PROGRESS REPORT 1700073 (1 of 10) © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.advelectronicmat.de Time-Resolved Plasmonics used to On-Line Monitor Metal/Elastomer Deposition for Low-Voltage Dielectric Elastomer Transducers Tino Töpper, Samuel Lörcher, Hans Deyhle, Bekim Osmani, Vanessa Leung, Thomas Pfohl, and Bert Müller* DOI: 10.1002/aelm.201700073 microfluidics [4] to hybrid devices involving CMOS technology. [5] The high efficiency and reliability combined with 10% strain at millisecond response make silicone- based polymers promising for electrically activated elastomer (EAP)-based devices, such as tactile displays, adaptable lenses and sensors. [6] Manufactured in a low- voltage configuration, the remarkable ability of simultaneous sensing and actu- ating distinguishes EAPs and allows them to mimic natural muscle functionality. [7] Therefore, nanostructured, stacked actua- tors have been proposed as smart artificial muscle implants. [8] However, to guarantee the long-term stability of such low-voltage hetero-nanostructures, the sub-nanometer homogeneity of nanometer-thin polymer and metal films is required. Recently, the precisely tailored molecular weight dis- tribution and functionality of thermally evaporated PDMS films has been demon- strated. [9] Contrary to micrometer-rough PDMS thin films fabricated by electro-spray deposition, [10] the high degree of experimental control possible with organic molecular beam deposition (MBD) provides the opportunity to engineer self-assembled PDMS as well as metal films with nanometer precision. Herein, we have fabricated thermally evaporated, self-assem- bled metal/PDMS nanostructures and monitored in situ the formation of deposited metallic layers from discontinuously arranged nanoparticles to confluent thin films by using spec- troscopic ellipsometry (SE). Collective electronic oscillations induced by incident photons yield surface plasmon resonances (SPRs). Plasmonics is an application-rich merging of photonics and electronics [11] that allows one to track intrinsic structural properties such as the size and morphology of organic-inor- ganic hetero-nanostructures, without the restrictions imposed by the diffraction limit. Plasmonic oscillations can be tuned from the mid-infrared, which is of special interest for ultrafast data transfer in telecommunications based on semiconducting composites, [12] down to UV visibility [13] for bio-sensing applica- tions [14] based on Au nanostructures. The combination of self- assembly by MBD, controlled by SE, paves the way for tailoring Au PDMS nanostructures towards homogeneous, multi-layer growth. Compliant hetero-nanostructures provide access to nano-photonics, flex- ible electronics, and artificial muscles. These nanometer-thin polymers and metals are regularly predicated on molecular beam deposition—a technique that leads reliably to homogeneous films and enables the precise in situ monitoring of forming nanostructures. Herein, it is demonstrated that spec- troscopic ellipsometry can be used to on-line monitor film formation with a sub-nanometer resolution and the evolution of the related optical properties of the hetero-nanostructure. The data recorded include plasmonic fingerprints of Au islands as well as film formation on self-assembled polydimethylsiloxane (PDMS). Bi-functionalized thiol-PDMS, tailored for thermal deposition, serves as a self-assembled adhesion layer for Au electrodes. Suppressed localized plasmonic activity indicates the formation of a homogeneous Au film on thiol- PDMS and wrinkled Cr/PDMS, contrary to the well-known establishment of Au islands on bare PDMS. The tailored hetero-nanostructures based on Au/ thiol-PDMS and Au on wrinkled Cr/PDMS adhesion layers enable the fabrica- tion of stretchable electronics and low-voltage dielectric elastomer sensors and actuators for artificial muscles and tunable optics. Dr. T. Töpper, Dr. H. Deyhle, B. Osmani, Dr. V. Leung, Dr. T. Pfohl, Prof. B. Müller Biomaterials Science Center Department of Biomedical Engineering University of Basel Gewerbestrasse 14, 4123 Allschwil, Switzerland E-mail: bert.mueller@unibas.ch S. Lörcher Chemistry Department University of Basel Klingelbergstrasse 80, 4056 Basel, Switzerland The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/aelm.201700073. Hetero-Nanostructures 1. Introduction Flexible and foldable conductors based on polymers are the foundation of “tissue-like” soft electronics. [1] Polydimethylsi- loxane (PDMS) is used widely due to its low cost, ease of fab- rication, biocompatibility, and optical transparency. [2] Areas of application have been extended from soft bioelectronics [3] and Adv. Electron. Mater. 2017, 3, 1700073