Capillary‐Force‐Driven Switchable Delamination of Nanofilms and Its Application to Green Selective Transfer

Abstract

Technology for transferring nanofilm patterns is important in the fabrication of next‐generation electronic devices. However, with existing transfer methods, selective control of the delamination region is challenging without recourse to conventional lithographic techniques, which involve equipment‐intensive and toxic‐chemical etching processes. Here, capillary‐force‐driven switchable delamination of nanofilms and its application to a green selective transfer process are presented. The capillary‐force‐driven delamination is easily and spontaneously implemented by dipping an Au–Si specimen into water at an oblique angle; no other chemicals or additional processes are required. Moreover, the delamination behavior is switched by changing the hydrophobic Au surface to hydrophilic. The mechanism of switchable delamination is investigated by considering the primary influencing factors which are wettability of Au surface and surface tension of water platform. The switchable delamination allows the selective transfer of nanofilm patterns by locally modulating surface wettability. Diverse nanofilm patterns and structures including spiral, serpentine, and van der Waals heterostructures are demonstrated. Furthermore, various nanofilm materials are used in the transfer process by exploiting Au nanofilm as a debonding layer. Finally, a unique technique for assembly and one‐step transfer of nanofilm devices is suggested using the selective transfer method.

Wafer‐Scale Van der Waals Assembly of Free‐Standing Near Atom Thickness Hetero‐Membranes for Flexible Photo‐Detectors

“…It is known that F = γ(1 − cosθ) where γ is the water surface tension capillary force, and θ is the water contact angle. [30] This equation indicates that thin films of higher hydrophobicity (thus, larger θ) are more prone to water-driven delamination with a larger driving force, F. To verify this idea, we identified the water wettability of PtS-grown SiO 2 /Si wafers by measuring their water contact angle (WCA) values (Figure 2c). An as-prepared PtS thin film sample exhibited modest hydrophobicity manifested by the WCA of ≈47.6° (Figure 2c, left) where it did not become delaminated in water.…”

“…The underlying principle for this water-assisted preparation of PtS membranes can be understood by the capillary force-driven delamination of thin films. [30] When "hydrophobic" thin films grown (or, deposited) on hydrophilic substrates such as SiO 2 /Si wafers are exposed to water, the film/substrate interfaces experience the capillary peeling force, F, which determines the surface properties of the www.advelectronicmat.de films. It is known that F = γ(1 − cosθ) where γ is the water surface tension capillary force, and θ is the water contact angle.…”

“…This observation supports that the delamination is indeed dictated by the capillary peeling force, F = γ(1 − cosθ) which should overcome a certain energy barrier for the initiation of the delamination. [30] The surface energy of the PtS film at the moment of its delamination is calculated to be ≈44.37 mN m −1 . [16] The air-exposure driven increase of hydrophobicity has also been observed with other vdW layered 2D TMD materials, [31,32] while its exact origin needs to be clarified with further investigations.…”

Peel-and-Stick Integration of Atomically Thin Nonlayered PtS Semiconductors for Multidimensionally Stretchable Electronic Devices

“…The freestanding membrane can be firmly “stuck” to the surface of any substratee.g., wafer, paper, plastic, etc.within the water, as fully demonstrated in Supporting Information, Video 1. It is interesting to note that this nonlayered PtS thin film can be spontaneously delaminated despite the absence of vdW physical gaps at its interface with the growth wafer, unlike the cases of vdW 2D TMD layers. ,− The working principle for this delamination phenomenon is believed to be an interplay of the water-driven exertion of a capillary force and the intrinsic surface wettability of the PtS thin film; i.e., the driving force, F , for the delamination of an as-grown thin film exposed to water is governed by the water surface tension capillary force, γ, and the water contact angle (WCA), θ, as in the equation F = γ (1 – cos θ). − This analysis leads to two conclusions; (1) films with higher hydrophobicity (i.e., a larger value for θ, a larger value for γ) are more prone to spontaneous delamination due to a stronger driving force (i.e., a larger value for F ), and (2) delamination efficacy can be controlled within the same sample by selectively adjusting its surface wettabilityi.e., spatially controlled value for θ. The distinct delamination characteristics of the PtS thin film determined by its surface hydrophobicity are illustrated in Supporting Information Figure S2.…”