合成與鑑定一維半導體奈米結構：矽奈米線、二氧化矽奈米管、二氧化錫奈米帶及銅銦化二硒奈米棒

Abstract

由於奈米科技的精進，使得製備奈米等級之材料技術得以成長與更形完備，也更具有不同維度及尺寸上之變化。在本論文中，藉由不同之物理或化學合成方式，能夠合成出不同半導體材料之一維奈米結構，包含有單晶矽奈米線、非晶系二氧化矽奈米管、單晶二氧化錫奈米帶以及單晶銅銦化二硒奈米棒。 以微米尺寸之矽粉末，混合金屬或者二氧化矽粉末作為催化劑，並輔佐以雷射剝蝕法（laser ablation）的技術，可以合成具有直徑尺寸5-40奈米、長度可達數十微米之單晶矽奈米線。當金屬催化劑（在此以鐵、釕及鐠等金屬）使用來製備單晶矽奈米線時，矽的{111}晶面由於能量最穩定而生長出來，且奈米線會沿著與晶面平行之<111>方向而成長。這樣的矽奈米線，是依循著氣液固法（vapor-liquid-solid，VLS）之生長機制而得到；相對而言，以二氧化矽做為催化劑時，矽的{111}晶面仍會生長，但奈米線生長方向則為<112>，也就是奈米線生長方向與晶面生長方向呈現垂直的現象，可歸類於利用氧化物輔助（oxide-assisted，OA）生長機制進行催化後所生成之矽奈米線。之外，由於合成時所使用壓力不同，可以發現隨著壓力增大，奈米線的直徑會增加，但長度則會縮短。利用拉曼光譜的技術，可以用來測量不同尺寸之矽奈米線其最強之聲子F2g mode的峰值與所產生的紅位移（red shift）現象。在塊材中之F2g mode的峰值約為520 cm-1，但隨著矽奈米線之直徑不斷縮小的情況下，此一侷限效應導致峰值產生紅位移至約505 cm-1，同時峰之半高寬（full-width at half maximum）也隨著直徑變小會產生變寬的現象。 利用化學氣相沈積（chemical vapor deposition，CVD）的方法，在覆有金的奈米粒子（覆金之薄膜在高溫下會先再結晶成粒子）之矽基板上可以得到二氧化矽奈米管之一維結構。這些二氧化矽奈米管的直徑在40-100奈米，長度亦可到達數十微米之等級。由電子顯微鏡之分析觀察，可以發現這些奈米管是無結晶性的，並且由於合成溫度上些微的差異之下，可以得到薄壁與厚壁這兩種不同管壁厚度之奈米管。另外，因為不同溫度下使得金奈米粒子之形狀有所不同，也是使得奈米管的管壁厚度有所不同。根據進一步分析，可以發現這些二氧化矽成分主要是沿著金奈米粒子之{111}晶面而長出，而管柱則會分別沿著厚壁奈米管之<022>方向及薄壁奈米管之<200>方向生長。同時，在較高的溫度下，也可以發現到二氧化矽奈米線的蹤跡。除此之外，以二氧化矽之微米尺寸粉末及二氧化矽奈米管之樣品，利用拉曼光譜的研究之中，可以發現到在~467 cm-1的位置都具有一個很強的拉曼峰出現，因此可作為另一證實奈米管為二氧化矽的證明。最後，利用光放光光譜（photoluminescence）可以發現此奈米管具有四個不同放光中心之放光，並且可由傅立葉轉換紅外光譜（Fourier-transform Infrared spectroscopy）得到造成奈米管與粉末之間強度差異的原因。 藉由一氧化錫微米尺寸之粉末在高溫反應下，利用熱蒸發凝聚（thermal evaporation-condensation）的方式，合成單晶二氧化錫奈米帶的結構。這些奈米帶具有30-90奈米之帶寬，20-30奈米的帶厚且達到數十微米的帶長。經由X光繞射圖譜的分析，可以得知這些二氧化錫奈米帶為金紅石（rutile）正方晶系（tetragonal）結構。在高解析電子顯微鏡的影像分析中，可以看到二氧化錫之{110}晶面清晰之生長，且奈米帶會沿著<130>方向成長。這樣二氧化錫奈米帶的生長，主要是以一氧化錫所產生之自身不均衡反應（self-disproportion reaction）而生成之二氧化錫，利用氣固法（vapor-liquid，VS）之生長機制而生成。在拉曼光譜測量上，可以發現到此金紅石二氧化錫奈米帶之拉曼光譜結果具有很好的信噪比，且其Eg（475.9 cm-1）、A1g（635.5 cm-1）及B2g（777.2 cm-1）等拉曼峰可以清楚的解析出來。 最後是關於在太陽能電池中逐漸廣泛利用之銅銦化二硒奈米棒的合成與製備。在合成上，使用了兩種方式：雷射剝蝕法/陽極氧化鋁孔洞薄膜（anodic aluminum oxide，AAO）及溶液熱合成法（solvothermal）。由於在陽極氧化鋁薄膜上之分佈均勻的孔洞，使得經由雷射剝蝕後之銅銦化二硒成分可以擴散進入孔洞，在和薄膜表面先行鍍上之金屬產生共熔組成而析出銅銦化二硒的一維奈米棒狀結構。其直徑約為150-200奈米，但只能到達約2微米的長度。相對地，以溶液相反應所得到之銅銦化二硒奈米棒狀結構，反應需要較長之反應時間，但可以發現因此能夠達到更佳之長寬比（aspect ratio）及產率。這樣的銅銦化二硒奈米棒，直徑可以達到50-100奈米以及長度可至數微米，並且可以在高解析電子顯微鏡中看到其{112}晶面存在之證據，並且由電子繞射圖形上之分析，可確定其為單晶之結構。而這樣的銅銦化二硒奈米棒主要沿著<331>的方向生長。藉由紫外光/可見光/近紅外光（UV/Vis/NIR）吸收光譜，可以發現到所合成之銅銦化二硒奈米棒的吸收峰峰頂（peak，~1162 nm）與升起處（onset，~1262 nm）相差了約100 nm，並且可發現與含銅量較高之銅銦化二硒的塊材有相當類似之光譜結果，因此，可以得到所合成之銅銦化二硒奈米棒之化學組成相當接近銅：銦：硒＝1：1：2的比例。同時，利用拉曼光譜的鑑定，可以得到銅銦化二硒最強的拉曼峰A1（175.1 cm-1）的存在，藉此再次證明所合成之奈米棒為純的銅銦化二硒之成分。另外，也對於這些成分相當一致的奈米棒做了光放光光譜的解析，發現到許多不同結構之缺陷有放光現象。

As the improvement in the nanoscience and nanotechnology, the synthesis and technology for the fabrication of nanosized materials have great development and become more complete than the past few years. In addition, it also has more structural changes in its dimensionality and size. In this thesis, four kinds of different one-dimensional semiconducting nanomaterials have been successfully fabricated using different physical or chemical synthetic methods and these nanomaterials are single-crystalline silicon nanowires, amorphous silicon dioxide nanotubes, single-crystalline tin dioxide nanobelts and single-crystalline copper indium diselenides nanorods. By mixing the pure silicon powders and the catalysts (including metal or silicon dioxide powders) and with assistance for the laser ablation technology, the single-crystalline silicon nanowires (SiNWs) can be fabricated with the diameters reach 5-40 nm and the lengths extend to tens of micrometers. While the metal powders (like Fe, Ru and Pr) are used as the catalysts for the syntheses of SiNWs, the most stable Si {111} facets are grown and the growth direction for the SiNWs is parallel to the facets growth direction, i.e., the wire growth direction is <111> for the metal-catalyzed SiNWs. Such SiNWs are grown via the typical vapor-liquid-solid (VLS) growth mechanism that existing the eutectic liquid droplet formation during the synthesis. On the other hand, as the silicon dioxide (SiO2) used as the catalysts for the fabrication of SiNWs, the Si {111} facets also grow; however, the wire growth direction, as the <112> direction, is perpendicular to the lattice plane growth direction. The SiNWs catalyzed by SiO2 follow an oxide-assisted (OA) growth mechanism during their growths. Furthermore, based on the different chamber pressure used during the experiments, it can be found that with the increasing of the pressure, the diameters for SiNWs enlarge and the lengths for SiNWs shorten. The Raman spectra for the different diameter SiNWs are measured and the most intense F2g phonon mode, which is located ~ 520 cm-1, can be found that with decreasing for the diameter of SiNWs, the red-shifted behavior of the F2g mode is clearly seen from the corresponding Raman spectra. By using the chemical vapor deposition method, the one-dimensional silicon dioxide nanotubes (SiO2NTs) are produced on the silicon substrate coated with Au nanoparticles which are preannealed at high temperature. The SiO2NTs can reach to 40-100 nm in diameters and extend to few micrometers in lengths. According to the electron diffraction (ED) pattern for the SiO2NTs, it can be confirmed that these nanotubes are amorphous. Besides this, the nanotubes can be separated into two groups, as thick- and thin-walled SiO2NTs, based on their different synthesis temperatures. Moreover, with the different reaction temperatures, the different shapes of Au nanoparticles are grown and this causes the different thicknesses of the SiO2NTs. With detailed analysis on the SiO2NTs, it can be figured out that the SiO2 species are diffused from the Au {111} facets and the walls of SiO2NTs are along the <022> direction of the thick-walled SiO2NTs while the <200> direction of the thin-walled SiO2NTs. Moreover, with the higher reaction temperature, the amorphous silicon dioxide nanowires (SiO2NWs) are synthesized on the silicon substrate. The Raman spectra of SiO2NTs and micro-crystallite SiO2 powders are taken and used for the characterization and both have the intense Raman peak (Si-O phonon mode) at ~ 467 cm-1. With the thermal evaporation-condensation method, the high purity single-crystalline tin dioxide nanobelts (SnO2NBs) are fabricated via the thermal heating of tin monoxide (SnO) powders in high temperature. The SnO2NBs have their belt width for 30-90 nm, the belt thickness for 20-30 nm and the belt length for tens of micrometers. Based on the X-ray diffraction (XRD) measurements of the SnO2NBs, it can be confirmed that the nanobelts are the pure rutile tetragonal structures. From the high-resolved transmission electron microscopic images, the {111} lattice planes are clearly seen and the SnO2 nanobelt grows along the <130> direction indexed from the corresponding ED pattern. The growth of the SnO2NBs can be attributed to the self-disproportion reaction of SnO bulk powders via the vapor-solid (VS) growth mechanism. In the Raman spectrum measurement, the rutile SnO2NBs have good signal to noise ratio and the peaks at 475.9, 635.5, and 777.2 cm-1 are resolved which are corresponding to the Eg, A1g, and B2g phonon modes, respectively. The last part in this thesis is the fabrication of the copper indium diselenide nanorods (CuInSe2NRs) which are commonly used in the solar cell technology. During the synthesis works, two ways are used for producing the CuInSe2 nanostructures, including the laser ablation/anodic aluminum oxide (AAO) membranes and the solvothermal methods. In the laser ablation/AAO membranes method, the AAO membranes have the highly uniform pore distribution and the CuInSe2 species can diffuse into the hollow channels to form the eutectic composites with the metal catalysts coated on the membranes and grow the one-dimensional CuInSe2 nanorods. The diameters of the CuInSe2NRs can reach 150-200 nm, however, the lengths of the can only extend ~2 micrometers. On the other hand, the CuInSe2NRs can also be synthesized by the solvothermal method, but the total reaction time is needed for at least 36 hours. Due to the long reaction time, the better aspect ratio and the product yield for the CuInSe2NRs can be acquired. The CuInSe2NRs fabricated by the solvothermal method have the diameter size of 50-100 nm and the lengths can extend to tens of micrometers. Moreover, from the high resolution image, the {112} lattice planes are found in the nanorods and can be indexed that the nanorods grow along the <331> direction. The Raman spectrum for CuInSe2NRs is taken and can be found that the most intense A1 phonon mode located at 175.1 cm-1 is clearly verified. This is another evidence tells us that the nanorods are purely with the CuInSe2 structures for the chemical composition.