by Dr Eleonora Cara and Dr Federico Ferrarese Lupi

The persistent effort of the scientific community in advancing the development of artificial nanomaterials, with precise control over their composition, dimensions, and functional properties, is pivotal for technological progress. This pursuit not only facilitates the exploration of a myriad of applications but also results in unprecedented societal impact.

In recent years, among the multitude of techniques devoted to realizing nanomaterials, sequential infiltration synthesis (SIS), also known as vapor-phase infiltration (VPI), has come to attention as a versatile materials synthesis method. This approach, based on standard atomic layer deposition (ALD) processes, allows for the controlled diffusion of metallic oxides in polymeric templates, resulting in the production of inorganic-organic hybrid materials [1] or inorganic replicas of nano templates [2].  


Impact on scientific and societal challenges

SIS has been proven to be a highly promising method for a broad spectrum of applications. Scientific breakthroughs associated with SIS encompass the creation of functional coatings with tailored optical properties and nanoscale dimensions [3]. Additionally, SIS has been instrumental in the development of artificial optical metamaterials [4],  significantly contributing to advancements in the expansive fields of research and industry within photonics [5]. Moreover, SIS-derived nanomaterials have demonstrated their utility in microelectronics applications, serving as an interesting strategy for controlling the doping level and conductivity of various functional polymers (e.g. polyaniline) with implications in several related fields including energy storage and conversion and water hydrolysis [6, 7]. In nanofabrication, it was proven to provide a solution for hardening polymeric masks for deep reactive ion etching processes [8] and allows high-contrast transmission electron microscopy characterization of polymeric nanostructures [9, 10].

The impact of SIS extends beyond the laboratory contributing to the development of resistive memories [11], and addressing environmental challenges such as oil spills through the realization of water cleaning membranes which are being scaled up to recover damages in open waters [12]. 


SIS fabrication: innovation in nanomaterial development and characterization

The development of the SIS process in terms of fabrication has progressed rapidly in recent years. Of the many chemical precursors used for the ALD growth of oxides, nitrides, selenides, and other chemical compounds, several have been implemented in SIS for the growth of oxides [13]. The combination of the precursors with a large number of polymers and a growing set of varying parameters regulating the infiltration process has fostered rapid progress of this method. The progress in the development of nanoscale materials requires comprehensive insights into the synthesis mechanism and control over the process parameters, considering their significant deviation from bulk materials. Numerous studies delve into SIS nanomaterials properties, employing a wide range of analytical tools including scanning electron microscopy (SEM), atomic force microscopy (AFM), in situ quartz crystal microgravimetry (QCM) and spectroscopic ellipsometry (SE),  as well as a wide range of others discussed in depth in the following scientific reviews [13, 14]. These diverse analytical techniques are essential for unravelling the intricate features of SIS-derived nanomaterials. Moreover, the concurrent development of dedicated analytical techniques should be sought for the exhaustive characterization mechanism and the materials' functional properties to follow through with the expanding fabrication capabilities.

In the current scenario, a hybrid metrology approach can be convenient for the characterization of nanomaterials. Hybrid metrology can be briefly described as the combination of two or more analytical methods to characterize an object of interest, such as a nanomaterial, providing a more extensive characterization of a given property of a material, with reduced uncertainties and reduced measurement time than they can independently give [15]. In this methodology, various techniques can be linked to distinct measurands, all with the common goal of characterizing a specific physical or chemical quantity [16]. As an example, to characterize the morphology of a thin film different methods can be combined, such as SEM, AFM, and spectroscopic ellipsometry or X-ray reflectivity (XRR), so that the data from one tool can be used to resolve another tool dataset and these can be convoluted for a general description of the morphology. Several European metrological research projects have been committed to advancing hybrid metrology methodologies tailored for characterizing diverse nanomaterials. Notable examples include 21GRD01 OpMetBat (Euramet website, Project website), devoted to the development of operando characterization of batteries through a hybrid approach, or previously-concluded 16ENG03 HyMet (Euramet website, Project website), dedicated to the hybrid metrology of thin films for energy applications.  

Encouraging the development and the systematic adoption of hybrid characterization methodologies is essential for a comprehensive understanding of process mechanisms and material properties. In the context of nanomaterials produced through SIS, a recent example of the development of a characterization method for the understanding of the SIS processes is reported in reference [17]. The study concerns the expansion of grazing-incidence X-ray fluorescence (GIXRF) for the non-destructive characterization of inorganic-organic polymeric layers and block copolymers (BCPs) templates. The method provides reference-free quantification of the mass per unit area of the infiltrated metallic compound, a method that could be relevant for calibrating mass uptake measurements via in situ quartz crystal microgravimetry (QCM) in SIS processes. In addition, to enhance the depth profiling capabilities of GIXRF, validation was carried out by scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) verifying that the presence of polystyrene in the infiltrated polymeric matrix, being chemically inert to the precursors and presenting large free volume, facilitates the precursors’ diffusion in the depth of the polymeric layer.

Building on these results, another recent work focuses on the study of the inorganic replicas of BCPs lamellar and cylindrical nanotemplates, obtained by SIS, through a hybrid approach [18]. The study targets multidimensional characterization of the oxide nanostructures including a dimensional characterization through grazing-incidence small angle X-ray scattering (GISAXS), SEM, and AFM, a chemical and compositional characterization employing near-edge X-ray absorption fine structure (NEXAFS) and XPS, and mass quantitative characterization and depth profiling by GIXRF and XPS. In addition, an evaluation of the material functional properties, in terms of optical constants, was performed by a combination of XRR and spectroscopic ellipsometry, to address the nanomaterial application as photonic metasurfaces.

The discussed cases offer a view of recent developments of hybrid metrology approach to SIS characterization. In light of these developments, a collaborative endeavor between the scientific and industrial communities is encouraged to leverage the capabilities of hybrid metrology for multidimensional characterization of nanomaterials. As we delve deeper into the intricacies of the nanoscale realm, these advancements not only contribute to the scientific understanding of materials but also hold the potential for transformative applications across various industries, thereby shaping the future of technology and its impact on society.


Part of the research discussed in this Nanopinion was supported by the European project 21GRD01 OpMetBat. The project has received funding from the European Partnership on Metrology, co-financed from the European Union’s Horizon Europe Research and Innovation Programme, and by Participating States. 




  1. 1. Ko, M., Kim, H. U., & Jeon, N. (2022). Sequential Infiltration Synthesis with Organic Co-reactants for Extensively Swollen Organic–Inorganic Hybrid Thin Films. ACS Applied Polymer Materials, 5(1), 50-56.
  2. 2. Peng, Q., Tseng, Y. C., Darling, S. B., & Elam, J. W. (2011). A route to nanoscopic materials via sequential infiltration synthesis on block copolymer templates. ACS nano, 5(6), 4600-4606.
  3. 3. Berman, D., Guha, S., Lee, B., Elam, J. W., Darling, S. B., & Shevchenko, E. V. (2017). Sequential infiltration synthesis for the design of low refractive index surface coatings with controllable thickness. ACS nano, 11(3), 2521-2530.
  4. 4. Murataj, I., Channab, M., Cara, E., Pirri, C. F., Boarino, L., Angelini, A., & Ferrarese Lupi, F. (2021). Hyperbolic metamaterials via hierarchical block copolymer nanostructures. Advanced Optical Materials, 9(7), 2001933.
  5. 5. Pitruzzello, G. (2023). Metaoptics for the consumer market. Nature Photonics, 17(1), 6-7.
  6. 6. Wang, W., Yang, F., Chen, C., Zhang, L., Qin, Y., & Knez, M. (2017). Tuning the conductivity of polyaniline through doping by means of single precursor vapor phase infiltration. Advanced Materials Interfaces, 4(4), 1600806.
  7. 7. Ham, J., Park, S., & Jeon, N. (2022). Conductive Polyaniline–Indium Oxide Composite Films Prepared by Sequential Infiltration Synthesis for Electrochemical Energy Storage. ACS omega, 8(1), 946-953.
  8. 8. Marneffe, J. F. D., Chan, B. T., Spieser, M., Vereecke, G., Naumov, S., Vanhaeren, D., ... & Knoll, A. W. (2018). Conversion of a patterned organic resist into a high performance inorganic hard mask for high resolution pattern transfer. ACS nano, 12(11), 11152-11160.
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  11. 11. Chakrabarti, B., Chan, H., Alam, K., Koneru, A., Gage, T. E., Ocola, L. E., ... & Guha, S. (2021). Nanoporous dielectric resistive memories using sequential infiltration synthesis. ACS nano, 15(3), 4155-4164.
  12. 12. Barry, E., Mane, A. U., Libera, J. A., Elam, J. W., & Darling, S. B. (2017). Advanced oil sorbents using sequential infiltration synthesis. Journal of Materials Chemistry A, 5(6), 2929-2935.
  13. 13. Waldman, R. Z., Mandia, D. J., Yanguas-Gil, A., Martinson, A. B., Elam, J. W., & Darling, S. B. (2019). The chemical physics of sequential infiltration synthesis—A thermodynamic and kinetic perspective. The Journal of chemical physics, 151(19).
  14. 14. Cara, E., Murataj, I., Milano, G., De Leo, N., Boarino, L., & Ferrarese Lupi, F. (2021). Recent advances in sequential infiltration synthesis (Sis) of block copolymers (bcps). Nanomaterials, 11(4), 994.
  15. 15. Vaid, A., Yan, B. B., Jiang, Y. T., Kelling, M., Hartig, C., Allgair, J., ... & Urensky, R. (2011, March). A holistic metrology approach: hybrid metrology utilizing scatterometry, CD-AFM, and CD-SEM. In Metrology, Inspection, and Process Control for Microlithography XXV (Vol. 7971, pp. 21-40). SPIE.
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Biographies of the authors

Dr Eleonora Cara is a technologist at INRiM, the Italian national metrology institute. She graduated in Physics at the University of Turin in 2015. In 2019, she received her PhD cum Laude at the Polytechnic University of Turin. Her PhD project focused on the development of self-assembled 3D plasmonic nanostructures for surface-enhanced Raman spectroscopy. In 2018, she joined the group of X-ray spectrometry at PTB Berlin in Bessy II as a visiting PhD student to work on mass quantification by reference-free X-ray fluorescence. Currently, her interests concern the realization and characterization of nanostructured materials for plasmonic-enhanced optical and IR spectroscopies and gas sensing. She received the Young Researcher Award at the EMRS Spring Meeting 2021. She is author and co-author of more than 15 peer-reviewed papers and 1 patent.


Dr Ferrarese Lupi is a researcher at INRiM. He graduated in Physics at the University of Turin in 2008. In 2012 he received his PhD in Physics cum Laude at the University of Barcelona, discussing a thesis entitled “Optically active substoichiometric Si3N4 micro-cavities for sensoristic applications”. Between 2012 and 2015, he worked as postdoctoral fellow at the MDM laboratory of the IMM–CNR institute in Agrate Brianza. During that period he focused on the fabrication of self-assembled nano-structures using block copolymers and its integration with the next generation of electronic devices. He is involved in several European metrology projects covering different aspects of the fabrication and characterization of materials and objects at the nanoscale. His main research activity is focused on the optical characterization (luminescence, lifetimes, propagation loss, optical gain, etc.) and nano-patterning (through the self-assembling systems) of polymeric and silicon-based materials with potential application in nanometrology. The main goal such investigation is to develop nanostructured model systems useful in several metrological fields such as the length metrology, the 3D chemical analysis and bacteria detection. Federico Ferrarese Lupi is member of the Italian macromolecules association (AIM) author or co-author of more than 60 scientific papers and 2 patents.





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