SIMS of organic anions adsorbed onto an aminoethanethiol self-assembled monolayer: an approach for enhanced secondary ion emission

Secondary ion mass spectrometry (SIMS) was used to monitor the uptake of organic anions from solution by aminoethanethiol (AET) monolayers on Au substrates, as a test of the applicability of this monolayer as a substrate for organic SIMS analysis. Event-by-event bombardment and detection mode coupled with coincidence counting allowed the atomic and polyatomic projectile impacts on a particular sample surface to be compared simultaneously and under the same experimental conditions. The mass spectra produced from the monolayer surface and those from Au and Si blanks demonstrate that the AET monolayer is important to the uptake of the organic anion. The exchanged monolayer surfaces were used to measure secondary ion yields, defined as the number of secondary ions detected per incident primary ion, produced from ultrathin films by (CsI)nCs+ (n = 0-2) projectiles at the limit of single-ion impacts. The yield of a tetradecyl sulfate (IDS) anion was improved by a factor of 200 using the AET substrate instead of the thick salt target. The intact ion and fragment ion yield trends produced from the AET surface were measured as a function of number of atoms in the primary projectile and energy. We observed a yield increase for both the intact ion and the fragment ion with the projectile complexity and energy. The increase in yield per projectile atom was linear for the emission of intact TDS and intact dodecyl sulfate from the AET surfaces. A supralinear yield enhancement, however, was observed for the fragment ion SO3- when the three-atom (CsI)Cs+ cluster was used. The experiments demonstrate that the various organosulfate and suffonates are weakly bound to the AET surface and their adsorption to the AET monolayer is reversible. The utility of the AET monolayer on Au was also tested as a general substrate for the characterization of derivatized organic molecules with biological and industrial importance by TOF-SIMS.     

The bulk piezoresistive characteristics of carbon nanotube composites for strain sensing of structures

The bulk piezoresistivity of carbon nanotube (CNT) in polymer matrix was discussed to develop a strain sensor for engineering applications. The polymer improves interfacial bonding between the nanotubes and the CNT composite and that enhances the strain transfer, repeatability, and linearity of the sensor. The largest contribution of piezoresistivity of the sensor may come from slippage of overlaying or bundled nanotubes in the matrix, from a macroscopic point of view. Nano interfaces of CNTs in a matrix polymer also contribute to the linear strain response compared to other micro size carbon filler. The strain sensor had a low bandwidth and adequate strain sensitivity. The nanocomposite strain sensor is particularly useful for detecting large strains which can monitor strain and stress on a structure with simple electric circuit for strain monitoring of structures.     

Analysis and optimization of silver nanoparticles laser synthesis with emission spectroscopy of induced plasma

Emission spectroscopy of the laser induced plasma is used to characterize the laser synthesis of silver nanoparticles in water via attributing the thermodynamic parameters of the plasma plume to qualitative features of the synthesized nanoparticles. In this approach, effects of the pulse energy and frequency of a pulsedNd:YAGlaser on nanoparticles synthesis yield and size distribution is studied by an analysis on the behavior of electron temperature and total density of the plasma dominant species (neutral Ag atoms; AgI). Variation of these thermodynamic parameters obtained from the time-integrated emission spectroscopy of the induced plasma was found to be in a closed correlation with the mentioned characteristics of the synthesized nanoparticles. Assessment of the qualitative features of nanoparticles was performed by evaluating the particles concentration in liquid, optical absorption spectroscopy and transmission electron microscopy. Finally, the optimum operating conditions for the synthesis of silver nanoparticles in pure water is determined by summarizing the results of emission spectroscopy observations attributed to the mentioned characteristics of synthesized nanoparticles.     

High-performance ambipolar diketopyrrolopyrrole-thieno[3,2-b]thiophene copolymer field-effect transistors with balanced hole and electron mobilities

Ambipolar OFETs with balanced hole and electron field-effect mobilities both exceeding 1 cm(2) V(-1) s(-1) are achieved based on a single-solution-processed conjugated polymer, DPPT-TT, upon careful optimization of the device architecture, charge injection, and polymer processing. Such high-performance OFETs are promising for applications in ambipolar devices and integrated circuits, as well as model systems for fundamental studies.     

Effects of block copolymer self-assembly on optical anisotropy in azobenzene-containing PS-b-PMMA films

Polystyrene-b-polymethylmethacrylate (PS-b-PMMA) was selected as the host for 4-(4-nitrophenylazo)aniline (Disperse Orange 3, DO3) based on a previous study of DO3/PMMA and DO3/PS binary blends. Selective location of DO3 into the PMMA block of the copolymer was expected during self-assembly of the block copolymer since a preferential interaction of DO3 with PMMA has been demonstrated. However, surface segregation of DO3 was found during the thermal annealing used to nanostructure the copolymer. To avoid this, a thermoplastic polymer (Azo-TP) was synthesized from the bulk reaction of DO3 and diglycidyl ether of bisphenol A (DGEBA). The choice of DGEBA as a co-reactant was an attempt to encourage the selective location of azo groups in the PMMA phase of PS-b-PMMA. An inspection of solutions of Azo-TP in PS and PMMA, corroborates the preferential affinity of Azo-TP for PMMA. The Azo-TP could be satisfactorily dissolved in PS-b-PMMA. We have investigated the growth and decay processes of the optically induced birefringence in films of PS-b-PMMA containing 12?wt% Azo-TP. The resulting materials showed a good photoinduced time response, high maximum birefringence and an elevated fraction of remnant anisotropy.     

Atmospheric Trace Molecule Spectroscopy (ATMOS) Experiment Version 3 data retrievals

Version 3 of the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment data set for some 30 trace and minor gas profiles is available. From the IR solar-absorption spectra measured during four Space Shuttle missions (in 1985, 1992, 1993, and 1994), profiles from more than 350 occultations were retrieved from the upper troposphere to the lower mesosphere. Previous results were unreliable for tropospheric retrievals, but with a new global-fitting algorithm profiles are reliably returned down to altitudes as low as 6.5 km (clouds permitting) and include notably improved retrievals of H2O, CO, and other species. Results for stratospheric water are more consistent across the ATMOS spectral filters and do not indicate a net consumption of H2 in the upper stratosphere. A new sulfuric-acid aerosol product is described. An overview of ATMOS Version 3 processing is presented with a discussion of estimated uncertainties. Differences between these Version 3 and previously reported Version 2 ATMOS results are discussed. Retrievals are available at http://atmos.jpl.nasa.gov/atmos.     

An assessment of peptide enrichment methods employing mTRAQ quantification approaches

The human plasma peptidome has potential in biomarker discovery not least because the plasma proteome is a challenging matrix due to its complexity and dynamic range. However, methods to significantly reduce the amount of protein present in plasma while retaining the less abundant peptides present in plasma samples has been a major issue. Here, we present a novel strategy which has been employed to assess the effectiveness of removing interfering proteins while retaining peptides of interest. To monitor peptide retention, a spiked in digested protein, in this case a synthetic QconCAT protein, was employed. This enabled a variety of target analytes (peptides) to be monitored for their retention in liquid phase, providing a broader picture of peptide loss from each method assessed. The incorporation of mTRAQ labeling allowed the presence of each peptide to be monitored, and accurate peptide losses to be determined in a Selected Reaction Monitoring (SRM) assay, thus, enabling an objective semiquantitative conclusion to be drawn regarding the suitability of each method for protein removal and peptide retention. We also assessed a range of methods for retaining nontryptic peptides in a plasma peptidomics workflow. From these data, we determined an optimal workflow for removing intact protein, while retaining peptides for MS-based analyses.     

Automated radioanalytical system incorporating microwave-assisted sample preparation, chemical separation, and online radiometric detection for the monitoring of total 99Tc in nuclear waste processing streams

An automated fluidic instrument is described that rapidly determines the total (99)Tc content of aged nuclear waste samples, where the matrix is chemically and radiologically complex and the existing speciation of the (99)Tc is variable. The monitor links microwave-assisted sample preparation with an automated anion exchange column separation and detection using a flow-through solid scintillator detector. The sample preparation steps acidify the sample, decompose organics, and convert all Tc species to the pertechnetate anion. The column-based anion exchange procedure separates the pertechnetate from the complex sample matrix, so that radiometric detection can provide accurate measurement of (99)Tc. We developed a preprogrammed spike addition procedure to automatically determine matrix-matched calibration. The overall measurement efficiency that is determined simultaneously provides a self-diagnostic parameter for the radiochemical separation and overall instrument function. Continuous, automated operation was demonstrated over the course of 54 h, which resulted in the analysis of 215 samples plus 54 hly spike-addition samples, with consistent overall measurement efficiency for the operation of the monitor. A sample can be processed and measured automatically in just 12.5 min with a detection limit of 23.5 Bq/mL of (99)Tc in low activity waste (0.495 mL sample volume), with better than 10% RSD precision at concentrations above the quantification limit. This rapid automated analysis method was developed to support nuclear waste processing operations planned for the Hanford nuclear site.