Traveling interface modulations and anisotropic front propagation in ammonia oxidation over Rh(110)

The bistable NH3 + O2 reaction over a Rh(110) surface was explored in the pressure range 10−6–10−3 mbar and in the temperature range 300–900 K using photoemission electron microscopy and low energy electron microscopy as spatially resolving methods. We observed a history dependent anisotropy in front propagation, traveling interface modulations, transitions with secondary reaction fronts, and stationary island structures.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Novel approaches towards highly selective self-powered gas sensors

The prevailing design approaches of semiconductor gas sensors struggle to overcome most of their current limitations such as poor selectivity, and high power consumption. Herein, a new sensing concept based on devices that are capable of detecting gases without the need of any external power sources required to activate interaction of gases with sensor or to generate the sensor read out signal. Based on the integration of complementary functionalities (namely; powering and sensing) in a singular nanostructure, self-sustained gas sensors will be demonstrated. Moreover, a rational methodology to design organic surface functionalization that provide high selectivity towards single gas species will also be discussed. Specifically, theoretical results, confirmed experimentally, indicate that precisely tuning of the sterical and electronic structure of sensor material/organic interfaces can lead to unprecedented selectivity values, comparable to those typical of bioselective processes. Finally, an integrated gas sensor that combine both the self-powering and selective detection strategies in one single device will also be presented

III V on silicon Observation of gallium phosphide anti phase disorder by low energy electron microscopy

The formation of anti phase disorder is a major obstacle in the heteroepitaxy of III V semiconductors on silicon. For an investigation of the anti phase domain APD structure of GaP Si 100 samples on mesoscopic length scales, we applied dark field imaging in a low energy electron microscope LEEM to thin GaP films grown on Si 100 substrates by metal organic vapor phase epitaxy MOVPE . A contamination free transfer of the samples from the MOVPE ambient to the ultra high vacuum chamber of the microscope ensured that the atomically well ordered, P rich 2 2 c 4 2 reconstruction of the surface was preserved. Mutually perpendicular oriented domains of the characteristic GaP 100 reconstruction identify the APDs in the GaP film at the surface and enabled us to achieve high contrast LEEM images. Striped patterns of APDs reflect the regular terrasse structure of the two domain Si 100 2 1 substrate far away from defects. APDs in the proximity of the defects have larger lateral extensions and are arranged in target pattern like structures around the defects. In contrast to transmission electronmicroscopy, which was also applied in a specific darkfield mode for comparison, the characterization of anti phase disorder by LEEM is non destructive, does not require elaborate sample preparation, and addresses extended length scale

Thermal stability of thin ZrO2 films prepared by a sol gel process on Si 001 substrates

ZrO2 films with a thickness as low as 4 nm and a roughness of about 0.2 nm have been deposited on Si(001) by a sol-gel process. After pyrolysis in air clean and dense ZrO2 films were obtained. To simulate the influence of thermal processes in complementary metal-oxide-semiconductor fabrication on high-k gate oxides, our samples have been subjected to heat treatments up to 1000 degrees C. The chemical composition of the ZrO2 films and of the interface region has been monitored by Auger electron spectroscopy (AES) and AES depth profiles. No notable chemical changes in the interface region have been detected after heating at 700 degrees C in 2 X 10(-5) mbar oxygen partial pressure and rapid annealing to 1000 degrees C. At 700 degrees C and 10(-4) mbar oxygen partial pressure an intermediate interface layer starts to grow by oxidation of the Si substrate. Annealing above 700 degrees C in UHV leads to the destruction of the sample. Loss of oxygen is accompanied with the formation of islands containing Zr and Si and of holes extending up to 200 nm deep into the Si substrate

Chemical cross-linking of anatase nanoparticle thin films for enhanced mechanical properties

Titania nanoparticle-based thin films are highly attractive for a vast range of commercial applications. Although their application on polymer-based substrates is particularly appealing, the requirement of low process temperatures results in low mechanical stability. Highly crystalline anatase nanoparticles were used as the building blocks for coatings through a two-stage process. The main benefits of this method, over the more common sol–gel ones, are the relatively low temperature required for the production of metal oxide coatings, allowing the use of polymer-based substrates, and the defined crystallinity of the resulting thin films. Although in several cases moderate temperatures can be utilized for drying the films, the mechanical stability of the respective coatings remains a critical issue. In this contribution, we present a strategy to achieve network formation between TiO₂ nanoparticles in a preformed thin film on the basis of the cross-linking of the functionalized nanoparticles. In the first stage, the nanoparticles were functionalized by dicarboxylic acids, concurrently leading to a stable colloidal dispersion that could be utilized for dip-coating to obtain TiO₂ thin films with high homogeneity and optical transparence. During the second stage, the films were immersed in a solution of a diamine as the linker molecule, to achieve cross-linking between the nanoparticles within the film. It is demonstrated that indeed covalent bonding was realized and functional coatings with significantly enhanced mechanical properties were obtained by our strategy