TY  - THES
AB  - A carbon nanosheet is a new type of two-dimensional material that is fabricated by the electron-induced crosslinking of aromatic self-assembled monolayers. A novel bulge test in an atomic force microscope has been used to study the mechanical properties of carbon nanosheets. The elastic behavior was investigated by analyzing the pressure-deflection relationship in the bulge test. Young’s moduli of carbon nanosheets as a function of irradiation electron doses can be determined. With an electron dose above 50 mC/cm2, BPT nanosheets exhibit a stable Young’s modulus ranging from 6 GPa to 8 GPa and NBPT nanosheets ranging from 8 GPa to 10 GPa. CBPS nanosheets have a similar mechanical stiffness which appears to increase slightly at higher electron doses. The residual stresses that have been introduced into carbon nanosheets through the crosslinking and the transferring process are in the range of 40 to 100 MPa. In addition to the adhesion and corrugation of a carbon nanosheet on a SiO2 substrate, the adhesion between an AFM tip and a freestanding nanosheet was also estimated and analyzed.
The viscoelasticity of carbon nanosheets was investigated with hysteresis, creep and stress relaxation being observed. We were able to probe the creep deformation with a strain rate above 1 percent and the resultant creep rates range from 10-6 s-1 to 6×10-6 s-1 with a dependence on stress levels. Recovery after creep unloading has also been demonstrated. The ultimate tensile strength of carbon nanosheets was also determined by performing bulge tests. BPT and NBPT nanosheets have tensile strength ranging from 400 MPa to 700 MPa.
We fabricated multilayer carbon nanosheets and the average Young’s modulus is demonstrated to be very similar to that of the single layer carbon nanosheet. Overlapping reduces the possibility of a rupture of a monolayer because of defects. Therefore it improves the mechanical stability and enhances the yield of suspended multilayer nanosheets in even larger sizes.
The structural transformation of carbon nanosheets upon annealing has been studied by various analytical techniques. From a mechanical point of view, annealing leads to a systematic increase of Young’s moduli with rising temperature, up to 48 GPa at ~1000 K.
Finally, polymer brushes grafted on biphenyl-based nanosheets provided a new class of material termed as "polymer carpet". Both bulge test and nanoindentation were used to characterize the mechanical properties of polymer carpets. The polystyrene carpets experience a decrease in stiffness with decreases of thickness smaller than 20 nm. The polystyrene brush component has a Young’s modulus of ~1.3 GPa for the thinnest polystyrene carpet. With a thicknesses over 30 nm, Young’s moduli range from 3 GPa to 4 GPa.
DA  - 2010
LA  - eng
PY  - 2010
TI  - Mechanical characterization of carbon nanosheets
UR  - https://nbn-resolving.org/urn:nbn:de:hbz:361-18269
Y2  - 2024-11-21T22:26:27
ER  -