Ragnar Erlandsson

Structure of 3-aminopropyl triethoxy silane on silicon oxide

Abstract 3-Aminopropyl triethoxy silane (APTES) was deposited onto silicon oxide surfaces under various conditions of solvent, heat, and time, and then exposed to different curing environments, including air, heat, and ethanol. The macro- and micromolecular structure of APTES was probed on different levels using different techniques. The thickness of APTES layers was measured by ellipsometry, macromolecular structures were identified using microscopic methods (scanning electron microscopy and atomic force microscopy), and chemical form was investigated using angle-resolved X-ray photoelectron spectroscopy and also reflection infrared spectroscopy of APTES on gold and aluminum oxide surfaces. Coverage equivalent to one monolayer was achieved using very mild reaction and curing conditions (reaction in dry toluene for 15 min at room temperature, curing in air, or 15 min in 200°C oven), whereas thick layers were made by increasing reaction and curing times. APTES initially adsorbed to the surface, and curing was necessary to complete covalent binding between APTES and the surface. Deposition of APTES from water gave thin layers, probably electrostatically bound to silicon.

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.

Sharp microfaceting of (001)-oriented cerium dioxide thin films and the effect of annealing on surface morphology

Cerium dioxide, CeO2, is a chemically stable oxygen-ion-conducting material, which has been extensively used as an additive or support in oxidation catalysts. The fact that catalytic behaviour is often surface structure sensitive and/or edge atom dependent suggests that different surfaces might be discernible in associated redox processes. Thus, it is desirable to realise CeO2 films with a well-defined microstructure and with crystallographically uniform surfaces. In this paper we present evidence of extremely sharp microfaceting on the surface of thin CeO2 films grown by r.f. magnetron sputtering, and the effect of annealing on the formed sharp ridges. The results show that nominally designated crystallographic surfaces may in fact not coincide with the surfaces exposed as-grown. Thus, there is a clear risk for erroneous interpretation of various orientation-dependent surface properties. Carefully controlled annealing of these films can be utilised as a method for tailoring the resulting surface morphology on the atomic scale.

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.

A method for in situ characterization of tip shape in ac-mode atomic force microscopy using electrostatic interaction

We present a method for in situ characterization of the tip shape in atomic force microscopes that can operate in noncontact ac mode. By sweeping the voltage between tip and sample while recording the sample position as it is regulated to give a constant force gradient, we obtain curves giving information about the tip geometry. The measurements were performed in ultrahigh vacuum using electrochemically etched tungsten tips against a surface of doped silicon. Our results show that the sphere model gives a good description of the interaction, and that the radii we obtain are consistent with data from scanning electron microscopy. The method can also be used to estimate the value of the Hamaker constant and the contact potential between tip and sample.We present a method for in situ characterization of the tip shape in atomic force microscopes that can operate in noncontact ac mode. By sweeping the voltage between tip and sample while recording the sample position as it is regulated to give a constant force gradient, we obtain curves giving information about the tip geometry. The measurements were performed in ultrahigh vacuum using electrochemically etched tungsten tips against a surface of doped silicon. Our results show that the sphere model gives a good description of the interaction, and that the radii we obtain are consistent with data from scanning electron microscopy. The method can also be used to estimate the value of the Hamaker constant and the contact potential between tip and sample.

Gas‐induced restructuring of palladium model catalysts studied with atomic force microscopy

The structure of thin Pd films evaporated onto planar SiO2 substrates changes dramatically during oxygen/hydrogen exposures in ultrahigh vacuum. In this work we have used an atomic force microscope(AFM), operated in the attractive mode, to obtain the three‐dimensional morphology of the Pd surface for different film thicknesses and treatments, and compared the data with transmission electron microscopy(TEM) micrographs. During restructuring, a 100‐A film changes from being a smooth continuous film with cracks into metal clusters dispersed on the SiO2 support. In the 5‐A case the metal films are already well dispersed as fabricated. Here the gas exposure instead results in a clustering effect resulting in larger particles. The AFM gives results which are consistent with TEM micrographs but also gives additional information on metal particle shape which can lead to a further understanding of the restructuring process.

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...

Spectroscopic Characterization of Some Polyanilines

Some previous studies of polyaniline, or (oN)x, using infrared spectroscopy, X-ray photoelectron spectroscopy and NMR, are reviewed. New results involving the optical absorption spectra of free-standing, electrochemically prepared (oN)x, in both the insulating (2A) and conducting (2S) form are presented. Use is made of spectra of nigrosine, which is a model molecule representative of a short (oN)x chain.

Morphology changes of thin Pd films grown on SiO2: influence of adsorbates and temperature

Under certain conditions morphology changes occur when thin Pd films, grown on SiO2 at room temperature, are subject to elevated temperatures. First holes in the metal are observed, followed by net ...

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.