Surface and Depth Profiling of Soft Organic Thin Films.
X-Ray Photoelectron Spectroscopy Study

X-ray Photoelectron Spectroscopy (XPS) is uniquely suited for the direct characterization of nanomaterials and thin films in terms of layer thicknesses, elemental composition and, frequently, the depth-distribution profile of elements across the film. In general, XPS is limited to probe the top

Recent advances in depth profiling of organic and biological materials are based on sputtering with large Argon ion clusters (Ar_n⁺).¹ Unlike monoatomic ions (Ar⁺), large cluster ions do not penetrate deeply into the material, therefore sputter material from the near-surface region only, leaving the subsurface layers undisturbed and undestroyed.

Here we present two examples of successful XPS depth profiling of composite metal-organic architectures self assembled on the pyridine terminated silicon/ ITO substrates. The samples consist of four main components: metal complexes ([M(mbpy-py)₃][PF₆]₂, M = Ru (1) or Os (2); Pd(PhCN)₂Cl₂ (3) and (1,4-bis[2-(4-pyridyl)ethenyl]benzene, BPEB, (4) spacer molecules.

The first system was prepared by sequential immersion of the substrate in solution 1 (alternating with solution 3) (4 layers) followed by 2 (alternating with 3) (4 layers). Each layer is ~ 6 nm thick, thus the consequent total thickness of the organic film reaches 40-50 nm.²

In the second example molecular assemblies consist of different layers of metal complexes 1 and 2, separated by repetitive spacers 4 alternated with 3. Total thickness of the analyzed [Ru-BPEB₁₂-Os] assembly is ~20 nm.³

1. J. Cumpson et. al., Surf. Interface Anal., 2013, 45, 1859-1868.
2. de Ruiter et. al., J. Am. Chem. Soc., 2013, 135, 16533-16544.
3. Balgley et. al., J. Am. Chem. Soc., 2016, in press.