Effects of growth pressure on the structural and optical properties of multi quantum wells (MQWs) in blue LED.

The effects of growth pressure in metal-organic chemical vapor deposition (MOCVD) on the structural and optical properties of InGaN/GaN multiple-quantum-wells (MQWs) grown on c-plane sapphire substrate were investigated by scanning transmission electron microscopy (STEM), atom probe tomography (APT), Raman spectroscopy and electroluminescence (EL) spectroscopy. As the growth pressure decreased, the growth rate of the InGaN layer increased, leading to a decrease in the frequency of the GaN A1(LO) mode peak and broadening of its full width half maximum (FWHM). The intensity of the EL spectra peaked at a growth pressure of 250 Torr with a narrow FWHM at high forward current. These optical properties are explained by either a high degree of compositional fluctuation of indium in the MQW and/or the high crystallinity of the InGaN layer due to the low growth rate under high pressure.

Separation of anionic and cationic compounds of biomedical interest by high-performance liquid chromatography on porous graphitic carbon.

The separation of small, ionizable compounds of biomedical interest on porous graphitic carbon is described. The retention of anionic compounds is dominated by electronic interaction between the solute and the delocalized electron clouds on the graphitized carbon, while cationic compounds are mainly retained by reversed-phase interaction with the hydrophobic carbon surface. Anionic and cationic compounds can be separated simultaneously with a mobile phase containing an electronic modifier (e.g., trifluoroacetic acid) and an organic modifier (e.g., acetonitrile) for elution. Examples of applications include the measurement of oxalic acid in urine, the determination of creatine and creatinine in urine and in serum, the separation of basic drugs (remoxipride and FLA 981) and the simultaneous analysis of pertechnetate anion and the cationic technetium-amine complexes.