Charge-induced Expansion And Mechanical Properties Study Of Nanomaterials

Recently mechanical and electrical properties of nanomaterials have attracted widespread attentions.The numberical calculation,theoretical simulation and experimental measurement of those properties for low-dimension materials are among the most important topics in the field of materials science.However,research in these fields is still very rare and diffcult,because of the small size,defects and complex sample preparation.This dissertation focuses on inverstigating the mechanical and electrical properties of nanomaterials,based on novel applications of bright field,phase contrast and surface plasmon resonance microscopy techniques.The main contents are as follows:1.Pauli Repulsion-Induced Expansion and Electromechanical Properties of GrapheneGraphene material shows many attractive properties,but lacks piezoelectric response,which limits its electro-mechanical applications.Charging monolayer graphene should overcome Pauli repulsion effect.At Dirac point,monolayer graphene shows nearly zero density of states.We demonstrate that this phenomenon can result in the expansion of graphene,which can be measured with an optical edge-tracking method.Our observation provides an alternative way to electrically control the dimension of monolayer graphene.It also provides a simple and direct method to measure the elastic properties of graphene and other low dimensional materials.2.Determining Electrochemical Surface Stress of Single Nanowires Electrochemical surface stress plays a key role in nano-materials due to their large surface-to-volume ratios,which lead to unique electromechanical and electrocatalytic properties.However,directly measuring the quantity of single nanomaterial is very challenging.Here we show the experimental determination of the surface stress,and associated electrochemical processes of a single gold nanowire with an optical imaging technique.The applied potential derivative of the surface stress closely resembles the cyclic voltammograms recorded by typical electrochemical method.We describe the reversible observations in terms of anion adsorption and surface oxidation/reduction of single nanowire.This study provides a novel and simple approach to study electrochemical processes and the associated surface stress changes of nanomaterials.3.Measuring Collision Process of NanoparticlesWe apply the surface plasmon resonance microscopy technique to image the collision process between single nanoparticle and substrate.From the observed kinetic process,we could characterize the property of single nanoparticle and measure the interaction between the nanoparticles and Au substrate.This project has great potential in the field of single molecule detection and defects characterization.