Conducting AFM based lithography for patterning and electrical characterization of nanomaterials

Abstract

The thesis pertains to investigations using conducting atomic force microscope (C-AFM), on nanopatterning Si and polymer surfaces and entrapping nanomaterials for electrical measurements. It is organized into seven chapters. Chapter 1 introduces the concept of nanoscale materials, their physical and chemical properties and importance of patterning materials. Different nanolithography techniques are discussed with emphasis on scanning probe based techniques. Chapter 2 details out a procedure for producing micron sized markers on Si substrates to repeatedly access the regions while performing nanolithography. It is a one step resistless photolithography method involving single nanosecond laser shots producing surface melting of the exposed substrate. The markers are robust against harsh chemical and high temperature treatments encountered usually prior to a nanolithography process. Chapter 3 presents a study of the nanoscale SiOx line patterns obtained by local anodic oxidation (LAO) of Si using CAFM. The nature of the oxide was found to vary with the crystallographic orientation of the substrate and the bias voltage applied between the tip and the substrate. In Chapter 4, the role of catalytically active Au nanoparticles in LAO patterning of Si is discussed. A novel method for the synthesis of ligated Au nanoparticles is also presented. With nanoparticles dispersed on Si substrate, LAO was enhanced by several times. The maximum catalytic activity was found for Au nanocrystal size of ~ 2.5 nm. A CAFM tip coated with a Au nanoparticle was shown to serve, for continuous writing of enhanced oxide lines. Electrostatic nanolithography on a water soluble polymer, polyvinyl pyrrolidone is the subject of investigation of Chapter 5. The trench patterns formed in the polymer film have been used as a mold for Au nanoparticle filling. The hydrolysis of PVP along the trench edges was availed for the selective adsorption of fullerenes. A C60 based device was fabricated and I-V characteristics were studied. Chapter 6 presents a method to fabricate a circuit for electrically contacting individual carbon nanotubes (across the length). The first part deals with electron beam induced carbonaceous deposit and its dielectric nature. When the deposition was made on a carbon nanotube lying on a Ag film on Si substrate, the tube instead of getting buried under the deposit, gets lifted up due to dewetting. This configuration where one end of the tube is in contact with the bottom electrode (Ag) and the other accessible for CAFM is ideal for a study of the electrical nature of the nanotube, using CAFM. Thus, semiconducting and metallic carbon nanotubes could be distinguished, further supported by Raman spectral measurements. Chapter 7 presents a combined CAFM and EFM (Electric force microscopy) study on individual InAs/GaAs quantum rings grown by MBE. Both the studies have shown that the torus volcano shaped rings have more conductivity on the rim than at the central hole, which was attributed to the oxide growth on the ring.