Roger Wigren

Structure of adsorbed fibrinogen obtained by scanning force microscopy

It is shown that scanning force microscopy (SFM), operated in the attractive mode, can be used to obtain high resolution pictures of adsorbed fibrinogen molecules on solid surfaces, without the need for staining or special microscope grids. SFM also reveals the three‐dimensional structure of the adsorbed molecules. Two forms of adsorbed fibrinogen are demonstrated on hydrophobic silicone dioxide surfaces; a trinodular about 60 nm long and a globular with about a 40 nm diameter. Polymeric networks formed after storage of the surface with adsorbed fibrinogen in PBS for 11 days are also shown. The SFM‐results for the trinodular structure suggest the existence of loops or peptide chains extending outside the basic structure of the fibrinogen molecule.

SiC Based Field Effect Gas Sensors for Industrial Applications

The development and field-testing of high-temperature sensors based on silicon carbide devices have shown promising results in several application areas. Silicon carbide based field-effect sensors can be operated over a large temperature range, 100-600 °C, and since silicon carbide is a chemically very inert material these sensors can be used in environments like exhaust gases and flue gases from boilers. The sensors respond to reducing gases like hydrogen, hydrocarbons and carbon monoxide. The use of different temperatures, different catalytic metals and different structures of the gate metal gives selectivity to different gases and arrays of sensors can be used to identify and monitor several components in gas mixtures. MOSFET sensors based on SiC combine the advantage of simple circuitry with a thicker insulator, which increases the long term stability of the devices. In this paper we describe silicon carbide MOSFET sensors and their performance and give examples of industrial applications such as monitoring of car exhausts and flue gases. Chemometric methods have been used for the evaluation of the data.

Interactions between cellulose and colloidal silica in the presence of polyelectrolytes

The forces acting between two cellulose surfaces and a cellulose surface and silica have been investigated using the interferometric surface force technique and the scanning force microscopy colloidal-probe technique. A key element in this study is the preparation of very smooth cellulose surfaces using the Langmuir-Blodgett technique, which facilitates a detailed characterization of the forces acting between the surfaces as a function of their separation. The main part of the investigation is concerned with the effect of a highly charged cationic polyelectrolyte, poly[[2-(propionyloxy)ethyl]trimethylammonium chloride] (PCMA), on the interaction between negatively charged silica and uncharged cellulose. It is found that the presence of the cationic polyelectrolyte reduces the force barrier against flocculation, but also the attractive pull-off force. The implications of these findings for the function of this polyelectrolyte as a retention aid and a wet strength additive is discussed. The ionic strength of the solution has profound effects on the interactions between cellulose and silica in the presence of PCMA. This is due to a decreased polyelectrolyte-surface affinity at higher ionic strengths.

Evaluation of on-line flue gas measurements by MISiCFET and metal-oxide sensors in boilers

Metal insulator silicon carbide field-effect transistor sensors, metal-oxide sensors, and a linear Lambda sensor in an electronic nose was used to measure on-line in hot flue gases from a boiler. Flue gas from a 100-MW pellets-fuelled boiler has been used to feed the experimental setup. Several reference instruments, which measure the flue gases in parallel to the sensor array, are connected to the electronic nose. Data was collected during six weeks and then evaluated. Using principal component analysis as the data evaluation method, different operating modes for the boiler have been identified in the data set. The different modes could be described in terms of high or low O/sub 2/ and CO concentration. Furthermore, we have shown that it seems possible to use a sensor array to determine the operating mode of the boiler and, by partial least-squares models, measure the CO concentration when the boiler operates in its optimum mode.

Ultrahigh vacuum scanning force/scanning tunneling microscope: Application to high‐resolution imaging of Si(111)7×7

We present a combined scanning force/scanning tunneling microscope (SFM/STM) operating in ultrahigh vacuum using a fiber‐optic laser interferometer to detect the lever deflection. As force microscope it operates in ac and dc mode with commercial (Si, Si3N4) or individually made (W) cantilevers. Samples and cantilevers can be inserted without breaking the vacuum using a load‐lock system. The force sensor includes a novel three‐dimensional micropositioner based on the piezoelectric slider principle. The system includes standard surface analytical techniques (low‐energy electron diffraction/Auger, prepared for x‐ray photoelectron spectroscopy) and is equipped for mass spectroscopic detection of reaction products from catalytic surfaces at elevated temperature. Tips are cleaned in situ using electron bombardment. By using tungsten cantilevers with a high spring constant (k=100–200 N/m), it is possible to switch directly between STM and SFM operation. As reference surface we have used the Si(111)7×7 reconstruc...

Interaction forces between a tungsten tip and methylated SiO2 surfaces studied with scanning force microscopy

Abstract Scanning force microscopy was used for studying the interaction between a tungsten tip and methylated silicon. The surface displayed patches with interaction properties differing from the surroundings. The patches, typically 100 nm in diameter, were imaged with the SFM, and were characterized by a liquid bridge formation occurring at large tip-surface separations. Outside the patches the tip-surface interaction was consistent with a van der Waals force, and indistinguishable from a non-methylated (hydrophilic) surface.

A quasi three-dimensional optical memory with n-bit memory cells based on the ellipsometric principle: concept and prototype devices

Abstract A concept of an optical memory with n -bit memory cells using ellipsometric read-out is presented. Prototypes with two-bit and three-bit read-only memory cells were fabricated by deposition of multilayers consisting of thin metal films and thin amorphous semiconductor films, respectively.

Evaluation of on-line hot flue gas measurements

Using Metal Insulator Silicon Carbide (MISiC) sensors, Semiconducing Metal Oxide sensors (SMO) and a linear lambda sensor in an electronic nose, we measure hot flue gases on-line. Flue gas from a 500 kW pellets fuelled boiler, which is used for heating apartment blocks, has been used to feed the experimental set-up. Several reference instruments, which measure the flue gases in parallel to the sensor array, are connected to the electronic nose. The gases which are interesting to measure are NO, CO, O2 and hydrocarbons, HC. Results on prediction for CO, NO, and O2 in the flue gases based on PLS- (and ANN-) models are here presented.

A prescan method improving the reproducibility of force‐distance curves obtained with a piezoelectric tube scanner

We present a method based on pre‐ and postscanning a piezoelectric tube scanner used in a force probe that improves the reproducibility of the scan lengths. Instead of prescanning in the same direction as when acquiring data (the z direction), which could destroy a sensitive surface, we perform lateral (x/y direction) prescans. As lateral motions of the tube scanner involve out of phase elongations and compressions of the tube in the z direction, these kinds of prescans will have a stabilizing effect on the z motion as well. By adding an additional postscan in the ±z directions, we reduce the piezoelectric creep following the data acquisition scan. When comparing the lengths of z scans with and without the pre/postscan procedure, preceded by a z voltage step 60 s before data acquisition, the deviation between four consecutive scans improved from 12% to 1.4%.

A scanning force microscope designed for fluid cell measurements

We present a scanning force microscope working in the repulsive force mode designed for fluid–cell measurements and tip–sample interaction studies. The instrument uses the optical beam deflection principle to measure cantilever motion and is compatible with commercially available microfabricated cantilevers. The instrument is designed to accommodate tube scanners with lengths up to 2 in. In order to minimize memory effects in the piezoelectric scanner, we have introduced a technique of pre‐ and postscanning to get reproducible force versus distance curves. Different linearizing algorithms to decrease the unlinearities of the scanner motions are demonstrated. As examples of the performance, we present an image of a mica surface obtained in air showing atomic scale stick–slip features, and a force measurement using the fluid cell with NaCl electrolyte showing the double layer interaction between a glass sphere and a mica surface.