13 research outputs found
Atomic and electronic structure of graphene oxide/Cu interface
The results of X-ray photoemission (XPS) and valence bands spectroscopy,
optically stimulated electron emission (OSEE) measurements and density
functional theory based modeling of graphene oxide (GO) placed on Cu via an
electrophoretic deposition (EPD) are reported. The comparison of XPS spectra of
EPD prepared GO/Cu composites with those of as prepared GO, strongly reduced
GO, pure and oxidized copper demonstrate the partial (until C/O ratio about
two) removal of oxygen-containing functional groups from GO simultaneously with
the formation of copper oxide-like layers over the metallic substrate. OSEE
measurements evidence the presence of copper oxide phase in the systems
simultaneously with the absence of contributions from GO with corresponding
energy gap. All measurements demonstrate the similarity of the results for
different thickness of GO cover of the copper surface. Theoretical modeling
demonstrates favorability of migration of oxygen-containing functional groups
from GO to the copper substrate only for the case of C/O ratio below two and
formation of Cu-O-C bonds between substrate and GO simultaneously with the
vanishing of the energy gap in GO layer. Basing on results of experimental
measurements and theoretical calculations we suggest the model of atomic
structure for Cu/GO interface as Cu/CuO/GO with C/O ratio in gapless GO about
two.Comment: 22 pages, 14 figures, accepted to Thin Solid Films journa
Influence of Alkali Treatment on Anodized Titanium Alloys in Wollastonite Suspension
The surface modification of titanium alloys is an effective method to improve their biocompatibility and tailor the material to the desired profile of implant functionality. In this work, technologically-advanced titanium alloys—Ti-15Mo, Ti-13Nb-13Zr and Ti-6Al-7Nb—were anodized in suspensions, followed by treatment in alkali solutions, with wollastonite deposition from the powder phase suspended in solution. The anodized samples were immersed in NaOH or KOH solution with various concentrations with a different set of temperatures and exposure times. Based on their morphologies (observed by scanning electron microscope), the selected samples were investigated by Raman and X-ray photoelectron spectroscopy (XPS). Titaniate compounds were formed on the previously anodized titanium surfaces. The surface wettability significantly decreased, mainly on the modified Ti-15Mo alloy surface. Titanium alloy compounds had an influence on the results of the titanium alloys’ surface modification, which caused the surfaces to exhibit differential physical properties. In this paper, we present the influence of the anodization procedure on alkali treatment effects and the properties of obtained hybrid coatings
Selective Area Band Engineering of Graphene using Cobalt-Mediated Oxidation
This study reports a scalable and economical method to open a band gap in single layer graphene by deposition of cobalt metal on its surface using physical vapor deposition in high vacuum. At low cobalt thickness, clusters form at impurity sites on the graphene without etching or damaging the graphene. When exposed to oxygen at room temperature, oxygen functional groups form in proportion to the cobalt thickness that modify the graphene band structure. Cobalt/Graphene resulting from this treatment can support a band gap of 0.30 eV, while remaining largely undamaged to preserve its structural and electrical properties. A mechanism of cobalt-mediated band opening is proposed as a two-step process starting with charge transfer from metal to graphene, followed by formation of oxides where cobalt has been deposited. Contributions from the formation of both CoO and oxygen functional groups on graphene affect the electronic structure to open a band gap. This study demonstrates that cobalt-mediated oxidation is a viable method to introduce a band gap into graphene at room temperature that could be applicable in electronics applications
Optical Transparency and Local Electronic Structure of Yb-Doped Y<sub>2</sub>O<sub>3</sub> Ceramics with Tetravalent Additives
The results of optical transmission and X-ray core-level spectra measurements of Yb:Y2O3 ceramics with different tetravalent sintering additives (ZrO2, CeO2 and HfO2) fabricated from nanopowders (produced by the laser ablation method) and then annealed at 1400 ℃ in air for 2 h are presented. It is found that the transmission values for ZrO2- and HfO2-doped ceramics at the lasing wavelengths are higher than those of CeO2-doped samples. The X-ray photoelectron spectra (XPS) O 1s spectra show that the relative intensity of oxygen defect peak detected for 3Yb:Y2O3 + 5CeO2 ceramics decreases substantially and consistently compared to that of 5Yb:Y2O3 + 5HfO2 and 3Yb:Y2O3 + 5ZrO2 samples. This can be attributed to a more complete filling of oxygen vacancies due to annealing-induced oxygen diffusion into the highly defective sintered ceramics. The measurements of XPS Ce 3d spectra showed that the insufficiently complete filling of the oxygen vacancies in the 3Yb:Y2O3 + 5CeO2 compound is due to the appreciable presence of trivalent cerium ions
The appearance of Ti3+ states in solution-processed TiOx buffer layers in inverted organic photovoltaics
We study the low-temperature solution processed TiOx films and device structures using core level and valence X-ray photoelectron spectroscopy (XPS) and electronic structure calculations. We are able to correlate the fraction of Ti3+ present as obtained from Ti 2p core level XPS with the intensity of the defect states that appear within the band gap as observed with our valence XPS. Constructing an operating inverted organic photovoltaic (OPV) using the TiOx film as an electron selective contact may increase the fraction of Ti3+ present. We provide evidence that the number of charge carriers in TiOx can be significantly varied and this might influence the performance of inverted OPVs
ITO Modification for Efficient Inverted Organic Solar Cells
We
demonstrate a facile approach to designing transparent electron-collecting
electrodes by depositing thin layers of medium and low work function
metals on top of transparent conductive metal oxides (TCOs) such as
ITO and FTO. The modified electrodes were fairly stable for months
under ambient conditions and maintained their electrical characteristics.
XPS spectroscopy data strongly suggested integration of the deposited
metal in the TCO structure resulting in additional doping of the conducting
oxide at the interface. Kelvin probe microscopy measurements revealed
a significant decrease in the ITO work function after modification.
Organic solar cells based on three different conjugated polymers have
demonstrated state of the art performances in inverted device geometry
using Mg- or Yb-modified ITO as electron collecting electrode. The
simplicity of the proposed approach and the excellent ambient stability
of the modified ITO electrodes allows one to expect their wide utilization
in research laboratories and electronic industry