氧化釤鋅氧化亞鈷多層膜結構的螢光及磁光特性

Abstract

本論文探討脈衝雷射蒸鍍法於c-sapphire基板製備單層氧化亞鈷(CoO)、氧化釤鋅(Zn1-xSmxO, ZSO)與CoO/ZSO多層結構薄膜之結構特性、光學特性與磁光特性。其中釤原子摻雜比例分別為0、1與3%，薄膜的製備條件為在氧氣壓力1×10^(-3) mbar，加熱棒溫度設定為400℃，脈衝雷射波長為266 nm，雷射能量密度為CoO 2.4 J/cm2、ZSO 2.0 J/cm2。利用X光繞射光譜與拉曼散射光譜分析結構特性，觀察到纖鋅礦結構的ZnO(002)與岩鹽結構的CoO(111)的特徵特徵峰，代表各層薄膜為單晶結構。並隨著摻雜比例的上升，晶格常數會變大、晶粒大小會變小。在多層膜結構中會因為熱退火效應與晶格間的不匹配度影響著薄膜的結晶性。拉曼散射光譜中，可以觀察到基板、氧化鋅、氧化鋅缺陷與CoO之特徵譜線。AFM結果顯示所有樣品表面呈現顆粒狀，表面形貌接近原子級的平坦。

光學特性由光致螢光光譜顯示在室溫中所有多層膜結構有氧化鋅之近能隙發光，以及部分樣品有鋅空缺、氧空缺與鋅間隙等缺陷所造成的發光，並無發現釤離子在4f軌域躍遷或CoO之螢光訊號，亦沒有ZnO/CoO/ZnO量子井相關的光學特性。

磁光特性由磁光法拉第磁滯曲線結果顯示所有樣品在室溫下皆為順磁性。薄膜之伐得常數隨著波長增加而減少，多層膜的伐得常數計算值與實驗值趨勢與數值相近。This thesis focused on the structural, optical and magneto-optical properties of single-layer Sm-doped ZnO (Zn1-xSmxO where x = 0, 0.01, 0.03, ZSO) films and three different types of ZSO/CoO multilayer films on c-sapphire were prepared by pulsed laser deposition. The preparation conditions of the films were as follows: the oxygen pressure was 1×10^(-3) mbar, the temperature of the heater was 400 °C, and the laser energy density of 266 nm wavelength for CoO and ZSO were 2.4 J/cm2 and 2.0 J/cm2, respectively.For the structural properties, the characteristic peaks of ZnO and CoO were observed in x-ray diffraction and Raman-scattering spectra, which show that the multilayer films are single-crystalline without interdiffusion. CoO is [111]-oriented on both ZnO and c-sapphire substrates. The bottom layers of the multilayer film structure had a better crystal structure due to the thermal annealing effect. Morphology of all samples show particle-like whose surface grain size are about 220–280 nm, and root mean roughness are less than 5 nm on both ZnO and CoO surface.In optical preperties, photoluminescence (PL) spectra showed near-band edge emissions of zinc oxide from all samples at room temperature, and samples with ZSO layer had defects emissions such as zinc vacancies, oxygen vacancies and zinc interstitials. Neither samarium ions 4f orbital transition nor the fluorescent signal of CoO had founded in the PL spectra.

The Magneto-optical Faraday effect (MOFE) spectroscopy showed only paramagnetic behavior at room temperature. MOFE presented stronger response at wavelength between 320 and 380 nm. The value of Verdet constant of all the films were about -300–500 rad/(T*cm) which decreases with increasing wavelength. Additionally, the estimated values of the effective Verdet constant trended to the measured values for the multilayer films.