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

Nickel(II) and Copper(II) Coordination Polymers Derived from 1,2,4,5-Tetraaminobenzene for Lithium-Ion Batteries

Highly conductive electrochemically active materials are required for developing a new generation of ultrafast lithium-ion batteries (LIBs). Recently, a novel family of transition metal coordination polymers derived from arylamines exhibited conductivities of over 1 S cm(-1). Low molecular weight analogues of these materials show rich and reversible electrochemical behavior. However, there are just very few reports on the application of such materials in LIBs. In this paper, linear nickel(II) and copper(II) coordination coordination polymers derived from 1,2,4,S-tetraaminobenzene are reported and investigated as anode and cathode materials for LIBs. In the anode mode, both materials show ultrafast cycling behavior with impressive stability. Particularly, for the nickel-based material, a specific capacity of 83 mA h g(-1) is reached at 20 A g(-1) current density, and 79% of this capacity is retained after 20 000 cycles. Moreover, the copper-based polymer used as a cathode component shows a specific capacity of up to 262 mA h g(-1) in the voltage range of 1.5-4.1 V vs Li/Li+, which corresponds to the energy density of 616 W h kg(-1)

Linking the HOMO-LUMO gap to torsional disorder in P3HT/PCBM blends

The electronic structure of [6,6]-phenyl C61 butyric acid methyl ester (PCBM), poly(3-hexylthiophene) (P3HT), and P3HT/PCBM blends is studied using soft X-ray emission and absorption spectroscopy and density functional theory calculations. We find that annealing reduces the HOMO-LUMO gap of P3HT and P3HT/PCBM blends, whereas annealing has little effect on the HOMO-LUMO gap of PCBM. We propose a model connecting torsional disorder in a P3HT polymer to the HOMO-LUMO gap, which suggests that annealing helps to decrease the torsional disorder in the P3HT polymers. Our model is used to predict the characteristic length scales of the flat P3TH polymer segments in P3HT and P3HT/PCBM blends before and after annealing. Our approach may prove useful in characterizing organic photovoltaic devices in situ or even in operando

Optical Transparency and Local Electronic Structure of Yb-Doped Y₂O₃ 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

Influence of Oxygen Ion Migration from Substrates on Photochemical Degradation of CH3NH3PbI3 Hybrid Perovskite

Measurements of XPS survey, core levels (N 1s, O 1s, Pb 4f, I 3d), and valence band (VB) spectra of CH3NH3PbI3 (MAPbI3) hybrid perovskite prepared on different substrates (glass, indium tin oxide (ITO), and TiO2) aged under different light-soaking conditions at room temperature are presented. The results reveal that the photochemical stability of MAPbI3 depends on the type of substrate and gradually decreases when glass is replaced by ITO and TiO2. Also, the degradation upon exposure to visible light is accompanied by the formation of MAI, PbI2, and Pb0 products as shown by XPS core levels spectra. According to XPS O 1s and VB spectra measurements, this degradation process is superimposed on the partial oxidation of lead atoms in ITO/MAPbI3 and TiO2/MAPbI3, for which Pb–O bonds are formed due to the diffusion of the oxygen ions from the substrates. This unexpected interaction leads to additional photochemical degradation

Realizing High Brightness Quasi‐2D Perovskite Light‐Emitting Diodes with Reduced Efficiency Roll‐Off via Multifunctional Interface Engineering

Abstract Quasi‐2D perovskites have recently flourished in the field of luminescence due to the quantum‐confinement effect and the efficient energy transfer between different n phases resulting in exceptional optical properties. However, owing to the lower conductivity and poor charge injection, quasi‐2D perovskite light‐emitting diodes (PeLEDs) typically suffer from low brightness and high‐efficiency roll‐off at high current densities compared to 3D perovskite‐based PeLEDs, which is undoubtedly one of the most critical issues in this field. In this work, quasi‐2D PeLEDs with high brightness, reduced trap density, and low‐efficiency roll‐off are successfully demonstrated by introducing a thin layer of conductive phosphine oxide at the perovskite/electron transport layer interface. The results surprisingly show that this additional layer does not improve the energy transfer between multiple quasi‐2D phases in the perovskite film, but purely improves the electronic properties of the perovskite interface. On the one hand, it passivates the surface defects of the perovskite film; on the other hand, it promotes electron injection and prevents hole leakage across this interface. As a result, the modified quasi‐2D pure Cs‐based device shows a maximum brightness of > 70,000 cd m−2 (twice that of the control device), a maximum external quantum efficiency (EQE) of > 10% and a much lower efficiency roll‐off at high bias voltages