Remote Internet access to advanced analytical facilities: a new approach with Web-based services.

Over the past decade, the increasing availability of the World Wide Web has held out the possibility that the efficiency of scientific measurements could be enhanced in cases where experiments were being conducted at distant facilities. Examples of early successes have included X-ray diffraction (XRD) experimental measurements of protein crystal structures at synchrotrons and access to scanning electron microscopy (SEM) and NMR facilities by users from institutions that do not possess such advanced capabilities. Experimental control, visual contact, and receipt of results has used some form of X forwarding and/or VNC (virtual network computing) software that transfers the screen image of a server at the experimental site to that of the users' home site. A more recent development is a web services platform called Science Studio that provides teams of scientists with secure links to experiments at one or more advanced research facilities. The software provides a widely distributed team with a set of controls and screens to operate, observe, and record essential parts of the experiment. As well, Science Studio provides high speed network access to computing resources to process the large data sets that are often involved in complex experiments. The simple web browser and the rapid transfer of experimental data to a processing site allow efficient use of the facility and assist decision making during the acquisition of the experimental results. The software provides users with a comprehensive overview and record of all parts of the experimental process. A prototype network is described involving X-ray beamlines at two different synchrotrons and an SEM facility. An online parallel processing facility has been developed that analyzes the data in near-real time using stream processing. Science Studio and can be expanded to include many other analytical applications, providing teams of users with rapid access to processed results along with the means for detailed discussion of their significance.

Unstable amplitude and noisy image induced by tip contamination in dynamic force mode atomic force microscopy.

Liquid 1-decanethiol was confined on an atomic force microscope (AFM) tip apex and the effect was investigated by measuring amplitude-distance curves in dynamic force mode. Within the working distance in the dynamic force mode AFM, the thiol showed strong interactions bridging between a gold-coated probe tip and a gold-coated Si substrate, resulting in unstable amplitude and noisy AFM images. We show that under such a situation, the amplitude change is dominated by the extra forces induced by the active material loaded on the tip apex, overwhelming the amplitude change caused by the geometry of the sample surface, thus resulting in noise in the image the tip collects. We also show that such a contaminant may be removed from the apex by pushing the tip into a material soft enough to avoid damage to the tip.

ToF-SIMS investigation of octadecylphosphonic acid monolayers on a mica substrate.

In this paper, time-of-flight secondary ion mass spectrometry (ToF-SIMS) under static conditions was used to investigate self-assembled monolayers (SAMs) of octadecylphosphonic acid (OPA) formed on freshly cleaved muscovite mica substrates. The coverage of OPA on mica ranged from 20 to 100%, with a film thickness of 1.7+/-0.2 nm, which was determined by atomic force microscopy (AFM) imaging. The relative intensity of the specific secondary ion species associated with the OPA and with the exposed mica substrate exhibited good correlation with surface coverage. An excellent correlation was also observed (R2=0.98) between the relative SIMS [OPA-H]- intensity and the surface carbon concentration (OPA C 1s, in atomic %) from XPS at the prescribed surface coverage. The observation of positive and negative OPA molecular attachment of secondary ions involving the substrate species is discussed in terms of the chemical affinity of the OPA phosphonate headgroup for the cleaved mica surface as well as the sampling depth. In addition, the OPA molecular attachment species formed with the potassium ions on the cleaved mica substrate dominated the positive secondary ion mass spectrum in the high-mass range. A temperature-dependent, ToF-SIMS study employing in situ heating of a 100% coverage OPA monolayer revealed that the molecules begin to diffuse above approximately 80 degrees C, resulting in a decrease in the relative secondary ion yield of the OPA-specific secondary ions. This observation is hypothesized to be due to a decrease in the effective coverage of the substrate by the OPA molecules, which in turn could be due to the formation of multilayers upon heating in an effort to minimize the energy of the system. The interesting behavior of the novel OPA dimer species as a function of temperature is also reported. It was observed that the relative intensity of OPA and the mica-specific secondary ion peak intensities to that of Si (mica substrate) provides an effective means to estimate the change in coverage at elevated temperatures.

Robust self-assembled octadecylphosphonic acid monolayers on a mica substrate.

As determined by scratch tests, self-assembled monolayers (SAMs) of octadecylphosphonic acid (OPA) on a muscovite mica substrate were found to be mechanically robust and to serve as a lubricant to protect the underlying mica substrate. For comparison purposes, three polymer films were subjected to scratch tests under the same conditions. The scratch tests were conducted using a diamond-tipped stylus, and the resultant scratches were examined using atomic force microscopy. The excellent mechanical strength of OPA SAMs is supported by analysis with time-of-flight secondary ion mass spectrometry, which suggests that the headgroup of the OPA is strongly bonded to the substrate atoms. The molecular lubrication provided by OPA SAMs suggests that the interaction between the headgroup and the substrate is sufficiently strong to endure significant shear force and that the hydrocarbon chains are able to dissipate shear energy.

Detection and Mapping of Chimassorb 944FD Antioxidant Additive in Polyethylene Using TOF-SIMS.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) with either gallium or indium primary beams, has been evaluated as a method to measure the homogeneity of distribution of an antioxidant, Chimassorb 944FD (C944), in linear low-density polyethylene. The parent ion for the oligomer at m/z 599 is sufficiently weak that it could not be used to map the distribution of the additive throughout its most commonly used concentration range (0.1-0.5% (w/w)) in polyethylene. Instead, a mass fragment at m/z 58 was found to be sufficiently clear of interferences that it could be used as a surrogate for the parent ion. As a result, imaging of the antioxidant distribution was possible to concentrations as low as 0.1%, and a linear concentration calibration curve was obtained. The use of an indium primary beam improved the correlation coefficient for the quantitative measurement of C944; moreover, indium reduced the contribution from the polyethylene background at m/z 58 in relation to the total counts acquired.

Studies on the adhesion of glass-ionomer cements to dentin.

This study investigated the bonding mechanisms of glass-ionomer cement to dentin. The approaches included mechanical determination of bond strengths, analysis of surface morphology by means of scanning electron microscopy (SEM) and confocal microscopy, and measurement of chemical changes of fracture bond sites by means of x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The highest bond strengths were obtained with light-cured glass-ionomer cement. SEM and confocal images showed evidence of mechanical interlocking of cement in dentinal tubules. SIMS depth profiles confirmed the ion-exchange process between the light-cured glass-ionomer cement and the dentin surface. From corresponding XPS results, it was clear that the adhesion characteristics were significantly affected by light-curing and the chemical structure of the polymer.

Dental implant materials. II. Preparative procedures and surface spectroscopic studies.

The tissue response to an implant may involve both physical and chemical factors. There is little reliable information on the effects of these parameters and the associated ionic release on the cell-material interaction because the majority of studies have not fully characterized the implant material. In this work surface spectroscopy using ISS, ESCA, and SIMS was carried out on Ti6A14V, Co-Cr-Mo, A12O3, and hydroxyapatite dental implant materials that had been subjected to six commonly used preparative procedures. The results showed that each procedure generated an individualistic composition for the outermost surface of each material. These differences could be significant in cellular and tissue response. Improved understanding of these factors requires defined and reproducible surfaces.