Molecular self-assembly of block copolymers is a recent bottom-up approach to create nanostructured surfaces for templating and lithographic processes. Microphase separation utilizes the incompatibility of polymer blocks that are covalently connected to each other. Applications in lithography require the capability to induce a macroscopic alignment, for example by directing the self-assembly along guiding lines.

The need for ever-decreasing nanostructure pitch sizes for next-generation lithography pushes this process to the limit, as increasingly smaller block copolymer chains used to minimize the pitch size leads to a reduced entropy of mixing with only a marginal driving force for microphase separation.

“This research elucidates how crystallization can be used to create nanostructured surfaces in a size regime towards sub-10 nm using the molecular self-assembly of a crystallizable, amphiphilic polyethylene-b-polyethylene oxide (PE-b-PEO) block co-oligomer”, explains the leader of the research project, Thomas Keller from DESY in Hamburg, Germany.

Ivan Maximov from Lund University in Sweden adds “Crystallization itself acts as a driving force for separation with a much higher segregation strength compared to the sole microphase separation”.

Alexander Meinhardt, researcher at the DESY NanoLab, describes his observation: “In situ AFM analysis at the DESY NanoLab indicates the PEO crystallization as a crucial step to form the nanostructures by triggering a morphological transition involving a rotation of the forming extended chain crystals in edge-on orientation.” 

“In this study, electron beam lithography is utilized to create a guiding pattern on which the block copolymer assembles in a macroscopic alignment”, adds Christian David from the Paul Scherrer Institute in Villigen-PSI in Switzerland.

AFM phase analysis of crystallization-induced directed self-assembly of extended PE-b-PEO chains. © Thomas F. Keller, Ivan Maximov, Christian David, et al.

“These results were made possible through our joint activities within NFFA-Europe, which gave us access to a collaborative network of leading scientific facilities and enabled us to pursue our research using advanced tools and expertise”, concludes Thomas Keller.

Thomas Keller explains “While common high molecular weight polymers adopt spaghetti-like conformations, the short chain length of the investigated PE-b-PEO system with only 16 ethylene and 41 ethylene oxide units permits the block copolymer to crystallize into extended chain crystals consisting of vertical lamellae.”

This dense packing provides enhanced thermodynamic stability beneficial for the following lithographic steps towards potential applications. Moreover, the observed mechanism to form stable edge-on lamellae could in the future be transferred to other crystallizable short chain BCPs, providing potential pathways for sub-10 nm nanotechnology.

Alexander Meinhardt, Peng Qi, Christian David, Ivan Maximov, Thomas F. Keller. A Pathway Toward Sub-10 nm Surface Nanostructures Utilizing Block Copolymer Crystallization Control. Advanced Marterials Interfaces, Volume12, Issue 6 March 16, 2025

EBL, PSI

EBL, NanoLund

AFM, DESY

Thomas Florian Keller is senior scientist at DESY in Hamburg, Germany. He leads the microscopy and nano-manipulation at the DESY NanoLab, and is lecturer at the University of Hamburg. His research is dedicated to surface and interface related phenomena and focuses on nano-catalysis and nanoscale polymer thin films. Within the NFFA consortium, he serves as local contact for the NFFA users at DESY and leads the NFFA working package “correlative nano-spectroscopy and nano-diffraction”. He studied at the Technical University of Darmstadt, Germany and at the Trinity College in Dublin, Ireland and received his Diploma in Physics from the Technical University of Darmstadt. He received his PhD from ETH Zurich, Switzerland, for his research at the Paul Scherrer Institute (PSI) in Villigen, Switzerland. In Jena, Germany, he habilitated on the “Self-Organization of Macromolecules and Biomacromolecules at Interfaces”. In 2011, he was awarded the Georg-Sachs Prize of the German Society of Materials (DGM). His peer-reviewed publications are listed here: https://orcid.org/0000-0002-3770-6344.

Christian David is Group Head of X-Ray Nano-Optics Group in the Photon Science Division of the Paul Scherrer Institute, Switzerland. He received his Diploma in Physics in 1989 and his PhD in 1993 from the Georg-August-University of Göttingen, Germany. After a postdoctoral stay at the Ruprecht-Karls-University of Heidelberg, Germany, he joined PSI in 1996, to work on the nanofabrication of optical and electronic devices by electron-beam lithography.  His present research focuses on applying micro- and nanofabrication techniques for advanced X-ray optics, imaging techniques, and instrumentation for synchrotrons and X-ray free-electron lasers. He was awarded the Röntgen Prize by the Justus-Liebig-University of Giessen for his work on x-ray phase contrast imaging (2010) and the Innovationspreis Synchrotronstrahlung by the Helmholtz-Zentrum Berlin (2018) for his developments in diffractive X-ray optics. Christian David is author or coauthor of more than 350 peer reviewed scientific publications (H-index 75) and holds 15 patents.