ZnO Nanorods Grown on p-GaN Using Hydrothermal Synthesis and Its Optoelectronic Devices Application

The ZnO nanorods with the length of 1-1.5 μm were deposited on p-GaN by hydrothermal synthesis at low temperature 100°C. The structural and optical properties of the as-grown ZnO rods were investigated by X-Ray diffraction (XRD) and photoluminescence (PL) spectra. After annealing treatment the as-grown films in air at 600°C, 30min, and the ZnO rods showed good crystallinity and optical properties with strong UV emission at 378 nm. In addition, a sharp UV emission peak at 369.45 nm with the FWHM 20 meV, which attributed to the bound exciton recombination, was also observed from the ZnO rods at 80K. Next, the e-beam evaporation method was used to deposit metal contact on n-ZnO and p-GaN. Here, we use Au and Ni/Au as metal contacts for n-ZnO and p-GaN, respectively. The current-voltage characteristics of the fabricated n-ZnO/p-GaN heterojunction revealed rectifying behavior with a leakage current of 10⁻⁸ A at -10V, a forward current 4x10⁻⁶ A at 10V bias. The heterojunction also showed a good photoresponse, with the change of the current – voltage characteristics under ultraviolet illumination. Under UV illumination, the forward turn on voltage changed to 7.5V. This result showed the ability to manipulate the electron transport in the ZnO based heterojunction devices.Singapore-MIT Alliance (SMA

Suppression of self-pulsing behavior in erbium-doped fiber lasers with resonant pumping: experimental results

Experimental results are presented showing that resonant pumping can significantly improve the stability of erbium-doped fiber lasers. In particular, it is observed that an erbium fiber laser that exhibits sustained spiking behavior when pumped at 980nm will revert to stable cw operation when pumped at 1510 nm

Characterization of ZnO Nanorods Grown on GaN Using Aqueous Solution Method

Uniformly distributed ZnO nanorods with diameter 70-100 nm and 1-2μm long have been successfully grown at low temperatures on GaN by using the inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. No catalyst is required. The XRD studies show that the ZnO nanorods are single crystals and that they grow along the c axis of the crystal plane. The room temperature photoluminescence measurements have shown ultraviolet peaks at 388nm with high intensity, which are comparable to those found in high quality ZnO films. The mechanism of the nanorod growth in the aqueous solution is proposed. The dependence of the ZnO nanorods on the growth parameters was also investigated. While changing the growth temperature from 60°C to 150°C, the morphology of the ZnO nanorods changed from sharp tip (needle shape) to flat tip (rod shape). These kinds of structure are useful in laser and field emission application.Singapore-MIT Alliance (SMA

Growth of ZnO Nanorods on GaN Using Aqueous Solution Method

Uniformly distributed ZnO nanorods with diameter 80-120 nm and 1-2µm long have been successfully grown at low temperatures on GaN by using the inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. No catalyst is required. The XRD studies show that the ZnO nanorods are single crystals and that they grow along the c axis of the crystal plane. The room temperature photoluminescence measurements have shown ultraviolet peaks at 388nm with high intensity, which are comparable to those found in high quality ZnO films. The mechanism of the nanorod growth in the aqueous solution is proposed. The dependence of the ZnO nanorods on the growth parameters was also investigated. While changing the growth temperature from 60°C to 150°C, the morphology of the ZnO nanorods changed from sharp tip with high aspect ratio to flat tip with smaller aspect ratio. These kinds of structure are useful in laser and field emission application.Singapore-MIT Alliance (SMA

Reaction Pairing: A Diversity-Oriented Synthesis Strategy for the Synthesis of Diverse Benzofused Sultams

A reaction pairing strategy centered on utilization of a reaction triad (sulfonylation, SNAr addition and Mitsunobu alkylation) generating skeletally diverse benzofused tricyclic and bicyclic sultams is reported. Pairing sulfonylation and SNAr reactions yields bridged, tricyclic and bicyclic benzofused sultams. Application of the Mitsunobu reaction in a sulfonylation–Mitsunobu–SNAr pairing allows access to benzo-oxathiazocine-1,1-dioxides, while a simple change in the order of pairing to sulfonylation–SNAr–Mitsunobu affords structurally different, benzofused bridged tricyclic sultams

Chemical composition of essential oil of exudates of Dryobalanops aromatica

Purpose: To identify the chemical composition of essential oil from the exudates of Dryobalanops aromatica from Malaysia.Methods: Exudate was collected from D. aromatica and subjected to fractional  distillation to obtain essential oil. Gas chromatography-mass spectrometry  (GC-MS) was used to characterize the composition of the isolated essential oil.Results: The yield of essential oil was 7.58 %, with the highest yield (3.24 %) within the first 2 h of fractional distillation. Thirty compounds which accounted for 97.56 % of essential oil composition were identified. These include sesquiterpenes (46.87 %), monoterpenes (31.05 %), oxygenated monoterpenes (16.76 %) and oxygenated  sesquiterpenes (2.13 %). Borneol accounted for 0.74 % of the essential oil.Conclusion: Essential oil from the exudates of D. aromatica contains terpenoid  compounds and borneol.Keywords: Dryobalanops aromatica, exudate, fractional distillation, essential oil, GS-MS, borneo

Determination of borneol and other chemical compounds of essential oil of Dryobalanops aromatica exudate from Malaysia

Purpose: To determine borneol and other chemical compounds of essential oil derived from the exudate of Dryobalanops aromatica in Malaysia.Methods: Exudate was collected from D. aromatica and subjected to fractional distillation to obtain essential oil. Gas chromatography-mass spectrometry (GC-MS) was performed to characterize the composition of the isolated essential oil.Results: Essential oil (7.58 %) was obtained with the highest yield (3.24 %) in the first 2 h of fractional distillation. Thirty compounds which accounted for 97.56 % of total essential oil composition were identified by GC-MS, and they include sesquiterpenes (46.87 %), monoterpenes (31.05 %), oxygenated monoterpenes (16.76 %) and oxygenated sesquiterpenes (2.13 %). Borneol (0.74 %) was also detected in the essential oil.Conclusion: Borneol and other terpenoid compounds are present in the essential oil of the exudate of D. aromatica.Keywords: Exudate, Dryobalanops Aromatica, Fractional distillation, Essential oil, Gaschromatography-mass spectrometry, Borneo

Order statistics of the early-type galaxy luminosity function

We apply order statistics (OS) to the bright end ($M_r < -22$) of the luminosity distribution of early-type galaxies spectroscopically identified in the SDSS DR7 catalog. We calculate the typical OS quantities of this distribution numerically, measuring the expectation value and variance of the $k^{th}$ most luminous galaxy in a sample with cardinality $N$ over a large ensemble of such samples. From these statistical quantities we explain why and in what limit the $k^{th}$ most luminous galaxies can be used as standard candles for cosmological studies. Since our sample contains all bright galaxies including the brightest cluster galaxies (BCG), based on OS we argue that BCGs can be considered as statistical extremes of a well-established Schechter luminosity distribution when galaxies are binned by redshift and not cluster-by-cluster. We presume that the reason behind this might be that luminous red ellipticals in galaxy clusters are \em not random \em samples of an overall luminosity distribution but biased by the fact that they are in a cluster containing the BCG. We show that a simple statistical toy model can reproduce the well-known magnitude gap between the BCG and the second brightest galaxy of the clusters