No abstract

Palladium was electrodeposited onto lithographically patterned Si(100) "micro-channels" with dimensions of 2 microm (width) x 100 microm (length). The properties of these Pd-covered Si micro-channels for detecting dihydrogen gas were then evaluated. Pd electrodeposition was carried out under conditions favoring an instantaneous nucleation and growth mechanism. This strategy produced size-similar Pd particles at a coverage of (4-6) x 10(9) cm(-2) within the confines of the Si micro-channel. When the mean particle radius, ro, was smaller than a critical value (ro < rc = 70-85 nm), each Pd particle was well separated on the surface from adjacent particles, on average, and no response to H2 gas attributable to the micro-channel was observed. As Pd particles were grown larger, to a mean radius of ro approximately equal to rc, adjacent particles on the surface touched and the electrical resistance of the micro-channel dropped by several orders of magnitude. These "type 2" H2 sensors exhibited a rapid (< 1 s), reversible decrease in their resistance in response to exposure to H2 above 0.5%, but a minimum resistance was observed at 1-2%, and a resistance increase was seen at higher H2 concentration. This complex behavior resulted from the existence of three mechanisms for charge transport across the micro-channel. If still larger quantities of Pd were deposited, the Pd particle ensemble coalesced into an electrically continuous film. These "type 3" sensors became more resistive in the presence of H2, not more conductive as seen for sensors of types 1 and 2, but the amplitude of this response was smaller than seen for type 2 sensors.

An experiment with five steps within a mass spectrometer (labeled MSn) showed that in the gas phase the naked Fe 4+ ion forms the molecule C6H6, probably benzene, from ethene via [Fe4(C2H2)m]+ complexes (m = 1–4), and thus acts as a catalytic center. The MS1–MS5 steps of the complex experiment are sketched below. CID = collision‐induced deactivation, a = isolation, m = 1–3.

No abstract

As previously described in greater detail, diverse transition metal cluster cations are produced in an external source by sputtering with 20 keV Xenon ions and transferred to the ICR cell of a home‐built Fourier transform mass spectrometer. There, they are thermalized by collisions with Neon atoms and stored for up to tens of seconds. They undergo a variety of reactions in the presence of ethene, benzene or ammonia, displaying different size‐specific effects. Depending upon the metal and the actual cluster size, mere physical adsorption or dehydrogenation is prevailing.

No abstract

Abb. 1. Molekulstruktur von 2 (Ellipsoide rnit 25% Aufenthaltswahrscheinlichkeit). Der Komplex hat die Eigensymmetrie T-C,. Eine hohere Koordinationszahl der Ni-Atome als vier kann ausgeschlossen werden, da sich folgende kurzeste Abstande zu Atomen benachbarter Molekiile errechnen: Ni-H 509, Ni-C 586pm. Ausgewahlte Bindungslingen [pm] und -winkel ["I mit

Mass spectra of various metal cluster ions, mainly of transition metals are presented. These clusters were sputtered by an external 20 keV Xe+ ion source and detected with a Fourier transform mass spectrometer (FT‐MS). Cluster ions could be efficiently trapped in the ion cyclotron resonance cell (ICR‐cell). In the case of indium, for instance, clusters containing more than 100 atoms could be observed. The sensitivity of our instrument was sufficient to even detect Au+85 cluster ions with mass 16745 u. “Magic numbers” are observed in the cluster cation distributions of indium and the d10S1 metals copper, silver and gold.