From Patterning of Polymer-Based Films to Their Subsequent Filling with Various Nanomaterials

polymers Review Multifunctional Structured Platforms: From Patterning of Polymer-Based Films to Their Subsequent Filling with Various Nanomaterials Madalina Handrea-Dragan 1,2 and Ioan Botiz 1,* 1 Interdisciplinary Research Institute in Bio-Nano-Sciences, Babes-Bolyai University, 42 Treboniu Laurian Str. 400271 Cluj-Napoca, Romania; [email protected] 2 Faculty of Physics, Babes-Bolyai University, 1 M. Kogalniceanu Str. 400084 Cluj-Napoca, Romania * Correspondence: [email protected] Abstract: There is an astonishing number of optoelectronic, photonic, biological, sensing, or storage media devices, just to name a few, that rely on a variety of extraordinary periodic surface relief miniaturized patterns fabricated on polymer-covered rigid or flexible substrates. Even more extraordinary is that these surface relief patterns can be further filled, in a more or less ordered fashion, with various functional nanomaterials and thus can lead to the realization of more complex structured architectures. These architectures can serve as multifunctional platforms for the design and the development of a multitude of novel, better performing nanotechnological applications. In this work, we aim to provide an extensive overview on how multifunctional structured platforms can be fabricated by outlining not only the main polymer patterning methodologies but also by emphasizing various deposition methods that can guide different structures of functional nanomaterials into periodic surface relief patterns. Our aim is to provide the readers with a toolbox of the most suitable patterning and deposition methodologies that could be easily identified and further combined when the fabrication of novel structured platforms exhibiting interesting properties is targeted. Citation: Handrea-Dragan, M.; Botiz, I. Multifunctional Structured Keywords: polymer film patterning; top–down and bottom–up lithography; material deposition Platforms: From Patterning of techniques; structured platforms Polymer-Based Films to Their Subsequent Filling with Various Nanomaterials. Polymers 2021, 13, 445. https://doi.org/10.3390/ polym13030445 1. Introduction In the past years, a variety of conventional [1–4] and less conventional [5–7] micro- and Received: 16 January 2021 nano-patterning methods have been used to generate periodic surface relief patterns. As a Accepted: 26 January 2021 consequence, a huge diversity of patterned materials developed in time. These materials Published: 30 January 2021 were shown to exhibit enhanced and/or novel properties and have been embedded in modern technological and engineering areas [8–10] in order to improve the quality and Publisher’s Note: MDPI stays neutral functionality of different devices. Nowadays, the number and diversity of such devices with regard to jurisdictional claims in significantly increased inclusively due to the fact that the periodic surface relief patterns published maps and institutional affil- can be routinely fabricated on (polymer-covered) solid or flexible substrates and can be iations. further filled with other (functional) materials by employing a variety of available deposition methodologies [11–14]. The resulting structured platforms (SPs), i.e., periodic surface relief patterns of certain shape and dimension that are filled in a disordered or (hierarchi- cally) ordered manner with various materials of different size, shape, and function [15–18], Copyright: © 2021 by the authors. are being currently used in a variety of optoelectronic [9,16,19], photonic [20], biologi- Licensee MDPI, Basel, Switzerland. cal [17,21,22], sensing [13], or storage media [18] applications. Therefore, it is obvious that This article is an open access article in order to further exploit such applications, we have to design and develop novel SPs with distributed under the terms and puzzling properties. This implies that we have to appropriately choose the most suitable conditions of the Creative Commons methods and approaches related both to the patterning of polymer-covered substrates and Attribution (CC BY) license (https:// to material deposition methodologies. To do this efficiently, we need to have at hand an creativecommons.org/licenses/by/ overview of all the advantages and disadvantages of the above-mentioned methodologies. 4.0/). Polymers 2021, 13, 445. https://doi.org/10.3390/polym13030445 https://www.mdpi.com/journal/polymers Polymers 2021, 13, x FOR PEER REVIEW 2 of 49 substrates and to material deposition methodologies. To do this efficiently, we need to have at hand an overview of all the advantages and disadvantages of the above‐men‐ tioned methodologies. In general, periodic surface relief patterns of various dimensions and shapes can be fabricated using either top–down or bottom–up lithographic methodologies (Figure 1), although other methods might work as well [5–7]. These methodologies can be used sep‐ arately [23–26] or combined [27,28]. The top–down methodology is breaking down the material system by removing molecules or atoms using electrons [29], ions [30], protons [31], light [32], etc. and leaving a clearer pattern on the surface of the material (Figure 1a), while the bottom–up methodology is based on building different blocks or stacking mol‐ ecules on top of each other (Figure 1b). Both approaches have advantages and limitations Polymers 2021, 13, 445 2 of 47 and are equally important in nanotechnology and modern technological industry. The bottom–up method is supposed to be more advantageous because the resulting patterns can be of better miniature and show less defects, exhibiting a more homogenous chemical composition. Nonetheless,In general, the top–down periodic surface approach relief seems patterns to display of various an overall dimensions better con and‐ shapes can be trol in pattern formationfabricated on using large either surfaces. top–down or bottom–up lithographic methodologies (Figure1 ), In this work,although we aim other to provide methods an mightoverview work on asthe well current [5–7 polymer]. These‐based methodologies SPs and can be used their use in nanotechnologicalseparately [23–26 applications,] or combined with [27,28 a ].direct The top–down emphasis methodologyon their fabrication is breaking down the methodology. Tomaterial accomplish system this by removingaim, in the molecules first part or of atoms the review, using electronswe are going [29], to ions offer [30 ], protons [31], an extensive outlinelight [ 32about], etc. the and main leaving (polymer a clearer film) pattern patterning on the methodologies, surface of the material including (Figure 1a), while top–down andthe bottom–up bottom–up approaches, methodology while is based in the on second building part different of the blocksreview, or we stacking will molecules on present and analyzetop of various each other deposition (Figure 1methodsb). Both used approaches for the guided have advantages deposition and of differ limitations‐ and are ent structures (nanoparticles,equally important nanorods, in nanotechnology nanospheres, and etc.) modern of functional technological materials industry. into pe The‐ bottom–up riodic surface reliefmethod patterns. is supposed At the to end be more of this advantageous work, readers because will have the resultingat hand a patterns toolbox can be of better of the most suitableminiature patterning and show and deposition less defects, methodologies exhibiting a more that could homogenous be easily chemical identi‐ composition. fied and furtherNonetheless, combined in the order top–down to fabricate approach interesting seems SPs to display possessing an overall puzzling better prop control‐ in pattern erties. formation on large surfaces. FigureFigure 1. (a 1.–b()a Illustration–b) Illustration of the of top–down the top–down (a) and (a) andbottom–up bottom–up (b) lithographic (b) lithographic principles. principles. 2. Top–Down LithographicIn this work, Methodologies we aim to provide an overview on the current polymer-based SPs and Many currenttheir nanotechnological use in nanotechnological advancements applications, rely on the with development a direct emphasis of novel on mi their‐ fabrication cro‐ and nanostructuredmethodology. materials To accomplish exhibiting this good aim, mechanical in the first properties, part of the flexibility, review, we and are going to offer robustness. Withinan extensive this category, outline patterned about the materials main (polymer displaying film) no patterning chemical methodologies, defects or including no mechanical top–downdeformations and at bottom–up edges are highly approaches, desirable. while Their in thefabrication second is part performed of the review, we will by employing differentpresent and top–down analyze variouspatterning deposition methods methods (Figure used1a) that for theare guidedbeing continu deposition‐ of different ously developedstructures and adapted (nanoparticles, and that include nanorods, photolithography, nanospheres, etc.) electron, of functional proton, materials as well into periodic as ion beam lithography,surface relief soft patterns. lithography, At the scanning end of this lithography, work, readers particle will lithography, have at hand or a toolbox of the stencil lithography.most suitable patterning and deposition methodologies that could be easily identified and further combined in order to fabricate interesting SPs possessing puzzling properties. 2. Top–Down Lithographic Methodologies Many current nanotechnological advancements rely on the development of novel micro- and nanostructured

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