Correlating Optical Reflectance with the Topology of Aluminum Nanocluster Layers Growing on Partially Conjugated Diblock Copolymer Templates

Abstract

Large-scale fabrication of metal cluster layers for usage in sensor applications and photovoltaics is a huge challenge. Physical vapor deposition offers large-scale fabrication of metal cluster layers on templates and polymer surfaces. In the case of aluminum (Al), only little is known about the formation and interaction of Al clusters during sputter deposition. Complex polymer surface morphologies can tailor the deposited Al cluster layer. Here, a poly­(methyl methacrylate)-block-poly­(3-hexylthiophen-2,5-diyl) (PMMA-b-P3HT) diblock copolymer template is used to investigate the nanostructure formation of Al cluster layers on the different polymer domains and to compare it with the respective homopolymers PMMA and P3HT. The optical properties relevant for sensor applications are monitored with ultraviolet-visible (UV-vis) measurements during the sputter deposition. The formation of Al clusters is followed in situ with grazing-incidence small-angle X-ray scattering (GISAXS), and the chemical interaction is revealed by X-ray photoelectron spectroscopy (XPS). Furthermore, atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) yield topographical information about selective wetting of Al on the P3HT domains and embedding in the PMMA domains in the early stages, followed by four distinct growth stages describing the Al nanostructure formation.

Chemical Reaction and Bonding Mechanism at the Polymer–Metal Interface

“…In addition, characterizing the valences of elements and bonding types at the interface is another key issue to understand the interfacial bonding mechanisms. As a complement to the electron microscopy characterization on the cross section of polymer–metal interfaces, X-ray photoelectron spectroscopy (XPS) is a powerful tool for characterizing chemical reactions at the polymer–metal interfaces, which is also a more direct and effective method to analyze the buried interface for the purpose of revealing molecular interactions. , Gensch et al , applied XPS to reveal the chemical interaction of poly­(3-hexylthiophene-2,5-diyl)- b -poly­(methyl methacrylate) (PMMA-b-P3HT) and metals (Ag and Al). As for the Al–polymer interface, the XPS results showed the high chemical interaction of Al with the molecular components of the polymers to form Al–O–C bonds, which were responsible for a reduced surface mobility and then affected the metal cluster growth kinetics.…”

Direct Observation of Two-Step, Stratified Crystallization and Morphology in Conjugated Polymer Thin Films

“…Reflectance spectra were calculated as the ratio between the reflected and reference intensity (acquired using a mirror). 46 The absorbance and reflectance spectra were averaged between 570 and 640 nm (Figure 1), then the numerical derivative with respect to temperature was calculated to assess the relative change with temperature. The 570−640 nm absorbance range encompasses the A 0−0 vibronic peak attributed to weakly interacting H-aggregates along the π−π stacking direction, 47,48 but random coiled chains in the molten state (Figure 1, 234 °C) do not significantly contribute to 570−640 nm absorbance.…”

“…Absorbance spectra were calculated as the natural log of the ratio between the incident (reference) and transmitted intensity. Reflectance spectra were calculated as the ratio between the reflected and reference intensity (acquired using a mirror) . The absorbance and reflectance spectra were averaged between 570 and 640 nm (Figure ), then the numerical derivative with respect to temperature was calculated to assess the relative change with temperature.…”

State of the art of ultra-thin gold layers: formation fundamentals and applications

“…Besides, the established geometrical model can be generally applied to any layer growth that follows the Volmer-Weber mode, and its applicability has been demonstrated by the subsequent studies, including sputter deposition of Au, silver (Ag), aluminum (Al), and copper (Cu) on both hard and so substrates. 52,56,[65][66][67] Although the in situ GISAXS technique demonstrated great potential to study the growth process of Au clusters and learn about the formation of UTGLs in real-time, it is difficult to obtain atomic-scale information due to the limited spatial resolution due to contrast limitations when studying single atoms. In order to probe the initial nucleation and growth behavior of Au clusters, scanning transmission electron microscopy (STEM) with atomic-scale spatial resolution was applied is related studies.…”

“…Besides, the established geometrical model can be generally applied to any layer growth that follows the Volmer–Weber mode, and its applicability has been demonstrated by the subsequent studies, including sputter deposition of Au, silver (Ag), aluminum (Al), and copper (Cu) on both hard and soft substrates. 52,56,65–67…”