Critical boron-doping levels for generation of dislocations in synthetic diamond

Defects induced by boron doping in diamond layers were studied by transmission electron microscopy. The existence of a critical boron doping level above which defects are generated is reported. This level is found to be dependent on the CH4 /H2 molar ratios and on growth directions. The critical boron concentration lied in the 6.5–17.0 X 10 20 at/cm3 range in the direction and at 3.2 X 1021 at/cm 3 for the one. Strain related effects induced by the doping are shown not to be responsible. From the location of dislocations and their Burger vectors, a model is proposed, together with their generation mechanism.6 page

Social Network Typologies of Black and White Married Couples in Midlife

Although research shows that conjoint social networks are associated with well‐being among newlyweds, little is known about how these network types are linked to marital quality and psychological well‐being for long‐term married couples and about potential race differences in their configurations and associations. Using a pattern‐centered approach to examine the social networks of 91 White and 62 Black couples in their 16th year of marriage, this study revealed four couple network types (friend‐focused, wife family‐focused, bilateral family‐focused, and diverse). Results suggested that spouses in the wife family‐focused network type (characterized by above‐average contact with the wife’s family and below average contact with the husband’s family and with nonkin) reported the lowest positive marital quality and highest negative marital quality. The association of network type with negative marital quality was also moderated by gender and race. The findings highlight the importance of considering the meaningful complexity within couples’ shared networks.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136463/1/jomf12330.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136463/2/jomf12330_am.pd

Quasiparticle bandgap engineering of graphene and graphone on hexagonal boron nitride substrate

Graphene holds great promise for post-silicon electronics, however, it faces two main challenges: opening up a bandgap and finding a suitable substrate material. In principle, graphene on hexagonal boron nitride (hBN) substrate provides potential system to overcome these challenges. Recent theoretical and experimental studies have provided conflicting results: while theoretical studies suggested a possibility of a finite bandgap of graphene on hBN, recent experimental studies find no bandgap. Using the first-principles density functional method and the many-body perturbation theory, we have studied graphene on hBN substrate. A Bernal stacked graphene on hBN has a bandgap on the order of 0.1 eV, which disappears when graphene is misaligned with respect to hBN. The latter is the likely scenario in realistic devices. In contrast, if graphene supported on hBN is hydrogenated, the resulting system (graphone) exhibits bandgaps larger than 2.5 eV. While the bandgap opening in graphene/hBN is due to symmetry breaking and is vulnerable to slight perturbation such as misalignment, the graphone bandgap is due to chemical functionalization and is robust in the presence of misalignment. The bandgap of graphone reduces by about 1 eV when it is supported on hBN due to the polarization effects at the graphone/hBN interface. The band offsets at graphone/hBN interface indicate that hBN can be used not only as a substrate but also as a dielectric in the field effect devices employing graphone as a channel material. Our study could open up new way of bandgap engineering in graphene based nanostructures.Comment: 8 pages, 4 figures; Nano Letters, Publication Date (Web): Oct. 25 2011, http://pubs.acs.org/doi/abs/10.1021/nl202725

Produção de massa seca de capim papuã (Brachiaria plantaginea) submetido à adubação nitrogenada com ou sem irrigação em integração lavoura-pecuária.

Este trabalho objetivou quantificar a resposta de níveis de nitrogênio e de irrigação, com ou sem adubação de base, sobre a produção de massa seca do capim papuã