DFT study of water on graphene: Synergistic effect of multilayer p-doping

Recent experiments related to a study concerning the adsorption of water on graphene have demonstrated the p-doping of graphene, although most of the ab initio calculations predict nearly zero doping. To shed more light on this problem, we have carried out van der Waals density functional theory calculations of water on graphene for both individual water molecules and continuous water layers with coverage ranging from one to eight monolayers. Furthermore, we have paid attention to the influence of the water molecule orientation toward graphene on its doping properties. In this article, we present the results of the band structure and the Bader charge analysis, showing the p-doping of graphene can be synergistically enhanced by putting 4-8 layers of an ice-like water structure on graphene having the water molecules oriented with oxygen atoms toward graphene.

Density functional study of gallium clusters on graphene: electronic doping and diffusion

Motivated by experimental results on transport properties of graphene covered by gallium atoms, the density functional theory study of clustering of gallium atoms on graphene (up to a size of 8 atoms) is presented. The paper explains a rapid initial increase of graphene electron doping by individual Ga atoms with Ga coverage, which is continually reduced to zero, when bigger multiple-atom clusters have been formed. According to density functional theory calculations with and without the van der Waals correction, gallium atoms start to form a three-dimensional cluster from five and three atoms, respectively. The results also explain an easy diffusion of Ga atoms while forming clusters caused by a small diffusion barrier of 0.11 eV. Moreover, the calculations show this barrier can be additionally reduced by the application of an external electric field, which was simulated by the ionization of graphene. This effect offers a unique possibility to control the cluster size in experiments only by applying a gate-voltage to the graphene in a field-effect transistor geometry and thereby without growth temperature assistance.

Electronic transport properties of graphene doped by gallium

In this work we present the effect of low dose gallium (Ga) deposition (<4 ML) performed in UHV (10^-7 Pa) on the electronic doping and charge carrier scattering in graphene grown by chemical vapor deposition. In situ graphene transport measurements performed with a graphene field-effect transistor structure show that at low Ga coverages a graphene layer tends to be strongly n-doped with an efficiency of 0.64 electrons per one Ga atom, while the further deposition and Ga cluster formation results in removing electrons from graphene (less n-doping). The experimental results are supported by the density functional theory calculations and explained as a consequence of distinct interaction between graphene and Ga atoms in case of individual atoms, layers, or clusters.

Interface-induced room-temperature ferromagnetism in hydrogenated epitaxial graphene

We show ferromagnetic properties of hydrogen-functionalized epitaxial graphene on SiC. Ferromagnetism in such a material is not directly evident as it is inherently composed of only nonmagnetic constituents. Our results nevertheless show strong ferromagnetism with a saturation of 0.9μ(B)/hexagon projected area, which cannot be explained by simple magnetic impurities. The ferromagnetism is unique to hydrogenated epitaxial graphene on SiC, where interactions with the interfacial buffer layer play a crucial role. We argue that the origin of the observed ferromagnetism is governed by electron correlation effects of the narrow Si dangling bond states in the buffer layer exchange coupled to localized states in the hydrogenated graphene layer. This forms a quasi-three-dimensional ferromagnet with a Curie temperature higher than 300 K.

[Treatment strategies of the colorectal anastomosis stricture]

INTRODUCTION

The treatment of the stenoses of colorectal anastomoses represents a difficult area of colonic surgery. This is partly connected to the introduction of staplers and an increasing amount of sphincter-preserving surgeries. At our clinic, we solve the stenoses of colorectal anastomoses using a surgical rectoscope with a good effect.

MATERIAL AND METHODS

We analysed retrospectively a group of 27 patients with benign stenosis of colorectal anastomosis of the medial and upper rectum who underwent surgery at our clinic in the period between January 2004 and December 2011. From the total amount of 27 patients, in 23 patients the stenosis was caused by the dehiscence of anastomosis, and in 4 patients the stenosis had a different etiology.

RESULTS

In the group of 27 patients, in 14 patients the stenosis of colorectal anatomosis was solved radiologically using a high pressure balloon. Total of 13 patients underwent surgery, in 10 of them we used the surgical rectoscope and 3 patients underwent an open abdominal procedure.

CONCLUSION

The first method of choice in treatment of the stenoses of the colorectal anastomoses is a balloon dilatation. If this is not successful we can use the surgical rectoscope as a minimally invasive though effective and safe method.

[The benefits of centralization of care for patients with acute upper gastrointestinal bleeding]

INTRODUCTION

Acute upper gastrointestinal bleeding still remains one of the serious conditions that require a rapid diagnostic and therapeutic intervention. Such procedure is highly dependent on good interdisciplinary cooperation, which, when centralized, may positively influence mortality and economic costs.

OBJECTIVE

To determine the benefits of centralization of care provided to patients with acute bleeding in the upper gastrointestinal tract.

PATIENTS AND METHODS

A total of 632 patients with acute bleeding were enrolled in the study at two different health-care establishments of the same type, however with a different organisation of care. We have evaluated the influence of the organisation of care on the length of hospitalization stay, mortality and economic costs.

RESULTS

Centralized treatment significantly shortens the interval from hospital admission to endoscopic examination and leads to a reduction in mortality, although not statistically significant. On the other hand, it does not affect the length of hospitalization, the distribution of patients between internal and surgical departments, and provides no guarantee of lower economic costs. Many other factors play an important role in that respect. It seems, that the importance of centralization plays the main role especially in the pre-hospital and early hospital period, when it accelerates and simplifies the diagnostic and therapeutic procedure.