HERVAIS EDONGUE

Coupled energy patterns in zigzag molecular chains

Bertrand Sadjo, Conrad Bertrand Tabi, Hervais Edongué, Alidou Mohamadou

Wave Motion

• #spectroscopy and quantum chemical studies
• #nonlinear photonic systems
• #advanced fiber laser technologies
• #zigzag

Surface structure influences contact killing of bacteria by copper

Marco Zeiger, Marc Solioz, Hervais Edongué, Eduard Arzt, Andreas S. Schneider

MicrobiologyOpen

Copper kills bacteria rapidly by a mechanism that is not yet fully resolved. The antibacterial property of copper has raised interest in its use in hospitals, in place of plastic or stainless steel. On the latter surfaces, bacteria can survive for days or even weeks. Copper surfaces could thus provide a powerful accessory measure to curb nosocomial infections. We here investigated the effect of the copper surface structure on the efficiency of contact killing of Escherichia coli, an aspect which so far has received very little attention. It was shown that electroplated copper surfaces killed bacteria more rapidly than either polished copper or native rolled copper. The release of ionic copper was also more rapid from electroplated copper compared to the other materials. Scanning electron microscopy revealed that the bacteria nudged into the grooves between the copper grains of deposited copper. The findings suggest that, in terms of contact killing, more efficient copper surfaces can be engineered.

• #infection control in healthcare
• #bacterial biofilms and quorum sensing
• #recycling and waste management techniques
• #copper

Wave patterns in α -helix proteins with interspine coupling

J. C. Mimshe Fewu, Conrad Bertrand Tabi, Hervais Edongué, H. P. Ekobena Fouda, Timoléon Crépin Kofané

Physica Scripta

Modulational instability is a direct way by which localized structures emerge in nonlinear systems. We investigate analytically, through the linear stability of plane wave solutions, the existence of localized structures in α -helix proteins with three spines. Through numerical simulations, trains of pulses are found and confirm our analytical predictions. The presence of higher-order interactions between adjacent spines tends to suppress the formed localized structures for erratic ones to emerge. These erratic structures are highly localized and rather reinforce the idea that the energy to be used in metabolic processes is rather confined to specific regions for its efficiency.

• #nonlinear photonic systems
• #nonlinear dynamics and pattern formation
• #quantum chaos and dynamical systems
• #modulational instability

Obtaining different orientation relationships for Cu films grown on (0001) α-Al 2 O 3 substrates by magnetron sputtering

Gerhard Dehm, Hervais Edongué, T. Wágner, Sang Ho Oh, Eduard Arzt

International Journal of Materials Research (formerly Zeitschrift fuer Metallkunde)

Cu films were grown on (0001) α-Al 2 O 3 single-crystals by magnetron sputtering. The growth behavior was manipulated by Ar + -ion sputter cleaning of the substrates at kinetic energies between 100 and 500 eV, changing the sputter rate from 0.75 to 1.1 nm/s, and using nominal substrate temperatures of 100 and 200°C, respectively. Polycrystalline Cu films formed on α-Al 2 O 3 substrates after an Ar + -ion bombardment at 500 eV, while epitaxial Cu films evolved when Ar + -ion energies of 100 and 200 eV were used. The epitaxial Cu films always consisted of two twin-related growth variants. However, two different orientation relationships emerged which differ by a 30° in-plane rotation of the (111) oriented Cu films when the deposition rate is changed from 0.75 to 1.1 nm/s. The results will be discussed on the basis of differences in the growth process.

• #copper interconnects and reliability
• #metal and thin film mechanics
• #semiconductor materials and devices
• #sputter deposition

Dünnschichtplastizität und Wechselwirkung von Gitterversetzungen mit der Film/Substrat Grenzfläche

Hervais Edongué

OPUS Publication Server of the University of Stuttgart (University of Stuttgart)

Die Gefüge und das thermomechanische Spannungsverhalten von 100-2000 nm dicken epitaktischen und polykristallinen Cu Schichten auf (0001)-alpha-Al2O3 Substraten, die in Ultrahochvakuum hergestellt und bei 600 °C ausgelagert wurden, wurden untersucht. Epitaktische Schichten zeigen zwei {111} zwillingsorientierte Domänen mit einer Domänengröße, die mehr als das 30-fache der Schichtdicke beträgt, während die lognormal verteilte Korngröße der ebenfalls {111} orientierten polykristallinen Schichten nur das 1-2-fache der Schichtdicke aufweist. Dieser Unterschied in den Gefügen macht sich bei dem Verformungsverhalten der beiden Schichtgruppen bemerkbar. Bei hohen Temperaturen werden die Spannungen in polykristallinen Schichten durch Diffusionsplastizität an den Korngrenzen abgebaut. Dagegen ist das plastische Verformen der epitaktischen Schichten unabhängig von der Temperatur immer auf Versetzungsplastizität zurückzuführen. Fließspannungen bei Raumtemperatur nehmen in epitaktischen und polykristallinen Schichten mit abnehmender Schichtdicke zu. Aufgrund ihrer großen Domänen sind epitaktische Schichten jedoch weicher als polykristalline Schichten gleicher Schichtdicke. Allerdings sind die Fließspannungswerte der epitaktischen Schichten größer als Vorhersagen durch ein Modell, das eine Einengung der Versetzungsbewegung durch die Schichtdicke annimmt. Diese Diskrepanz liegt in Zwillingsgrenzen begründet, die parallel zur Schicht-Substratgrenzfläche verlaufen und die Versetzungsbewegung in der Schicht zusätzlich einengen, ähnlich wie die Schicht-Substratgrenzfläche selbst. Diese Einengung der Versetzungsbewegung in dünnen Schichten durch Grenzflächen führt zu den erhöhten Fließspannungswerten.

• #copper interconnects and reliability
• #aluminum alloys composites properties
• #advanced ceramic materials synthesis
• #chemistry

Mechanical Size-Effects and Dislocation Dynamics in Cu Thin Films

Gerhard Dehm, Hervais Edongué, T. John Balk, Eduard Arzt

Microscopy and Microanalysis

Gerhard Dehm, Hervais Edongue, T John Balk, Eduard Arzt; Mechanical Size-Effects and Dislocation Dynamics in Cu Thin Films, Microscopy and Microanalysis, V

• #copper interconnects and reliability
• #surface and thin film phenomena
• #metal and thin film mechanics
• #materials science

Small-scale plasticity in thin Cu and Al films

Gerhard Dehm, T. John Balk, Hervais Edongué, Eduard Arzt

Microelectronic Engineering

• #metal and thin film mechanics
• #copper interconnects and reliability
• #semiconductor materials and devices
• #materials science