Roland A. Fischer

Synthesis of CdSe nanoparticles using various organometallic cadmium precursors

Investigations into replacing Me2Cd as a common precursor for the synthesis of CdSe nanoparticles by pyrolysis in a hot coordinating solvent have proven that more stable, less volatile or even crystalline organometallic cadmium compounds can be used instead of Me2Cd. Dineopentylcadmium, bis(3-diethylaminopropyl)cadmium and (2,2′-bipyridine)dimethylcadmium have been used successfully as cadmium sources for the preparation of tri-n-octylphosphine oxide (TOPO)-capped CdSe nanoparticles. The resulting nanocrystallites have been characterized by UV–VIS and IR spectroscopy, photoluminescence spectroscopy (PL), mass spectrometry and transmission electron microscopy (TEM). They consist of separated, well defined spherical particles and show a small size distribution as well as a characterisitic blue shift due to quantum confinement in their optical spectra. The replacement of Me2Cd by less dangerous organometallic precursors thus results in nanocrystallites that show no reduction in quality when compared to the standard method.

Low-Temperature Atomic Layer Deposition of Copper Metal Thin Films: Self-Limiting Surface Reaction of Copper Dimethylamino-2-propoxide with Diethylzinc†

A uniform, conformal, pure copper metal thin film was grown at very low substrate temperatures (100-120 degrees C) on Si(100) substrates by atomic layer deposition involving the ligand exchange of [Cu(OCHMeCH(2)NMe(2))(2)] with Et(2)Zn (see scheme). Patterned copper thin films of Cu nanotubes (diameter 150 nm, length 12 microm) were fabricated.

A colloidal ZnO/Cu nanocatalyst for methanol synthesis

Free-standing, ZnO surface decorated Cu nanoparticles of 1-3 nm size were obtained by sequential co-pyrolysis of [Cu(OCHMeCH2NMe2)2] and ZnEt2 in squalane in the absence of additional surfactants and proved to be highly active quasi homogeneous catalysts for methanol synthesis from CO and H2.

Synthesis, characterization, and thermal properties of homoleptic rare-earth guanidinates: promising precursors for MOCVD and ALD of rare-earth oxide thin films.

Eight novel homoleptic tris-guanidinato complexes M[(N(i)Pr)(2)CNR(2)](3) [M = Y (a), Gd (b), Dy (c) and R = Me (1), Et (2), (i)Pr (3)] have been synthesized and characterized by NMR, CHN-analysis, mass spectrometry and infrared spectroscopy. Single crystal structure analysis revealed that all the compounds are monomers with the rare-earth metal center coordinated to six nitrogen atoms of the three chelating guanidinato ligands in a distorted trigonal prism geometry. With the use of TGA/DTA and isothermal TGA analysis, the thermal characteristics of all the complexes were studied in detail to evaluate their suitability as precursors for thin film deposition by MOCVD and ALD. The (i)Pr-Me(2)N-guanidinates of Y, Gd and Dy (1a-c) showed excellent thermal characteristics in terms of thermal stability and volatility. Additionally, the thermal stability of the (i)Pr-Me(2)N-guanidinates of Y and Dy (1a, c) in solution was investigated by carrying out NMR decomposition experiments and both the compounds were found to be remarkably stable. All these studies indicate that (i)Pr-Me(2)N-guanidinates of Y, Gd and Dy (1a-c) have the prerequisites for MOCVD and ALD applications which were confirmed by the successful deposition of Gd(2)O(3) and Dy(2)O(3) thin films on Si(100) substrates. The MOCVD grown films of Gd(2)O(3) and Dy(2)O(3) were highly oriented in the cubic phase, while the ALD grown films were amorphous.

The two-step chemical vapor deposition of Pd(allyl)Cp as an atom-efficient route to synthesize highly dispersed palladium nanoparticles on carbon nanofibers

Highly dispersed palladium nanoparticles supported on carbon nanofibers, which show high catalytic activity and stability in the hydrogenation of cyclooctene, were synthesized by the two-step metal organic chemical vapor deposition (MOCVD) of allylcyclopentadienylpalladium (Pd(allyl)Cp) as precursor at atmospheric pressure.

Homoleptic Gadolinium Guanidinate: A Single Source Precursor for Metal−Organic Chemical Vapor Deposition of Gadolinium Nitride Thin Films

Deposition of a rare earth nitride thin film using a chemical gas phase deposition technique is reported for the first time. The gadolinium tris-guanidinate complex [Gd{((i)PrN)(2)CNMe(2)}(3)] is found to be an effective single source precursor for the MOCVD growth of gadolinium nitride (GdN) thin films.

Oxidative addition of group 13 and 14 metal halides and Alkyls to Ga(DDP) (DDP = bulky bisimidinate).

The oxidative addition of a variety of group 13 and group 14 halides and alkyls R aMX to the mono valent group 13 bis-imidinate Ga(DDP) (DDP = 2-{(2,6-diisopropyl-phenyl)amino}-4-{(2,6-diisopropylphenyl)imino}-2-pentene) is reported. Accordingly, the insertion of Ga(DDP) into the Ga-Me bond of GaMe 3 yield in the complexes [{(DDP)GaMe}GaMe 2] ( 1) and [{(DDP)GaMe} 2GaMe] ( 2), respectively, which show a temperature-dependent equilibrium between 1 at higher temperatures and 2 at lower temperatures. In the case of GaCl 3, the only isolable product is [{(DDP)GaCl} 2GaCl] ( 3). The related reaction of SnMe 2Cl 2 with Ga(DDP) yields the compound [Me 2Sn{ClGa(DDP)} 2] ( 4), whereas SnMe 4 behaves inert. In the case of SiCl 4, only the monoinsertion product [Cl 3Si{ClGa(DDP)}] ( 5) was observed. Finally, [(CH 3) 3C{ClGa(DDP)}] ( 6) is synthesized by insertion of Ga(DDP) into the C-Cl bond of ClC(CH 3) 3. All new compounds were fully characterized by elemental analysis, NMR-spectroscopy, and single-crystal X-ray diffraction analysis.

Hafnium oxide thin film grown by ALD: An XPS study

Hafnium(IV) oxide thin films were synthesized by atomic layer deposition (ALD) on Si(100) substrates, using an innovative guanidinate-stabilized hafnium amide precursor, [Hf(NEtMe)2(EtMeNC(NiPr)2)2]. In the present work, our attention is focused on a detailed XPS characterization of a representative HfO2 coating grown at 350 °C. Beside the wide scan spectrum, detailed spectra for the O 1s, Hf 4f, Hf 4d and C 1s regions and related data are presented and discussed. The obtained results point out to the formation of HfO2 coatings characterized by the presence of -OH groups, whose main origin is attributed to the use of water as oxidizing agent during the preparation process.

Ligand properties of Cp*Ga: new examples of Mo–Ga and W–Ga complexes

The compounds [ fac -(Cp*Ga) 3 M(CO) 3 ] ( 1a , M=Mo: 1b , M=W) were synthesized by reaction of [ fac -(RCN) 3 M(CO) 3 ] (R=Me, Et) with Cp*Ga. The treatment of 1a with one equivalent of [ fac -(MeCN) 3 Mo(CO) 3 ] gives the dimeric cluster compound [Mo 2 (CO) 6 (μ 2 -(GaCp*)) 3 ] ( 2 ). Addition of Cp*Ga to the Lewis-acidic unsaturated metal centres of [CpM(CO) 2 ] 2 (M=Mo, W) yields the dimeric complexes [(OC) 2 (Cp)M(μ 2 -(η 1 -GaCp*))] 2 ( 3a : M=Mo, 3b : M=W). The new compounds 1 – 3 were characterized fully including single crystal X-ray diffraction studies.

Synthesis of periodic mesoporous organosilicas with chemically active bridging groups and high loadings of thiol groups

Chemically active isocyanurate-bridged periodic mesoporous organosilica materials with high loadings of pendant thiol groups have been synthesized via co-condensation under acidic conditions, using the triblock copolymer EO20PO70EO20 (P123) as template and a mixture of mercaptopropyl-containing silane and isocyanurate-containing silsesquioxane to form the framework. The obtained SH–ICS–PMOs were characterized by XRD, transmission electron microscopy (TEM), solid state 13C and 29Si MAS NMR spectroscopy, and N2 physical sorption. The data show that well-ordered SH–ICS–PMOs were obtained with 40% of the framework Si atoms bearing the thiol pendant groups. Interestingly, the introduction of the thiol groups improved the mesostructural ordering and favored the cross-linking of the pore walls. The determination of Hg2+ uptake from aqueous solution as a test case showed that both the bridging ICS groups and the pendant thiol groups in the SH–ICS–PMOs are active in adsorbing Hg2+. Our study demonstrated that well-ordered periodic mesoporous organosilicas are capable of supporting both chemically active bridging groups and active pendant groups with high loadings.