the Optical Near-Field Region

Laser light can induce many effects on the vicinity of the sample surface due to the proximity effects,such as the field enhancement at the surface of a small conducting particle;plasma exchange effect between the metallic tip and substrate surface.We have observed a new optical tip-sample interaction:laser induced force as the results of light pressure in the near-field region.Under the side illumination of a laser light,an additional attractive force was observed between a dielectric tip and various samples of C60,optical glass,YBa_(2)Cu_(3)O_(7-d)(YBCO)thin film.No such effect was observed in metallic samples.This optical binding force is due to the multiple scattering of light between two close objects.The results are in good agreement with the recent theoretical calculation.The effects of the optical refraction index,thermal expansion of probe tip due to laser radiation are discussed.

Distinguish Different Factors Dominating Superconductivity in Y-Doped Bi_(2)Sr_(2)CaCu_(2)O_(y)

We observed in Y-doped Bi_(2)Sr_(2)CaCu_(2)O_(y) superconductors an interesting phenomenon,the T_(c)(onset)of the Y-doped samples is highcr,but the T_(c)(end)is lower than thatof Y-free sanples.After annealing in N_(2) atmosphere,the Te(end)is increased,butthe T_(c)e(onset)is hardly changed.Aftcr careful studying,by structure analysis,x-ray photoelectron spectroscopy,R-T relationship measurement,and Hall effect,we successfully distinguish the different factors that dominate the superconductivity,of which one is carrier concentration,others may possibly be structure change andcharges redistribution.