No abstract

This paper describes the oriented nucleation of calcite controlled by self-assembled monolayers (SAMs) of ω-terminated alkanethiols (HS(CH2) n X) supported on metal films. The effect of the chemistry and geometry of the organic surfaces was surveyed by using different functional groups (X = CO2 -, SO3 -, PO3 2-, OH, N(CH3)3 +, CH3) and different supporting metals (Au and Ag). Optical microscopy, SEM with image analysis, and XRD were employed to characterize density and orientation of the crystals. Compared to the control surfaces of bare metal films, SAMs terminated in CO2 -, SO3 -, PO3 2-, and OH groups were more active in inducing nucleation, whereas SAMs terminated in N(CH3)3 + and CH3 inhibited nucleation. The crystallographic orientations of the crystals were distinct and highly homogeneous for each surface, but different on different surfaces. SAMs of CO2 -/Au, CO2 -/Ag, OH/Au, OH/Ag, SO3 -/Au, and SO3 -/Ag induced the face-selective nucleation of calcite from the (015), (012), (104), (103), (1 0 12), and (107) crystallographic planes, respectively. SAMs of PO3 2-/Au and PO3 2-/Ag were specific for a family of planes that form an angle of 24° and 40° with the c-axis, respectively. The high degree of orientational uniformity of the overgrown crystals (97−100% oriented crystals for well-ordered SAMs) and the decrease of uniformity as the defect density in the SAMs increased imply that nucleation takes place from the oriented, homogeneous SAM and that the specific interfacial structure is controlling orientation of crystal growth. The possible correlation between the differences in the structure of SAMs supported on Au and Ag and the orientation of the incipient crystals is discussed. Varying the geometry, chemistry, and pattern of the functional groups on SAMs provides, therefore, a tool for a fine-tuning of the orientation of crystal growth and for the formation of high-resolution patterns of oriented crystals.

Monolayer films of several primary substituted hydrocarbons CH3(CH2) n CH2X (X = CH3, OH, NH2, SH, Cl, Br, I; n = 16−30) have been imaged on graphite at the solution−substrate interface using a scanning tunneling microscope (STM). The straight chain hydrocarbons form well-ordered 2-D films on graphite and physisorb with their molecular axes parallel to the surface. The NH2, SH, Br, and I end groups are observed as bright spots in the STM image corresponding to an enhancement in the tunnel current in the vicinity of the functional group, relative to the remainder of the carbon chain. On the other hand, the OH and Cl substituents were not distinguishable from the alkyl chain in the STM images. Comparison of the relative “brightness” of the functional groups with respect to the carbon chain reveals an empirical relationship between increasing relative brightness and increasing molecular polarizability. A model is proposed to describe the STM imaging mechanism for these insulating, physisorbed films in which the role of the adsorbate's polarizability, electronic structure, and orientation with respect to the surface are considered.

No abstract

This paper describes the development of a new methodology, “topographically directed etching” or TODE, that relies on patterned regions of disorder in SAMs to generate features specifically at the edges of topographically patterned metal films. The features that are produced have lateral dimensions of <50 to 200 nm and are at least an order of magnitude smaller than those patterned originally in the material, when the original patterning is at the scale of μm. Several variations of this methodology are described, the results of which include the generation of 100-nm trenches in silver, gold, SiO2/Si, and Al2O3/Al, 100-nm lines of silver, asymmetric structures in aluminum and silver, and 50-nm features in curved silver surfaces. Although the techniques can be combined with photolithography, the pattern transfer step is based on chemical reaction and is therefore not limited by diffraction or depth of focus. This methodology makes the fabrication of ∼100-nm structures accessible to chemists/materials scientists without access to tools required for electron-beam writing and other procedures of nanofabrication.

Lateral spinal decompression was performed in 39 dogs. Twenty‐seven (67‐5 per cent) showed significant neurological improvement within 72 hours of surgery. All 36 dogs included in the long term follow up walked or were pain free in an average time of two to two‐and‐a‐half weeks.

Several non-photolithographic methods for growing patterned films of parylene-based polymers prepared by chemical vapor deposition are presented. These patterns were generated using transition metals and metal salts known to inhibit polymer deposition, in combination with alkanethiols deposited by microcontact printing. By patterning the alkanethiols on gold or silver surfaces, well-defined selectively grown structures of vapor-deposited parylene-N and parylene-C were realized, with lateral dimensions ranging from 1.5 to 35 µm. Using carboxylic acid-terminated alkanethiols deposited by microcontact printing to define regions of iron salt exposure on the surface, selectively grown films of poly(p-phenylene vinylene) were generated, with features having lateral dimensions of 12.5 µm separated by 2.5 µm, and thicknesses of 750 Å. The structures fabricated with this approach have dimensions relevant to applications in microelectromechanical systems and polymer-based displays.

Dogs treated for congenital medial patellar luxation were reviewed for the purpose of determining the incidence of postoperative major complications requiring surgical revision and the risk factors for their occurrence. Major complications occurred in 18.5% of the patellar luxation stabilization procedures with implant associated complications being the most frequent, patellar reluxation the second, and tibial tuberosity avulsion the third most common major complication. Other complications included patellar ligament rupture and trochlear wedge displacement. When recession trochleoplasty was performed in addition to tibial tuberosity transposition, a 5.1-fold reduction in the rate of patellar reluxation was observed. Release of the cranial belly of the sartorius muscle further reduced the incidence of patellar reluxation, while patella alta (pre- or postoperative) and patellar luxation grade were not found to influence the rate of reluxation. Tibial tuberosity avulsion was 11.1-times more likely when using a single Kirschner wire to stabilize a transposition, compared with two Kirschner wires. Independent to the number of Kirschner wires used, the more caudodistally the Kirschner wires were directed, the higher the risk for tibial tuberosity avulsion. Tension bands were used in 24.4% of the transpositions with no tuberosity avulsion occurring in stifles stabilized with a tension band. Overall, grade 1 luxations had a significantly lower incidence of major complications than other grades, while body weight, age, sex, and bilateral patellar stabilization were not associated with risk of major complication development.