Morphology of Graphene on SiC(000-1) Surfaces

Graphene is formed on SiC(000-1) surfaces (the so-called C-face of the crystal) by annealing in vacuum, with the resulting films characterized by atomic force microscopy, Auger electron spectroscopy, scanning Auger microscopy and Raman spectroscopy. Morphology of these films is compared with the graphene films grown on SiC(0001) surfaces (the Si-face). Graphene forms a terraced morphology on the C-face, whereas it forms with a flatter morphology on the Si-face. It is argued that this difference occurs because of differing interface structures in the two cases. For certain SiC wafers, nanocrystalline graphite is found to form on top of the graphene.Comment: Submitted to Applied Physics Letters; 9 pages, 3 figures; corrected the stated location of Raman G line for NCG spectrum, to 1596 cm^-

Interface Structure of Graphene on SiC(000-1)

Graphene films prepared by heating the SiC(000-1) surface (the C-face of the {0001} surfaces) in vacuum or in a Si-rich environment are compared. It is found that different interface structures occur for the two situations. The former yields a well known 3x3 reconstructed interface, whereas the latter produces an interface with rt(43)xrt(43)-R\pm7.6 degrees symmetry. This structure is shown to contain a graphene-like layer with properties similar to the 6rt(3)x6rt(3)-R30 degrees "buffer layer" that forms on the Si(0001) surface (the Si-face).Comment: 9 pages, 4 figures; added Refs. 16 and 20, and made minor revisions to tex

Graphene formed on SiC under various environments: Comparison of Si-face and C-face

The morphology of graphene on SiC {0001} surfaces formed in various environments including ultra-high vacuum, 1 atm of argon, and 10^-6 to 10^-4 Torr of disilane is studied by atomic force microscopy, low-energy electron microscopy, and Raman spectroscopy. The graphene is formed by heating the surface to 1100 - 1600 C, which causes preferential sublimation of the Si atoms. The argon atmosphere or the background of disilane decreases the sublimation rate so that a higher graphitization temperature is required, thus improving the morphology of the films. For the (0001) surface, large areas of monolayer-thick graphene are formed in this way, with the size of these areas depending on the miscut of the sample. Results on the (000-1) surface are more complex. This surface graphitizes at a lower temperature than for the (0001) surface and consequently the growth is more three-dimensional. In an atmosphere of argon the morphology becomes even worse, with the surface displaying markedly inhomogeneous nucleation, an effect attributed to unintentional oxidation of the surface during graphitization. Use of a disilane environment for the (000-1) surface is found to produce improved morphology, with relatively large areas of monolayer-thick graphene.Comment: 22 pages, 11 figures, Proceedings of STEG-2 Conference; eliminated Figs. 4 and 7 from version 1, for brevity, and added Refs. 18, 29, 30, 31 together with associated discussio

The Huisgen 1,4-dipolar cycloaddition involving isoquinoline, dimethyl butynedioate and activated styrenes: a facile synthesis of tetrahydrobenzoquinolizine derivatives

A three-component reaction involving isoquinoline, dimethyl butynedioate and electrophilic styrenes is described. The reaction proceeds through a Huisgen 1,4-dipolar cycloaddition pathway

The three-component reaction of dicarbomethoxycarbene, aldehydes, and β-nitrostyrenes: a stereoselective synthesis of substituted tetrahydrofurans

The Rh(II)-catalyzed reaction of dimethyl diazomalonate with aryl aldehydes and β-nitrostyrenes results in the formation of highly substituted tetrahydrofurans. The reaction may be considered to involve the Huisgen dipolar cycloaddition of the carbonyl ylide, generated from the dicarbomethoxycarbene and the aldehyde, to the β-nitrostyrene. The diastereoselectivity of the reaction may be attributed to the concerted nature of the carbonyl ylide cycloaddition

Synthesis of novel heterocyclic calixarenes via the Diels-Alder reaction of calix[4]bis(spirodienones)

1071-1079The reactivity of calix[4]bis(spirodienones) depends on the nature of the dienophile used. With 1,4-benzoquinones it acts as a 4π component whereas with 1,2-benzoquinones as a 2π system, yielding benzodioxin derived macrocycles in good yield. Bis(spirodienones) can thus perform as a diene as well as a dienophile in cycloaddition reactions

Association of primary open-angle glaucoma with systemic hypertension

Open-angle glaucoma is a slowly progressive neurodegeneration of retinal ganglion cells and their axonscharacterized by a specific pattern of optic nerve head and visual field damage. Glaucoma is probably one of the most prominentocular outcomes of systemic hypertension (HTN). In the light of foregoing background and considering glaucoma havingprobable association with systemic HTN, the present study was undertaken. Materials and Methods: This study was donein a tertiary care hospital over a period of 18 months, after the ethical clearance and informed written consent of the patients.All individuals above 40 years of age regardless of gender were included in the study. Included patients underwent detailedocular and systemic history and detailed examination which included visual acuity by Snellen drum, refraction, intraocularpressure by Schiotz tonometer, gonioscopy using Zeiss four-mirror lens to evaluate the anterior chamber, visual field changesseen by Humphrey field analyzer, slit-lamp examination, fundus evaluation by both direct and indirect ophthalmoscopy, and90D lens with special attention to glaucomatous fundus changes using optical coherence tomography (OCT) with Cirrus SDOCT Carl Zeiss Meditec. Apart from ocular examination, patient’s blood pressure was taken with sphygmomanometer, anddemographic and anthropometric details were also noted. Result: A case-control study was conducted on 510 individuals ofage 40 years and above, irrespective of sex. Out of them, 340 (66.7%) patients were hypertensives with systemic blood pressureof >140/90 mmHg, whereas 170 (33.3%) patients were non-hypertensives so were taken as controls. On looking for the presenceof glaucoma in both the groups, it was observed that 13.8% of cases and 5.9% of controls had signs of glaucoma (P = 0.003,χ2= 8.58). On the further distribution of glaucoma into established and preclinical type, we found that 53.19% of glaucomatouscases and 70% of glaucomatous controls had established glaucoma (P = 0.150), while 46.8% and 30% were having preclinicalglaucoma, respectively (P = 0.020). Conclusion: A positive association was seen between HTN and primary open-angleglaucoma (POAG) prevalence. A significant difference in the distribution pattern of different clinical signs of POAG betweenhypertensives and controls was observed. The findings show that regardless of pathophysiology operating for development ofglaucoma, the clinical manifestation does not vary significantly between normotensives and hypertensives. Optic disc changesand as a result field changes are more pronounced among hypertensives as compared to normotensives, though the analysisstatistically is not significant. Thus, patients of systemic HTN are at high risk of glaucoma as HTN is contributing to bothphysiological as well as pathological damage