Investigations of metal and metal-organic bilayer nanostructures employing atomic force microscopy and related techniques

Abstract

The thesis pertains to investigations on metal and metal-organic bilayer nanostructures employing atomic force microscopy and related techniques. It is organized into six chapters. Chapter 1 introduces the concept of nanoscale materials, their important properties and atomic force microscopy as an enabling tool for the study. Chapter 2 discusses the optimization and performance of gold-coated cantilever probes for use in conducting-atomic force microscopy (C-AFM), which is essentially a two-probe multimeter with nanometer precision. The mechanical and electrical stability of the nanocontact between a gold-coated tip and a graphite substrate has been studied in relation to the contact force and circuit current. The nature of electrical conduction in a nanorectifier system–a Langmuir-Blodgett (L-B) film of alkanethiol capped Au nanocrystals supported on an organic monolayer deposited on a SiO2-Si substrate – are described in relation to the film morphology in Chapter 3 employing C-AFM. The effect of monolayer compression on the morphology of the L-B films and the monolayer-bilayer transition has been studied. The I-V plots acquired at different locations on the nanocrystal film are analyzed and the large rectification ratios observed, have been explained on the basis of asymmetric tunnel junction model. Chapter 4 presents the structural aspects of lamellar bilayer systeM.S. of Pd(II)- and Ni(II) alkanethiolates (PdSR, NiSR) and their electrical and magnetic properties respectively. Hybrid bilayers, consisting of binary mixtures of PdSR, have been prepared for the first time and the structural aspects relating to bilayer spacing and chain conformation have been studied. The electrical properties of individual bundles of PdSR at room temperature are investigated by C-AFM and the influence of chain length is discussed. A solventless thermolysis method for producing Pd nanocrystals and metallic Pd films from PdSR and the effect of chain length on nanocrystal size have also been studied. The magnetic properties of lamellar NiSR of different chain lengths exhibiting intralayer and interlayer interactions at low temperatures have also been examined. Deposition of metal cuplike structures with femtoliter capacity by pulsed laser ablation, their characterization using scanning electron microscopy and AFM and also their applications as containers, are discussed in Chapter 5. The optimal conditions for obtaining femto-cups of various metals on different substrates are explored. An understanding of the underlying mechanism is also provided in terM.S. of droplet flow dynamics. Transforming the metal cups to oxide ones and their chemical mapping by scanning Auger microscopy are also discussed. In Chapter 6, dip-pen lithography (DPN), an AFM based technique is demonstrated for patterning of–colloids of luminescent doped LaPO4 and ZnO on different substrates, precursors for metal and semiconductor nanopatterns and also molecules. A laboratory method has been developed to produce AFM tips of different sizes by laser irradiation of commercial tips. A study of colloidal ink deposition from such blunt tips is also presented.