Michaela Zirngast

Seedless growth of sub-10 nm germanium nanowires.

We report the self-seeded growth of highly crystalline Ge nanowires, with a mean diameter as small as 6 nm without the need for a metal catalyst. The nanowires, synthesized using the purpose-built precursor hexakis(trimethylsilyl)digermane, exhibit high aspect ratios (>1000) while maintaining a uniform core diameter along their length. Additionally, the nanowires are encased in an amorphous shell of material derived from the precursor, which acts to passivate their surfaces and isolates the Ge seed particles from which the nanowires grow. The diameter of the nanowires was found to depend on the synthesis temperature employed. Specifically, there is a linear relationship between the inverse radius of the nanowires and the synthesis temperature, which can be explained by a model for the size-dependent melting of simple metals.

Group 4 metallocene complexes of disilenes, digermenes, and a silagermene.

Reactions of 1,2-dipotassiotetrakis(trimethylsilyl)disilane with group 4 metallocene dichlorides lead to the formation of the respective metallocene 1,1,2,2-tetrakis(trimethylsilyl)disilene complexes. While the disilene titanocene complex could be structurally characterized, the zirconocene and hafnocene compounds, which are believed to possess some degree of bis-[bis(trimethylsilyl)silylene] character, can only be isolated in substance as the respective trimethylphosphane adducts. Analogous metallocene 1,1,2,2-tetrakis(trimethylsilyl)digermene complexes and a tetrakis(trimethylsilyl)silagermene complex were prepared. Instead of metallocene 1,1,2,2-tetrakis(trimethylsilyl)distannene complexes, four-membered rings composed of a metallocene and three bis(trimethylsilyl)stannylene units were obtained.

Formation of Formal Disilene Fluoride Adducts

Reactions of trisilylated silylfluorides with potassium tert-butoxide were found to give disilylated fluorosilylenoids. The latter undergo a self-condensation reaction, leading to the formation of beta-fluorodisilanyl anions, which may also be considered as fluoride adducts of disilenes. The stereochemical outcome of this self-condensation depends on the bulkiness of the silyl substituents. Thus, mixtures of diastereomers are obtained in some cases. Reaction of a disilene adduct with magnesium bromide triggers metal fluoride elimination and formation of the respective tetrasilylated disilene. Attempts to exchange one silyl group of the starting material for a methyl, phenyl, or tert-butyl group led to a different course of reaction for the methyl and phenyl cases. The tert-butyl-substituted example gave the expected disilene adduct, but it was not the main product.

Synthesis of Oligosilanyl Compounds of Group 4 Metallocenes with the Oxidation State +3

Recently, we showed that titanocene silyls are much more stable with Ti in the oxidation state +3. The current study demonstrates that analogous Zr and Hf compounds can also be obtained by reaction of a suitable metalate precursor with an oligosilanyl dianion. As the obtained complexes formally possess a d1 electron configuration, they were investigated using EPR spectroscopy. The corresponding spectra indicate that the compounds can be considered to also exhibit some cyclosilanyl radical anion character. In order to understand the strong preference of disilylated titan(IV)ocenes for reductive elimination, a theoretical study of the thermodynamics of these reactions was conducted, revealing that this behavior is essentially caused by the weak Si–Ti(IV) bond.

Single step synthesis of Ge–SiOx core-shell heterostructured nanowires

The ability to control the morphology of heterostructured nanowires, through the design of precursors and by careful manipulation of reaction parameters, is important if these materials are to be utilised as components in future nanodevices. Traditionally core-shell heterostructured nanowires have been synthesised through multi-precursor and/or multi-step synthetic routes. In this paper we discuss the synthesis of core-shell, Ge–SiOx heterostructured nanowires using a single source precursor and a single step supercritical fluid reaction process.