ZnO nanoparticle growth on single-walled carbon nanotubes by atomic laye r deposition and a consequent lifetime elongation of nanotube field emission emission

ZnO nanoparticles were grown on single-walled carbon nanotubes (SWNTs) by atomic layer deposition using diethylzinc (DEZ) and water. The athors discuss that, because of chemical inertness of nanotubes to DEZ and water molecules, such nanoparticles are not likely to grow on the wall of clean and perfect nanotubes. Rather, the growth of ZnO nanoparticles should be attributed to imperfection of nanotubes, such as defects and carbonaceous impurities. Lifetime of field emission from SWNTs with the ZnO nanoparticles is 2.5 times longer than that from the as-grown nanotubes. It is thought that the protection of the defects or impurities by ZnO nanoparticles mainly contributed to the improvement of the field emission lifetime from SWNTs.open262

Vacuum microbalance investigations on heterogeneous surface reaction mechanisms

A vacuum apparatus including a microbalance and a gas-inlet system was designed. The microbalance had two symmetric reaction tubes which were heated with temperature-controlled furnaces. A cooling trap was built into the tubes above the furnaces to freeze out the reaction products. Thus, the thermodynamical equilibrium of the reaction and the reflection of the products from the tubewalls was avoided and the kinetics of the reaction could be studied. With the totally symmetric design, thermodiffusion of the reaction gas and other disturbances caused by thermal gasflow were minimized. Electrostatic effects were suppressed by a special grounding device inside the reaction tubes. The reduction of zinc oxide powder, pellets, and single crystals with carbon monoxide and hydrogen was studied in the temperature range of 450–950 °C and pressure range from 10−2 to 5 Torr

Vacuum microbalance investigations on the pressure and temperature dependence of solid/gas reactions

The pressure and temperature dependdence of the evaporation-analogous heterogeneous reaction ZnO(s) + CO(v), H2(v) → Zn(v) + CO2(v), H2O(v) was studied with a vacuum microbalance apparatus. The reaction rate as a function of pressure, temperature and surface structure of the solid was determined. It was found that the order n and the activation energy EA depend on temperature and pressure. The results can be explained by the assumption of different reaction mechanisms. At high temperatures and small pressures the activation of the Zn–O bond on the surface of the solid is rate determining. For high temperatures and hogh pressures the reflection of the reaction products Zn(v) and Co2(v) from the gas phase on the surface auses the change in the order n and hast to be considered. At low temperature the desorption of the products become rate determining. Experiments with Co/argon mixtures confirm the proposed interpretation for higher pressures

The decomposition of [Mn(CO)\u3csub\u3e5\u3c/sub\u3e]\u3csub\u3e2\u3c/sub\u3e(μ-SiH\u3csub\u3e2\u3c/sub\u3e)

The prospect of using chemical vapor deposition to deposit mixed metals and silicides from a single source compound is attractive but largely uninvestigated. Studies of decomposition energies of such compounds are nearly nonexistent. One such compound which has successfully been used to make a silicide coating is [Mn(CO)5 12 (μ-SiH2). We have used electron impact mass spectroscopy, photoionization mass spectroscopy, and photoabsorption to determine bond energies within this compound. The combination of methods allows a high degree of confidence in the resultant ionization and fragment appearance potentials. Some possible mechanisms of decomposition are discussed. A complete ionic decomposition thermodynamic cycle has been generated, and the results are used to illuminate the coating processes previously observed

The effect of attractive lateral interactions on flash-desorption spectra

We will discuss the effect of attractive lateral interactions on flash-desorption spectra for molecular and dissociatively adsorbed species. Attractive interactions lead to characteristic coverage dependent variations in the shape and in the temperature maximum of desorption peaks which are quite distinct from desorption traces without lateral interactions. These variations are modelled for first and second order desorption kinetics with and without precursor states. As an example for attractive lateral interactions we will present flash-desorption results of moleculary adsorbed N2 on a Ni(110) surface

The reduction of cadmiumoxid with CO

The interaction of N2 with an Fe(100) surface was studied by means of Auger electron spectroscopy and LEED. Adsorption takes place above room temperature with an initial sticking coefficient in the order of 10−7 and with an activation energy of about 5 kcal/mole. The activation energy for desorption is estimated to be in the range of 50–60 kcal/mole. The LEED pattern exhibits the formation of a c 2×2 structure. It is concluded that atomic nitrogen forms this strongly chemisorbed phase. Dissolution of nitrogen atoms in the bulk complicates the quantitative analysis of the experimental data

Struktur- und Fehlordnungsabhängigkeit der Reduktion von Zinkoxid mit Kohlenmonoxid und Wasserstoff, Teil IV: Modellvorstellungen und formalkinetische Behandlung

The kinetics of the reduction of zinc oxide wtih H2 and CO was investigated by thermogravimetry in dependendence on temperature, pressure, intrinsic dismechanism does not depend on the type of reduction gas, but depends on the reaction parameters mentioned. The results support model which comprises the following steps as rate determining in the different regions: 1. activatin of the surface bond of oxygen to the lattice, influenced by instrinsic disorder, 2. inhibited desorption of products, 3. equilibration with transport hindrance. Transitions between 1., 2. and 3. occur, depending on the stage of reaction as well as superimposition of 2. and 3. The results are of general importance in heterogeneous catalysis.Die Kinetik der Reduktion von Zinkoxid mit H2 und Co wurde thermogravimetrisch als Funktion der Temperatur, des Gasdrucks, der Eigenfehlordnung und der Mikro- und Makrostruktur untersucht. Aus den Ergebnissen ist zu folgern, daß der Mechanismus unabhängig vom Reaktionsgas ist, jedoch von den Reaktionsparametern abhängt. Die Ergebnisse werden am besten durch ein Modell repräsentiert, das folgende Teilschritte unter den verschiedeen äußeren Bedinungen als geschwindigkeitsbestimmend annimmt: 1. fehlerordnungsbeeinflußte Aktivierung von Oberflächensauerstoff, 2. gehemmte Produktdesorption, 3. transportbedingte Geleichgewichtseinstellung, wobei je nach Reaktionsstadium Übergänge zwischen 1., 2. und 3. sowie Überlagerungen von 2. und 3. auftreten. Die Ergebnisse sind von allgemeiner Bedeutung für die Katalyse