Mark D. Ellison

Reactions of substituted aromatic hydrocarbons with the Si(001) surface

The interactions of toluene, para-xylene, meta-xylene and ortho-xylene with the (001) surface of silicon have been investigated using Fourier-transform infrared spectroscopy. Infrared spectra show that these methyl-substituted aromatic hydrocarbons are chemisorbed and oriented on the Si(001) surface at both 110 and 300 K. Peaks in the Si–H stretching region indicate that some dissociation occurs upon adsorption. Comparisons of infrared spectra of these molecules with deuterated and nondeuterated methyl groups reveal that the major source of decomposition is likely from C–H cleavage of the substituent groups, leaving the ring intact. Additionally, the striking similarity of the infrared spectra of benzene, toluene and the xylene isomers suggests that the methyl-substituted aromatic rings interact with the Si(001) surface in much the same way as benzene. Differences in relative peak intensity point to the possibility that the methyl substituent groups may steer the ring into different ratios of specific bon...

Scattering of N2 from Ni(111)

A cold (T rot <10 K ) beam of N 2 with an initial translational energy of 0.40 eV strikes an Ni(111) surface at surface temperatures from 300 to 873 K at several incident angles from 15 to 60°. The rotational energy and angular distributions of the scattered molecules are probed using (2+1) resonance-enhanced multiphoton ionization. Molecules scattered in the specular direction have mean rotational energies that are independent of surface temperature, whereas those scattered at angles far from the specular show a dependence on surface temperature, caused likely by multiple collisions with the surface before escape. A rotational rainbow, seen in systems such as CO‐Ni(111) and N 2 ‐Ag(111), is not seen in this system. For molecules that scatter close to the specular direction, approximately 10% of the initial translational energy is converted into rotational energy of the scattered N 2 . For surface temperatures above room temperature, the angular distributions indicate that molecules that scatter into low-J states also tend to exit in a broad peak (10‐20° FWHM ) near the specular, and this peak is broadened with increasing incident angle. The molecules that scatter into high-J states have a much broader distribution, indicating that they are trapped rotationally during the initial collision and suVer multiple collisions before leaving the surface.

Scattering of xenon from Ni(111): Collision-induced corrugation and energy transfer dynamics

Experiments have been conducted in which a beam of xenon atoms collides with a clean Ni(111) surface, and the speed and angular distributions of the scattered Xe atoms are measured for different incident energies, incident angles, and surface temperatures. At high incident energies, the translational energy of the scattered Xe is independent of initial and final scattering angles. This result is attributed to multiple xenon-surface collisions prior to Xe escape. At lower incident energies, the scattering behavior depends more on the scattering angle. Interestingly, a small fraction of Xe is trapped on a 250 K Ni(111) surface at high incident translational energies.

Ultrathin Organic Layers on Silicon Surfaces

Ultrathin organic layers of organic molecules can be produced on the Silicon(001) surface using surface analogs of well-known cycloaddition reactions from organic chemistry. Molecules containing one or more unsaturated C=C can readily bond to the surface at room temperature. Since these reactions form two bonds between the molecule and the surface, the attached molecules are also oriented. More complex molecules containing conjugated pi-electron systems such as styrene can also be bonded to the surface with high selectivity for specific bonds. This manuscript reviews recent progress in forming ultrathin organic layers on silicon, and the current understand of the relevant reaction mechanisms.

Construction of the Electronic Angular Wave Functions and Probability Distributions of the Hydrogen Atom

This Mathcad document allows students to explore the characteristics of the components of the angular electronic wave function of the hydrogen atom.

Symbolic Mathematics Engines in Teaching Chemistry: A Symposium Report.

At the ACS National Conference in Philadelphia, a panel of educators discussed the use of Symbolic Mathematics Engines (SMEs) in chemical education. The importance of utilizing SMEs in undergraduate education was stressed, and caveats were noted. Audience participation led to a vigorous discussion, and the future of the field was envisioned.