Stability of monomolecular films of archaebacterial tetraether lipids on silicon wafers: a comparison of physisorbed and chemisorbed monolayers.

The monomolecular organisation of symmetric, chemically modified tetraether lipids caldarchaeol-PO(4) was studied using Langmuir film balance, ellipsometry, and atomic force microscopy (AFM). Solid silicon wafer substrates were modified to hydrophobic, hydrophilic, and amino-silanised surfaces; and Langmuir-Blodgett (LB)-films were transferred onto each. LB-caldarchaeol-PO(4) films were subjected to further rinsing with organic solvent and additional physical treatments, to compare their resistance and stability on chemisorbed (amino-silanised) and physisorbed (hydrophobic and hydrophilic) surfaces. The resistance and stability of these monolayer films was characterized by ellipsometry and AFM, and film thickness was determined using ellipsometry. AFM was also employed to observe surface morphology. Monolayer films on hydrophobic surfaces were found to be more resistant to rinsing with organic solvent and additional physical treatments than monolayer films on either amino-silanised or hydrophilic surfaces. The hydrophobic effect with hydrophobic surfaces appears to support the formation of stronger caldarchaeol-PO(4) films on silicon wafer substrates, with increased resistance and stability.