Fabrication of functional silicon-based nanoporous membranes

Abstract

Abstract. Macroscopic porous membranes with pore diameter uniformity approaching the nanometer scale have great potential to significantly increase the speed, selectivity, and efficiency of molecular separations. We present fabrication, characterization, and molecular transport evaluation of nanoporous thin silicon-based sieves created by laser interferometric lithography (LIL). This fabrication approach is ideally suited for the integration of nanostructured pore arrays into larger microfluidic processing systems, using a simple all-silicon lithographic process. Submillimeter-scale planar arrays of uniform cylindrical and pyramidal nanopores are created in silicon nitride and silicon, respectively, with average pore diameters below 250 nm and significantly smaller standard error than commercial polycarbonate track etched (PCTE) membranes. Molecular transport properties of short cylindrical pores fabricated by LIL are compared to those of thicker commercial PCTE membranes for the first time. A 10-fold increase in pyridine pore flux is achieved with thin membranes relative to commercial sieves, without any modification of the membrane surface.

Molecular transport of proteins through nanoporous membranes fabricated by interferometric lithography

“…Uniform arrays of cylindrical pores are formed in 200 nm thick silicon nitride using an optimized interferometric lithography process as described previously by Ileri et al 19 Interferometric lithography is a maskless photolithographic technique which enables definition of nanoscale features through interference of two laser beams incident at the same area. The final freestanding membranes are square, 270 microns on a side.…”

“…16,17 More recently, Rivera et al created biodegradable sieves in PLLA using UV interference lithography. 18 Limited pyridine diffusion data have been presented only in Ileri et al 19 In this work we report protein transport properties of thin (200 nm) silicon nitride membranes fabricated by an interferometric lithography process that can be adapted for large scale production and easily integrated with lab-on-a-chip platforms. The advantages of these silicon nitride-based filters over conventional PCTE or AAO sieves are increased mechanical strength, wellcontrolled pore dimensions, compatibility with MEMS devices/ technologies, and adjustable surface properties.…”

Effect of geometrical dimension, shape, thickness, material & applied pressure on nanopore thin filtration membrane strength

“…which is just about 1.5% greater than the value using a more elaborate approach, and thus other terms could be neglected. Since square membrane is used, then a b , and thus Equation (1) Et D ( 6 ) On the other hand, using von Mises stress [11], the tensile strength at the center of the membrane will be Again, since a b due to square membrane is used, then Equation (7) …”

“…This stress value is still far away from the Young's value of each material as summarized in Table 1, thus the studied membrane still can withstand the applied pressure without membrane crack even until 55 mmHg applied pressure as shown. 4.0x10 6 6.0x10 6 8.0x10 6 1.0x10 7 …”

“…Therefore, a miniaturized dialysis machine that is wearable or implantable is anticipated; which patient could have uninterrupted treatment without having to sacrifice their time and mobility laying down on bed for treatment in health facilities [5]. Various types of filtration membrane has been studied by researchers around the globe to realize a miniaturized device that utilizes small-sized filtration membrane [6,7], where some of the membrane types have an ununiformed pores [8] that cause leak out of essential solutes from the body due to lack of performance in molecule size selectivity. The effect of the artificial filtration membrane geometry, shape, thickness, material and applied pressure in terms of its strength need to be taken into account so that it can withstand the continuous pressure applied caused by blood flow during filtration process.…”