The grafting of molecular layers to carbon-based materials provides a way to combine the high chemical and thermal stability of these materials with surface properties such as chemical recognition or reactivity. The functionalization of surfaces with ultraviolet light has emerged as a way to modify difficult-to-functionalize materials, such as diamond. We have performed a combined experimental and computational investigation of the photochemical reaction of terminal alkenes with hydrogen-terminated carbon surfaces. 1-Alkenes carrying various terminal functional groups (-NHCOCF3, -NHCOO(tert-butyl), -COOCH3, -CH3) were grafted from the neat liquids using 254 nm light. These layers were characterized using X-ray Photoelectron Spectroscopy and Infrared Reflectance Absorption Spectroscopy. Pronounced differences in reactivity were observed between the molecules: trifluoroacetamide-terminated alkenes grafted the fastest and yielded self-terminating layers after approximately 4 h. Ultraviolet photoelectron spectroscopy and photocurrent measurements show that the grafting reaction involves photoemission of electrons into the liquid. Density functional calculations show that the reactivities of the four molecules are correlated with their electron affinities, with the trifluoroacetamide group acting as the best electron acceptor and having the highest reactivity. Our results demonstrate that photoejection of electrons from the solid into the acceptor levels of the alkenes initiates the functionalization reaction and controls the overall rate. Finally, marginally reactive n-alkenes were induced to react and form dense monolayers by seeding the carbon surface with small amounts of a good electron acceptor, such as the trifluoroacetamide moiety. This study provides important new mechanistic insights into the use of ultraviolet light to initiate grafting of alkenes onto surfaces.

Recent studies have demonstrated that carbon, in the form of diamond, can be functionalized with molecular and/or biomolecular species to yield interfaces exhibiting extremely high stability and selectivity in binding to target biomolecules in solution. However, diamond and most other crystalline forms of carbon involve high-temperature deposition or processing steps that restrict their ability to be integrated with other materials. Here, we demonstrate that photochemical functionalization of amorphous carbon films followed by covalent immobilization of DNA yields highly stable surfaces with excellent biomolecular recognition properties that can be used for real-time biological detection. Carbon films deposited onto substrates at 300 K were functionalized with organic alkenes bearing protected amine groups and characterized using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The functionalized carbon surfaces were covalently linked to DNA oligonucleotides. Measurements show very high selectivity for binding to the complementary sequence, and a high density of hybridizing DNA molecules. Samples repeatedly hybridized and denatured 25 times showed no significant degradation. The ability to use amorphous carbon films as a basis for real-time biosensing is demonstrated by coating quartz crystal microbalance (QCM) crystals with a thin carbon film and using this for covalent modification with DNA. Measurements of the resonance frequency show the ability to detect DNA hybridization in real time with a detection limit of <3% of a monolayer, with a high degree of reversibility. These results demonstrate that functionalized films of amorphous carbon can be used as a chemically stable platform for integrated biosensing using only room-temperature processing steps.

The solid state structures of three compounds that contain a perfluorinated chain, CF(3)(CF(2))(5)CH(2)CH(CH(3))CO(2)H, CF(3)(CF(2))(5)(CH(2))(4)(CF(2))(5)CF(3) and {CF(3)(CF(2))(5)CH(2)CH(2)}(3)P═O have been compared and a number of C-F···F-C and C-F···H-C interactions that are closer than the sum of the van der Waals radii have been identified. These interactions have been probed by a comprehensive computational chemistry investigation and the stabilizing energy between dimeric fragments was found to be 0.26-29.64 kcal/mol, depending on the type of interaction. An Atoms-in-Molecules (AIM) study has confirmed that specific C-F···F-C interactions are indeed present, and are not due simply to crystal packing. The weakly stabilizing nature of these interactions has been utilized in the physisorption of a selected number of compounds containing long chain perfluorinated ponytails onto a perfluorinated self-assembled monolayer, which has been characterized by IRRAS (Infrared Reflection Absorption Spectroscopy).

Mixed Mn/Ru oxide thermally prepared electrodes using different compositions of Mn and Ru precursor salts have been fabricated on Ti supports via thermal decomposition at two annealing temperatures. Subsequently, the oxygen evolution reaction (OER) activities of these electrodes were determined. A majority of the mixed Mn/Ru catalysts are highly active for the OER, exhibiting lower overpotential values compared to those of the state-of-the-art RuO 2 and IrO 2 type materials, when measured at a current density of 10 mA cm −2 . These Mn/Ru oxide materials are also cheaper to produce than the aforementioned platinum group materials, therefore rendering the Mn/Ru materials more practical and economical. The Mn/Ru catalysts are also evaluated with respect to their Tafel slopes and turnover frequency numbers. Interestingly, scanning electron microscopy reveals that the morphologies of the electrodes change to a mud-cracked morphology, similar to that of the RuO 2 , with minimal amounts of the Ru precursor salt added to the Mn salt. Fourier transform infrared spectroscopy and X-ray diffraction show that the Mn material fabricated in this study at the two annealing temperatures is largely Mn 3 O 4 , while the Ru material is predominately RuO 2 . X-ray photoelectron spectroscopy was also used to investigate the Mn and Ru composition ratios in each of the films.

Amorphous carbon materials find numerous applications in diverse areas ranging from implantable biodevices to electronics and catalysis. The spontaneous grafting of aryldiazonium salts is an important strategy for the modification of these materials and it is widely used in order to display a range of functionalities or to provide anchoring groups for further functionalization. We have investigated the spontaneous attachment of 4-nitrobenzenediazonium salts from aqueous solutions onto amorphous carbon materials that differ in their sp 2 content with the aim of understanding to what extent bulk composition affects rates and yields of aryldiazonium adsorption at the carbon/solution interface. Amorphous carbons were deposited in the form of thin films via reactive magnetron sputtering, and were characterized using a combination of Raman, infrared, UV-Vis and X-ray Photoelectron Spectroscopy in order to determine their sp 2 content. Attenuated Total Internal Reflection Fourier Transform Infrared spectroscopy (ATR-FTIR) was used to monitor in situ and in real time the aryldiazonium adsorption process at the carbon/solution interface. These measurements demonstrate that rates and yields of adsorption for the same aryldiazonium salt increase non-linearly vs. sp 2 concentration. Studies of aryldiazonium salt grafting as a function of time carried out ex situ via cyclic voltammetry showed that the amorphous carbon film with highest sp 2 content displays significantly lower grafting yields than glassy carbon, a material with 100% sp 2 content. Intercalation experiments using 4-nitrobenzylamine suggest that the difference in relative density of graphitic edge planes exposed at the carbon surface is in excellent agreement with the observed relative grafting yields. We discuss the implications of these results for the development of structure/reactivity relationships that can be leveraged for understanding the surface chemistry of disordered carbon materials.

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.

We have investigated the functionalization of vertically aligned carbon nanofibers with the redox-active protein cytochrome c and have characterized the resulting chemical and electrochemical activity. A comparison of monolayers with different terminal groups shows that those exposing carboxylic acid groups are most effective at binding active cytochrome c to carbon nanofibers. Cyclic voltammetry (CV) measurements reveal redox peaks due to electrochemical activity of the nanofiber-bound protein. CV and chemical measurements of enzymatic activity both show that nanofibers modified with cytochrome c yield approximately 10 times more activity than similarly modified surfaces of glassy carbon and gold. However, cytochrome c-modified nanofibers yield a high capacitive background, reducing the signal-to-noise ratio of the electrical measurements. We attribute this in part to inhomogeneous functionalization of the nanofibers at edge-plane versus basal-plane sites on the nanofiber surface, leading to leaky monolayers that yield increased capacitance. Our results demonstrate the ability to link chemically and electrochemically active proteins to nanofibers in a manner that preserves their activity and provide insight into the nanometer-scale factors that control the resulting chemical and electrochemical properties of biologically modified nanostructured electrodes.

The use of ultraviolet light to functionalize the surface of carbon-based materials with terminal alkenes has emerged as a way to overcome the high chemical stability of these surfaces to create functional interfaces. It was previously shown that surface-bound trifluoroacetic acid protected 10-aminodec-1-ene (TFAAD) can be used to promote the grafting of unreactive alkenes using 254 nm light, but the mechanism by which this enhancement occurs was not understood. Here, we present a detailed study of how surface-bound TFAAD enhances the grafting of organic molecules to the surface of hydrogen-terminated amorphous carbon. Infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy experiments show that pregrafting TFAAD onto carbon surfaces greatly enhances the subsequent grafting of 1-dodecene, dodecane and dodecane-d 26 by locally facilitating photoemission of electrons. Using a photopatterned TFAAD “seed” layer, we demonstrate that subsequent grafting of these hydrocarbons is enhanced in regions immediately adjacent to the seed and proceeds almost exclusively parallel to the carbon surface. The roles of liquid-phase radical species, valence band holes, and the photochemical fragmentation of surface species in controlling the overall reaction mechanism are discussed.