Selective Dewetting Research Articles

Solvent-Assisted Filling of Liquid Metal and Its Selective Dewetting for the Multilayered 3D Interconnect in Stretchable Electronics.

As stretchable electronics are rapidly developing and becoming complex, the requirement for stretchable, multilayered, and large-area printed circuit boards (PCBs) is emerging. This demands a stretchable electrode and its vertical interconnect access (via) for 3-dimensional (3D) connectivity between layers. Here, we demonstrate solvent-assisted liquid metal (LM) filling into the submicrometer channel (∼400 nm), including via-hole filling and selective dewetting of LM. We provide the theoretical background of solvent-assisted LM filling and selective dewetting and reveal the osmotic pressure arising from anomalous mass transport phenomena, case II diffusion, which drives negative pressure, the spontaneous pulling of LM into the open channel. Also, we suggest design criteria for the geometry and dimension of LM interconnects to obtain structural stability without dewetting, based on the theoretical and computational background. We demonstrate a simple stretchable near-field communication (NFC) device including transferred micrometer-size light-emitting diodes (LEDs) with only 230 μm to the stretchable liquid metal PCB, without any soldering process. The device operates stably under repetitive stretching and releasing (∼50% uniaxial strain) due to the stable connection through the LM via between the upper and lower layers. Finally, we propose a concept for modular-type stretchable electronics, based on the cohesive liquid nature of LM. As a building block, the functional module can be easily removed from a mainframe, and replaced by another functional module, to suit user demand.

High‐Resolution Patterned Functionalization of Slippery “Liquid‐Like” Brush Surfaces via Microdroplet‐Confined Growth of Multifunctional Polydopamine Arrays

AbstractSlippery omniphobic covalently attached liquids enable smooth, transparent, pressure‐ and temperature‐resistant, and liquid‐repellent coatings. Patterned functionalization of such surfaces would drive technology developments and fundamental understandings in broad applications from biosensors to sustainable smart surfaces. Herein an additive microcontact printing approach in combination with the microdroplet‐confined synthesis is developed to functionalize slippery surfaces tethered with “liquid‐like” linear poly(dimethylsiloxane) by multifunctional polydopamine (PDA) arrays. Using glycerol and non‐ionic surfactant Tween‐20, microdroplet arrays containing dopamine monomers are printed onto the slippery surfaces and serve as microreactors for the in situ growth of PDA micropatterns. The confined growth approach enables tunable feature size, height, and morphology of the patterns, through which sub‐micrometer PDA dot arrays over centimeter‐square patterning area can be reliably achieved. Furthermore, the reactive and hydrophilic PDA micropatches allow further functionalization of the slippery surfaces with a diverse variety of materials, meanwhile the anti‐fouling and dynamically dewetting “liquid‐like” brushes permit minimum background contamination. Proof‐of‐concept demonstrations include PDA‐initiated photografting for stimuli‐responsive polymer functionalization, protein immobilization for microarray‐based immunoassays, as well as sliding‐induced selective dewetting of organic solutions to pattern photoluminescent perovskite microcrystals and nanoparticles. The current approach illustrates the potential for applying patterned slippery surfaces with multifunctional architectures in many fields.

Nanoscale-Dewetting-Based Direct Interconnection of Microelectronics for a Deterministic Assembly of Transfer Printing.

As electronics dramatically advance, their components should be fabricated for miniaturized scale, and integrated on limited-size substrates with extremely high density. Current technologies for the integration and interconnection of electronics show some critical limitations in the application of microscale electronics. To address these problems, herein, a new direct and vertical interconnection driven by selective dewetting of a polymer adhesive is introduced. The interconnection system consists of the polymer adhesive and nanosized metal particles, or structured electrodes. Nanoscale-dewetting windows formed by controlling the stability and wetting property of the adhesive polymer are controlled by the interfacial property of the coated polymer adhesive. The adhesive is coated on substrate by a simple spin-coating process, and its ultraviolet curable property allows only the device-mounted parts to be selectively conductive and sticky, while the other parts form insulation and protection layers. The interconnection of the electronics and substrate by adhesive makes it possible to apply the technique to various microsize electronics with electrode size and pitch of 20 µm or less, and endure dramatic temperature change and a long-term high humidity environment. Moreover, over display comprising over 10 000 microscale light-emitting diodes (micro-LEDs), and commercialized microchips are demonstrated with monolithic integration on flexible and transparent substrate.

Thermocapillary Multidewetting of Thin Films

ABSTRACTThermocapillary dewetting of liquids and molten films has recently emerged as a viable alternative to conventional microprocessing methods. As this thermal gradient-induced mechanism is universal, it can be applied to any material. This work explores the sequential dewetting of materials with varying melting points, including polymers and metals, to create aligned morphologies. The variation in melting point allows for the dewetting of single layers at a time or mobility-limited simultaneous dewetting. As a result, a variety of multimaterial structures can be produced with built-in alignment, such as arrays of concentric circles, lines with periodic segmentation, or islands on holes. This approach employs photothermal methods to induce the necessary thermal gradient, manipulating several variables in order to influence the consequent structures. Adjusting laser power and light intensity allows for the control of temperature for selective dewetting of films; altering beam size and exposure time affects the extent of dewetting in terms of diameter size; overlap effects and simultaneous dewetting can result in complex architectures. This controlled writing of patterns also presents a technique to create both masks at low temperatures for conductive multilayers as well as templates for electrospray deposition.

Fabrication of poly(ε-caprolactone) (PCL) particles with non-spherical geometries via selective dewetting and deposition of the polymer

This paper describes a simple, inexpensive method for the fabrication of non-spherical polymeric particles. This method involves the use of a mechanical rubbing-assisted colloidal crystal to generate a substrate with an array of dimples on its surface, followed by selectively depositing a polymer into the dimples. As a proof-of-concept experiment, we demonstrated the fabrication of poly(e-caprolactone) (PCL) particles with non-spherical shape. The shape of the polymer particles could be controlled from disk to hemisphere by changing the surface structure and property of the substrate and the concentration of the polymer solution. When functional components including drug molecules and inorganic NPs were used together with the polymer, we could easily obtain the non-spherical particles loaded with the components. Furthermore, non-spherical particles with a hollow structure were formed with the use of immiscible polymer blend consisting of PCL and poly(ethyleneoxide) (PEO).

Fluorosurfactant-assisted photolithography for patterning of perfluoropolymers and solution-processed organic semiconductors for printed displays

A photolithographic patterning technique of perfluoropolymers was developed for the micropatterning of solution-processed organic semiconductors. We found that a small amount of fluorosurfactant additives in photoresist solutions enabled preparation of the spin-coated films even on the dewetting surfaces of perfluoropolymers. Subsequent photolithography and dry/wet etching achieved excellent patterning of perfluoropolymers, which provided a high contrast of wettability in microscale on the substrate. The dewetting patterns were applied for isolating solution-processed organic thin-film transistor arrays for a 100 ppi active-matrix display by selective dewetting. The isolation of the semiconducting layers achieved significant improvement in the current on/off ratio with a high mobility of >1 cm2 V−1 s−1.

Spatially Selective Formation of Hydrocarbon, Fluorocarbon, and Hydroxyl-Terminated Monolayers on a Microelectrode Array

A protection-deprotection strategy, using gold oxide as a passivating layer, was used to direct the self-assembly of monolayers (SAMs) selectively at individual gold microelectrodes in an array. This approach allowed the formation of hydroxyl-terminated monolayers, without side reactions, in addition to hydrocarbon and fluorocarbon SAMs. Fluorescence microscopy was used to visualize selective dewetting of hydrophobic monolayers by an aqueous dye solution, and spatially resolved X-ray photoelectron spectroscopy was used to demonstrate a lack of cross-contamination on neighboring microelectrodes in the array.

Charge-induced local dewetting on polymer electrets studied by atomic force microscopy.

Polymer electrets are one of the most important series of electrets, which are widely used both in academic research and industrial applications. The effect of trapped charges on dielectric properties of the polymer electret is critical for more intelligent utilization of these materials. Herein we report the charge-induced polymer relaxation reflected by the local dewetting of the polymer electrets with charge patterns. Because the difference in charge-induced relaxation results in selective dewetting of thin polymer films, polymers in the charged areas are preferentially dewetted from the substrate compared with the neutral areas under heating or solvent annealing, leading to the appearance of hole arrays. Therefore, the effect of trapped charges on relaxation was also studied via monitoring the relaxation behaviours of homo-polymer and block copolymer films as well as measuring the mechanical properties of homo-polymers with charge patterns. These results demonstrate that the charge trapped in polymer electrets could accelerate relaxation and drive the dewetting process of thin polymer films.

High-Throughput and High-Intensive Biosensor Microarray Fabrication by Selective Dewetting on a Wettability Controlled Substrate

In a microarray biosensor, the surface characteristic for reducing background nonspecific binding is a critical aspect for achieving the high sensitivity and accurate detection. In this paper, we proposed a new high-intensity and reduced nonspecific binding microarray fabrication method with a selective dewetting process on a mixed self-assembled monolayer (SAM), consisting of methyl-terminated and methoxy-[poly(ethylene glycol) (PEG)]-terminated silanes. The combination of hydrophobic and hydrophilic properties of the mixed SAM background layer provided the hydrophobicity that allowed the selective dewetting of the protein solution at specific versus nonspecific regions and reduced the nonspecific binding owing to hydrated PEG chains in the mixed SAM. The wiping process was applied for obtaining high throughput and reducing protein usage. Finally, the background non-specific binding was significantly reduced by 78% with a selective dewetting method compared with the standard method using a cover slip. Furthermore, the peak intensity was increased by 20% and the protein usage was reduced versus the standard method.

Low temperature, template-free route to nickel thin films and nanowires

In this manuscript, we report on the elaboration of nickel thin films, isolated clusters and nanowires on silicon, glass and polymers by a low temperature deposition technique. The process is based on the thermal decomposition of Ni (η(4)-C(8)H(12))(2) at temperatures as low as 80 °C, which exclusively yields metallic Ni and a volatile by-product. The low temperature of the process makes it compatible with most of the substrates, even polymers and organic layers. Several deposition techniques are explored, among them spin coating of the organometallic complex in solution, which allows controlling nickel film thickness down to several nanometers. The density of the film can be varied by the speed of the spin coater with the formation of nanowires being observed for an optimized speed. The nanowires form a network of parallel lines on silicon and the phenomenon will be discussed as a selective dewetting of the organometallic precursor. All samples are fully characterized by SEM, EDS, cross-sectional HRTEM, ellipsometry, AFM, MFM and SQUID magnetic measurements.

Highly effective gold nanoparticle-enhanced biosensor array on the wettability controlled substrate by wiping

We demonstrate the use of a highly effective biosensor array to fulfill the requirements of high intensity, reduced nonspecific adsorption (NSA), and low sample usage. The mixed self-assembled monolayers (SAMs), consisting of methyl-terminated and methoxy-(polyethylene glycol (PEG))-terminated silanes, were newly applied as the background layer to reduce the background NSA via wettability control. The surface was modified by a plasma process with a pattern mask. Gold nanoparticles (AuNPs) were grafted within pattern-modified regions to increase intensity and were modified with protein G variants with cysteine residues to immobilize the antibody proteins directly. The target protein samples were selectively dewetted by the high throughput wiping process, while retaining semi-contact with the substrate. The data revealed that the background NSA was significantly reduced by 78% with selective dewetting compared to the standard method. Furthermore, the peak intensity was improved 5 times by applying AuNPs as compared to that of a planar surface, and the protein requirement was significantly reduced versus the standard process.

Shaping Mesoporous Films Using Dewetting on X-ray Pre-patterned Hydrophilic/Hydrophobic Layers and Pinning Effects at the Pattern Edge

Ordered mesoporous silica micrometer-sized structures have been fabricated via selective dewetting of the coating sol on a hydrophilic/hydrophobic fluorinated silica substrate, which had been pre-patterned using deep X-ray lithography with a synchrotron radiation source. We have observed that deposition of mesoporous films on the pre-patterned areas can be used as a design tool for obtaining regions of specific geometry and dimensions. The evaporation of the solution in constrained conditions because of pinning at the pattern edges gives layers with thicker edges. This edge effect appears dependent upon the dimension of the pre-patterned hydrophilic/hydrophobic layer; in smaller patterns, the evaporation is too fast and thickening of the edges is not observed. We have used infrared imaging, optical profilometry, and atomic force microscopy to characterize the patterned layers and the edge effect, produced by pinning at the border of the microstructures.

Patterning Block Copolymer Aggregates via Langmuir−Blodgett Transfer to Microcontact-Printed Substrates

We demonstrate a new strategy for producing hierarchical polymer nanostructures, which combines nanoscale self-assembly of amphiphilic block copolymers at the air-water interface with microscale templated assembly of the resulting aggregates on chemically patterned substrates. Aggregates are formed via interfacial self-assembly of 141k polystyrene-b-poly(ethylene oxide) (PS-b-PEO, MW = 141k, 11.4 wt % PEO) or a blend of 185k PS-b-PEO (MW = 185k, 18.9 wt % PEO) and PS-coated CdS nanoparticles to form strandlike copolymer or copolymer-nanoparticle aggregates. Using Langmuir-Blodgett (LB) techniques, the aggregates are then transferred to patterned substrates possessing alternating hydrophilic/hydrophobic stripes, obtained by microcontact printing octadecyltrichlorosilane (OTS) on glass. The aggregates are transferred under various conditions of surface pressure, orientation of the patterned substrate, and withdrawal speed. Templated assembly of aggregates into the hydrophilic substrate domains is achieved when the hydrophilic/hydrophobic stripes are oriented perpendicular to the water surface during LB transfer; this is explained by surface energy heterogeneities along the subphase-substrate contact line, which induce selective dewetting and concomitant monolayer rearrangement at the drying front. In contrast, parallel orientation of stripes results in nonselective transfer of the monolayer without registration to the underlying surface pattern. By studying the effect of surface pressure, we show that packing constraints imposed by compression of aggregates to high surface densities prevent the formation of patterned LB films that match the established periodicity of the OTS-patterned glass. As well, it is shown that efficient transfer of aggregates to the patterned glass requires slower substrate withdrawal speeds compared to transfer to unpatterned hydrophilic glass.

Organic transistors realized by an environmental friendly microcontact printing approach

Abstract A patterning method was developed that allows for combining the advantages of a low cost microcontact printing process on rigid and flexible substrates with the advantages of conventional semiconductor processing. The patterning approach combines printing of self-assembled monolayers with selective dewetting while being compatible with conventional semiconductor processes. Alkyl thiol self-assembled monolayers were printed on gold and silver films on rigid and flexible substrates. The printed regions turn hydrophobic while the bare regions remain hydrophilic. The hydrophilic regions of the surface were selectively wetted by a polymer like poly-methyl methacrylate. The selectively patterned poly-methyl methacrylate is used as etch resist while the bare regions of the gold film were patterned by a potassium iodide/iodine solution. The potassium iodide/iodine etchant is compatible with conventional semiconductor processing in contrast to the commonly used ferri/ferrocyanide etching solutions. The method allows for patterning of gold and silver films with submicron dimension on flexible and rigid substrates. Organic thin-film transistors were realized with drain and source fabricated by the proposed approach. The performance of the organic transistor is comparable to devices fabricated by photolithography.

Microstructuring by microcontact printing and selective surface dewetting

A universal microstructuring approach was developed for patterning surfaces by microcontact printing in combination with selective surface dewetting. Self-assembled monolayers such as octadecyltrichlorosilane [CH3(CH2)17SiCl3] were printed on glass or silicon substrates by microcontact printing. The octadecyltrichlorosilane-coated regions became hydrophobic, whereas the uncoated regions remained hydrophilic. Such functionalized substrates facilitate selective wetting/dewetting of surfaces by polymers or resists. Resists such as poly(methyl methacrylate) were selectively deposited on the hydrophilic regions of the substrate, whereas the hydrophobic regions remained uncoated. The approach allows for patterning of resist on substrates without using photolithography. In this study, the resist was used to lift off metallic microstructures such as microcoils for radio-frequency identification tags and source-drain electrodes for organic field-effect transistors.

Selective dewetting of polymers on metal/silicon micro-patterns

Modification of electrode surfaces plays an important role for electronics. Most often, lithography techniques are used, but they suffer from high fabrication cost, material restrictions and size limitations. Here we investigate if dewetting can be used to selectively coat a micron-sized gold stripe electrode on a silicon substrate. [DOI: 10.1380/ejssnt.2006.656]

Selective Dewetting for General Purpose Patterning

General purpose patterning based on selective dewetting with an elastomeric mold is described. Several well‐defined nanostructures obtained by this method are presented (see Figure for an example). Unlike other patterning techniques, the same mold can be used to generate features ranging in size from the nanometer to the micrometer, simply by changing the duration of dewetting.

Organic polymeric thin-film transistors fabricated by selective dewetting

Thin-film transistors (TFTs) of polymeric semiconductors were fabricated using selective dewetting in the patterning process. The process consists of: (i) patterning the wettability of the substrate using a protective layer of printed wax and a self-assembled monolayer, and (ii) patterning a polymeric semiconductor by selective dewetting from an organic solution. The method has been used to fabricate small arrays of TFTs with a regioregular poly(thiophene) and poly(9-9′-dioctyl-fluorene-co-bithiophene). The TFTs exhibited mobilities of 0.5–1.0×10−3 cm2 V−1 s−1 and on-to-off ratios on the order of 104.