Investigation Of The Growth And Decay Of Pb Island On Si Substrate With Low Energy/Photoemission Electron Microscope

Nanotechnology has gotten a rapid development in the past decades and the research of materials on the nanometer scale has both important theoretical value and potential applications. People carried out extensive research with the electron microscope and other instruments. Low energy electron microscopy (LEEM) and photoelectron microscopy (PEEM) due to the ability of real-time observation have been widely applied.The electronic irradiation systems and imaging systems of standard LEEM/PEEM system are independent of each other, bulky and complicated to operate. So germanic Elmitec corporation and Dalian institute of chemical physics 11T1 group jointed together and developed integrated low-energy/photoelectron microscopy (LEEM-IV). The equipment is small, easy to operate and highly integrated. Their electronic irradiation systems and imaging system were integrated into a CF250 flange. LEEM-IV breaks the LEEM/PEEM status as an independent system, making it used as independent component and easily connected with other systems.When the material is sufficiently small size, quantum size effects will become significant. So far, many systems with quantum size effect have been found, and people have done a lot of work. Pb/Si(111) system with its unique physical properties has been widespread concerned. In 1964, Estrup and Morrison deposited Pb on Si(111) surface, and studied the system with low-energy electron diffraction (LEED). They found that Pb and Si were not compatible with each other in almost any temperature, and formed a typical non-chemical reaction of quantum confinement system. Then people used a variety of characterization techniques, such as STM, LEED, X-ray diffraction on Pb/Si system and found many new phenomena. We observed the process of growth and melting of Pb islands on Si(111) substrate with LEEM-IV in real time. After flashing Si(111)(1200℃), Si (111)-(7×7) was obtained. Maintained the substrate temperature of 140℃and started evaporation source. The Pb growth on Si(111) surface is typical of S-K model. Pb initially layered growth, to about 3 atomic layers, the layered growth stopped, and three-dimensional island growth began. S-K model is that the atoms or molecules of deposited material tended to bond with each other, and the growth of Pb changed from two-dimensional to island according to the competition of energy.Mirror electron microscope(MEM) showed that the area and height of Pb island grew together. Pb atoms which arrived on Pb film didn't increase the film thickness, but moved to the nearby Pb island. Pb atoms which directly arrived on Pb island accumulated layer by layer and increased the height of Pb island. We also observed that the Pb island more easily grew at the step edges of Si(111) substrate or the point of SiC, for the two factors were more likely to cause the stress of Pb films. The results showed that each corner of the Pb island was multiples of 60°. This was the result of quantum control by Si (111) surface. The melting of Pb island under high temperature on Si(111) substrate was a fully reversible process of its growth. Pb island began to melt at 256℃, reduce its height and area at the same time. When the residual amount of Pb is small, the surface tension force divided Pb island into several small balls. Continuing toheat would make Pb disappear.We obtained PEEM images using mercurial lamp and saw clearly the quantum Pb ball at the steps on Si(111) surface. We estimated preliminarily that the size of quantum Pb ball was 400nm. In addition, because UV radiated the sample surface in an angle, we also saw the diffraction rings of Pb ball. The appearance of diffraction rings showed that the wavelength of mercurial lamp closed to the size of Pb ball. The energy of mercurial lamp is 4.9eV, and its wavelength is 253nm. So we knew that experimental result was close to theoretical values.