Defined Surface Structure Research Articles

Atomic-Scale Imprinting by Sputter Deposition of Amorphous Metallic Films.

With its ease of implementation, low cost, high throughput, and excellent feature replication accuracy, nanoimprinting is used to fabricate structures for electrical, optical, and biological applications or to modify surface properties. If ultraprecise and/or subnanometer-sized patterns are desired, nanoimprinting has shown only limited success with polymers, silica glasses, or crystalline materials. In contrast, the absence of an intrinsic length scale that would interfere with imprinting resolution enables bulk metallic glasses (BMGs) to replicate structures down to the atomic scale through thermoplastic forming (TPF). However, only a small number of BMG-forming alloys can be used for TPF-based atomic-scale imprinting. Here, we demonstrate an alternative sputter deposition-based approach for the replication of atomic-scale features that is suited for a very broad range of amorphous alloys, thereby dramatically extending the available chemistries. Additional advantages are the method's scalability, its ability to replicate a wide range of molds, its low material consumption, and the fact that the films can readily be applied onto almost any workpiece, which together open up new avenues to atomically defined surface structuring and functionalization. Our method constitutes the advancement from proof of concept to a practical and highly versatile toolbox of atomic-scale imprinting to be explored for the science and technology of atomic-scale imprinting.

Bonding mechanisms in laser-assisted joining of metal-polymer composites

Metal-Plastic hybrid components and assemblies are gaining importance due to novel lightweight constructions and a growing integration of functions by using the right material at the right place. Thermal joining enables a joining technology for thermoplastic materials and engineering metals without using adhesive or joining elements. The paper provides novel investigations on the interaction between form fit and physicochemical interactions due to the combined use of specifically used oxide layers, interaction barriers and defined surface structuring by laser processing. Thereby, the design of experiments allows the investigation of the form fit as dominant interaction mode.

Electrodeposition and Characterization of Pt(100) Nanostructures

In the last decade, approaches to increase the electrocatalytic activity of platinum based catalysts have focus on decreasing the particle size or using nanostructures to increase the surface to mass ratio. Significant improvements were also obtained by mixing Pt with various elements to form alloys and improve the poisoning tolerance to CO and other oxygenated compounds.[1, 2] However, an increasingly promising approach has focus on taking advantages of the surface sensitivity of electrochemical reactions to use catalysts with a specific surface structure, such as single crystals, shape-controlled nanoparticles or preferentially oriented films to increase the activity of a given catalyst.[3, 4] Unfortunately, the preparation and use of these catalysts is not trivial. Single crystals have a very well defined surface structure, but their low electrochemical surface area limits the interest of such structure to fundamental studies. Nanoparticles offer a promising surface to mass ratio, but are often prepared by colloidal methods. The ligand shell employed in the synthesis can therefore be challenging to remove without altering the surface structure. However, it was recently shown that platinum films could be prepared by potentiostatic deposition in the absence of any organic surfactants. The blank voltammogram of such film (Fig.1) clearly displays features associated with a preferential (100) orientation, namely a h2 peak higher then h1, as well as the presence of h3, associated with (100) terraces. In this study, we will focus on influence of some of the parameters influencing the electrodeposition of such preferentially (100) oriented films. The influence of parameters such as the deposition potential, charge and the nature of the Pt salt used have a critical influence on the fraction of (100) and (111) sites that can be obtained. The analysis of this films will be discussed in light of the results obtained by bismuth irreversible adsorption and deconvolution of the hydrogen desorption region, according to the method described by Solla-Gullón et al.[5] A fine tuning of the deposition parameters can allow one to control the total fraction of (100) sites (up to 47%) and the fraction of Pt atoms in (100) terraces. The fraction of (111) sites can also be adjusted and reached a maximum value of 23 %.[5, 6] The advantages of these structures for electrocatalytic reactions (ammonia, formic acid oxidation) will also be discussed. Finally, in the last part of our work, we have studied the electrodeposition of such kind of preferentially oriented nanostructures through a homemade, porous AAO membrane. The parameters influencing the membrane preparation will be briefly discussed, before introducing the new results we obtained in the preparation of nanowires and nanotubes with a preferential (100) orientation.

Design and Verification of Geometric Roughness Standards by Reverse Engineering

In order to ensure a reliable calibration of surface topography measuring instruments the use of practical calibration strategies is required. This requirement can be fulfilled when measurement standards with a defined surface structure in accordance to the later obsessed application are used. Different examples for the design and manufacturing of accordant measurement standards have been investigated by the authors. Within this publication a generic reverse engineering approach for the design of geometrical measurement standards is deducted from these results. The physical effects that occur because of the manufacturing with an ultraprecision turning machine and the sampling of the measurement standards are mathematically inversed and considered. The practical abilities of the approach are illustrated exemplarily. These theoretical considerations for the design can be verified experimentally by the manufacturing of the samples with an ultra-precision turning process. In doing so, the high precision of the new design approach can be validated. The examinations confirm the universality of the reverse engineering approach for the design of measurement standards.

Surface topography enhances differentiation of mesenchymal stem cells towards osteogenic and adipogenic lineages

Surface topography impacts on cell growth and differentiation, but it is not trivial to generate defined surface structures and to assess the relevance of specific topographic parameters. In this study, we have systematically compared in vitro differentiation of mesenchymal stem cells (MSCs) on a variety of groove/ridge structures. Micro- and nano-patterns were generated in polyimide using reactive ion etching or multi beam laser interference, respectively. These structures affected cell spreading and orientation of human MSCs, which was also reflected in focal adhesions morphology and size. Time-lapse demonstrated directed migration parallel to the nano-patterns. Overall, surface patterns clearly enhanced differentiation of MSCs towards specific lineages: 15 μm ridges increased adipogenic differentiation whereas 2 μm ridges enhanced osteogenic differentiation. Notably, nano-patterns with a periodicity of 650 nm increased differentiation towards both osteogenic and adipogenic lineages. However, in absence of differentiation media surface structures did neither induce differentiation, nor lineage-specific gene expression changes. Furthermore, nanostructures did not affect the YAP/TAZ complex, which is activated by substrate stiffness. Our results provide further insight into how structuring of tailored biomaterials and implant interfaces – e.g. by multi beam laser interference in sub-micrometer scale – do not induce differentiation of MSCs per se, but support their directed differentiation.

Influence of Machine Hammer Peening on the Tribology of Sheet Forming

The recently developed machine hammer peening process is used at the die shop of the Mercedes-Benz plant in Sindelfingen in order to replace manual surface finish of deep drawing dies. The goal of the process is surface roughness reduction after milling to ensure the tribological properties, which are necessary for the sheet metal forming process. Using machine hammer peening it is also possible to create defined surface structures that may be employed to influence local friction conditions and therewith overcome current limitations of the forming process. To take advantage of the surface structuring capabilities it is necessary to understand how to create defined surface structures using machine hammer peening and how the created structures affect friction and material flow behavior. In this work an approach is presented to describe the interaction of milling and machine hammer peening parameters on the created topography by wave theory. Especially the influence of tool path parameters of milling and consecutive machine hammer peening is investigated. The results, which are calculated using wave theory, are verified by FEM simulations and real experiments. In addition, suitable process parameters for machine hammer peening are derived from the obtained results, as they are used at the Mercedes-Benz die shop today.

MALDI Mass Spectrometry Imaging in Microscope Mode with Infrared Lasers: Bypassing the Diffraction Limits

This letter demonstrates the use of infrared matrix-assisted laser desorption/ionization coupled with microscope mode mass spectrometry imaging. It is aimed to explore the use of intrinsic water in tissue as a matrix for imaging at spatial resolutions below the diffraction limit of the employed IR optics. Stigmatic ion optics with a magnification factor of ~70 were used to project the spatial distribution of produced ions onto a detector while separating ions with different mass-to-charge ratios using a time-of-flight mass spectrometer. A pixelated detector was used to simultaneously record arrival time and impact position. A previously described dried-droplet sample system of 2,5-dihydroxybenzoic acid (DHB) and 5 peptides covered by a copper grid for defined surface structure was used to benchmark the light- and ion-optical setup for spatial resolution and mass spectrometric performance. A spatial resolving power of 9.8 μm, well below the optical limit of diffraction (14 μm for the given setup), was established. After, frozen cryo-sections from a biological model system were measured by exploiting the endogenous water content as a matrix. Principal component analysis enabled a clear distinction between distinct tissue regions identified by both light microscopy and MS imaging.

Tuning Polarity of Polyphenylene Dendrimers by Patched Surface Amphiphilicity—Precise Control over Size, Shape, and Polarity

In the ideal case, a precise synthesis yields molecules with a constitutional as well as a conformational perfectness. Such a case of precision is demonstrated by the synthesis of semi-rigid amphiphilic polyphenylene dendrimers (PPDs). Polar sulfonate groups are precisely placed on their periphery in such a manner that patches of polar and non-polar regions are created. Key structural features are the semi-rigid framework and shape-persistent nature of PPDs since the limited flexibility introduces a nano-phase-separated amphiphilic rim of the dendrimer. This results in both attractive and repulsive interactions with a given solvent. Frustrated solvent structures then lead to a remarkable solubility in solvents of different polarity such as toluene, methanol, and water or their mixtures. Water solubility combined with defined surface structuring and variable hydrophobicity of PPDs that resemble the delicate surface textures of proteins are important prerequisites for their biological and medical applications based upon cellular internalization.

Exploiting shape effects of La2O3 nanocatalysts for oxidative coupling of methane reaction

High activity towards oxidative coupling of methane and high selectivity for C2 hydrocarbons could be achieved over La2O3 nanorods with a large surface area, strong surface basic sites, electron deficient surface oxygen species and defined surface structure compared with La2O3 nanoparticles at low temperature.

Friction and Adhesion Forces of Bacillus thuringiensis Spores on Planar Surfaces in Atmospheric Systems

The kinetic friction force and the adhesion force of Bacillus thuringiensis spores on planar surfaces in atmospheric systems were studied using atomic force microscopy. The influence of relative humidity (RH) on these forces varied for different surface properties including hydrophobicity, roughness, and surface charge. The friction force of the spore was greater on a rougher surface than on mica, which is atomically flat. As RH increases, the friction force of the spores decreases on mica whereas it increases on rough surfaces. The influence of RH on the interaction forces between hydrophobic surfaces is not as strong as for hydrophilic surfaces. The friction force of the spore is linear to the sum of the adhesion force and normal load on the hydrophobic surface. The poorly defined surface structure of the spore and the adsorption of contaminants from the surrounding atmosphere are believed to cause a discrepancy between the calculated and measured adhesion forces.

Influence of Structuring by Abrasive Machining on the Tribological Properties of Workpiece Surfaces

Surface structuring of workpieces has a significant influence on the tribological properties of contact partners and can therefore lead to a significant increase of the life time of components [1]. To identify an appropriate surface structure, analytical and experimental investigations were done at the Institute for Machine Tools and Factory Management (IWF) in order to improve the tribological properties in the contact area appreciably. To validate the theoretical analyses, technological investigations were carried out. 3D-surface structures were created on workpiece surfaces by varying process variables for a high speed 5-axes machine system to generate knowledge for developing defined surface structures by using kinematically modified grinding processes. Initial results show a positive influence of defined surface structures on the performance of contact partners.

Surface nanopatterning of phosphorylcholine unit by well-defined block copolymer containing 2-methacryloyloxyethyl phosphorylcholine

Ordered surface patterning of biocompatible microdomain is potentially needed in many applications such as high sensitive biochips, biosensors, and nanobio devices for cell culturing. One of the efficient ways in the fabrication of patterned surface is using the microphase separation of well-defined block copolymers by controlling molecular weight and film formation process. Thus we synthesize several compositions of block copolymers containing 2-methacryloyloxyethyl phosphorylcholine (MPC) which is hydrophilic and shows excellent biocompatibility, and polydimethylsiloxane (PDMS) which has hydrophobic nature and usually used as soft lithography materials. All of the copolymers were synthesized by the atom transfer radical polymerization (ATRP) method at room temperature. The kinetics plot and molecular weight plot shows that the polymerizations of block copolymers were well controlled, thus the compositions of block copolymers were controllable. Two kinds of synthesized copolymers: the longest MPC segment and the shortest one, were cast on Si(100) substrate by spin casting or solvent casting. By using the IR-multichannel viewer and atom force microscope, we could conclude that the film formed by the longest MPC segment could not generate the well defined surface structure due to its long chain aggregation. By using the copolymer containing the shortest MPC segment, we could generate a nanoscale ordered surface patterning of phorsphorylcholine unit.

Controlling Adhesion with Surface Hole Patterns

Defined surface structures of various shapes and length scales can impact the adhesion of polymer interfaces. Most recent research has focused on the use of high-aspect-ratio post-like structures to modify the formation and separation mechanisms for a contacting interface. These mechanisms for controlling adhesion were inspired by the natural mechanisms present in examples such as the gecko and jumping spider. Although post-like structures are effective, numerous other geometries can impact adhesion properties through different mechanisms. In this article, we present and discuss the impact of surface hole patterns on the adhesion of soft, elastomeric interfaces. The surface holes are shallow, cylindrical depressions that decorate the surface of the elastomer and alter the separation mechanisms from rigid surfaces. We specifically focus on the effect of hole radius and nearest hole spacing on the overall adhesion descriptors. Using contact adhesion experiments largely based on the theory of Johnson, Kendall, and Roberts (JKR), we demonstrate that surface holes can alter the stability of the contact edge during interfacial separation. This stability does not affect the overall work of adhesion for a crosslinked polydimethylsiloxane interface, but it does permit tuning of the maximum separation force. These results emphasize the importance of measuring the interfacial area during adhesion testing, the significance of the contact edge, and the opportunities for using surface holes to tune the dissipative processes of interfaces that involve viscoelastic materials. These conclusions are particularly significant in the context of characterization techniques that do not allow for the direct measurement of contact area, such as nanoindentation or scanning probe microscopy measurements.

Laser-assisted structuring of ceramic and steel surfaces for improving tribological properties

Tribological properties of a system are very important for saving energy or increasing service life as in automotive industry. It is known that wear and friction behaviour is strongly influenced by the topography of the mated surfaces. In case of lubricated sliding contact the tribological properties can be improved by generating a defined surface structure in form of small channels or isolated pits. Depending on the structure it may act as a reservoir for the lubricant and hampers the drain of the lubricant. In addition, wear particles can be removed from the contact area and can be collected inside the structures. In the present paper, a Nd:YAG-laser was used to generate different structures on ceramic (Al 2O 3) and steel (100Cr6) surfaces. Microchannels and micropits were generated onto an otherwise flat surface by a laser ablation process. Due to the high flexibility of the laser system, structural features such as size, density and orientation could be varied easily by changing the laser parameters. The effects of different topographies on friction and wear behaviour were examined using a cylinder/plate tribometer for lubricated and reversed sliding contact. Laser structured 100Cr6 and alumina surfaces mated to 100Cr6 cylinders showed that a reduction of friction could be achieved in comparison to the polished surfaces. Dependent on the kind of the surface structure the coefficient of friction could be reduced up to 30%, especially in the initial period of the tribological experiment. The results show that the laser technique is an effective tool to optimise the topography of tribological surfaces.

Intumescent Coatings and the Processes that Take Place in Them

Based on the results of the study, calcium borate and metal-containing tubulenes are effective as cross-linking agents in coked foam formation. We can hypothesize that addition of metal-containing tubulenes affects the change in the structure of the stimulator and foaming agent together with an effect on the structure of the hardening polymer which causes the formation of coked foam of defined surface structure and composition.

Identification of a bisegmented double-stranded RNA virus (picobirnavirus) in calf faeces

To determine the incidence of rotavirus infection among dairy herds in the State of São Paulo, Brazil, 576 faecal samples obtained from calves aged 1–45 days with and without diarrhoea, reared on 63 dairy cattle farms, were analyzed. Polyacrylamide gel electrophoresis (PAGE) identified 28 samples positive for group A rotavirus, while four samples, two diarrhoeic and two non-diarrhoeic, showed a bisegmented genome with a typical picobirnavirus pattern. Electron microscopy revealed spherical virus particles with a diameter of 37 nm and without a defined surface structure. The present study is the first report of a bisegmented virus identified in cattle in Brazil.

Biodegradable comb polyesters containing polyelectrolyte backbones facilitate the preparation of nanoparticles with defined surface structure and bioadhesive properties

AbstractA major challenge in oral peptide and protein delivery remains the search for suitable carrier systems. Therefore, a new concept was investigated combining a modified three‐dimensional architecture, increased hydrophilicity of poly(lactic‐co‐glycolic acid) (PLGA) and charged groups in a single polymer. Biodegradable comb PLGA were synthesized by grafting short PLGA chains onto different poly(vinyl alcohol) (PVA) based backbone polyols, poly(2‐sulfobutyl‐vinyl alcohol) and poly(diethylaminoethyl‐vinyl alcohol). The polyelectrolyte backbones were obtained by etherification of PVA with charge‐containing pendent groups. The comb polymer structure could be confirmed by nuclear magnetic resonance, infrared spectroscopy, differential scanning calorimetry, elemental analysis and measurement of intrinsic viscosity. Nanoparticles (NP), as potential mucosal carriers systems, were prepared by controlled precipitation and investigated as a function of polymer composition. The amphiphilic character and the three‐dimensional architecture of the novel polyesters allowed the preparation of small nanoparticles even without the use of surfactants. Surface NMR, surface charge and hydrophobicity determination indicate a core–corona‐like NP structure, especially in the case of negatively charged polyesters. A structural model is proposed for the NP with an inner polyester core and an outer charged‐groups‐containing surface, depending on polymer composition and backbone charge density. The higher the polymer backbone charge density, the more pronounced its influence on the nanoparticle surface properties. The possibility of preparing NP without the use of a surfactant, as well as of designing the NP surface characteristics by polymer backbone charge density and polymer hydrophilic–hydrophobic balance, will be a major advantage in protein adsorption, bioadhesion and organ distribution. This makes these biodegradable polymers promising candidates for colloidal protein and peptide delivery. Copyright © 2003 John Wiley & Sons, Ltd.

Bacterial fibronectin-binding proteins and endothelial cell surface fibronectin mediate adherence of Staphylococcus aureus to resting human endothelial cells.

Adhesion of Staphylococcus aureus to human endothelial cells is implicated in the pathogenesis of invasive staphylococcal disease. The adhesion to endothelial cells of isogenic mutants defective in defined surface structures was studied. Three strains of S. aureus defective in fibronectin-binding proteins FnBPA and FnBPB showed reduced adhesion. This was fully restored by complementation of a FnBPA- FnBPB- mutant derived from strain 8325-4 with a multicopy plasmid encoding FnBPA or FnBPB. Adhesion of mutants defective in other surface structures was unaffected. Anti-fibronectin antibodies blocked adhesion of 8325-4 to endothelial cells, while adhesion of strains 8325-4, P1 and five clinical isolates was inhibited by the recombinant form of the binding domain of FnBPB (rFNBD) from Streptococcus dysgalactiae. Adherence of bacterial aggregates resulting from the presence of purified fibrinogen was also inhibited by rFNBD protein. Three strains of S. aureus defective in FnBPA and FnBPB were not internalized by endothelial cells. S. aureus FnBPs mediate adhesion to human endothelial cells and are required for subsequent internalization, interactions of potential relevance to pathogenesis and treatment.

Fe 3O 4(111) surface structure determined by LEED crystallography

The surface structure formed on epitaxial Fe 3O 4(111) magnetite films grown onto Pt(111) was re-examined by a full dynamical low energy electron diffraction (LEED) intensity analysis. Prior to the LEED measurements the films were investigated with scanning tunneling microscopy regarding their surface defect concentrations and the possible coexistence of different surface terminations. After a final oxidation at 1000 K in 10 −6 mbar oxygen partial pressure one defined surface structure is formed, and for films with low surface defect concentrations the best fit structure reveals a Pendry R-factor of 0.20 based on a data set with a total energy range of 1300 eV. It corresponds to an unreconstructed bulk termination of Fe 3O 4(111), which exposes 1/4 monolayer of iron atoms over a hexagonal close-packed oxygen layer underneath. The outermost iron plane is relaxed inward towards the underlying oxygen plane by 41±7% of the corresponding bulk spacing, followed by strong relaxations of the next three interlayer spacings. The same surface termination with slightly different relaxations was obtained in an earlier analysis, which corresponded to a local R-factor minimum in parameter space [W. Weiss et al., Phys. Rev. Lett. 71 (1993) 1848]. The energetics of the Fe 3O 4(111) surface structure is discussed considering the mixed iono-covalent bond character in this oxide.

A-site layer terminated perovskite substrate: NdGaO3

A perovskite single-crystal substrate, NdGaO3 (001), was thermally annealed in air to give an atomically defined surface structure. From analysis with coaxial impact-collision ion scattering spectroscopy, the terminating atomic layer was identified to be NdO1+δ , i.e., the A-site oxide monolayer in perovskite ABO3. This result is contrary to the B-site oxide (BO2−δ) termination observed in other perovskite surfaces, such as wet etched SrTiO3 and LaAlO3 or annealed (LaAlO3)0.3–(Sr2AlTaO6)0.7 (LSAT).