MFM and gas adsorption isotherm analysis of proton beam irradiated multi-walled carbon nanotubes.

To enhance the gas adsorption properties and modify the physical properties of carbon nanotubes, multi-walled carbon nanotubes (MWCNTs) were irradiated by high-energy proton beams, and the physical properties including morphology and local surface structure were investigated by using a transmission electron microscope (TEM), magnetic force microscope (MFM) and a gas adsorption isotherm apparatus which can deeply probe the fine structure of surface. Interestingly, clearer MFM images were obtained from the proton irradiated samples which supports that carbon exhibits magnetism under proton bombardments, although the intrinsic magnetic property is not understood. The layering properties of argon on MWCNTs were measured from 59 to 69 K and the interaction of argon on the surface was analyzed. The calculated values of isosteric heat of adsorption demonstrated that higher interaction of gas molecules with surface is found from the proton irradiated MWCNTs. This result strongly supports that the local surface modification, partial defects, for example, were created due to the external high energy impacts. Our results are worthy to note that gas adsorption technique can provide the fine atomic resolution which beyond the one of TEM and MFM.

Surface characterization of carbon nanotubes irradiated by electron beam.

Multiwalled carbon nanotubes (MWCNTs) were irradiated by high-energy electron beams with different dosing amounts, and the physical properties including morphology and local surface structure were investigated by using a gas adsorption isotherm apparatus. The layering properties of argon on MWCNTs were measured from 65 to 80 K, and the interaction of argon on the surface was analyzed. Little change of surface structure between unirradiated and irradiated MWCNT samples was found. Interestingly, broader isotherm steps from the electron beam irradiated samples were found, although the amount of gas molecules forming the first atomic layer remains the same for the samples before and after irradiating the beams. This observation was supported by calculated values of the two-dimensional compressibility. Our combined results suggest that dosing of the electron beam on the carbon nanotubes induced the local surface defects, while no structural modification occurs.