Covalent attachment of nanometer-scale colloidal Au particles to organosilane-coated substrates is a flexible and general approach to formation of macroscopic Au surfaces that have well-defined nanostructure. Variations in substrate (glass, metal, Al2O3), geometry (planar, cylindrical), functional group (−SH, −P(C6H5)2, −NH2, −CN), and particle diameter (2.5−120 nm) demonstrate that each component of these assemblies can be changed without adverse consequences. Information about particle coverage and interparticle spacing has been obtained using atomic force microscopy, field emission scanning electron microscopy, and quartz crystal microgravimetry. Bulk surface properties have been probed with UV−vis spectroscopy, cyclic voltammetry, and surface enhanced Raman scattering. Successful application of the latter two techniques indicates that these substrates may have value for Raman and electrochemical measurements. The assembly method described herein is compared with previous methods for controlling the nanoscale roughness of metal surfaces, and its potential applicability to the assembly of other colloidal materials is discussed.

Raman microscopy also appeared (12). The latter had chapters on basic aspects of Raman microscopy, as well as chapters on applications in materials science, in earth, planetary, and environmental sciences, in biology, in medicine, and in forensic science. The proceedings of a conference on the spectroscopy of biological molecules was published, with the

Generation of combinatorial libraries has become an essential tool in synthetic organic chemistry, 1 but only recently have these methods been used for rapid screening of materials properties of inorganic substances. 2,3 The initial report described the use of vapor deposition and masking techniques to vary the composition of multi-metal superconducting materials; 2 more recently, a similar mask-driven approach to spatially-selective vapor deposition led to discovery of materials exhibiting colossal magnetoresistance. 3 Compared to traditional routes to property optimization in mixed-metal systems, e.g. preparation of separate samples with varying metal ratios, 4 combinatorial methods potentially offer significant advantages in speed and cost. We recently described a new approach to fabrication of macroscopic Au surfaces that is based on self-assembly of nanosized Au particles from solution. 5,6 Reductive deposition of Ag onto these substrates leads to Ag-clad colloidal Au arrays 7 that exhibit an increased enhancement factor (EF) for surface enhanced Raman scattering (SERS). 8 We describe herein a new, solution-based combinatorial strategy for synthesis of surfaces exhibiting nanometer-scale variation in mixed-metal composition and architecture. With this method, continuous or stepped gradients in the size and number density of surface features can be generated simultaneously over different regions of a single substrate. To demonstrate this approach, we have optimized the SERS response of a glass slide upon which the coverage of colloidal Au and the extent of Ag coating were varied. Over a 2 cm × 2 cm sample area, changes in EF spanning almost three orders of magnitude were realized, and the changes in nanostructure responsible for these effects were elucidated using atomic force microscopy (AFM). Our results show significant changes in SERS EFs over small alterations in surface morphology, demonstrating the power of solution-based combinatorial approaches for synthesis of mixed-metal materials.The general combinatorial assembly approach is described in Scheme 1. Prior work has shown that the number of colloidal Au particles bound to functionalized surfaces can be predicted from immersion times in colloidal solution using initial (time) 1/2 kinetics. 9 Thus, when a (3-mercaptopropyl)trimethoxysilane (MPTMS)-coated glass slide attached to a motorized translation stage is immersed at a fixed rate into a 17 nM aqueous solution of 12-nm diameter colloidal Au, a gradient in particle coverage is generated in the direction of immersion. After sample rotation by 90°, fixed-rate immersion into a Ag + -containing solution designed to specifically deposit Ag on Au 7b leads to a gradient in particle size over the new immersion direction. The resulting surface exhibits a continuous variation in nanometer scale morphologysas defined by particle coverage and particle sizesthat results from known, repeatable immersion conditions. 10 In our apparatus, a stepper motor with a 2°step yields a 3 µm translation. Over a 3 cm × 3 cm r...

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