Research efforts in diverse fields have resulted in improving some basic techniques which have been incorporated into the nano-technological sector in the creation of tools and devices.
These tools and techniques are harnessed in the production and imaging of nano-scaled objects, exertion of various processes in diverse fields, and refinement of production outputs. In the table below are commonly used tools and their basic working principle:
|Tools||Primary Working Principle|
|Electron Microscopes||Electron Microscopy|
|Fabrication Systems||Molecular Self-Assembly|
|Carrier Concentration Profiles||Profiling|
|Atomic Layer Deposition Systems||Deposition|
|Dynamic Light Scattering Systems||Diffraction|
|Microfluidic Devices||Conventional Machining|
Each nano-technological tool possesses a set of principles or techniques which determine its mode of operation. The following are a few techniques applied in nano-technological systems and operations:
Electron Microscopy: A system designed for obtaining high-resolution images of biological and non-biological specimens. Its top-quality image production is due to the use of electrons as an illuminating energy source. Electron microscopy is often used alongside various ancillary techniques such as immune-labeling, negative staining, etc. There are two primary forms of electron microscopy, namely:
Scanning electron microscopy (SEM): This is a technique operative on only solid specimens which employs focused high-energy electron beam to generate 2-D images for obtaining surface information on the sample.
SEM is routinely used to detect spatial variations in chemical compositions by acquiring elemental maps, analyzing phases with their mean atomic number, and compositional mapping based on differences in trace element “activators.”
Transmission electron microscopy (TEM): TEM is used in the observation of internal features of tiny specimens using an accelerated beam of electrons. It provides the composition, crystallization, structure, and stress of the substance at a relatively higher resolution than as observed with SEM.
However, Transmission electron microscopy is only efficient with very thin samples and is therefore not as time-efficient as SEM. Common sample preparation techniques utilized in this method include ultrasonic disk cutting, dimpling, and ion milling.
Adsorption: Adsorption is a surface phenomenon that involves the transfer of a liquid substance – the sorbate, onto a solid material – the sorbent, and the subsequent binding of both by physical and chemical interactions.
It is dependent on several parameters like; temperature, pH, sorbent dose, sorbate concentration, size, and surface morphology. This technique is most promising in contaminant elimination due to its high efficiency, low cost, and simplicity of action.
Nanopore DNA sequencing: Nanopore DNA sequencing is a unique technology that allows direct, real-time analysis of long DNA or RNA fragments. By the tracking of electrical current alterations produced from the passage of nucleic acid through protein nanopores, a signal is generated and decoded to give the target DNA or RNA sequence.
The use of DNA in nano-fabrication processes is categorized into three distinct functions:
- Creation of artificial networks made up of native DNA.
- Attachment or Integration of DNA onto solid surfaces.
- Formation of metallic or semiconductor nanoparticles along DNA.
Photocatalysis: This belongs to the family of Advanced Oxidation Processes, which are used in the mineralization of toxic and ardent biodegradable substances. Photocatalysis is the catalytic acceleration of a photoreaction on the surface of a semiconductor. It is vital to note that in the process, there should be no alteration to the catalyst.
During photocatalysis, a series of reactions take place:
- Light absorption to generate electron-hole pairs.
- Separation of excited charges.
- Transfer of electrons and holes to the surface of the photocatalyst.
- Utilization of charges on the surface.
Molecular self-assembly (MSA): MSA imitates the anabolic ability of biological systems to formulate complex structures from simpler ones. This process is the spontaneous assembly of molecules without guidance into structurally defined, stable arrangements through non-covalent interactions.
Nanotechnology is set on incorporating this process into the build-up and fabrication of nanostructures via the bottom-up technique. There are two forms of molecular self-assembly, and they are:
- Electrostatic Self-Assembly (ESA).
- Self-Assembled Monolayers (SAMs).
Electrostatic Self-Assembly: It is also known as layer-by-layer assembly because it involves the fabrication of layered structures through the alternate adsorption of anionic and cationic electrolytes onto a suitable substrate.
In the multiple layers, there is a single active layer, while other layers function as complements in enabling the composite multi-layered film via electrostatic attraction.
Self-Assembled Monolayers: This is the synthetic construction of basic building blocks to which other blocks are subsequently arranged on and bound, to obtain an amalgam by the aid of weak intermolecular forces of attraction.
This form of assembly is most preferred in the industry due to its reversible nature (owed to the weak forces of attraction), which is beneficial in mass production, error correction, and for cost-effective processes.
Other techniques employed in nanotechnology include membrane processes, quantum dot probes, protein analysis, atomic force microscopy, X-ray diffraction, electron-spinning, and others.
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