STM investigation of temperature-dependent two-dimensional supramolecular architectures of C60 and amino-tetraphenylporphyrin on Ag(110)

Multicomponent supramolecular self-assemblies of exceptional long-range order and low defectivity are obtained if C(60) and 5-(4-aminophenyl)-10,15,20-triphenylporphyrin (TPP-NH2) are assembled on Ag(110) by sequential evaporation in the submonolayer range of TPP-NH2 and fullerene on the substrate surface and subsequent annealing. A (+/-2 -3, 6 +/- 3) array consisting of supramolecular stripes of a 1:1 C(60)/TPP-NH2 2D adduct develops at 410 K (the low temperature, LT, phase). If the LT phase is annealed at 470 K, then a 3:1 fullerene/TPP-NH2 (+/-3 -5, 5 +/- 5) nanoporous array (the HT phase) forms, with each pore containing a single porphyrin molecule. Phase separation occurs by annealing the HT phase at 520 K. Structural models are proposed and discussed on the basis of the experimental scanning tunneling microscopy results.

Mesoporous silicas impregnated with cobalt and nickel oxide nanoparticles and the growth of carbon nanotubes there from

Metal oxide-based nanoparticles of cobalt or nickel were deposited inside the pores and on the surface of hexagonal mesoporous silicas by a direct synthesis technique using Pluronic P85 and P123 surfactants as structure directing agents with the appropriate metal phthalocyanine as a metal precursor. Metal loadings were between 0.4-3.2 wt.%. XPS studies showed that the initial form of the metal oxide nanoparticles were [CoO] and [NiO] respectively. Samples of these materials formed from the P85 surfactant and 3.0 wt.% were used to grow carbon nanotubes (CNTs) from acetylene feedstock in a catalytic chemical vapour deposition (CCVD) reactor at 800 degrees C. CNT growth appeared to be random and the CNTs had diameters ranging from < 10 to > 90 nm. Treatment of the metal impregnated silicas with nitric acid produced materials which, under the same CNT growth conditions, afforded more uniform CNTs with diameters between 5-15 nm. No significant loss in mesophase ordering was seen in the TEM, PXRD or nitrogen physisorption analysis of the acid washed samples. CNTs grown with cobalt impregnated silicas formed with the P123 surfactant had diameters in the range 15-25 nm. Raman spectroscopy of the CNT products showed the nanotubes were highly graphitised and of good quality.

Electron transport through single Mn12 molecular magnets

We report transport measurements through a single-molecule magnet, the Mn12 derivative [Mn12O12(O2C-C6H4-SAc)16(H2O)4], in a single-molecule transistor geometry. Thiol groups connect the molecule to gold electrodes that are fabricated by electromigration. Striking observations are regions of complete current suppression and excitations of negative differential conductance on the energy scale of the anisotropy barrier of the molecule. Transport calculations, taking into account the high-spin ground state and magnetic excitations of the molecule, reveal a blocking mechanism of the current involving nondegenerate spin multiplets.

Electrospray ionization mass spectrometric study of the hydrolysis-polycondensation process of Sn(OBu(t))(4)

The oligomerization of Sn(OBu(t))(4) in the sol-gel process has been studied by several different analytical approaches. Electrospray ionization (ESI) mass spectrometry was highly effective in describing the first species produced by the hydrolysis-polycondensation reactions. Mössbauer spectroscopy has elucidated the fast behavior of the hydrolytic oligomerization process, while calorimetric data have demonstrated the high enthalpy of the reaction in the presence of different solvents.

Electrospray ionization in the study of the polycondensation of Ti(O-i-C3H7)4 and Ti(O-n-C4H9)4

The polycondensation of Ti(O-i-C3H7)4 (1) and Ti(O-n-C4H9)4 (2), precursors widely employed in sol-gel processes, has been investigated by electrospray ionization mass spectrometry. By analysis of 10(-6) M methanol solutions of compounds 1 and 2, the same ionic species are detected, proving that the first step in the polycondensation reaction is the i-propyl (or n-butyl) alcohol-methanol complete exchange. This reaction leads to the Ti(OCH3)4 (3) species, representing the synthon of the polycondensation. Various oligomers of 3 have been detected and characterized by MS/MS experiments, and the related mechanisms have been discussed. A minor oligomeric series due to hydroxyl-containing polycondensation products has also been characterized.