Eur. Phys. J. E (2012) 35: 79
https://doi.org/10.1140/epje/i2012-12079-8

Regular Article

Role of metal ions in growth and stability of Langmuir-Blodgett films on homogeneous and heterogeneous surfaces

¹ Surface Physics Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, 700064, Kolkata, India
² Physical Sciences Division, Institute of Advanced Study in Science and Technology, Vigyan Path, Paschim Boragaon, Garchuk, 781035, Guwahati, Assam, India

^* e-mail: jayanta.bal@gmail.com

Received: 3 March 2012
Revised: 27 May 2012
Accepted: 18 July 2012
Published online: 24 August 2012

Abstract

Structure and stability of cadmium arachidate (CdA) Langmuir-Blodgett (LB) films on homogeneous (i.e., OH-, H-passivated Si(001) substrates) and heterogeneous (i.e., Br-passivated Si(001) substrates) surfaces were studied using X-ray reflectivity and atomic force microscopy techniques and compared with those of nickel arachidate (NiA) LB films. While on OH-passivated Si, an asymmetric monolayer (AML) structure starts to grow, on H-passivated Si, a symmetric monolayer (SML) of CdA forms, although for both the films, pinhole-type defects are present as usual. However, on heterogeneous Br-passivated Si substrates, a combination of AML, SML, shifted SML and SML on top of AML (i.e., AML/SML), all types of structures are found to grow in such a way that, due to the variation of heights in the out-of-plane direction, ring-shaped in-plane nanopatterns of CdA molecules are generated. Probably due to stronger head-head interactions and higher metal ion-carboxylic ligand bond strength for CdA molecules compared to NiA, easy flipping of SML on top of another preformed SML, i.e. a SML/SML structure formation was not possible and as a result a wave-like modulation is observed for the CdA film on such heterogeneous substrate. The presence of hydrophilic/hydrophobic interfacial stress on the heterogeneous substrate thus modifies the deposited molecular structure so that the top surface morphology for a CdA film is similar to monolayer buckling while that for NiA film is similar to monolayer collapse.