Structural effects on the quantum conductance and mechanical deformation of metallic nanowires

Author(s)

Maureen Joel Lagos Paredes

• Document type: Doctoral Thesis
• Press: Campinas, SP. , ilustrações.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin
• Defense date: 2010-09-09

Examining board members

Daniel Mário Ugarte; Ado Jorio de Vasconcelos; Antonio Jose Roque da Silva; Maurice de Koning; Fernando Iikawa

• Advisor: Daniel Mário Ugarte
• Field of knowledge: Physical Sciences and Mathematics - Physics
• Indexed in: Biblioteca Digital da UNICAMP
• Location: Universidade Estadual de Campinas. Biblioteca Central Cesar Lattes; T/UNICAMP; L137e; Universidade Estadual de Campinas. Biblioteca do Instituto de Física Gleb Wataghin; T/UNICAMP; L137e

Abstract

Atomic-size metallic nanowires (NWs) display new physical and chemical effects, for example the quantum conductance. NWs can be usually generated by means of a simple experimental procedure: two metallic surfaces are put into contact and then they are retracted in a controlled way. During the last stages before the rupture, a wire containing a few atoms is created and its conductance can be measured simultaneously during the elongation process. This approach represents a scenario which allows us to study its conductance and mechanical properties. This thesis aims to study the thermal energy effects on NW's atomic arrangement and the corresponding influence on quantum conductance and mechanical deformation. The atomic arrangement was studied using time-resolved high resolution transmission electron microscopy. The conductance was measured using an experimental technique called mechanically controllable break junctions. Experiments were performed at ~ 150 K and 300 K. In this work were studied NW's that exhibit different morphologies, sizes and chemical composition. Firstly, the study of the atomic arrangement influence on the mechanical deformation was developed on one-nm wide gold nanorods (NRs). It was found that temperature induces drastic changes in the NR mechanical behavior. Moreover, it was shown that the NR size and shape play an essential role during the process of mechanical deformation. Second, the detailed study of the formation of anomalous silver square-cross section nanotube was performed. This revealed the strong influence of surface effects on atomic arrangement. Third, the study of atomistic aspects associated with mechanical deformation of gold-copper alloy NWs was also developed. Segregation events at atomic scale, induced by surface effects, and significant variations of the nanoalloy mechanical behavior were observed. Fourth, the analysis of the origin of formation of anomalous interatomic distances in suspended gold atom chains was performed. Our results indicate that carbon represents the most probable contaminant which induces the generation of anomalous distances (3.2 Å). Finally, the study of the atomic arrangement effects on conductance of gold and silver NWs as function of temperature was developed. Our experimental results revealed that thermal energy induces drastic changes of structural behavior, generating planar defects at low temperatures. Conductance measurements obtained at ~150 K also display significant variations. Considering structural information derived from microscopy observations, simple geometric models were defined and the conductance was calculated theoretically in order to correlate the gold and silver NW conductance and structural information (AU)