The directed self-assembly (DSA) of block copolymers (BCPs) can be used to produce nanoscale patterns without the cost and process complexity of state-of-the-art optical lithography. Thus, DSA may be useful in a wide variety of semiconductor applications such as fin field-effect transistors and biosensors. To create technologically useful patterns with aligned BCP domains, conventional DSA mechanisms often rely on topographically complex structures or high-resolution chemical patterns to direct the self-assembly, that are difficult to fabricate. In comparison, a newly discovered mechanism for DSA, termed boundary-directed epitaxy (BDE), utilizes chemical contrast at the boundaries between a substrate and relatively wide chemical stripe. Here, we demonstrate the use of BDE to template the fabrication of sub-10 nm features for the first time. BDE is used in conjunction with selective infiltration to create ultranarrow line-space arrays of alumina. These results demonstrate a proof-of-concept for BDE as a method for ultrahigh-resolution feature formation.
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Orbital Angular Momentum from Self‐Assembled Concentric Nanoparticle Rings
Ring‐shaped nanostructures can focus, filter, and manipulate electromagnetic waves, but are challenging to incorporate into devices using standard nanofabrication techniques. Directed self‐assembly (DSA) of block copolymers (BCPs) on lithographically patterned templates has successfully been used to fabricate concentric rings and spirals as etching masks. However, this method is limited by BCP phase behavior and material selection. Here, a straightforward approach to generate ring‐shaped nanoparticle assemblies in thin films of supramolecular nanocomposites is demonstrated. DSA is used to guide the formation of concentric rings with radii spanning 150–1150 nm and ring widths spanning 30–60 nm. When plasmonic nanoparticles are used, ring nanodevice arrays can be fabricated in one step, and the completed devices produce high‐quality orbital angular momentum (OAM). Nanocomposite DSA simplifies and streamlines nanofabrication by producing metal structures without etching or deposition steps; it also introduces interparticle coupling as a new design axis. Detailed analysis of the nanoparticle ring assemblies confirms that the supramolecular system self‐regulates the spatial distribution of its components, and thus exhibits a degree of flexibility absent in DSA of BCPs alone, where structures are determined by polymer‐pattern incommensurability. The present studies also provide guidelines for developing self‐regulating DSA as an alternative to incommensurability‐driven methods.
more » « less- NSF-PAR ID:
- 10446205
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 33
- Issue:
- 40
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Methods Self‐assembled complexes were synthesized by reacting a bis(terpyridine) ligand exhibiting a 60odihedral angle between the two ligating terpyridine sites (
T ) with divalent Zn, Ni, Cd, or Fe. The products were isolated as (Metal2+[T ])n (PF6)2n salts and analyzed using IM‐MS after electrospray ionization (ESI) which produced several charge states from eachn ‐mer, depending on the number of PF6ˉ anions lost upon ESI. Experimental Ω data, derived using IM‐MS, and computational Ω predictions were used to elucidate the size and architecture of the complexes.Results Only macrocyclic dimers, trimers, and tetramers were observed with Cd2+, whereas Zn2+formed the same plus hexameric complexes. These two metals led to the simplest product distributions and no linear isomers. In sharp contrast, Ni2+and Fe2+formed all possible ring sizes from dimer to hexamer as well as various linear isomers. The experimental and theoretical Ω data indicated rather planar macrocyclic geometries for the dimers and trimers, twisted 3D architectures for the larger rings, and substantially larger sizes with spiral conformation for the linear congeners. Adding PF6ˉ to the same complex was found to mainly cause size contraction due to new stabilizing anion–cation interactions.
Conclusions Complete structural identification could be accomplished using ESI‐IM‐MS. Our results affirm that self‐assembly with Cd2+and Zn2+proceeds through reversible equilibria that generate the thermodynamically most stable structures, encompassing exclusively macrocyclic architectures that readily accommodate the 60oligand used. In contrast, complexation with Ni2+and Fe2+, which form stronger coordinative bonds, proceeds through kinetic control, leading to more complex mixtures and kinetically trapped less stable architectures, such as macrocyclic pentamers and linear isomers.
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