Formation and structure of ordered pentachlorobenzenethiol self-assembled monolayers on Au(111) studied by scanning tunneling microscopy.

Molecular-scale surface structures of self-assembled monolayers (SAMs) prepared by the adsorption of pentafluorobenzenethiols (PFBT) and pentachlorobenzenethiols (PCBT) on Au(111) were investigated by scanning tunneling microscopy (STM). High-resolution STM imaging revealed that PFBT SAMs on Au(111) have long-range ordered domains with a row structure at room temperature, whereas PCBT SAMs have small ordered domains, with disordered domains as the main phase. This may reflect the larger diffusion barriers of PCBT molecules on Au(111) surfaces compared to PFBT molecules during SAM formation. The structural transitions of PCBT SAMs from the mixed phase containing disordered and ordered domains to the uniform ordered domains were observed at 50 degrees C depending on immersion time. The ordered packing structure of PCBT SAMs is an incommensurate (square root of 3 x square root of 10)R45 degrees structure, which differs from that of PFBT SAMs with a (2 x 5 square root of 13)R30 degrees structure. We found that a small modification in the chemical structures of aromatic rings using a halo-substituent strongly affects the self-assembly mechanism and packing structure of aromatic thiol SAMs on Au(111). Moreover, we demonstrated that highly ordered PCBT SAMs can be obtained at a solution temperature of 50 degrees C after immersion for 60 min.

A new type of strong metal-support interaction and the production of H2 through the transformation of water on Pt/CeO2(111) and Pt/CeO(x)/TiO2(110) catalysts.

The electronic properties of Pt nanoparticles deposited on CeO(2)(111) and CeO(x)/TiO(2)(110) model catalysts have been examined using valence photoemission experiments and density functional theory (DFT) calculations. The valence photoemission and DFT results point to a new type of "strong metal-support interaction" that produces large electronic perturbations for small Pt particles in contact with ceria and significantly enhances the ability of the admetal to dissociate the O-H bonds in water. When going from Pt(111) to Pt(8)/CeO(2)(111), the dissociation of water becomes a very exothermic process. The ceria-supported Pt(8) appears as a fluxional system that can change geometry and charge distribution to accommodate adsorbates better. In comparison with other water-gas shift (WGS) catalysts [Cu(111), Pt(111), Cu/CeO(2)(111), and Au/CeO(2)(111)], the Pt/CeO(2)(111) surface has the unique property that the admetal is able to dissociate water in an efficient way. Furthermore, for the codeposition of Pt and CeO(x) nanoparticles on TiO(2)(110), we have found a transfer of O from the ceria to Pt that opens new paths for the WGS process and makes the mixed-metal oxide an extremely active catalyst for the production of hydrogen.

High catalytic activity of Au/CeOx/TiO2(110) controlled by the nature of the mixed-metal oxide at the nanometer level.

Mixed-metal oxides play a very important role in many areas of chemistry, physics, materials science, and geochemistry. Recently, there has been a strong interest in understanding phenomena associated with the deposition of oxide nanoparticles on the surface of a second (host) oxide. Here, scanning tunneling microscopy, photoemission, and density-functional calculations are used to study the behavior of ceria nanoparticles deposited on a TiO(2)(110) surface. The titania substrate imposes nontypical coordination modes on the ceria nanoparticles. In the CeO(x)/TiO(2)(110) systems, the Ce cations adopt an structural geometry and an oxidation state (+3) that are quite different from those seen in bulk ceria or for ceria nanoparticles deposited on metal substrates. The increase in the stability of the Ce(3+) oxidation state leads to an enhancement in the chemical and catalytic activity of the ceria nanoparticles. The codeposition of ceria and gold nanoparticles on a TiO(2)(110) substrate generates catalysts with an extremely high activity for the production of hydrogen through the water-gas shift reaction (H(2)O + CO --> H(2) + CO(2)) or for the oxidation of carbon monoxide (2CO + O(2) --> 2CO(2)). The enhanced stability of the Ce(3+) state is an example of structural promotion in catalysis described here on the atomic level. The exploration of mixed-metal oxides at the nanometer level may open avenues for optimizing catalysts through stabilization of unconventional surface structures with special chemical activity.

Gold, copper, and platinum nanoparticles dispersed on CeO(x)/TiO(2)(110) surfaces: high water-gas shift activity and the nature of the mixed-metal oxide at the nanometer level.

At small coverages of ceria on TiO(2)(110), the CeO(x) nanoparticles have an unusual coordination mode. Scanning tunneling microscopy and density-functional calculations point to the presence of Ce(2)O(3) dimers, which form diagonal arrays that have specific orientations of 0, 24, and 42 degrees with respect to the [1 -1 0] direction of the titania substrate. At high coverages of ceria on TiO(2)(110), the surface exhibits two types of terraces. In one type, the morphology is not very different from that observed at low ceria coverage. However, in the second type of terrace, there is a compact array of ceria particles with structures that do not match the structures of CeO(2)(111) or CeO(2)(110). The titania substrate imposes on the ceria nanoparticles nontypical coordination modes, enhancing their chemical reactivity. This phenomenon leads to a larger dispersion of supported metal nanoparticles (M = Au, Cu, Pt) and makes possible the direct participation of the oxide in catalytic reactions. The M/CeO(x)/TiO(2)(110) surfaces display an extremely high catalytic activity for the water-gas shift reaction that follows the sequence Au/CeO(x)/TiO(2)(110) < Cu/CeO(x)/TiO(2)(110) < Pt/CeO(x)/TiO(2)(110). For low coverages of Cu and CeO(x), Cu/CeO(x)/TiO(2)(110) is 8-12 times more active than Cu(111) or Cu/ZnO industrial catalysts. In the M/CeO(x)/TiO(2)(110) systems, there is a strong coupling of the chemical properties of the admetal and the mixed-metal oxide: The adsorption and dissociation of water probably take place on the oxide, CO adsorbs on the admetal nanoparticles, and all subsequent reaction steps occur at the oxide-admetal interface. The high catalytic activity of the M/CeO(x)/TiO(2)(110) surfaces reflects the unique properties of the mixed-metal oxide at the nanometer level.

Adsorbate-driven morphological changes of a gold surface at low temperatures.

Using STM, infrared absorption reflection spectroscopy experiments and density functional calculations we show that low temperature adsorption of CO on gold surfaces modified by vacancy islands leads to morphological changes and the formation of nanosized Au particles. These results demonstrate a dynamic response of a surface during adsorption with consequences for the surface reactivity.

Quasi-static and dynamic nanoindentation studies on highly crosslinked ultra-high-molecular-weight polyethylene.

In four separate studies, the effect of three methods used to highly crosslink ultra-high-molecular-weight polyethylene (UHMWPE) (gamma irradiation, electron beam irradiation, and peroxide treatment) on the polymer's stiffness was investigated using quasi-static and dynamic nanoindentation. From the quasi-static studies, it was found that (a) the highest value of the elastic modulus, E (2240 +/- 157 MPa) was obtained from specimens prepared from direct compression molded UHMWPE crosslinked using gamma irradiation, with a dosage of 7.5 Mrad; (b) the value of E for specimens formed from direct compression molded UHMWPE was higher (1950 +/- 255 MPa) compared to results obtained from specimens formed from ram extruded UHMWPE (1583 +/- 140 MPa); and (c) the magnitude of the decrease in the value of E as a result of subjecting a highly crosslinked UHMWPE specimen to uniaxial tensile forces depends on the method used for the crosslinking. From the dynamic study, (d) it was found that the extent of the change in both the storage modulus and the loss modulus, as a result of subjecting a highly crosslinked UHMWPE specimen to uniaxial tension forces, depends on the method used for the crosslinking.

Spontaneous desorption and phase transitions of self-assembled alkanethiol and alicyclic thiol monolayers chemisorbed on Au(111) in ultrahigh vacuum at room temperature.

Scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) were used to examine the surface structure and adsorption conditions of hexanethiol (HT) and cyclohexanethiol (CHT) self-assembled monolayers (SAMs) on Au(111) as a function of storage period in ultrahigh vacuum (UHV) conditions of 3×10(-7) Pa at room temperature (RT). STM imaging revealed that after storage for 7 days, HT SAMs underwent phase transitions from c(4×2) phase to low coverage 4×√3 phase. This transition is due to a structural rearrangement of hexanethiolates that results from the spontaneous desorption of chemisorbed HT molecules on Au(111) surface. XPS measurements showed approximately 28% reduction in sulfur coverage, which indicates desorption of hexanethiolates from the surfaces. Contrary to HT SAMs, the structural order of CHT SAMs with (5×2√3)R35° phase completely disappeared after storage for 3 or 7 days. XPS results show desorption of more than 80% of the cyclohexanethiolates, even after storage for 3 days. We found that spontaneous desorption of CHT molecules on Au(111) in UHV at RT occurred quickly, whereas spontaneous desorption of HT molecules was much slower. Thermal desorption spectroscopy (TDS) results suggest CHT SAMs in UHV at RT can desorb more efficiently than HT SAMs due to formation of thiol desorption fragments that result from chemical reactions between surface hydrogen atoms and thiolates on Au(111) surfaces. This study clearly demonstrated that organic thiols chemisorbed on gold surfaces are desorbed spontaneously in UHV at RT and van der Waals interactions play an important role in determining the structural stability of thiolate SAMs in UHV.

Systematic analysis of palladium-graphene nanocomposites and their catalytic applications in Sonogashira reaction.

Graphene has been modified with palladium nanoparticles (Pd NPs) to develop high performance catalysts for the Sonogashira cross coupling reaction. In this research, graphite oxide (GO) sheets exfoliated from graphite were impregnated with Pd(OAc)2 to prepare Pd(2+)/GO. Thermal treatments of the Pd(2+)/GO in H2 flow at 100°C produced Pd/graphene (Pd/G) nanocomposites. TEM images show that Pd NPs were distributed quite uniformly on the graphene sheet without obvious aggregation, and the mean size of Pd NPs was determined to be less than 2 nm in diameter. Morphological and chemical structures of the GO, Pd(2+)/GO, and Pd/G were investigated using FT-IR, XRD, XPS, and XAFS. The resulting Pd/G showed excellent catalytic efficiency in the Sonogashira reaction and offers significant advantages over inorganic supported catalysts such as simple recovery and recycling. Finally, deactivation process of the Pd/G in recycling was investigated. We believe that the remarkable reactivity of the Pd/G catalyst toward the Sonogashira reaction is attributed to the high degree of the Pd NP dispersion and thus the increased low coordination numbers of smaller Pd NPs.

Adsorption and thermal decomposition of 2-octylthieno[3,4-b]thiophene on Au(111).

The adsorption and thermal stability of 2-octylthieno[3,4-b]thiophene (OTTP) on the Au(111) surfaces have been studied using scanning tunneling microscopy (STM), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). UHV-STM studies revealed that the vapor-deposited OTTP on Au(111) generated disordered adlayers with monolayer thickness even at saturation coverage. XPS and TPD studies indicated that OTTP molecules on Au(111) are stable up to 450 K and further heating of the sample resulted in thermal decomposition to produce H(2) and H(2)S via C-S bond scission in the thieno-thiophene rings. Dehydrogenation continues to occur above 600 K and the molecules were ultimately transformed to carbon clusters at 900 K. Highly resolved air-STM images showed that OTTP adlayers on Au(111) prepared from solution are composed of a well-ordered and low-coverage phase where the molecules lie flat on the surface, which can be assigned as a (9×2√33)R5° structure. Finally, based on analysis of STM, TPD, and XPS results, we propose a thermal decomposition mechanism of OTTP on Au(111) as a function of annealing temperature.

Effect of shear force on intervertebral disc (IVD) degeneration: an in vivo rat study.

Mechanical stress on the intervertebral disc (IVD) may contribute significantly to IVD degeneration, although its pathomechanism has not been fully understood. The purpose of this study was to test the hypothesis that sustained application of static shear force would result in IVD degeneration with minimum injury. We applied shear force on the rat lumbar spine (L5-L6) using a custom-designed loading device for 1 or 2 weeks. Degenerative changes such as nucleus pulposus cavity loss and border disruption were observed from the histology sections, indicating that the application of sustained dorsoventral shear force on the L6 vertebra induced degeneration of the IVDs in L5-L6 and adjacent levels of motion segment in 1 and 2 weeks. The findings of the present study could be useful for gaining a more relevant understanding of the biomechanical load factors of IVD degeneration not only for enabling better therapeutic interventions but also reducing the risk of low back injury.

Intradiscal drug delivery system for the treatment of low back pain.

Possible solution to the long-term control of the low back pain (LBP) would be by using an injectable pain drug carrier that can be delivered locally. The drug can be released in a controlled manner. It is also allowed to inject repeatedly more drugs percutaneously with a minimal invasion. The main objective of this study was to develop such a drug delivery system (DDS) for long-term control of discogenic LBP. The DDS consists of in situ forming hydrogel matrix (Pluronic F127 plus sodium hyaluronate) containing microspheres (MS). The solid MS were used for long-term release of the drugs. Both hydrogel matrix and MS contained a model drug, bupivacaine base (BB). The phase transition (liquid at room temperature, gel at around body temperature) could be manipulated by changing the composition of the hydrogel. In vitro test showed that approximately 3% (w/w) of the BB loaded to MS were released during 42 days, demonstrating a good potential for sustained release of bupivacaine.

A field-focusing device to increase power output of ThermoRod trade mark implants for thermal ablation of tissue.

Induction heating of small, cylindrical ferromagnetic implants (1.4 cm long and 1 mm in diameter) is a method for treating deep-seated tumors. These implants, or ThermoRods trade mark, are placed within a lesion in 1-cm(2) arrays and are exposed to an alternating magnetic field. The implants absorb energy from that field and transfer it as heat to the surrounding tissue. Each ThermoRod trade mark offers approximately 400 mW of power, and to kill cells, the target temperature must be greater than 42 degrees C. In this work, a magnetic field-focusing device is employed to concentrate the induced magnetic flux toward a local region near the base of the prostate to increase the power output of proximal ThermoRods trade mark. This, in turn, allows for more complete thermal ablation of lesions near the base of the prostate where the heat-sink characteristics of the bladder can cause significant power losses. Boundary element analysis and in vitro testing have shown that the use of a ferrofluid-based field-focusing device can lead to a significant increase in power output of approximately 25% and 13%, respectively, of proximal ThermoRods trade mark. These preliminary results indicate that the incorporation of such a ferrofluid-based focusing device into ThermoRod trade mark treatments is promising for the avoidance of significant power loss and for assuring complete thermal ablation of prostatic lesions.

The effects of localized cold work on the heating characteristics of thermal therapy implants.

The use of cylindrical palladium-cobalt alloy rods has proven effective in the clinical ablation of prostate cancer. In order to thermally destroy tissue, the ferromagnetic implants must heat to temperatures greater than 42 degrees C and produce a power output of at least 400 mW. However, localized cold work such as bending may effect the heating characteristics of these rods and have detrimental clinical effect. Three different types of test devices were manufactured to introduce cold work at one point in the implant: a sharp bend, a curvature, and an MTS three-point bend. After bending, each rod was then restraightened. Rod power output before and after bending was measured by calorimetry. Statistical comparison of power output for prebent and restraightened rods versus degrees bent was performed through the use of the SAS MIXED procedure to fit a mixed-model repeated-measures ANOVA with the use of multivariate models. In vitro testing showed that there was only a small change in the power output before and after rods were cold worked regardless of the type of bending. Therefore, localized cold work does not affect the clinical heating characteristics of rods.