CdSe nanocrystals ͑NCs͒ have been decorated on single-walled carbon nanotubes ͑SWCNTs͒ by combining a method of chemically modified substrate along with gate-bias control. CdSe/ ZnS core/shell quantum dots were negatively charged by adding mercaptoacetic acid. The silicon oxide substrate was decorated by octadecyltrichlorosilane and converted to hydrophobic surface. The negatively charged CdSe NCs were adsorbed on the SWCNT surface by applying a negative gate bias. The measured photocurrent clearly demonstrates that CdSe NCs decorated SWCNT can be used for photodetector and solar cell that are operable over a wide range of wavelengths.
We measured the content of single-walled carbon nanotubes (SWCNTs) in SWCNT soot within 3.7% error using UV-VIS-NIR absorption spectroscopy. We also propose a better overall evaluation method by combining thermogravimetic analysis with UV-VIS-NIR absorption spectroscopy to analyze the purity of SWCNT providing the accurate assessment of the amounts of noncarbonaceous impurity, carbonaceous impurity, and SWCNT each with respect to a highly purified reference.
We have investigated the correlation between V-shaped defect formation and the optical properties of AlGaN/(In)GaN multiple quantum wells (MQWs) grown under different growth conditions and then demonstrated the characteristics of fabricated ultraviolet (UV) light emitting diodes (LEDs). From the temperature-dependent photoluminescence (PL) measurement, the internal quantum efficiency for 300 K was obtained as 43.6% for a sample with a low density of V-defects in a MQW and 13.7% for a sample with a high density of V-defects. The carrier lifetime based on the time resolved PL measurement at room temperature was 0.32 ns for a sample with a high density of V-defects and 1.26 ns for a sample with a low density of V-defects. And we also found that the density of V-defects affected the external quantum efficiency and wall plug efficiency of the fabricated UV LEDs.
We investigated spatial light emission from a periodic inverted polygonal deflector, which included six {10-1-1} facets and six {11-2-2} facets embedded in an InGaN∕GaN light emitting diode by using confocal scanning electroluminescence microscopy. We found a noticeable crown shape with the contrast of luminescence intensity and wavelength observed on these facets mainly due to the variation of growth rate for the InGaN quantum wells. In addition, a very low intensity and blueshifted emission wavelength on the {11-2-2} facets indicated the deficiency of indium incorporation and/or much thinner well thickness as compared to that of the {10-1-1} facets.
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