The interaction of vapor-deposited Al atoms with self-assembled monolayers (SAMs) of HS(CH2)15CH3 and HS(CH2)15CO2CH3 chemisorbed at Au{111} surfaces was studied using X-ray photoelectron spectroscopy, infrared spectroscopy, time-of-flight secondary ion mass spectrometry, and spectroscopic ellipsometry. For the CH3-terminated SAM, no reaction with C−H or C−C bonds was observed. For total Al doses up to ∼12 atoms/nm2, penetration to the Au−S interface occurs with no disruption of the average chain conformation and tilt, indicating formation of a highly uniform ∼1:1 Al adlayer on the Au. Subsequently, penetration ceases and a metallic overlayer begins to form at the SAM−vacuum interface. These results are explained in terms of an initial dynamic hopping of the −S headgroups on the Au lattice, which opens transient diffusion channels to the Au−S interface, and the closing of these channels upon completion of the adlayer. In contrast, Al atom interactions with the CO2CH3-terminated SAM are restricted to the vacuum interface, where in the initial stages discrete organometallic products form via reaction with the CO2CH3 group. First, a 1:1 complex forms with a reduced CO bond and an intact CH3 moiety. Further exposure leads to the additional reaction of about four Al atoms per ester, after which a metallic overlayer nucleates in the form of clusters. After the growth progresses to ∼30 Å, the clusters coalesce into a uniform metallic film. These results illustrate the extraordinary degree of control that organic substrates can exert during the course of metal film formation.

We have determined the parameters necessary to fabricate reproducible neuronal patterns which we are using to begin studying fundamental issues in developmental neurobiology. The addition of a beam homogenizer, as well as a new surface preparation, has enabled the routine production of reproducible, high-resolution (2−20 μm) organosilane patterns. The effects of surface preparation and beam dosage were monitored using X-ray photoelectron spectroscopy (XPS) and proof of patterning is provided by high-resolution imaging XPS. We also report the guidance of neuronal adhesion and neurite outgrowth and the creation of reproducibly defined circuits of embryonic (E18−19) rat hippocampal neurons using these patterned surfaces in vitro. We have achieved a >50% rate of pattern formation, and at times the rate approaches 90%. We are using these patterns to address the issue of how geometric pattern cues might be used to affect cell-to-cell communication and we report the preliminary results on the synaptic development of the hippocampal neurons using dual patch-clamp electrophysiology. We monitored neurite outgrowth and the emergence of both spontaneous and evoked synaptic activity for both patterned and unpatterned (control) hippocampal cultures. The results indicate the intriguing possibility that geometry itself may be a modulating or trophic factor for cell development.

The purpose of research on metals (M) deposited onto self-assembled monolayers (SAMs) is to understand the interactions between metal (M) and eventually metal oxide overlayers on well-ordered organic substrates. Application of WSAM and inorganic/SAM research results to the understanding of real inorganic/ organic interfaces in vacuum and under environmental conditions can potentially play a key role in the development of advanced devices with stable interfacial properties. The M/SAM approach to interface research is delineated as a new subfield in surface science in the context of other approaches to inorganic/organic interface research. Current issues in M/SAM research are outlined, including chemical compound formation, the morphology (spreading, clustering. or penetration) of the metal species, the kinetics of the metal morphology, the effect of the metal on the degree of order in the SAM, and the rate of metal penetration into the SAM. Probes are recommended that are suitable for M/SAM research. The results of M/SAM studies to date are reviewed, and M/SAM combinations are ranked according to reactivity and penetration. Key probes for addressing gaps in the research results are identified. The effects of defects, disordering, air exposure, and X-ray and electron beam exposure on the experimental results to date are evaluated. Thus far, the results have successfully revealed qualitative relationships of M/SAM chemistry, temperature, and penetration. The chemical interactions that have been found are applicable to real M/polymer interfaces as formed in vacuum. It has yet to be shown that WSAM research will yield quantitative understanding of interface formation or that WSAM interfaces are entirely analogous to M/polymer interfaces in the details of interface formation. The future of this subfield of surface science lies in its expansion from M/SAM interfaces in vacuum to other inorganic/SAM interfaces in vacuum and. eventually, under environmental conditions. KEY WORDS: self-assembled monolayer, metal/organic interface, surface chemistry. LIST OF ACRONYMS AND ABBREVIATIONS* USED IN THIS ARTICLEAES, auger electron spectroscopy; AFh4, atomic force microscopy; BE, binding energy; BIS, bremsstrahlung isochromat spectroscopy; FITR, Fourier transform infrared spectroscopy; FT'-RAIRS, Fourier transform reflection absorption infrared spectroscopy; HAS, helium atom scattering; HREELS, high-resolution electron energy loss spectroscopy; IFM, interfacial force microscopy; ISS. ion scattering spectroscopy; LB, Langmuir-Blodgett; LEED. low-energy electron diffraction; M or MO, metal or metal oxide; MMHD. methyl 16-mercaptohexadecanoate. HS(CH,),,COOCH,; M/SAM, metayself-assembled monolayer;