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Steinau an der Straße, Germany

Tchoua Ngamou P.H.,Bielefeld University | Tchoua Ngamou P.H.,Julich Research Center | El Kasmi A.,Bielefeld University | El Kasmi A.,Abdelmalek Essaadi University | And 7 more authors.
Zeitschrift fur Physikalische Chemie | Year: 2015

Thin films and coatings are a basis for many technological processes, including microelectronics, electrochemistry and catalysis. The successful deposition of metal films and nanoparticles by chemical vapour deposition (CVD) needs control over a number of physico-chemical processes such as precursor and substrate selection, delivery, temperature, pressure and flow conditions. Here, cobalt thin films were deposited by means of pulsed-spray evaporation chemical vapour deposition (PSE-CVD) from ethanol solutions of Co(acac)2 and Co(acac)3 on bare glass and silicon substrates. The physico-chemical properties of the grown films were characterised by XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy) and HIM (helium ion microscopy). Co(acac)2 enabled the growth of cobalt metal at lower temperatures than Co(acac)3. The difference in deposition temperature was attributed to the ability of ethanol to reduce Co(acac)2 better than Co(acac)3. In addition, the film deposited from Co(acac)2 exhibited a higher metal content and a less porous structure than that deposited from Co(acac)3. Increasing the substrate temperature enhanced the carbon content because of the thermal decomposition of both precursors. Using a nickel seed layer improved the growth rate until a critical temperature of 360 °C, at which the thermal decomposition of the precursor becomes predominant. A decrease in the deposition temperature when using the nickel seed layer was only observed with Co(acac)2 precursor; the growth behaviour under these conditions was monitored with a unique UHV-compatible PSE-CVD reactor directly attached to an XPS system and ascribed to an enhancement of its catalytic reduction by ethanol. © 2015 Walter de Gruyter Berlin/Boston.

Takei H.,Toyo University | Saito J.,Toyo University | Kato K.,Toyo University | Vieker H.,Toyo University | And 3 more authors.
Journal of Nanomaterials | Year: 2015

We report on a thin layer chromatograph (TLC) with a built-in surface enhanced Raman scattering (SERS) layer for in-situ identification of chemical species separated by TLC. Our goal is to monitor mixture samples or diluted target molecules suspended in a host material, as happens often in environmental monitoring or detection of food additives. We demonstrate that the TLC-SERS can separate mixture samples and provide in-situ SERS spectra. One sample investigated was a mixture consisting of equal portions of Raman-active chemical species, rhodamine 6 G (R6G), crystal violet (CV), and 1,2-di(4-pyridyl)ethylene (BPE). The three components could be separated and their SERS spectra were obtained from different locations. Another sample was skim milk with a trace amount of melamine. Without development, no characteristic peaks were observed, but after development, a peak was observed at 694 cm-1. Unlike previous TLC-SERS whereby noble metal nanoparticles are added after development of a sample, having a built-in SERS layer greatly facilitates analysis as well as maintaining high uniformity of noble metal nanoparticles. © 2015 H. Takei et al.

Zhang X.,Bielefeld University | Waitz R.,University of Konstanz | Waitz R.,Rational AG | Yang F.,University of Konstanz | And 6 more authors.
Applied Physics Letters | Year: 2015

We report measurements of vibrational mode shapes of mechanical resonators made from ultrathin carbon nanomembranes (CNMs) with a thickness of approximately 1nm. CNMs are prepared from electron irradiation induced cross-linking of aromatic self-assembled monolayers and the variation of membrane thickness and/or density can be achieved by varying the precursor molecule. Single- and triple-layer freestanding CNMs were made by transferring them onto Si substrates with square/rectangular orifices. The vibration of the membrane was actuated by applying a sinusoidal voltage to a piezoelectric disk on which the sample was glued. The vibrational mode shapes were visualized with an imaging Mirau interferometer using a stroboscopic light source. Several mode shapes of a square membrane can be readily identified and their dynamic behavior can be well described by linear response theory of a membrane with negligible bending rigidity. By applying Fourier transformations to the time-dependent surface profiles, the dispersion relation of the transverse membrane waves can be obtained and its linear behavior verifies the membrane model. By comparing the dispersion relation to an analytical model, the static stress of the membranes was determined and found to be caused by the fabrication process. © 2015 AIP Publishing LLC.

El Kasmi A.,Abdelmalek Essaadi University | El Kasmi A.,Bielefeld University | Tian Z.-Y.,Bielefeld University | Tian Z.-Y.,CAS Institute of Engineering Thermophysics | And 4 more authors.
Applied Catalysis B: Environmental | Year: 2016

The present work reports on a one-step synthesis of thin Cu2O films deposited at 250°C using pulsed-spray evaporation chemical vapor deposition (PSE-CVD). Of interest, water addition (0, 2.5 and 5vol.%) in the liquid feedstock of Cu(acac)2 and ethanol was found to have a significant effect on the catalytic performance of these films towards CO oxidation. The obtained films were comprehensively characterized with X-ray diffraction (XRD), Helium ion microscopy (HIM), X-ray photoelectron spectroscopy (XPS) and Ultraviolet-visible (UV-vis) spectrometry. Both the surface composition and optical properties exhibited good correlation with the catalytic activity. The adopted empirical catalytic screening based on light-off curves measurement demonstrated that Cu2O prepared with 5vol.% of water in the reactant feedstock exhibited the best performance with respect to complete oxidation of CO at 175°C. This finding is reproducible and tentatively attributed to reduced crystallite grain size and more surface oxygen species generated when water was added in the feedstock. Accordingly, the innovative combination of water addition in the feedstock and the use of PSE-CVD technique is expected to assist further synthesis of new efficient thin films paving the way for catalytic applications. © 2015 Elsevier B.V..

CNM Technologies GmbH | Date: 2014-09-30

A heterostructure comprising at least one carbon nanomembrane on top of at least one carbon layer, a method of manufacture of the heterostructure, and an electronic device, a sensor and a diagnostic device comprising the heterostructure. The heterostructure comprises at least one carbon nanomembrane on top of at least one carbon layer, wherein the at least one carbon nanomembrane has a thickness of 0.5 to 5 nm and the heterostructure has a thickness of 1 to 10 nm.

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