Large Block Copolymer Self-Assembly for Fabrication of Subwavelength Nanostructures for Applications in Optics

Abstract

Nanostructured surfaces are common in nature and exhibit properties such as antireflectivity (moth eyes), self-cleaning (lotus leaf), iridescent colors (butterfly wings), and water harvesting (desert beetles). We now understand such properties and can mimic some of these natural structures in the laboratory. However, these synthetic structures are limited since they are not easily mass produced over large areas due to the limited scalability of current technologies such as UV-lithography, the high cost of infrastructure, and the difficulty in nonplanar surfaces. Here, we report a solution process based on block copolymer (BCP) self-assembly to fabricate subwavelength structures on large areas of optical and curved surfaces with feature sizes and spacings designed to efficiently scatter visible light. Si nanopillars (SiNPs) with diameters of ∼115 ± 19 nm, periodicity of 180 ± 18 nm, and aspect ratio of 2-15 show a reduction in reflectivity by a factor of 100, <0.16% between 400 and 900 nm at an angle of incidence of 30°. Significantly, the reflectivity remains below 1.75% up to incident angles of 75°. Modeling the efficiency of a SiNP PV suggests a 24.6% increase in efficiency, representing a 3.52% (absolute) or 16.7% (relative) increase in electrical energy output from the PV system compared to AR-coated device.

Automated solvent vapor annealing with nanometer scale control of film swelling for block copolymer thin films

“…The possibility of large area self-assembly was also explored since BCP lithography would be ideal for engineering materials with new surface properties. Subwavelength BCP patterns have been already used to produce nanostructured antireflective coatings 17 and anisotropic refractive index metamaterials. 19 So far, we have managed to optimize the whole BCP self-assembly and SVA process for quarter pieces of 2-inch Si wafers.…”

“…[7][8][9] Considerable effort has been put into directing the self-assembly (DSA) of low molecular weight BCPs into sub-10 nm sized structures for semiconductor industry applications including high-density memory devices, 10,11 integrated circuit layouts, 12,13 and most recently, Fin field-effect transistors (FinFETs). 14 High molecular weight BCPs have found their uses in applications where dense patterning and large-area coverage is needed such as in filtration membranes, 15 antireflective coatings, 16,17 and optical metamaterials. 18,19 For application purposes, the main challenges of BCP-based nanofabrication have been related to self-assembly; control of the pattern features and minimization of defects.…”

Design and Fabrication of Moth-Eye Subwavelength Structure with a Waist on Silicon for Broadband and Wide-Angle Anti-Reflection Property

“…Munday et al (at the University of Maryland) deposited SiO 2 nanospheres on the surface of semiconductor materials to improve the efficiency of semiconductor light absorption by approximately 15%-20% [19]. Mokariantabari et al, using block copolymers as a template, decreased the reflection on silicon substrates to below 0.2% at lower angles of incidence (AOIs), and below 2% at higher AOIs [20]. In addition, with the development of advanced and alternate fabrication structures [21,22], efforts to increase the AR performance have led to the development of moth-eye structures with various morphologies, such as cylindrical, conical, and spherical pits, and pyramidal structures [23,24].…”

Micellar‐Mediated Block Copolymer Ordering Dynamics Revealed by In Situ Grazing Incidence Small‐Angle X‐Ray Scattering during Spin Coating

“…Periodic structures of nanometer length scale formed by ordered block copolymer (BCP) thin films constitute a versatile platform to provide significant development in many technological applications such as data storage, lithography, nanostructured membranes, sensors, photonics, and solar cells . In all the aforementioned fields, the BCP ordering pathways can be tailored to achieve a multitude of nanostructures with the desirable orientation and periodicity.…”

“…nanostructured membranes, [8][9][10] sensors, [11] photonics, [12][13][14] and solar cells. [15,16] In all the aforementioned fields, the BCP ordering pathways can be tailored to achieve a multitude of nanostructures with the desirable orientation and periodicity.…”