矽奈米線之Ｘ光非對稱表面繞射研究

國立清華大學物理系碩士學位論文
題目：矽奈米線之Ｘ光非對稱表面繞射研究
學生：林家正
指導教授：張石麟

摘要

　　本文嘗試於厚度為675μm，表面晶向為[ 0 0 1 ]之6吋矽單晶表面蝕刻出長4mm，高1μm，寬350nm至20um之奈米級線型結構，並於其矽單晶上下被覆厚 150nm之金薄膜。並以光子能量為8.8785kev，由（1 1 3）原子面形成之表面繞射光入射前述之覆金矽奈米線結構。
　　
　　實驗上，我們證實了Ｘ光之能夠被矽奈米線之左右金薄膜邊界來回反射，使Ｘ光只能行走於矽奈米線中，顯示此種結構對於Ｘ光具有波導效應的潛力。可惜Ｘ光於矽中行走時，由於矽對於Ｘ光之吸收率過大因此（1 1 3）繞射光之強度有過於微弱之缺點。
　　
　　另外，當貼近於晶體表面的（1 1 3）繞射光於矽奈米線之結構穿出時，實驗上可以觀察到其繞射峰之波形具有不對稱性。利用直角座標之動力繞射理論（Stetsko & Chang ,1997）分析電場於矽晶體內部的行為模式後，推測此不對稱性乃肇因於不同模式之繞射光於晶體表面之電場互相疊加和相互干涉的結果。
　　
　　不僅如此，於實驗中還可觀測到Ｘ光繞射峰之峰型具有類似於光學中之單狹縫繞射光的週期性震盪現象。承上之分析，亦可推論出其原因乃為晶體中洽有一模式之繞射光，因其隨晶體深度之吸收效應較不明顯，以至於波長約為1之Ｘ繞射光能於高1μm之奈米線側面形成單狹縫繞射現象。

ABSTRACT
Asymmetric Surface X-Ray Diffraction of Nanometer Silicon Lines

Chia-Cheng Lin, Advisor : Professor Shih-Lin Chang
Master of Physics,
National Tsing Hua University, Taiwan, Republic of China

This work aims to develop a kind of nanometer silicon lines which allow wide-angle incident X-rays to propagate in a special direction, say the [113] of Si, the so-called waveguiding effect. Moreover, this nanometer silicon line can be used to exhibit the single-slit diffraction phenomenon and multiple-mode interference of the ( 1 1 3 ) dynamical diffraction.

Nanometer silicon lines about 1μm high, 4mm long along [110], and 350nm to 20um wide were prepared by the Nano Device Laboratory (NDL) on a 4 inches silicon [001] waver. The lines were then covered by 150nm thick gold film. The ( 113 ) diffraction beam propagates along the surface of the waver at the photon energy 8.8785kev. The propagation direction is also along the [110].

The diffraction experiments show that X-rays can be guided within the nanometer silicon lines, but with a very low guiding efficiency due to crystal absorption. Most importantly, the single-slit diffraction phenomenon and multiple-mode interference of the (113) reflection are clearly observed. The dynamical theory of X-ray diffraction in the Cartesian coordinate representation is employed to analyze the X-ray wavefield in the silicon crystal and to account for the interference phenomenon.

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