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The atomic structure of single steps on the Si(111)- 3 3 ? -Sn surface and the dynamics of Sn adatoms in the vicinity of these steps were studied. The work was performed using scanning tunneling microscopy (STM) and ab initio calculations based on the density functional theory. The atomic structure model of the single steps consisting of Sn atomic chains along the steps was developed. This structure leads to the formation of potential double-wells near the steps acting as traps for Sn atoms and explains the fluctuating tunneling current recorded in these areas.

The atomic structure of well-ordered single steps on the $\mathrm{Si}(111)\ensuremath{-}\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\ensuremath{-}\mathrm{Sn}$ surface and the dynamics of Sn adatoms in the vicinity of these steps was studied. The work was performed using low-temperature scanning tunneling microscopy (STM) and ab initio calculations based on the density-functional theory. The STM tip was used to record the tunneling current versus time on top of oscillating adatoms, keeping the feedback loop turned off. The dynamics of adatoms, detected as the telegraph noise present in the tunneling current, was registered near the steps at 80 K. The atomic structure model of the single steps consisting of Sn atomic chains along the steps was developed. This structure leads to the formation of potential double wells near the steps acting as traps for Sn atoms and explains the fluctuating current recorded in these areas.

We report a combined experimental and theoretical study on the formation of dumbbell silicene structures on Ag(110). High-resolution scanning tunneling microscopy (STM) reveals a rich tapestry of adatom-free and -decorated bidimensional silicene phases covering the whole Ag(110) surface. The most thermodynamically stable silicene models obtained from density-functional theory (DFT) perfectly reproduce all features observed by STM. These phases correspond to different Si buckled honeycomb reconstructions ((13 × 4), c(18 × 4), and c(8 × 4)) composed of two periodic motifs common to all structural models. DFT calculations show that these reconstructions are stabilized by the presence of ordered arrays of Si adatoms adsorbed on top of silicene in a dumbbell configuration. Grazing incidence X-ray diffraction (GIXD) measurements confirm the growth of a dumbbell silicene layer. The structure factor values are well reproduced by a (13 × 4) model with 4 Si adatoms per unit cell and a slight distortion of the hexagonal unit cell. Our STM-DFT-GIXD study demonstrates the formation of dumbbell silicene, a theoretically predicted two-dimensional Si allotrope. This opens up perspectives for tuning the peculiar properties of silicene.

Silicene, the 2D silicon allotrope analogue of graphene, was theoretically predicted in 1994 as a metastable buckled honeycomb silicon monolayer. Similarly to its carbon counterpart it was predicted to present an electronic structure hosting Dirac cones. In the last decade a great deal of work has been done to synthesize silicene and exploit its properties. In this paper we will review our research group activity in the field, dealing in particular with silicon-substrate interaction upon silicon deposition, and discuss the still debated silicene formation starting from the chemistry of silicon unsaturated compounds.

We report the discovery of a temperature-induced phase transition between the α and β structures of antimonene. When antimony is deposited at room temperature on bismuth selenide, it forms domains of α-antimonene having different orientations with respect to the substrate. During a mild annealing, the β phase grows and prevails over the α phase, eventually forming a single domain that perfectly matches the surface lattice structure of bismuth selenide. First-principles thermodynamics calculations of this van der Waals heterostructure explain the different temperature-dependent stability of the two phases and reveal a minimum energy transition path. Although the formation energies of freestanding α- and β-antimonene only slightly differ, the β phase is ultimately favored in the annealed heterostructure due to an increased interaction with the substrate mediated by the perfect lattice match.

We report the discovery of a temperature induced phase transition between the \alpha and \beta structures of antimonene. When antimony is deposited at room temperature on bismuth selenide, it forms domains of \alpha-antimonene having different orientations with respect to the substrate. During a mild annealing, the \beta phase grows and prevails over the \alpha phase, eventually forming a single domain that perfectly matches the surface lattice structure of bismuth selenide. First principles thermodynamics calculations of this van der Waals heterostructure explain the different temperature-dependent stability of the two phases and reveal a minimum energy transition path. Although the formation energies of free-standing \alpha- and \beta-antimonene only slightly differ, the \beta phase is ultimately favoured in the annealed heterostructure due to an increased interaction with the substrate mediated by the perfect lattice match.

In this paper we report on an x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) investigation of the Mn/GaAs(001) interface. The deposition of Mn in the submonolayer regime on the GaAs(001) surface at $390{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ induces a ($2\ifmmode\times\else\texttimes\fi{}1$) reconstruction which evolves to a ($2\ifmmode\times\else\texttimes\fi{}2$) by increasing the Mn amount. The combined information from XAS and XMCD indicates that the Mn atoms are located on surface sites possessing an almost square symmetry with a limited hybridization of the Mn electronic levels with the GaAs ones. The Mn atoms present a magnetic moment ranging between 4.9 and $4.2\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{B}$ depending on the surface reconstruction. The Mn/GaAs(001) interface shows a paramagnetic behavior with an average magnetic moment which decreases by increasing the Mn amount. This variation of the surface magnetization is interpreted as an antiferromagnetic coupling of the Mn magnetic moments as the surface density of Mn atoms is increased. A further increase of the Mn amount after the ($2\ifmmode\times\else\texttimes\fi{}2$) transition leads to the formation of Mn aggregates on the sample surface.

We report the first experimental study of graphene transferred on \b{eta}-Si3N4(0001)/Si(111). Our work provides a comprehensive quantitative understanding of the physics of ultrathin Si3N4 as a gate dielectric for graphene-based devices. The Si3N4 film was grown on Si(111) under ultra-high vacuum (UHV) conditions and investigated by scanning tunneling microscopy (STM). Subsequently, a graphene flake was deposited on top of it by a polymer-based transfer technique, and a Hall bar device was fabricated from the graphene flake. STM was employed again to study the graphene flake under UHV conditions after device fabrication and showed that surface quality is preserved. Electrical transport measurements, carried out at low temperature in magnetic field, revealed back gate modulation of carrier type and density in the graphene channel and showed the occurrence of weak localization. Under these experimental conditions, no leakage current between back gate and graphene channel was detected.

The possibility to intercalate noble gas atoms below epitaxial graphene monolayers coupled with the instability at high temperature of graphene on the surface of certain metals has been exploited to produce Ar-filled graphene nanosized blisters evenly distributed on the bare Ni(111) surface. We have followed in real time the self-assembling of the nanoblisters during the thermal annealing of the Gr/ Ni(111) interface loaded with Ar and characterized their morphology and structure at the atomic scale. The nanoblisters contain Ar aggregates compressed at high pressure arranged below the graphene monolayer skin that is decoupled from the Ni substrate and sealed only at the periphery through stable C-Ni bonds. Their in-plane truncated triangular shapes are driven by the crystallographic directions of the Ni surface. The nonuniform strain revealed along the blister profile is explained by the inhomogeneous expansion of the flexible graphene lattice that adjusts to envelop the Ar atom stacks.

We report a study of the interface between antimony and the prototypical topological insulator Bi2Se3. Scanning tunnelling microscopy measurements show the presence of ordered domains displaying a perfect lattice match with bismuth selenide. Density functional theory calculations of the most stable atomic configurations demonstrate that the ordered domains can be attributed to stacks of β-antimonene.

The surface electronic structure of Si(1 1 1)-[Formula: see text] has been studied by angle-resolved photo electron spectroscopy. Replicas of the S 1 surface state are found in correspondence with several [Formula: see text] unit cells in the reciprocal space. This observation resolves in a direct way the long-standing dichotomy between the structural and electronic properties of the system previously discussed on the basis of the [Formula: see text] or [Formula: see text] R30° surface models.

The chirality transfer control from a single molecule to the surface molecular superstructures and to the substrate is a challenging and important aspect of two-dimensional chiral nanostructures for tailoring the functionality of molecular--metal interfaces. However, how the chiral transfer takes place still remains an open question. In this paper, we combine data from scanning tunneling microscopy, low-energy electron diffraction and circular dichroism in the angular distribution of valence photoelectrons measurements to interpret the formation of extended chiral self-assembled domains obtained by adsorption of the chiral amino-alcohol alaninol on Cu(100). We find that the deposition of alaninol enantiomers results in the formation of isolated tetramers that are aligned along the directions of the substrate at low coverage, whereas a rotation of 14A degrees with respect to the Cu(100) unit vectors is observed when small clusters of tetramers are formed. This suggests that the reorientation originates from forces acting when tetramers pack together in the self-assembling process. Direct information on the chirality transfer from molecules to the substrate has been obtained by the dichroic behavior of a mixed molecule-copper valence state showing that the presence of molecular chiral domains induces asymmetric interaction with the substrate and locally transfers chiral character to the underlying metal atoms participating in the adsorption process.

The Si/Ag(110) interface is attracting increasing interest since the recent claim that the one-dimensional (1D) nanostructures formed at this surface would be silicene nanoribbons. Lately, the synthesis of multilayer silicene nanoribbons was reported as well. In this paper, we report on the scanning tunneling microscopy, low-energy electron diffraction, and density functional theory study of the 1D nanostructures forming on Ag(110) upon Si deposition at temperatures above 460 K. Two different kinds of nanostructures are here described: nanodikes and nanotrenches, respectively protruding from and engraved on the Ag(110) substrate. The first kind of structure was recently reported to be constituted by multistacks of silicene nanoribbons. We show here that nanodikes and nanotrenches are the result of silver faceting stabilized by silicon atoms. Indeed, such nanostructures share the very same facet crystallographic features, namely inclination and reconstruction: the top and base parts are Ag(110) planes, while their sides are Ag(221) and Ag(22$\overline{1}$) facets stabilized by Si atoms. Finally, density functional theory calculations suggest that Si atoms may substitute Ag atoms in such facets, casting doubts on the usual assumption that Ag is a suitable substrate for silicene growth because it is inert against silicon.

Fast pump-probe magneto-optic techniques have been used to investigate the hot carrier and magnetization dynamics in InAs nanostructures deposited on GaAs(001). From these time resolved reflectivity and Faraday rotation measurements, different dynamics responses were found for samples containing different InAs thicknesses. We also present some results of near field spectroscopy with infrared radiation emitted by a free electron laser to investigate biological samples. The local reflectivity revealed features as a function of photon energy that were not present in the corresponding shear-force (topology) images and were due to localized changes in the bulk properties of the sample.

The formation of 2D chiral monolayers obtained by self-assembly of chiral molecules on surfaces has been widely reported in the literature. Control of chirality transfer from a single molecule to surface superstructures is a challenging and important aspect for tailoring the properties of 2D nanostructures. However, despite the wealth of investigations performed in recent years, how chiral transfer takes place on a large scale still remains an open question. In this paper we report a coupling of scanning tunneling microscopy and low energy electron diffraction measurements with an original theoretical approach, combining molecular dynamics and essential dynamics with density functional theory, to investigate self-assembled chiral structures formed when alaninol adsorbs on Cu(100). The peculiarity of this system is related to the formation of tetrameric molecular structures which constitute the building blocks of the self-assembled chiral monolayer. Such characteristics make alaninol/Cu(100) a good candidate to reveal chiral expression changes. We find that the deposition of alaninol enantiomers results in the formation of isolated tetramers that are aligned along the directions of the substrate at low coverage or when geometrical confinement prevents long-range order. Conversely, a rotation of 14° with respect to the Cu(100) unit vectors is observed when small clusters of tetramers are formed. An insight to the process leading to a 2D globally chiral surface has been obtained by monitoring molecular assemblies as they grow from the early stages of adsorption, suggesting that the distinctive orientation of the self-assembled monolayer originates from a balance of cooperating forces which start acting only when tetramers pack together to form small clusters.

Examination of several solid acid catalysts of different nature (acid resins, zeolites, mixed oxides, Nb-oxide, and Nb-phosphate) was performed for the direct iodination reaction of phenol by using molecular iodine. The experiments were carried out in mild and green conditions (50 °C at ambient pressure) in methanol in the presence of H2O2 as oxidant agent. Iodine was introduced in reduced amount, stoichiometric for the formation of di-iodinated phenol, to obtain information on the regio-selectivity of the iodination reaction. The catalysts proved to be all efficient for the introduction of iodine into the aromatic substrate, yielding mono-, di-, and tri-iodo derivates. Different selectivity distributions to the iodo-compound formed were observed over the different catalysts. Catalysts could be grouped into distinct families on the basis of their ortho/para orientation. Several solid acid catalysts of different nature were examined for the iodination reaction of phenol by molecular iodine in the presence of H2O2 as oxidant agent. All the catalysts were efficient for the introduction of iodine in the substrate yielding mono-, di-, and tri-iodo derivates. Different selectivity distributions to the ortho- and para-orientation were observed over the different catalysts.

The biocatalytic oxidation of racemic O - S -dimethyl O - p -nitrophenyl phosphorodithioate 5 catalyzed by chloroperoxidase from Caldariomyces fumago resulted in the formation of the (−)-( S )-enantiomer of the corresponding oxon 4 and unoxidized substrate 5 with a (+)-( R )-configuration. Both compounds were obtained with very high enantiomeric excesses, 99.6% and 97%, respectively. The thionation reaction of the resulting (−)-( S )-oxon 4 with Lawesson’s reagent gave (−)-( S ) - phosphorodithioate 5 with full stereoselectivity, while the oxidation of unreacted substrate (+)-( R )- 5 with iodoxybenzene afforded oxon (+)-( R )- 4 with 94.9% ee.

In this paper, we present a comprehensive study of the carrier dynamics and optical properties of ZnSe nanowires (NWs). The transparency of the sample, obtained by the growth of the ZnSe NWs on glass, allowed us to perform transmittance, reflectance, photoluminescence (PL), time-resolved PL, and pump-probe transient absorption spectroscopy on as-grown samples. All measurements were performed at room temperature. Strong light trapping at the band-gap energy has been observed in reflectivity measurements. Fast transient absorption bleaching due to band filling and band-gap renormalization has been observed. The band-gap renormalization has a rise time constant of about 170 fs and a decay time of about 4 ps. Fast transient absorption bleaching is also observed at energies below the band gap, suggesting that intrinsic processes prevail over extrinsic photoinduced transitions in our high-quality NWs. The PL reveals the presence at room temperature of excitonic emission that shows a decay time of 0.5 ns. All of these features indicate that our ZnSe NWs have quality comparable to epitaxial films and can be used for optical devices and nonlinear optics.

The low-temperature phase of Sn/Ge(1 1 1) 3 × 3 is studied by means of first-principle calculations at the DFT level and in the GW approximation. Experimental STM images taken at 80 K are presented and compared with theoretical predictions. This analysis allows to give support to a geometry in which one Sn adatom is higher than the other two in the surface unit cell and excludes the complementary geometry in which two Sn adatoms are higher than the third. Concerning the very low temperature phase (T < 30 K), we show that from a purely energetic point of view a sqrt3xsqrt3 geometry cannot be excluded, being almost degenerate with the 3 × 3 phase.

Polyleucines of various lengths act as enantioselective catalysts in the aldol condensation between cyclohexanone and a series of aromatic aldehydes, a reaction which may be of prebiotic significance.

Polyamino acids, such as polyleucine, behave as synthetic enzymes in the asymmetric epoxidation of chalcone and other electron-deficient alkenes (the Julia–Colonna reaction). The influences of reaction conditions, of the molecular structure of the catalysts and of the scaling-up of the process on the enantioselectivity of the reaction have been determined. The kinetics and mechanism have been investigated using a soluble PEG-polyleucine conjugate, which behaves in a similar way to an enzyme, showing saturation kinetics for both chalcone and HOO − . Enantioselective catalysis is achieved with peptides with as few as five residues and scalemic catalysts show high chiral amplification. Here, we discuss the relevance of these-enzyme like catalysts to prebiotic processes, such as the role of small peptides in the formation of optically active cyanohydrins.

Enantioselectivities up to 75 % have been found in the catalytic mono-oxidation of di-tert-butyl disulfide and related compounds as well as of ketene-S,S-acetals with an in situ generated chiral dioxirane. The effect of solvents on the enantiomeric excess has also been examined. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The effect of nitrite in the sulfoxidation of organic sulfides catalyzed by myoglobin (Mb) in the presence of hydrogen peroxide has been investigated. A general improvement in enantioselectivity was found for the reaction catalyzed by horse heart metMb and a series of sperm whale metMb derivatives including the wild type protein, the active site mutants T67K Mb, T67R Mb, T67R/S92D Mb, and the T67K Mb derivative reconstituted with the modified prosthetic group protohemin- l - histidine methyl ester.

Using Surface Differential Reflectivity (SDR) we have studied the optical properties of a PbSe(100) surface obtained by cleaving a PbSe sample in ultra-high-vacuum environment. SDR showed the existence of a gap of approximately 1.6 eV. The derived surface dielectric function showed, in the energy range of the present study (1.2–3.6 eV), three optical transitions observed at energies of 1.59, 2.01 and 2.39 eV. By putting together angle resolved photoemission data and theoretical calculations, these transitions have been, tentatively, assigned to different points in the surface Brillouin zone. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Rhodium nanoparticles supported on γ-Al 2 O 3 , derived from arene-solvated Rh atoms stabilized by trioctylamine (TOA), are valuable catalysts in hydrogenation and silylformylation reactions. They are largely more active than the analogous commercial catalyst, as well as of a sample similarly prepared in the absence of TOA. HRTEM measurements, IR studies on adsorbed CO species and extended X-ray absorption fine structure analyses evidenced the role of TOA in controlling the particle growth in the preparative process and in stabilizing the resulting Rh particles against erosion by CO and oxidation.

We report the discovery of a nearly-free electronlike resonant state for a $\ensuremath{\beta}{\text{-Si}}_{3}{\text{N}}_{4}(0001)\ensuremath{-}8\ifmmode\times\else\texttimes\fi{}8$ layer grown on Si(111), as observed by angle-resolved photoemission and scanning tunneling spectroscopy. Comparison with measurements performed on a $\mathrm{Si}(111)\ensuremath{-}7\ifmmode\times\else\texttimes\fi{}7$ surface helped us in the identification of the band. It is found that this parabolic state is degenerate with surface projected bulk bands of the Si(111) substrate.

Silicon reactivity at the Ag(111) surface M. Sattaa, S. Colonnab, R. Flamminib, A. Cricentib, F. Ronci*b a CNR-Istituto per lo Studio dei Materiali Nanostrutturati, Dipartimento di Chimica, Università di Roma "La Sapienza", P.le Aldo Moro 5, I-00185, Roma, Italy b CNR-Istituto di Struttura della Materia, Via Fosso del Cavaliere 100, I-00133 Roma, Italy *e-mail: fabio.ronci@ism.cnr.it Keywords: Silicon, silver, silicene, STM, plane-wave DFT Introduction In the last years a large number of papers reported the synthesis of silicene, a 2D silicon allotrope analogue of graphene, on Ag(110) and Ag(111) substrates [1], attracting a large interest in the scientific community. The modelization of silicene on silver substrates is generally based on the assumption of a complete immiscibility between silicon and silver. Recent results, however, revealed that in both cases the silver substrate is significantly altered upon silicon deposition, inducing either substrate reconstructions [2], faceting [3] or domains growth inside the first Ag(111) layer rather than on top of it [4-5]. Results and Discussion In this talk our recently published results on the Si/Ag(111) system [6] will be described. Through a combined DFT and STM study, the basic exchange mechanism between Si and the topmost layer Ag atoms is explained. We provide a description of the nucleation process, demonstrating that the impinging Si atoms can actually penetrate the first silver layer by exchanging position with Ag atoms. Indeed, despite the quite high energy barrier, the Si/Ag exchange process is made possible by exploiting the excess energy released upon the Si atoms adsorption process. Figure 1: Schematic picture describing the silicon atoms adsorption and thermalization processes at the Ag(111) surface Conclusions We demonstrate that Si atoms are embedded and confined in the first Ag(111) layer where they act as seeds for the growth of recessed islands. Our results demonstrate that surface reactivity cannot be neglected when describing the Si/Ag(111) interface formation. References: [1]H. Oughaddou, H. Enriquez, M. R. Tchalala, H. Yildirim, A. J. Mayne, A. Bendounan, G. Dujardin, M. Ait Ali, A. Kara; Silicene, a promising new 2D material; Progr. Surf. Sci.; 90(2015) 46 and references therein. [2]R. Bernard, T. Leoni, A. Wilson, T. Lelaidier, H. Sahaf, E. Moyen, L. Assaud, L. Santinacci, F. Leroy, F. Cheynis, A. Ranguis, H. Jamgotchian, C. Becker, Y. Borensztein, M. Hanbücken, G. Prévot, and L. Masson; Growth of Si ultrathin films on silver surfaces: Evidence of an Ag(110) reconstruction induced by Si; Phys. Rev. B; 88 (2013) 121411. [3]F. Ronci, G. Serrano, P. Gori, A. Cricenti, S. Colonna; Silicon-induced faceting at the Ag(110) surface; Phys. Rev. B; 89 (2014) 115437. [4]J. Sone, T. Yamagami, Y. Aoki, K. Nakatsuji, H. Hirayama; Epitaxial growth of silicene on ultra-thin Ag(111) films; New J. Phys. 16 (2014) 095004. [5]G. Prévot, R. Bernard, H. Cruguel, Y. Borensztein; Monitoring Si growth on Ag(111) with scanning tunneling microscopy reveals that silicene structure involves silver atoms; Appl. Phys. Lett.; 105 (2014) 213106. [6]M Satta, S. Colonna, R. Flammini, A. Cricenti, F. Ronci; Silicon Reactivity at the Ag(111) Surface; Phys. Rev. Lett.; 115 (2015) 026102.

Using a combination of scanning tunneling microscopy (STM) imaging and total-energy calculations within density functional theory, we evaluate a range of new and existing reconstruction models for Si nanoribbons that form on Ag(110). We propose two models that are consistent with experimental estimates of the Si coverage and the previously reported formation of Ag missing rows. The models yield STM images in excellent agreement with experiment, and are thermodynamically stable. This work provides clear evidence for a strongly bound Si-Ag reconstruction on Ag(110), and does not find any support for models based on silicene.

The modelization of the Si/Ag(110) and Si/Ag(111) systems is generally based on the assumption of a complete immiscibility between silicon and silver. Recent results, on the contrary, demonstrated that in both cases the silver substrate is altered upon silicon deposition through Si-Ag exchange processes, either inducing substrate reconstructions [1] and faceting [2], or suggesting that Si-Ag reactivity must be taken into account. In this talk, I will at first survey our recent results on the Si/Ag(110) system [5], showing novel structural models for nanoribbons obtained considering missing-row reconstructions of the Ag(110) substrate. On the basis of STM measurements, Si coverage evaluation and density functional theory simulations, our models result to be thermodynamically stable, consistent with the experimental Si and Ag coverages, and yield simulated STM images in agreement with the measured data; in contrast, silicene-based models yield unsatisfactory results. Next, I'll discuss about our recently published paper [6] on the Si/Ag(111) that describes, through a combined DFT and STM study, the basic exchange mechanism between Si and the topmost layer Ag atoms that results in the growth of the well-known different kind of reconstructed domains inside, rather than on top, the first Ag(111) layer. [1] R. Bernard, T. Leoni, A. Wilson, T. Lelaidier, H. Sahaf, E. Moyen, L. Assaud, L. Santinacci, F. Leroy, F. Cheynis, A. Ranguis, H. Jamgotchian, C. Becker, Y. Borensztein, M. Hanbücken, G. Prévot, and L. Masson, Phys. Rev. B 88, 121411 (2013). [2] F. Ronci, G. Serrano, P. Gori, A. Cricenti, and S. Colonna, Phys. Rev. B 89, 115437 (2014). [3] J. Sone, T. Yamagami, Y. Aoki, K. Nakatsuji, and H. Hirayama, New J. Phys. 16, 095004 (2014). [4] G. Prévot, R. Bernard, H. Cruguel, and Y. Borensztein, Appl. Phys. Lett. 105, 213106 (2014). [5] C. Hogan, S. Colonna, R. Flammini, A. Cricenti, and F. Ronci, submitted. [6] M Satta, S. Colonna, R. Flammini, A. Cricenti, and F. Ronci, Phys. Rev. Lett. 115, 026102 (2015).

A number of studies have proposed that silicene--a single layer of a buckled honeycomb structure of Si atoms--is responsible for the one-dimensional nanoribbon (NR) structures observed to form when silicon is evaporated on Ag(110) [1]. Recent works using Raman and surface differential reflectance spectroscopy have cast doubts upon this interpretation, however [2,3]. Here we propose new reconstruction models for Ag(110)/Si nanoribbon structures based on new Si coverage measurements and evaluate them using density functional theory simulations[4]. Our models are shown to be thermodynamically stable, are consistent with the experimental Si and Ag coverages [5], and yield simulated STM images in excellent agreement with the measured data; in contrast, silicene-based models yield unsatisfactory results. This work provides clear evidence for strongly bound Si-Ag reconstructions on Ag(110), and finds little support for silicene-like structures [1]. [1] A. Kara et al, Journal of Superconductivity and Novel Magnetism 22, 259 (2009); P. De Padova, et al, Applied Physics Letters 96, 261905 (2010); B. Aufray et al, Applied Physics Letters 96, 183102 (2010); C. Lian and J. Ni, Physica B: Condensed Matter 407, 4695 (2012). [2] E. Speiser et al, Applied Physics Letters 104, 161612 (2014). [3] Y. Borensztein, et al, Physical Review B 89, 245410 (2014). [4] C. Hogan et al, in preparation. [5] R. Bernard et al, Physical Review B 88, 121411 (2013)

Enantiomerically pure sulfoxides are excellent chiral auxiliares for asymmetric synthesis and in the preparation of several enantiopure biologically active compounds. We have explored biocatalytic approaches based on the use of heme peroxidases and flavin monooxygenases such as chloroperoxidase and cyclohexanone monooxygenase respectively. By using isolated enzymes or whole-cell biotransformations, we have prepared alkyl aryl sulfoxides, 1,3-dithioacetal-1-oxides, dialkyl sulfoxides, and thiosulfinates in high enantiomeric excess. An active site model of cyclohexanone monooxygenase has been proposed in order to explain and to predict the absolute configuration of the product. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:467–473, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10074

The first in situ time-resolved X-ray diffraction study of MnF3 crystal structure evolution during its thermal decomposition was performed on the GILDA beam line at the European Synchrotron Radiation Facility (ESRF, France). Mn2F5(s) was observed as intermediate phase during the process of decomposition of MnF3(s) to MnF2(s).

The ee values of lactone 3 , and not of lactone 2 , obtained from the enantiodivergent oxidation of racemic bicyclo[3.2.0]hept-2-en-6-one 1 , catalyzed by cyclohexanone monooxygenase from Acinetobacter calcoaceticus , were found to be markedly dependent on the degree of conversion and substrate concentration. The results are rationalized on the basis of a model which hypothesizes the binding of a second substrate molecule to an enzyme site distinct from the catalytic site.

The chloroperoxidase catalyzed oxidation of methyl phenyl sulfide to (R)-methyl phenyl sulfoxide was investigated, both in batch and membrane reactors, using as oxidant H2O2, or O2 in the presence of either dihydroxyfumaric acid or ascorbic acid. The effects of pH and nature and concentration of the oxidants on the selectivity, stability, and productivity of the enzyme were evaluated. The highest selectivity was displayed by ascorbic acid/O2, even though the activity of chloroperoxidase with this system was lower than that obtained with the others. When the reaction was carried out in a membrane reactor, it was possible to reuse the enzyme for several conversion cycles. The results obtained with ascorbic acid/O2 and dihydroxyfumaric acid/O2 as oxidants do not seem to be compatible with either a mechanism involving hydroxyl radicals as the active species or with the hypothesis that oxidation occurs through the initial formation of H2O2. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 62: 489–493, 1999.

Skin involvement is common in sinus histiocytosis with massive lymphadenopathy (SH, Rosai-Dorfman disease), but pure cutaneous cases are rare. A 70-year-old woman presented with a 10-year history of large red-orange nodules and plaques on her upper arms, face, and buttocks, without evidence of lymphadenopathy or internal involvement. Distinctive histopathologic differences were observed according to the duration of the lesions. In recent lesions, the dermal infiltrate was mostly composed of sheets of characteristic SH cells; on the other hand, in long-lasting lesions, the presence of xanthomatous changes and prominent fibrosis, in keeping with the self-limited nature of this disease, raises problems of differential diagnosis with other xanthohistiocytic disorders. Immunophenotypic studies showed that the SH cells are S-100+ CD1a negative-activated macrophages, capable of lysosomal activity. The adhesion molecule pattern of SH cells (CD11b+, CD11c+, CD18+, CD62L+, and CD103+) was similar to that of circulating monocytes, suggesting their recent migration from the bloodstream.

We present scanning tunneling microscopy (STM) measurements at the TaSe2 surface showing a first order process leading to a surface Mott transition. This metal to insulator transition is triggered by the commensurate charge density wave (CDW) which set up at 475 K. The electronic structure rearrangement due to the new periodicity gives rise to a half filled sub-band prone to the localization phenomena. This transition results fully developed below 250 K in agreement with previous photoemission measurements.

Chiral self-assembled molecular networks (SAMNs) are important for technological and fundamental reasons. In spite of the large number of works in this field, the mechanism of chirality transfer from single molecules to large-scale two-dimensional (2D) networks is not fully understood yet. This work reports on the self-assembly of simple amino alcohols with different chirality measures on Cu(100). Ethanolamine (2-amino-1-ethanol), alaninol (2-amino-1-propanol) and butanolamine (2-amino-1-butanol) adsorbed on Cu(100) have been investigated with scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), photoelectron spectroscopy (PES) and density functional theory (DFT) calculations. This study addresses the role of the single-molecule handedness in the global chirality expression, showing how the chirality measure of the precursors plays an important role in the formation of globally chiral superstructures. © 2014 Elsevier B.V. All rights reserved.

Nonplanar titanyl phthalocyanine (TiOPc) molecules, characterized by a central, highly dipolar Ti-O group, can offer further degrees of freedom in tailoring the properties of hybrid organic-inorganic structures. Here, we combine scanning tunneling microscopy and low-energy electron diffraction measurements with ab initio density functional theory calculations to investigate the interaction of TiOPc molecules with the Ag(100) surface. Isolated molecules are adsorbed with the macrocycle parallel to the surface in two different configurations: with the O atom pointing outward (UP configuration) or with the O atom pointing toward the surface (DOWN configuration). A different interaction of UP and DOWN molecules with the surface can account for their different orientation on the surface as well as for the observation of marked chiral effects only for UP molecules. Self-assembled domains of randomly mixed UP and DOWN molecules form at the monolayer coverage, driven by a subtle interplay between the molecule-surface interaction, the intermolecular dipolar attraction, and the side interaction between adjacent molecules. Chiral patterns of isolated molecules, observed by STM, are transferred to these domains. Remarkably, theoretical calculations disclose an interfacial nature of such chiral properties. Finally, a metallic behavior observed for the monolayer disappears for TiOPc molecules in a second layer, which are electronically decoupled from the substrate.