ABSTRACT
Gallium nitride (GaN) is a wide bandgap semiconductor with remarkable chemical and thermal stability, making it a competitive candidate for a variety of optoelectronic applications. In this study, GaN films are grown using a plasma-enhanced atomic layer deposition (PEALD) with trimethylgallium (TMG) and NH3 plasma. The effect of substrate temperature on growth mechanism and properties of the PEALD GaN films is systematically studied. The experimental results show that the self-limiting surface chemical reactions occur in the substrate temperature range of 250-350 °C. The substrate temperature strongly affects the crystalline structure, which is nearly amorphous at below 250 °C, with (100) as the major phase at below 400 °C, and (002) dominated at higher temperatures. The X-ray photoelectron spectroscopy spectra reveals the unintentional oxygen incorporation into the films in the forms of Ga2O3 and Ga-OH. The amount of Ga-O component decreases, whereas the Ga-Ga component rapidly increases at 400 and 450 °C, due to the decomposition of TMG. The substrate temperature of 350 °C with the highest amount of Ga-N bonds is, therefore, considered the optimum substrate temperature. This study is helpful for improving the quality of PEALD GaN films.
Subject(s)
Plasma , Semiconductors , Oxygen , Photoelectron SpectroscopyABSTRACT
The deformation behaviors and fracture features of GaP(100) single-crystal are investigated by using nano- and micro-scale indentation techniques. The hardness and Young's modulus were measured by nanoindentation using a Berkovich diamond indenter with continuous contact stiffness measurements (CSM) mode and the values obtained were 12.5 ± 1.2 GPa and 152.6 ± 12.8 GPa, respectively. In addition, the characteristic "pop-in" was observed in the loading portion of load-displacement curve, which was caused by the nucleation and/or propagation of dislocations. An energetic estimation methodology on the associated nanoindentation-induced dislocation numbers resulting from the pop-in events was discussed. Furthermore, the Vickers indentation induced fracture patterns of GaP(100) single-crystal were observed and analyzed using optical microscopy. The obtained fracture toughness KC of GaP(100) single-crystal was ~1.7 ± 0.1 MPa·m1/2, which is substantially higher than the KIC values of 0.8 MPa·m1/2 and 1.0 MPa·m1/2 previously reported for of single-crystal and polycrystalline GaP, respectively.
ABSTRACT
The indentation-induced deformation mechanisms in InP(100) single crystals were investigated by using nanoindentation and cross-sectional transmission electron microscopy (XTEM) techniques. The results indicated that there were multiple "pop-in" events randomly distributed in the loading curves, which were conceived to arise primarily from the dislocation nucleation and propagation activities. An energetic estimation on the number of nanoindentation-induced dislocations associated with pop-in effects is discussed. Furthermore, the fracture patterns were performed by Vickers indentation. The fracture toughness and the fracture energy of InP(100) single crystals were calculated to be around 1.2 MPa·m1/2 and 14.1 J/m², respectively.
ABSTRACT
Chlorella is a type of unicellular fresh water algae. In an attempt to develop new agents for handling insulin resistance, Chlorella was employed to screen the effect on insulin resistance in rats induced by fructose-rich chow. A single oral administration of Chlorella for 90 min decreased the plasma glucose in a dose-dependent manner in rats receiving 4-week fructose-rich chow. In addition, chronic treatment with Chlorella for 15 days also lowered plasma glucose in the same manner. Then, the insulin action on glucose disposal rate was measured using the glucose-insulin index, values of the areas under the curves of glucose and insulin during the intraperitoneal glucose tolerance test (IPGTT). Oral administration (three times daily for 5 days) of Chlorella to rats receiving 4 weeks of fructose-rich chow abolished the elevated value of the glucose-insulin index, indicating that Chlorella has an ability to improve insulin resistance. An increase of insulin sensitivity by Chlorella was further evaluated using the plasma glucose lowering action of exogenous insulin in streptozotocin-induced diabetic rats (STZ-diabetic rats). Oral administration of Chlorella three times daily to STZ-diabetic rats increased the response to exogenous insulin 15 days later. The obtained results suggest that oral administration of Chlorella has the ability to improve insulin sensitivity, which may be used as an adjuvant therapy for patients with insulin resistance.