1. Vassiliki Tsukala, Dimitris Kouzoudis
Zeolite LTA micromembrane fabrication on Metglas using E-Beam Lithography
Vassiliki Tsukala, Dimitris Kouzoudis
Department of Engineering Sciences, University of Patras, GR-26504, Patras, Greece
E-Beam Lithography Laboratory
Introduction
Objectives
Zeolites are aluminosilicate nanoporous crystalline materials which, in their membrane form, demonstrate controllable surface properties, well-defined porosity, large surface area along with chemical, thermal and mechanical stability. As a result, they can be utilized in new advanced applications like sensors, microreactors, microseparators, as low-k materials for microelectronic devices, microelectrochemical cells and biomedical.
The ability of tailoring and controlling zeolite membrane size in small-scale offers numerous advantages, therefore many researches have focused on patterning zeolite membrane1. They have employed three methods: microcontact printing, photoetching and photolithography, resulting in micro-scale structures and they have fabricated only siliceous zeolite membranes (MFI, ZSM-5, Sil1) on glass or silicon substrates2.
The use of a more versatile technique, like Electron Beam Lithography (EBL), other functional substrates and various zeolite types could enhance micromembrane technology and applications.
This study focused on three major goals:
To employ EBL for the patterning of the substrate surface in the micro-scale
To use a magnetoelastic material (Metglas, Fe40Ni38Mo4B18) as a substrate for future sensing applications
To fabricate LTA zeolite type (|Na+12(H2O)27|8 [Al12Si12O48]8) micromembranes onto magnetoelastic substrate as candidate sensitizing layer
The experimental procedure consists of the following steps
E-beam lithography
The Metglas substrate was cleaned and spin-coated with PMMA (polymeric photoresist, 5% in PGMEA). Patterns were generated with the XeDraw 2 (XENOS GmbH) system attached to the SEM (JEOL, JSM-6610LV) for various dosages and developed with IPA/H2O (7:3).
Seeding
The Metglas substrate was drop-seeded with LTA nanocrystals (1% in H2O) synthesized hydrothermally from a mixture with molar ratio: Al2O3/6SiO2/0,32Na2O/7,27(TMA)2O/350H2O at 80oC for 24 hrs.
Fabrication methods
Hydrothermal synthesis was carried out for various crystallization duration in order to examine membrane formation
Results
Acknowledgments
Conclusions
In order to investigate the conditions of zeolite micromembrane fabrication,
Tests were performed to evaluate the optimum EBL dosage of the PMMA film coated on Metglas and 40μC/cm2 was chosen for minimum proximity effect and high accuracy.
Nano-sized LTA crystals were synthesized with average diameter of approximately 95nm.
1. J. Coronas, J. Santamaria, Chem. Eng. Sci., 59 (2004)
2. Z. Ming, Z. BaoQuan, L. XiuFeng, Chin. Sci. Bull., 53 (2008) 6,
3. E. Yilmaz, H. Sezen, S. Suzer, Angew. Chem. Int. Ed., (2012) 51,
Hydrothermal synthesis was carried out for various durations, in order to examine membrane formation, and it was concluded that the crystallization was complete in less than 24 hrs. Both nanozeolites and membranes were attached only on the exposed Metglas surface, due to repulsive forces of the negatively charged PMMA surface and LTA precursors3.
3 hrs hrs hrs hrs
Finally, LTA micromembranes were synthesized using EBL dose of 40μC/cm2 and seed crystals with 95nm average size under hydrothermal conditions at 85oC for 20 hrs. The LTA type zeolite was confirmed by XRD while structures as small as 50x20μm (parallelogram) and 40μm (circle) were achieved.
Both LTA seed crystals and membrane were successfully attached on the exposed Metglas surface.
Appropriate conditions for LTA micromembrane fabrication on Metglas were investigated.
It is the first time that continuous LTA film was fabricated in the micro-scale and also the first time that EBL was employed for this purpose.
1. Substrate
2. Coating
3. EBL
4. Seeding
5. Synthesis
6. Lift-off
Synthesis
The LTA micromembranes grew hydrothermally onto the patterned and seeded surface of Metglas at 85oC from a solution with molar ratio:
4,17Na2O/Al2O3/1,87SiO2/460H2O.
The Metglas was dried and treated with acetone in ultrasonic bath for the lift-off of PMMA.
References
SiO2 Source
Base
Water
Al2O3 Source
SiO2
Al2O3
H2O
M+OH-
Heating
This study is funded by the Research Committee of the University of Patras, under the “K. Karatheodori “Grand (Project No. D-153).
Contact Information
D. Kouzoudis
V. Tsukala
ICSAAM 2013
5th International Conference on Structural Analysis of Advanced Materials
September 2013, Island of Kos, Greece