Nanomechanical properties of single-walled carbon nanotube (SWNT) reinforced epoxy composites with varying weight percentage (0, 1, 3, and 5 wt%) of nanotubes were measured by nanoindentation and nanoscratch techniques. Hardness and elastic modulus were measured using a nanoindenter. Scratch resistance and scratch damage were studied using the AFM tip sliding against the SWNT reinforced sample surfaces. Nanoindentation/nanoscratch deformation and fracture behaviour was studied by in situ imaging of the indentation impressions/scratch tracks. Viscoelastic properties of the nanocomposites were measured using nanoindentation dynamic mechanical analysis tests. The reinforcing mechanisms are discussed with reference to the nanotube dispersion, interfacial bonding, and load transfer in the SWNT reinforced polymer composites.

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Methods for patterning metal thin films at the microscale and nanoscale by applying the patterns to metallic and polymeric materials for use in shape and deformation measurements in a scanning electron microsope (SEM) or other high magnification imaging system are described. In one approach, thin films of metallic materials (e.g., Au, Ag, Cu, and Cr) are applied to a variety of substrates. The coated samples are then placed into a reaction vessel, where the specimens are heated and exposed to a nitrogen atmosphere saturated with selected volatile chemicals. This process results in nano-scale remodeling of the metallic films, thereby affording high contrast random patterns with different morphologies. In a second approach, thin films of metallic materials, including gold and silver, also have been applied using a simplified UV photolithographic method requiring a minimum amount of laboratory preparation. Using selected substrates, both methods have been used successfully to transfer patterns onto polymeric and metallic materials ranging from 50-500 nanometers with chemical vapor rearrangement and 2 to 20 microns with UV photolithography, providing a pattern that can be used with digital image correlation to quantify both the surface profile and also surface deformations at reduced length scales.

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A quantitative comparison of Raman and Fourier transform near-infrared (FT-NIR) spectroscopic techniques for the analysis of epoxy curing is performed. It is shown that the Raman technique yields a linear calibration curve much like FT-NIR. Band assignments in the Raman spectrum of diglycidyl ether of bisphenol-A (DGEBA) were performed by studying Raman spectra of smaller model compounds.

We report the in situ replacement of conjugated molecules in an insulating matrix by scanned probe microscope lithography. High yield, programmable patterning of a self-assembled monolayer of dodecanethiol was performed by applying voltage pulses from a scanning tunneling microscope. Conjugated oligomers were observed to be subsequently chemisorbed onto the patterned sites. © 1999 American Institute of Physics. ͓S0003-6951͑99͒01031-1͔Scanned probe microscopy offers a method for manipulating and modifying materials at the atomic level. 1-3 Preliminary work has been done utilizing self-assembled monolayers ͑SAMs͒ as a substrate. [4][5][6][7][8][9] In this letter, we demonstrate reproducible in situ scanning tunneling microscope ͑STM͒ lithographic SAM patterning and subsequent replacement of conjugated molecules in an insulating matrix at selectively patterned locations. A schematic of the process is shown in Fig. 1.The initial substrate is a gold surface with an adsorbed SAM. An annealed Au/Cr ͑250 nm/50 nm͒ film on glass exhibited a Au͑111͒ surface with terraces of up to several hundred nanometers with herringbone reconstruction. 10 A dodecanethiol SAM was deposited from solution at room temperature. 11 Subsequent mounting in a Teflon liquid cell of an ambient STM chamber allowed for immersion in 1,4-dioxane ͑Aldrich͒ solvent for the replacement experiments.A Park Scientific ͓Universal SA1͔ tube-scanning ambient STM was used for both imaging and lithographic patterning. Tips were prepared from Pt/Ir ͑70%/30%͒ wires and then coated with epoxy leaving the end exposed. 12 Images were taken in constant current mode with 1.5 V tip bias (V b ) and approximately 15 pA set-point tunneling current (I t ).To perform lithography, we applied square voltage pulses to the SAM substrate with pulse amplitude (V p ) varying from 1.8 to 3.6 V and pulse duration (T p ) from 0.5 s to 0.5 s. A constant dc bias voltage (V b ) of 0.1 V was kept on the STM tip during the voltage pulses. A larger time constant ͑relative to the pulse width͒ in the feedback electronics is used to both maintain the tip at a constant height and avoid tip crashing. Figure 2 is an image of a sample after three consecutive voltage pulses with V p of 3.0 V and T p of 0.5 s. The tip was biased at V b of 0.1 V with I t of 0.5 nA. To have a better view of the profile of the patterned structures ͑pits͒, we invert the image by plotting the depth of the pits as positive z. The diameters and depths of the patterned structures are approximately 10 and 1.4 nm, respectively. The pit depth is the length of dodecanethiol SAM to within the measurement resolution of the STM system. A lithographic positioning program was used to move the tip to obtain these distinct, spatially separated patterns.We have studied the patterning yield of this STM lithography as a function of pulse voltage and pulse width ͑Fig. 3͒. The yield was defined as the percent of successful patterned structures ͑out of 50 pulses͒. Under appropriate pulse conditions patterns were produced with over 90% yiel...

A spectrofluorometer capable of dispersed-spectrum, simultaneous, multiwavelength UV excitation and collection of luminescence has been constructed for the purpose of qualitatively and quantitatively determining aromatic hydrocarbon pollutants dissolved in ocean water. Hydrocarbon fluorescence data produced by this instrument were in the form of excitation/emission matrices, which provide more spectral information about these complex mixtures than is available from conventional excitation or emission fluorescence profiles. Second-order statistical methods were applied to these data to determine low partper-billion concentrations of two primary fluorescent compounds, naphthalene and styrene, found in ocean water exposed to gasoline despite the presence of uncalibrated interference from similar aromatic compounds, the ocean water matrix, and the instrumental background.

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