Hydrofluoric acid

About: Hydrofluoric acid is a research topic. Over the lifetime, 5577 publications have been published within this topic receiving 51599 citations. The topic is also known as: Hydrofluoric acid.

Chemically etched open tubular and monolithic emitters for nanoelectrospray ionization mass spectrometry.

Abstract: We have developed a new procedure for fabricating fused-silica emitters for electrospray ionization-mass spectrometry (ESI-MS) in which the end of a bare fused-silica capillary is immersed into aqueous hydrofluoric acid, and water is pumped through the capillary to prevent etching of the interior Surface tension causes the etchant to climb the capillary exterior, and the etch rate in the resulting meniscus decreases as a function of distance from the bulk solution Etching continues until the silica touching the hydrofluoric acid reservoir is completely removed, essentially stopping the etch process The resulting emitters have no internal taper, making them much less prone to clogging compared to, eg, pulled emitters The high aspect ratios and extremely thin walls at the orifice facilitate very low flow rate operation; stable ESI-MS signals were obtained for model analytes from 5-μm-diameter emitters at a flow rate of 5 nL/min with a high degree of interemitter reproducibility In extensive evaluatio

Reaction of water with hydrofluoric acid treated silicon(111) and (100) surfaces

Abstract: Si wafers with (100) or (111) oriented surfaces were treated in hydrofluoric acid (40% HF, 1 min) and then water rinsed for different times from 10 s to more than 50 h. Oxygen uptake and oxide formation were investigated by x‐ray photoelectron spectroscopy and high‐resolution electron energy‐loss spectroscopy. The initial state after the HF dip is characterized by a coverage with Si–hydride and small amounts of oxygen and fluorine. The interaction with the liquid phase of water was investigated up to the monolayer range. It shows distinct features: The first step is a rapid exchange of Si–F with H2 O to form Si–OH groups followed by a slow nucleophilic attack of OH− on surface Si–H to produce Si–OH. Growth law is logarithmic and extends to 3–5 h of water contact. The surface Si–OH act as nuclei for the attack of water on the polarized Si–SiOH backbonds. Interior Si–H and Si–OH groups develop. Further attack of OH− on interior Si–H yields Si–OH. Condensation of Si–OH forms Si–O–Si bridges and SiO2−x nuclei appear. Strain and altered surface topography lead to a changed rate of the logarithmic oxide growth. The oxide formation is accompanied by a slight corrosive attack of H2 O, leading to roughening of the surface.

Chemical Etching of Silicon II . The System , , , and

Abstract: The kinetics of the etching of silicon in the system , , and was studied as a function of the composition of the etchant at 25°C. A triaxial plot of the etch rate vs. composition of the etchant shows two extreme modes of behavior. In the region of high nitric acid compositions, etch rates are functions only of the hydrofluoric acid concentration. In the region of high hydrofluoric acid compositions, nitric acid concentration determines the etch rates. The kinetic behavior in the latter region is complicated by autocatalysis in which the reduction products of nitric acid are involved.The reaction proceeds by an oxidation step followed by the dissolution of the oxide. In the high hydrofluoric acid region the oxidation step is rate limiting. In the high nitric acid region the dissolution step is rate limiting. In both regions the flow of reagent to the surface by diffusion determines the etch rates. A plot of the etch rates as a function of the concentration of the rate‐limiting reagent indicates an exponential relationship between the etch rates and the concentration. This relationship has been explained qualitatively on the basis of a second, nonchemical autocatalytic factor, the heat of reaction.