The Efficiency Droop of InGaN-Based Green LEDs with Different Superlattice Growth Temperatures on Si Substrates via Temperature-Dependent Electroluminescence

InGaN-based green light-emitting diodes （LEDs） with different growth temperatures of superlattice grown on Si （111） substrates are investigated by temperature-dependent electroluminescence between 100 K and 350K. It is observed that with the decrease of the growth temperature of the superlattice from 895℃ to 855℃, the forward voltage decreases, especially at low temperature. We presume that this is due to the existence of the larger average size of V-shaped pits, which is determined by secondary ion mass spectrometer measurements. Meanwhile, the sample with higher growth temperature of superlattice shows a severer efficiency droop at cryogenic temperatures （about 100 K-150 K）. Electron overflow into p-GaN is considered to be the cause of such phenomena, which is relevant to the poorer hole injection into multiple quantum wells and the more reduced effective active volume in the active region.

Influence of the Source to Substrate Distance on the Growth,Tribological Properties and Optical Properties of Be Films

The Be films were prepared by thermal evaporation at different sources to substrate distances（SSD） on glass substrates. The decrease of SSD from 90 mm to 50 mm caused the increase of substrate temperature and the rising density of incident Be atoms, thus the properties of Be films greatly changed accordingly. The experimental results showed that the grain diameter in the Be films transited from below 100 nm to 300 nm, the film growth rate increased from 2.35 nm/min to 4.73 nm/min and the roughness increased from 7 nm to 49 nm. The performance study suggested that the friction coefficient of Be films increased from 0.13 to 0.27 and was related to the surface roughness and inner structure, the near-infrared reflectance of Be films increased from 40% to 85% with the increase of wavelength and concurrently decreased with the decrease of SSD, respectively. The performance study indicated that the Be film had the potential application in specific near-infrared reflectance optical system.

EFFECT OF SUBSTRATE TEMPERATURE ON Y-Ba-Cu-O THIN FILMS IN SITU GROWTH BY MOCVD

Superconducting thin films of YBa2Cu3O7-x（Y-Ba-Cu-O） with Tc more than 85K have been deposited in situ by metalorganic chemical vapor deposition （MOCVD） on yttria stabilized zirconia（YSZ） substrates. The relationship of film orientation on substrate temperature and the lowest formation temperature region of superconducting phase have been obtained after changing the substrate temperature. The epitaxial relation between Y-Ba-Cu-O films and the YSZ su bstrates were discussed.

Theoretical studies on alloying of germanene supported on Al (111) substrate

Using density functional theory,we study the alloying of the buckled hexagonal germanene superlattice supported on Al(111)-(3×3),the sheet composed of triangular,rhombic,and pentagonal motifs on Al(111)-(3×3),and the buckled geometry on Al(111)-(√7×√7)(19°),which are denoted,respectively,by BHS,TRP,and SRT7,to facilitate the discussion in this paper.They could be alloyed in the low doping concentration range.The stable configurations BHS,TRP,and SRT7 of the pure and alloyed germanenes supported on both Al(111) and its Al2 Ge surface alloy,except the SRT7 pure germanene on Al2 Ge,could re-produce the experimental scanning tunneling microscopy images.The relatively stable AlGe alloy species are the Al3 Ge5 BHS-2 T,Al3 Ge5 TRP-2 T,and Al3 Ge3 SRT7-1 T on Al(111) while they are the Al4 Ge4 BHS-1 T,Al3 Ge5 TRP-2 T,and A127 Ge27 SRT7-(3×3)-9 T on Al2 Ge(the n in the nT means that there are n Ge atoms per unit which sit at the top sites and protrude upward).In addition,the Al3 Ge5 BHS-2 T and Al4 Ge4 BHS-1 T are the most stable alloy sheets on Al(111) and Al2 Ge,respectively.Comparing with the experimental studies,there exists no structural transition among these alloyed configurations,which suggests that the experimental conditions play a crucial role in selectively growing the pure or the alloyed germanene sheets,which may also help grow the one-atomic thick honeycomb structure on idea Al(111).

Differential roles of EPS8 in carcinogenesis:Loss of protein expression in a subset of colorectal carcinoma and adenoma

AIM:To analyze the epidermal growth factor receptor pathway substrate 8(EPS8) expression status and role in colorectal carcinogenesis given that EPS8 has a conserved actin barbed-end capping function that is required for proper maturation in intestinal cells.METHODS:We studied 8 colon cancer cell lines and 58 colorectal tumors(19 adenomas and 39 carcinomas).We performed expression microarray analysis of colon cancer cell lines followed by loss of heterozygosity(LOH)analysis and immunohistochemistry for EPS8 expression in colon tumors.Subsequently,we performed mutation analysis by direct sequencing and methylation analysis by bisulfite sequencing and methylation-specific polymerase chain reaction assays.RESULTS:Expression microarray analysis of colon cancer cell lines showed overexpression of EPS8 transcript in all lines but RKO.Genome wide loss of heterozygosity(LOH) analysis of colon tumors,showed considerable LOH at the EPS8 gene locus.Immunohistochemically,EPS8 was constitutively expressed in normal colonic mucosa with a dot-like supranuclear localization with accentuation at the luminal surface supporting its proposed role in epithelial maturation.Nineteen colon tumors(4 adenoma,15 carcinoma) out of 51(37%) showed strikingly tumor specific EPS8 protein loss.Of the remaining tumors,5/51(2 adenoma,and 3 carcinoma,10%) showed marked overexpression,while 27/51 tumors(53%) showed retained expression.Mutation analysis revealed a missense mutation(c.794C>T,p.R265C) in exon 8 in RKO.The EPS8 promoter was also methylated in RKO,but there was no significant methylation in other cell lines or carcinoma specimens.CONCLUSION:The loss of EPS8 expression in colorectal adenomas and carcinomas suggests that down regulation of this gene contributes to the development of a subset of colorectal cancers,a finding which could have applications in diagnosis and treatment.

Self-formation of hexagonal nanotemplates for growth of pyramidal quantum dots by metalorganic vapor phase epitaxy on patterned substrates

We demonstrate the self-formation of hexagonal nanotemplates on GaAs （111）B substrates patterned with arrays of inverted tetrahedral pyramids during metal-organic vapor phase epitaxy and its role in producing high-symmetry, site-controlled quantum dots （QDs）. By combining atomic force microscopy measurements on progressively thicker GaAs epitaxial layers with kinetic Monte Carlo growth simulations, we demonstrate self-maintained symmetry elevation of the QD formation sites from three-fold to six-fold symmetry. This symmetry elevation stems from adatom fluxes directed towards the high-curvature sites of the template, resulting in the formation of a fully three-dimensional hexagonal template after the deposition of relatively thin GaAs layers. We identified the growth conditions for consistently achieving a hexagonal pyramid bottom, which are useful for producing high-symmetry QDs for efficient generation of entangled photons.