RESUMEN
Raman spectroscopy was used to investigate the phase transition of n-hexacosane for real-time cooling run. In the cooling process, the n-hexacosane experienced the melt phase --> rotator phase --> monoclinic crystal phase transition. The changes in band intensity and frequency in the CH2 bending, CH2 twisting, skeletal C-C stretching, and CH3 rocking regions were mainly analyzed in order to know the changing sequence and process of these vibrational modes, and to reflect the relationship between these vibrational modes and molecular structure. Besides, the changes in band intensity and frequency revealed both transitions, particularly when using band components related to gauche bonds. Our research shows that Raman spectroscopy is an effective tool to monitor the phase transition of n-alkanes or even long-chain polymers. In addition, by analyzing the Raman peaks in 800-1 500 cm(-1) in the cooling process of n-hexacosane, the temperature range of rotator phase was obtained, proving that Raman spectroscopy can be used to observe the rotator phase occurring during the phase transition of paraffin.
RESUMEN
Raman spectroscopy was used to investigate the order-disorder phase transition of n-eicosane for real-time cooling run. At the phase transition temperature, the integrated intensity of the 1 300 cm(-1) spectra range changes greatly, which requires further consideration of 1 300 cm(-1) as a reference in the research on polymer and biomembrane using Raman spectroscopy. The experiment support was provided for doubt about order parameter based on 1 130 cm(-1) that it did not refer to generally accepted interpretation of an order parameter and it proved that the order definition could just be used as a relative measure method for disorder.
RESUMEN
InGaN/GaN, InGaN/InGaN and InGaN/AlInGaN multi-quantum-well (MQW) laser diodes (LDs) were grown on (0001) sapphire substrate by metalorganic chemical vapor deposition (MOCVD). The GaN (0002) synchrotron X-ray diffraction (XRD), electroluminescence (EL) and optical power-current (L-I) measurement reveal that AlInGaN quaternary alloys as barriers in MQWs can improve the crystal quality, optical emission performance, threshold current and slope efficiency of the laser diode structure to a large extent compared with other barriers. The relevant mechanisms are that: 1. The Al component increases the barrier height of the MQWs so that more current carriers will be caught in. 2. The In component counteracts the strain in the MQWs that decreases the dislocations and defects, thereby the nonradiative recombination centers are decreased. 3. The In component decreases the piezoelectric electric field that makes the electrons and the holes recombine more easily.
RESUMEN
Raman spectra of ZnO powders prepared by firing ZnO2 precipitate were reported in detail for the first time. By comparing the spectra with that of the sample fabricated by another method and analyzing frequency difference between the focused-laser irradiated samples with different firing temperature in preparation, it was concluded that the -333 cm(-1) peak is ascribed to E2 (high)-E2 (low) and the -661 cm(-1) peak to its overtone. In addition, a new interpretation for the observed Raman peaks between 400 and 500 cm(-1) in ZnO2 powders was presented based on the IR data and ab initio calculation.
RESUMEN
Transparent conductive current-spreading layer is important for quantum efficiency and thermal performance of light-emitting diodes (LEDs). The increasing demand for tin-doped indium oxide (ITO) caused the price to greatly increase. Super-aligned carbon nanotubes (SACNTs) and Au-coated SACNTs as current-spreading layer were applied on AlGaInP LEDs. The LEDs with Au-coated SACNTs showed good current spreading effect. The voltage bias at 20 mA dropped about 0.15 V, and the optical power increased about 10% compared with the LEDs without SACNTs.