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Self Assembled Monolayer - What is Self Assembled Monolayer ( SAM )


Post by Jawad Ahmad Riaz

Self assembled monolayer is properly organized structure of amphiphilic molecules.They are aslo known as SAM.  In these self assembled layer all the molecules have head group at end  which has the capability to the affinite  the reagrding substarte.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 beginnig the crystalization all the disordered or unordered molecules are arranged into a lower systemetic layer.These layers can appear on the surface of substarte in crystalline form.After that the head group assembles the  spreaded 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.


SAMS Applications

Self assembled monolayer is considered to be one of the most useul method for recogniziing 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 patterened surfaces nad materials, in sensing devices and electric conduction wires.

 

Types of SAMs

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 atomsphere.
Alkanethiol SAMs
Alkanethiol SAMs can be produced by absorption technique and then consctructed and developed which is dilluted with dry nitrogen in room temparture for atleast 72 hours.
Vapourized SAMs
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 subtrate.

 

Risks & Defects

There are sevral factors which are considered to the defetc s and risky for the practice.

 

  • Some times defects are found in the final strcuture of self assembled monolayer.They could appear  due to the external or internal properties. Many of the SAM characteristics , such as thickness, can be dtermined  in the few minutes. but removing defects coud take hours.
  • Extrnal and intrinsic factors can cause the absorption of varipus kind of unwanted molecules which makes SAM hihly unstable to be implemnted in thermodynamics.
  • Temperatures over the growt 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 rae joint to form one smooth layer Nanoparticle properties.
  • Chemical compositions of self assembled layers can be some times highly reactive with the substarte on the surface which can produced poisnous gas and fire too.
  • Low concentartion of absorbent and solevent can take long immersion time which can form large crystalline undesired sequence.
  • Dust or contaminted substrate can unsmooth materilas can cause defects in SAM.to properly handel and reduce the defects room temperature should be normal.so that best and perfect SAMs could be produced.




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