Free‐Standing Ultrathin Ceramic Foils

Abstract

Ceramic thin films are used in various applications for their structural or functional properties. Below a thickness of approximately 25 μm, ceramic films are typically deposited, sintered, and used on a supporting substrate due to their fragility. Here, we present a set of easy and versatile green film deposition and sintering techniques that allow the fabrication of free‐standing micrometer‐thin alumina and yttria‐stabilized zirconia foils. Because of their extremely low thickness, the foils were transparent and flexible but still strong enough that they were self‐supporting and could be handled manually. The presented concepts are not limited to the materials used here and can potentially be extended to most ceramic materials and glasses. So prepared free‐standing ultrathin ceramic foils allow new assembly and fabrication methods of devices and novel materials that contain thin ceramic membranes.

Free‐Standing Patterned Ceramic Structures Obtained by Soft Micromolding

“…3), thus proving the necessity of the second plate to provide better geometrical constraint. This effect was also observed by Bonderer et al [14] Here, no additional compressive load was applied during sintering. The weight of the upper carbon plate (2.5 g) resulted in an additional pressure completely negligible compared to the sintering stress of the alumina powder used.…”

“…Pressure should be applied progressively, as the fracture strength of the sintering layer increases, to avoid damage and cracking. Bonderer et al [14] using a sol-gel route for the production of their alumina layers needed temperatures of about 1 600 8C under 10 À2 MPa pressure to get dense material. When increasing the compressive stress between 10 and 100 MPa, it was possible to decrease the temperature for full densification down to 1 450 8C.…”

“…To minimize film adhesion onto the substrate and to get free-standing structures, diffusion, or chemical reaction between film and substrate should be prohibited. This technological challenge was solved very recently by Bonderer et al, [14] who proposed to sinter ceramic layers directly on carbon. They obtained continuous, dense, and translucent ceramic layers which were flexible due their reduced thickness compared to their lateral dimensions (1-2 mm or even less if pressed).…”

Platinum-Based Nanowire Networks with Enhanced Oxygen-Reduction Activity

“…As the overall fuel cell's power density scales linearly with the thickness of a purely ionic conducting electrolyte [25,33,34], it can be concluded that the electrode performance of herein analysed Pt-based nanowire networks is roughly a factor 3 higher than the conventional nanoporous Pt electrodes [22] and non-precious electrodes [23]. As proof that the electrolyte thickness is indeed the limiting factor for the cell-performance, symmetric fuel cells with Pt-Al electrodes and a 5 µm thin ceramic YSZ foil [26,27] as electrolyte were fabricated as well. The FIB cross-sectional image of such a fuel cell shown in Fig.…”

“…2(a)): Nanoporous Pt-Al thin film electrodes and nanoporous Pt-Y-Al thin film electrodes. Both electrodes were deposited at room temperature by magnetron cosputtering onto single crystalline yttrium-stabilised zir-50 nm PtAl as dealloyed [21] PtAl annealed [21] height conia (YSZ) substrates and in the case of the Pt-Al electrodes also on 5 µm thin ceramic YSZ foils [26,27]. A detailed description is given in the Supplemental Material [28].…”