Search results for "Surfaces"

Multi-bit storage through Si nanocrystals embedded in SiO2

2004

We have realized Si nanocrystal memory cells in which the Si dots have been deposited by CVD on SiO2 and then covered by a CVD control oxide. In this paper, we report a study on the potential of these cells for dual bit storage. © 2004 Elsevier B.V. All rights reserved.

Structure of amorphous SiO 2 nanoparticles probed through the E′ γ centers

2011

We report an experimental investigation by electron paramagnetic resonance (EPR) spectroscopy on the properties of the E′ γ centers induced by β-ray irradiation in nanoparticles of amorphous SiO 2 (fumed silica) with mean diameters from 7 up to 40 nm. We found that the E′ γ centers are induced in all the fumed silica types in the dose range 4-400 kGy. They are characterized by an EPR line shape similar to that observed in common bulk silica materials independently on the particle diameter. Moreover, the E′ γ center concentration decreases on decreasing of the particle size for each given dose. Our findings are interpreted in terms of a shell-like model of nanoparticles in which it is assume…

Effects of Pressure, Thermal Treatment, and O2 Loading in MCM41, MSU-H, and MSU-F Mesoporous Silica Systems Probed by Raman Spectroscopy

2015

We present a Raman study of the effects induced by pressure, thermal treatments, and O2 loading in MCM41, MSU-H, and MSU-F representative mesoporous silica. We compared the starting powders with the mechanically pressed tablets produced applying pressures of ∼0.2 and ∼0.45 GPa. The spectra of the three untreated tablets evidence that the main value of the Si-O-Si angle decreases and that in the MCM41 and the MSU-H Si-O-Si hydrolysis occurs, whereas such a process is absent or much less efficient in the MSU-F. Despite their different networks, the three powders tend to crystallize in cristobalite when treatments are at 1000 °C. The MCM41 and MSU-H tablets exhibit behavior similar to their st…

Halloysite Nanotubes and Metal Corrosion Inhibitors: A Computational and Experimental Study

2019

Halloysite nanotubes are widely used as a substrate for the controlled release of various types of molecules in an increasing number of applications. In this work, the interactions of halloysite silicic and aluminic surfaces with corrosion inhibitor compounds, such as benzotriazole, 8-hydroxyquinoline, 2-mercaptobenzimidazole, and 2-mercaptobenzothiazole, were investigated from a computational point of view. Two new halloysite compounds with salicylaldoxime and quinaldic acid were designed. Here we propose their synthesis, evaluate amounts of loading, and analyze the adsorption behavior.

Tailoring the Emission Color of Carbon Dots through Nitrogen-Induced Changes of Their Crystalline Structure

2018

Nitrogen content in carbon dots (CDs) plays a crucial role both on the structure and on the optical properties. We synthesized two distinct families of CDs which differ both in structure and in optical emission, demonstrating how nitrogen determines the structure and the optical properties of N-CDs in two main cases: low content and high content of nitrogen. While the low-nitrogen-content family is characterized by blue-emitting nanoparticles with a N-doped hexagonal C-graphite crystalline core structure and a complex surface structure, the high-nitrogen-content family is composed of nanoparticles behaving as dual emitters (blue and green) with a hexagonal β-C3N4crystalline core structure a…

Photoinduced Electron Transfer Reactions in a Porphyrin−Viologen Complex:  Observation of S2 to S1 Relaxation and Electron Transfer from the S2 State

1999

Photoinduced Energy Transfer Reactions in a Porphyrin-Viologen Complex: Observation of S2 to S1 Relaxation and Electron Transfer from the S2 state

Influence of plasticizers and cryogenic grinding on the high-cooling-rate solidification behavior of PBT/PET blends

2015

Two structurally different plasticizers (cyclic and linear) and the effect of cryogenic grinding on the solidification behavior at high cooling rates by a continuous cooling transformation approach of poly(butylene terephthalate)/poly(ethylene terephthalate), PBT/PET, blends are described. The solidification curve (density versus cooling rate) is confirmed as an effective tool to compare the differences in crystallization behavior under conditions mimicking processing. In comparison to the bulky cyclic plasticizer, the linear oligomeric one was found to have a more pronounced influence on the crystallization behavior. A 60/40 by weight PBT/PET blend shows a drop-off of density at ∼50 K/s. I…

Role of Intrinsic Dipoles in the Evaporation‐Driven Assembly of Perovskite Nanocubes into Energy‐Harvesting Composites

2020

Structure of the Metal–Support Interface and Oxidation State of Gold Nanoparticles Supported on Ceria

2012

An Au/CeO2 model catalyst was prepared by deposition–precipitation, with the aim of obtaining a sample suitable for a detailed X-ray absorption fine structure (XAFS) analysis of the gold–ceria interface structure. The results demonstrate the existence of a large interface between the gold particle and the support oxide, characterized by well-defined Au–O and Au–Ce interactions extending up to ∼6.4 A. The complex interface structure is retained after CO treatment up to 250 °C and subsequent reoxidation at 400 °C. The analysis of the XANES spectra, and the Au–O distance of 2.21 A, longer than Au–O bond lengths previously reported for Au/ceria catalysts, suggest a low oxidation state for the g…

Formation and Growth of Pd Nanoparticles Inside a Highly Cross-Linked Polystyrene Support: Role of the Reducing Agent

2014

Simultaneous time-resolved SAXS and XANES techniques were employed to follow in situ the formation of Pd nanoparticles in a porous polystyrene support, using palladium acetate as a precursor and gaseous H2 or CO as reducing agents. These results, in conjunction with data obtained by diffuse reflectance UV–vis and DRIFT spectroscopy and TEM measurements, allowed unraveling of the different roles played by gaseous H2 and CO in the formation of the Pd nanoparticles. In particular, it was found that the reducing agent affects (i) the reduction rate (which is faster in the presence of CO) and (ii) the properties of the hosted nanoparticles, in terms of size (bigger with CO), morphology (spherica…