拓樸絕緣體近年來成為許多人研究的主力，因為擁有許多舊的材料所沒有的特性，所以近年來大量的研究產生。許多人認為拓樸絕緣體有這很大的應用潛力，因為拓樸絕緣體在理論上會有機會出現無耗散的導電特性，若拿來做成應用將會是非常受到歡迎的材料。
有許多研究著重於不同比例和元素的摻雜，也有許多研究著重於不同層之間的交互作用，而在不同層之間的需要先克服一個問題--厚度，先解決厚度的問題才有辦法往下做更精確的調控或是原件上的製作，以達到最好的電或磁性效果。
本實驗樣品是透過分子束磊晶成長的拓樸絕緣體，在經過厚度的調整後，發現經過磁性摻雜後的拓樸絕緣體在8~10奈米左右會有最佳的電性，而若是降到低溫則電性表現會更加良好，此外，我們也在四元樣品中改變Sb比例，利用超導量子干涉儀看樣品的磁性貢獻，發現Sb在某一個比例時，會有最大的磁性貢獻效果，若是將此一比例繼續延用至厚度改變上，相信會有著更多的磁性特性出現。

Topological insulator is a kind of new material which attracted a lot of research devoted in it. The reason that caused so many research focus on it is its special transport property. We can tune its fermi level by varying the thickness so that the fermi level lies in the band gap, and it can prevent our measurement being affected by the bulk conduction band. In our experiment, all the films are grown by molecular beam epitaxy (MBE) which is an ultra-high vacuum epitaxy equipment. We use sapphire as our substrate. By varying the thickness of magnetic doping films, the resistance of Cr-doped (Bi, Sb)2Se3 topological insulators are larger in the thicker sample. But the carrier density has the minimum at the thickness around 8 nm. Besides, we found that the magnetization will be affected by the doping quantity of Sb. In the measurement by SQUID, there is a specific Sb/Bi ratio that we can observe the greatest magnetization. No matter raising or lowering the portion of Sb, the magnetization will become less. The temperature will also change the carrier density. At temperature of 17K, the carrier density is even lower, and the trend of different thickness remains the same. The lowest carrier density is still at around 8 nm.

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