Kawagishi Takayoshi, Kato Atsushi, Hoshi Yasuo, Kawakatsu Hideki
Institute of Industrial Science, University of Tokyo, Japan.
Ultramicroscopy. 2002 May;91(1-4):37-48. doi: 10.1016/s0304-3991(02)00080-3.
Lateral vibration of the tip in atomic force microscopy was mapped at the torsional resonance of the cantilever by attaching a shear piezo element at the base of the cantilever or under the sample. Fixed frequency excitation and self-excitation of torsional motion were implemented. The lateral vibration utilized as measured by an optical lever was in the order of 10 pm to 3 nm, and its frequency approximately 450 kHz for a contact-mode silicon nitride cantilever. The amplitude and phase of the torsional motion of the cantilever was measured by a lock-in-amplifier or a rectifier and plotted in x and y as the sample was raster scanned. The imaging technique gave contrast between graphite terraces, self-assembled monolayer domains, silicon and silicon dioxide, graphite and mica. Changing contrast was observed as silicon islands oxidized in atmosphere, showing that the imaging technique can detect change in lateral tip mobility due to changes occurring near the surface. Torsional self-excitation showed nanometric features of self-assembled monolayer islands due to different lateral dissipation. Dependence of torsional resonance frequency on excitation amplitude, and contrast change due to driving frequency around resonance were observed.
在原子力显微镜中，通过在悬臂梁底部或样品下方附着一个剪切压电元件，在悬臂梁的扭转共振频率下对针尖的横向振动进行映射。实现了扭转运动的固定频率激励和自激。通过光杠杆测量得到的横向振动幅度在10皮米到3纳米之间，对于接触模式的氮化硅悬臂梁，其频率约为450千赫兹。在对样品进行光栅扫描时，通过锁相放大器或整流器测量悬臂梁扭转运动的幅度和相位，并在x和y方向上绘制出来。该成像技术能够区分石墨平台、自组装单分子层区域、硅和二氧化硅、石墨和云母。当硅岛在大气中氧化时，观察到对比度发生变化，这表明该成像技术能够检测到由于表面附近发生的变化而导致的针尖横向移动性的改变。由于不同的横向耗散，扭转自激显示出自组装单分子层岛的纳米级特征。观察到扭转共振频率对激励幅度的依赖性，以及在共振附近由于驱动频率引起的对比度变化。
