利用掃描穿隧電子顯微鏡觀察錳薄膜在銅三金上的表面形貌、磁性及電子結構

Abstract

根據之前在鐵/錳/銅三金(100)上的實驗結果，該系統表現出交換偏耦合的行為。 為了更加深入了解這個系統，我們利用掃描穿隧電子顯微鏡解析錳在銅三金(100)上的表面結構、電子結構以及磁性結構。在銅三金(100)的表面上，我們量測穿隧電流對偏壓的微分曲線(dI/dU)以了解其不同能量下的態密度。在特定偏壓下(1.27 V)我們發現該曲線有特徵的尖峰，從該尖峰的大小在空間中的分佈情形，我們可以觀察到拼圖狀的圖形，並且發現在拼圖形狀的邊界上其態密度較其他區域為低。利用原子解析的影像，我們發現這些拼圖狀的邊界直接對應到表面不同結構之間的邊界。 關於錳在銅三金(100)上，我們觀察了二十一層原子層厚的錳薄膜以及較薄的薄膜。在二十一層的錳薄膜上我們利用自旋解析掃描穿隧電子顯微鏡觀察到錳薄膜有反鐵磁的對比訊號，更進一步的分析推測錳表面的磁結構應該是具有未抵消的磁性。我們也量測錳薄膜上穿隧電流對偏壓的微分曲線，在七層半及二十一層的錳薄膜上我們發現了相似的特徵。

In previous experiments, Fe/Mn/Cu3Au(100) was fabricated and characterized as an exchange bias system. In order to understand this system further, the electronic and magnetic structure of Mn/Cu3Au(100) are of crucial importance. Therefore, in this thesis, the studies of Cu3Au(100) and Mn/Cu3Au(100) by scanning tunneling microscopy (STM) and spectroscopy (STS) are presented. On the surface of Cu3Au(100), tunneling spectra were measured and a characteristic peak around 1.27 V was observed. Conductance mapping (dI/dU) at this voltage shows puzzle-like patterns, and the density of states is observed to be lower on their boundaries. Topography with atomic resolution directly points out those as structural antipahse domain boundaries (APB) for the c(2x2) ordering. The results on Mn/Cu3Au(100) films are categorized into two parts. The first part is concerning the electronic and magnetic structure of thick Mn film (21 ML) deposited at room temperature, which is observed to have inplane spin contrast at room temperature by ring-type spin-polarized STM. Analyses dealing with the correlation between relative height and relative spin signal suggest uncompensated antiferromagnetism. We also investigated its electronic structure by STS at 4.7 K, which reveals feature near Fermi level. In the second part, the thinner Mn films, ranged from submonolayer to 7.5 ML, were deposited on Cu3Au(100) and experiments on STS were performed, which reveals feature on the 7.5 ML Mn.