Vacuum annealing phenomena in ultrathin TiDy/Pd bi-layer films evaporated on Si(100) as studied by TEM and XPS

Using a combination of TEM and XPS, we made an analysis of the complex high-temperature annealing effect on ultrathin titanium deuteride (TiDy) films evaporated on a Si(100) substrate and covered by an ultrathin palladium layer. Both the preparation and annealing of the TiDy/Pd bi-layer films were performed in situ under UHV conditions. It was found that the surface and bulk morphology of the bi-layer film as well as that of the Si substrate material undergo a microstructural and chemical conversion after annealing and annealing-induced deuterium evolution from the TiDy phase. Energy-filtered TEM (EFTEM) mapping of cross-section images and argon ion sputter depth profiling XPS analysis revealed both a broad intermixing between the Ti and Pd layers and an extensive inter-diffusion of Si from the substrate into the film bulk area. Segregation of Ti at the Pd top layer surface was found to occur by means of angle-resolved XPS (ARXPS) and the EFTEM analyses. Selected area diffraction (SAD) and XPS provided evidence for the formation of a new PdTi2 bimetallic phase within the top region of the annealed film. Moreover, these techniques allowed to detect the initial stages of TiSi phase formation within the film–substrate interlayer

Identification and characterization of antibacterial compound(s) of cockroaches (Periplaneta americana)

Infectious diseases remain a significant threat to human health, contributing to more than 17 million deaths, annually. With the worsening trends of drug resistance, there is a need for newer and more powerful antimicrobial agents. We hypothesized that animals living in polluted environments are potential source of antimicrobials. Under polluted milieus, organisms such as cockroaches encounter different types of microbes, including superbugs. Such creatures survive the onslaught of superbugs and are able to ward off disease by producing antimicrobial substances. Here, we characterized antibacterial properties in extracts of various body organs of cockroaches (Periplaneta americana) and showed potent antibacterial activity in crude brain extract against methicillin-resistant Staphylococcus aureus and neuropathogenic E. coli K1. The size-exclusion spin columns revealed that the active compound(s) are less than 10 kDa in molecular mass. Using cytotoxicity assays, it was observed that pre-treatment of bacteria with lysates inhibited bacteria-mediated host cell cytotoxicity. Using spectra obtained with LC-MS on Agilent 1290 infinity liquid chromatograph, coupled with an Agilent 6460 triple quadruple mass spectrometer, tissues lysates were analyzed. Among hundreds of compounds, only a few homologous compounds were identified that contained isoquinoline group, chromene derivatives, thiazine groups, imidazoles, pyrrole containing analogs, sulfonamides, furanones, flavanones, and known to possess broad-spectrum antimicrobial properties, and possess anti-inflammatory, anti-tumour, and analgesic properties. Further identification, characterization and functional studies using individual compounds can act as a breakthrough in developing novel therapeutics against various pathogens including superbugs

The Response of Work Function οf Thin Metal Films to Interaction with Hydrogen

The aim of this paper is to summarize the results of experiments carried out at our laboratory on the response of the work function of several thin films of transition metals and rare earth metals to interaction with molecular hydrogen. The main focus concerns the description of surface phenomena accompanying the reaction of hydride formation as a result of the adsorbate's incorporation into the bulk of the thin films. Work function changes Δ Φp caused by adsorption and reaction concern the surface, hence this experimental method is appropriate for solving the aforementioned problem. A differentiation is made between the work function changes ΔΦp due to creation of specific adsorption states characteristic of hydrides, and ΔΦp arising as a result of surface defects and protrusions induced in the course of the reaction. The topography of thin metal films and thin hydride films with defects and protrusions was illustrated by means of atomic force microscopy. For comparison, the paper discusses work function changes caused by $H_2$ interaction with thin films of metals which do not form hydrides (for example platinum), or when this interaction is performed under conditions excluding hydride formation for thermodynamic reasons. Almost complete diminishing of ΔΦp was observed, in spite of significant hydrogen uptake on some rare earth metals, caused by formation of the ordered H-Y-H surface phase

The Response of Work Function οf Thin Metal Films to Interaction with Hydrogen

The aim of this paper is to summarize the results of experiments carried out at our laboratory on the response of the work function of several thin films of transition metals and rare earth metals to interaction with molecular hydrogen. The main focus concerns the description of surface phenomena accompanying the reaction of hydride formation as a result of the adsorbate's incorporation into the bulk of the thin films. Work function changes Δ Φp caused by adsorption and reaction concern the surface, hence this experimental method is appropriate for solving the aforementioned problem. A differentiation is made between the work function changes ΔΦp due to creation of specific adsorption states characteristic of hydrides, and ΔΦp arising as a result of surface defects and protrusions induced in the course of the reaction. The topography of thin metal films and thin hydride films with defects and protrusions was illustrated by means of atomic force microscopy. For comparison, the paper discusses work function changes caused by $H_2$ interaction with thin films of metals which do not form hydrides (for example platinum), or when this interaction is performed under conditions excluding hydride formation for thermodynamic reasons. Almost complete diminishing of ΔΦp was observed, in spite of significant hydrogen uptake on some rare earth metals, caused by formation of the ordered H-Y-H surface phase

Metal-Semiconductor Transition on the Surface and in the Bulk of Europium Hydride Thin Film

Thin europium films (20-50 nm thick) on a glass substrate were transformed into $EuH_x$ (0 < x < 2) by interaction with H_2 introduced into the reactor in successive calibrated doses. By measuring the pressure, the hydrogen uptake (H/Eu) was determined at every step of the reaction. In situ monitoring of bulk properties (electrical resistance R(H/Eu), relative transparency to light T(H/Eu)/$T_0$ and (H/Eu) dependent light transparency spectrum) confirms metal-semiconductor transition at room temperature. Both the electrical resistance and optical transparency of the film strongly increase with hydrogen concentration as a consequence of the resulting increase of the content of semiconducting dihydride. Moreover, the course of work function changes ΔΦ(H/Eu) indicates inversion of the charge-transfer direction on the surface. The transition at room temperature from positively to negatively polarized hydrogen adsorbate was observed in situ during hydrogen uptake. As a result, the work function at equilibrium state varies with hydrogen content from +18 to -18 mV with respect to pure metal film, reflecting the change of "mirror potential" generated on the surface due to the accumulation of hydrogen adsorbates in the subsurface region