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Controlled size reduction and its underlying mechanism to form solid-state nanopores via electron beam induced carbon deposition
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.ORCID iD: 0000-0002-7584-6479
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
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2019 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 30, no 45, article id 455303Article in journal (Refereed) Published
Abstract [en]

Solid-state nanopores have drawn considerable attention for their potential applications in DNA sequencing and nanoparticle analysis. However, fabrication of nanopores, especially those of diameter below 30 nm, requires sophisticated techniques. Here, a versatile method to controllably reduce the diameter of prefabricated large-size pores down to sub-30 nm without greatly increasing the effective pore depth from the original membrane thickness is shown. This method exploits carbon deposition achieved via hydrocarbon evaporation, induced by an incident beam of electrons, and subsequent dissociation of hydrocarbon to solid carbon deposits. The carbon deposition employs a conventional scanning electron microscope equipped with direct visual feedback, along with a stable hydrocarbon source nearby the sample. This work systematically studies how electron beam accelerating voltage, imaging magnification, initial pore size and membrane composition affect the process of pore size reduction. Secondary electrons generated in the membrane material are confirmed to be the main cause of the dissociation of hydrocarbon. Thicker carbon deposited on one side than on the other of the membrane results in an asymmetric nanopore shape and a rectifying ionic transport. A physico-phenomenological model combined with Monte Carlo simulations is proposed to account for the observed carbon deposition behaviors.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD , 2019. Vol. 30, no 45, article id 455303
Keywords [en]
solid-state nanopore, pore size reduction, electron beam induced carbon deposition, secondary electrons, effective pore depth, rectifying behavior
National Category
Nano Technology
Identifiers
URN: urn:nbn:se:uu:diva-394045DOI: 10.1088/1361-6528/ab39a2ISI: 000483100000001PubMedID: 31394513OAI: oai:DiVA.org:uu-394045DiVA, id: diva2:1357710
Funder
Swedish Research Council, 621-2014-6300Swedish Foundation for Strategic Research , FFL15-0174Available from: 2019-10-04 Created: 2019-10-04 Last updated: 2020-01-08Bibliographically approved
In thesis
1. Solid-state nanopores: fabrication and applications
Open this publication in new window or tab >>Solid-state nanopores: fabrication and applications
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanopores are of great interest in study of DNA sequencing, protein profiling and power generation. Among them, solid-state nanopores show obvious advantages over their biological counterparts in terms of high chemical stability and reusability as well as compatibility with the existing CMOS fabrication techniques. Nanopore sensing is most frequently based on measuring ionic current through a nanopore while applying a voltage across it. When an analyte passes through the pore, the ionic current temporarily changes, providing information of the analyte such as its size, shape and surface charge. Although many magnificent reports on using solid-state nanopores have appeared in the literature, several challenges still remain for their wider applications, which include improvement of fabrication reproducibility for mass production of ultra-small nanopores and minimization of measurement instability as well as control of translocation speed and reduction of background noise. This thesis work explores different techniques to achieve robust and high throughput fabrication of sub-10 nm nanopores for different applications.

The thesis starts with presenting various fabrication techniques explored during my PhD studies. Focused ion beam method was firstly employed to drill nanopores in free-standing SiNx membranes. Sub-10 nm nanopores could be obtained with a focused helium ion beam. But the fabrication throughput was limited with this technique. A new fabrication process combing electron beam lithography (EBL) with reactive ion etching/ion beam etching, which is compatible with the existing CMOS fabrication technology, was developed to realize a high throughput, mass production of nanopores in free-standing SiNx membranes. However, the smallest size that could be controllably achieved with this process was around 40 nm, which is still far from sub-10 nm in size required for, e.g., DNA sequencing. Finally, by using anisotropic etching of single-crystal silicon in KOH solution, sub-5 nm truncated pyramidal nanopores were mass produced with good process controllability in a silicon-on-insulator (SOI) substrate. In addition, nanopore arrays were also successfully fabricated using a modified EBL based fabrication process.

Then, several sensing application examples using either single nanopores or nanopore arrays were investigated. Translocation of nanoparticles, DNA and proteins were demonstrated using the fabricated single nanopores or nanopore arrays in a single freestanding membrane. Moreover, the kinetics and mechanism of the lipid bilayer formation in nanopore array, aiming to prevent non-specific adsorption, were studied using ionic current measurements. In addition, individual addressability of a solid-state nanopore array on separated freestanding membranes was realized by integrating microfluidics and a customized multiplexer.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2020. p. 82
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1890
Keywords
solid-state nanopore, truncated-pyramidal nanopore, nanopore array, pore size reduction, individual addressability, microfluidics, translocation.
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-399726 (URN)978-91-513-0838-8 (ISBN)
Public defence
2020-02-21, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2020-01-31 Created: 2019-12-16 Last updated: 2020-01-31

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Zeng, ShuangshuangWen, ChenyuLi, ShiyuChen, XiChen, SiZhang, Shi-LiZhang, Zhen

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