Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/36550
Title: Reactions of Pyridazine and Some Gaseous Oxides on the GE(100) Surface
Authors: HE JINGHUI
Keywords: Surface chemistry, STM, Ge(100), DFT calculation, orbital resolution
Issue Date: 13-Sep-2012
Source: HE JINGHUI (2012-09-13). Reactions of Pyridazine and Some Gaseous Oxides on the GE(100) Surface. ScholarBank@NUS Repository.
Abstract: Study on adsorption of inorganic gas molecules and multifunctional heterocyclic on Ge(100) is important to the application of Ge in microelectronics, molecular devices and catalysis. Advanced surface analytical techniques, including high resolution electron energy loss spectroscopy (HREELS) and scanning tunneling microscope (STM), together with density functional theory calculation (DFT) were used to investigate the reactions of pyridazine, CO and NO on Ge(100) surfaces. Imaging orbitals of individual organic molecules by scanning tunneling microscope (STM) is critical in developing molecular devices. We demonstrated for the first time that the orbitals of pyridazine on semiconductor surface Ge(100) can be directly imaged by STM. Two distinct features with three and four lobes were imaged by STM. They were identified as N-dative-B and NN-dative bonding configurations. The surface states from the substrate do not strongly couple with molecules orbitals, due to the stand-up configurations through dative bonding. The orbital resolved STM is capable of determining the complex surface chemistry of organic molecules on semiconductors. CO adsorption on the Ge(100) surface was investigated using a slab model with density functional theory. CO is exclusively adsorbed on the asymmetric dimer with C binding to the lower Ge dimer atom. The crystal orbital Hamilton analysis showed that the bonding between Ge and CO is mainly attributable to the Ge 4 pz orbital overlapping with C 2s, or with CO molecular orbitals 3s and 4s. The calculated adsorption energy and vibration frequencies are comparable to previous experimental results. The adsorbate interaction, adsorption barrier, diffusion barrier were also investigated. Understanding the atomic processes of NO on Ge(100) is highly desirable to optimize the N incorporating efficiency of oxynitridation. Adsorption and dissociation of NO on Ge(100) were investigated on periodic models. Six non-dissociative and 12 dissociative products were found. The transition state search demonstrated that the monomeric dissociation in an inter-dimer route is kinetically unfavorable whereas the intradimer pathways are preferred. The dimeric ONNO chains with OO-attachment are easy to form on Ge but the further release of N2 is unfavorable due to high barriers.
URI: http://scholarbank.nus.edu.sg/handle/10635/36550
Appears in Collections:Ph.D Theses (Open)

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