鈷島在銀/鍺(111)上的成長行為與電子結構

Abstract

藉由STM觀察高溫(400℃)下蒸鍍鈷原子在銀/鍺(111)- (4×4)與(√3×√3)介面上的成長行為。隨著鈷鍍量增加，(4×4)露出的面積較(√3×√3)迅速減少，除了(4×4)介面對鈷的束縛較強外，在(4×4)介面上成核的鈷島可能會推動銀原子，讓銀原子有機會移動到(4×4)與(3×1)形成更多的(√3×√3)，並且為了降低整體的表面自由能，小面積的鈷島會與大面積的鈷島合併，此為Ostwald ripening現象。 在銀/鍺(111)- (√3×√3)介面上利用高溫蒸鍍做(400℃)熱處理後，表面上的鈷原子具有足夠的動能找到最安定的位置再進行成核，與室溫蒸鍍後再熱處理比較，此種熱處理方法更可以讓鈷島在表面上形成大面積且具有平台的結構。 藉由STS發現侷域電子態密度(LDOS)在臺階邊緣以及平臺上具有不同的特徵能態。在銀/鍺(111)表面上會形成兩種重構鈷島，一種為√13×√13重構鈷島，另一種為2×2重構鈷島。因為介面效應，√13×√13重構鈷島在(4×4) 與(√3×√3)介面上具有不同的LDOS。當鈷島往上成長且島層數為7~8層時，此時2×2重構鈷島與低層數的2×2重構鈷島的LDOS並不完全相同。 By Scanning Tunneling Microscopic (STM) we can understand the growth behavior of cobalt islands on Ag/Ge(111)- (4×4) and (√ 3×√ 3) surface at high temperature (400 ℃) . With the increase of cobalt coverage, the exposure area of (4×4) decrease more apparently then √ 3×√ 3 does. Besides the stronger binding at the interface of cobalt and (4×4), nucleation of Cobalt Island on the (4×4) interface may result silver atoms to move to other (4×4) and (3×1) area and form more area of (√ 3×√ 3). In order to reduce the total surface free energy, small islands combine with large island that is Ostwald ripening. After high-temperature (400 ℃) evaporation on the Ag/Ge(111)- √3×√3, the cobalt atom has sufficient kinetic energy to find the most stable position, and heat treatment allow cobalt islands to form terrace. By STS we could find local density of states (LDOS) at the step edge and terrace are different, and find that the filled state of cobalt islands show different features at step edge and terrace. In the Ag/Ge(111) surface will form two kinds of reconstruction cobalt island, one was √ 13 × √ 13 reconstruction of cobalt islands, and the other was 2 × 2 reconstruction of cobalt islands. √13×√ 13 cobalt islands have different LDOS on (4×4) and (√3×√3) due to interface effect. When 2 × 2 cobalt island are of 7~8 layers height, the LDOS of cobalt islands are different from the 2×2 reconstruction low coverage sample.