pH driven addressing of silicon nanowires onto Si₃N₄/SiO₂micro-patterned surfaces

Abstract

pH was used as the main driving parameter for specifically immobilizing silicon nanowires onto Si3N4 microsquares at the surface of a SiO2 substrate. Different pH values of the coating aqueous solution enabled to experimentally distribute nanowires between silicon nitride and silicon dioxide: at pH 3 nanowires were mainly anchored on Si3N4; they were evenly distributed between SiO2 and Si3N4 at pH 2.8; and they were mainly anchored on SiO2 at pH 2. A theoretical model based on DLVO theory and surface protonation/deprotonation equilibria was used to study how, in adequate pH conditions, Si nanowires could be anchored onto specific regions of a patterned Si3N4/SiO2 surface. Instead of using capillary forces, or hydrophilic/hydrophobic contrast between the two types of materials, the specificity of immobilization could rely on surface electric charge contrasts between Si3N4 and SiO2. This simple and generic method could be used for addressing a large diversity of nano-objects onto patterned substrates.

Assessing the Adsorption of Bipyridinium Herbicides on Model Soil Granular Media

“…The phenomenon is the most common adsorption mechanism for organic contaminants on soil substrates and are attributed to electrostatic bonds as result of the charged charging forces associated between the sorbent and sorbate (Al-Ghouti and Da'ana, 2020). This seems to agree with the results observed at solutions with an acidic pH where the expected electrostatic forces at the sand grain will be less negative (pzc ∼ 2.4 pH) (Cloarec et al, 2016). Also, the adsorption on silanized sand (SS) seems to exhibit a comparable behavior as it was on clean sand.…”

Electrochemical Detection of Acetaminophen with Silicon Nanowires

“…The isoelectric point of APAP as measured by the pK a value is 9.7 ; hence, under pH 7.4 conditions, the protonated form of APAP is dominant and is positively charged. SiNWs are known to have a PZC of 2.9 , and therefore adopts a negative charge at this solution pH. Le Châtelier's principle also plays a role contributing to the enhanced oxidation.…”

Voltammetric behaviour of cationic redox probes at mesoporous silica film electrodes

“…In addition, the vertically-ordered silica nanochannels are otherwise characterized by charge selectivity issues. At pH greater than 3, the silica surface is expected to be negatively charged owing to its isoelectric point of 2-3 [59,60]. As a consequence, when working in usual media (at moderately acidic or neutral pH values), the mesoporous silica films on electrodes acted as a permselective membrane, enabling an easy transport of positively-charged redox probes (such as ruthenium hexamine, Ru(NH3)6 3+ , for instance) while rejecting the anionic ones (as ferricyanide, Fe(CN)6 3-), resulting in large electrochemical signals for cations (sometimes larger than at bare electrode due to some accumulation) and low currents for anions (as a result of electrostatic repulsions preventing the negatively-charged redox probes to reach the underlying electrode surface) [44,61].…”