Dynamics of tip-substrate interactions in atomic force microscopy

Dynamical interactions between a scanning tip and a silicon substrate are investigated using molecular dynamics simulations of both the constant-height and constant-force scan modes. Localized temporary and permanent modifications of the substrate occur, depending on tip-substrate-strate separation and scan geometry. Implications for resolving structural and force characteristics in scanning tip spectroscopies, employing atomically sharp as well as large ordered of disordered tips are discussed.     

Study of the formation of Cs inclusions in refractory bcc metals by133Xe(Cs) Mössbauer resonance

The formation and properties of Cs inclusions in Mo and W are observed through a preimplanted¹³³Xe(Cs) local probe, which is found to reside in three sites: a substitutional site, an interfacial one and a further site which is not detectable directly, but the presence of which can be inferred from the Mössbauer measurements. The location of the probe at the interface of small Cs inclusions is characterized by large Debye temperatures of around 200 K, a quadrupole interaction of +1.86(15) mms^–1, which is close to known surface site values, and an isomer shift of –0.33(12) mms^–1. From the latter value an approximate local pressure of 5 GPa is deduced. In W the site populations are followed as a function of Cs dose. The observed interchange of populations in the low dose range is thought to represent the initial formation of the second phase inclusions.     

Experimental identification of nonpointlike dark-matter candidates

We show that direct dark-matter detection experiments can distinguish between pointlike and nonpointlike dark-matter candidates. The shape of the nuclear recoil-energy spectrum from pointlike dark-matter particles, e.g., neutralinos, is determined by the velocity distribution of dark matter in the galactic halo and by nuclear form factors. Typical cross sections of nonpointlike dark matter, for example, Q-balls, have a new form factor, which decreases rapidly with the recoil energy. A signal from nonpointlike dark matter is expected to peak near the experimental threshold and to fall off rapidly at higher energies.     

Molecular wires acting as coherent quantum ratchets

The effect of laser fields on electron transport through a molecular wire weakly coupled to two leads is investigated. The molecular wire acts as a coherent quantum ratchet if the molecule is composed of periodically arranged, asymmetric chemical groups. This setup presents a quantum rectifier with a finite dc response in the absence of a static bias. The nonlinear current is evaluated in closed form within the Floquet basis of the isolated, driven wire. The current response reveals multiple current reversals together with a nonlinear dependence on the amplitude and the frequency of the laser field. The current saturates for long wires at a nonzero value, while it may change sign upon decreasing its length.     

Propellanes. Part LXXXII. Preparation and Labelling of [20.3.3]Propellane-24,27-dione

The title diketone has been prepared by a synthetic sequence beginning with decane-1,10-dicarboxylic acid.     

Enhancement by polar solute of interaction-induced IR absorption in liquid CS2

The enhancement of the “forbidden” infrared absorption in the ν₁, symmetric stretch, band of CS₂ by small concentrations of CH₃CN, was studied both experimentally and via MC simulation.