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"Oxides Surfaces."
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Metal oxide nanostructures chemistry : synthesis from aqueous solutions
An overview of metal oxide nanoparticle fabrication in aqueous solution.
Book
Formation and stability of Fe-rich terminations of the Fe3O4(001) surface
Understanding how the structure of iron oxide surfaces varies with their environment is essential for rationalizing their role in (geo-)chemistry and optimizing their application in modern technologies. In this paper, we create Fe-rich terminations of Fe3O4(001) by depositing iron directly onto the ‘subsurface cation vacancy’-reconstructed surface, which is the most stable surface under ultrahigh vacuum conditions. Scanning tunneling microscopy and x-ray photoelectron spectroscopy data reveal that the excess iron is initially accommodated as two-fold coordinated adatoms and later incorporates into the subsurface cation vacancies. As the coverage increases, small patches of the octahedral pair termination (also known as the ‘Fe dimer’ termination) nucleate, eventually covering the entire surface after the deposition of 2 iron atoms per (√2×√2)R45° unit cell. This conclusion effectively rules out some existing models for the termination and provides support for the model proposed by Rustad et al (Surface Science 432, L583-L588, 1999), highlighting the need for further theoretical work to complete the Fe3O4(001) surface phase diagram. The octahedral pair termination is found to be unstable above 523 K and upon exposure to molecular O2 because the excess iron atoms agglomerate to form small FeOx clusters.
Journal Article
Surface complexation modeling
This book provides a description of the generalized two layer surface complexation model, data treatment procedures, and thermodynamic constants for sorption of metal cations and anions on gibbsite, the most common form of aluminum oxide found in nature and one of the most abundant minerals in soils, sediments, and natural waters.
eBook
Review: 3-Aminopropyltriethoxysilane (APTES) Deposition Methods on Oxide Surfaces in Solution and Vapor Phases for Biosensing Applications
Surface functionalization and bioreceptor immobilization are critical processes in developing a highly sensitive and selective biosensor. The silanization process with 3-aminopropyltriethoxysilane (APTES) on oxide surfaces is frequently used for surface functionalization because of beneficial characteristics such as its bifunctional nature and low cost. Optimizing the deposition process of the APTES layer to obtain a monolayer is crucial to having a stable surface and effectively immobilizing the bioreceptors, which leads to the improved repeatability and sensitivity of the biosensor. This review provides an overview of APTES deposition methods, categorized into the solution-phase and vapor-phase, and a comprehensive summary and guide for creating stable APTES monolayers on oxide surfaces for biosensing applications. A brief explanation of APTES is introduced, and the APTES deposition methods with their pre/post-treatments and characterization results are discussed. Lastly, APTES deposition methods on nanoparticles used for biosensors are briefly described.
Journal Article
Anisotropic two-dimensional electron gas at SrTiO3(110)
Two-dimensional electron gases (2DEGs) at oxide heterostructures are attracting considerable attention, as these might one day substitute conventional semiconductors at least for some functionalities. Here we present a minimal setup for such a 2DEG—the SrTiO3(110)-(4 × 1) surface, natively terminated with one monolayer of tetrahedrally coordinated titania. Oxygen vacancies induced by synchrotron radiation migrate underneath this overlayer; this leads to a confining potential and electron doping such that a 2DEG develops. Our angle-resolved photoemission spectroscopy and theoretical results show that confinement along (110) is strikingly different from the (001) crystal orientation. In particular, the quantized subbands show a surprising \"semiheavy\" band, in contrast with the analog in the bulk, and a high electronic anisotropy. This anisotropy and even the effective mass of the (110) 2DEG is tunable by doping, offering a high flexibility to engineer the properties of this system.
Journal Article
Transient oxide formation on APS NiCrAlY after oxidation heat treatment
In this study, the transient surface oxide formation on APS NiCrAlY samples was examined after oxidation heat treatment at temperatures between 1000 and 1100 °C. The surface oxides observed on the NiCrAlY surface included a sporadic top layer of NiO and a continuous layer of alumina immediately adjacent to the NiCrAlY coating. Cr-rich oxide in smaller quantities than alumina was also found surrounding the NiO and dispersed within alumina. The alumina assumed whisker-shaped morphology when being observed from the surface but formed continuous film along the NiCrAlY surface. Although the formation of alumina has been observed on all the samples examined in this study, the NiCrAlY sample heat treated at 1050 °C for 5 h generated more continuous α-alumina layer and also contained less surface NiO and Cr-rich oxide. Based on the results, it is believed that NiO developed first upon exposure to an oxidizing environment at high temperature, and stable alumina began to form with the increase in heat treatment temperature and time. © 2010 ASM International.
Journal Article
Exploring partially reduced CeO 2 (111) surface at the atomic scale using scanning probe microscopy
Cerium dioxide (CeO
) is extensively studied due to its exceptional redox properties, which are closely related to oxygen vacancy formation and the associated charging of cerium atoms from Ce
to Ce
. These charged species play an important role in promoting active sites in CeO
-based catalysts. The existence of Ce
atoms is typically characterized by means of surface spectroscopic techniques, because the direct atomic-scale observation and discrimination of Ce
ions from Ce
atoms remains challenging. Here, we use simultaneous scanning tunneling microscopy (STM) and atomic force microscopy (AFM) complemented by force spectroscopy to characterize candidates to Ce
atoms on partially reduced CeO
(111) samples. While STM images reveal electronic modulations of the atomic contrast in the form of an inhomogeneous shading, AFM clearly differentiates these electronic features from the true topographic atomic structure. The chemical reactivity of these candidates to Ce
atoms is quantified against the Ce
counterparts by means of force spectroscopy using carbon monoxide functionalized probes. This study demonstrates that the combination of STM with AFM and force spectroscopy bears great potential to provide robust atomic-level insights into the chemistry of defects at ceria surfaces.
Journal Article
Exploring partially reduced CeO2(111) surface at the atomic scale using scanning probe microscopy
IMPACT STATEMENT We directly visualize and chemically distinguish Ce, O, and defective Ce sites of the CeO2(111) surface, as well as CO molecules on top of it, using high-resolution STM, AFM, and force spectroscopy with functionalized probes.
Journal Article
Strong Metal–Support Interaction and Reactivity of Ultrathin Oxide Films
Noble metal particles supported on transition metal oxides (TMO) may undergo a so-called strong metal–support interaction via encapsulation. This perspective addresses catalytic properties of the metal catalysts in the SMSI state which can be explained on the basis of complementary studies performed on well-defined, metal-supported TMO films. In particular, the results of low temperature CO oxidation revealed the key role of weakly bound oxygen species provided by a two-dimensional (“monolayer”) oxide film. The binding energy of such oxygen atoms can be used as a descriptor for oxidation activity. Reaction rate enhancement often observed for TMO films partially covering the metal surface is rationalized within a mechanism in which the metal acts as a promoter to create the most active “oxide
red
/oxide
ox
” interface formed by reduced and oxidized phases in the film. Although only low temperature CO oxidation is considered, it is tempting to generalize these ideas to other oxidation reactions following the Mars–van Krevelen type mechanism. In addition, metal-supported ultrathin TMO films may serve as well-defined model systems to examine different aspects of the “electron theory of catalysis” which was proposed long ago and which is based on electron transfer mechanisms.
Graphical Abstract
Journal Article