Introduction

Nanomaterials with precisely controlled patterns and morphology over large macroscopic length scales have garnered significant attention due to their potential applications in energy, sensors, biomedicine, and various other technologies [1][2][3][4]. As technological advancements drive the demand for smaller devices and enhanced performance, advanced lithography and nanopatterning techniques become essential for fabricating nanoscale features that traditional methods cannot achieve, pushing the boundaries of what is technologically possible. In this context, Sequential Infiltration Synthesis (SIS) is an effective and advanced process for creating periodic nanopatterns with dimensions as small as sub-20 nm [5][6][7][8][9]. The SIS process is performed in an atomic layer deposition (ALD) chamber, but unlike conventional ALD, SIS exploits the chemical affinity between inorganic precursors and functional groups in a polymer template. Typically, a first precursor such as trimethylaluminum (TMA) diffuses into the polymer matrix and forms coordinative or covalent interactions with reactive groups (e.g. carbonyl or hydroxyl moieties). A subsequent exposure to a co-reactant such as H 2 O completes the binary reaction, generating an inorganic species (e.g. Al-O-Al) tethered within the polymer domains. Repetition of these exposures increases inorganic loading, and because the precursor-polymer interaction is selective, infiltration occurs only in targeted domains of the polymer containing suitable functional groups. SIS offers several advantages over conventional top-down lithography methods used for nanopatterning, particularly in preventing pattern collapse, achieving precise control, and potentially reducing costs [7][8][9][10][11][12][13]. Additionally, the lower temperature range of the SIS process (approximately 60 • C-150 • C) compared to conventional ALD makes it suitable for use with flexible substrates and in applications that require low-temperature processing. As mentioned, to achieve selective and targeted infiltration, SIS relies on effective interactions between the functional groups of the guiding polymer (homopolymer or block copolymers (BCPs)) and the inorganic precursors used for deposition. BCPs comprise chemically distinct polymer blocks that are covalently bonded together yet thermodynamically incompatible, leading to microphase separation. The self-assembly of BCPs is driven by the immiscibility of covalently linked polymer blocks, which undergo microphase separation into periodic nanostructures. The resulting morphology (e.g. lamellae, cylinders, spheres) is determined by the balance between interfacial energy (χN) and block volume fraction, leading to well-ordered domains at the 10-100 nm scale [14,15]. In this regard, polymers such as polymethylmethacrylate (PMMA) and Polyvinylpyrrolidone-both in homopolymer form and as one of the copolymers of BCPs, which contain active functional groups like carbonyl (C=O), ester (C-O-R), and pyridine groups, have been widely studied and utilized in SIS. These functional groups facilitate infiltration by providing coordination or covalent interaction sites for the inorganic precursors (e.g. TMA), enabling selective incorporation of inorganic species into specific polymer domain. Among these, PMMA has been the most extensively used guiding pattern, especially for enhanced lithography resists and nanopatterning applications due to the extensive database available for this polymeric material [8,[16][17][18][19][20][21].

In the field of research focused on nanopatterning and polymer-inorganic hybrid nanomaterials, the development and introduction of polymers with enhanced chemical reactivity are vital for fostering technological innovation while minimizing processing costs. New polymers as scaffold materials can offer additional benefits over traditional polymers, such as improved conductivity and biocompatibility. In this context, researchers, including the authors, have investigated several unconventional polymers, like poly(acrylic acid) (PAA), polypropylene (PP), and poly(epoxyisoprene) (PIO), for nanopatterning applications and SIS research [22][23][24]. Recently, one of our studies on various polymer-precursor interactions for the SIS method using homopolymer films led us to identify polycaprolactone (PCL) as a promising new polymer [21]. Enhanced chemical interactions between PCL and SIS precursors were observed through in situ Fourier transform infrared spectroscopy (FTIR) measurements without any degradation of the polymer. This observation opened new possibilities for utilizing patterned PCL polymers as templates in nanopatterning and the fabrication of hybrid nanostructures. PCL can serve as an effective templating polymer for various nanopatterning strategies, and its biocompatibility makes it potentially attractive for bio-related applications.

PCL's ability to serve as a template for inorganic material deposition at lower temperatures than other conventional polymers, due to its high reactivity with inorganic precursors even at lower temperatures, is desirable and beneficial for minimizing inorganic deposition resources for nanopatterning. FTIR analysis and comparison between PCL and PMMA in our previous study [21] indicate that the oxygenbearing functional groups of both polymers exhibit similar Lewis base properties. However, the much lower glass transition temperature and melting point of PCL lead to a greater degree of interaction with metallic precursors such as TMA. The lower temperature requirement also broadens its applicability for substrates requiring low-temperature processing for nanopatterning. PCL has also attracted attention due to its amphiphilic character and ability to form diverse nanostructures in different environments. Recent studies have shown that PCL-based BCPs can generate solvent-dependent porous and nonporous capsules, underscoring their versatility in selfassembly and nanostructure design [25]. These structure modification capabilities, together with its low glass transition temperature, provide favorable conditions for efficient precursor infiltration during SIS, making PCL a suitable guiding polymer for oxide nanopatterning. In addition, the biodegradability and biocompatibility of PCL and its inorganic hybrids make them attractive for biomedical applications such as membranes, scaffolds, and drug delivery systems [26][27][28][29][30]. To cite a few examples from the literature, eco-friendly membrane of PCL microsphere loaded with SiO 2 nanoparticles was shown to be effective for oil/water separation [26], high antipathogen activity was demonstrated using PCL/ZnO nanocomposite membrane fabricated by electrospun method [30], and non-cytotoxic effect on target cells was shown from PCL/TiO 2 hybrid materials synthesized using sol-gel method [29], PCL-MXene nanofibrous scaffolds was demonstrated for effective tissue engineering [29]. Therefore, the fabrication of nanostructures using SIS for potential biological applications would open new possibilities in this field of research.

Here, we demonstrate the fabrication of aluminum oxide (Al 2 O 3 ) nanostructured patterns using the SIS method, with self-assembled polystyrene-block (PS-b-PCL) BCPs as the template, where the Al 2 O 3 nanostructures conform to the shape of the PCL nanodomains. The findings reveal the successful incorporation of inorganic oxide material into the PCL domain of the template, which can be utilized as both inorganic-organic hybrids and purely inorganic nanostructures. To the best of our knowledge, this is the first demonstration of using PS-b-PCL BCPs for templated nanostructure fabrication and nanopatterning. The SIS process on PS-b-PCL templates was performed at various temperatures and with different numbers of SIS cycles to compare deposition results. The resulting nanopatterns, after polymer etching, are visualized using field emission scanning electron microscopy (FESEM). The infiltration within the PCL polymer of PSb-PCL and the Al-O growth were confirmed through FTIR. Additionally, Al 2 O 3 nanopatterning using PS-b-PMMA as a template, a well-established template for various nanopatterning processes, was performed under the same experimental conditions to compare the nanopatterns generated from PSb-PCL with those derived from PS-b-PMMA.

The key finding from our experiments is the demonstrated effectiveness of PCL for fabricating hybrid and inorganic nanostructures when using PS-b-PCL as a template for SIS. The successful formation and patterning of nanostructures with PS-b-PCL is evident from the development of welldefined and continuous Al 2 O 3 patterns after the first SIS cycle, following mostly the PCL domain pattern as observed after polymer etching. The effectiveness in growth is attributed to significant deposition during the first cycle, facilitated by enhanced chemical interactions between the polymer and precursors, enabling efficient SIS growth. Significant deposition and continuity achieved in the first cycle itself reduce the need for multiple cycles and conserve deposition resources while also promoting targeted, homogeneous, and well-ordered nanostructure formation. This represents an advancement in the nanostructure growth and patterning process compared to the traditional use of PS-b-PMMA as a template, which typically requires multiple deposition cycles to achieve continuous nanostructures [31]. Furthermore, experiments conducted with PS-b-PCL at different temperatures (60 • C and 80 • C) revealed only a slight difference in the formed nanostructure width at the 60 • C temperatures, with no major deformation of the PCL template observed at either of these temperature ranges. Ex situ FTIR measurements confirmed the complete interaction of all PCL functional groupscarbonyl (C=O) and ester (C-O-R)-from the PS-b-PCL template after SIS deposition, indicating effective and bulk interactions of the PCL polymer. The Al-O peak observed from FTIR data confirms the formation of Al 2 O 3 material after the SIS and etching. Our results align with previous in-situ FTIR observations of PCL homopolymer and Al 2 O 3 precursor chemistry, which also showed significant and complete interactions of PCL functional groups in the first cycle [21].

Experiments

Polymer Deposition: The BCP templates were prepared on silicon (Si) substrates using the spin-casting technique. Before deposition, the Si substrates were cleaned with a solution of NH 4 OH, H 2 O 2 , and deionized (DI) water at 65 • C for 2.5 h. The PS-b-PCL and PS-b-PMMA BCP solutions for spin casting were prepared with a 2 wt % solution of PS(M w = 27 000)-b-PCL(M w = 10 000) and PS(M w = 52 000)-b-PMMA(M w = 52 000) BCP powders and dissolved in toluene. The BCPs were purchased from Polymer Sources, Inc., and the polymer characteristics (nuclear magnetic resonance and size exclusion chromatography data were provided by the vendor [32,33]. To form the PSb-PCL nanostructure film, the BCP films were spin-coated at 5500 rpm for 45 s. After spin coating, the films were annealed at 120 • C for 72 h in an inert gas-filled glove box (Vigor Tech.) to achieve microphase separation and nanostructure formation. The selected PS-b-PCL BCP and the process we used are expected to form horizontal cylindrical nanostructures. For the formation of PS-b-PMMA BCP vertical lamellar nanostructure films (which form similar-looking nanostructures as horizontal cylindrical phase from top-view), a brush layer of PSrandom(r)-PMMA film was applied prior to BCP deposition to ensure the perpendicular alignment of the PS-b-PMMA lamellar structures during microphase separation [34,35]. For the brush layer, a solution of PS (Mn = 14 500)-r-PMMA (Mn = 17 200) (Polymer Sources, Inc.) in toluene was prepared and deposited on Si substrates using a spin coater at 2000 rpm for 40 s. The PS-r-PMMA film was then annealed in the glove box at 240 • C for 40 min, followed by three rinses with toluene to create a thin brush layer only a few nanometers thick. After forming the brush layer, PS-b-PMMA films were spin-coated onto the substrate at 2500 rpm for 45 s. These films were then annealed at 180 • C for 24 h in the glove box to achieve microphase-separated nanostructure formation. The as-spun film thickness of the BCP films was ∼50 nm for both BCPs.

For the FTIR experiments, self-assembled nanostructured PS-b-PCL films were prepared on IR-transparent, double-sided polished Si substrates with high resistivity (>10 000 Ω cm). The fabrication process for the PS-b-PCL nanostructured films was the same as that of the samples whose images are presented in this paper, following the procedure described above.

SIS Deposition:

The Al 2 O 3 SIS depositions were conducted on PS-b-PCL and PS-b-PMMA templated samples by alternating exposures of TMA (Aldrich, 97%) and DI water (H 2 O) using an ALD tabletop setup (Anric AT401) for each SIS cycle. (Note that TMA is a pyrophoric liquid.) The SIS process was carried out in static mode, where the vacuum pump valve was closed during pulsing and exposure to maintain the static deposition mode. In the first step of each cycle, a TMA precursor vapor was introduced into the chamber with a 10 s dosing pulse (at a 500 mTorr TMA pressure) and a 5 sccm flow of N 2 carrier gas, followed by a 60 s exposure period after closing the TMA dosing valve. The chamber was then purged of unreacted reactants for 60 s by opening the pump valve and increasing the N 2 flow to 35 sccm, completing half of one SIS cycle. In the next step, to complete the SIS cycle, H 2 O precursor vapor (with a 500 mTorr H 2 O pressure) was introduced and exposed in the sample chamber, and then purged using the same steps and time periods as described for the TMA precursor. For certain experiments, multiple SIS cycles were performed using this same procedure and timing. The temperature used for PS-b-PCL templated samples was 60 • C and 80 • C. For templated samples, the deposition temperature was set at 80 • C, as SIS deposition has been well-studied for PS-b-PMMA templated nanopatterning approximately at this temperature [6,31,36].

Characterizations:

The BCP polymer nanopatterns and the Al 2 O 3 nanopatterns formed after SIS were imaged and morphologically characterized using a Zeiss Sigma VP300 FESEM. Before imaging the Al 2 O 3 nanopatterns presented in this work, the polymers were etched and removed by annealing the samples in air at 500 • C for 2 h. Image processing and nanostructure dimension calculations were performed using ImageJ software.

FTIR Experiments: FTIR measurements were performed on PS-b-PCL nanostructured films using a Thermo Fisher Nicolet iS50 FTIR Spectrometer in transmission mode, both before and after SIS. All spectra were recorded with a liquid nitrogencooled MCT detector using 256 scans at a resolution of 4 cm -1 , averaging 320 s. A background spectrum of a bare Si substrate was recorded at the beginning of each measurement and subtracted using the FTIR software. FTIR measurements of the as-grown microphase-separated BCPs were carried out prior to SIS deposition to identify the chemical species associated with the pristine polymers. The SIS depositions on the PS-b-PCL templated samples were performed following the same procedures and durations as for the other PS-b-PCL samples shown in this work. The SIS temperature used for the samples in the FTIR study was 80 • C. After SIS, another spectrum of the same sample was recorded using the same FTIR settings to detect any changes or new species present post-deposition.

Results & discussion

The fabrication steps for nanostructure patterns using a PSb-PCL template and the SIS process are illustrated in the schematic diagram in figure 1. The experimental details are provided above in section 2. Briefly, as depicted in figure 1, self-assembled, microphase-separated cylindrical nanostructures of PS-b-PCL were fabricated from a blended PS-b-PCL BCP film after annealing. Next, SIS was performed inside an ALD chamber by sequentially exposing the PS-b-PCL nanostructured sample to TMA and H 2 O under various conditions detailed in section 2. Following the SIS process, the samples were removed from the ALD chamber, and the polymers were etched by annealing in air to complete the fabrication of the Al 2 O 3 nanostructure pattern.

FESEM images of the self-assembled cylinder-forming PSb-PCL nanostructures and the Al 2 O 3 nanostructures fabricated using these in-plane cylinders and the SIS process are shown in figure 2. Figure 2(a) shows the FESEM image of the PS-b-PCL as grown, with the PCL domain expected to form stripelike horizontal cylinders. Based on the block volume fraction and phase diagram analysis [14,15], and given the absence of any surface treatment before BCP deposition, the PS-b-PCL system used here is expected to self-assemble into the cylindrical regime, consistent with our SEM observations of stripe-like features corresponding to in-plane horizontal cylinders. The SEM image shown in figure 2, with clear separation of the domains, indicates formation of a single cylinder layer, and is consistent with the reported literature on other BCPs of similar thickness (∼50 nm) [31,37]. The mean width of the PCL cylinders is ∼22 nm as calculated from 20 data points for each area from figure 2(a). Note that the formation of self-assembled nanostructures with PS-b-PCL BCPs has been shown in only a limited number of studies [38].

Figures 2(b)-(d) show images of Al 2 O 3 nanostructures fabricated on PS-b-PCL nanostructure-templated samples (similar to the one shown in figure 2(a)). The SIS process was conducted at a chamber temperature of 80 • C, using sequential exposures of TMA and H 2 O, as detailed in the experimental section. During the SIS process used in this work, the first precursor, TMA, infiltrates throughout the PS-b-PCL films and interacts selectively with the C=O and C-O-R functional groups of the PCL polymer. This is followed by the completion of a binary reaction with the second precursor, H 2 O. Any non-bound excess TMA is removed by a purge step with high-purity 2 , ensuring the reaction remains self-limited and preventing homogeneous reactions. The first monolayer of coordinated precursors with the polymer provides reactive sites for subsequent ALD cycles, which selectively functionalize the active polymer domains. This functionalization proceeds for a few cycles until infiltration saturates at the surface. Importantly, infiltration of SIS precursors is not confined strictly to polymer regions with active functional groupsthe reaction can also occur at both surface and sub-surface levels of the films. The development of morphology with varying SIS cycle numbers is illustrated in figures 2(b)-(d). All three images were recorded after SIS deposition, followed by polymer removal through annealing in an air atmosphere. The Al 2 O 3 nanostructures formed after one cycle (figure 2(b)), five cycles (figure 2(c)), and ten cycles (figure 2(d)) are presented in figure 2. As shown in figure 2(b), even after just one SIS cycle, substantial deposition occurs, resulting in continuous structures that closely resemble the PCL domain regions observed in figure 2(a). The calculated linewidth of the deposited nanostructures in the straight line region is ∼12 nm and continuous. The linewidth and the continuity of nanostructures (∼12 nm linewidth) in figure 2(b) are smaller and mostly follow the pattern and linewidth of the PCL area shown in figure 2(a). Additional SIS cycles led to further deposition, primarily increasing the area width of the nanostructure deposition, as evident from the increase in width of the nanostructures from top-view images, especially in the regions where the nanostructures are bending, as seen in figure 2(c) after five cycles and in figure 2(d) after ten cycles. However, the morphological development in terms of shape remains consistent up to five cycles. Beyond this point, there appears to be an excessive amount of Al 2 O 3 deposition, resulting in the formation of white spots, as seen in figure 2(d) for ten cycles. Image analysis and quantitative area determination were performed to estimate the amount of deposited nanostructure after one, five, and ten cycles. The area percentages of the bright regions corresponding to nanostructure deposition were 51% after one cycle (figure 2(b)), 58% after five cycles (figure 2(c)), and 67% after ten cycles (figure 2(d)). These images and image area calculation results indicate a gradual increase in deposition from one to five to ten cycles, with a substantial amount being deposited during the first cycle.

To study the effect of temperature, we performed SIS at 60 To compare the nanostructure patterning between PS-b-PCL and a widely utilized BCP, PS-b-PMMA, we performed Al 2 O 3 SIS using the same experimental parameters and in the same setup on the PS-b-PMMA self-assembled vertical nano lamellar shape template [6,31]. The nanostructures patterned after the SIS deposition of different cycle numbers at 80 • C and after polymer etching are shown in figure 4. Figure 4(a) is the FESEM image of the as-grown PS-b-PMMA microphaseseparated sample recorded without any treatment. The brighter domain corresponds to PS, and the darker domain corresponds to PMMA. The mean linewidth for white-contrasted PS lamellar area is ∼25 nm and for black-contrasted PMMA area is ∼14 nm, as calculated from twenty data points for each area from figure 4(a). Upon comparing deposition across the three cycles, a wellknown trend emerges for PS-b-PMMA templated samplesnanostructure width and continuity grow with an increase in the number of SIS cycles, with a minimum deposition after just one cycle-consistent with findings from other studies [31]. The mean linewidth of the deposited nanostructures is ∼9 nm, which is narrower (PMMA linewidth is ∼14 nm as calculated from figure 4 FTIR is a powerful technique and provides the opportunity to study interactions between chemical species by measuring the absorption peaks corresponding to distinct vibrational frequencies of the precursor, polymer, and any potential complex or reaction product between them, which can be acquired before and after reaction, and to identify the functional groups and species involved in the interactions. We performed FTIR (ex-situ) measurements on PS-b-PCL BCP samples before SIS deposition and on samples after ten cycles of SIS deposition on the PS-b-PCL template to get insight into the chemical interactions between the PS-b-PCL template and the SIS precursors. The FTIR study confirmed that SIS deposition occurred by the infiltration of precursors into the PCL polymer, rather than as a surface deposition, as such occurs in ALD, as discussed below. Figure 5 shows the FTIR spectra recorded before and after SIS. In figure 5, spectrum 1 is of an as-grown PS-b-PCL nanostructured film sample before SIS treatment, spectrum 2 is recorded after ten cycles of Al 2 O 3 (TMA-H 2 O sequential exposures) SIS cycles on the same sample shown in spectrum 1, and spectrum 3 is the calculated difference spectrum (from spectrum 2 to spectrum 1). Spectrum 1 shows all the chemical functional groups that are present in a PS-b-PCL BCP sample. It includes carbonyl (C=O) ∼1727 cm -1 , ester (C-O-R) ∼1196 and 1246 cm -1 , and methyl (CH 3 ) group (∼2950 cm -1 ) region of the spectrum, which can be attributed to the species in the PCL polymer [21,39]. PS is a hydrocarbon-based polymer and shares some common peaks with PCL around the 2800-2900 cm -1 region, but usually shows peaks around the 1400 cm -1 and 1000 cm -1 regions [40].

We note some small peaks at ∼1476 and ∼1050 cm -1 for the PS polymer. From the recorded spectrum after SIS (spectrum 2), we observe that the C=O peak and the majority of the C-O-R peaks from PCL are no longer visible, confirming the interaction or consumption of C=O and C-O-R species with the TMA and H 2 O precursors. However, we do not observe any distinct negative peaks at ∼1476 and 1050 cm -1 , indicating the participation of PCL groups only (not PS) in the interaction. In the difference spectrum shown as spectrum 3, the negative peaks indicate the interacted or consumed species from the pristine polymer, and the positive peak indicates the appearance or formation of new species in the sample after the SIS treatment. Spectrum 3 clearly shows the interactions of all C=O and almost all C-O-R groups from PCL, and no distinguished PS peak participation as mentioned above. In addition, it shows the participation of some CH 3 group from the PS-b-PCL sample as observed from the negative peak ∼2950 cm -1 and the appearance of a weak broad peak ∼800-850 cm -1 , which can be attributed to the Al-O phonon mode from Al 2 O 3 complex formation in the polymer, as observed before in our previous work [5,6]. The ex-situ FTIR data measured for PSb-PCL is consistent with our previous work on in-situ FTIR study on PCL polymer interactions with TMA and H 2 O. In our previous study, we also observed nearly complete consumption of C=O species and participation of C-O-R. We concluded that the PCL-TMA interaction was stable and irreversible, which is beneficial for avoiding the desorption of formed complexes before the H 2 O exposure. This significant interaction and the irreversible nature of the interaction were hypothesized to be beneficial for nanopatterning purposes, where significant deposition can be expected in the first cycle itself.

The FESEM images and FTIR data presented here experimentally demonstrate and provide evidence of Al 2 O 3 nanostructured pattern fabrication using PS-b-PCL as a template. Our results not only demonstrate the fabrication of PCLtemplated targeted nanostructures using SIS but also prove the effectiveness of PCL and SIS precursor chemistry for significant and continuous deposition in the first cycle itself. The FTIR data provide insight into the chemical interactions between PS-b-PCL BCPs and Al 2 O 3 SIS precursors. As observed from the FTIR data, interactions between the PCL functional groups and the TMA-H 2 O precursors generate Al-O species within the polymer, indicating the formation of a polymer-Al-O hybrid material. The Al 2 O 3 -only nanostructures (after polymer etching) may find applications as dielectric or functional coatings in optoelectronics, the hybrid polymer-Al-O as robust etch masks for pattern transfer in microelectronics, and as hybrid oxide-polymer nanostructures in biointerfaces and biomedical devices. This hybrid structure can be potentially used for biodegradable applications with appropriate processing steps, as PCL is biodegradable, whereas PS is not. To achieve a fully biodegradable system from PS-b-PCL template, a selective dry etching process can be employed after SIS to remove the PS component [41], leaving behind PCL loaded with inorganic material. At the application site, the PCL is expected to degrade, ultimately leaving only the inorganic material. Furthermore, instead of PS, other SIS-inert biodegradable secondary polymers can also be potentially used for this purpose, which requires further exploration. Additionally, our approach can be extended to use PCL-only nanostructures (such as PCL nanobeads and nanocapsules) as templates, eliminating the need for processing any secondary polymer.

Further studies on PCL-inorganic hybrid materials for various applications, as well as PCL nanostructures of different shapes and morphologies for nanopatterning applications, would be of interest. Although not investigated in the present study, solvent imprinting and solvent-mediated interactions may also play a significant role in the self-assembly and nanoscale morphology of PCL-related systems [42,43], thereby influencing porosity and precursor infiltration during SIS. Exploring these effects will be an important direction for future work, while utilizing PCL as a template. Additionally, we have selected aluminum oxide as a model SIS material to demonstrate for the first time that nanopatterning and inorganic material deposition selectively in PCL. Other materials that can be deposited using the SIS process, such as TiO 2 , SiO 2 , ZnO, and nitrides, can also be explored using different PCL nanostructures as templates. In the future, nanostructures fabricated using PCL as a template can be further explored to gain deeper insights, including investigations into their mechanical strength and thermal stability for various applications.

Conclusion

We demonstrate that PCL-based nanostructures can serve as templates for precise hybrid nanostructure growth and for advanced nanopatterning processes, such as the SIS process, for the first time. The results highlight that the enhanced interaction between PCL and organometallic precursors such as TMA during SIS can lead to substantial deposition and the formation of continuous structures during the first deposition cycle. FESEM images reveal the deposition of Al 2 O 3 nanopatterns using self-assembled PS-b-PCL BCP nanostructures as templates and the SIS method. The observed Al 2 O 3 nanopatterns align with the nanostructures of the PCL domain, showing continuous and significant deposition during the first SIS cycle. A temperature-dependent study demonstrates that nanostructure fabrication is achievable at both 60 • C and 80 • C, which is advantageous for applications requiring lower temperatures due to substrate constraints. FTIR spectroscopy further elucidates the interaction between the PCL polymer from the PS-b-PCL template and the SIS precursors, confirming Al-O bond formation as indicated by a weak but broad peak in the FTIR spectrum. The results confirm that nanopatterns from the PS-b-PCL template are formed within the PCL domain, driven by chemical interactions during the SIS process, with significant deposition occurring due to the reactivity of nearly all PCL functional groups with SIS precursors. This work's findings are valuable for a broad range of applications that require nanostructured patterns ranging from micrometers to sub-20 nm dimensions in hybrid or inorganic material forms. These results can be transformative for many applications where just one cycle of SIS deposition of inorganic materials in PCL nanopatterns might be sufficient, and fabrication can be performed by utilizing fewer resources. The pronounced interactions between PCL functional groups and inorganic precursors will also facilitate precise deposition in targeted space. PCL, being a biodegradable polymer, will also unlock research pathway with PCL as a template for bio applications. PCL offers potential for further exploration in other nanopatterning processes where the reactivity of its polymer functional groups can be leveraged to improve deposition. Therefore, this work advances the fields of nanofabrication, nanopatterning, and bio-nanomaterials by introducing PCL as a promising template for cutting-edge and emerging nanopatterning techniques.