b₂ Peaks in SERS Spectra of 4‑Aminobenzenethiol: A Photochemical Artifact or a Real Chemical Enhancement?

Strong b₂ peaks (1142, 1391, 1438, and 1583 cm^–1) in the SERS spectra of 4-aminobenzenethiol (ABT) have been regarded by many as a textbook example of chemically enhanced SERS signals. However, this interpretation is in serious doubt after the recent claim that they arise from 4,4′-dimercaptoazobenzenes (DMAB) photogenerated during the acquisition of SERS, not the genuine chemically enhanced signals of ABT. Subsequent attempts to prove or disprove this claim have failed to provide any decisive verdict. Here we present spectroscopic and mass spectrometric evidence that further support the photogeneration of DMABs from ABTs on an Ag surface. Furthermore, we show that the amount of the DMAB is sufficient to explain the b₂ intensities of ABT

Electrochemical Release of Amine Molecules from Carbamate-Based, Electroactive Self-Assembled Monolayers

In this paper, carbamate-based self-assembled monolayers (SAMs) of alkanethiolates on gold were suggested as a versatile platform for release of amine-bearing molecules in response to the electrical signal. The designed SAMs underwent the electrochemical oxidation on the gold surface with simultaneous release of the amine molecules. The synthesis of the thiol compounds was achieved by coupling isocyanate-containing compounds with hydroquinone. The electroactive thiol was mixed with 11-mercaptoundecanol [HS(CH₂)₁₁OH] to form a mixed monolayer, and cyclic votammetry was used for the characterization of the release behaviors. The mixed SAMs showed a first oxidation peak at +540 mV (versus Ag/AgCl reference electrode), indicating the irreversible conversion from carbamate to hydroquinone groups with simultaneous release of the amine molecules. The analysis of ToF-SIMS further indicated that the electrochemical reaction on the gold surface successfully released amine molecules

Measuring Compositions in Organic Depth Profiling: Results from a VAMAS Interlaboratory Study

We report the results of a VAMAS (Versailles Project on Advanced Materials and Standards) interlaboratory study on the measurement of composition in organic depth profiling. Layered samples with known binary compositions of Irganox 1010 and either Irganox 1098 or Fmoc-pentafluoro-l-phenylalanine in each layer were manufactured in a single batch and distributed to more than 20 participating laboratories. The samples were analyzed using argon cluster ion sputtering and either X-ray photoelectron spectroscopy (XPS) or time-of-flight secondary ion mass spectrometry (ToF-SIMS) to generate depth profiles. Participants were asked to estimate the volume fractions in two of the layers and were provided with the compositions of all other layers. Participants using XPS provided volume fractions within 0.03 of the nominal values. Participants using ToF-SIMS either made no attempt, or used various methods that gave results ranging in error from 0.02 to over 0.10 in volume fraction, the latter representing a 50% relative error for a nominal volume fraction of 0.2. Error was predominantly caused by inadequacy in the ability to compensate for primary ion intensity variations and the matrix effect in SIMS. Matrix effects in these materials appear to be more pronounced as the number of atoms in both the primary analytical ion and the secondary ion increase. Using the participants’ data we show that organic SIMS matrix effects can be measured and are remarkably consistent between instruments. We provide recommendations for identifying and compensating for matrix effects. Finally, we demonstrate, using a simple normalization method, that virtually all ToF-SIMS participants could have obtained estimates of volume fraction that were at least as accurate and consistent as XPS