Complex Surface Structures Research Articles

The application of oxidative chemical vapor deposited (oCVD) PEDOT to textured and non-planar photovoltaic device geometries for enhanced light trapping

In organic photovoltaics (OPVs), active layer thicknesses are limited by exciton diffusion length. Thus, non-planar surfaces and device architectures are desired for enhancing the light absorption in OPVs. The oxidative chemical vapor deposition (oCVD) process enables the formation of conformal films of conducting polymers on complex surface structures. oCVD poly(3,4 ethylenedioxythiophene) (PEDOT) is demonstrated to be compatible with a wide range of nano- to macro-scale textured and non-planar architectures that have been demonstrated to enhance light absorption in photovoltaics by various mechanisms of light trapping, such as lengthening optical pathways and taking advantage of reflective light bouncing. Here, conformal oCVD (PEDOT) layers are demonstrated over submicron features including submicron nanowedges and nanocones (with 70–100nm groove depth and 100nm pitch) and square gratings (50–350nm groove depth and 139–833.3nm pitch). In contrast, solution-applied PEDOT:PSS exhibits blanketing, thinning at the top of the features, and welling up of material in the bottom of the features, thus failing to conformally coat the complex surfaces. The application of oCVD PEDOT to macro-scale 3D OPV architectures was also explored. Enhanced active layer absorbance is shown using tetraphenyldibenzoperiflanthene (DBP) as the absorbing layer over the PEDOT.

Back Cover: Resolving oxide surfaces – From point and line defects to complex network structures (Phys. Status Solidi B 5/2013)

High resolution imaging and spectroscopy signifi cantly improves our understanding of surface structure and chemistry for complex materials. In the Feature Article by Markus Heyde et al. (pp. 895–921) low temperature ultrahigh vacuum noncontact atomic force and scanning tunneling microscopy has been employed to characterize surface structures ranging from periodic and ordered via defective towards amorphous networks. In the presented studies it has been shown how modern scanning probe microscopy techniques can complete and clarify the atomistic models, which have been derived so far mainly from diffraction experiments. The benefi ts of locally resolving complex surface structures are obvious. A direct atomic assignment from the obtained images is possible. Surface structures with increasing dimensionality from 0D to 2D are discussed. In this article three different sample systems are highlighted, namely, magnesia on Ag(001), alumina on NiAl(110) and silica on Ru(0001).

A putative bactoprenol glycosyltransferase, CsbB, in Bacillus subtilis activates SigM in the absence of co-transcribed YfhO

Bacteria are equipped with complex cell surface structures, such as cell walls. How they maintain cell surface integrity through cell wall metabolism during growth and adaptation to unfavorable environmental conditions is still elusive. In the Gram-positive soil bacterium Bacillus subtilis, one extracytoplasmic function (ECF) sigma factor, SigM, is believed to play a primary role in cell surface integrity. Here, we find that expression of CsbB, which is known to be involved in the extracellular stress response, causes constitutive activation of SigM when YfhO, a membrane protein with unknown function, is lost. CsbB has similarity with the well-characterized bactoprenol glucosyltransferase GtrB found in Gram-negative bacteria. Substitution of a single amino acid residue at the putative catalytic site of CsbB abolishes this constitutive activation, and expression of Escherichia coli GtrB in B. subtilis causes similar effects as expression of CsbB, suggesting that SigM is activated by the glycosyltransferase activity of CsbB. A comparison with the Gtr system in Gram-negative bacteria suggests that accumulation of glycosylated bactoprenol catalyzed by CsbB reduces the bactoprenol pool in the absence of YfhO. Reduction of bactoprenol synthesis causes similar effects as expression of CsbB. We propose that it is the shortage of available bactoprenol within a cell that induces SigM activity.

Insights into Propranolol Adsorption on TiO2: Spectroscopic and Molecular Modeling Study

Insights from molecular-level mechanisms of propranolol adsorption can further our understanding of the fate and transport of beta blockers in the environment. The motivation of our study is to explore the dynamic adsorption process of propranolol at the TiO2/aqueous interface on the molecular scale. Multiple complementary techniques including macroscopic adsorption experiments, flow-cell ATR-FTIR measurement, XPS, and quantum chemical calculations were used to study the adsorption mechanisms. Our results show that propranolol adsorption on TiO2 increased from 0.3 to 2.3 μmol/g in the pH range 5 to 9. The ATR-FTIR and XPS analysis indicated that the hydroxyl and amino groups of propranolol strongly interacted with the TiO2 surface. The DFT calculations suggested the molecular structure of surface complexes with hydrogen bonding and the charge transfer from propranolol to TiO2 surface upon adsorption.

An Atomic Scale View of Methanol Reactivity at the Cu(1 1 1)/CuOx Interface

AbstractThe interaction and reaction of MeOH with Cu is of foremost importance in a range of heterogeneously catalyzed processes. A critical intermediate in the molecular transformation of MeOH on Cu‐based catalysts is the methoxy species, the formation of which comprises the first elementary step in the MeOH steam reforming reaction. The interface length between metallic Cu(1 1 1) and copper oxide dictates the conversion of MeOH to formaldehyde (H2CO), although the microscopic details of MeOH’s adsorption, diffusion, and reaction at this complex interface are not clear. Here, STM was used to study the reaction of MeOH with the morphologically complex Cu(1 1 1)/copper oxide [Cu(1 1 1)/CuOx] surface. STM is the only technique that can simultaneously characterize various complex oxide surface structures and MeOH’s adsorption and reaction sites at the atomic scale. Variable‐temperature STM measurements enabled the spatial distribution of both intact and dissociated MeOH to be tracked as the reaction proceeded and revealed that diffusion and spillover are key processes in MeOH decomposition. The presence of extended metallic Cu areas interconnected with disordered oxide structures, coupled with the weak binding of MeOH on Cu, provides the driving force for MeOH to migrate to interfacial sites at which deprotonation occurs. At elevated temperatures, methoxy buildup at the Cu(1 1 1)/CuOx interface is observed along with evidence consistent with spillover. These data provide the first clear atomic scale picture of the interaction and reaction of MeOH with oxidized Cu(1 1 1), the most common facet of Cu in nanoparticle catalysts.

Detection of karstic limestone bedrock by shallow seismic refraction in an area west of Assiut, Middle Egypt

The main goal of this study was the detection of complex surface and internal structures of limestone bedrock over the entire area planned for urban development on the lower Eocene plateau, west of Assiut, Egypt. A 2.5D shallow seismic refraction survey provided sufficient resolution for mapping faults and karst at the scale required for civil engineering plans. The 3D P-wave seismic velocity map was developed from integration of a series of 2D spreads recorded along a 2D grid using only inline spreads.

Weaverbird: Topological Mesh Editing for Architects

AbstractDesign and computation consultant Giulio Piacentino is the developer of WeaverBird. Here he describes how the plug‐in ‘gives architects more geometric control and allows them to create complex surface structures that join in orderly ways, yet in arbitrary configurations’.

Annexin A1 is a biomarker of T‐tubular repair in skeletal muscle of nonmyopathic patients undergoing statin therapy

Skeletal muscle complaints are a common consequence of cholesterol-lowering therapy. Transverse tubular (T-tubular) vacuolations occur in patients having statin-associated myopathy and, to a lesser extent, in statin-treated patients without myopathy. We have investigated quantitative changes in T-tubular morphology and looked for early indicators of T-tubular membrane repair in skeletal muscle biopsy samples from patients receiving cholesterol-lowering therapy who do not have myopathic side effects. Gene expression and protein levels of incipient membrane repair proteins were monitored in patients who tolerated statin treatment without myopathy and in statin-naive subjects. In addition, morphometry of the T-tubular system was performed. Only the gene expression for annexin A1 was up-regulated, whereas the expression of other repair genes remained unchanged. However, annexin A1 and dysferlin protein levels were significantly increased. In statin-treated patients, the volume fraction of the T-tubular system was significantly increased, but the volume fraction of the sarcoplasmic reticulum remained unchanged. A complex surface structure in combination with high mechanical loads makes skeletal muscle plasma membranes susceptible to injury. Ca(2+)-dependent membrane repair proteins such as dysferlin and annexin A1 are deployed at T-tubular sites. The up-regulation of annexin A1 gene expression and protein points to this protein as a biomarker for T-tubular repair.

Possibility of VOx/SiO2 Complexes Speciation: Comparative Multi-wavelength Raman and DR UV-vis Study

Raman spectroscopy is one of the very often used spectroscopic methods for characterization of vanadium surface species. However, Raman spectra of VOx-silica systems are more complex and interpretation is more difficult in comparison with other supports (like Al2O3, ZrO2, TiO2 or Nb2O5) because there is strong vibrational coupling between the vanadia species and the silica support. Therefore, assignment and interpretation of some vibrational bands is still subject of controversy. This fact results in incongruity of suggested molecular structure and population of individual vanadium surface complexes. In this contribution, we present systematic comparative study of diffuse reflectance UV-vis spectra and Raman spectra excited by 325 and 514.5 nm lasers obtained on set of dehydrated vanadium modifed hexagonal mesoporous silica (VOx-HMS) samples with vanadium loading from 2 up to 12 wt. %. We prove that changes in population of oligomeric and monomeric VOx species in individual samples are not manifested by significant changes in the character of Raman signals. On the other hand it is evident that with increasing of vanadium loadings the UV-vis spectra show systematic changes. Raman spectroscopy is useful characterization technique for detection presence of very small amount of V2O5 microcrystallites, especially if suitable wavelength of laser is used for remarkable resonant enhancement of Raman intensity of its bands (e.g. 514.5 nm).

EptC of Campylobacter jejuni Mediates Phenotypes Involved in Host Interactions and Virulence

Campylobacter jejuni is a natural commensal of the avian intestinal tract. However, the bacterium is also the leading cause of acute bacterial diarrhea worldwide and is implicated in development of Guillain-Barré syndrome. Like many bacterial pathogens, C. jejuni assembles complex surface structures that interface with the surrounding environment and are involved in pathogenesis. Recent work in C. jejuni identified a gene encoding a novel phosphoethanolamine (pEtN) transferase, EptC (Cj0256), that plays a promiscuous role in modifying the flagellar rod protein, FlgG; the lipid A domain of lipooligosaccharide (LOS); and several N-linked glycans. In this work, we report that EptC catalyzes the addition of pEtN to the first heptose sugar of the inner core oligosaccharide of LOS, a fourth enzymatic target. We also examine the role pEtN modification plays in circumventing detection and/or killing by host defenses. Specifically, we show that modification of C. jejuni lipid A with pEtN results in increased recognition by the human Toll-like receptor 4-myeloid differentiation factor 2 (hTLR4-MD2) complex, along with providing resistance to relevant mammalian and avian antimicrobial peptides (i.e., defensins). We also confirm the inability of aberrant forms of LOS to activate Toll-like receptor 2 (TLR2). Most exciting, we demonstrate that strains lacking eptC show decreased commensal colonization of chick ceca and reduced colonization of BALB/cByJ mice compared to wild-type strains. Our results indicate that modification of surface structures with pEtN by EptC is key to its ability to promote commensalism in an avian host and to survive in the mammalian gastrointestinal environment.

Kinetic ATR-FTIR Studies on Phosphate Adsorption on Iron (Oxyhydr)oxides in the Absence and Presence of Surface Arsenic: Molecular-Level Insights into the Ligand Exchange Mechanism

The surface chemistry of phosphorus and arsenic compounds in their organic and inorganic forms is of great interest to the scientific and industrial communities due to its role in controlling their transport, bioaccessibility and speciation. We report herein in situ and surface-sensitive rapid kinetic studies on the adsorption of phosphate to Fe (oxyhydr)oxides in the presence and absence of dimethylarsinic acid (DMA) and arsenate. These studies were conducted at pH 7 using ATR-FTIR in the flow mode, which were complemented with detailed kinetic analysis of the desorption behavior of DMA and arsenate over the same range of aqueous [phosphate]. Values for apparent rates of adsorption and desorption were extracted from the time dependence of given spectral components characteristic of surface phosphate, DMA, or arsenate. Results show that pseudo adsorption rate constants of phosphate on Fe (oxyhydr)oxide films increase in this order: arsenate-covered < DMA-covered ≤ freshly prepared. Also, pseudo desorption rate constants of DMA complexes are 7-12 times higher than arsenate using phosphate as a desorbing agent. When these results are combined with earlier work on the thermodynamics, kinetics, and structure of surface complexes, they suggest that, during initial times of surface interactions, increasing organic substitution on arsenate increases the proportion of relatively weakly bonded complexes (monodentate and outer-sphere).

Contrast inversion of the h-BN nanomesh investigated by nc-AFM and Kelvin probe force microscopy

Single sheets of hexagonal boron nitride (h-BN) on transition metals provide a model system for layered insulating materials as well as a functional substrate for molecules and metal clusters. The progress in the understanding of h-BN layers on transition metals was mainly driven by scanning tunnelling microscopy (STM) and photoelectron spectroscopy (PES) measurements within the last decade, while direct measurements of mechanical and electrical properties are still rare. Our investigations of the two-dimensional (2D) h-BN nanomesh on a Rh(111) substrate by high-resolution noncontact atomic force microscopy (nc-AFM) reveal a complex surface structure including a frequently observed contrast inversion. Detailed 2D force spectroscopy measurements are revealing towards a mechanical elastic deformation of the h-BN monolayer caused by the tip–sample interaction. Furthermore, Kelvin probe force microscopy (KPFM) and spectroscopy measurements show local work function variations of the nanomesh, proving the results obtained by PES but additionally providing detailed local information.

Atomic imaging and direct phase retrieval using anomalous surface x-ray diffraction

The application of multi-wavelength anomalous diffraction to thin films, interfaces and surface structures is presented. The method directly determines the amplitudes and phases of the complex surface structure factors from surface x-ray diffraction data, measured at three different energies around the absorption edge of one of the elements present in the film. Thereby, one is able to directly Fourier transform the data, which immediately provides meaningful and unambiguous electron-density distributions. These serve as a starting point for subsequent structural refinement. The robustness of the algorithm was evaluated on simulated data as a proof of principle. The experimental limitations and their effect on the method will be discussed as well as stability tests for the algorithm, such as the positions of the anomalous scatterers and the interfacial roughness. It will be shown that the method can be applied to real structures. The algorithm was tested on real data from a thin film of SrTiO3 grown on NdGaO3(110).

Nanoscale Films: Path‐Guided Wrinkling of Nanoscale Metal Films (Adv. Mater. 22/2012)

Path-guided wrinkling enables the fabrication of defect-free and arbitrary-shaped wrinkle patterns. R. Huang, Q. Liu, and co-workers describe on page 3010 an approach for the production of well-defined wrinkle structures using laser direct writing to make guiding paths in a metal/polymer bilayer, followed by thermal heating. They also introduce a new concept of the unit-wrinkle, through which more complex surface structures can be quantitatively designed and realized. This approach is suitable for making wavy-surfaced complexities and devices.

Growth of single-crystalline Cu2O (111) film on ultrathin MgO modified α-Al2O3 (0001) substrate by molecular beam epitaxy

We report the synthesis of Cu2O single crystalline films on the c-plane α-Al2O3 substrate by radio-frequency plasma assisted molecular beam epitaxy. An ultrathin MgO layer was adopted to modify the complex surface structure of sapphire (0001) and engineer the interfacial atomic matching between the epilayer and the substrate. The experimental results solidly proved the single crystallinity of cubic Cu2O (111) without twin crystals. A coincident match mode was proposed to explain the unusual in-plane orientation between strained MgO (111) and Cu2O (111). It was found that the crystal quality of Cu2O is very sensitive to the thickness of MgO layer, which is optimized to be ∼2nm. The reason why MgO has a critical thickness in Cu2O single crystal growth was also tentatively discussed.

Pattern formation and mixing in three-dimensional film flow

The effect of inertia on gravity-driven free surface flow over different three-dimensional periodic corrugations is considered analytically, numerically and experimentally. In the case of high bottom amplitudes, compared to the film thickness, the results predict complex free surface structures especially in cases where the topography is not fully flooded by the liquid film. The investigation of the flow field shows a rich variety of pattern formation phenomena depending on the interplay between the geometry of the topography and the inertia of the film. Finally, we show how the complex topographical structure enhances the laminar mixing within the film.

Enhanced atomic corrugation in dynamic force microscopy—The role of repulsive forces

Full range two dimensional (2D) force mapping was performed by means of low temperature dynamic force microscopy (DFM) on a highly complex surface structure. For this purpose, we used a thin film of vitreous silica on a Ru(0001)-support, which is a 2D structural equivalent to silica glass. The 2D spectroscopy shows that the contrast generating shift in vertical distance between two sites on the surface is twice as large on the repulsive branch of the frequency shift-distance curve as compared to the attractive branch. The results give insight into the origin of the formation of atomic resolution in DFM.

Development of a charge-perturbed particle-in-a-sphere model for nanoparticle electronic structure

The complex surface structure of gold-thiolate nanoparticles is known to affect the calculated density functional theory (DFT) excitation spectra. However, as the nanoparticle size increases, it becomes impractical to calculate the excitation spectrum using DFT. In this study, a new method is developed to determine the energy levels of the thiolate-protected gold nanoparticles [Au(25)(SR)(18)](-), Au(102)(SR)(44) and Au(144)(SR)(60). A 3 nm thiolate-protected nanoparticle is also modeled. The particle-in-a-sphere model is used to represent the core while the ligands are treated as point charge perturbations. The electronic structures obtained with this model are qualitatively similar to DFT results. The symmetry of the arrangement of the perturbations around the core plays a major role in determining the splitting of the orbitals. The radius chosen to represent the core also affects the orbital splitting. Increasing the number of perturbations around the core shifts the orbitals to higher energies but does not significantly change the band gaps and orbital splitting as long as the symmetrical arrangement of the perturbations is conserved. This model can be applied to any gold nanoparticle with a spherical core, regardless of its size or the nature of the ligands, at very low computational cost.

Characterization of Unique Modification of Flagellar Rod Protein FlgG by Campylobacter jejuni Lipid A Phosphoethanolamine Transferase, Linking Bacterial Locomotion and Antimicrobial Peptide Resistance

Gram-negative bacteria assemble complex surface structures that interface with the surrounding environment and are involved in pathogenesis. Recent work in Campylobacter jejuni identified a gene encoding a novel phosphoethanolamine (pEtN) transferase Cj0256, renamed EptC, that serves a dual role in modifying the flagellar rod protein, FlgG, and the lipid A domain of C. jejuni lipooligosaccharide with a pEtN residue. In this work, we characterize the unique post-translational pEtN modification of FlgG using collision-induced and electron transfer dissociation mass spectrometry, as well as a genetic approach using site-directed mutagenesis to determine the site of modification. Specifically, we show that FlgG is modified with pEtN at a single site (Thr(75)) by EptC and demonstrate enzyme specificity by showing that EptC is unable to modify other amino acids (e.g. serine and tyrosine). Using Campylobacter strains expressing site-directed FlgG mutants, we also show that defects in motility arise directly from the loss of pEtN modification of FlgG. Interestingly, alignments of FlgG from most epsilon proteobacteria reveal a conserved site of modification. Characterization of EptC and its enzymatic targets expands on the increasingly important field of prokaryotic post-translational modification of bacterial surface structures and the unidentified role they may play in pathogenesis.

As(III) immobilization on gibbsite: Investigation of the complexation mechanism by combining EXAFS analyses and DFT calculations

The complexation of aqueous As(III) species on gibbsite was investigated as a function of pH. Theoretical calculations and X-ray absorption fine structure spectroscopy (XAFS) were combined to elucidate the structure of arsenite surface complexes on synthetic gibbsite. Several adsorption sites were evaluated using the self-consistent charge corrected density-functional based tight-binding (SCC-DFTB) method. The formation of bidentate–binuclear, bidentate–mononuclear, monodentate–mononuclear, and monodentate–binuclear complexes by means of both acid–base and non-dissociative mechanisms was studied in detail. The SCC-DFTB calculations showed the bidentate–binuclear/acid–base complex as the most thermodynamically stable geometry for As(III) bonding to gibbsite surface, estimating As–O and As–Al distances of 1.75 and 3.24Å, respectively. EXAFS results also demonstrated As(III) complexation to three oxygen atoms in the first shell, at a distance of 1.77Å, and to aluminum in the second shell at a distance of 3.21Å, characteristic of bidentate–binuclear configuration, at pH 5.0, 7.0 and 9.0. Another As–Al interaction, attributed to the monodentate–binuclear complex due to its distance of 3.49Å, was shown from EXAFS results to provide a minor contribution to As(III) sorption on gibbsite. Therefore, results from theoretical calculations and experimental measurements confirmed the occurrence of inner-sphere complexation during the As(III) adsorption on gibbsite, in a pH range of 5–9. Hence, the higher As(III) mobility in the environment, when compared to As(V), was suggested to be related to the protonation of the As(III) adsorbed complexes. This protonation would restore the neutral H3AsO3 molecule, which could be then released from the mineral surface. These results might be useful to predict and control arsenic mobility in aqueous environments, particularly where Al oxy-hydroxides are often found.