Theo P. J. Peters

Etching AlAs with HF for Epitaxial Lift-Off Applications

The epitaxial lift- off process allows the separation of a thin layer of III/ V material from the substrate by selective etching of an intermediate AlAs layer with HF. In a theory proposed for this process, it was assumed that for every mole of AlAs dissolved three moles of H-2 gas are formed. In order to verify this assumption the reaction mechanism and stoichiometry were investigated in the present work. The solid, solution and gaseous reaction products of the etch process have been examined by a number of techniques. It was found that aluminum fluoride is formed, both in the solid form as well as in solution. Furthermore, instead of H-2 arsine (AsH3) is formed in the etch process. Some oxygen- related arsenic compounds like AsO, AsOH, and AsO2 have also been detected with gas chromatography/ mass spectroscopy. The presence of oxygen in the etching environment accelerates the etching process, while a total absence of oxygen resulted in the process coming to a premature halt. It is argued that, in the absence of oxygen, the etching surface is stabilized, possibly by the sparingly soluble AlF3 or by solid arsenic

Dioxygen Activation by a Mononuclear IrII–Ethene Complex

In an attempt to gain a mechanistic insight into the rhodiumand iridium-catalyzed oxygenation of olefins, we have recently investigated stoichiometric oxygenation of N ligand RhI± and IrI ± olefin complexes by O2 (olefin ethene, propene, 1,5-cyclooctadiene).[1, 2] The reactivity of RhI± and IrI ± ethene fragments towards dioxygen varied between ethene displacement (Figure 1a), formation of mixed O2 ± ethene complexes (Figure 1b), C O bond making (giving a 3-metalla( )-1,2-dioxolane; Figure 1c), and combined C O bond making and O O bond breaking (giving a 2-metalla( )oxetane; Figure 1d) The outcome of the oxygenation reaction varies with the N ligand and the central metal.

Dioxygenation of Sterically Hindered (Ethene)RhI and -IrI Complexes to (Peroxo)RhIII and (Ethene)(peroxo)IrIII Complexes

New cationic, five-coordinate bis(ethene)iridium(I) complexes [(κ3-Me3-tpa)IrI(ethene)2]+ (12+) and [(κ3-Me2-dpa-Me)IrI(ethene)2]+ (13+) have been prepared {Me3-tpa = N,N,N-tris[(6-methyl-2-pyridyl)methyl]amine, Me2-dpa-Me = N-methyl-N,N-bis[(6-methyl-2-pyridyl)methyl]amine}. Complexes 12+ and 13+ lose one ethene fragment in solution, yielding the five-coordinate mono(ethene) complex [(κ4-Me3-tpa)IrI(ethene)]+ (14+) and the four-coordinate mono(ethene) complex [(κ3-Me2-dpa-Me)IrI(ethene)]+ (15+), respectively. [(κ4-Me3-tpa)RhI(ethene)]+ (11+), the rhodium analogue of 14+, was also prepared. Whereas rhodium complex 11+ is stable in acetonitrile at room temperature, the iridium analogue 14+ converts to the cyclometallated (acetonitrile)(hydrido) complex 16+ within 72 h by dissociation of the unique 6-methylpyridyl fragment and oxidative addition of the 6-methylpyridyl C3−H bond. The four-coordinate mono(ethene) complex 15+ is even less stable in solution; it converts to a mixture of compounds within 18 h. Reaction of the mono(ethene)RhI complex 11+ with O2 yields the peroxo complex 17+ by ethene displacement. In contrast, the mono(ethene)IrI complexes 14+ and 15+ bind O2 without the loss of ethene, leading to unprecedented (ethene)(peroxo)IrIII complexes 18+ and 19+. At room temperature, peroxo complex 17+ does not react with ethene and, quite remarkably, C−O bond formation does not occur in the (ethene)(peroxo) complexes 18+ and 19+. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Controlled templating of porphyrins by a molecular command layer

The copper porphyrin (5,10,15,20-tetraundecylporphyrinato)copper(II) can be templated in a well-defined arrangement using p-(hexadecyloxycarbonyl)phenylacetylene as a command layer on graphite. The bicomponent system was characterized at the submolecular level at a solid/liquid interface by scanning tunneling microscopy (STM). It is proposed that the layer of copper porphyrins is templated on top of the command layer in a hierarchical fashion, via a combination of intermolecular π-π stacking and van der Waals interactions. A very subtle effect, i.e., a superstructure in the alkyl chain region of the phenylacetylene monolayers, was identified as a decisive factor for the templating process.

Amido-bridged dinuclear rhodium(I) complexes by deprotonation of mononuclear rhodium(I) amine complexes

The preparation of a series of new amido bridged binuclear complexes [(N/N/N)Rh I (cod)2] (cod� /Z ,Z -1,5-cyclooctadiene), [(N/N/N)Rh I (hed)2] (hed� /1,5-hexadiene) and [(N/N/N)Rh I (CO)4] is reported. These complexes contain chelating imidazole/ amido/imidazole, pyridine/amido/pyridine and pyridine/amido/pyrrolate ligands (N/N/N). The cod complexes have been prepared through deprotonation of their mononuclear amine precursors [(N/HN/N)Rh I (cod)] in the presence of [Rh I (cod)] � . Reaction of the binuclear complexes [(N/N/N)Rh I (cod)2] with CO results in the complexes [(N/N/N)Rh I (CO)4]. For N/N/N/ chelating imidazole/amido/imidazole ligand, the X-ray structures of [(N/N/N)Rh I (cod)2], [(N/N/N)Rh I (CO)4], and their mononuclear amine precursor [(N/HN/N)Rh I (cod)] are reported. Electrochemical oxidation of the complexes is related to the