單晶鎳矽化物奈米線之合成與特性分析

Abstract

由於半導體產業當中電子元件的尺寸日益縮小，為了克服奈米尺度下的特殊性質變化，低維度奈米材料如奈米管、奈米線等，因為具有特殊物理以及化學性質，而逐漸受到重視。本研究採用熱蒸鍍法，使用氯化鎳作為前驅物，並控制水平三區加熱式爐管中的各項參數如溫度、腔體壓力、成長時間與載流氣體流量等，合成單晶鎳矽化物奈米線。藉由改變試片所在溫區(750℃、800℃與850℃)，成功合成出相對應Ni31Si12、Ni3Si、Ni2Si等相，並探討各個不同參數下所成長鎳化矽奈米線所展現的表面形貌，找出最適成長參數。並根據上述結果，討論鎳矽化物奈米線的成長機制，是藉由V-S(Vapor-Solid)機制所成長。三種不同相之奈米線進行電子、磁性與場發射性質的量測，在電性量測結果顯示，Ni31Si12與Ni2Si奈米線相對應的電阻率為61μΩcm與130μΩcm。場發特性量測結果顯示Ni2Si、Ni3Si與Ni31Si12相的奈米線為高度場發射特性的材料，增強因子(enhancement factor, β)分別可達1132、951與1172，起始電場分別為4.2 V/μm、4.12 V/μm與3.39V/μm。最後，在磁性量測結果當中，三者皆展示出了典型鐵磁性材料的特性，Ni2Si、Ni3Si、Ni31Si12奈米線分別經由計算後，低溫下(2K)單位體積飽和率可分別高達2.28 emu/cm3、3.68 emu/cm3與12.8emu/cm3，矯頑磁場分別為409 oe、1015 oe與169.5 oe。Ni3Si擁有最大矯頑場，是由於其不同晶格結構所造成磁性空間異相性(magnetic anisotropy)。立方晶系的Ni3Si磁軸方向向量與外加磁場方向(垂直基板)最為接近，因此擁有最高矯頑磁場。Ni31Si12擁有三者之中最大飽和磁化率，推測是由於晶格結構與單位晶格當中鎳原子所占百分比不同，造成單位體積飽和磁化率的差異。

Nano-scaled and one-dimensional materials have been widely studied for the past decades. Transition-metal silicide nanowires are the extremely broad set of refractory materials and were widely researched for their unique physical properties including low resistivity, and excellent compatibility with contemporary silicon device processing. Here, we report the synthesis of single-crystalline nickel silicide nanowires (NWs) with high-yield and high aspect ratio (~100) by chemical vapor deposition (CVD) methods. By altering growth parameters such as temperature and chamber pressure, we can synthesize the phase Ni2Si, Ni3Si and Ni31Si12 NWs under 750℃, 800℃ and 850℃, respectively. By altering various parameters such as pressure, time and carrier gas flow, we can control the morphology of the NWs. The plausible growth mechanism of the Ni2Si NWs has been also discussed in this work. Furthermore, the resistivity of Ni31Si12 and Ni2Si NWs are 61μΩcm and 130μΩcm, respectively. In field emission property measurements, we found that Ni2Si, Ni3Si and Ni31Si12 NWs were suitable materials for field emission which with high enhancement factors of 1132, 1172 and 951, and small values of turn-on field of 4.2V/μm, 3.39 V/μm and 4.12V/μm, respectively. The SQUID measurements were demonstrated at 300K and 2K and all three phases showed classic ferromagnetism property. Due to the magnetic anisotropy, Ni3Si (cubic system) represented a larger coercivity (Hc, oe) than the other two phases (hexagonal system). While Ni31Si12 NWs showed biggest magnetization per unit volume(Ms, emu/cm3) among the three phases and this might be caused by the two reasons: (1) configurations (cubic and hexagonal) and (2) higher Ni atoms ratios in the unit cell compared to Ni2Si.