Chemical state

About: Chemical state is a research topic. Over the lifetime, 2378 publications have been published within this topic receiving 78183 citations.

Non-chemical fluorination of hexagonal boron nitride by high-energy ion irradiation.

Abstract: Two-dimensional materials such as hexagonal boron nitride (h-BN) and graphene have attracted wide attention in nanoelectronics and spintronics. Since their electronic characteristics are strongly affected by the local atomic structure, the heteroatom doping could allow us to tailor the electronic and physical properties of two-dimensional materials. In this study, a non-chemical method of heteroatom doping into h-BN under high-energy ion irradiation was demonstrated for the LiF/h-BN/Cu heterostructure. Spectroscopic analysis of chemical states on the relevant atoms revealed that 6% ± 2% fluorinated h-BN is obtained by the irradiation of 2.4 MeV Cu2+ ions with the fluence up to 1014 ions cm-2. It was shown that the high-energy ion irradiation leads to a single-sided fluorination of h-BN by the formation of the fluorinated sp 3-hybridized BN.

XEOM 1 - A novel microscopy system for the chemical imaging of heritage metal surfaces

Abstract: Background: We describe a novel microscopy system which can obtain chemical maps from the surfaces of heritage metals in air or a controlled environment. The microscope, x-ray excited optical microscope Mk 1 (XEOM 1), forms images from x-ray excited optical luminescence (XEOL) induced by illuminating a few square millimetres of the sample with monochromated x-rays (broad beam or macroprobe illumination). XEOL is a spectroscopy tool in its own right and can, under the right circumstances, also be a vehicle for x-ray absorption spectroscopy. This (usually) synchrotron based technique provides information on the chemical state and short-range atomic order of the top few microns of a surface. It is thus well suited to heritage metal corrosion studies and is complementary to synchrotron x-ray diffraction. Results: Imaging can be performed by scanning the sample under an x-ray microprobe. We show elsewhere that the power density needed for image acquisition on a reasonable time-scale is high enough to damage a patina and modify its chemistry. Although the damaged region may be invisible to the human eye, the data are characteristic of the damage and not the native chemistry of the surface. A macrobeam power density can be 4 orders of magnitude smaller than that for a microbeam and no surface modification was observed on test samples. Features of the instrument are demonstrated using copper test surfaces with a spatially varying patination to establish the ground work for the imaging of copper, cuprite, nantokite and atacamite/paratacamite and a first application from a bronze chain mail link. In parallel we have developed a suite of imaging software which can process XEOM image stacks to produce reduced data sets characteristic of various aspects of the surface chemical map. These include edge-shift (oxidation state) images and edge height (high contrast) images and spectra from user defined regions of interest. Conclusions: The technique can map the oxidation state of a surface from shifts in the absorption edge energy across columns of pixels in an image set, and map particular compounds from their characteristic XANES spectra. Optically filtered images give improved chemical selectivity and the data sets contain as yet untapped information sources.

Intermediate Cu-O-Si Phase in the Cu-SiO2/Si(111) System: Growth, Elemental, and Electrical Studies.

Abstract: We investigate here the strain-induced growth of Cu at 600 °C and its interactions with a thermally grown, 270 nm-thick SiO2 layer on the Si(111) substrate. Our results show clear evidence of triangular voids and formation of triangular islands on the surface via a void-filling mechanism upon Cu deposition, even on a 270 nm-thick dielectric. Different coordination states, oxidation numbers, and chemical compositions of the Cu-grown film are estimated from the core level X-ray photoelectron spectroscopy (XPS) measurements. We find evidence of different compound phases including an intermediate mixed-state of Cu-O-Si at the interface. Emergence of a mixed Cu-O-Si intermediate state is attributed to the new chemical states of Cu x+, O x , and Si x+ observed in the high-resolution XPS spectra. This intermediate state, which is supposed to be highly catalytic, is found in the sample with a concentration as high as ∼41%. Within the Cu-O-Si phase, the atomic percentages of Cu, O, and Si are ∼1, ∼86, and ∼13%, respectively. The electrical measurements carried out on the sample reveal different resistive channels across the film and an overall n-type semiconducting nature with a sheet resistance of the order of 106 Ω.

Gold alloys for resin bonding including small amount base metals--structural changes of alloy surface by the high-temperature oxidation.

Abstract: To achieve durable bonding with adhesive resin, the surface roughness and the kinds of oxides, respectively to increase mechanical retention to enhance the chemical affinity of adhesive monomer with the gold alloy, were regulated by high-temperature oxidation together with the addition of small amounts of base metals. Alloys containing 2mass% of Ni, In, or Cr with Cu were oxidized at 800°C for 20min in air, pickled in thioglycolic acid, and subsequently oxidized at 500°C for 10min in air. The morphology of the internal oxidation zone changed markedly according to the added base metals. Alhough the internal oxide particle composed of only Cu2O was removed by pickling, NiO, In2O3, and chromium oxides could not removed and remained on the alloy surface. The surface roughness was increased by addition of Ni, In, or Cr. Applying the present method can control the roughness and chemical states on a gold alloy surface to increase its adhesive ability with adhesive resins.