Professor Jan Krzek (1946–2015)

JPC – Journal of Planar Chromatography – Modern TLC -     

Charge accumulation in the dielectric of the nanocluster NVM MOS structures under anti- and unipolar W/E window formation

This paper focuses on the detailed study of the unipolar recharging phenomenon of the nanocluster NVM cells based upon the electron emission from the nanodots and their subsequent neutralization. It is shown that electron emission from nanodots is a very fast and effective process with a time constant <5 ms, but the subsequent neutralization of the positive accumulated charge is strongly dependent on the excess of Si atoms stored in the nanodots.     

Thermal and photochemical reactivity of oxygen atoms on gold nanocluster surfaces

Reduction of oxidized gold nanoclusters by exposures to foreign gases and irradiation of UV photons has been investigated using X-ray photoelectron spectroscopy. Gold nanoclusters with narrow size distributions protected by alkanethiolate ligands were deposited on a TiO₂(1 1 0) surface with dip coating. Oxygen plasma etching was used for removal of alkanethiolate ligands and oxidization of gold clusters. The oxidized gold clusters were exposed to CO, C₂H₂, C₂H₄, H₂, and hydrogen atoms. Although, C₂H₄ and H₂ did not show any indications of reduction of oxidized gold clusters, CO, C₂H₂, and hydrogen atoms reduced the oxides on gold cluster surfaces. Among them, hydrogen atoms were most effective for reduction. Irradiation of UV photons around 400 nm could also reduce the oxidized gold clusters. The photochemical reduction mechanism was proposed as follows. The photo-reduction was initiated by electronic excitation of gold clusters and oxygen atoms activated reacted with carbon atoms at the surfaces of gold clusters. Carbon species were likely absorbed in gold clusters or remained at the boundaries between gold clusters when gold clusters agglomerated during oxygen plasma exposures. As the photochemical reduction progressed, carbon atoms segregated to the surfaces of gold clusters.     

On the way to sol–gels: an analysis of the intra‐ and intermolecular hydrogen bonding in [Ba(OH)I(H2O)4]

We have been able, via a new synthetic route, to obtain a complete crystal structure of the title compound, tetra­aqua­barium hydro­xide iodide, [Ba(OH)I(H₂O)₄], for which the heavy atoms only were characterized by Kellersohn, ­Beckenkamp & Lutz [Z. Naturforsch. TeilB (1991), 46 , 1279–1286]. In the present results, the H‐atom positions could be located using X‐ray data collection at low temperature. A three‐dimensional network is built up via hydrogen bonds. It was also observed that the title compound undergoes hy­drolysis and might therefore be regarded as an intermediate in the formation of sol–gels, starting from BaI₂ and leading to [Ba(OH)₂(H₂O)_x].     

Complexes of mixed silicon halides with 4‐picoline

The reaction products of an addition reaction of five different silicon tetrahalides with the aromatic nitro­gen base 4‐methyl­pyridine are presented. The following five structures are isomorphous: (I) tetra­chloro­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄­Cl₄­N₂Si, (II) bromo­tri­chloro­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄­Br­Cl₃N₂Si, (III) di­bromo­di­chloro­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄­Br₂­Cl₂N₂Si, (IV) tri­bromo­chloro­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄Br₃­Cl­N₂Si, and (V) tetra­bromo­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄Br₄N₂Si. The mol­ecules of (I) and (V), with D_2h symmetry, have crystallographic C_2h symmetry, while the molecules of (II), (III) and (IV) have a lower molecular symmetry, but as a result of the disorder of the halogen ligands, they appear to be of the same crystallographic symmetry. The environment around the Si atom can be described as a slightly distorted octahedron with the methyl­pyridine ligands occupying axial positions and the four halogen ligands in the equatorial plane. In spite of the different substitution pattern of the silicon centre, there are only insignificant differences between these five structures.