1. TR-TUNA mode of AFM application in soft materials’ conductivity measurement
Wei Wang,1 Dong Xiao Niu,2 Xinju Yang1
1Phys. Dept., Fudan Univ., Shanghai, People’s Republic of China
2Shanghai Institute of Applied Physics, Chinese Academy of Science
The investigation of the electrical response of nanostructures to external stimuli is important for many fields in nanoscience and molecular biology. Due to the strong interaction between tip and sample, only when the tested material have stable surface then traditional AFM mode can get its conductive proprieties. Here a gentle method that combines torsion mode topography imaging with conductive scanning force microscopy which named TR-TUNA mode is presented. By applying an electrical bias voltage between tip and sample surface, changes in the local sample conductivity can be mapped. The topography and local conductivity variations on some fragile samples were investigated.
I. Measurement principle
1. (a)The cantilever is excited at its torsional resonance frequency by two piezoelectric elements attached to the holder.
(b)The cantilever undergoes a combination of torsion and lateral bending.
2. In TR-TUNA mode, a bias voltage (Us) is applied to the sample and the tip sample current is measured (Itip).
1. Schematic diagram of TR mode.
2. Schematic diagram of TR-TUNA mode.
IV. Application 2 –fractal growth polypeptide and ionic liquids mixed
II. Sample preparation
The graphite we used as electrode in our experiment, and the height of its thinnest part is about several nanometers.
The tested sample we used includes DNA, metallic DNA, polypeptide, graphene and etc. .
Schematic diagram of sample preparation
I-V curve of ionic liquids
TR Height image
III. Application 1 -- graphene
TR Current image
TR Phase image
I-V curve of polypeptide
TR Height image
TR Current image
V. Conclusions
As a novel application of AFM, TR-TUNA mode can present local conductivity and topography imaging of fragile nanostructures simultaneously without mechanical damage. Combined with thin graphite electrode technique, conductivity prosperities of soft materials such as graphene and polypeptide were measured.