Hans-Jörg Himmel

An orientation analysis of differently endgroup-functionalised alkanethiols adsorbed on Au substrates

The molecular orientation in self-assembled fims of methyl-, hydroxyl-, and carboxylic acid-terminated alkanethiols of different chain lengths (n-docosanethiol [DCT], 22-mercaptodocosanol [MDO], 22-mercaptodocosanoic acid [MDC], n-hexadecanethiol [HDT], 16-mercaptohexadecanol [MHO], 16-mercaptohexadecanoic acid [MHC]) on Au substrates has been investigated by near edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). Whereas XPS-measurements do not reveal changes in thickness upon replacing the endgroups, the degree of orientation as determined with NEXAFS exhibits significant differences. The two methyl-terminated thiols show the same alkyl-chain tilt-angle α of 39°. For the short-chain OH-terminated films no significant difference could be detected, but the monolayers formed from the long-chain OH-terminated chains exhibit a slightly stronger anisotropy and thus a smaller tilt-angle α than the corresponding CH3-terminated thiol. NEXAFS-spectra recorded for films from COOH-terminated thiols reveal only a very small anisotropy which indicates the absence of significant molecular orientation resulting from a high degree of disorder.

Self-Terminated CVD-Functionalization of Organic Self-Assembled Monolayers (SAMs) with Trimethylamine Alane (TMAA)

Chemoselective deposition of alane and patterned deposition of alane and aluminum oxide on ultrathin organic selfassembled monolayers (SAMs) were investigated. Information about elementary steps of the interaction of trimethyl amine alane (TMAA) with appropriately functionalized HO- and HOOC-terminated SAMs under UHV conditions is presented. The self-terminated growth of an alane bilayer on HO-terminated SAMs was established on the basis of quantitative X-ray photoelectron spectroscopy (XPS) analysis. A patterned deposition of 2 nm of aluminum oxide on patterned SAMs obtained by microcontact printing is demonstrated.

Adsorption of organic monolayers on pyrite (FeS2)(100)

Abstract A systematic study has been carried out in order to investigate the possibility to grow ultrathin organic films by self-assembly on pyrite (FeS 2 ) from solutions of triphenylphosphine, n -alkanethiols and n -alkylamines. The adsorption of the different molecules on pyrite(100) surfaces was studied with regard to chemical composition using X-ray photoelectron spectroscopy and with regard to molecular orientation by near-edge X-ray absorption fine structure and IR spectroscopy. Triphenylphosphine readily adsorbs from a solution in ethanol and forms dense monolayers. The adsorption of n -alkylamines is found to result in the formation of highly oriented films, n -alkanethiols, which form well defined monolayers on Au, Ag and Cu surfaces are not found to adsorb on pyrite from solutions in ethanol.

Compounds featuring a bond between a Group 13 (M) and a Group 15 element (N or P) and with the formulae HmMNHn and HmMPHn: structural aspects and bonding

Following studies of the thermal and photoactivated reactions of the Group 13 metal atoms Al, Ga or In (M) with NH3 or PH3 in solid argon matrices, the properties of the observed or potential reaction products are discussed. These are molecules with the general formula HmMEHn, where Mxa0=xa0Al, Ga or In, Exa0=xa0N or P, and m, nxa0=xa00–3. All the molecules have been characterised structurally, energetically and vibrationally by Density Functional Theory (DFT) calculations. The following products have been identified experimentally by their IR spectra: the adducts M·EH3, the metal(II) insertion products HMEH2, the metal(III) derivatives H2MNH2 and H2MPH, and the metal(I) amides MNH2. The observation of most of the IR-active fundamentals for different isotopic forms of the molecules MNH2 and H2MNH2 allowed normal coordinate analysis calculations to be performed, thereby endorsing the vibrational assignments and affording reliable force constants. Observed and hypothetical HmMEHn molecules have been compared with particular reference to structural and energetic differences according to whether Exa0=xa0N or P. Questions of bonding have been addressed through calculations of barriers to rotation of planar molecules and of barriers to inversion for molecules containing pyramidal MPH2 moieties. π-Type interactions play only a minor part in the bonding of planar molecules like H2MNH2. The much larger barrier to inversion of PH3 compared with NH3 results in pyramidal MPH2 but planar MNH2 fragments. With the help of an appropriate MO scheme it is possible to rationalise how the inversion barrier changes when one hydrogen of PH3 is replaced by an MHm group.

Methylgallium and methylindium: the first sighting of the simplest organic derivatives of Ga(I) and In(I)

Gallium or indium atoms are shown to react with methane in solid Ar matrices upon UV photolysis (λ = 200–400 nm) to give initially the methylmetal hydride which undergoes photodissociation on broad-band irradiation (λ = 200–800 nm) to yield the methylmetal(I) compound, CH3M (M = Ga or In); the products are characterised by their IR spectra afforced by the results of DFT calculations.

Chemical properties of hydrogen-bonded organic bilayers fabricated via self-assembly of COOH-functionalised oligophenylthiols on Au substrates

Abstract Here we present an investigation of chemical reactions induced by exposing organic, hydrogen-bonded films prepared from COOH-terminated oligophenylthiol molecules on Au to solutions of different reactants. Our study includes reactions with acids (trifluoroacetic acid, TFA) and metal ions (potassium (K + )- and copper (Cu 2+ )-ions). On the basis of XPS measurements the film thickness and the elemental ratios of the elements involved in the process have been quantified. Our results reveal that treatment of the bilayers with trifluoroacetic acid results in the removal of the second layer and the formation of highly oriented, COOH-terminated monolayers. While the immersion of the bilayers in solutions containing Cu 2+ -ions leads to the removal of the second layer and the formation of a Cu 2+ -terminated monolayer-surface, potassium ions are incorporated in the bilayers by immersion into an ethanolic solution of potassium hydroxide. The reasons of these differences are related to the different coordination spheres of the ions and their compatibility with the structure of the self-assembled film.