Self assembled monolayer is properly organized structure of amphiphilic molecules.They are also known as SAM. In these self assembled layer all the molecules have head group at end which has the capability to the affinity the regarding substrate. On the other end group is present which is called “tail” SAM has functional group terminal. SAMs can be constructed by using various kinds of molecules with different substrates, for instance fatty acids monolayer ad oxides materials. For the proper development of layer all the systems were keenly observed by the scientists such as organics and biometrics, and it was discovered that the self assembled layer could be of great use for the world and they have great structural and functional importance.
Creation and work
SAMs can be created by the chemisorption of “head groups” of substrates in both liquid and vapourization stage.This process of development is then repeated by the tail groups terminals of the molecules as well.Before beginning the crystallization all the disordered or unordered molecules are arranged into a lower systematic layer.These layers can appear on the surface of substrate in crystalline form.After that the head group assembles the spreader substrate together to form a complete structure.Substrates are assembled till the time when no growing area left on the surface ,forming the totally covered and packed single SAM.Molecules are slowly absorbed into the lower surface energy layer because of the stronger composition of head groups .SAM are used to form the fully new layered structure with different arrangements every time.
Self assembled monolayer is considered to be one of the most useful method for recognizing molecule and building structures.They are widely used in organics and biometrics for binding enzyme surfaces, metallic organic stuff, chemical force microscope process, protection, crystal growth, growing patterned surfaces and materials, in sensing devices and electric conduction wires.
Various kinds of SAMs can be produced according to the different situations of implementation.In different scenarios they varies in their wetting and properties according to the atmosphere.
Alkanethiol SAMs can be produced by absorption technique and then constructed and developed which is diluted with dry nitrogen in room temperature for at least 72 hours.
Self assembled monolayers can slo be produced by evaoupization and they are absorbed during the liquid stage for example chlorosilane SAMs, they are usually reactive to the substrate.
There are several factors which are considered to the defect s and risky for the practice.
- Some times defects are found in the final structure of self assembled monolayer.They could appear due to the external or internal properties. Many of the SAM characteristics , such as thickness, can be determined in the few minutes. but removing defects could take hours.
- External and intrinsic factors can cause the absorption of various kind of unwanted molecules which makes SAM highly unstable to be implemented in thermodynamics.
- Temperatures over the growth point can make Sam complex .this could take multiple path in SAM organization.in first path only heads are entertained and in second one tails are properly organized then these two paths are joint to form one smooth layer Nanoparticle properties.
- Chemical compositions of self assembled layers can be some times highly reactive with the substrate on the surface which can produced poisonous gas and fire too.
- Low concentration of absorbent and solvent can take long immersion time which can form large crystalline undesired sequence.
- Dust or contaminated substrate can unsmooth materials can cause defects in SAM.to properly handle and reduce the defects room temperature should be normal.so that best and perfect SAMs could be produced.