Every time I have not a continuous thin film , my sample deposit in a dispersed areas after spin coating, what can i do or what is the problem for me?
Its really difficult to get uniform and continuous film with spin coating process. You can try with 1000 rpm or 1500 rpm. Still it will not be fully uniform. Thermal evaporation or chemical bath deposition will be good options for continuous and uniform coating.
I agree with the Tasnim Kamal. Spin coated films are always nonuniform whatever may be the rotation speed used in this process. For uniform and continuous coating, i will prefer sputtering because It works in both level laboratory as well as industrial.
Some classic substrate's functionalization (surface modifications), as well as heating during coating, might help[1], at least, in certain cases.
1. As useful parameters for quasi-continuous and more uniform coating(s).
Spin coating is a technique used in design of a particular device without considering uniformity. One can improve the coating through thermal methods. Sputtering is preferred in uniform thin films.
Dear Islam Al-Shurman, your film coating depends on several issues.
1. Viscosity, 2. Spin rate, 3. Substrate surface property and 4. Solution property.
Let's consider you solution viscosity is less and spin rate is within the range of 2000 rpm to 4000 rpm. In this case your solution will uniformly spread on the substrate depending upon the wetting angle of that solution to the substrate. Please solve that issue.
Accelerate the spin coater gentely. Number of the coating required. Preparation of the substrate is also important. After one coating heat treatment is necessary. Repeat the deposition two to four time. Decide the molar concentration very precisely. You can follow following literature Article Effects of Annealing Temperature on the Structural, Optical,...
.Which equipment you are using for film deposition that is also important. 'You can contact me this regard.
Aniruddh Bahadur Yadav
i have the same problem with coating silicon substate by graphene, i see cracks in graphene layer. i put drops on surface and start rotation with lower rpm like 5oo and increase rpm after 60 sec is that correct?
how i test or know its Viscosity? i see small particles in suspension.
i dissolve it in water 1mg-1ml and sonicate for 30 min
Mohamed Refaey Please treat the silicon substrate first. You should clean properly then UV-Ozone treatment. You can also try different SAMs treatment of the substrate ie. hydrophilic or hydrophobic surface group SAMs. For further information or discussion, you can msg me.
Totally agree with Rahim Abdur and Ravi Pendurthi that viscosity and spin rate are the important parameter to govern spin coat process.
Spin coat is basically a physical process and its merit lies in its operational convenience, the process depends upon:
the thickness of a spin coated film is proportional to the inverse of the spin speed squared .
Following links may be useful please go through it-
https://www.ossila.com/pages/spin-coating#spin-coating-thickness-equation
http://www.laurell.com/support/spin-speed-calculator.php
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