The optical response of nanostructured surfaces and the composite diffracted evanescent wave model

Investigations of the optical response of subwavelength-structure arrays milled into thin metal films have revealed surprising phenomena, including reports of unexpectedly high transmission of light. Many studies have interpreted the optical coupling to the surface in terms of the resonant excitation of surface plasmon polaritons (SPPs), but other approaches involving composite diffraction of surface evanescent waves (CDEW) have also been proposed. Here we present a series of measurements on very simple one-dimensional subwavelength structures to test the key properties of the surface waves, and compare them to the CDEW and SPP models. We find that the optical response of the silver metal surface proceeds in two steps: a diffractive perturbation in the immediate vicinity (2–3 mu m) of the structure, followed by excitation of a persistent surface wave that propagates over tens of micrometres. The measured wavelength and phase of this persistent wave are significantly shifted from those expected for resonance excitation of a conventional SPP on a pure silver surface.

Nanoscale Oxidative Patterning of Metallic Surfaces to Modulate Cell Activity and Fate

In the field of regenerative medicine, nanoscale physical cuing is clearly becoming a compelling determinant of cell behavior. Developing effective methods for making nanostructured surfaces with well-defined physicochemical properties is thus mandatory for the rational design of functional biomaterials. Here, we demonstrate the versatility of simple chemical oxidative patterning to create unique nanotopographical surfaces that influence the behavior of various cell types, modulate the expression of key determinants of cell activity, and offer the potential of harnessing the power of stem cells. These findings promise to lead to a new generation of improved metal implants with intelligent surfaces that can control biological response at the site of healing.

Anisotropic surface properties of micro/nanostructured a-C:H:F thin films with self-assembly applications

The singular properties of hydrogenated amorphous carbon (a-C:H) thin filmsdeposited by pulsed DC plasma enhanced chemical vapor deposition (PECVD), such as hardness and wear resistance, make it suitable as protective coating with low surface energy for self-assembly applications. In this paper, we designed fluorine-containing a-C:H (a-C:H:F) nanostructured surfaces and we characterized them for self-assembly applications. Sub-micron patterns were generated on silicon through laser lithography while contact angle measurements, nanotribometer, atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the surface. a-C:H:F properties on lithographied surfaces such as hydrophobicity and friction were improved with the proper relative quantity of CH4 and CHF3 during deposition, resulting in ultrahydrophobic samples and low friction coefficients. Furthermore, these properties were enhanced along the direction of the lithographypatterns (in-plane anisotropy). Finally, self-assembly properties were tested with silicananoparticles, which were successfully assembled in linear arrays following the generated patterns. Among the main applications, these surfaces could be suitable as particle filter selector and cell colony substrate.

'Bio-nano interactions: new tools, insights and impacts': summary of the Royal Society discussion meeting

Bio-nano interactions can be defined as the study of interactions between nanoscale entities and biological systems such as, but not limited to, peptides, proteins, lipids, DNA and other biomolecules, cells and cellular receptors and organisms including humans. Studying bio-nano interactions is particularly useful for understanding engineered materials that have at least one dimension in the nanoscale. Such materials may consist of discrete particles or nanostructured surfaces. Much of biology functions at the nanoscale; therefore, our ability to manipulate materials such that they are taken up at the nanoscale, and engage biological machinery in a designed and purposeful manner, opens new vistas for more efficient diagnostics, therapeutics (treatments) and tissue regeneration, so-called nanomedicine. Additionally, this ability of nanomaterials to interact with and be taken up by cells allows nanomaterials to be used as probes and tools to advance our understanding of cellular functioning. Yet, as a new technology, assessment of the safety of nanomaterials, and the applicability of existing regulatory frameworks for nanomaterials must be investigated in parallel with development of novel applications. The Royal Society meeting 'Bio-nano interactions: new tools, insights and impacts' provided an important platform for open dialogue on the current state of knowledge on these issues, bringing together scientists, industry, regulatory and legal experts to concretize existing discourse in science law and policy. This paper summarizes these discussions and the insights that emerged.

Thickness and Annealing Temperature Effects on the Optical Properties and Surface Morphology of Layer-by-Layer Poly(p-phenyline vinylene) plus Dodecylbenzenesulfonate Films

The fabrication of controlled molecular architectures is essential for organic devices, as is the case of emission of polarized light for the information industry. In this study, we show that optimized conditions can be established to allow layer-by-layer (LbL) films of poly(p-phenylene vinylene) (PPV)+dodecylbenzenesulfonate (DBS) to be obtained with anisotropic properties. Films with five layers and converted at 110 degrees C had a dichroic ratio delta = 2.3 and order parameter r = 34%, as indicated in optical spectroscopy and emission ellipsometry data. This anisotropy was decreased with the number of layers deposited, with delta = 1.0 for a 75-layer LbL PPV + DBS film. The analysis with atomic force microscopy showed the formation of polymer clusters in a random growth process with the normalized height distribution being represented by a Gaussian function. In spite of this randomness in film growth, the self-covariance function pointed to a correlation between clusters, especially for thick films. In summary, the LbL method may be exploited to obtain both anisotropic films with polarized emission and regular, nanostructured surfaces. (c) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 206-213, 2011

Crescimento de nanotubos de TiO2 na superfície da liga Ti-7,5Mo empregando oxidação anódica

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Complex materials via colloidal crystallization

The work presented in this thesis deals with complex materials, which were obtained by self-assembly of monodisperse colloidal particles, also called colloidal crystallization. Two main fields of interest were investigated, the first dealing with the fabrication of colloidal monolayers and nanostructures, which derive there from. The second turned the focus on the phononic properties of colloidal particles, crystals, and glasses. For the fabrication of colloidal monolayers a method is introduced, which is based on the sparse distribution of dry colloidal particles on a parent substrate. In the ensuing floating step the colloidal monolayer assembles readily at the three-phase-contact line, giving a 2D hexagonally ordered film under the right conditions. The unique feature of this fabrication process is an anisotropic shrinkage, which occurs alongside with the floating step. This phenomenon is exploited for the tailored structuring of colloidal monolayers, leading to designed hetero-monolayers by inkjet printing. Furthermore, the mechanical stability of the floating monolayers allows the deposition on hydrophobic substrates, which enables the fabrication of ultraflat nanostructured surfaces. Densely packed arrays of crescent shaped nanoparticles have also been synthesized. It is possible to stack those arrays in a 3D manner allowing to mutually orientate the individual layers. In a step towards 3D mesoporous materials a methodology to synthesize hierarchically structured inverse opals is introduced. The deposition of colloidal particles in the free voids of a host inverse opal allows for the fabrication of composite inverse opals on two length scales. The phononic properties of colloidal crystals and films are characterized by Brillouin light scattering (BLS). At first the resonant modes of colloidal particles consisting of polystyrene, a copolymer of methylmethacrylate and butylacrylate, or of a silica core-PMMA shell topography are investigated, giving insight into their individual mechanical properties. The infiltration of colloidal films with an index matching liquid allows measuring the phonon dispersion relation. This leads to the assignment of band gaps to the material under investigation. Here, two band gaps could be found, one originating from the fcc order in the colloidal crystal (Bragg gap), the other stemming from the vibrational eigenmodes of the colloidal particles (hybridization gap).

Spektroelektrochemische Untersuchungen mittels oberflächenverstärkter Infrarotabsorptionsspektroskopie (SEIRAS) an Multi-Redox-Center-Proteinen in einer biomimetischen Membranumgebung

Die optische Eigenschaften sowie der Oberflächenverstärkungseffekt von rauen Metalloberflächen sowie Nanopartikeln wurden intensiv für den infraroten Bereich des Spektrums in der Literatur diskutiert. Für die Präparation solcher Oberflächen gibt es prinzipiell zwei verschiedene Strategien, zum einen können die Nanopartikel zuerst ex-situ synthetisiert werden, der zweite Ansatz beruht darauf, dass die Nanopartikel in-situ hergestellt und aufgewachsen werden. Hierbei wurden beide Ansätze ausgetestet, dabei stellte sich heraus, dass man nur mittels der in-situ Synthese der Goldnanopartikel in der Lage ist nanostrukturierte Oberflächen zu erhalten, welche elektronisch leitfähig sind, nicht zu rau sind, um eine Membranbildung zu ermöglichen und gleichzeitig einen optimalen Oberflächenverstärkungseffekt zeigen. Obwohl keine ideale Form der Nanopartikel mittels der in-situ Synthese erhalten werden können, verhalten sich diese dennoch entsprechend der Theorie des Oberflächenverstärkungseffekts. Optimierungen der Form und Grösse der Nanopartikel führten in dieser Arbeit zu einer Optimierung des Verstärkungseffekts. Solche optimierten Oberflächen konnten einfach reproduziert werden und zeichnen sich durch eine hohe Stabilität aus. Der so erhaltene Oberflächenverstärkungseffekt beträgt absolut 128 verglichen mit dem belegten ATR-Kristall ohne Nanopartikel oder etwa 6 mal, verglichen mit der Oberfläche, die bis jetzt auch in unserer Gruppe verwendet wurde. Daher können nun Spektren erhalten werden, welche ein deutlich besseres Signal zu Rauschverhältnis (SNR) aufweisen, was die Auswertung und Bearbeitung der erhaltenen Spektren deutlich vereinfacht und verkürzt.rnNach der Optimierung der verwendeten Metalloberfläche und der verwendeten Messparameter am Beispiel von Cytochrom C wurde nun an der Oberflächenbelegung der deutlich größeren Cytochrom c Oxidase gearbeitet. Hierfür wurde der DTNTA-Linker ex-situ synthetisiert. Anschließend wurden gemischte Monolagen (self assembeld monolayers) aus DTNTA und DTP hergestellt. Die NTA-Funktionalität ist für die Anbindung der CcO mit der his-tag Technologie verantwortlich. Die Kriterien für eine optimale Linkerkonzentration waren die elektrischen Parameter der Schicht vor und nach Rekonstitution in eine Lipidmembran, sowie Elektronentransferraten bestimmt durch elektrochemische Messungen. Erst mit diesem optimierten System, welches zuverlässig und reproduzierbar funktioniert, konnten weitere Messungen an der CcO begonnen werden. Aus elektrochemischen Messungen war bekannt, dass die CcO durch direkten Elektronentransfer unter Sauerstoffsättigung in einen aktivierten Zustand überführt werden kann. Dieser aktivierte Zustand zeichnet sich durch eine Verschiebung der Redoxpotentiale um etwa 400mV gegenüber dem aus Gleichgewichts-Titrationen bekannten Redoxpotential aus. Durch SEIRAS konnte festgestellt werden, dass die Reduktion bzw. Oxidation aller Redoxzentren tatsächlich bei den in der Cyclovoltammetrie gemessenen Potentialen erfolgt. Außerdem ergaben die SEIRA-Spektren, dass durch direkten Elektronentransfer gravierende Konformationsänderungen innerhalb des Proteins stattfinden. rnBisher war man davon ausgegangen, aufgrund des Elektronentransfers mittels Mediatoren, dass nur minimale Konformationsänderungen beteiligt sind. Vor allem konnte erstmaligrnder aktivierte und nicht aktivierte Zustand der Cytochrom c Oxidase spektroskopisch nachweisen werden.rn

Dipodal Ferrocene Derivatives for Nanostructured Redox-Functionalised Surfaces

Self-assembled monolayers (SAMs) on solid surfaces are of great current interest in science and nanotechnology. This thesis describes the preparation of several symmetrically 1,1’-substituted ferrocene derivatives that contain anchoring groups suitable for chemisorption on gold and may give rise to SAMs with electrochemically switchable properties. The binding groups are isocyano (-NC), isothiocyanato (-NCS), phosphanyl (-PPh2), thioether (-SR) and thienyl. In the context of SAM fabrication, isothiocyanates and phosphanes are adsorbate systems which, surprisingly, have remained essentially unexplored. SAMs on gold have been fabricated with the adsorbates from solution and investigated primarily by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The results of these analytical investigations are presented and discussed in matters of the film quality and possible binding modes. The quality of self-assembled monolayers fabricated from 1,1’-diisocyanoferrocene and 1,1’-diisothiocyanatoferrocene turned out to be superior to that of films based on the other adsorbate species investigated. Films of those absorbates as well as of dppf afforded well-defined SAMs of good quality. All other films of this study based on sulfur containing anchoring groups exhibit chemical inhomogeneity and low orientational order of the film constituents and therefore failed to give rise to well-defined SAMs. Surface coordination chemistry is naturally related to molecular coordination chemistry. Since all SAMs described in this thesis were prepared on gold (111) surfaces, the ferrocene-based ligands of this study have been investigated in their ability for complexation towards gold(I). The sulfur-based ferrocene ligands [fc(SR)2] failed to give stable gold(I) complexes. In contrast, 1,1’-diisocyanoferrocene (1) proved to be an excellent ligand for the complexation of gold(I). Several complexes were prepared and characterised utilising a series of gold(I) acetylides. These complexes show interesting structural motifs in the solid state, since intramolecular aurophilic interactions lead to a parallel orientation of the isocyano moieties, combined with an antiparallel alignment of neighbouring units. The reaction of 1 with the gold(I) acetylide [Au(C≡C–Fc)]n turned out to be very unusual, since the two chemically equivalent isocyano groups undergo a different reaction. One group shows an ordinary coordination and the other one undergoes an extraordinary 1,1-insertion into the Au-C bond. As a sideline of the research of this thesis several ferrocene derivatives have been tested for their suitability for potential surface reactions. Copper(I) mediated 1,3-dipolar cycloadditions of azidoferrocene derivatives with terminal alkynes appeared very promising in this context, but failed to a certain extent in terms of ‘click’ chemistry, since the formation of the triazoles depended on the strict exclusion of oxygen and moisture and yields were only moderate. Staudinger reactions between dppf and azidoferrocene derivatives were also tested. The nucleophilic additions of secondary amines to 1,1’-diisothiocyanatoferrocene led to the respective thiourea derivatives in quantitative yields.

Design, physico-chemical characterization and bioactivity studies of hybrid nanostructured titanium surfaces for enhanced osseointegration

170 p.

TiB2 nanostructured coating for GFRP injection moulds

In the injection moulding of polypropylene reinforced with hard glass fibres, die materials are commonly subjected to severe abrasive wear. In order to improve its wear resistance, an unbalanced magnetron sputtering PVD compositional monolayered coating has been produced. The film was composed by a nanostructured TiB2 monolayer. Microstructure characterization and thickness evaluation were conducted by scanning electron microscopy (SEM). Film topography and roughness were accessed by SEM and Atomic Force Microscopy (AFM). The phase analyse was investigated by X-ray diffraction (XRD), using Cu Kalpha radiation. Scratch tests were conducted in order to study the film adhesion to the substrate. Load-Displacement curves (nanoindentation analysis) allowed measuring the film hardness and Young's modulus. A ball-cratering tribometer was used to determine the micro-abrasion laboratorial wear resistance, under different tests conditions, using SiC particles in distilled water slurry. At the end of these tests, the worn surfaces were analyzed by SEM and Energy Dispersive X-ray Spectroscopy (EDS) in order to compare these results with some other coatings already tested in the same conditions. To test the practical wear resistance, 135000 injection cycles were done in a plastic injection industrial mould. Coated samples were put on the plastic feed canal, after a turbulent zone. In these tests, a 30% (wt) glass fibres reinforced polypropylene was used. Worn sample surfaces were analyzed by SEM after 45.000 and 90.000 cycles. Image analyses were made in order to evaluate the damage increases and to observe the wear mechanisms involved.

Micro-abrasion wear behaviour of TiAlCrSiN nanostructured coatings

The injection process of glass fibres reinforced plastics promotes the moulds surface degradation by erosion. In order to improve its wear resistance, several kinds of PVD thin hard coatings were used. It is well-known that nanostructures present a better compromise between hardness and toughness. Indeed, when the coating is constituted by a large number of ultra-thin different layers, cracks and interface troubles tend to decrease. However, it is not clear that these nanostructures present a better wear behaviour in erosion processes. In order to study its wear behaviour, a sputtered PVD nanostructured TiAlCrSiN coating was used. The substrate and film surfaces topography were analyzed by profilometry and atomic force microscopy techniques. Film adhesion to the substrate was evaluated by scratch tests. The surface hardness was measured with a Vickers micro-hardness tester. The wear resistance was evaluated by micro-abrasion with a rotating ball tribometer tests. Slurry of SiC particles in distilled water was used in order to provoke the surface abrasion. Different duration tests were performed in order to analyze the wear evolution. After these tests, the wear mechanisms developed were analyzed by scanning electron microscopy. Wear craters were measured and the wear rate was calculated and discussed. With the same purpose, coated inserts were mounted in an injection mould working with a 30% glass fibres reinforced polypropylene. After 45 000 cycles no relevant wear was registered.

Light responsive multilayer surfaces with controlled spatial extinction capability

Multilayer systems obtained using the Layer-by-Layer (LbL) technology have been proposed for a variety of biomedical applications in tissue engineering and regenerative medicine. LbL assembly is a simple and highly versatile method to modify surfaces and fabricate robust and highly-ordered nanostructured coatings over almost any type of substrates and with a wide range of substances. The incorporation of polyoxometalate (POM) inorganic salts as constituents of the layers presents a possibility of promoting light-stimuli responses in LbL substrates. We propose the design of a biocompatible photo-responsive multilayer system based on a Preyssler-type POM ([NaP5W30O110]14â ) and a natural origin polymer, chitosan, using the LbL methodology. The photo-reduction properties of the POM allow the spatially controlled disruption of the assembled layers due to the weakening of the electrostatic interactions between the layers. This system has found applicability in detaching devices, such as the cell sheet technology, which may solve the drawbacks actually found in other cell treatment proposals.

Role of structural saturation and geometry in the luminescence of silicon-based nanostructured materials

The structural saturation and stability, the energy gap, and the density of states of a series of small, silicon-based clusters have been studied by means of the PM3 and some ab initio (HF/6-31G* and 6-311++G**, CIS/6-31G* and MP2/6-31G*) calculations. It is shown that in order to maintain a stable nanometric and tetrahedral silicon crystallite and remove the gap states, the saturation atom or species such as H, F, Cl, OH, O, or N is necessary, and that both the cluster size and the surface species affect the energetic distribution of the density of states. This research suggests that the visible luminescence in the silicon-based nanostructured material essentially arises from the nanometric and crystalline silicon domains but is affected and protected by the surface species, and we have thus linked most of the proposed mechanisms of luminescence for the porous silicon, e.g., the quantum confinement effect due to the cluster size and the effect of Si-based surface complexes.

Role of structural saturation and geometry in the luminescence of silicon-based nanostructured materials

The structural saturation and stability, the energy gap, and the density of states of a series of small, silicon-based clusters have been studied by means of the PM3 and some ab initio (HF/6-31G* and 6-311++G**, CIS/6-31G* and MP2/6-31G*) calculations. It is shown that in order to maintain a stable nanometric and tetrahedral silicon crystallite and remove the gap states, the saturation atom or species such as H, F, Cl, OH, O, or N is necessary, and that both the cluster size and the surface species affect the energetic distribution of the density of states. This research suggests that the visible luminescence in the silicon-based nanostructured material essentially arises from the nanometric and crystalline silicon domains but is affected and protected by the surface species, and we have thus linked most of the proposed mechanisms of luminescence for the porous silicon, e.g., the quantum confinement effect due to the cluster size and the effect of Si-based surface complexes.