Monte-Carlo study of a model for the roughening transition of high-index crystal faces

A simple terrace-step-kink model is studied using Monte-Carlo techniques. In the nearly isotropic case where the energy to form a kink within a step,W ₀, is equal to the energy to shift a step by one interatomic spacing,w _n, the roughening transition is determined numerically in accordance with the Kosterlitz-Thouless theory. In the anisotropic case,w _nW ₀, results can be related to atomic beam-diffraction experiments on Cu(1,1,3). Additional evidence for a roughening transition of that face is given; the transition, however, seems to occur at a temperature somewhat higher than has been previously anticipated.     

Asymmetric hydrogenation - influence of the structure of carbohydrate derived catalysts on the relative enantioselectivity QH/Me regarding acid and ester substrates and its inversion - selectivity increase in water by amphiphiles

4,6-O-Benzylidene protected 2,3-bis(O-diphenylphosphino)-δ-glycopyranoside rhodium(I) chelate precatalysts 1-4 e,f showed for the hyrogenation of methyl (Z)-2-N-acylamidoacrylates 6-8 a stepwise decrease of the enantioselectivity with increasing number of axially oriented hexopyranoside substituents. The decrease is even stronger for the analogous substrate acids 6h-8h resulting in an unusual low relative enantioselectivity Q=q_H/q_Me of 0.3 for the precatalysts 4e and 4f. Deprotected, 4,6-OH-group bearing catalysts 1-4g,h generally show smaller differences of %ee in methanol or benzene, however, not in water. Under addition of amphiphiles a in comparison with blanks b the relative enantioselectivity Q=q_a/q_b clearly increases for both groups of catalysts - in most cases to Q-values between 3 up to 8 - independent of a neutral or ionic nature of the amphiphile.     

Enhanced ethanol sensing properties of WO3 modified TiO2 nanorods

Pristine and WO₃ decorated TiO₂ nanorods (NRs) were synthesised to investigate n-n-type heterojunction gas sensing properties. TiO₂ NRs were fabricated via hydrothermal method on fluorine-doped tin oxide coated glass (FTO) substrates. Then, tungsten was sputtered on the TiO₂ NRs and thermally oxidised to obtain WO₃ nanoparticles. The heterostructure was characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy. Fabricated sensor devices were exposed to VOCs such as toluene, xylene, acetone and ethanol, and humidity at different operation temperatures. Experimental results demonstrated that the heterostructure has better sensor response toward ethanol at 200 °C. Enhanced sensing properties are attributed to the heterojunction formation by decorating TiO₂ NRs with WO₃.     

The mean field theory of the three-dimensional ANNNI model

The mean field equations of the simple cubic or tetragonal ANNNI model are studied on finite lattices. Structure combination branching processes are found which allow us to considerably refine previous mean field calculations on the model.     

Singlet Oxygen Generation by Cyclometalated Complexes and Applications

While cyclometalated complexes have been extensively studied for optoelectronic applications, these compounds also represent a relatively new class of photosensitizers for the production of singlet oxygen. Thus far, singlet oxygen generation from cyclometalated Ir and Pt complexes has been studied in detail. In this review, photophysical data for singlet oxygen generation from these complexes are presented, and the mechanism of ¹O₂ generation is discussed, including evidence for singlet oxygen generation via an electron‐transfer mechanism for some of cyclometalated Ir complexes. The period from the first report of singlet oxygen generation by a cyclometalated Ir complex in 2002 through August 2013 is covered in this review. This new class of singlet oxygen photosensitizers may prove to be rather versatile due to the ease of substitution of ancillary ligands without loss of activity. Several cyclometalated complexes have been tethered to zeolites, polystyrene, or quantum dots. Applications for photooxygenation of organic molecules, including “traditional” singlet oxygen reactions (ene reaction, [4 + 2] and [2 + 2] cycloadditions) as well as oxidative coupling of amines are presented. Potential biomedical applications are also reviewed.     

Chemistry of trans-resveratrol with singlet oxygen: [2+2] addition, [4+2] addition, and formation of the phytoalexin moracin M

Resveratrol (1) reacts with singlet oxygen by two major pathways: A [2+2] cycloaddition forming a transient dioxetane that cleaves into the corresponding aldehydes and a [4+2] cycloaddition forming an endoperoxide that, upon heating, undergoes a rearrangement to moracin M. The rate constant by which singlet oxygen is removed by 1 (k(T)) was determined by time-resolved infrared luminescence spectroscopy to be 1.5 × 10(6) M(-1) sec(-1) in CD(3)OD, smaller than previously reported values. Chemical reaction accounts for ca. 25% of k(T).     

Interface properties of the three-state potts model in two dimensions

Interface properties, in particular the interface free energy and the interface profile of the three-state Potts model in two dimensions are studied using Monte Carlo techniques and a generalized version of the method of Müller-Hartmann and Zittartz. The role of the third state in characterizing the interface between the two other states is elucidated.     

Rectangular lattice gas model with competing interactions and the two-dimensional ANNNI model in a field

A lattice gas model with short range competing interactions for adsorption on (110) surfaces of fcc crystals, in particular for O/Pd(110), as well as its Ising analog, the two-dimensional ANNNI model with antiferromagnetic axial nearest and next-nearest neighbour interactions in a field, are studied using the free fermion approximation and Monte Carlo techniques. The phase diagrams display different commensurate phases and incommensurate regions. Static and dynamic aspects of topological defects (walls and dislocations) characterising the incommensurate structures are investigated.     

Two-dimensional ising models with competing interaction—a Monte Carlo study

Two-dimensional Ising models on a square lattice with competing interactions along one axis or both axes are studied primarily by the Monte Carlo method. Several commensurate-incommensurate transitions are found. Dislocation-like configurations are identified near the sinusoidal — paramagnetic transition in accordance with the idea that the transition might be of Kosterlitz-Thouless, XY-like character.