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.

我们设置了可以在超低温度和高磁场下操作的超高真空扫描隧道显微镜（UHV-STM），并确认它在11T的磁场下在4K下工作。 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比在AU（111）或Cu（111）底物上观察到的要长。 PD层上的较长时期表明PD层上表面状态的能级较高，因此与基板相比，状态中的电子密度较低。表面状态的修饰是通过考虑表面状态的形成机理来解释的，并且归因于以下事实：表面状态的能级位于PD电子状态的L间隙的下边缘下方。对于我们项目的最终目标：表征具有高空间分辨率的STM表面二维电子系统，上述结果是第一步，因为必须降低地面状态的电子密度，以便观察磁场对2D电子系统的影响。我们还观察到对AU（111）表面上的某些吸附物在AU（111）表面上显示出与STM的相反范围的磁性变化。它们在没有磁场下作为亮点出现，但是在高磁场（6T）下，它们显示出与站立波相同振荡的甜甜圈样对比。现在，我们正在尝试通过更受控的实验和与理论组的合作来阐明对比变化的机制。

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。

S.Kurokawa, A.Sakai, Y.Hasegawa: "STM barrier-height imaging of Shockley dislooations on a Au(111) recobstructed 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。