Atomic Layer Deposition on Self-Assembled-Monolayers

A sophisticated method for developing thin-film structures is atomic layer deposition (ALD). In 1974, Tuomo Suntola and colleagues created ALD. The procedure was initially known as Atomic layer epitaxy (ALE). Today, however, the name “ALD” is more popular. The aim to establish a method for producing thin-film electroluminescent (TFEL) flat panel displays served as the driving force behind the development of ALD.

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Atomic Layer Deposition on Self-Assembled-Monolayers

1. Principle of technique

ALD is a self-limiting growth chemical vapour deposition (CVD) technology where the film is created via dividing a chemical reaction into two independent half processes. The precursor ingredients must be kept apart during the whole process. There are four phases in a development cycle.

Exposure of the first precursor, followed by a purge of the reaction chamber, exposure of the second precursor, and a final purge

The first precursor interacts in the first step with every site on the substrate that has received a single-molecule layer of the first precursor. In order to prevent unintended gas-phase reactions between precursors, which would impede acceptance of a single molecular layer, the second stage entails Argon flowing and pumping of the first precursor’s residue. To create a single-molecule layer of the target substance, the second precursor interacts with one molecular layer of the first ALD precursor in the third stage. Pumping the leftovers from the second precursor constitutes the fourth step.

2. Advantages and disadvantages

The ALD method offers several benefits, including that ALD can adjust film thickness at the angstrom or monolayer level; the film thickness is only dependent on the number of reaction cycles. The size of the area that can be deposited using ALD depends only on the size of the ALD chamber. For the deposition of thin films with three-dimensional structures, ALD is an excellent technique.

ALD has very good conformality to substrate surfaces as a consequence. ALD is a repeatable technique that employs highly reactive precursors and can operate at low temperatures. The ALD approach enables the continuous processing of many materials.

3. ALD process at low temperature

It’s crucial to be able to do ALD at low temperatures (ALD-LT). It is the focus of this chapter and essential for ALD on SAMs. SAMs are thermally sensitive materials, just as polymers or biological samples. They deteriorate at high temperatures.

Disabsorption from the surface also occurs in the case of SAMs. High-temperature processes cause inter-diffusions of materials, which are disastrous for nanostructured devices. Low-temperature ALD prevents these consequences.

Although certain reactions take place without catalysts, a catalyst is occasionally employed in ALD-LT. The effects of biological nanostructures are particularly intriguing. A lotus leaf, for instance, has very hydrophobic behaviour as a result of its nanostructures. ALD-LT can mimic the lotus leaf’s coat to provide results that are comparable. Additionally, protein spheres and cellulose fibres from filter paper were subjected to ALD-LT treatment for a tobacco mosaic virus (TMV).

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