Static SIMS studies of carboxylic acids on gold and aluminium–magnesium alloy surfaces

Abstract

Static secondary ion mass spectrometry was used to study the surface reactions and lateral distributions of fatty carboxylic acid molecules on sputter-deposited gold and aluminium surfaces, as well as commercial aluminium-magnesium alloy surfaces, cleaned using UV/ozone. Films were prepared by spin coating dilute solutions of stearic acid and lauric acid onto the above surfaces. These carboxylic acids were shown to react with the oxide formed on the aluminium and aluminum-magnesium alloy substrates to produce a deprotonated acid anion, stabilized by the formation of a magnesium soap on the aluminium-magnesium alloy surface. Secondary ion imaging of stearic acid films revealed the formation of C-type crystals. Copyright  2003 John Wiley & Sons, Ltd. KEYWORDS:ToF-SIMS; carboxylic acids; aluminium-magnesium alloys; magnesium soap formation; C-type crystals Traditionally, mass spectrometry of organic molecules such as carboxylic acids has involved the introduction of the sample of interest into a heated ionization chamber, followed by the measurement of the mass to charge ratio using mass analysers such as quadrupoles, magnetic sector fields and time-of-flight tubes.1 The development of static secondary ion mass spectrometry by Benninghoven 2 has since allowed researchers to generate gas-phase ions from a solid surface containing species of high molecular mass, such as single layers of long-chain organic molecules held on a solid substrate.The study of organic molecules on surfaces using traditional instrumentation, such as x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), has not developed as rapidly as areas that are considered to be inorganic in nature, 3 such as the study of crystalline metal oxides. Progress in these areas has been hindered by the knowledge that organic thin films are often damaged by electron bombardment used for charge neutralization, they become unstable under high vacuum conditions or undergo charge shifting due to an electrically insulating nature. Techniques such as static SIMS and XPS have been used to confirm the damaged structures that arise when molecules of an organic film are subjected to severe x-ray or electron bombardment inside a spectrometer. Studies indicate that the damage induced is primarily due to photon-induced electrons that cause bond cleavage. 4 -6 Static SIMS, by contrast, uses a gentle ionization technique that can provide information about the surface chemistry of the outermost layers of a material while causing Ł Correspondence to: D. J. Miller, Surface Science Western, Western Science Centre, University of Western Ontario, London, Ontario, Canada N6A 5B7. E-mail: dmiller3@uwo.ca negligible surface damage. In general, static SIMS involves the use of mass spectrometry to measure the mass to charge ratio of secondary ions emitted from a solid surface when bombarded with a primary ion beam. The positively and negatively charged secondary ions emitted from the surface due to bombardment of the primary ion beam contain both elemental and m...

Static SIMS studies of fatty alcohols, amines and esters on gold and aluminium–magnesium alloy surfaces

“…The asymmetric and symmetric stretching vibrations of the laurate are assigned to peaks at 1600 and 1462 cm 1 (Fig. 3); this is in accord with our previous analyses 5 and by analogy to spectra of absorbed hexadecanoic acid. 6 Positive secondary ion imaging (Fig.…”

“…10). Peaks due to asymmetric and symmetric stretching 5 of the surface-bonded laurate are present at 1601 cm 1 and 1465 cm 1 . A peak at 1711 cm 1 indicates the presence of lauric acid.…”

“…A peak at 1711 cm 1 indicates the presence of lauric acid. 5 Positive secondary ion mass spectra (Fig. 11) indicate that a peak with a mass corresponding to the molecular weight of protonated ethyl laurate, […”

Enhancement of the static SIMS secondary ion yields of lipid moieties by ultrathin gold coating of aged oil paint surfaces

“…13 However, the system described in our paper differs because in our case the gold is on top of the sample and not underneath a thin layer of stearic acid as is the case in Ref. 13. Positively charged gold ions with neutral fatty acids are not observed in our data.…”

“…According to the literature, these types of ions are only found in the positive mode. 13 However, the system described in our paper differs because in our case the gold is on top of the sample and not underneath a thin layer of stearic acid as is the case in Ref. 13.…”