The scanning tunnelling microscope as an operative tool: doing physics and chemistry with single atoms and molecules

The scanning tunnelling microscope, initially invented to image surfaces down to the atomic scale, has been further developed in the last few years to an operative tool, with which atoms and molecules can be manipulated at will at low substrate temperatures in different manners to create and investigate artificial structures, whose properties can be investigated employing spectroscopic dI/dV measurements. The tunnelling current can be used to selectively break chemical bonds, but also to induce chemical association. These possibilities give rise to startling new opportunities for physical and chemical experiments on the single atom and single molecule level. Here we provide a short overview on recent results obtained with these techniques.     

Amorphous silicon exhibits a glass transition

Amorphous silicon is a semiconductor with a lower density than the metallic silicon liquid. It is widely believed that the amorphous-liquid transition is a first-order melting transition. In contrast to this, recent computer simulations and the experimental observation of pressure-induced amorphization of nanoporous silicon have revived the idea of an underlying liquid-liquid phase transition implying the existence of a low-density liquid and its glass transition to the amorphous solid. Here we demonstrate that during irradiation with high-energy heavy ions amorphous silicon deforms plastically in the same way as conventional glasses. This behaviour provides experimental evidence for the existence of the low-density liquid. The glass transition temperature for a timescale of 10 picoseconds is estimated to be about 1,000 K. Our results support the idea of liquid polymorphism as a general phenomenon in tetrahedral networks.     

Infrared Detection of Defects in Powder-Metallic Compacts

Electric Joule heating of low-conductivity media through direct current excitation can be used to generate a temperature profile throughout a powdermetallic (P/M) compact. When recording the surface temperature distribution with an infrared (IR) camera important information regarding the integrity of the sample can be gained. Unlike most existing IR techniques, this research concentrates on obtaining the temperature distribution and heat flow behavior in P/M parts when they are subjected to active electric current injection. The practical measurements are supported and complemented by a simple theoretical model that serves as a calibration tool to aid in the evaluation of the infrared signatures that are recorded over the sample surface and correlated with the detection of surface and subsurface flaws. In this paper we will report on the design of the active infrared detection system and a basic theoretical testbed that is suitable for calibration. Specifically, we state the governing equations and boundary conditions, followed by devising numerical solutions that enable a comparison to the measured thermal response. In addition, the numerical modeling approach can also serve as a method to model various flaw sizes and orientations in an effort to practically determine flaw resolution limits as a function of minimally detectable temperature distribution. Preliminary measurements with controlled and industrial samples indicate that this IR testing methodology can successfully be employed to inspect both green-state and sintered P/M compacts.     

Thin Film Deposition Using Spray Pyrolysis

Spray pyrolysis has been applied to deposit a wide variety of thin films. These films were used in various devices such as solar cells, sensors, and solid oxide fuel cells. It is observed that often the properties of deposited thin films depend on the preparation conditions. An extensive review of the effects of spray parameters on film quality is given to demonstrate the importance of the process of optimization. The substrate surface temperature is the most critical parameter as it influences film roughness, cracking, crystallinity, etc. Processes involved in the spray pyrolysis technique are discussed in this review as well.     

From anisotropic photo-fluidity towards nanomanipulation in the optical near-field

An increase in random molecular vibrations of a solid owing to heating above the melting point leads to a decrease in its long-range order and a loss of structural symmetry. Therefore conventional liquids are isotropic media. Here we report on a light-induced isothermal transition of a polymer film from an isotropic solid to an anisotropic liquid state in which the degree of mechanical anisotropy can be controlled by light. Whereas during irradiation by circular polarized light the film behaves as an isotropic viscoelastic fluid, it shows considerable fluidity only in the direction parallel to the light field vector under linear polarized light. The fluidization phenomenon is related to photoinduced motion of azobenzene-functionalized molecular units, which can be effectively activated only when their transition dipole moments are oriented close to the direction of the light polarization. We also describe here how the photofluidization allows nanoscopic elements of matter to be precisely manipulated.     

Constructive dimension equals Kolmogorov complexity

We derive the coincidence of Lutz's constructive dimension and Kolmogorov complexity for sets of infinite strings from Levin's early result on the existence of an optimal left computable cylindrical semi-measure M via simple calculations.     

Hatch-Waxman in the Federal Courts: from 1994--2004

Decisions of the federal courts play a crucial role in drug development. Litigation related to drug development and approval under the abbreviated new drug application (“ANDA”) process over the past 10 years was evaluated, examining over 300 written decisions from 22 U.S. District Courts and the U.S. Court of Appeals for the Federal Circuit. These written decisions represent the majority of patent litigation between brand and generic drug manufacturers. The reported data set provides critical information for the drug development and litigation strategies of both brand and generic manufacturers. The examination also provides a realistic portrayal of the anticipated outcome if a legal action is initiated.     

Solid-state magic-angle spinning NMR of outer-membrane protein G from Escherichia coli

Uniformly 13C-,15N-labelled outer-membrane protein G (OmpG) from Escherichia coli was expressed for structural studies by solid-state magic-angle spinning (MAS) NMR. Inclusion bodies of the recombinant, labelled protein were purified under denaturing conditions and refolded in detergent. OmpG was reconstituted into lipid bilayers and several milligrams of two-dimensional crystals were obtained. Solid-state MAS NMR spectra showed signals with an apparent line width of 80-120 Hz (including homonuclear scalar couplings). Signal patterns for several amino acids, including threonines, prolines and serines were resolved and identified in 2D proton-driven spin-diffusion (PDSD) spectra.