Enhanced hydrophobicity of CeO2 thin films: Role of the morphology, adsorbed species and crystallography

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Controlling the growth of epitaxial graphene on metalized diamond (111) surface

The 2-dimensional transformation of the diamond (111) surface to graphene has been demonstrated using ultrathin Fe films that catalytically reduce the reaction temperature needed for the conversion of sp(3) to sp(2) carbon. An epitaxial system is formed, which involves the re-crystallization of carbon at the Fe/vacuum interface and that enables the controlled growth of monolayer and multilayer graphene films. In order to study the initial stages of single and multilayer graphene growth, real time monitoring of the system was preformed within a photoemission and low energy electron microscope. It was found that the initial graphene growth occurred at temperatures as low as 500 degrees C, whilst increasing the temperature to 560 degrees C was required to produce multi-layer graphene of high structural quality. Angle resolved photoelectron spectroscopy was used to study the electronic properties of the grown material, where a graphene-like energy momentum dispersion was observed. The Dirac point for the first layer is located at 2.5 eV below the Fermi level, indicating an n-type doping of the graphene due to substrate interactions, while that of the second graphene layer lies close to the Fermi level. (C) 2015 AIP Publishing LLC

Degradation of the chemotherapy drug 5-fouorouracil on medical-grade silver surfaces

The degradation of the chemotherapy drug 5-fluorouracil by a non-pristine metal surfaces is studied. Using density functional theory, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy we show that the drug is entirely degraded by medical-grade silver surfaces, already at body temperature, and that all of the fluorine has left the molecule, presumably as HF. Remarkably, this degradation is even more severe than that reported previously for 5-fluorouracil on a pristine monocrystalline silver surface (in which case 80% of the drug reacted at body temperature) [1]. We conclude that the observed reaction is due to a reaction pathway, driven by H to F attraction between molecules on the surface, which results in the direct formation of HF; a pathway which is favoured when competing pathways involving reactive Ag surface sites are made unavailable by environmental contamination. Our measurements indicate that realistically cleaned, non-pristine silver alloys, which are typically used in medical applications, can result in severe degradation of 5-fluorouracil, with the release of HF – a finding which may have important implications for the handling of chemotherapy drugs

Tunable high aspect ratio polymer nanostructures for cell interfaces

Nanoscale topographies and chemical patterns can be used as synthetic cell interfaces with a range of applications including study and control of cellular processes. Herein, we describe the fabrication of high aspect ratio nanostructures using electron beam lithography in the epoxy-based polymer SU-8. We show how nanostructure geometry, position and fluorescent properties can be tuned, allowing flexible device design. Further, thiol-epoxide reactions were developed to give effective and specific modification of SU-8 surface chemistry. SU-8 nanostructures were made directly on glass cover slips, enabling the use of high resolution optical techniques such as live-cell confocal, total internal reflection and 3D structured illumination microscopy to investigate cell interactions with the nanostructures. Details of cell adherence and spreading, plasma membrane conformation and actin organization in response to high aspect ratio nanopillars and nanolines were investigated. The versatile structural and chemical properties combined with high resolution cell imaging capabilities of this system are an important step towards better understanding and controlling cell interactions with nanomaterials

Tautomerization of Thymine Using Ultraviolet Light

Ultraviolet-light-induced changes to the nucleobase thymine deposited onto a MoS₂ surface were studied using photoelectron spectroscopy and first-principles calculations. These measurements suggest changes in the molecular structure indicated by changes in core electron binding energies. The experimental work has been interpreted by means of ab initio calculations using coupled cluster singles and doubles (CCSD) linear response theory. Contrary to the expected behavior, i.e., the dimerization of two thymine molecules into a pyrimidine dimer, a shift between two tautomeric forms was observed upon UV-exposure. Exposure to ionizing radiation is known to induce damage in many biological molecules, and the present work gives additional insight into its effects on thymine, the interactions of the molecules, and finally how certain UV photoproducts may be avoided

One-dimensional spin-polarized surface states: A comparison of Bi(112) with other vicinal bismuth surfaces

Vicinal surfaces of bismuth are unique test beds for investigating one-dimensional (1D) spin-polarized surface states that may one day be used in spintronic devices. In this paper, such states have been observed for the (112) surface when measured using angle- and spin-resolved photoemission spectroscopy, and also when calculated using a tight-binding model and with density functional theory. The surface states appear as elongated Dirac-cones which are 1D and almost dispersionless in the ky direction, but disperse with energy in the orthogonal kx direction to form two ×-like features centered at the ky line through Γ. Unlike many materials considered for spintronic applications, their 1D nature suggests that conductivity and spin-transport properties are highly dependent on direction. The spin polarization of the surface states is mainly in plane and parallel to the 1D states, but there are signs of a tilted out-of-plane spin-vector component for one of the features. The Bi(112) surface states resemble those found for other vicinal surfaces of bismuth, strongly indicating that their existence and general properties are robust properties of vicinal bismuth surfaces. Furthermore, differences in the details of the states, particularly related to their spin polarization, suggest that the electronic band structure may be engineered simply by precise cutting and polishing of the crystal.publishedVersio

In Situ Patterning of Ultrasharp Dopant Profiles in Silicon

We develop a method for patterning a buried two-dimensional electron gas (2DEG) in silicon using low kinetic energy electron stimulated desorption (LEESD) of a monohydride resist mask. A buried 2DEG forms as a result of placing a dense and narrow profile of phosphorus dopants beneath the silicon surface; a so-called δ -layer. Such 2D dopant profiles have previously been studied theoretically, and by angle-resolved photoemission spectroscopy, and have been shown to host a 2DEG with properties desirable for atomic-scale devices and quantum computation applications. Here we outline a patterning method based on low kinetic energy electron beam lithography, combined with in situ characterization, and demonstrate the formation of patterned features with dopant concentrations sufficient to create localized 2DEG states