Substrate-mediated interactions on solid surfaces: theory, experiment, and consequences for thin-film morphology

When two or more atoms bind to a solid surface, the substrate can mediate an interaction between them. In this review, we discuss the origins of this interaction and the theories that describe substrate-mediated interactions, including recent studies with electronic density-functional theory. We summarize the results of experimental studies, in particular those with scanning–tunneling microscopy, aimed at quantifying substrate-mediated interactions. Over the intermediate range, these interactions can be strong enough to influence the ordering of adsorbates at surfaces. We discuss the results of recent studies, employing kinetic Monte Carlo simulations that probe the ramifications of these interactions for the morphology in thin-film epitaxy.     

Light-induced excited spin state trapping and charge transfer in trigonal bipyramidal cyanide-bridged complexes

Three members of the family of trigonal bipyramidal (TBP) complexes of general formula [M(tmphen)(2)](3)[M'(CN)(6)](2) (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline) or [M(3)M'(2)], which are known to exhibit thermally induced spin crossover and charge transfer, have been investigated for optical and photomagnetic properties. The light-induced excited spin-state trapping (LIESST) effect found in classical spin crossover compounds, such as [Fe(phen)(2)(NCS)(2)], was explored for the [Fe(3)Fe(2)] and [Fe(3)Co(2)] compounds. Similarly, inspired by the light-induced charge-transfer properties of K(0.2)Co(1.4)[Fe(CN)(6)]·6.9H(2)O and related Prussian blue materials, the possibility of photo-induced magnetic changes was investigated for the [Co(3)Fe(2)] TBP complex. Optical reflectivity and magnetic susceptibility measurements were used to evaluate the photoactivity of these compounds. A comparison of these data before and after light irradiation demonstrates that (i) the spin crossover of the Fe(II) centers in the [Fe(3)Fe(2)] and [Fe(3)Co(2)] analogues and the (ii) charge transfer events in the [Co(3)Fe(2)] complex occur with temperature and irradiation. In addition, photomagnetic behavior is exhibited by all three compounds. The photo-conversion efficiency has been estimated at 20% of photo-induced high spin Fe(II) centers in [Fe(3)Co(2)], 30% of paramagnetic Co(II)-Fe(III) pairs in [Co(3)Fe(2)], and less than 2% of photo-induced high spin Fe(II) centers in [Fe(3)Fe(2)].     

Gas Phase Reactions of 1,3,5-Triazine: Proton Transfer,Hydride Transfer,and Anionic σ-Adduct Formation

The gas phase reactivity of 1,3,5-triazine with several oxyanions and carbanions, as well as amide, was evaluated using a flowing afterglow-selected ion flow tube mass spectrometer. Isotopic labeling, H/D exchange, and collision induced dissociation experiments were conducted to facilitate the interpretation of structures and fragmentation processes. A multi-step (→ HCN + HC₂N₂⁻ → CN⁻ + 2 HCN) and/or single-step (→ CN⁻ + 2 HCN) ring-opening collision-induced fragmentation process appears to exist for 1,3,5-triazinide. In addition to proton and hydride transfer reactions, the data indicate a competitive nucleophilic aromatic addition pathway (S_NAr) over a wide range of relative gas phase acidities to form strong anionic σ-adducts (Meisenheimer complexes). The significant hydride acceptor properties and stability of the anionic σ-adducts are rationalized by extremely electrophilic carbon centers and symmetric charge delocalization at the electron-withdrawing nitrogen positions. The types of anion-arene binding motifs and their influence on reaction pathways are discussed.     

Long-range alignment of gold nanorods in electrospun polymer nano/microfibers

In this study, a scalable fabrication technique for controlling and maintaining the nanoscale orientation of gold nanorods (GNRs) with long-range macroscale order has been achieved through electrospinning. The volume fraction of GNRs with an average aspect ratio of 3.1 is varied from 0.006 to 0.045 in aqueous poly(ethylene oxide) solutions to generate electrospun fibers possessing different GNR concentrations and measuring 40-3000 nm in diameter. The GNRs within these fibers exhibit excellent alignment with their longitudinal axis parallel to the fiber axis n. According to microscopy analysis, the average deviant angle between the GNR axis and n increases modestly from 3.8 to 13.3° as the fiber diameter increases. Complementary electron diffraction measurements confirm preferred orientation of the {100} GNR planes. Optical absorbance spectroscopy measurements reveal that the longitudinal surface plasmon resonance bands of the aligned GNRs depend on the polarization angle and that maximum extinction occurs when the polarization is parallel to n.     

On the Image of the Totaling Functor

Let A be a differential graded (DG) algebra with a trivial differential over a commutative unital ring. This paper investigates the image of the totaling functor, defined from the category of complexes of graded A-modules to the category of DG A-modules. Specifically, we exhibit a special class of semifree DG A-modules which can always be expressed as the totaling of some complex of graded free A-modules. As a corollary, we also provide results concerning the image of the totaling functor when A is a polynomial ring over a field.     

Krull dimension for differential graded algebras

We introduce a naive notion of a system of parameters for a homologically finite complex over a commutative noetherian local ring and compare it to the system of parameters defined by Christensen. We show that these notions differ in general but that they agree when the complex in question is a DG R-algebra. In this case we also show that the Krull dimension defined in terms of the lengths of such systems of parameters agrees with Krull dimensions defined in terms of certain chains of prime ideals.     

Parallel EPI artifact correction (PEAC) for N/2 ghost suppression in neuroimaging applications

Echo Planar Imaging (EPI) is a neuroimaging tool for clinical practice and research investigation. Due to odd-even echo phase inconsistencies, however, EPI suffers from Nyquist N/2 ghost artifacts. In standard neuroimaging protocols, EPI artifacts are suppressed using phase correction techniques that require reference data collected from a reference scan. Because reference-scan based techniques are sensitive to subject motion, EPI performance is sub-optimal in neuroimaging applications. In this technical note, we present a novel EPI data processing technique which we call Parallel EPI Artifact Correction (PEAC). By introducing an implicit data constraint associated with multi-coil sensitivity in parallel imaging, PEAC converts phase correction into a constrained problem that can be resolved using an iterative algorithm. This enables “reference-less” EPI that can improve neuroimaging performance. In the presented work, PEAC is investigated using a standard functional magnetic resonance imaging (fMRI) protocol with multi-slice 2D EPI. It is demonstrated that PEAC can suppress ghost artifacts as effectively as the standard reference-scan based phase correction technique used on a clinical MRI system. We also found that PEAC can achieve dynamic phase correction when motion occurs.     

Interfacial ketene via the photo‐Wolff rearrangement for the modification of monolayer protected gold nanoparticles

An interfacial diazoketone‐modified gold nanoparticle (AuNP) was prepared and characterized by ¹H NMR and IR spectroscopy, TGA and TEM. Irradiation of the diazoketone leads to loss of nitrogen and the formation an interfacial ketene–AuNP via the photo‐Wolff rearrangement, evidenced by the loss of the characteristic C = N = N signal at 2068 cm^?1 in the IR spectrum and the growth of a new signal at 2100 cm^?1 indicative of the ketene. This ketene is relatively stable in the absence of added nucleophiles, but reacts quickly with oxygen nucleophiles illustrating the potential use of this ketene–AuNP as a template for a wide range of surface modifications. Copyright © 2013 John Wiley & Sons, Ltd.     

Expansion of the Na3MIII(Ln/An)6F30 Series: Incorporation of Plutonium into a Highly Robust and Stable Framework

Na_nMAn₆F₃₀ is an extremely versatile framework structure for incorporating tetravalent actinides (An) and cerium along with divalent or trivalent d-metals (M); moreover, the structure exhibits a high resistance to harsh chemical conditions. This extreme robustness can potentially be exploited for the sequestration of plutonium in a stable matrix; however, no Na_nMPu₆F₃₀ compounds have been reported so far. Herein, we present four new plutonium fluorides that have been prepared as single crystals by mild hydrothermal synthesis methods. Structural characterizations revealed their compositions to be Na₃AlPu₆F₃₀, Na₃FePu₆F₃₀, Na₃CoPu₆F₃₀, and Na_2.4Mn_1.6Pu₆F₃₀. Surprisingly, in the plutonium series, it was found that Co²⁺ and Mn²⁺ precursors oxidized to form Na₃Co^IIIPu₆F₃₀ and Na_2.4Mn^II/III_1.6Pu₆F₃₀, whereas the analogous reactions for cerium result in reduction of the transition metal, even when beginning with a M³⁺ precursor. While cerium is often used as a surrogate for plutonium, this work serves as an example that deviations between their chemistries do occur.