Measurement of local contact potential difference of atomic scale Au/Si(111)-(7×7) delocalized adsorption state in room-temperature and ultra-high vacuum environment

Hui-Yun Wang,Yan-Jun Li,Zong-Min Ma,Yun-Bo Shi,Jun Liu, ,Xu-Dong Wang,Jie Feng,Huan-Fei Wen,Yang Wen,Jiu-Yan Wei

doi:10.7498/aps.71.20211853

Abstract

The structural properties and local contact potential difference of Au on Si(111)-(7×7) surface are studied by the homemade ultra-high vacuum non-contact Kelvin probe force microscope. Although scanning tunneling microscopy has been widely used to study the metal- adsorbed semiconductor surfaces on an atomic scale, the tunnel current measured by scanning tunneling microscopy is easy to lead the charge states to accidentally switch in the measurement process, and it is limited only to the observation of metal and semiconductor surfaces. Kelvin probe force microscope allows us to directly measure the charges at different positions of various flat surfaces by local contact potential difference on an atomic scale, which has become a more convenient and accurate means of charge characterization. In this paper, the topography and local contact potential difference of Au adsorbed Si(111)-(7×7) surface are measured on an atomic scale by Kelvin probe force microscope at room temperature, and the corresponding adsorption model and first principle calculation are established. The differential charge density distribution of the stable adsorption position of Au/Si(111)-(7×7) is obtained, and the local contact potential energy difference relationship of the stable adsorption position of Au on Si surface is given, The mechanism of charge transfer between Au atom and Si(111)-(7×7) surface during adsorption is analyzed. The experimental results show that at room temperature, single Au atom will form triangular delocalized adsorption state in the half unit cell of Si(111)-(7×7). The delocalized adsorption state is due to the fact that the moving speed of a single Au atom in the HUC is faster than the scanning speed of Kelvin probe force microscope, and the local contact potential difference measurement of Au/Si(111)-(7×7) adsorbed surface can effectively identify Au and Si atoms. Obviously, this research is of great significance in promoting the development of surface charge precision measurement, and is expected to provide some insights into the charge properties of metal adsorbed semiconductor surfaces.

Highlights

由于 KPFM 可以用于亚纳米分辨率成像表面的电位分布,使其成为目前表征纳米结构电学特性的最佳技术。2009 年,Sadewasser S 等人[21]利用低温超高真空(UHV)KPFM 实验和 DFT 计算,通过将 KPFM 和偏置光谱成像与力和偏置距离光谱成像相结合,测量了 Pb 吸附在 Si(111)-(7×7)上的短程相互作用力谱与 LCPD 谱。显示了 Pb 原子 LCPD 的显著下降,这与探针针尖与样品表面不同原子间力的变化有关,由此得出结论,在不同原子位点上 LCPD 的下降是导致 KPFM 和偏置光谱成像中原子识别的原因。
图 4 (a), (b), (c)分别为吸附在 Si(111)-(7×7)表面 Au 原子的 AFM 图像。用探针分别观察到 Si(111)-(7×7)表面上的 Au 原子是较亮的突起。成像参数:悬臂的共振频率f0 = 160.288kHz, 振荡幅值 A = 7nm,悬臂的弹性系数 k=45N/m,在样品上施加的直流偏置电压VBias = 120mV, 恒定频率模式,(a)40×40nm2,设定值⁡∆f⁡= 25Hz;(b)10×10nm2,设定值∆f⁡= 33Hz;(c)5× 5nm2,设定值∆f = 45Hz。 Figure 4 (a), (b), (c) are AFM images of Au atom adsorbed on the surface of Si (111) - (7×7), respectively
Imaging parameters: the resonance frequency of the cantilever is f0 = 160.288kHz, the oscillation amplitude is A = 7nm, the elasticity coefficient of the cantilever is k = 45N/m, the DC bias voltage applied on the sample is VBias = 120mV, constant frequency mode, (a) 40×40nm2, the set point of ∆f = 25Hz; (b)10×10nm2, the set point of ∆f = 33Hz; (c)5×5nm2, the set point of ∆f = 25Hz

Summary

Introduction

由于 KPFM 可以用于亚纳米分辨率成像表面的电位分布,使其成为目前表征纳米结构电学特性的最佳技术。2009 年,Sadewasser S 等人[21]利用低温超高真空(UHV)KPFM 实验和 DFT 计算,通过将 KPFM 和偏置光谱成像与力和偏置距离光谱成像相结合,测量了 Pb 吸附在 Si(111)-(7×7)上的短程相互作用力谱与 LCPD 谱。显示了 Pb 原子 LCPD 的显著下降,这与探针针尖与样品表面不同原子间力的变化有关,由此得出结论,在不同原子位点上 LCPD 的下降是导致 KPFM 和偏置光谱成像中原子识别的原因。. 图 4 (a), (b), (c)分别为吸附在 Si(111)-(7×7)表面 Au 原子的 AFM 图像。用探针分别观察到 Si(111)-(7×7)表面上的 Au 原子是较亮的突起。成像参数:悬臂的共振频率f0 = 160.288kHz, 振荡幅值 A = 7nm,悬臂的弹性系数 k=45N/m,在样品上施加的直流偏置电压VBias = 120mV, 恒定频率模式,(a)40×40nm2,设定值⁡∆f⁡= 25Hz;(b)10×10nm2,设定值∆f⁡= 33Hz;(c)5× 5nm2,设定值∆f = 45Hz。 Figure 4 (a), (b), (c) are AFM images of Au atom adsorbed on the surface of Si (111) - (7×7), respectively.

Results

Conclusion