Veranstaltungsdetails

7.3.2007, 10:00
Jungiusstr. 11, Hörsaal AP

SFB 668 - Seminar Sondertermin

Dr. Allen Chang (Academia Sinica, Taiwan):

Finite-size effects on 2D thin film growth and structural phase transition of 2D nanoislands

We study finite-size effects on two-dimensional (2D) systems by a variable-temperature scanning tunneling microscope (VT-STM). For 2D thin film growth, flat-top Pb islands with critical and magic thickness have been observed in the Pb/Si(111)7×7 system at 200 K. Quantized states on the Pb islands of varying thickness from 4 to 9 ML are detected by the scanning tunneling spectroscopy (STS). Our observation of asymmetrical and oscillatory relaxation in the island thickness reveals that the charge distribution of confined electrons can influence the interlayer spacing. A simple model based on the infinite potential well can explain well all of our results. On the other hand, we find finite-size effect also affect structural phase transition temperature of 2D Pb/Si(111) nanoislands. Our quantitative measurements indicate that the transition temperature decreases with decreasing island and domain size. The boundaries of the nanoislands also influence the transition. Careful examination of the change in the interior structure of nanoislands near the transition temperature allows us to image the effects of the thermal fluctuations.