Deep ultraviolet (UV) irradiation is shown to modify organosilane self-assembled monolayer (SAM) films by a photocleavage mechanism, which renders the surface amenable to further SAM modification. Patterned UV exposure creates alternating regions of intact SAM film and hydrophilic, reactive sites. The exposed regions can undergo a second chemisorption reaction to produce an assembly of SAMs in the same molecular plane with similar substrate attachment chemistry. The UV-patterned films are used as a template for selective buildup of fluorophores, metals, and biological cells.

The photochemistry of organosilanes was used to (1) create mixed monolayers having continuously adjustable surface free energies and (2) affect high resolution adhesion and spatial orientation of biological cells on silica substrates. Monolayers were formed from two materials, an aminoalkylsilane, NH2(CH2)2NH(CH2)3Si(OCH3)3 (EDA), and a perfluorinated alkylsilane, CF3(CF2)s(CH2)2Si(CH3)zC1 (1 3F), and were characterized by ellipsometry and water contact angle measurements. Deep UV (193 nm) radiation was used to induce photochemical changes in the cell-adhesive EDA monolayers. X-ray photoelectron spectroscopy indicated that the amine groups of EDA were removed by the exposure, leaving only Si-OH or alkyl fragments having 5 3 carbons. The exposed substrates were then reacted with 13F to form mixed monolayers or hydrophobic monolayers that inhibited cell adhesion in the irradiated regions. The degree of 13F reactivity with EDA in the unirradiated regions was observed to be solvent-dependent, suggesting that conformational states of the surface amine groups lead to a reduction in their accessibility. The selective photochemistry was exploited to produce high resolution molecular patterns, defined using patterned irradiation, that were mapped with scanning Auger electron spectroscopy. The patterns were used to spatially control the adhesion and direct the outgrowth of rat hippocampal neurons and porcine aortic endothelial cells in vitro. Patterns of controlled geometry may provide new approaches to the study of surface-directed growth, intercellular communication, and organogenesis or be used to control the alignment of individual cells with transducer elements in biosensors and implants. IntroductionRecent reports have indicated that monolayer systems can be targeted for a variety of applications, including cell adhesion and patterning.',2 Several techniques have been introduced in the past few years for the production of patterned self-assembled monolayers (SAMs) of organic functionalitie~.~~~ One approach utilizes conventional photoresist methodology to produce high resolution patterns for the adhesion and growth of cells.2 A fundamentally new technique involves direct modification of SAMs by patterned deep UV e x p o s~r e .~~~ Molecules in the exposed regions of a SAM absorb the radiation and undergo photocleavage to yield surface residues. These residues can then be modified with a second type of functionality. This technique offers several

A new approach for the selective electroless (EL) metallization of surfaces is described. Surfaces are modified with a chemisorbed ligand-bearing organosilane film, and then catalyzed with an aqueous Pd(II) catalyst solution. The catalyzed substrate is then immersed in an EL metal deposition bath to complete the metallization process. The ligating surfaces are produced by molecular self-assembly of 2-(trimethoxysilyl)ethyl-2-pyridine (PYR) on silicon or silica substrates. The catalyst consists of chloride-containing aqueous Pd(II) solutions buffered at pH 5.0 to 6.4; oligomeric chloro and/or hydroxo-bridged Pd(II) complexes act as the catalytic species at the surface. The activity of the catalyst has been characterized and modeled as a function of solution pH, [C1-], and time from preparation. Adhesion of the Pd(II) EL catalyst to the substrate involves covalent bond formation with the surface ligand. An average minimum Pd(II) level on the surface of -10 '~ Pd atom cm 2 is shown to be necessary to initiate EL metallization of the substrate with an EL Co bath. This process involves fewer steps and displays improved selectivity compared to processes that involve a conventional Pd/Sn catalyst. Fabrication of high resolution metal patterns using the new metallization chemistry in conjunction with deep UV patterning of PYR films is demonstrated.

The work function of indium tin oxide (ITO) substrates was modified with phosphonic acid molecular films. The ITO surfaces were treated prior to functionalization with a base cleaning procedure. The film growth and coverage were quantified by contact angle goniometry and XPS. Film orientation was determined by reflection/absorption infrared spectroscopy using ITO-on-Cr substrates. The absolute work functions of nitrophenyl- and cyanophenyl-phosphonic acid films in ITO were determined by Kelvin probe measurement to be 5.60 and 5.77 eV, respectively.

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Quantitative determination of surface coverage, film thickness and molecular orientation of DNA oligomers covalently attached to aminosilane self-assembled monolayers has been obtained using complementary infrared and photoelectron studies. Spectral variations between surface immobilized oligomers of the different nucleic acids are reported for the first time. Carbodiimide condensation was used for covalent attachment of phosphorylated oligonucleotides to silanized aluminum substrates. Fourier transform infrared (FTIR) spectroscopy and x-ray photoelectron spectroscopy (XPS) were used to characterize the surfaces after each modification step. Infrared reflection-absorption spectroscopy of covalently bound DNA provides orientational information. Surface density and layer thickness are extracted from XPS data. The surface density of immobilized DNA, 2-3 (×10 13 ) molecules cm −2 , was found to depend on base composition. Comparison of antisymmetric to symmetric phosphate stretching band intensities in reflection-absorption spectra of immobilized DNA and transmission FTIR spectra of DNA in KBr pellet indicates that the sugar-phosphate backbone is predominantly oriented with the sugar-phosphate backbone lying parallel to the surface, in agreement with the 10-20Å DNA film thickness derived from XPS intensities.

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The deep ultraviolet (λ < ∼250 nm) photochemistry of chemisorbed organosilane self-assembled films of the type R(CH2) n SiO−surface where n = 0, 1, 2 and R = phenyl, naphthyl, or anthracenyl is explored. Photochemistry is examined using 193 and 248 nm laser irradiation as well as deep ultraviolet lamp sources. It is demonstrated for a variety of systems, including single and multiple rings as well as heterocycles, that the primary photochemical mechanism is cleavage of the Si−C bond. Photocleavage of the organic group generates a polar, wettable silanol surface that is amenable to subsequent remodification by organosilane chemisorption, allowing the fabrication of high-resolution patterns of chemical functional groups in a single molecular plane. The use of patterned monolayers as templates of reactivity for subsequent selective chemical reactions is demonstrated.