鎳矽多層膜的自蔓延反應不穩定性

Abstract

反應性多層膜是由兩放熱反應物以奈米級的厚度交互堆疊至微米級而成的能源材料，藉由瞬間的局部刺激如脈衝雷射，一部分材料會藉由交互擴散來快速釋放儲存的反應熱，並且觸發周圍區域的擴散反應，產生不須氣體參與的自蔓延火焰使整片樣品反應，此種反應具有極高升溫速率(106 K/s)與降溫速率(103 K/s)，一般具有700℃以上峰值溫度、微小的總放熱量以及極快速的自蔓延速度(0.1-100 m/s)，並且產生單相的產物。 然而，在某些具有較低放熱量的材料組合，其中也包含本論文研究之鎳矽多層膜，自蔓延火焰會有不穩定前進的現象，並且由於此現象產生的溫度分布，造成產物的不平整以及多相的產物，本研究藉由磁控濺鍍機以固定鎳矽原子比例為1:1，調變鎳矽雙層厚度的方式交互沉積出鎳矽多層膜，利用高速攝影機、X光繞射儀以及掃描電子顯微鏡、穿透電子顯微鏡等技術，觀察鎳矽多層膜中之反應速率、不穩定蔓延的變化、形成的產物結構、晶相與雙層厚度之關係，並藉由觀察之結果提出反應模型來解釋產物結構的成因，以此推測若要達到平整、單相產物，除了需要使多層膜在反應後均勻的降溫，還需要適當的雙層厚度使反應功率最大化，在本研究中發現若以53 nm之雙層厚度設計製備鎳矽多層膜，能使反應的產物最接近NiSi單相產物。

Reactive multilayers are energetic material composed of nanoscale interlaced exothermic reactants. By a localized heat treatment like pulse laser, a portion of multilayers intermixes and releases latent heat of reaction, which further mixes the adjacent region and generates self-propagating flame without involvement of gas. The reaction features extremely high heating(106 K/s) and quenching rate(103 K/s), temperature generally higher than 700℃, small total amount of heat release and unusual high propagating rate(up to tens of meters per second), furthermore, single phase product in most of material systems. However, in few material systems including Ni/Si with low exothermicity, self-propagating flame propagates in an unsteady manner, resulting rough surface and multi-phase products due to the temperature distribution during reaction. In this thesis, nickel/amorphous-silicon were alternatively sputtered, forming Ni/α-Si reactive multilayers, while keeping the overall atomic ratio 1 Ni to 1 Si. High-speed photography, scanning electron microscope, transmission electron microscope and X-ray diffractometer were utilized to investigate the speed of self-propagating flame, unsteady propagating properties, structure and phase of reaction product with respect to different Ni/α-Si bilayer thickness. By the results of observation, we proposed reaction model to explain the formation of microstructure in Ni/α-Si multilayers. We speculated a uniform quenching process and enhancement of reaction kinetics are prerequisite for flat and single phase products. We found Ni/α-Si multilayers with 53 nm bilayer thickness formed product composed primarily of NiSi.