Study On Mechanical And Electrical Properties Of Materials Surface On Nano-Scale Using Atomic Force Microscopy

Besides the ability to obtain topographical image on atomic scale, atomic force microscopy (AFM) can also carry through local processing and study the local physical characteristics on nano-scale. Therefore, AFM is becoming one of the most useful tools to study the surface characteristics in nano-scale region. In this paper, the above functions were used to study the mechanical properties of carbon-carbon (C-C) sp~2 bonded network under outside force and the electric characteristics near conductor surface.Carbon nanotubes (CNTs) have received significant attention since their discovery due to the measured and theoretically predicted impressive mechanical properties. Its strength is 100 times higher than steel, but its weight is just one-sixth of the steel. And also its plasticity and toughness are very excellent. So it was considered to be used as super fiber material in the future. CNTs can be seen as graphene sheet wrapped into cylinders with its diameter being just several nanometers. Thus the graphene sheet has the very similar mechanical properties with CNTs. The graphene sheet is constructed by carbon-carbon (C-C) sp~2 bonded network. So the study of mechanical properties on C-C sp~2 bonded network under outside force would be of great importantance to study the mechanical properties of CNTs. In this paper, it is found that the C-C sp~2 bonded network can only be torn and folded along symmetrical axis under the outside force. But when the directions of the force and tearing are different, the tearing might not be along the symmetrical axis on macro-scale. However, on micro-scale, the tearing is along a zigzag way, a mixture of different symmetrical directions. And when the outside force is large enough, the torn sheet might be deformed plasticallyThe second part of this paper is to study the electron standing waves between the conductive probe and conductor sample using AFM. Up to now, there have been many studies on electron standing waves through the oscillation of the differential conductance spectra versus the applied bias voltage under constant tunneling current using scanning tunneling microscopy. But all these works did not study the electron standing wave through observation of the oscillation of I-V curve. So our works open a new way in this region. Using this method, the value of work function and the electrode separation can be calculated.The third part of this paper is the study on the potential barrier outside the surface of a conductor. Conductor is a fundamental material in the nature. The knowledge about materials is mainly based on the theory about conductor. So any further understanding of the conductor would be of great importantance for solid-state physics and materials science. In this paper, through the experimental study on the tunneling current between the conductive probe and layered graphite sample, we proposed that conductor should be a"potential cup"rather than a"potential well", which is commonly accepted for more than one century. This conclusion would have great influence on solid-state physics, materials science and semiconductor physics.