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Isoelectric focusing 2. Two-dimensional gel electrophoresis in proteomics; a tutorial. The application of 2D gel. Magdalena Pattarachalit Dec. Good luck! GayathriGayu76 Nov. Reshma Ray Sep. Show More. Total views. You just clipped your first slide! Clipping is a handy way to collect important slides you want to go back to later. Now customize the name of a clipboard to store your clips. Visibility Others can see my Clipboard.
Cancel Save. Exclusive 60 day trial to the world's largest digital library. Activate your free 60 day trial. It is a direct bandgap semiconductor with a puckered honeycomb structure. The bandgap can be tuned throughout the visible region by stacking layers on top of each other. Phosphorene's corrugated structure means that its properties can vary significantly, depending on which direction the material is measured along.
Monolayers of silicon silicene , germanium germanene and tin stanene , are collectively known as Xenes following the naming convention of graphene. They have a hexagonal structure similar to graphene, but are buckled to varying degrees. Unlike graphene, they cannot be exfoliated from bulk material and must be epitaxially grown on a substrate, and generally retain a strong interaction with that substrate.
While still very much in their infancy, potential applications range from field-effect transistors to topological insulators. Recently, 2D analogues of antimony [4] and bismuth [5] antimomene and bismuthine respectively have also been grown.
Bismuth shows potential for magneto-electronic applications [6]. It is possible to take any material and thin it down until it has a thickness of only a few atoms to create a 2D material. However, many materials e. A 2D material created in this way will have a high density of dangling bonds, which are chemically and energetically unstable, and can force the material to rearrange its structure to lower its surface energy.
Another allotrope of carbon — graphite — has strong chemical bonds only along planes within the bulk material. These planes are stacked on top of each other and held together by weak van der Waals interaction, and so can be separated without leaving any dangling bonds.
In the case of graphite, a single plane is called graphene. Most of the 2D materials being studied therefore belong to the broader class of layered materials or van der Waals materials.
Within each of these approaches are several subcategories, each with their own advantages and disadvantages - explained below. A piece of sticky tape is applied to the surface of a layered material and then peeled off, taking flakes consisting of a small number of layers with it.
The tape can then be pressed onto a substrate to transfer the flakes for study. The monolayer yield of this process is low the flakes obtained are mostly multilayer , with no control over the size and shape. It is also a suitable technique for all van der Waals materials. For these reasons, mechanical exfoliation remains popular for lab-based studies, but it is not scalable for integration into new technologies.
Sonication causes tensile stress to be applied to the layers, forcing them apart. To improve monolayer yield, variations exist - such as introducing reactive ions between the material layers that create hydrogen bubbles that push the layers apart, or that rapidly mix the solution to create additional shear force on the layers.
This method is highly scalable but has several drawbacks. The monolayer yield is again generally low, and the flakes are often less than nm in size due to the applied forces breaking them apart.
The resultant flakes may also potentially have a high density of defects and residual solvent when removed from solution, making them unsuitable for many optoelectronic applications.
Chemical vapour deposition — This process involves passing one or more precursor gases which usually contain the atomic ingredients of the required film through a heated furnace, where they will react together or with a substrate and form a thin layer of the required material. This process has been successfully applied to grow graphene and TMDCs. Several parameters such as gas pressures and compositions, temperature, and reaction times need to be controlled as they will affect the thickness, quality and composition of the films.
While this process is more complex and expensive than most top-down techniques, it is highly scalable, and the quality of the films produced approaches that of mechanically-exfoliated layers. Solution-based chemical synthesis — A vast variety of techniques have been developed to synthesise 2D materials through wet chemical techniques.
These include high-temperature chemical reactions in solution, interface-mediated growth reactions occur only at the surface of a liquid , fusion of nanoparticles into larger nanosheets, and many more.
Each method is particularly well-suited to a certain type of 2D material, and everything from graphene and TMDCs to monolayer metals can be synthesised using the appropriate technique. However, for certain applications, the scalability, low cost and versatility of these techniques makes chemical synthesis the best method for large-scale production.
Removal of van der Waals interactions — A layered bulk material consists of many covalently-bonded planes held together by weak van der Waals interactions. When a force is applied to a material, these van der Waals forces can be easily overcome and the material breaks — making it seem weak.
Conversely, the covalent bonds that hold the atoms together in the layers are actually very strong. A monolayer will only have covalent bonds. For example, graphene has a tensile strength times greater than graphite, and while a graphite pencil can be easily broken, graphene is over times stronger than steel. An increase in the ratio of surface area-to-volume — The surface area-to-volume ratio of a material defines how much of it is exposed to its environment. This is important for chemical reactions — the more reactant that is in contact with the material, the faster the reaction can occur, so 2D materials tend to be more reactive their bulk counterparts.
It also makes 2D materials more sensitive to their surroundings, an effect that is exploited for sensors based on 2D materials. Confinement of electrons in a plane — The electronic and optical properties of a material depend upon its electronic band structure. This describes how electrons move through the material, and is a result of the periodicity of its crystal structure. When a material goes from bulk to 2D, the periodicity is removed in the direction perpendicular to the plane, which can greatly change the band structure.
The modified band structures are responsible for the extremely high conductivity of graphene and the fluorescence of monolayer MoS 2. Another effect of dimensional confinement is reduced dielectric screening between electrons and holes in semiconductors.
When there is less material to screen the electric field, there will be an increase in Coulomb interaction and more strongly-bound excitons — making them more stable than excitons found in bulk materials.
If the excitons are confined in a plane that is thinner than their Bohr radius as is the case for many 2D semiconductors , quantum confinement will result in an increase in their energy compared to bulk excitons, changing the wavelength of light they absorb and emit.
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