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Development of Microsystems based on nanostructured materials

Microfabrication using zeolite membranes as structural layers
  
 
Important developments in the realm of microdevices for the chemical and process industries have taken place during the last 15 years, mainly in the fields of microreactors and sensors. We are interested in the fabrication of microstructures for chemical processes, where the incorporation of zeolite films adds valuable features to the microdevice. Typically, the approach involves the preparation of a defect-freee zeolite thin layer onto the Si substrate followed by lithography and etching process for the zeolite micropatterning. In the following sections you could find some of our developed Zeolite based Microsystems.
 
 
Zeolite Microchannels for Reaction and Preconcentration Applications
 

 
Standard Si based technologies have been used to prepare MFI zeolite-coated microreactors with ultrahigh external surface to volume ratios. The thin zeolite coating (< 1 micron) provided a short diffusion path length, and the external area of the zeolite films was 400000-750000 m2/m3 of reactor volume, underlying the potential of these microstructures as highly efficient contactors for mass transfer limited reactions. 
 
ZSM-5 Si/Al=100 coatings onto regular structures of SiO2 micromonoliths and microneedles
 
The micropatterning of well intergrown zeolite layers over Si wafers have been successfully used for the development of either hydrophobic (silicalite, ZSM-5) or hydrophobic (NaA, NaY) microchanneled structures suitable for sample conditioning (dewatering, preconcentration) or reaction purposes in “lab on chip” applications.
  
  
Micropatterned Sil-1 c oriented microchannels after BHF etching:  a), b) top view; and, c) cross section.
 

Nanoporous Zeolite Cantilevers: Proof of Concept

Nanoporous microcantilevers entirely constituted by silicalite type zeolite have been fabricated and successfully applied to ethanol detection at ppm level. The polycrystalline, zeolite-only cantilevers are able to maximize the mass sensitivity and the intrinsic features related to zeolite adsorption capability (i.e. available microporous surface).

 

 
Nanoporous silicalite only cantilevers released by TMAH wet etching of Si underneath.
 
 
 
Collaborations:
1. Dr. G. Abadal NANERG LAB. Departament d’Enginyeria Electrònica, Universitat Autónoma de Barcelona, E-08193 Bellaterra (Spain).
2. Prof. A. Boissen. Department of Micro and Nanotechnology. DTU Nanotech. Technical University of Denmark. 2800 Kgs Lyngby (Denmark)
 
Zeolite Micromembranes for Gas Separation
 
While the process of scaling up zeolite membranes is affected by materials cost or development of inter-crystalline defects, the same problems are alleviated in scaled-down systems. SIL-1 zeolite micromembranes 4 microns in thickness and up to 0.2 cm2 of permeable area per cm2 of silicon chip have been obtained and successfully applied for CO2/H2 separation at room conditions.
 
 
Free standing silicalite micromembranes for CO2/H2 separation applications at room conditions.
 
Incorporation of Nanostructured Materials on Polymer Based Microsystems
 
Our research efforts are focused on the application of micro-patterned polymeric films for applications demanding harsh conditions (high temperature, extreme pH or oxidant-reducing conditions) to fill the existing gap in lab on chip applications, mainly dealing with biomedical applications.
 
Microstructured Polybenzimidazole films prepared by microtransfer moulding.
 
Nanostructured Electrolyte Membrane for High Temperature PEM (http://ina.unizar.es/zeocell) based on porous PBI membranes (a) with microporous top layers (b) and (c) to avoid protic conductor dragging.
 
Chemical Sensors
 
While many types of sensors display remarkable sensitivity (e.g. down to the femtogram level for cantilever mass sensors) they often lack selectivity, reacting similarly to a variety of substances. New sensors are needed that are not only fast, inexpensive and sensitive, but also highly selective, capable of discriminating among different molecules in a mixture. In our laboratory we have employed the molecular recognition capabilities of nanoporous solids (zeolites, mesoporous silica) to enhance the selectivity of chemical sensors. Thus, we have deployed zeolite films on the surface of reactive (doped SnO2) sensors to strongly reduce the sensor sensitivity towards interfering molecules. We have also developed zeolite coatings on top of mass sensing devices (QCMs) where zeolite particles with suitable pore sizes and composition impart the desired selectivity to the sensing function. Recently, we have coated standard Inter-digital capacitors (IDCs) with electrode gaps of 10 or 50 microns have with zeolite films consisting of different zeolites with Si/Al ratios ranging from 1.5 (zeolite A) to infinite (silicalite) for humidity sensing.

We are now immersed in the development of a new generation of cantilevers also based on nanoporous solids where the chemical composition has been tailored to enhance selectivity, and the detection limits have been lowered by optimizing sensor design. Our concept goes a step further because the partial selectivity achieved with nanoporous solid based selective layers will be used in conjunction with the thermally induced properties of adsorbed molecules over the meander-shaped resistor for Joule heating.
 
 
Different Si based cantilever designs for gas sensing applications: before (a) and (b) and after (c) discrete zeolite crystals deposition
 
 Collaboration: Dr. J. Sesé. Institute of Nanoscience of Aragon. Edificio I+D+i. Campus Río Ebro. 50018, Zaragoza (Spain).
 
 
Applications: Hazardous Detection: nitro-compounds and Environmental Monitoring
 
In spite of research efforts in recent years, the accurate, fast and economical detection of explosives/explosive related materials by easy to operate chemical sensors which can mimic the olfaction of dogs remains unsolved. In view of the molecular recognition properties that nanoporous solids can afford, our strategy for vapor detection of explosives involves the use of Si based nanoporous solids (micro and mesoporous; i.e zeolites, M41S, titanosilicates) as chemical receptors.. Moreover, the use of meander shaped resistor on the cantilever tip as heater has been revealed as a valuable tool not only for zeolite refreshment with time on stream but also to enhance the capability of the sensor to discriminate the presence of interferences.
 
Collaborations:
1. Dr. J. Sesé. Institute of Nanoscience of Aragon. Edificio I+D+i. Campus Río Ebro. 50018, Zaragoza (Spain).
2. Prof. I. Dufour. L´IMS. Université Sciences et Technologies, Bordeaux (France).
 
Applications: Inmunodection of Pathogens and Biomarkers
There is an urgent need to develop cost effective POC multiplexed diagnostic instruments able to rapidly processing and screening a patient sample to identify a collection of bacterial and viral pathogens. In this field, our strategy combines the recent advances of MEMS with the excellent features of the antibodies as biorecognition elements to develop novel molecular diagnostic tools.
 
Collaboration: Dr. J.M. de La Fuente. Institute of Nanoscience of Aragon. Edificio I+D+i. Campus Río Ebro. 50018, Zaragoza (Spain).  
 
RECENT PUBLICATIONS
[1] Development of etching processes for the micropatterning of silicalite films. I. Pellejero, M. Urbiztondo, M.Villarroya, J. Sesé, M.P. Pina, J. Santamaría. Microporous and Mesoporous Materials, 2008, Vol. 114.
[2] Development of etching processes for the micropatterning of silicalite films. I. Pellejero, M. Urbiztondo, M.Villarroya, J. Sesé, M.P. Pina, J. Santamaría. Microporous and Mesoporous Materials, 2008, Vol. 114.
[3] Optical vibrometer for mechanical properties characterization of silicalite-only. J. Agustí, I. Pellejero , G. Abadal , G. Murillo , M.A. Urbiztondo , J. Sesé , M. Villarroya-Gaudó, M.P. Pina, J. Santamaría, N. Barniol.  Microelectronic Engineering, 2010, Vol.87.
[4] Nanoporous Silicalite-only Cantilevers as Micromechanical Sensors: fabrication, resonance response and VOCs sensing performance. I. Pellejero, J. Agustí, M.A. Urbiztondo , J. Sesé , M.P.Pina, J. Santamaría, G. Abadal. Sensors & Actuators: B. Chemical. doi:10.1016/j.snb.2012.01.041
[5] Novel Hybrid Membranes based on Polybenzimidazole and ETS-10 titanosilicate type material for High Temperature PEMFCs: a comprehensive study on dense and porous systems. A. Eguizábal, J.Lemus, O. Garrido, M.Urbiztondo, J. Soler, A. Blazquez,  M.P. Pina. Journal of Power Sources. doi:10.1016/j.jpowsour.2011.03.006.
[6] Nanostructured electrolyte membranes based on zeotypes, protic ionic liquids and porous PBI membranes: preparation, characterization and MEA testing. A. Eguizábal, J. Lemus, V. Roda, M.Urbiztondo, F. Barreras, M.P. Pina. International Journal of Hydrogen Energy. http://dx.doi.org/10.1016/j.ijhydene.2011.11.074.
[7] Gas sensing with silicon-based nanoporous solids, M. Urbiztondo, M.P. Pina, J. Santamaria, in “Ordered Porous Solids”, Valtchev, V. and Mintova S. (Eds.), Elsevier, pp. 381-405, (2008).
[8] Zeolite-coated Interdigital capacitors for humidity sensing. M. Urbiztondo , I. Pellejero, A. Rodriguez, M.P. Pina, J. Santamaria, Sensors & Actuators B., 157, 450-59, (2011).
[9] Zeolite-modified cantilevers for the sensing of nitrotoluene vapors, M.A.  Urbiztondo, I. Pellejero, M. Villarroya, J. Sese, M.P. Pina, I. Dufour, J. Santamaria. Sensors and  Actuators B, 137, 608-16, (2009).
[10] Explosives detection using porous coatings. M.P. Pina, I. Pellejero, M.A. Urbiztondo, J. Sese, J. Santamaria. SPIE Proceedings. Proc. SPIE 8031, 803124 (2011); doi:10.1117/12.883780.

 

 
 
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