SSL Seminar Series 2005 No.6

Combined talks (two speakers)

Date: 28 June (Teusday), 2005
Time: 4:00pm-5:00pm
Venue: Physics Resource Room (Blk S13 # 02-16)

Speaker I: Dr. Wang Li
Title: Intra-molecular charge transfer screening in (C59N)2: Core-hole hourglass molecule

The discovery of metallic behaviour and superconductivity in alkali metal-interacted fullerene solids has led to great interest in the electronic structure of doped fullerene compounds. A detailed study of the occupied and unoccupied electronic structure of a on-site doped (C 59 N) 2 film was performed by means of photoemission (PES) and x-ray absorption spectroscopy (XAS). A key objective of the work was to determine the effects of strong intermolecular coupling (via dimerisation) on electron transfer (as compared to the purely van der Waals bonded C 60 system).

he highest occupied molecular orbitals in (C 59 N) 2 have significant N character, in contrast, the lowest unoccupied molecular orbitals are dominated by p contributions from the carbon atoms located well away from the dimer bond. The screening effect involving intra-dimer charge transfer accounts for a unobserved feature in the shakeup spectrum of C 1s core level for (C 59 N) 2 . In terms of electron transfer, the C 59 N units in dimerized (C 59 N) 2 behave as the bulbs of an hourglass with the dimer bond representing the neck. Once a core electron has been excited in one unit, the hourglass is turned and a fast conduction track through the neck starts.

Speaker II: Mr. Chung Hong Jing
Title: Local oxidation and in-situ characterization by atomic force microscope lithography

Atomic force microscopy (AFM) based local oxidation has shown a promising potential in growing of local oxide (AFM oxide) on semiconductor surfaces with controllable size in nanometer scale. However due to its nanoscale lateral dimensions, it is difficult to study the properties of ultrathin AFM oxide, particularly due to the lateral resolution limit of the spectroscopy analysis, (as the analysis are always performed on global scale SiO 2 grown on semiconductor wafers) the lack of precision in locating the exact position of the nanoscale AFM, and also the accuracy and sensitivity of vertical measurement of the change of oxide thickness especially with oxide thickness < 0.5 nm using existing conventional methods. Here we demonstrate an in-situ method to investigate the HF-chemical etching of ultrathin oxide film by contact mode AFM. In addition, we will give some examples of in-situ investigation of local current-voltage (I-V) characteristics of AFM pattern by conductive AFM (C-AFM).