X光廣角入射波導管之波導干涉

Guiding and interference effects of wide-angle X-ray incident waveguide

黃志仁(Chih-Jen Huang)

指導教授 ： 張石麟

國立清華大學/理學院/物理學系/碩士(2009年)

摘要

本論文主要是探究X光廣角入射奈米級波導管之波導干涉現象。透過實驗上的量測，我們發現X光在經過波導管時，能量以幾乎不衰減的方式傳遞。同時波導管還可以導引X光的方向，我們稱之為導引效應。然而當X光在行經波導管後，我們觀察在2θ方向的強度分佈圖，似乎是由不同模式的繞射光所干涉而成。
此次實驗不同於許多文獻中所使用的以掠角(小角度)方式入射波導管，而是使用廣角(大角度)入射的方式。為了採取廣角的方式入射波導管，我們選取了8.8785keV的X光來入射波導管內的矽(113)原子面，當符合繞射定律時，此時即會產生表面繞射光，且知波導管設計於矽的表面上，因此這繞射光即是入射波導管的光源。至於波導管的設計，我們是採用晶向為[001]且厚度為675um 的6吋矽晶圓(Si)當基底，而設計的波導管是沿著[110]方向。波導管的長度為5mm，寬度分別是700nm、450nm、400nm、350nm的四根波導管，而高度的控制是委請國家奈米元件實驗室(NDL)工程師在波導管以外的區域往下蝕刻1μm。最後我們在波導管的上、左、右三面鍍上150nm的金(Au)、下方鍍上300nm的金(Au)。
理論分析的部份，是採取以直角座標系所描述的動力繞射理論。當入射光以符合矽(113)原子面的布拉格角入射矽(Si)時，以產生兩光(two-beam)繞射的情形來看，晶體內部會被激發出8個模式(modes)的繞射光。此8個模式(modes)的繞射光之波向量若與矽-金界面的夾角小於0.460時，則會在波導管內產生全反射，而不會穿透波導管，所以此八個模式(modes)的繞射光較為容易彼此產生干涉，而導致在2θ方向的強度產生振盪。依據這樣的理論基礎下，我們計算出在2θ方向上的強度分佈，此結果近似於實驗的結果。

關鍵字

廣角入射 ； 波導 ； 干涉

並列摘要

This work reports mainly on the diffraction phenomena of X-rays in nano-scale waveguides in wide-angle incidence geometry. Through measurements we find that X-ray beam passing through a waveguide is guided along the waveguide without energy loss. We also observe that interference among different modes of wave propagation gives rise to intensity undulation in the transverse 2θ scan.
This type of wave guides is different from the conventional types where grazing incidence or normal incidence of X-rays is adopted. In order to bend a wide-angle incident beam along the crystal surface, the (113) reflection of silicon at the 8.8785keV is used. The wave guides are prepared on a [001] Si wafer of 6 inches in diameter and 675 um in thickness. The designed waveguides are along [110] direction. The sizes of the waveguides are 5mm long and 700, 450, 400, and 350nm wide, respectively. The sample wave guides are prepared at the National Nano Device Laboratories (NDL) by etching the Si wafer by 1um in depth. The waveguides are then plated with gold for about 150nm in thickness on the top, the left and right surface and 300nm for the bottom surface.
We adopt the dynamical theory of X-ray diffraction in a Cartesian system of coordinates to carry out theoretical calculations. For the (113) surface diffraction, the incident X-ray beam excites eight modes of wave-propagation, thus some of generating eight diffracted beams nearly parallel to the crystal surface. If the angles between the wavevectors of these eight modes and the Si-Au interface are less than 0.460 , then total external reflection takes place for these eight diffracted beams. The interference among the eight diffracted beams results in intensity undulation along 2θ direction. This is in good agreement with the experimental result.

並列關鍵字

wide-angle incident ； waveguide ； interference

參考文獻

[11] 顏銘裕(2008) , 廣角入射X光波導管之X光干涉效應 ,國立清華大學碩士論文

[12] 邱茂森(2008) , X光共振腔之24光動力繞射計算 ,國立清華大學博士論文

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