Alternating layers of two different organic materials, Irganox1010 and Irganox3114, have been created using vapor deposition. The layers of Irganox3114 were very thin ( approximately 2.5 nm) in comparison to the layers of Irganox1010 ( approximately 55 or approximately 90 nm) to create an organic equivalent of the inorganic 'delta-layers' commonly employed as reference materials in dynamic secondary ion mass spectrometry. Both materials have identical sputtering yields, and we show that organic delta layers may be used to determine some of the important metrological parameters for cluster ion beam depth profiling. We demonstrate, using a C(60) ion source, that the sputtering yield, S, diminishes with ion dose and that the depth resolution also degrades. By comparison with atomic force microscopy data for films of pure Irganox1010, we show that the degradation in depth resolution is caused by the development of topography. Secondary ion intensities are a well-behaved function of sputtering yield and may be employed to obtain useful analytical information. Fragments characteristic of highly damaged material have intensity proportional to S, and those fragments with minimal molecular rearrangment exhibit intensities proportional to S(2). We demonstrate quantitative analysis of the amount of substance in buried layers of a few nanometer thickness with an accuracy of approximately 10%. Organic delta layers are valuable reference materials for comparing the capabilities of different cluster ion sources and experimental arrangements for the depth profiling of organic materials.

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The aim of this paper is twofold: first to report on the lateral and vertical characterisation of a surface chemical gradient of carboxylic-acid functionality and second, to demonstrate the use of said gradient to probe the passive adsorption of immunoglobulin G (IgG) as a function of the density of surface carboxylic-acid groups.A surface chemical gradient of carboxylic-acid functionality was fabricated by the plasma copolymerisation of octadiene (OD) and acrylic acid (AA). The plasma-polymerised gradient was over 12 mm, with 2 mm of plasma-polymerised OD at one end and 2 mm of plasma-polymerised AA at the other. By means of linescan angle resolved x-ray photoelectron spectroscopy (ARXPS) it is shown precisely how acid functionality varies from the 2 mm position (OD end) on the gradient to the 10 mm position (AA end). By recording data from 16 angles at each of the 25 sampling points along the gradient, it is shown that the surface gradient also changes vertically, most notably in the thickness of the plasma polymer. At the OD end the plasma-polymerised layer is 6.3 nm thick, while at the AA end the plasma-polymerised layer is 5 nm. More subtle changes in chemistry through the plasma-polymerised layer are shown at the 7.5 and 10 mm points.An identical gradient is used to probe IgG adsorption along the length of the gradient. ARXPS is used to monitor the nitrogen 1s (N1s) signal at 25 points, the N1s signal being unique to adsorbed IgG. It is demonstrated that IgG adsorbs in far greater amount (IgG per unit area) at the OD end, and the amount of adsorbed IgG decreases along the length of the gradient. It is estimated that >200 ng/cm 2 adsorbed at the OD, while at the AA the amount adsorbed was <20 ng/cm 2 .

Sputter-depth profiles of model organic thin films on silicon using C 60 primary ions have been employed to measure sputtering yields and depth resolution parameters. We demonstrate that some materials (polylactide, Irganox 1010) have a constant and high sputtering yield, which varies linearly with the primary ion energy, whereas another material (Alq 3 ) has lower, fluence-dependent sputtering yields. Analysis of multi-layered organic thin films reveals that the depth resolution is a function of both primary ion energy and depth, and the sputtering yield depends on the history of sputtering. We also show that ∼30% of repeat units are damaged in the steady-state regime during polylactide sputtering.  Crown