Swelling-Assisted Sequential Infiltration Synthesis of Nanoporous ZnO Films with Highly Accessible Pores and Their Sensing Potential for Ethanol

Abstract

Here, we report a swelling-assisted sequential infiltration synthesis (SIS) approach for the design of highly porous zinc oxide (ZnO) films by infiltration of block copolymer templates such as polystyrene-block-polyvinyl pyridine with inorganic precursors followed by UV ozone-assisted removal of the polymer template. We show that porous ZnO coatings with the thickness in the range between 140 and 420 nm can be obtained using only five cycles of SIS. The pores in ZnO fabricated via swelling-assisted SIS are highly accessible, and up to 98% of pores are available for solvent penetration. The XPS data indicate that the surface of nanoporous ZnO films is terminated with −OH groups. Density functional theory calculations show a lower energy barrier for ethanol-induced release of the oxygen restricted depletion layer in the case of the presence of −OH groups at the ZnO surface, and hence, it can lead to higher sensitivity in sensing of ethanol. We monitored the response of ZnO porous coatings with different thicknesses and porosities to ethanol vapors using combined mass-based and chemiresistive approaches at room temperature and 90 °C. The porous ZnO conformal coatings reveal a promising sensitivity toward detection of ethanol at low temperatures. Our results suggest the excellent potential of the SIS approach for the design of conformal ZnO coatings with controlled porosity, thickness, and composition that can be adapted for sensing applications.

Al2O3 Dot and Antidot Array Synthesis in Hexagonally Packed Poly(styrene-block-methyl methacrylate) Nanometer-Thick Films for Nanostructure Fabrication

“… 56 The fundamental role of the interface between the polymeric domains was investigated using a different approach by Berman and Shevchenko. 15 , 27 , 29 They took advantage of the swelling of the PS- b -P4VP matrix to control the porosity of BCP materials. BCP swelling increases free volume in the polymer matrix and consequently diffusivity of TMA and H 2 O precursors promoting incorporation of Al 2 O 3 into the P4VP component of the polymer matrix.…”

“…Overall, these features implied that the trapping of the metal precursor within PMMA nanodomains is more efficient that in a homogenous PMMA film due to the presence of the percolation pathways provided by the PS domains inside the self-assembled BCP film . The fundamental role of the interface between the polymeric domains was investigated using a different approach by Berman and Shevchenko. ,, They took advantage of the swelling of the PS- b -P4VP matrix to control the porosity of BCP materials. BCP swelling increases free volume in the polymer matrix and consequently diffusivity of TMA and H 2 O precursors promoting incorporation of Al 2 O 3 into the P4VP component of the polymer matrix.…”

“… 8 − 11 The understanding of the basic mechanisms governing the process allowed expanding the list of materials that can be grown using this technique. In particular, the growth of several oxides, like Al 2 O 3 , TiO 2 , 12 ZnO, 12 − 15 WO x , 16 VO x , 12 In 2 O 3 , 17 , 18 Ga 2 O 3 , 18 and SnO 2 , 19 has been already reported in the literature for different applications, such as high-resolution hard masks, 20 − 25 nanoparticle coatings and decoration, 8 , 26 , 27 superhydrophobic coatings, 28 optical materials and antireflection coatings, 29 , 30 enhancer of the contrast and scattering of nanostructures, 24 , 31 , 32 3D superlattices, 33 oil sorbents, 34 UV and thermal protection, 14 tuning of mechanical propertries, 35 sensing applications, 15 membranes, 36 − 38 elastic energy-storage structures, 39 electrical devices, 13 , 17 , 40 , 41 and resistive switching devices. 42 In addition, SIS can be also exploited as a postlithography technique to improve the extreme ultraviolet patterning process.…”

Porous but Mechanically Robust All-Inorganic Antireflective Coatings Synthesized using Polymers of Intrinsic Microporosity

“…The infiltration of polymer templates with alumina precursors was performed using a SIS method that has been described earlier. ,− A GEMStar thermal atomic layer deposition (ALD) system was used for the process for convenience, though we note that our process is not an ALD process (deposition rates are much higher and the deposition is not atomic layer-by-layer) and could be carried out in other appropriately configured chemical vapor deposition systems as well. TMA and H 2 O were used as gas-phase precursors.…”

Templating Functional Materials Using Self-Assembled Block Copolymer Thin-Film for Nanodevices

“…VPI, which is also referred to as sequential infiltration synthesis (SIS), has been demonstrated for enhancing various properties of polymers such as mechanical, (Dusoe et al, 2017); (Lee et al, 2009); (Lee et al, 2010); (Gregorczyk et al, 2015) chemical, (Tseng et al, 2011;TsengTseng et al, 2011;McGuinness et al, 2020), electrical, (Nam et al, 2015a;Subramanian et al, 2019), optical, (Rahman et al, 2014;Rahman et al, 2015;Ocola et al, 2016), triboelectric, (Yu et al, 2015;Yu and Wang, 2016), and thermal properties. (Bamford et al, 2021) These hybrids have been useful for a wide variety of applications (Subramanian et al, 2018); (Berman and Shevchenko, 2020) such as gas separation, (Greil et al, 2017), oil absorption, (Barry et al, 2017), photodetectors, (Nam and Stein, 2017), gas sensors, (Pleshek et al, 2021), energy conversion. (Yu et al, 2015) and filteration.…”