Study on True Atomic Resolution Imaging Using Noncontact Atomic Force Microscopy

1)利用原子力显微镜（AFM）在超高真空（UHV）中以非接触方式工作，观察了InP（110）1 × 1和GaAs（110）表面。包括原子尺度点缺陷的矩形晶格已被清楚地和可重复地解决。这些结果表明，非接触式超高真空原子力显微镜具有真正的原子尺度横向分辨能力，是真实的空间中原子表面结构分析的有效手段。2）比较了非接触式原子力显微镜中的恒定振动模式和恒定激励模式，研究了针尖与表面之间的力相互作用。当针尖接触表面时，由于悬臂梁振动幅度的减小，在等幅激励模式下排斥力相互作用减弱，而在等幅激励模式下排斥力相互作用保持不变。3）利用原子力显微镜（AFM）在超高真空（UHV）中以非接触方式工作，观察了Si（111）7*7表面的反应性。在7*7重构表面上发现了单个吸附原子和角孔，这些吸附原子可以用DAS模型描述，也可以用缺失的吸附原子来描述。4）发现了反应性Si（111）7*7重构表面上力梯度曲线的不连续性。在不连续的情况下获得强对比度，而在不连续的情况下获得弱对比度。因此，由于力梯度曲线的不连续性的存在，图像对比度急剧增加。力梯度曲线的不连续性可以用物理键和化学键相互作用之间的交叉来解释。

1) With an atomic force microscope (AFM) operating in the noncontact mode in an ultrahigh vacuum (UHV), the InP (110) 1x1 and GaAs (110) surfaces were observed. Rectangle lattice including the atomic-scale point defects have been clearly and reproducibly resolved. These results clearly show that the noncontact UHV AFM has true atomic-scale lateral resolution and is quite effective for atomic surface structure analysis in real space.2) The constant vibration mode and the constant excitation mode in noncontact atomic force microscopy were compared to investigate the force interaction between tip and surface. When the tip touch the surface, the repulsive force interaction is weakened in the constant excitation mode because of the decrease of the vibration amplitude of the cantilever, while it is maintained in the constant amplitude mode. This means that the constant excitation mode is much more gentle than the constant vibration mode.3) With an atomic force microscope (AFM) operating in the noncontact mode in an ultrahigh vacuum (UHV), the reactive Si (111) 7*7 surface was observed. The individual adatoms and the corner holes in the 7*7 reconstruction, described by the dimer-adatom-stacking fault (DAS) model and also missing adatoms, can be observed.4) We found the discontinuity of the force gradient curve on reactive Si (111) 7*7 reconstructed surface. A strong contrast has been obtained with discontinuity, while weak contrast has been obtained without discontinuity. Thus, the image contrast is drastically increased by the presence of the discontinuity of the force gradient curve. The discontinuity of the force gradient curve can be explained by the crossover between the physical and chemical bonding interaction.