Paper SS1-MoM1
Reaction of Phenylenediamines on Ge(100)-2x1: The Effects of Functional Group Spacing on Reactivity

Monday, November 9, 2009, 8:20 am, Room M

While silicon is the current material of choice in the electronics industry, next-generation device requirements make the largely unexplored surface chemistry on germanium, a Group IV homolog with promising electrical properties, an interesting area of study. Multifunctional adsorbates are of particular interest, since they inherently offer a greater degree of tailorability and the potential for subsequent reaction. The adsorption of the o-, m- and p- structural isomers of phenylenediamine on Ge(100)-2x1 at room temperature was investigated to gain a fundamental understanding of how surface bonding of these molecules is affected by the distance between two NH₂ groups attached to a rigid benzene ring. Vibrational spectra of the adsorption products of these three molecules, obtained via multiple internal reflection Fourier transform infrared (MIR-FTIR) spectroscopy in ultrahigh vacuum (UHV), show that all three isomers adsorb via N-H dissociation. The corresponding X-ray Photoelectron Spectroscopy (XPS) results support the MIR-FTIR data and further reveal the bonding configurations of the N-H dissociated adducts at the surface: While there is evidence of both singly and dually N-H dissociated adducts for the ortho isomer, N-H dissociation of only one amino group is observed for the para isomer, while N-H dissociation of both amino groups is observed for the meta adducts. Dative bonding was not observed for reaction of any of the phenylenediamine isomers with the Ge(100)-2x1 surface. The difference in reactivity between isomers likely results from how closely the spacing between NH₂ groups on the benzene ring matches the distance between adjacent surface dimers. The distance is in closest agreement for the meta isomer, which adsorbs exclusively via dual N-H dissociation, and is most mismatched for the para isomer, which adsorbs only via single N-H dissociation. Adsorption of the ortho isomer, which represents an intermediate case geometrically, leads to a mixture of singly and dually N-H dissociated adducts. DFT calculations support the experimental results. The results will be compared to those obtained for reaction of aniline, the monofunctional analog to the phenylenediamine isomers, on Ge(100)-2x1.