Using wet-chemical self-assembly, we demonstrate that standard surface reactions can be markedly altered. Although HF etching of Si surfaces is known to produce H-terminated surfaces, we show that up to approximately 30% of a monolayer of stable Si-F bonds can be formed on atomically smooth Si(111) surfaces on HF reaction, when chemically isolated Si atoms are the target of the reaction. Similarly, approximately 30% Si-OH termination can be achieved by immersion of the partially covered F-Si(111) surface in water without oxidation of the underlying Si substrate. Such reactions are possible when H-terminated (111)-oriented Si surfaces are initially uniformly patterned with methoxy groups. These findings are contrary to the knowledge built over the past twenty years and highlight the importance of steric interactions at surfaces and the possibility to stabilize products at surfaces that cannot be obtained on chemically homogeneous surfaces.
Efficient functionalization of silicon substrates is important for the development of silicon-based sensors. Organic monolayers directly bonded to hydrogen-terminated silicon substrates via Si−C bonds display enhanced stability toward hydrolytic cleavage. Here, we show that monolayers presenting a high density of terminal azide groups are amenable to bioconjugation with alkynyl-derivatized glycans via a copper-catalyzed azide−alkyne 1,3-dipolar cycloaddition. The prerequisite azide-functionalized silicon surface is fabricated via hydrosilylation of undecylenic acid with hydrogen-terminated silicon substrate followed by reaction of the thus formed monolayer of acid groups with short, bifunctional oligoethylene oxide chains carrying an amine function at one terminus and an azido group at the other. The possibility to functionalize these azido-surfaces with alkynyl-derivatized glycans such as propargyl mannose through a click protocol is demonstrated and evidenced using X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. In addition, the interaction of these mannose-adorned silicon substrates with glycan binding proteins such as Lens culinaris lectin is investigated. The data establishes clearly the specificity of the interaction of this newly fabricated silicon surface for mannose-selective proteins as well as its reusability, thereby demonstrating its potential as a sensor.
We describe an experimental method to probe the adsorption of water at the surface of isolated, substrate-free TiO2 nanoparticles (NPs) based on soft X-ray spectroscopy in the gas phase using synchrotron radiation. To understand the interfacial properties between water and TiO2 surface, a water shell was adsorbed at the surface of TiO2 NPs. We used two different ways to control the hydration level of the NPs: in the first scheme, initially solvated NPs were dried and in the second one, dry NPs generated thanks to a commercial aerosol generator were exposed to water vapor. XPS was used to identify the signature of the water layer shell on the surface of the free TiO2 NPs and made it possible to follow the evolution of their hydration state. The results obtained allow the establishment of a qualitative determination of isolated NPs’ surface states, as well as to unravel water adsorption mechanisms. This method appears to be a unique approach to investigate the interface between an isolated nano-object and a solvent over-layer, paving the way towards new investigation methods in heterogeneous catalysis on nanomaterials.
Photovoltaic generation has stepped up within the last decade from outsider status to one of the important contributors of the ongoing energy transition, with about 1.7% of world electricity provided by solar cells. Progress in materials and production processes has played an important part in this development. Yet, there are many challenges before photovoltaics could provide clean, abundant, and cheap energy. Here, we review this research direction, with a focus on the results obtained within a Japan–French cooperation program, NextPV, working on promising solar cell technologies. The cooperation was focused on efficient photovoltaic devices, such as multijunction, ultrathin, intermediate band, and hot-carrier solar cells, and on printable solar cell materials such as colloidal quantum dots.
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