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Chemical state

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


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TL;DR: In this paper, the structural and chemical properties of SiO2 aerogel were investigated using X-ray photoelectron spectroscopy (XPS) and Fourier transformed infrared spectroscopic (FT-IR) for their chemical states, and the improved electrical properties after annealing at 450°C were interrelated with the thermal evolution of these surface species.

39 citations

Journal ArticleDOI
TL;DR: Chemical capacitance measurements are used to study the defect chemistry of La0.6Sr0.4FeO3–δ thin films and their polarization (η) and pO2 dependence.
Abstract: La0.6Sr0.4FeO3-δ (LSF) thin films of different thickness were prepared by pulsed laser deposition on yttria stabilized zirconia (YSZ) and characterized by using three electrode impedance spectroscopy. Electrochemical film capacitance was analyzed in relation to oxygen partial pressure (0.25 mbar to 1 bar), DC polarization (0 m to -600 m) and temperature (500 to 650 °C). For most measurement parameters, the chemical bulk capacitance dominates the overall capacitive properties and the corresponding defect chemical state depends solely on the oxygen chemical potential inside the film, independent of atmospheric oxygen pressure and DC polarization. Thus, defect chemical properties (defect concentrations and defect formation enthalpies) could be deduced from such measurements. Comparison with LSF defect chemical bulk data from the literature showed good agreement for vacancy formation energies but suggested larger electronic defect concentrations in the films. From thickness-dependent measurements at lower oxygen chemical potentials, an additional capacitive contribution could be identified and attributed to the LSF|YSZ interface. Deviations from simple chemical capacitance models at high pressures are most probably due to defect interactions.

39 citations

Journal ArticleDOI
TL;DR: It is demonstrated here that these chemical treatments significantly contaminate graphene with heteroatoms/metals, depending on the procedures followed, which may alter the electronic and catalytic properties of graphene.
Abstract: Chemical synthesis of graphene relies on the usage of various chemical reagents. The initial synthesis step, in which graphite is oxidized to graphite oxide, is achieved by a combination of chemical oxidants and acids. A subsequent chemical reduction step eliminates/reduces most oxygen functionalities to yield graphene. We demonstrate here that these chemical treatments significantly contaminate graphene with heteroatoms/metals, depending on the procedures followed. Contaminations with heteroatoms (N, B, Cl, S) or metals (Mn, Al) were present at relatively high concentrations (up to 3 at %), with their chemical states dependent on the procedures. Such unintentional contaminations (unwanted doping) during chemical synthesis are rarely anticipated and reported, although the heteroatoms/metals may alter the electronic and catalytic properties of graphene. In fact, the levels of unintentionally introduced contaminants on graphene are often higher than typical levels found on intentionally doped graphene. Our findings are important for scientists applying chemical methods to prepare graphene.

39 citations

Journal ArticleDOI
TL;DR: In this paper, the relative atomic concentration and the chemical states of the elements in the surface layer were determined by means of x-ray photoelectron spectroscopy, and the composition and chemical states were taken to represent for the stoichiometric TiNx not affected by ion sputtering.
Abstract: TiN layers produced by the PVD method were subjected to bombardment by different ion species applied in sequence. The relative atomic concentration and the chemical states of the elements in the surface layer were determined by means of x-ray photoelectron spectroscopy. The composition and chemical states of a reference sample after wet chemical etching were taken to be representative for the stoichiometric TiN not affected by ion sputtering. For this sample characteristic line energies of Ti 2p3/2 = 454.7 eV and N 1s = 396.7 eV were found. Alternate bombardment with Ar+, N2O+ ions (1–5 keV) results in significant compositional and chemical state changes. Ar+ bombardment leads to preferential loss of N from the outermost (1–3 nm) surface layers of the nearly stoichiometric TiNx (x = 1.0–1.1) without observable changes in the chemical state of the constituents. Bombardment with N2+ ions leads to a build-up of excess N (x ≫ 1) followed by the appearance of new N 1s and Ti 2p lines at 395.8 ± 0.3 eV and at 456.3 ± 0.3 eV, respectively. N2O+ bombardment increases the O and decreases the N concentration together with a concomitant shot out of a Ti 2p3/2 component peak at about 457.6 eV assignable to Ti2O3.

38 citations

Journal ArticleDOI
TL;DR: In this article, the chemical bonding structure of the HfO2∕Si stack after the SiO2 interfacial layer (IL) is partially removed by a reactive titanium metal overlayer was investigated.
Abstract: The authors report on the chemical bonding structure of the HfO2∕Si (001) stack after the SiO2 interfacial layer (IL) is partially removed by a reactive titanium metal overlayer. Using synchrotron photoelectron spectroscopy, they found that ultrathin SiO2-like IL ∼6.5A thick, which is significantly less than the initial SiO2 IL thickness of ∼15A, exists at the HfO2∕Si interface with an overlying Ti electrode. The dissociated Si from SiO2 IL is believed to go onto Si substrate where it regrows epitaxially. The interfacial trap density of the Ti-electrode sample was extracted to be ∼1.6×1011eV−1cm−2 near the midgap of Si, which was comparable to that of the control sample with W electrode.

38 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202326
202249
202184
202089
201987
201894