Controlled Gold Nanoparticle Placement into Patterned Polydimethylsiloxane Thin Films via Directed Self-Assembly

Table 1

Characteristics and outcomes of current self-assembly processes compared with the self-assembly process introduced in this work.

Structure and dimensions	Conditions/state	Substrate	Fidelity	Characterization/modeling techniques
Template-assisted self-assembly [4, 19]
Array dimensions: Diameter: 230, 270, 330, 440, and 960 nm; Spacing: 400, 500, 600, 740, and 1600 nm; AuNP diameter: ~52 nm; Array dimensions: Diameter: 195 and 260 nm; Depth: 150 and 350 nm; Spacing: 600 and 700 nm; AuNP diameter: 76 and 100 nm	AuNP dispersion between the hydrophilized coverslip and the patterned PDMS at room temperature; Patterned PDMS-PEO contained within a walled cage and AuNP dispersion between the substrate in cage and the glass coverslip superstrate	Hydrophilized coverslip; Templated PDMS-PEO	Large-area arrays with ~17 NPs per cavity, ~100% density of filled cavities, inconsistent size and number of NPs in each cavity; Large-area arrays with 1-20 NPs per cavity, 50-90% density, inconsistent number of NPs in each cavity, wave-like deposition	Characterization: UV-Vis, FTIR, SEM, TEM, and SERS; Modeling: FDTD; Characterization: UV-Vis and dark-field microscopy; Modeling: COMSOL, Mie theory, and CDA
Dip-coating self-assembly [28, 29]
Array dimensions: Grooves: 40, 50, and 100 nm periods and 50-100 nm depths; Holes: 70, 85, 100, and 115 nm periods and 50-100 nm depths; AuNP diameter: 15 and 50 nm; Silica NP diameter: 50 nm; Array dimensions: Diameter: 160-180, 200, and 220 nm; Depth: 50 nm; Spacing: 6 μm; NP diameter: 10-100 nm	Hydraulic actuation, antivibratory system, ultrasonic treatment, sodium hydroxide, and nitric acid required; Dip velocity: 0.3-10 mm/min; pH: 2, 6, or 10; Polyamine-based silane, piranha, methanol, mercaptoundecanoic acid, and 24 hr incubation period in NP suspension required at room temperature	Si substrate coated with a layer of SiO2/Cr and an additional layer of PMMA; Etched PMMA on a hydroxylated silicon wafer	Grooves resulted in 30-90% density with varying NP type and size as well as pH of the solution; Holes also resulted in 30-90% density with varying NP type and with/without ultrasonic treatment; arrays with 1-6 NPs per cavity resulting in 40-100% filled cavities depending on spacing and time pattern remained in solution	Characterization: High-resolution SEM (HRSEM) and photon correlation spectrometer (PCS); Modeling: linear standard approximation (LSA); Characterization: Dark-field microscopy, SEM, % of filled cavities vs. time, and AFM
Directed self-assembly [26, 27]
Array dimensions: Diameter: 200, 250, 300, and 370 nm; Depth: 120 nm; Spacing: 1500, 2000, and 3000 nm; NP diameter: 40, 100, and 250 nm; Array dimensions: Diameter: 580 nm; Depth: 140 nm; Spacing: 1300-2000 nm; NP diameter: ~176 nm	Linear translation stage, fixed glass superstrate, 25 μL drop of AuNPs, 27°C set temperature, 1 μm/s substrate velocity, and 1 wt% Triton X-100; Linear translation stage, fixed glass superstrate, silica-gold nanoshells, 21°C set temperature, and 0.6 μm/s substrate velocity	Templated PDMS; Templated PDMS	100 μm^2 array with 1-5 NPs per cavity resulting in ~85% density of filled cavities; 1-8 NPs per cavity resulting in ~100% density of filled cavities and ~30% yield of desired heptamers	Characterization: Dark-field microscopy and SEM; Characterization: SEM and scattering spectra; Modeling: COMSOL
Modified directed self-assembly (this work)
Array dimensions: Diameter: 195 nm; Depth: 150 nm; Spacing: 600 nm; NP diameter: 100 and 150 nm	Linear translation stage, modified fixed glass superstrate, 3 μL drop of AuNPs, 1 wt% Triton X-100 precoat of substrate at 8 μm/s velocity, and 1.2-2.1 μm/s substrate velocity for AuNP deposition	Templated PDMS	array with 1 NP per cavity resulting in ~100% density of filled cavities at optimal conditions and ~85% density at less optimal conditions	Characterization: Dark-field microscopy, UV-Vis spectroscopy, and extinction per NP calculations; Modeling: Mie theory, DDA, CDA, and rsa-CDA