Precise and fast secondary ion mass spectrometry depth profiling of polymer materials with large Ar cluster ion beams

We demonstrate depth profiling of polymer materials by using large argon (Ar) cluster ion beams. In general, depth profiling with secondary ion mass spectrometry (SIMS) presents serious problems in organic materials, because the primary keV atomic ion beams often damage them and the molecular ion yields decrease with increasing incident ion fluence. Recently, we have found reduced damage of organic materials during sputtering with large gas cluster ions, and reported on the unique secondary ion emission of organic materials. Secondary ions from the polymer films were measured with a linear type time‐of‐flight (TOF) technique; the films were also etched with large Ar cluster ion beams. The mean cluster size of the primary ion beams was Ar₇₀₀ and incident energy was 5.5 keV. Although the primary ion fluence exceeded the static SIMS limit, the molecular ion intensities from the polymer films remained constant, indicating that irradiation with large Ar cluster ion beams rarely leads to damage accumulation on the surface of the films, and this characteristic is excellently suitable for SIMS depth profiling of organic materials. Copyright © 2009 John Wiley & Sons, Ltd.     

Secondary ion emission from Si bombarded with large Ar cluster ions under UHV conditions

Si was bombarded with size-selected 40 keV Ar cluster ions and positive secondary ions were measured using the time-of-flight technique under high and ultra-high vacuum (HV and UHV respectively) conditions. Si⁺ ions were main species detected under the incidence of 40 keV Ar cluster ions, and the yields of Si cluster ions such as Si₄⁺ were also extremely high under both conditions. On the other hand, oxidized secondary ions such as SiO⁺ were detected with high intensity only under the HV condition. The yield ratios of oxidized ions decreased in UHV to less than 1% of their values in HV. The effect of residual gas pressure on Si cluster ion yields is relatively low compared to oxidized ions, and the UHV condition is required to obtain accurate secondary ion yields.     

Molecular photoelectric switch using a mixed SAM of organic [60]fullerene and [70]fullerene doped with a single iron atom

We describe a photoswitch fabricated on indium tin oxide (ITO) as a self-assembled monolayer (SAM) of two fullerene molecules, a purely organic [60]fullerene that generates an anodic current and a [70]fullerene doped with a single iron atom. This device generates a bidirectional photocurrent upon irradiation at 340 and 490 nm. The new [70]fullerene iron complex bearing three rigid carboxylic acid legs, Fe[C(70)(C(6)H(4)C(6)H(4)COOH)(3)]Cp, generates only a cathodic current upon photoexcitation between 350 and 700 nm, whereas the organic [60]fullerene absorbs at wavelengths shorter than 500 nm. The quantum efficiency of the photocurrent generation by the mixed SAM is comparable to that of a single-component SAM, indicating that the individual diode molecules on ITO generate photocurrents independently with little cross talk.     

Enantioselective Total Synthesis of (+)‐Neostenine

A chirality transfer approach using acyclic polyol intermediates for the synthesis of (+)‐neostenine ( 1 ) has been developed. The sequential Overman/Claisen rearrangement of an allylic 1,2‐diol was especially useful, installing two contiguous stereocenters with complete diastereoselectivity in a one‐pot sequence. The SmI₂‐mediated cyclization and the subsequent chemoselective reduction of a lactam moiety accomplished the first enantioselective total synthesis of (+)‐neostenine ( 1 ).     

Molecular depth profiling of multilayer structures of organic semiconductor materials by secondary ion mass spectrometry with large argon cluster ion beams

In this study, we present molecular depth profiling of multilayer structures composed of organic semiconductor materials such as tris(8‐hydroxyquinoline)aluminum (Alq₃) and 4,4′‐bis[N‐(1‐naphthyl)‐N‐phenylamino]biphenyl (NPD). Molecular ions produced from Alq₃ and NPD were measured by linear‐type time‐of‐flight (TOF) mass spectrometry under 5.5 keV Ar₇₀₀ ion bombardment. The organic multilayer films were analyzed and etched with large Ar cluster ion beams, and the interfaces between the organic layers were clearly distinguished. The effect of temperature on the diffusion of these materials was also investigated by the depth profiling analysis with Ar cluster ion beams. The thermal diffusion behavior was found to depend on the specific materials, and the diffusion of Alq₃ molecules was observed to start at a lower temperature than that of NPD molecules. These results prove the great potential of large gas cluster ion beams for molecular depth profiling of organic multilayer samples. Copyright © 2009 John Wiley & Sons, Ltd.     

Totally asymmetric simple exclusion process on a periodic lattice with Langmuir kinetics depending on the occupancy of the forward neighboring site

We generalize the totally asymmetric simple exclusion process with Langmuir kinetics on aperiodic lattice. In the extended model, the rates of attachment and detachment depend onthe occupancy of the forward neighboring site. Using a mean-field theory, we obtain theanalytical expression of the density profile in the steady state and the relaxationdynamics in our model. We verify their accuracy by comparing the results with Monte Carlosimulations.     

Constraints from the Wilkinson microwave anisotropy probe on decaying cold dark matter

We reformulate cosmological perturbations in the decaying cold dark matter model, and calculate cosmological microwave background anisotropies. By comparing our predictions with data from the Wilkinson Microwave Anisotropy Probe, we derive a new bound on the abundance and lifetime of decaying dark matter particles. The lifetime is constrained to Gamma(- 1)> or =123 Gyr at 68% C.L. (52 Gyr at 95.4% C.L.) when cold dark matter consists only of such decaying particles. We also consider a more general case and show that the constraint generalizes to Omega(DDM )h2 less, similar -0.5(Gamma (-1)/1 Gyr) (-1)+0.12 for Gamma(- 1)> or =5 Gyr at 95.4% C.L.     

Electroosmosis injection of blood serum into biocompatible microcapillary chip fabricated on quartz plate

A chip which allows the detection of various human health markers from a trace amount of blood has been studied. As a goal, a microcapillary with a 30 x 30 microm cross-section was fabricated using all-dry etching technologies on a 2 x 2 cm SiO2 chip. The coating of the biocompatible 2-methacryloyloxyethylphosphorylcholine (MPC) polymer on the inner quartz wall of the microcapillary demonstrated a sufficiently long adsorption suppression of proteins in the serum on the quartz surface, while rapid stopping occurred for serum injected into the microcapillary with a bare quartz surface. The latter rapid stopping corresponded well to fast electroosmosis flow due to the negatively increasing zeta-potential by the adsorption of proteins on the quartz surface. The electroosmosis pump arranged a downstream of the microcapillary was also developed to inject serum into it. As a preliminary application, a given concentration-standard solution was injected into the ion-sensitive field-effect transistor (ISFET) embedded in the chip, employing the electroosmosis pump arranged downstream of the sensor position. Hence, the pH and Na+ and K+ cation concentrations were measured.