We report in situ atomic-resolution transmission electron microscopy observations of the oxidation of stepped Cu surfaces. We find that the presence of surface steps both inhibits oxide film growth and leads to the oxide decomposition, thereby resulting in oscillatory oxide film growth. Using atomistic simulations, we show that the oscillatory oxide film growth is induced by oxygen adsorption on the lower terrace along the step edge, which destabilizes the oxide film formed on the upper terrace.
Novel hybrid nanocomposites of Cu2O nanoparticles (NPs) partially embedded in CuO nanowires (NWs) were produced by simple thermal reduction of CuO NWs in a vacuum. It is found that most Cu2O NPs adopt two regular shapes, one being cubic and the other being octahedral. The shape selection of the Cu2O nanocrystals is governed by the orientation relationship between Cu2O NPs and CuO NWs. The formation of such hierarchical hybrid nanostructures is induced by the topotactic reduction of CuO NWs. Compared with pure CuO NWs, the polyhedral Cu2O NP-CuO NW hierarchical hybrid nanostructures exhibit enhanced ability to photodegrade methyl orange under visible light, which is attributed to the synergic effects of CuO NWs and Cu2O NPs.
The oxidation of NiAl(100) surfaces by water vapor is studied using X-ray photoelectron spectroscopy (XPS) to elucidate the effect of temperature and vapor pressure on the surface passivation mechanism of the NiAl alloy. The water-vapor oxidation at ambient temperature (25 °C) results in self-limiting Al(OH)3/Al2O3 bilayer film growth to a less extent of the limiting thickness regimes, in which the growth of the inner Al2O3 layer occurs via dehydration of the outer Al(OH)3 layer. The growth of the passivating overlayer at the ambient temperature depletes Al and forms a Ni-rich layer at the oxide/alloy interface that impedes supply of Al atoms to the outer surface for Al(OH)3 formation via the hydration reaction, whereby resulting in a more Al-deficient structure of the outer Al(OH)3 layer upon increasing the vapor pressure. In contrast, the water-vapor oxidation at 300 °C results in Al2O3 single-layer film growth to a larger limiting thickness without involving the transient hydroxide phase of Al(OH)3. It is shown that increasing the oxidation temperatures results in the formation of a more compact Al2O3 film owning to the enhanced bulk diffusion rate that maintains an adequate supply of Al atoms to the oxide/alloy interface to sustain the oxide film growth to the full extent of the limiting thickness.
Oxidation of Cu occurs via Cu2O islanding on an oxide wetting layer at a critical thickness of two atomic layers. The transition from 2D wetting-layer growth to 3D oxide islanding is driven energetically arising from the Cu-Cu2O interfacial interaction.
Oxidation of metals usually results in the formation of an oxide nanostructure with poorly controlled growth morphologies. By employing a simple mechanical approach that uses sandblasting to modify the surface roughness of iron substrates, we demonstrate that the morphologies of hematite (?-Fe2O3) nanostructures varying from the growth of one-dimensional nanowires to two-dimensional nanoblades can be achieved during the thermal oxidation of iron. Electron microscopy studies show that the effect of surface sandblasting is to effectively modify the oxide nucleation locations that define the growth shapes. The optical properties of hematite nanowires and nanoblades are examined for the demonstration of the morphology-property correlations.
We report an x-ray photoelectron spectroscopy study of the oxidation of Al(111) surfaces at room temperature, which reveals that the limiting thickness of an aluminum oxide film can be tuned by using oxygen pressure. This behavior is attributed to a strong dependence of the kinetic potential on the oxygen gas pressure. The coverage of oxygen anions on the surface of the oxide film depends on the gas pressure leading to a pressure dependence of the kinetic potential. Our results indicate that a significantly large oxygen pressure (>1??Torr) is required to develop the saturated surface coverage of oxygen ions, which results in the maximum kinetic potential and therefore the saturated limiting thickness of the oxide film.
Multiple endocrine neoplasia type 1 (MEN 1) is an autosomal dominant disorder characterized by the development of parathyroid hyperplasia, pancreatic endocrine tumors, pituitary adenomas, and adrenal adenomas. We reported 1 case of MEN 1 simultaneous with gastrinoma and insulinoma; meanwhile, insulinomas were ectopic and recurrent. The genetic screening showed the mutation of 427del AT of the MEN 1 gene. Surgical removal is considered the treatment of choice, with limited adverse effects and relatively low morbidity and mortality. She was treated by means of several surgical strategies, resulting in improvement of the frequency and severity of the hypoglycemic episodes and a better quality of life.
Our work was to study the protective effect of cobalt protoporphyrin (CoPP) on islet xenograft and its mechanism. According to CoPP induction of rat pancreas islet cells in different concentration and time, the optimal CoPP dosage to induce high expression of HO-1 would be determined by examining expression of HO-1 mRNA and protein in graft and islet function. Subsequently, islet cells with untreated, CoPP-induced, and CoPP-induced with zinc protoporphyrin (ZnPP)-blocked were randomly transplanted into murine subrenal capsule, then the survival time among these different treated groups was compared by blood glucose level and pathologic examination and meanwhile the IFN-?, TNF-?, IL-10, and IL-1? level in serum and their mRNA and protein expression would be examined in grafts. CoPP at 50 mmol/L for 36 h incubation induced the highest HO-1 mRNA and protein expression in islets. CoPP treated islets under low glucose and high glucose stimulation exhibited insulin secretion of 30.52 ± 2.04 ?IU/mL and 104.60 ± 5.10 ?IU/mL, respectively in comparison to control (20.35 ± 1.79 ?IU/mL and 62.39 ± 2.50 ?IU/mL, respectively) (P<0.05). CoPP induction could increase higher expression of HO-1 in graft (mRNA: 3.33-fold; protein: 2.85-fold), but ZnPP-blocked would decrease expression of HO-1 (mRNA: 0.72-fold; protein: 0.68-fold). The survival time in induction group (14.63 ± 1.19 d) was significantly longer than untreated group (9.88 ± 2.17 d) and ZnPP-blocked group (9.38 ± 1.60 d). Serum C-peptide in induction group (60.67 ± 9.87 pmol/L) was significantly higher than that in untreated group (35.67 ± 11.72 pmol/L) and blockage group (34.67 ± 12.90 pmol/L) (P<0.05). HbA1C in induction group (2.37% ± 0.21%) was significantly lower than that in untreated group (3.00% ± 0.17%) and blockage group (3.07% ± 0.15%) (P<0.01). The pathologic examination showed that lymphocyte infiltration to the graft in induction group was obviously less serious than other two groups. The Il-10 level in the serum in induction group (72.97 ± 9.74 pg/mL) was significantly higher than untreated group (30.57 ± 3.94 pg/mL) and blocked group (45.55 ± 8.26 pg/mL), and the expression of IL-10 mRNA in graft was in the same condition. The higher expression of HO-1 induced by CoPP in vitro would significantly improve pancreatic function, prolong graft survival time, and reduce lymphocyte infiltration to the graft. The CoPP induction could be inhibited by ZnPP and its mechanism could be related to immune modulation of IL-10.
Using in situ atomic-resolution electron microscopy observations, we report observations of the oxide growth during the oxidation of stepped Cu surfaces. Oxidation occurs via direct growth of Cu(2)O on flat terraces with Cu adatoms detaching from steps and diffusing across the terraces. This process involves neither reconstructive oxygen adsorption nor oxygen subsurface incorporation and is rather different from the mechanism of solid-solid transformation of bulk oxidation that is most commonly postulated. These results demonstrate that the presence of surface steps can promote the development of a flat metal-oxide interface by kinetically suppressing subsurface oxide formation at the metal-oxide interface.
A variety of approaches are being made to enhance the performance of lithium ion batteries. Incorporating multivalence transition-metal ions into metal oxide cathodes has been identified as an essential approach to achieve the necessary high voltage and high capacity. However, the fundamental mechanism that limits their power rate and cycling stability remains unclear. The power rate strongly depends on the lithium ion drift speed in the cathode. Crystallographically, these transition-metal-based cathodes frequently have a layered structure. In the classic wisdom, it is accepted that lithium ion travels swiftly within the layers moving out/in of the cathode during the charge/discharge. Here, we report the unexpected discovery of a thermodynamically driven, yet kinetically controlled, surface modification in the widely explored lithium nickel manganese oxide cathode material, which may inhibit the battery charge/discharge rate. We found that during cathode synthesis and processing before electrochemical cycling in the cell nickel can preferentially move along the fast diffusion channels and selectively segregate at the surface facets terminated with a mix of anions and cations. This segregation essentially can lead to a higher lithium diffusion barrier near the surface region of the particle. Therefore, it appears that the transition-metal dopant may help to provide high capacity and/or high voltage but can be located in a "wrong" location that may slow down lithium diffusion, limiting battery performance. In this circumstance, limitations in the properties of lithium ion batteries using these cathode materials can be determined more by the materials synthesis issues than by the operation within the battery itself.
Using density-functional theory within the generalized gradient approximation, we investigate the energetics of oxygen subsurface adsorption governing the onset of bulk oxidation of Cu(100) surface. It shows that the presence of boundaries formed from merged missing-row nanodomains mismatched by a half unit-cell leads to preferred oxygen adsorption at the subsurface tetrahedral sites. The resulting Cu-O tetrahedrons along the domain boundary strikingly resemble that of the bulk oxide phase of Cu(2)O. These results provide direct atomic-scale insight into the microscopic origin of the crystallographic orientation relationships for oxide overlayer growth. Our results also suggest that the oxidation of an atomically flat terrace can still be a heterogeneous nucleation process controlled by defects in the oxygen-chemisorbed adlayer.
Because environmental stability is an essential property of most engineered materials, many theories exist to explain oxidation mechanisms. Yet, nearly all classical oxidation theories assume a uniform growing film, where structural changes were not considered because of the previous lack of experimental procedure to visualize this non-uniform growth in conditions that allowed for highly controlled surfaces and impurities. With the advent of vacuum technologies and advances in microcopy techniques, especially in situ, one can now see structural changes under controlled surface conditions. Here, we present a review of our systematic studies on the transient oxidation stages of a model metal system, Cu, and its alloys, Cu-Au and Cu-Ni, by in situ ultra-high vacuum transmission electron microscopy (UHV-TEM). The dependence of the oxidation behavior on the crystal orientation, oxygen pressure, temperature and alloying is attributed to the structures of the oxygen-chemisorbed layer, oxygen surface diffusion, surface energy and the interfacial strain energy. Heteroepitaxial concepts, developed to explain thin film formation on a dissimilar substrate material (e.g., Ge on Si), described well these initial oxidation stages.
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