Park Jeong Young, Qi Yabing, Ratera Imma, Salmeron M
Materials Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, USA.
J Chem Phys. 2008 Jun 21;128(23):234701. doi: 10.1063/1.2938085.
The mechanical interaction between a scanning tunneling microscopy (STM) probe and hexadecane (C16) alkylthiol molecules in a self-assembled monolayer was investigated by sensing the force during constant current mode STM imaging. The force regime changed from attractive to repulsive over the insulating molecule islands under feedback control of the current. The repulsive force on the molecule was strongly dependent on the setpoint value of the current during STM operation. In our experiments, the threshold for contact was found at a tunneling current of 1 pA when the sample bias is 2 V. At higher current, the apparent height of molecular islands changed logarithmically with current. In addition, the current as a function of applied load revealed a stepwise increase, indicative of discrete molecular tilting events. A tunneling decay constant beta of =0.53+/-0.02 A(-1) was obtained based on the measurement of the height of molecules and the tunneling current.
通过在恒流模式扫描隧道显微镜（STM）成像过程中感应力，研究了STM探针与自组装单分子层中的十六烷（C16）烷基硫醇分子之间的机械相互作用。在电流的反馈控制下，力的状态在绝缘分子岛上方从吸引力变为排斥力。在STM操作期间，分子上的排斥力强烈依赖于电流的设定值。在我们的实验中，当样品偏压为2 V时，在1 pA的隧穿电流下发现了接触阈值。在更高的电流下，分子岛的表观高度随电流呈对数变化。此外，电流作为施加负载的函数显示出逐步增加，表明存在离散的分子倾斜事件。基于对分子高度和隧穿电流的测量，获得了隧穿衰减常数β = 0.53±0.02 Å⁻¹ 。
