由於鎵金屬本身性質具有無毒、室溫為液態與緻密氧化層等特性，且鎵奈米顆粒有較高的等離子體能量 (plasma energy（14 eV）)，並可藉由改變它們的形狀和大小，來調變局部表面電漿子共振 (localized surface plasmon resonance, LSPR) 特徵範圍，可獲得從紫外波段到可見波段調控的優勢，因此為近年來電漿子學中熱門研究主題之一。 我們利用表面陽極處理方式改變液態鎵奈米顆粒表面形貌而形成窩坑結構(dimple structure)，其中電壓與反應時間將影響鎵奈米顆粒表面凹陷程度，其形成原因來液態鎵金屬表面能變化與氧化層生成時所產生的壓應力造成淺層凹痕，此凹痕導致後續的陽極反應集中於特定區域造成嚴重變形形成dimple結構。透過XPS計算陽極處理過程中氧化層生成之厚度，並利用熱氧化法與FDTD模擬結果說明本研究中氧化層對紅移現象影響有限，藉此證明液態Ga NPs的形貌變化為造成LSPR特徵波峰波長發生紅移現象的主要原因。 利用此方式可調變Ga NPs的LSPR特徵波峰波長之最大紅移量達77 nm左右，透過FDTD模擬不同凹陷程度之光學變化，此結果與實驗結果具有相同趨勢進行，並由近場分佈顯示金屬表面尖端與銳利邊緣區域產生”熱點”(hotspots)，此尖端與銳利邊緣是伴隨凹陷結構所產生。透過此方式我們以短時間(反應時間10秒以內)與簡易製程方式即可調整液態Ga NPs之LSPR特徵波峰波長位置。 ;Gallium, whose melting point is near the room temperature, is relatively non-toxic and will form the compact oxide layer. With a bulk plasmon resonance energy of 13.9 eV, Ga has recently been proved to be a good candidate for UV plasmonics with a Drude-like dielectric function extending from the vacuum ultraviolet into the infrared spectral region. In this work, the dimple textures were formed on the surface of gallium nanoparticles (Ga NPs) through the anodization treatment, using the applied voltage and the reaction time to control the degree of deformation. During the treatment, the increasing oxide layer would produce the compression stress, leading the formation of dimple textures. The nanoscale dimple-like textures led to changes in the localized surface plasmon resonance (LSPR) wavelength. A maximal LSPR red-shift of ~77 nm was preliminarily achieved using an anodization voltage of 0.7 V. The finite-difference time-domain (FDTD) simulations also suggested that the LSPR tunability was primarily determined by the shape of the deformed particles, which was also in good agreement with the trend in the LSPR shift obtained from the experimental results. The near electric field simulated by FDTD was concentrated near spikes or narrow walls, and thus the hotspots could clearly be observed. The extent of particle deformation could be adjusted in a very short period of anodization time (~7 s), which offers an efficient way to tune the LSPR response of Ga NPs.
