Semiconductor Molecular Sieves With Shape-Selective Nanoscale Apertures
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Solution Overview
Problem
Conventional molecule filtration systems fail to discriminate between molecules based on shape due to their reliance on molecular weight and cylindrical pores, leading to increased impedance and long fluid passage times, especially with small nanoscale pores, and electron beam lithography is expensive and difficult to scale.
Innovation Solution
The development of molecular sieves with non-circular, nanoscale apertures and tapered depth profiles, fabricated using electron beam lithography and anisotropic chemical etching on single-crystalline semiconductor membranes, allowing for shape-based separation of molecules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional cylindrical pores are used for molecule filtration, then the system can separate molecules based on molecular weight, but it cannot discriminate between molecules based on molecular shape
Solution Approach 1:
The patent transforms the conventional symmetric cylindrical pore structure into asymmetric non-circular apertures (such as slit-shaped, rectangular, or triangular cross-sections). This asymmetry enables the molecular sieve to discriminate between molecules of similar size but different shapes, as the non-circular geometry creates shape-selective steric hindrance that cylindrical pores cannot provide.
Solution Approach 2:
The patent introduces a new dimensional parameter by varying the aspect ratio and orientation of the non-circular apertures. By controlling the dimensions in different spatial directions (width, height, depth), the molecular sieve can selectively pass or block molecules based on their shape characteristics, adding a shape-discrimination dimension to the traditional size-based separation.
2Measurement precision
If pore size is decreased to improve separation precision, then molecular weight discrimination improves, but impedance against fluid flow increases and passage time becomes inordinately long
Solution Approach 1:
The patent segments the pore structure into multiple sections with varying dimensions, particularly creating tapered depth profiles where the aperture size changes gradually from the entrance to the base. This segmentation allows molecules to be progressively filtered at different stages, maintaining high separation precision while reducing overall flow impedance compared to uniform narrow pores.
Solution Approach 2:
The patent applies different aperture dimensions at different locations within the membrane structure. The non-circular apertures have specific width-to-depth ratios that are optimized locally to balance separation precision and flow characteristics, rather than using a uniform pore structure throughout, thereby improving both precision and productivity.
3Manufacturing precision
If electron beam lithography is used to form openings in substrate, then precise pore patterns can be achieved, but the process is expensive and not easily scalable
Solution Approach 1:
The patent uses a master template with the desired non-circular aperture pattern that can be replicated multiple times across the substrate. This copying approach allows precise pore patterns to be achieved through stamping or imprinting techniques, eliminating the need for expensive and time-consuming electron beam lithography while maintaining manufacturing precision and enabling scalability.
Solution Approach 2:
The patent prepares a master template or stamp with the precise non-circular aperture pattern in advance. This preliminary action allows the complex patterning to be performed once at high precision, and then the template can be used to rapidly replicate the pattern across multiple substrates, improving both manufacturing precision and scalability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient separation and detection of biomolecules and other particles by shape, improving filtration speed and precision, and is applicable in chromatography and clinical filtering, such as separating diseased prions from normal proteins.
Implementation Method 1
etching a pattern of apertures into the single-crystalline semiconductor membrane using the mask and an anisotropic chemical etch
Implementation Method 2
transferring the pattern of holes into the layer of masking material using a plasma- or wet chemical-etch to form a mask
Data Source
AI summary
Methods for making molecular sieves are provided. The molecular sieves are comprised of thin semiconductors films in which a plurality of apertures is defined. The apertures are non-circular, nanoscale openings with tapered sidewalls that selectively pass certain molecules, while discriminating against the passage of other molecules.