Morphology and conductivity of Au films on polydimethylsiloxane using (3-mercaptopropyl)trimethoxysilane (MPTMS) as an adhesion promoter

Osmani, Bekim; Deyhle, Hans; Weiss, Florian M.; Töpper, Tino; Karapetkova, Maria; Leung, Vanessa; Müller, Bert

doi:10.1117/12.2219199

Cited by 12 publications

(11 citation statements)

References 25 publications

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“…Synthesized thiol-terminated polydimethylsiloxane (SH-PDMS) was evaporated using low-temperature effusion cells (NTEZ, Dr. Eberl MBE Komponenten GmbH, Weil der Stadt, Germany) with a 2 cm 3 crucible. The material was evaporated at a crucible temperature of 140°C, well below the thermal degradation temperature of vinyl and thiol end groups 22,25 and corresponding to a deposition rate of about 30 nm h −1 . Stretchable substrates of 1-mm thick were prepared by casting PDMS (Dow Corning, Sylgard ® 184 and OS-20 Fluid, Dow Corning Europe SA, Belgium) at a ratio of 10∶1∶10 of elastomer to curing agent to solvent on polystyrene films.…”

Section: Molecular Beam Deposition Of Nanometer-thin Elastomer Filmsmentioning

confidence: 99%

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Conducting and stretchable nanometer-thin gold/thiol-functionalized polydimethylsiloxane films

2018

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Abstract. Future low-voltage dielectric elastomer transducers (DETs), based on nanometer-thin elastomer membranes, will rely on soft and compliant electrodes with reasonable electrical conductivity and sound adhesion to the elastomer. State-of-the-art adhesion promoters, including nanometer-thin Cr/Ti films, result in defects for applied areal strains larger than 3% and lead to increases in the stiffness of DETs. To generate forces in the Newton range, these low-voltage DETs have to be stacked in thousands of layers. Herein, we present a compliant electrode, which consists of gold bonded covalently to thiol-functionalized polydimethylsiloxane (SH-PDMS) films. The membranes were fabricated using molecular beam deposition and in situ and/or subsequent ultraviolet light (UV) radiation. Peel-off tests demonstrate the expected strong binding of Au to the SH-PDMS network, with this highly stretchable Au/SH-PDMS layer capable of withstanding strains of at least 60%, without losing conductivity. Optical micrographs show signs of cracks for strained pure Au and Au/Cr electrodes but not for the Au/SH-PDMS layer. The mechanical properties and adhesion forces of Au/SH-PDMS were extracted by means of atomic force microscopy (AFM), using a spherical Au tip coated with methyl groups (CH 3 ). The elastic modulus of ð12 AE 9Þ MPa increased slightly against the 20-nm-thin Au/PDMS example, but it can be tailored by the cross-linking density of Au/SH-PDMS via the UV irradiation dose. Unloading nanoindentation curves revealed pull-off forces between the CH 3 -functionalized AFM tip and the Au/SH-PDMS layer at the time of separation. For Au/SH-PDMS, the spectral distribution of pull-off forces exhibits repulsive forces with the CH 3 groups of the PDMS network as well as adhesive forces resulting from interactions with the nanometer-sized Au clusters. This approach provides the means to bind gold clusters homogenously within the SH-PDMS film. Such compliant electrodes are the prerequisite for fabricating low-voltage DETs that can be stretched by more than 50%.

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Section: Molecular Beam Deposition Of Nanometer-thin Elastomer Filmsmentioning

confidence: 99%

“…19 This methodology, however, requires silanol functional groups on the PDMS surface to be achievable via oxygen plasma and ultraviolet/ozone treatments. [20][21][22] These treatments evoke a silica-like surface layer, which gives rise to cracks for strains above 10%.…”

Section: Introductionmentioning

confidence: 99%

Conducting and stretchable nanometer-thin gold/thiol-functionalized polydimethylsiloxane films

2018

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“…Another approach to stretchable electronics, presented by Hirsch et al, is based on biphasic AuGa 2 /Ga solid–liquid thin metal films. However, rigid 60 nm sputtered Au metallization is still required, which significantly stiffens the overall thin‐film DEA . A related challenge is the low adhesion of Au to PDMS, which can be improved via Cr or Ti layers but also increases the overall stiffness .…”

Section: Introductionmentioning

confidence: 99%

“…In addition, Mahapatro et al have demonstrated that deposited Au on a self‐assembled monolayer of MPTMS on an oxidized Si substrate has a root‐mean‐square surface roughness in the sub‐nanometer scale . MPTMS is a bifunctional molecule, its thiol head (SH) binds to Au and the three methoxy (OCH 3 ) functional groups bind to hydroxy PDMS (OH) surfaces, which can be introduced by oxygen plasma or ultraviolet/ozone treatments . Oxygen plasma forms a silica‐like film on top of the PDMS layer, thereby leading to a wrinkled surface, as its thermal expansion coefficient is several orders of magnitude lower compared to that of the underlying bulk PDMS .…”

Section: Introductionmentioning

confidence: 99%

Gold Layers on Elastomers near the Critical Stress Regime

Osmani

Deyhle

Töpper

et al. 2017

Adv Materials Technologies

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Soft electrodes are essential components of soft robotics, tunable optics, microfluidics, flexible electronics, neuroprosthetics, and dielectric elastomeric transducers (DET). The two main paths employed to increase an electrode's compliance involve the manipulation of either its intrinsic material properties or its structural features, such as the introduction of wrinkles, which arise above the critical stress of metal films on elastomeric substrates. Herein, this study demonstrates that the interplay between functionalized oxygen‐plasma‐treated polydimethylsiloxane (PDMS) films and sputter‐deposited metal electrodes allows for conserving compressive stress within the electrode. Insulator–metal transition already occurs for 10 nm thin Au electrodes, and below this electrode thickness, atomic force microscopy nanoindentations with sub‐micrometer resolutions reveal no stiffening of the Au/PDMS heterostructure. These DETs exhibit reduced electrocreasing, which is a significant contributor to structural failure, while their enhanced dielectric breakdown field of up to 120 V µm–1 enables calculated strains above 10% — a crucial requirement for thin‐film DETs such as those used for artificial muscles.

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“…17 In a previous study, these mechanical properties have been determined by nanoindentation (NI) measurements with a spherical indenter using atomic force microscopy (AFM). 18 The elastic modulus of the thin-film DET sandwich structure increased by a factor of three after the deposition of a 10 nm Au electrode. The observed force-distance-curves allow us not only to extract the mechanical properties of thin polymeric films but also to study the related adhesion forces.…”

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confidence: 99%

Nanomechanical probing of thin-film dielectric elastomer transducers

Osmani

Seifi

Park

et al. 2017

Applied Physics Letters

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Dielectric elastomer transducers (DETs) have attracted interest as generators, actuators, sensors, and even as self-sensing actuators for applications in medicine, soft robotics, and microfluidics. Their performance crucially depends on the elastic properties of the electrode-elastomer sandwich structure. The compressive displacement of a single-layer DET can be easily measured using atomic force microscopy (AFM) in the contact mode. While polymers used as dielectric elastomers are known to exhibit significant mechanical stiffening for large strains, their mechanical properties when subjected to voltages are not well understood. To examine this effect, we measured the depths of 400 nanoindentations as a function of the applied electric field using a spherical AFM probe with a radius of (522 ± 4) nm. Employing a field as low as 20 V/μm, the indentation depths increased by 42% at a load of 100 nN with respect to the field-free condition, implying an electromechanically driven elastic softening of the DET. This at-a-glance surprising experimental result agrees with related nonlinear, dynamic finite element model simulations. Furthermore, the pull-off forces rose from (23.0 ± 0.4) to (49.0 ± 0.7) nN implying a nanoindentation imprint after unloading. This embossing effect is explained by the remaining charges at the indentation site. The root-mean-square roughness of the Au electrode raised by 11% upon increasing the field from zero to 12 V/μm, demonstrating that the electrode's morphology change is an undervalued factor in the fabrication of DET structures.

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Morphology and conductivity of Au films on polydimethylsiloxane using (3-mercaptopropyl)trimethoxysilane (MPTMS) as an adhesion promoter

Cited by 12 publications

References 25 publications

Conducting and stretchable nanometer-thin gold/thiol-functionalized polydimethylsiloxane films

Conducting and stretchable nanometer-thin gold/thiol-functionalized polydimethylsiloxane films

Gold Layers on Elastomers near the Critical Stress Regime

Nanomechanical probing of thin-film dielectric elastomer transducers

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