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Phosphorus Specialties for Surface Treatment

Alkylphosphonic and dialkyphosphinic acids

Phosphorus chemistry is critical in surface engineering, particularly in applications where there is an inorganic – organic interface. Phosphorus derivatives offer a range of chemistries that can bind with different types of surfaces and enable stronger interactions. If the phosphorus chemical is structured so that it can form a monolayer the polar ‘head’ group binds to the inorganic surface and the surface takes on the properties of the 'tail' group attached to the phosphorus atom.(1-4) In the products shown below the 'tail' group is the long alkyl chain. So, for example, where we have phosphonate groups bonding to an inorganic surface such as a metal or metal oxide, the alkyl group attached to the phosphorus can be tailored to provide a range of properties to the surface. These include hydrophobic coatings, adhesion promotion & corrosion protection. Monolayers, obviously, can cover large surface areas with a small volume of product whilst providing a long lasting surface treatment.



In this experiment, we took a standard industrial grade metal oxide and treated it with a variety of phosphonated species, we then did a contact angle test by dropping water onto the surface. You can see clearly in the picture to the left that the original surface is hydrophilic, but the use of the phosphonic acid treatment on the surface gives hydrophobic properties. In the middle three pictures there is a trend of increased contact angle with increasing alkyl chain length, but when treated with a very high molecular weight species, phosphonylated mineral oil, the surface reverts to being hydrophilic.(5)


Thermal Stability

Thermal stability is very important for some surface treatment applications. Here we see the impact of switching alkoxy groups to alkyl groups on thermal stability. The presence of a P-C bond makes a big difference with significant weight loss not occurring until ~350oC rather than 250oC. In contrast moving from the alkyl acid phosphate to the dialkyphosphate – an increase in molecular weight without changing the type of structure has little impact.(5)


Surface Protection

In the semiconductor fabrication process, phosphine derivatives can be used to bind to one part of the surface preferentially over another. This protection allows for the selective deposition of other materials on certain parts of the chip, for example deposition of Zinc oxide or alumina on silicon rather than copper as shown in the TEM and EDX/EELS images.


The octadecylphosphonic acid protects the copper and a layer of zinc oxide is deposited on the silicon. The use of area selective deposition simplifies the overall manufacturing process (less total steps are required).(6)


Similarly, as electronic components, for example PCBs in 5G applications, become smaller they are subjected to higher heat stresses. This requires new adhesives be developed to maintain the integrity of the copper clad laminate components. The high stability of alkylphosphonic and dialkyphosphinic acids means they can play a role here, maintaining adhesion at the high temperatures.


CYTOP® 501 (Strem: 15-7555) is a commercial scale, liquid dialkylphosphinic acid.

RHODAFAC® LPA 100P (97-1001) is a commercial scale, solid alkylphosphonic acid.

To learn more about other specialty phosphorus products, please refer to the Solvay offering at Strem or the Solvay website.



  1. Surface Science, 2008, 602, 1347-1359.
  2. Langmuir., 2001, 17, 5736-5738.
  3. Applied Surface Science, 2010, 256, 7146-7150.
  4. Langmuir., 2010, 26, 14747-14754.
  5. Solvay, unpublished results
  6. Chem. Mater., 2019, 31, 1635-1645.



Featured Products:

15-7555 Phosphorus › Bis(2,4,4-trimethylpentyl)phosphinic acid, min. 85%, CYTOP® 501 (83411-71-6)

97-1001 n-Dodecylphosphonic acid, min. 90% [RHODAFAC® LPA 100P] (5137-70-2)


Related Products:

CYTOP Products

Phosphorus Ligands and Compounds Booklet

All products sold in collaboration with Solvay




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