Spin-Valley Kondo Effect in Multi-electron Silicon Quantum Dots

We study the spin-valley Kondo effect of a silicon quantum dot occupied by $\mathcal{N}$ electrons, with $\mathcal{N}$ up to four. We show that the Kondo resonance appears in the $\mathcal{N}=1,2,3$ Coulomb blockade regimes, but not in the $\mathcal{N}=4$ one, in contrast to the spin-1/2 Kondo effect, which only occurs at $\mathcal{N}=$ odd. Assuming large orbital level spacings, the energy states of the dot can be simply characterized by fourfold spin-valley degrees of freedom. The density of states (DOS) is obtained as a function of temperature and applied magnetic field using a finite-U equation-of-motion approach. The structure in the DOS can be detected in transport experiments. The Kondo resonance is split by the Zeeman splitting and valley splitting for double- and triple-electron Si dots, in a similar fashion to single-electron ones. The peak structure and splitting patterns are much richer for the spin-valley Kondo effect than for the pure spin Kondo effect.Comment: 8 pages, 4 figures, in PRB format. This paper is a sequel to the paper published in Phys. Rev. B 75, 195345 (2007

The reaction of formic acid with RaneyTM copper

The interaction of formic acid with RaneyTM Cu proves to be complex. Rather than the expected generation of a monolayer of bidentate formate, we find the formation of a Cu(II) compound. This process occurs by direct reaction of copper and formic acid; in contrast, previous methods are by solution reaction. This is a rare example of formic acid acting as an oxidant rather than, as more commonly found, a reductant. The combination of diffraction, spectroscopic and computational methods has allowed this unexpected process to be characterized

Valley Splitting Theory of SiGe/Si/SiGe Quantum Wells

We present an effective mass theory for SiGe/Si/SiGe quantum wells, with an emphasis on calculating the valley splitting. The theory introduces a valley coupling parameter, $v_v$, which encapsulates the physics of the quantum well interface. The new effective mass parameter is computed by means of a tight binding theory. The resulting formalism provides rather simple analytical results for several geometries of interest, including a finite square well, a quantum well in an electric field, and a modulation doped two-dimensional electron gas. Of particular importance is the problem of a quantum well in a magnetic field, grown on a miscut substrate. The latter may pose a numerical challenge for atomistic techniques like tight-binding, because of its two-dimensional nature. In the effective mass theory, however, the results are straightforward and analytical. We compare our effective mass results with those of the tight binding theory, obtaining excellent agreement.Comment: 13 pages, 7 figures. Version submitted to PR

Carbidisation of Pd nanoparticles by ethene decomposition, with methane production

In the presence of oxygenated organic molecules pure Pd, which is widely used in chemicals processing and the pharmaceutical industry, tends to defunctionalise and dehydrogenate such molecules to H2, CO and surface/bulk carbon, in the form of a palladium carbide. We have investigated the formation of this carbide by ethene adsorption using a variety of techniques, including pulsed flow reaction measurements, XAS and DFT calculations of the lattice expansion during carbidisation. These experiments show that two main reactions take place above 500K, that is, both total dehydrogenation, but also disproportionation to methane and the carbide, after which the activity of the Pd is completely lost. We estimate the value of x in PdCx to be 0.28 (±0.03), and show by computer modelling that this fits the lattice expansion observed by XAFS, and that there is charge transfer to C from Pd of around 0.2-0.4 e

Catalytic activity of dicarbonylrhodium complexes of aminobenzoic acid ligands on carbonylation of alcohol

Rhodium(I) complexes of the type, [Rh(CO)2ClL] (1), where L = 2-aminobenzoic acid (a), 3-aminobenzoic acid (b) and 4-aminobenzoic acid (c), have been synthesised. Oxidative addition (OA) of complexes 1 with electrophiles like RI (R = CH3, C2H5) produce Rh(III) complexes of the type [Rh(CO)(COCH3)IClL] (2) and [Rh(CO)(COC2H5)IClL] (3). The OA reactions of complexes 1 with RI follow a two stage kinetics and the observed rate constants are in the order 1b > 1c > 1a irrespective of stages. The complexes 1 show higher catalytic activity for carbonylation of methanol and ethanol than that of the well known species [Rh(CO)2I2]"12

Adsorption of formate species on Cu(h,k,l) low index surfaces

We report a density functional theory study on the relative stability of formate species on Cu(h,k,l) low index surfaces using a range of exchange-correlation functionals. We find that these functionals predict similar geometries for the formate molecule adsorbed on the Cu surface. A comparison of the calculated vibrational transition energies of a perpendicular configuration of formate on Cu surface shows an excellent agreement with the experimental spectrum obtained from inelastic neutron spectroscopy. From the calculations on adsorption energy we find that formate is most stable on the Cu(110) surface as compared to Cu(111) and Cu(100) surfaces. Bader analysis shows that this feature could be related to the higher charge transfer from the Cu(110) surface and optimum charge density at the interfacial region due to bidirectional electron transfer between the formate and the Cu surface. Analysis of the partial density of states finds that in the –5.5 eV to –4.0 eV region, hybridization between O p and the non-axial Cu dyz and dxz orbitals takes place on the Cu(110) surface, which is energetically more favourable than on the other surfaces

Oxidative addition reaction of rhodium(I) carbonyl complexes of the pyridine-aldehyde ligands and their catalytic activity in carbonylation reaction

Rhodium(I) carbonyl complexes [Rh(CO)2ClL] (1) where L = Py-2-CHO (a), Py-3-CHO (b) and Py-4-CHO (c) have been synthesized and characterized by elemental analyses, IR, 1H and 13C NMR spectroscopy. The complexes 1 undergo oxidative addition reactions with different types of electrophiles such as CH3I, C2H5I, C6H5CH2Cl and I2 to yield [Rh(CO)(COCH3)ClIL] (2), [Rh(CO)(COC2H5)ClIL] (3), [Rh(CO)(COCH2C6H5)Cl2L] (4) and [Rh(CO)ClI2L] (5) complexes, respectively. The kinetic study of the complexes1 with CH3I reveals a two-stage kinetics and the second-stage reactions are faster than that of the first stage by about 80–100 times. The rate of reaction of 1a is higherthanthatof1band1c.Thecatalyticactivityofcomplexes1incarbonylationofmethanol,ingeneral,ishigher(TON800–1250)than that of the well-known species [Rh(CO)2I2]− (TON 650)

Towards microfluidic reactors for in situ synchrotron infrared studies

Anodically bonded etched silicon microfluidic devices that allow infrared spectroscopic measurement of solutions are reported. These extend spatially well-resolved in situ infrared measurement to higher temperatures and pressures than previously reported, making them useful for effectively time-resolved measurement of realistic catalytic processes. A data processing technique necessary for the mitigation of interference fringes caused by multiple reflections of the probe beam is also describe

Antifungal activity and chemical composition of Citrus reticulata Blanco essential oil against phytopathogens from North East India

The essential oil (EO) isolated by hydro-distillation from the peel of fully matured ripen fruits of Citrus reticulata Blanco were analyzed by GC and GC 13MS. Thirty seven different components were identified constituting approximatel