Nanofabrication refers to the methods of preparing nanotechnology, and there are two main methods of doing so.
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Top-Down Strategy: Basically refers to the need to miniaturize current technologies.
It starts from a bulk material with the capacity to incorporate nanoscale information. In the field of biomedical engineering, techniques involve engineering a biomaterial so it will be broken down into its component parts. This method efficiently produces structures with long-range order along with macroscopic connections. A primary example of the top-down strategy in the field of medicine is the creation of small crystals from a bulk of mineralized tissue.
A more specific example of producing seed crystallites is the partial demineralization of mineralized collagen matrix by acids produced by bacteria. Top-down mineralization approaches are mostly preceded by existing seed crystallites to aid epitaxial growth. Throughout the evolution of biomineralization, the importance of matrix proteins are seen as they help regulate the mineral nucleation and growth even with the absence of seed crystallites.
Moreover, in the field of integrated circuit manufacture, a key advantage of this method is the removal of the assembly step. Generally because the parts are already patterned and built in place. The most common top-down strategy for this is lithographic patterning wherein short-wavelength optical sources are used for the refinement of microelectric chip manufacturing. Extreme ultraviolet and X-rays are also being developed to allow lithographic printing techniques to reach even dimensions of 10 to 100 nanometers.
In this approach the mechanical printing of nanoscale size is also possible. This involves the imprinting, stamping, and molding techniques which can reach dimensions of 20 to 40 nanometer size! This is achieved through several means but most commonly via high-resolution method stamping using electron-beam lithography which stamps or marks a material’s surface repeatedly to create a specific pattern.
Such nanoscale printing techniques offer several advantages as some can also be done in ordinary laboratories. The big challenge though is ensuring that when these submicron techniques are used in the nanoscale dimension, they will still exhibit the same efficiency. Additionally, it is hard to construct three-dimensional objects through this approach because the main principle of creating structures here is via addition and subtraction of patterned layers.
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Bottom-Up Strategy: This approach enables the formation of materials from the nanoscope dimension (i.e. molecules and atoms) to larger structures. This method utilizes physical and chemical forces to assemble basic units into large structures.
The principle of the bottom-up strategy came from biological systems – which were basically generated from the same chemical forces used to create the structures needed by life. Researches aim to mimic the same thing so that when small clusters of specific atoms are produced, they will automatically self-assemble into elaborate structures. A sample of this self-assembly is when carbon nanotubes form under prime chemical and temperature conditions.
Biomineralization is also a specific type of process under this approach as it involves the regulation of amorphous phases via matrix proteins so that crystalline mineral units are formed in the nanoscopic dimension.
The characteristics for DNA-assisted assembly may also be studied to generate a method of integrating hybrid heterogenous parts into a single device or even to explore new methods of initiating self-assembly of molecules in the nanoscale dimension. Advantages of this approach are:
- DNA molecules can easily be sequenced and replicated in large quantities;
- Sequences of the DNA act as codes so they can easily recognize their complementary pairs (notably, hybridized strands form stronger bonds to said complementary strands);
- and of course, such DNA strands can further be used as labels by joining them on to different devices.
Other techniques under the realm of bottom-up strategy involves the condensation of atomic vapors on surfaces of liquids to induce coalescence of atoms. Even the inverse of globules of lipid molecules with polar hydrophobic tails jutting inward, have been further developed to produce size-selected particles for use in semiconductor and magnetic industries.
References:
- Anon. (2020). Nanoparticle production – How nanoparticles are made. Retrieved on 11 December 2020. Retrieved from: https://www.nanowerk.com/how_nanoparticles_are_made.php
- Britannica.(2020). Nanofabrication. Retrieved on 11 December 2020. Retrieved from: https://www.britannica.com/technology/invention-technology/A-chronology-of-invention
- Liu Y., Mai S., Li N., Yiu C.K.Y., Mao J., Pashley D., & Tay F. (2010). Differences between top-down and bottom-up approaches in mineralizing thick, partially-demineralized collagen scaffolds. NCBI. 10.1016/j.actbio.2010.11.028. Retrieved on 11 December 2020. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3050119/
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