Department of Materials Science, Graduate School of Saitama Institute of Technology, 1690 Fusaiji, Fukaya-city, Saitama 369-0293, Japan.
J Phys Condens Matter. 2011 Feb 2;23(4):045008. doi: 10.1088/0953-8984/23/4/045008. Epub 2011 Jan 7.
To elucidate electron states confined within steps on metal surfaces, we demonstrated a new point of view that a linear step on a noble metal surface can be treated as a dipole potential composed of delta functions. For an electron confined by two pairs of dipole potentials, we derived quasi-stationary eigenstates whose eigenenergies are complex numbers which lead to the lifetime of the electron. To derive the local density of states (LDOS), scanning tunneling microscopy (STM) images and scanning tunneling spectra (STS) for stepped surfaces, we incorporated the lifetime effect on them and clarified the relation between the LDOS and the STM current by applying the expression for the STM current derived by Selloni et al (1985 Phys. Rev. B 31 2602). Although, in previous studies, the Fabry-Pérot interference mechanism has been used to explain electron states confined within two steps, it requires four fitting parameters, in contrast our method requires one fitting parameter which specifies the height of the delta functions. Our results for LDOS images, topographical images and STS are consistent with experimental ones for both the cases where electrons stay on a terrace confined by two steps and on a wide terrace outside the step, which confirms the validity of our model.
为了阐明金属表面台阶上受限的电子态，我们提出了一种新观点，即将贵金属表面上的线性台阶视为由δ函数组成的偶极势。对于被两对偶极势限制的电子，我们推导出了准稳态本征态，其本征能是复数，导致电子的寿命。为了推导台阶表面的局域态密度（LDOS）、扫描隧道显微镜（STM）图像和扫描隧道谱（STS），我们将寿命效应纳入其中，并通过应用 Selloni 等人（1985 年 Phys. Rev. B 31 2602）推导出的 STS 电流表达式来阐明 LDOS 和 STS 电流之间的关系。尽管在以前的研究中，已经使用法布里-珀罗干涉机制来解释局限在两个台阶内的电子态，但它需要四个拟合参数，而我们的方法只需要一个拟合参数来指定δ函数的高度。我们对 LDOS 图像、形貌图像和 STS 的结果与电子停留在由两个台阶限制的平台上和台阶外的宽平台上的实验结果一致，这证实了我们模型的有效性。
