nano-scale real-space observation of surface two-dimensional electron system under ultra-low temperature and magnetic field

超低温磁场下表面二维电子系统纳米级实空间观测

• 批准号: 12450020
• 负责人: HASEGAWA Yukio
• 金额: $ 9.15万
• 依托单位: The University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2001
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12450020/
• 关键词: scanning tunneling microscopy; electron standing waves; surface states; two-dimensional electronic states; 表面電子状態; 2次元電子系

We set up ultrahigh vacuum scanning tunneling microscope (UHV-STM) which can be operated under ultra-low temperature and high magnetic field, and confirmed that it works at 4K under a magnetic field of 11T. Using the instrument, we were successfully able to take images of standing wave pattern spreading in several hundred angstrom on Au(111) and Cu(111) surfaces.We observed standing wave images on Pd/Au(111) and Pd/Cu(111) surfaces, trying to find a method to control and reduce electron density occupied in the surface electronic states, and found that a period of electron standing waves observed on monolayer-high Pd thin film is longer than those observed on Au(111) or Cu(111) substrate. The longer period on Pd layers indicates higher energy level of the surface states on the Pd layer, and thus lower electron density in the states than the substrates. The modification of the surface states is explained by considering a formation mechanism of the surface states, and is attributed to the fact that an energy level of the surface states is located just below the lower edge of the L gap of Pd electronic states. For the final goal of our project: characterization of surface two-dimensional electron system with STM in high spatial resolution, the above result is a first step since electron density in the surface states has to be reduced in order to observe effects of magnetic field to the 2D electron system.We also observed some adsorbates on the Au(111) surface which show contrast variation in STM with a amount of magnetic field. They appear as a bright spot under no magnetic field, but at high magnetic field (6T) they show a donut-like contrast with a same period of oscillation with the standing waves. We are now trying to elucidate a mechanism of the contrast variation through more controlled experiments and a collaboration with a theoretical group.

建立了可在超低温和强磁场下工作的超高真空扫描隧道显微镜（UHV-STM），并证实其工作温度为4K，磁场强度为11 T。利用该仪器，我们成功地拍摄到了Au（111）和Cu（111）表面上几百埃范围内的驻波图像，并在Pd/Au（111）和Pd/Cu（111）表面上观察到了驻波图像，试图找到一种控制和降低占据表面电子态的电子密度的方法，并且发现在单层高Pd薄膜上观察到的电子驻波的周期比在Au（111）或Cu（111）衬底上观察到的电子驻波的周期长。Pd层上的较长周期表明Pd层上的表面态的能级较高，并且因此状态中的电子密度比衬底低。表面态的改性是通过考虑表面态的形成机制来解释的，并且归因于表面态的能级恰好位于Pd电子态的L能隙的下边缘之下的事实。为了实现我们的最终目标：利用STM高空间分辨率表征表面二维电子系统，上述结果是第一步，因为为了观察磁场对二维电子系统的影响，必须降低表面态的电子密度，我们还观察到了Au（111）表面上的一些吸附物，它们在STM中显示出随磁场大小的对比度变化。它们在无磁场下表现为亮点，但在高磁场（6 T）下，它们表现出与驻波相同周期振荡的甜甜圈状对比。我们现在正试图通过更多的控制实验和与理论小组的合作来阐明对比度变化的机制。

项目成果

T. Suzuki, Y. Hasegawa, et al: "Electron standing-wave observation in the Pd overlayer on Au(111) and Cu(111) surface by STJM"Physical Review. B64. 081403R (2001)

T. Suzuki、Y. Hasekawa 等人：“STJM 在 Au(111) 和 Cu(111) 表面 Pd 覆盖层中的电子驻波观测”物理评论。

S.Kurokawa, A.Sakai, Y.Hasegawa: "STM barrier-height imaging of Shockley dislocations on a Au(111) reconstructed surface"Japanese Journal of Applied Physics. 40. 4277-4280 (2001)

S.Kurokawa、A.Sakai、Y.Hasekawa：“Au(111) 重建表面上肖克利位错的 STM 势垒高度成像”日本应用物理学杂志。

Y. Hasegawa, T. Suzuki, and T. Sakurai: "Modification of electron density in surface states"Surface Science. (to be published).

Y. Hasekawa、T. Suzuki 和 T. Sakurai：“表面态电子密度的修改”表面科学。

S. Kurokawa, A. Sakai, and Y. Hasegawa: "STM barrier-height imaging of Shockley dislocations on a Au(111) reconstructed surface"Japanese Journal of Applied Physics. 40. 4277-4280 (2001)

S. Kurokawa、A. Sakai 和 Y. Hasekawa：“Au(111) 重建表面上肖克利位错的 STM 势垒高度成像”日本应用物理学杂志。

T.Suzuki, Y, Hasegawa, et al.: "Electron standing-wave observation in the Pd overlayer on Au(111) and Cu(111) surface by STM"Physical Review. B64. 081403R1-081403R4 (2001)

T.Suzuki, Y, Hasekawa, et al.：“通过 STM 对 Au(111) 和 Cu(111) 表面 Pd 覆盖层中的电子驻波进行观察”物理评论。