Structure formation induced by electrohydrodynamic instability and its applications

(Performed by Hyunje Park, Tae Kyu Kang, and May Myat Noe Oo)

(Courtesy of Mr. Jae Seok Hwang & Hyunje Park at ASDNL)

Project description

(Courtesy of Mr. Jae Seok Hwang & Hyun Jae Park at ASDNL)
✔ Strong electric field in the capacitor-like structure generates the interfacial pressure that can destabilize the liquid film surface
✔ Electrohydrodynamic Lithography (EHL) is a process for electrically replicating the micro- or nanostructures on a master stamp onto a fluidic thin film
✔ EHL has drawn great attention recently owing to its versatility and scalability. In spite of its merits, the exact physical mechanisms of pattern formation and its applications are still under study
✔ Our study are supported by Center for BioNano Health-Guard funded by the Ministry of Science, ICT & Future Planning as Global Frontier Project

Main findings

(Courtesy of Mr. Jae Seok Hwang & Hyunje Park at ASDNL)
✔ Theoretically, amplitude parameter is the most critical factor for pattern replication if the wavelength parameter is about 2
✔ Practically, increasing the values of the applied voltage and air gap thickness are helpful to fabricate nanostructures with a great fidelity
✔ Experimentally, a change in wettability was observed on the patterned surface with an increased aspect ratio

The merits of EHL

(ref. Ning Wu, et al, EPL, 2008, 53, 518) (ref. Shaeffer, et al, EPL, 2001, 53, 518)
✔ Controlling the nano-scale features
- In the theory of EHL, there are many complicated parameters.
- To simplify parameters, a variety of mathematical approaches, including dimension less parameter analysis and computer simulation, are required.
✔ Fabricating biomimetic surface
- The high aspect ratios of the pattern creates a reduction in surface energy.

What was found

(Courtesy of Mr. Jae Seok Hwang & Hyunje Park at ASDNL)
✔ High-voltage EHL enables a large air gap (up to several micrometer) to be tolerated in forming well-defined hierarchical heterostructure patterns, which is impossible to form with a smaller air gap

✔ High-voltage EHL enables a significant increase in aspect ratio and the ability to replicate the nano-size patterns over a large area

Why? The reasons of the research

(Courtesy of Mr. Jae Seok Hwang & Hyunje Park at ASDNL)
✔ Until now, the key issue in EHL is large-area fabrication of micro- / nanostructures since pattern formation is vulnerable to the nanoscale air gap between the top electrode and the top surface of the resist

✔ To overcome this, we have developed the new EHL system using the pulsed high-voltage with microscale air gap


(Courtesy of Mr. Jae Seok Hwang & Hyunje Park at ASDNL)(Ref. Chiara Bus, et al, Nanoscale, 2017, 9, 1625)
✔ HV-EHL can facilitate the perfect replication process
✔ HV-EHL can desirably modulate the geometric features of replica
✔ HV-EHL can be explored for various substrates such as the strong insulating substrates due to the strong electric field