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Structure and Permeability of Porous Silicon Investigated by Self-Diffusion NMR Measurements of Ethanol and Heptane
摘要： The adsorption and phase transitions of con?ned ?uids in nanoporous materials have been studied intensely because of both their fundamental interest and their crucial role in many technologies. Questions relating to the in?uence of the con?nement of ?uids, and the disorder or elastic deformation of porous solids on the liquid-gas phase transition are still under debate. Model systems are needed to understand the adsorption phenomenon. In this context, Porous Silicon (PoSi), which is a single crystal obtained by etching a (100) silicon wafer is an excellent candidate. Indeed, it consists of non-connected tubular pores running parallel to the [100] axis perpendicular to the wafer surface, with transverse sections with a polygonal shape of nanometric size whose areas are widely distributed. Once detached from the wafer, free PoSi membranes can be considered a nanoscale disordered honeycomb. Adsorption/desorption experiments have been performed to characterize the structure: they have shown that evaporation occurs collectively, an intriguing observation generally associated with a disordered pore structure with many interconnections through narrow necks. The characterization of ?uid mobility inside the pores should give complementary information about the pore structure and topology. This paper focuses on the dynamics of a ?uid con?ned inside the structure of porous silicon, and in particular the self-diffusion measurements (pulsed ?eld gradient spin echo Nuclear Magnetic Resonance (NMR)). The results show a strong anisotropy of the self-diffusion tensor, as expected in this highly anisotropic structure. However, a non-zero self-diffusion in the directions perpendicular to the pore axis is observed. In order to interpret these puzzling results, molecular and Brownian dynamics calculations are underway.
关键词： Ethanol,Porous Silicon,Permeability,Heptane,Self-Diffusion NMR
更新于2025-09-09 09:28:46
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UV distributed Bragg reflectors build from porous silicon multilayers
摘要： UV Distributed Bragg reflectors were fabricated by a two-step thermal oxidation process over porous silicon multilayers (PS-ML), which were prepared by room-temperature electrochemical anodization of silicon wafers. The optical behavior of the PS-ML before and after oxidation was studied by reflectance measurements. It was observed an UV shift from 430 to 300 nm in the peak of the reflectance spectrum after oxidation of the PS-ML. This was attributed to the presence of silicon oxide over the surface of the silicon filaments. Such oxide also reduced the refractive index of each porous silicon monolayer. The bandgap of the PS-ML was calculated by the Kubelka-Munk approximation, which showed an increase in the bandgap from 3.11 to 4.36 eV after the thermal oxidation process. It was suggested that the observed optical response could opens the possibility of fabrication of UV optoelectronic devices based entirely in the silicon technology.
关键词： Porous silicon,thermal oxidation,multilayers,ultraviolet (UV)
更新于2025-09-09 09:28:46
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Porous Silicon Bragg Reflector/Carbon Dot Hybrids: Synthesis, Nanostructure, and Optical Properties
摘要： Carbon dots (C-dots) exhibit unique fluorescence properties, mostly depending upon their physical environments. Here we investigate the optical properties and nanostructure of Carbon dots (C-dots) which are synthesized in situ within different porous Silicon (PSi) Bragg reflectors. The resulting hybrids were characterized by photoluminescence, X-ray photoelectron, and Fourier Transform Infrared spectroscopies, as well as by confocal and transmission electron microscopy. We show that by tailoring the location of the PSi Bragg reflector photonic bandgap and its oxidation level, the C-dots emission spectral features can be tuned. Notably, their fluorescence emission can be significantly enhanced when the high reflection band of the PSi host overlaps with the confined C-dots’ peak wavelength, and the PSi matrix is thermally oxidized at mild conditions. These phenomena are observed for multiple compositions of PSi Bragg reflectors/C-dots hybrids.
关键词： optical properties,fluorescence,Fabry–Pérot,Bragg reflectors,porous silicon,photoluminescence,carbon dots
更新于2025-09-09 09:28:46
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Micropatterning of Porous Silicon Bragg Reflectors With Poly(Ethylene Glycol) to Fabricate Cell Microarrays: Towards Single Cell Sensing
摘要： The work presented here describes the development of optical label-free biosensor based on PSi Bragg reflector to study heterogeneity in single cells. Photolithographic patterning of poly(ethylene glycol) hydrogel with photoinitiator was employed on RGD peptide-modified PSi to create micropatterns with cell adhesive and cell repellent areas and J774 macrophage cells were incubated to form cell microarrays and single cell arrays. Moreover, cells on the microarrays were lysed osmotically with Milli-Q? water and the infiltration of cell lysate into the porous matrix was monitored by measuring the red shift in the reflectivity. On average, the magnitude of red shift increased with the increase in the number of cells on the micropatterns. The red shift from the spots with single cells varied from spot to spot emphasizing the heterogeneous nature of the individual cells.
关键词： porous silicon (PSi),cell patterning,cell lysis,label-free biosensing,poly(ethylene glycol (PEG) hydrogel
更新于2025-09-04 15:30:14