Precision dip coating for the fabrication of thin films

Paul Boughton

Dip coating is the precision controlled immersion and withdrawal of any substrate into a reservoir of liquid for the purpose of depositing a layer of material. Nick Hardy reports.

Many chemical and nanomaterials engineering research projects make use of the dip coating technique. Dip coater customers are found worldwide in both academia and industry.

The dip coating technique is used for the fabrication of thin films by self-assembly and the sol-gel technique. Self-assembly can give film thicknesses of exactly one monolayer. The sol-gel technique creates films of increased, precisely controlled thickness, determined mainly by the deposition speed and solution viscosity.

Many factors contribute to determining the final state of a dip coated thin film. By controlling the functionalisation of the initial substrate surface, submersion time, withdrawal speed, number of dipping cycles, solution composition, concentration and temperature, number of solutions in each dipping sequence and environment humidity, a large variety of repeatable dip coated film structures and thicknesses can be fabricated. The technique of dip coating can give uniform, high quality films even on bulky, complex shapes.

A variety of dip coaters are available from Nima to suit your specific application. Dip coaters are available with a range of vertical travel lengths, dipping speeds and substrate holder types including a multiple substrate holder for upscaling production. If more than one solution reservoir is desired, Nima can provide dip coaters with programmable, rotating carousels that can house many vessels of solution for cleaning, multiple solution deposition cycles and rinse sequences.

Magnetic stirrer options and monitoring and control of the solution temperature are also available providing a further means of controlling the deposited film quality. Containment of the equipment within our dust and draught reduction cabinets offers improved reproducibility of samples when ideal cleanroom environments are not available.

Software-controlled deposition features include setting the upper and lower substrate resting positions, immersion speed, submersion period, withdrawal speed, drying period, number of dip cycles and solution holder rotation sequence for multiple solution depositions.

DC motor control of the dipping arm provides smooth linear motion of the substrate at all dipping speeds. A variety of speed ranges are available with the slowest possible speed being 0.1mm per minute. The fastest model dips at a speed of up to 500mm per minute. If deposition at an angle other than orthogonal to the liquid surface is required, an angled dip coater is available for dipping at angles of 30 and 45 degrees from vertical.

Nima have made many custom dip coaters over the years for customers with specific requirements and will happily consider any design modifications that you desire.

Besides dip coaters, Nima manufacture monolayer fabrication technology in the form of Langmuir troughs for monolayer investigations at the air-water interface. Langmuir-Blodgett (LB) deposition troughs allow the deposition of ordered, compacted monolayer films onto solid substrates. This technique provides homogenous, multilayer, nanoscale films built up to any desired thickness on solid substrates for investigation using a broad range of thin film characterisation techniques. Alternate layer LB troughs can even build up films of two alternating monolayer materials.

Visualisation of monolayer films can now easily be performed using the new Nima MicroBAM monolayer imaging tool that employs the technique of Brewster Angle Microscopy to detect changes in the refractive index of the water surface in the presence of surfactant molecules.

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Nick Hardy is the Applications Scientist at Nima Technology Ltd, Coventry, UK.