Effect of Head‐Group Chemistry on Surface‐Mediated Molecular Self‐Assembly

Surface molecular self‐assembly is a fast advancing field with broad applications in sensing, patterning, device assembly, and biochemical applications. A vast number of practical systems utilize alkane thiols supported on gold surfaces. Whereas a strong Au? S bond facilitates robust self‐assembly, the interaction is so strong that the surface is reconstructed, leaving etch pits that render the monolayers susceptible to degradation. By using different head group elements to adcust the molecule–surface interaction, a vast array of new systems with novel properties may be formed. In this paper we use a carefully chosen set of molecules to make a direct comparison of the self‐assembly of thioether, selenoether, and phosphine species on Au(111). Using the herringbone reconstruction of gold as a sensitive readout of molecule–surface interaction strength, we correlate head‐group chemistry with monolayer (ML) properties. It is demonstrated that the hard/soft rules of inorganic chemistry can be used to rationalize the observed trend of molecular interaction strengths with the soft gold surface, that is, P>Se>S. We find that the structure of the monolayers can be explained by the geometry of the molecules in terms of dipolar, quadrupolar, or van der Waals interactions between neighboring species driving the assembly of distinct ordered arrays. As this study directly compares one element with another in simple systems, it may serve as a guide for the design of self‐assembled monolayers with novel structures and properties.     

Measurement of the coefficient of thermal slip of gases and the thermophoreses velocity of large-size aerosol particles

Four different experimental methods were applied to finding the values of the thermal slip coefficient of gases. The values obtained, k_t = 1.05 ÷ 1.13, tally well with the value k_t = 1.17, calculated by Ivchenko and Yalamov (4) for the case of full accomodation, and with the value k_t′ = 1.17, derived from irreversible thermodynamics by Bakanov, Derjaguin and Roldugin (23) for the same case.     

Towards a new edition of the “Guide to the expression of uncertainty in measurement”

The “Guide to the expression of uncertainty in measurement” (GUM) is an extremely important document. It unifies methods for calculating measurement uncertainty and enables the consistent interpretation and comparison of measurement results, regardless of who obtained these measurements and where they were obtained. Since the document was published in 1995, it has been realised that its recommendations do not properly address an important class of measurements, namely, non-linear indirect measurements. This drawback prompted the initiation of the revision of the GUM in the Working Group 1 of the Joint Committee for Guides in Metrology, which commenced in October 2006. The upcoming revision of the GUM provides the metrological community with an opportunity to improve this important document, in particular, to reflect developments in metrology that have occurred since the first GUM publication in 1995. Thus, a discussion of the directions for this revision is important and timely. By identifying several shortcomings of the GUM and proposing directions for its improvement, we hope this article will contribute to this discussion. Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher.     

Essential spectrum of pseudodifferential operators with operator-valued symbols

Doklady Mathematics -     

Stochastic oscillations in dissipative systems

The recent discovery of simple deterministic systems, the behaviour of which is intrinsically stochastic, has led to a new approach to the problem of turbulence. This paper is devoted to the discussion of some physical mechanisms for the appearance of chaos in simple dissipative systems. The authors show that stochastic behaviour is the result of the self-disorganization of such systems. Examples from electronics, chemistry, theory of nonlinear oscillations and waves are given as illustrations to the theoretical findings.     

Syntheses and structures of methyltris(pyrazolyl)silane complexes of the group 6 metals

The methyltris(3,5-dimethylpyrazolyl)silane ligand, TpsMe2, was readily prepared by the metathesis reaction of methyltrichlorosilane with 3 equiv of lithium 3,5-dimethylpyrazolate. The octahedral tricarbonyl complexes (TpsMe2)M(CO)3 were synthesized either by ligand exchange with the labile nitrile adducts M(CO)3(NCR)3 (M = Cr, Mo, R = Me; M = W, R = Et) or thermally by direct substitution on the hexacarbonyls M(CO)6 (M = Cr, Mo). The three new complexes were characterized by a combination of analytical and spectroscopic techniques, including electrospray ionization mass spectrometry and single-crystal X-ray diffraction. They are all isostructural and display in the solid state the expected distorted octahedral geometries with facially coordinated tris(pyrazolyl)silane ligands. Crystallographic data were used to calculate the ligand cone angles (251-264 degrees) in (TpsMe2)M(CO)3 and also to estimate a value of 1.59 A for the covalent radius of octahedral W(0).     

Surface tension of equilibrium spherical drops in the vapor phase

The properties of metastable and equilibrium drops that occur in the vapor phase and differ in the size and position of the dividing surface are compared. Using an equimolecular dividing surface, it was found that the total free energy and the total mass of the substance in drops of the same size over a broad temperature range differ by not more than 0.3%. A similar comparison for a dividing surface chosen from the equality condition of the moments of forces gives rather similar results. Using the surface where the maximum surface tension is attained as the dividing surface is impossible at low temperatures, because under these conditions, the notion of surface tension has no physical meaning. At high temperatures, the difference between the total mass of the substance for metastable and equilibrium drops does not exceed 0.6%. The calculations were carried out over a broad temperature range on the basis of the lattice-gas model in the quasichemical approximation.