Tailoring the hexagonal boron nitride nanomesh on Rh(111) with gold.

It is known that the hexagonal boron nitride (h-BN) monolayer has a periodically corrugated structure on Rh(111), termed "nanomesh", while the h-BN layer is planar on the close packed surfaces of coinage metals (Cu, Ag, Au) due the weak interactions. Our studies are aimed at understanding the metal-h-BN interaction, when both Rh and Au are present. On the one hand, the growth and thermal properties of gold deposited on h-BN nanomesh prepared on Rh(111) were studied. On the other hand, the formation of h-BN was examined on Au/Rh surface alloys prepared by the deposition of Au on Rh(111) and subsequent annealing at 1000 K. In each case, the h-BN was prepared by the decomposition of borazine at about 1000 K. Low energy ion scattering (LEIS), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) measurements revealed that the growth of Au on h-BN/Rh(111) at room temperature leads to the formation of mainly three dimensional (3D) gold nanoparticles, although at low coverages (<0.2 ML) 2D particles formed as well. Stepwise annealing to higher temperatures induces the intercalation of Au below the nanomesh, which was complete at around 1050 K. Some agglomeration and desorption of Au also took place. Interestingly, the nanomesh structure was observable after intercalation up to relatively large Au coverages. Measurements performed in the reverse order, namely exposing a Au/Rh(111) surface alloy to borazine, revealed that Rh atoms get covered by h-BN (or by its precursors) at significantly smaller borazine exposures than Au atoms. The nanomesh structure was essentially present up to a gold coverage of 0.9 ML, but with a smaller pore diameter, while it gradually disappeared at higher gold amounts. In this way the application of surface alloy supports provides a key for gradual tuning of the mesh morphology. Density functional theory calculations confirmed the decreased pore diameter of the BN layer upon the formation of a surface Rh-Au alloy layer.

LEIS and XPS investigation into the growth of cerium and cerium dioxide on Cu(111).

The controlled growth of Ce and CeO2 on Cu(111) was investigated applying low energy ion scattering spectroscopy (LEIS) and X-ray photoelectron spectroscopy (XPS). Previous LEIS studies on metallic and oxidised cerium deposits using other metallic substrates reported serious difficulties related to the neutralization of noble gas ions. For this reason, special attention was paid here to reveal possible matrix effects for the neutralization ("neutralization effects"), which would severely hinder quantitative evaluation of the LEIS data. The adsorption of O2 on Cu(111) induced no neutralization effects either with He(+) or Ne(+). Similarly, no neutralization effects were identified using He(+) upon the deposition of metallic Ce on Cu(111), but it arises for the Ce peak monitored with Ne(+). The initial growth of Ce is two dimensional up to ΘCe ∼ 0.5 ML, while almost complete coverage of Cu(111) is achieved at ΘCe = 2 ML. CeO2(111) was deposited evaporating Ce in a background of O2 at a sample temperature of 523 K. No neutralization effects were observed either with He(+) or Ne(+). In harmony with literature data, the growth mode is three dimensional. Here it was demonstrated that the continuity of the film, which could be efficiently checked by LEIS, is influenced by the applied oxygen pressure in the range of 5 × 10(-7)-3 × 10(-6) mbar. At pO2 = 3 × 10(-6) mbar the film was not completely closed even at relatively large coverages (16 ML), and a significant part of copper atoms were oxidized to Cu(1+). Deposition of CeO2 at pO2 = 5 × 10(-7) mbar was characterized by a nearly perfect wetting, with metallic copper atoms at the interface, and with a slightly more reduced ceria layer.

Probing the interaction of Rh, Co and bimetallic Rh-Co nanoparticles with the CeO2 support: catalytic materials for alternative energy generation.

The interaction of CeO2-supported Rh, Co and bimetallic Rh-Co nanoparticles, which are active catalysts in hydrogen production via steam reforming of ethanol, a process related to renewable energy generation, was studied by X-ray diffraction (XRD), high resolution electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS). Furthermore, diffuse reflectance infrared spectroscopy (DRIFTS) of adsorbed CO as a probe molecule was used to characterize the morphology of metal particles. At small loadings (0.1%), Rh is in a much dispersed state on ceria, while at higher contents (1-5%), Rh forms 2-8 nm particles. Between 473-673 K pronounced oxygen transfer from ceria to Rh is observed and at 773 K significant agglomeration of Rh occurs. On reduced ceria, XPS indicates a possible electron transfer from Rh to ceria. The formation of smaller ceria crystallites upon loading with Co was concluded from XRD and HRTEM; for 10% Co, the CeO2 particle size decreased from 27.6 to 10.7 nm. A strong dissolution of Co into ceria and a certain extent of encapsulation by ceria were deduced by XRD, XPS and LEIS. In the bimetallic system, the presence of Rh enhances the reduction of cobalt and ceria. During thermal treatments, reoxidation of Co occurs, and Rh agglomeration as well as oxygen migration from ceria to Rh are hindered in the presence of cobalt.

Growth of gold on a pinwheel TiO(∼1.2) encapsulation film prepared on rhodium nanocrystallites.

Rh nanoparticles of 50-100 nm diameter and 20-40 atomic layer thickness with a (111) flat top facet parallel to the support surface were grown on a TiO2(110) surface via physical vapor deposition (PVD) at room temperature (RT) followed by annealing at 1050 K. These nanoparticles were completely encapsulated by an ordered hexagonal pinwheel TiO∼1.2 ultrathin oxide (w-TiO-UTO) film. STM, XPS, and low energy ion scattering (LEIS) methods were used to characterize the postdeposition of gold and the effects of annealing on the Au/w-TiO-UTO/Rh-particle system. The adlayer exhibits 3D growth and Rh-Au bond formation at 500 K. The 3D Au nanoparticles of 2-3 nm diameter and ∼1 nm height are partially covered by TiOx species at RT and sinter via an Ostwald-ripening in the range of 500-800 K. The adparticles are gradually getting free of TiOx decoration, and at around 900 K they exhibit a double layer height with 2D character. Two different arrangements were found for these Au particles: (i) a compressed Au(111)-(1 × 1) and (ii) a reconstructed Au(111)-(2 × 1), both of them pseudomorphic with the Rh lattice underneath. Above 900 K, the thickness of these 2D particles tends to become a single layer, while they spread out and form a continuous gold layer on the Rh nanoparticles. This behavior indicates a thermally activated replacement of the w-TiO-UTO film by an Au ultrathin layer. The gold layer is stable up to 1000 K, where extended 1D interfaces are formed between gold and w-TiO-UTO layers.

Influence of gold additives on the stability and phase transformation of titanate nanostructures.

Gold nanoparticles were prepared and characterized on protonated (H-form) titanate nanotubes (TiONTs) and nanowires (TiONWs). The chemical nature and morphology of gold particles were monitored by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD) and high resolution electron microscopy (HRTEM). The optical properties of Au-containing titanate nanowires were explored by means of ultraviolet-visible diffuse reflectance spectroscopy. The size distribution and homogeneity of gold particles depend on the reduction mode from the corresponding gold salt to metal particles. Smaller clusters (3-8 nm) were obtained with the NaBH4 reactant at 293 K than with molecular hydrogen reduction. An unexpectedly high binding energy gold state was found by XPS in gold-loaded titanate nanostructures. This state was absent from the spectra of gold-loaded TiO2(110). A likely explanation for this phenomenon, supported also by the characteristic decrease of band gap energy from 3.10 eV to 2.74 eV with increasing Au content, is that depending on the metal loading and titanate structure, Au is stabilized on titanate nanowires partially in positively charged gold form by ion exchange and also as Au clusters. Our important new finding is that the thermal annealing behavior of Au-loaded titanate nanotubes and nanowires is different. The former lose their tubular morphology and are readily transformed into anatase even at a very low temperature of 473 K. On the other hand, gold stabilizes the layered structure of titanate nanowires up to 873 K.

Metal-based non-enzymatic systems for cholesterol detection: mechanisms, features, and performance.

Metal based catalysts and electrodes are versatile tools known for their redox properties, catalytic efficiency, and stability under various conditions. Despite the absence of significant scientific hurdles, the utilization of these methods in cholesterol detection, particularly in non-enzymatic approaches, has been relatively underexplored. To this end, there is a pressing need to delve deeper into existing metal-based systems used in non-enzymatic cholesterol sensing, with the goal of fostering the development of innovative practical solutions. Various electrode systems, such as those employing Ni, Ti, Cu, Zn, W, Mn, and Fe, have already been reported for non-enzymatic cholesterol detection, some of them elucidated sensing mechanisms and potential in physiological detection. A detailed mechanistic understanding of oxide-based cholesterol sensors, along with the methodologies for constructing such systems, holds promise of advancing the exploration of practical applications. This review aims to provide a broad perspective on metal oxide systems and their characteristics that are conducive to non-enzymatic cholesterol sensing. It is intended to serve as a springboard with offering a guide to the design and development of efficient and sensitive electrochemical cholesterol sensors.

Interaction of Rh with Rh nanoparticles encapsulated by ordered ultrathin TiO(1+x) film on TiO2(110) surface.

Rh films of 5-50 monolayers (ML) were grown on TiO2(110)-(1 × 1) surface by physical vapor deposition (PVD) at 300 K followed by annealing at max. 1050 K. In the coverage range of 5-15 ML, separated stripe-like Rh nanoparticles of approximately 30 × 150 nm lateral size and 10-20 layer thickness with a flat top (111) facet were formed. At higher coverages (15-50 ML), the Rh film sustained its continuity at least up to 950 K. For both cases, the Rh(111) top facets were completely covered by a long-range ordered hexagonal "wagon-wheel" TiO(1+x) ultrathin oxide (hw-TiO-UTO) film. STM-STS, XPS, LEIS, and TDS methods were used for morphologic and electronic characterization of surfaces prepared in this way. The main part of this study is devoted to the study of postdeposition of Rh on the hw-TiO-UTO layer at different temperatures (230 K, 310 K, 500 K) and to the effect of subsequent annealing. It was found that 2D nanoparticles of 0.2-0.3 nm height and 1-2 nm diameter are formed at RT and their average lateral size increases gradually in the range of 300-900 K. The LEIS intensity data and the CO TDS titration of the particles have shown that an exchange of the postdeposited Rh atoms with the hw-TiO-UTO layer proceeds to an extent of around 50% at 230 K and this value increases up to 80-90% in the range of 300-500 K. The total disappearance of the characteristic LEIS signal for Rh takes place at around 900 K where a complete hw-TiO-UTO adlayer forms on top of the postdeposited metal (100% exchange).

Rh-induced support transformation phenomena in titanate nanowire and nanotube catalysts.

High-aspect-ratio titanate nanotubes (NT) and nanowires (NW) were produced by the hydrothermal conversion of TiO2 at 400 K. The titanate morphology was studied by high-resolution transmission electron microscopy (HRTEM). The formation of ordered titanate nanoobjects depended on the time of conversion. Shorter synthesis times favored hollow nanotube production while during prolonged treatment the thermodynamically more stable nanowires were formed. Titanate nanotubes and nanowires were decorated by Rh nanoparticles. The structure and stability of titanate nanocomposites were studied by thermal gravimetric (TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopic (XPS), Fourier transformed infrared spectroscopic (FTIR), and Raman spectroscopic methods. The nanowires preserve their structure up to 850 K, while the nanotubes start to recrystallize above 600 K. FTIR measurements showed that the water and hydroxyl content gradually decreased with increasing temperature in both cases. XPS data revealed the existence of high binding energy, highly dispersed Rh species on both supports. A small portion of Rh may participate in an ion exchange process. Support transformation phenomena were observed in Rh containing titanate nanowires and nanotubes. Rh decorated nanowires transform into the ß-TiO2 structure, whereas their pristine counterparts' recrystallize into anatase. The formation of anatase was dominant during the thermal annealing process in both acid treated and Rh decorated nanotubes. Transformation to anatase was enhanced in the presence of Rh. The average diameters Rh nanoparticles were 4.9 ± 1.4 and 2.8 ± 0.7 nm in the case of nanowires and nanotubes, respectively.

Metal loading determines the stabilization pathway for Co2+ in titanate nanowires: ion exchange vs. cluster formation.

Co nanoparticles were produced and characterized on protonated titanate nanowires. Co deposits were obtained after low-temperature decomposition of Co2(CO)8 on titanate nanostructures. The carbonylation was carried out by vapor-phase adsorption in a fluidized bed reactor and the decarbonylation processes were followed by FT-IR spectroscopy and microbalance combined with temperature programmed reaction mass spectrometry. The band gap of Co-decorated titanate nanostructures determined by UV-VIS diffuse reflectance spectroscopy decreased sharply from 3.14 eV to 2.41 eV with increasing Co content up to 2 wt%. The Co-decorated titanate morphology was characterized by high-resolution transmission electron microscopy (HRTEM) and electron diffraction (ED). The chemical environment of Co deposition was studied by photoelectron spectroscopy (XPS). A certain amount of cobalt underwent an ion exchange process. Higher cobalt loadings led to the formation of nanosized-dispersed particles complexed to oxygen vacancies. The average sizes were found to be mostly between 2 and 6 nm. This size distribution and the measured band gap could be favorable regimes for some important low-temperature thermal- and photo-induced catalytic reactions.

Repeated simultaneous cortical electrophysiological and behavioral recording in rats exposed to manganese-containing nanoparticles.

Male Wistar rats wearing chronically implanted cortical electrodes were exposed to Mn-containing nanoparticles via the airways for 8 weeks following a 2-week pre-exposure period. The rats' cortical electrical activity and open field motility was recorded simultaneously, in weekly repetitions. It was supposed that this technique can provide better insight in the development of Mn-induced CNS damage. Decreased motility (less distance covered, longer periods of immobility) and increased total power of cortical electrical activity developed in parallel in the first 4-5 weeks of treatment but showed little change afterwards. Both the behavioral and the electrophysiological effect were in fair correlation with the rats' internal Mn exposure determined from brain samples. The results confirmed the non-linear dose- and time-dependence of Mn effects suggested by previous studies. Repeated simultaneous behavioral and electrophysiological recording during a longer treatment with neurotoxic metals (or other xenobiotics) seems to be a promising method.

One-step preparation of FeCo nanoparticles in a SBA-16 matrix as catalysts for carbon nanotubes growth.

Nanocomposites containing FeCo alloy nanoparticles dispersed in a highly ordered 3D cubic Im3m mesoporous silica (SBA-16) matrix were prepared by a novel, single-step templated-assisted sol-gel technique. Two different approaches were used in the synthesis of nanocomposites; a pure SBA-16 sample was also prepared for comparison. Low-angle X-ray diffraction, transmission electron microscopy and N2 physisorption at 77 K show that after metal loading, calcination at 500 degrees C and reduction in H2 flux at 800 degrees C the nanocomposites retain the cubic mesoporous structure with pore size not very different from the pure matrix. X-ray absorption fine structure (EXAFS) analysis at Fe and Co K-edges demonstrates that the FeCo nanoparticles have the typical bcc structure. The final nanocomposites were tested as catalysts for the production of carbon nanotubes by catalytic chemical vapour deposition and high-resolution TEM shows that good quality multi-walled carbon nanotubes are obtained.

Adsorption of Azobenzene on Hexagonal Boron Nitride Nanomesh Supported by Rh(111).

Adsorption properties of azobenzene, the prototypical molecular switch, were investigated on a hexagonal boron nitride (h-BN) monolayer ("nanomesh") prepared on Rh(111). The h-BN layer was produced by decomposing borazine (B3N3H6) at 1000-1050 K. Temperature-programmed desorption (TPD) studies revealed that azobenzene molecules adsorbed on the "wire" and "pore" regions desorb at slightly different temperatures. Angle-resolved high-resolution electron energy loss spectroscopy (HREELS) measurements demonstrated that the first molecular layer is characterized predominantly by an adsorption geometry with the molecular plane parallel to the surface. Scanning tunneling microscopy (STM) indicated a clear preference for adsorption in the pores, manifesting a templating effect, but in some cases one-dimensional molecular stripes also form, implying attractive molecule-molecule interaction. Density functional theory (DFT) calculations provided further details regarding the adsorption energetics and bonding and confirmed the experimental findings that the molecules adsorb with the phenyl rings parallel to the surface, preferentially in the pores, and indicated also the presence of an attractive molecule-molecule interaction.

On-chip integrated vertically aligned carbon nanotube based super- and pseudocapacitors.

On-chip energy storage and management will have transformative impacts in developing advanced electronic platforms with built-in energy needs for operation of integrated circuits driving a microprocessor. Though success in growing stand-alone energy storage elements such as electrochemical capacitors (super and pseusocapacitors) on a variety of substrates is a promising step towards this direction. In this work, on-chip energy storage is demonstrated using architectures of highly aligned vertical carbon nanotubes (CNTs) acting as supercapacitors, capable of providing large device capacitances. The efficiency of these structures is further increased by incorporating electrochemically active nanoparticles such as MnOx to form pseudocapacitive architectures thus enhancing device capacitance areal specific capacitance of 37 mF/cm2. The demonstrated on-chip integration is up and down-scalable, compatible with standard CMOS processes, and offers lightweight energy storage what is vital for portable and autonomous device operation with numerous advantages as compared to electronics built from discrete components.

On the growth mechanism of single-walled carbon nanotubes by catalytic carbon vapor deposition on supported metal catalysts.

A comprehensive kinetic study was performed to throw light on the formation mechanism of single walled carbon nanotubes (SWNTs) in chemical vapor deposition processes. SWNTs were synthesized by catalytic decomposition of methane or ethylene on supported transition metal catalysts. Kinetic curves (the amount of SWNT as a function of time) were obtained as a function of the nature and the preparation of the supported catalysts, temperature, the fluxes of the gases (the reagent hydrocarbon and the carrying gas), and the partial pressure of the hydrocarbon. The final products were characterized by transmission electron microscopy, Raman spectroscopy, chemical analysis, and thermogravimetric measurements. The fundamental factors determining the SWNT formation are discussed in detail, taking into consideration several observations from the literature as well.

[Pregnancy interruption by means of vibrodilation and vacuum aspiration]. / Beiträge zur Frage der Schwangerschaftsunterbrechung mit Vibrodilatation und Vakuumaspiration.

PIP: A method of abortion by vibrodilatation of the cervix followed by vacuum aspiration of the contents of the uterus, employed by the authors since 1966, is presented, and experience with 4682 cases is reported. The techniques and instrumentation developed for these procedures are described in detail. Vibrodilatation of the cervix offers the advantages of speed, reduced risk of infection or injury, and a high success rate. Vacuum aspiration combines the desiderata of speed, a smaller loss of blood, reduced anesthesia, and a greatly reduced rate of postoperative complications. Precautionary procedures are discussed, and recommendations concerning the use of these techniques are given. In particular, they are not recommended after week 10 of pregnancy.^ieng

Conformational mapping of amyloid peptides from the putative neurotoxic 25-35 region.

The secondary structure of amyloid beta A(25-35) and its deletion analogues was studied by circular dichroism (CD), Fourier transform infrared (FTIR) spectroscopy and molecular dynamics calculation. Data of our comparative CD and FTIR measurements in trifluoroethanol suggest that beta A(25-35)NH2 has a preferred beta-sheet conformation. Contrary to this beta A(31-35)NH2 tends to adopt a beta-turn conformation. Based on the comparable neurotoxic effect of beta A(25-35)NH2 and beta A(31-35)NH2 the neurotoxicity likely involves the same 31-35 core sequence and the "biologically active conformation" is a beta-turn rather than a beta-sheet structure.