In Situ ATR−FTIR Analysis of Surfactant Adsorption onto Silicon from Buffered Hydrofluoric Acid Solutions

Abstract

Buffered hydrofluoric acid (BHF) solutions containing HF and NH4F are widely used in the manufacturing of silicon-based integrated circuits. The adsorption/desorption characteristics of a commercially available, high purity, polyglycidol type surfactant (OHS) onto/from silicon from buffered hydrofluoric acid (BHF) solutions was studied by in situ attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). The challenge in these measurements was to resolve the C-H peaks, in the 2800-3000 cm -1 region of the surfactant spectrum, that were masked by the strong absorbance due to N-H caused by a large amount of NH4 + ions in the solution. A technique has been developed to overcome this limitation. The principle of this technique is to carry out the surfactant adsorption in BHF solutions followed by the replacement of NH4 + ions by alkali-metal cations, such as K + and Cs + , to allow better resolution of the C-H peaks from the baseline. Extrapolation of the adsorption density to time zero yields the adsorption density in the presence of NH4 + . Using this technique, the adsorption density of OHS surfactant in a buffered HF solution containing 7 parts of NH4F (40%) and 1 part of HF (49%) was found to be approximately 20% higher than that in dilute HF solutions.

Surface-Enhanced Raman Spectroscopy Studies of Surfactant Adsorption to a Hydrophobic Interface

“…Pendant bubble tensiometry has also been used to measure non-ionic surfactant adsorption at an air-water interface, where the equilibria and kinetics were fit to Langmuir and Frumkin models. 48 Attenuated total reflection (ATR) Fourier transform infrared (FT-IR) measurements have also been employed to investigate surfactant adsorption kinetics on the surfaces of infrared-transparent substrates such as silicon 49 and germanium. 50 In the present study, in situ SERS is employed to measure the equilibria and kinetics of surfactant adsorption from aqueous solution to a hydrophobic surface prepared by the assembly of an alkylsilane monolayer on an immobilized gold colloid film.…”

Design of Mineral Oil/Stearic Acid Hybrid Coatings for Reducing Hygroscopicity of Ammonium Nitrate

“…In the Fourier transform infrared (FT-IR) spectrum of AN (Figure e), the characteristic peaks at 3100–3300, 3032, and 2798 cm –1 are assigned to the NH 4 + cations of AN . Additionally, the characteristic peaks of the NO 3 – anions are observed at 1384 and 826 cm –1 .…”

“…52,53 In the Fourier transform infrared (FT-IR) spectrum of AN (Figure 3e), the characteristic peaks at 3100−3300, 3032, and 2798 cm −1 are assigned to the NH 4 + cations of AN. 54 Additionally, the characteristic peaks of the NO 3 − anions are observed at 1384 and 826 cm −1 . 55 In the FT-IR spectrum of the MO/SA@AN particles, however, new adsorption bands assigned to −CH 3 (2954 cm −1 ), −CH 2 (2915 and 2851 cm −1 ), and −C�C− (1626 cm −1 ) groups appear, 56 indicating that the MO/SA hybrid coating has been successfully deposited on the AN particles.…”

Two-Step Adsorption of a Switchable Tertiary Amine Surfactant Measured Using a Quartz Crystal Microbalance with Dissipation

“…Furthermore, studies have shown that protonated amine groups are strongly hydrated compared to unprotonated amine groups. 17,18 Previously, surfactant adsorption has been studied using a variety of methods, including high-performance liquid chromatography, 19,20 reflectometry, 21 UV spectrophotometry, 22 Fourier transform infrared (FTIR) spectrocopy, 23,24 and ellipsometry, 25 and while they have captured the equilibrium adsorption of a wide variety of surfactants and substrates, they have difficulty capturing adsorption dynamics. Methods such as in situ attenuated total reflection−FTIR, which is able to measure the kinetics of surfactant adsorption, are limited by the need for approximations of numerous fitting parameters during data analysis.…”