Surface segregation of silicon impurities in organic materials

Abstract

The present revolution in novel organic materials is driven by the synthesis of new materials exhibiting specific functional properties. Traces of silicon compounds are often present in these materials and, although the bulk concentrations of these impurities may be low, segregation can seriously modify the surface composition. Surfaces and interfaces play an important role in many applications, and the intrinsic properties of the materials are thus often obscured by the presence of segregated impurities.By studying silicon impurity segregation in poly-dialkoxy phenylenevinylene (PPV), polycarbonate and dendrimer macromolecules, we demonstrate how low-energy ion scattering may be used to determine the surface impurity fraction and to observe which groups at the surface are shielded by the segregated species. We demonstrate that the performance of PPV-based light-emitting diodes is significantly reduced for submonolayer coverages of siloxanes. We find that the kinetics of the segregation process depend strongly on the materials and the sample preparation conditions. We find that the presence of solvents is needed to enable segregation at room temperature. Heating does enable siloxane impurity segregation in polycarbonate in the solid phase, whereas for polydimethylsiloxane in PPV films we find that segregation in the solid phase does not occur up to 200• C. The siloxane molecules are found to segregate to preferential sites at the surface, shielding the polar groups. Finally, we demonstrate that purification of the surface is often possible through simple procedures that provide an easy way to study the intrinsic properties of the materials.

Quantitative analysis of complex amino acids and RGD peptides by X‐ray photoelectron spectroscopy (XPS)

“…Siloxanes are a common trace impurity with organic compounds, usually at low enough bulk levels to be insignificant for bulk properties. However, they have a low solubility in the crystal bulk and therefore have a tendency to accumulate at the surface, resulting in a significant contribution to the photoemission . The presence of siloxanes would increase the carbon and oxygen content, just as seen in the data (Table ), particularly an enhanced C − C component at 285 eV.…”

“…Both RGD and RGDSC exhibit a Si signal in XPS, signifying a further impurity. The BE of the Si 2p signal around 102 eV is indicative of Si − O species, such as those found in siloxanes, Si(−R)O, where R is a hydrocarbon chain . Siloxanes are a common trace impurity with organic compounds, usually at low enough bulk levels to be insignificant for bulk properties.…”

Selective adsorption of atomic hydrogen on a h-BN thin film

“…λ N 1s in BN and λ B 1s in BN are inelastic mean free paths (IMFP) of the photoelectrons in the BN film with kinetic energies that correspond to the N and B core levels, respectively. The IMFP values were obtained from a recent report by Tanuma et al 39 IMFP values of graphite are available in the report, but, while those of BN are not available. We assumed the same IMFP for both graphite and BN for the following reason.…”

“…I Ni 3s is the intensity of the photoelectron peak of the Ni 3s level, which was obtained from Fig. 1 39,42 Due to the difference of the IMFP values between the two methods, the thickness of the BN film was estimated to be 6.6 Å by the new IMFP values and 7.5 Å by the IMFP values from the TPP-2M equation. For further discussion, we suppose that the thickness of the film as 6.6 Å.…”

A molecular dynamics study of siloxane diffusion in a polyester–melamine solution

“…Gorelova et al [12] reported that the surface segregation of a dilute blend of PDMS with polychloroprene (PCP) decreased substantially with increasing molecular weight of the siloxane. Reijme et al [13] also noted that traces of silicon-based impurities in organic materials can also segregate to the surface and may seriously modify the surface composition, sometimes adversely.…”