Glass-ceramic coated Mg-Ca alloys for biomedical implant applications.

Biodegradable metals and alloys are promising candidates for biomedical bone implant applications. However, due to the high rate of their biodegradation in human body environment, they should be coated with less reactive materials, such, for example, as bioactive glasses or glass-ceramics. Fort this scope, RKKP composition glass-ceramic coatings have been deposited on Mg-Ca(1.4wt%) alloy substrates by Pulsed Laser Deposition method, and their properties have been characterized by a number of techniques. The prepared coatings consist of hydroxyapatite and wollastonite phases, having composition close to that of the bulk target material used for depositions. The 100µm thick films are characterized by dense, compact and rough morphology. They are composed of a glassy matrix with various size (from micro- to nano-) granular inclusions. The average surface roughness is about 295±30nm due to the contribution of micrometric aggregates, while the roughness of the fine-texture particulates is approximately 47±4nm. The results of the electrochemical corrosion evaluation tests evidence that the RKKP coating improves the corrosion resistance of the Mg-Ca (1.4wt%) alloy in Simulated Body Fluid.

Systematic STM and LEED investigation of the Si/Ag(110) surface.

Interest in the Si/Ag(110) system, which forms highly ordered linear nanostructures coined 'silicon nanoribbons', was recently boosted by the claim that such nanoribbons may be formed by silicon atoms arranged in a 2D honeycomb structure as in graphene, i.e. silicene. Despite such a revived interest, many discrepancies still exist in the recently reported results. This paper reports on a systematic investigation by scanning tunneling microscopy and low-energy electron diffraction of the Si/Ag(110) system as a function of the amount of deposited silicon and the deposition temperature. This reveals a complex interplay between these two factors, resulting in a rich array of possible self-assembled nanostructures and surface reconstructions. Several novel findings and clarification of the contradictory results reported in the literature are discussed in this work. In particular, the deposition temperature is demonstrated to be a key parameter to control the width of the Si nanoribbons produced. Recently, massive linear nanostructures were reported to be 'multilayer silicene', forming once the deposited silicon amount exceeds full coverage. However, we show that such nanostructures are also observed at low silicon coverage, demonstrating that their formation is exclusively determined by a deposition temperature higher than 460 K. On the other hand, for Si amounts higher than one monolayer the surface presents a novel c(8 × 4) reconstruction, which is responsible for the ×4 periodicity detected by LEED measurements, previously attributed to the 1.6 nm-wide nanoribbons overlayer or to 'multilayer silicene'. Finally, the large collection of acquired data also allowed us to single out image artifacts that may explain the contradictory results appearing in previous papers.

Ferromagnetic Mn-doped Si0.3Ge0.7 nanodots self-assembled on Si(100).

Densely packed epitaxial Mn-doped Si(0.3)Ge(0.7) nanodots self-assembled on Si(100) have been obtained. Their structural properties were studied using reflection high-energy electron diffraction, energy dispersive x-ray diffraction, atomic force microscopy, extended x-ray absorption fine structure measurements and high-resolution transmission electron microscopy. Mn(5)Ge(1)Si(2) crystallites embedded in Si(0.3)Ge(0.7) were found. They exhibit a ferromagnetic behaviour with a Curie temperature of about 225 K.

Control of structural, electronic, and optical properties of eumelanin films by electrospray deposition.

The capability to monitor finely the physical properties of eumelanin, an important class of biopolymers, involved in melanoma cancer pathologies, whose function and intrinsic disorder still collects the interest of many investigators, was achieved by means of electrospray deposition (ESD). By alleviating the problem of the solubility of melanin through the realization of high-quality films it was possible to spread light on the unknown biopolymer supramolecular organization. In fact, on the basis of scanning probe microscopies, electron spectroscopies, and transport properties, it was possible to delineate peculiar features of the melanin organization varying from heteropolymeric to oligomeric in character and eventually turning in a cross-linked secondary molecular structure.

Chirality transfer from a single chiral molecule to 2D superstructures in alaninol on the Cu(100) surface.

The formation of 2D chiral monolayers obtained by self-assembly of chiral molecules on surfaces has been widely reported in the literature. Control of chirality transfer from a single molecule to surface superstructures is a challenging and important aspect for tailoring the properties of 2D nanostructures. However, despite the wealth of investigations performed in recent years, how chiral transfer takes place on a large scale still remains an open question. In this paper we report a coupling of scanning tunneling microscopy and low energy electron diffraction measurements with an original theoretical approach, combining molecular dynamics and essential dynamics with density functional theory, to investigate self-assembled chiral structures formed when alaninol adsorbs on Cu(100). The peculiarity of this system is related to the formation of tetrameric molecular structures which constitute the building blocks of the self-assembled chiral monolayer. Such characteristics make alaninol/Cu(100) a good candidate to reveal chiral expression changes. We find that the deposition of alaninol enantiomers results in the formation of isolated tetramers that are aligned along the directions of the substrate at low coverage or when geometrical confinement prevents long-range order. Conversely, a rotation of 14° with respect to the Cu(100) unit vectors is observed when small clusters of tetramers are formed. An insight to the process leading to a 2D globally chiral surface has been obtained by monitoring molecular assemblies as they grow from the early stages of adsorption, suggesting that the distinctive orientation of the self-assembled monolayer originates from a balance of cooperating forces which start acting only when tetramers pack together to form small clusters.

AFM for diagnosis of nanocrystallization of steels in hardening processes.

INTRODUCTION: The aim of this study is to investigate the nanocrystallization of steels caused by the transformation from the austenitic to the martensitic phase induced by a severe plastic deformation (SPD) treatment. In this framework, we applied an air blast shot peening treatment, which is a simple protocol widely used for industrial purposes. METHODS: AISI 286 and AISI 316 specimens were peened for different times and polished using diamond pastes in order to remove corrugations higher than 1 mum. The characterization of the steel surfaces was performed by atomic force microscopy (AFM) operating in contact mode. Additional EDXD measurements were performed to confirm the phase transition. RESULTS AND DISCUSSION: An AFM-based characterization at nanometric level of the steel surfaces is provided. When the peening exceeds a threshold time that, as expected, depends on the steel composition, a uniform nanostructuration is detected. It is well known that such rearrangement is associated to the growth of a martensitic phase. To date, AFM has been employed in this field only for few applications and to solve specific problems. On the other hand, our results demonstrate that this is a useful technique for the characterization of hardened surfaces, especially when non-destructive sample preparation treatments are required. Moreover, we show that AFM can be a useful tool also for in situ industrial diagnostics of metallic parts.

Nano-Raman mapping of a porous glass-ceramic SERS substrate in collection mode.

Porous glass-ceramics is an extremely important material to be used in combination with metallic nanolayers as a Surface-Enhanced Raman Scattering (SERS) substrate for biological and chemical analysis, demonstrating excellent biocompatibility and chemical inertness. These materials show their own Raman background signal lateral distribution, mostly from crystalline skeleton, which has to be considered. A nano-Raman setup using the optical fibre of a Scanning Near-Field Optical Microscope (SNOM), working in collection mode, is described and applied for mapping of such glass-ceramic. The collected Raman signal of Ti and P containing phase distribution in this near-field geometry reaches spatial resolution around 50 nm.

Implementation of a bimorph-based aperture tapping-SNOM with an incubator to study the evolution of cultured living cells.

We present the implementation of a tapping-mode aperture scanning near-field optical microscope (Tapping-SNOM) to a Binder CB incubator (Istituto di Struttura della Materia, Rome, Italy). The microscope operates in the intermittent contact mode using a nonbent optical fibre allowing to reduce the perturbation exerted on the sample, while the incubator maintains a constant temperature, humidity and CO(2) level. This instrument can maintain and analyse in a controlled environment different samples, both organic and nonorganic. In particular, the Tapping-SNOM can study different cell lines at nanometric resolution and in physiological buffer, following the evolution of the living cells almost indefinitely. We will present several examples of the capabilities of the tapping scanning near-field optical microscope in the study of different lines of living cells, showing corresponding topographical, optical or phase-lag images of the live samples, evidencing the excellent stability, versatility and resolution of the system.

SNOM images of X-ray radiographs at nano-scale stored in a thin layer of lithium fluoride.

In this work, we report a method to observe soft X-ray radiographs at nanoscale of various kind of samples, biological and metallic, stored in a thin layer of lithium fluoride, employing scanning near-field optical microscopy with an optical resolution that reaches 50 nm. Lithium fluoride material works as a novel image detector for X-ray nano-radiographs, due to the fact that extreme ultraviolet radiation and soft X-rays efficiently produce stable point defects emitting optically stimulated visible luminescence in a thin surface layer. The bi-dimensional distribution of the so-created defects depends on the local nanostructure of the investigated sample.

Low-frequency electromagnetic field effects on functional groups in human skin keratinocytes cells revealed by IR-SNOM.

Human HaCaT cells, exposed for 24 h to a 1 mT (rms) 50 Hz sinusoidal magnetic field in a temperature-regulated solenoid, suffer detectable changes in their biochemical properties and shapes. By using infrared wavelength-selective scanning near-field optical microscopy, we observed changes in the distribution of the inner chemical functional groups and in the cell morphology with a resolution of 80-100 nm.

Infrared scanning near-field optical microscopy investigates order and clusters in model membranes.

Due to its surface sensitivity and high spatial resolution, scanning near-field optical microscopy (SNOM) has a significant potential to study the lateral organization of membrane domains and clusters. Compared to other techniques, infrared near-field microscopy in the spectroscopic mode has the advantage to be sensitive to specific chemical bonds. In fact, spectroscopic SNOM in the infrared spectral range (IR-SNOM) reveals the chemical content of the sample with a lateral resolution around 100 nm (Cricenti et al., 1998a, 1998b, 2003). Model lipid membranes were studied by IR-SNOM at several wavelengths. Topographical micrographs reveal the presence of islands at the surface and the optical images indicate the formation of locally ordered multiple bilayers - both critically important features for biotechnology and medical applications.

Roughness of the plasma membrane as an independent morphological parameter to study RBCs: a quantitative atomic force microscopy investigation.

A novel approach to the study of RBCs based on the collection of three-dimensional high-resolution AFM images and on the measure of the surface roughness of their plasma membrane is presented. The dependence of the roughness from several parameters of the imaging was investigated and a general rule for a trustful analysis and comparison has been suggested. The roughness of RBCs is a morphology-related parameter which has been shown to be characteristic of the single cells composing a sample, but independent of the overall geometric shape (discocyte or spherocyte) of the erythrocytes, thus providing extra-information with respect to a conventional morphology study. The use of the average roughness value as a label of a whole sample was tested on different kinds of samples. Analyzed data revealed that the quantitative roughness value does not change after treatment of RBCs with various commonly used fixation and staining methods while a drastic decrease occurs when studying cells with membrane-skeletal alteration both naturally occurring or artificially induced by chemical treatments. The present method provides a quantitative and powerful tool for a novel approach to the study of erythrocytes structure through an ultrastructural morphological analysis with the potential to give information, in a non-invasive way, on the RBCs function.

An AFM investigation of oligonucleotides anchored on unoxidized crystalline silicon surfaces.

Carboxylic terminated monolayers have been covalently attached on phosphorous doped crystalline (100) silicon surfaces using a cathodic electro grafting technique. The functionalization concentration and efficiency have been evaluated with different techniques. In particular, topographic images, performed with an atomic force microscope, were used to optimize the protocol in order to obtain a surface whose characteristics of uniformity and reproducibility are ideal for a bio-electronic device. Phase lag images of the functionalized surfaces were also performed, and show non-topographic structures that have been interpreted as areas of different molecule self-orientation. Poly-thymine oligonucleotides have been anchored on such a surface to form a nano-biosensing device capable to react selectively with a specific target molecule, a poly-adenine oligonucleotide. AFM images of high density (approximately 3x10(12) mol/cm2) single strand and double strand covered samples show toroidal shaped structures formed by the self-assembly of the oligonucleotides on the silicon surface.

AFM characterization of solid-supported lipid multilayers prepared by spin-coating.

Lipids are the principal components of biologically relevant structures as cellular membranes. They have been the subject of many studies due to their biological relevance and their potential applications. Different techniques, such as Langmuir-Blodgett and vesicle-fusion deposition, are available to deposit ordered lipid films on etched surfaces. Recently, a new technique of lipid film deposition has been proposed in which stacks of a small and well-controlled number of bilayers are prepared on a suitable substrate using a spin-coater. We studied the morphological properties of multi-layers made of cationic and neutral lipids (DOTAP and DOPC) and mixtures of them using dynamic mode atomic force microscopy (AFM). After adapting and optimizing, the spin-coating technique to deposit lipids on a chemically etched Silicon (1,0,0) substrate, a morphological nanometer-scale characterization of the aforementioned samples has been provided. The AFM study showed that an initial layer of ordered vesicles is formed and, afterward, depending on details of the spin-coating preparation protocol and to the dimension of the silicon substrate, vesicle fusion and structural rearrangements of the lipid layers may occur. The present data disclose the possibility to control the lipid's structures by acting on spin-coating parameters with promising perspectives for novel applications of lipid films.

SNOM and AFM microscopy techniques to study the effect of non-ionizing radiation on the morphological and biochemical properties of human keratinocytes cell line (HaCaT).

In this study we have employed atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) techniques to study the effect of the interaction between human keratinocytes (HaCaT) and electromagnetic fields at low frequency. HaCaT cells were exposed to a sinusoidal magnetic field at a density of 50 Hz, 1 mT. AFM analysis revealed modification in shape and morphology in exposed cells with an increase in the areas of adhesion between cells. This latter finding was confirmed by SNOM indirect immunofluorescence analysis performed with a fluorescent antibody against the adhesion marker beta4 integrin, which revealed an increase of beta4 integrin segregation in the cell membrane of 50-Hz exposed cells, suggesting that a higher percentage of these cells shows a modified pattern of this adhesion marker.

Artificially induced unusual shape of erythrocytes: an atomic force microscopy study.

We used air operating atomic force microscopy (AFM) to study several morphological modifications of human erythrocytes, artificially produced by addition of exogenous agents including phospholipids, low ionic strength media and drugs. Most experiments were performed on unfixed samples to avoid treating red blood cells (RBCs) with chemical agents that can, in principle, induce morphological alteration. After detailed quantitative AFM characterization, the artificially produced abnormally shaped RBCs were compared with cells that occur with high incidence in blood pathologies. This morphological approach suggests a new strategy to describe and understand the biochemical and/or mechanical modifications responsible for the underlying pathologically induced changes and prove AFM to be a suitable tool to study erythrocyte deformation.

Spectroscopic scanning near-field optical microscopy with a free electron laser: CH2 bond imaging in diamond films.

Hydrogen chemistry in thin films and biological systems is one of the most difficult experimental problems in today's science and technology. We successfully tested a novel solution, based on the spectroscopic version of scanning near-field optical microscopy (SNOM). The tunable infrared radiation of the Vanderbilt free electron laser enabled us to reveal clearly hydrogen-decorated grain boundaries on nominally hydrogen-free diamond films. The images were obtained by SNOM detection of reflected 3.5 microm photons, corresponding to the C-H stretch absorption, and reached a lateral resolution of 0.2 microm, well below the lambda/2 (lambda = wavelength) limit of classical microscopy.

Three dimensional (3D) analysis of the morphological changes induced by 50 Hz magnetic field exposure on human lymphoblastoid cells (Raji).

Human Raji B lymphoid cells after exposure for 64 h to a 1 mT (rms) 50 Hz sinusoidal magnetic field showed a reorganization of membrane and cytoskeletal components. Atomic force microscopy in air revealed several modifications in 80% of the exposed cells, such as loss of microvilli-like structures followed by progressive appearance of membrane introflections. This change in plasma membrane morphology was also accompanied by a different actin distribution, as detected by phalloidin fluorescence. These observations support our previous hypothesis that electric and magnetic fields may modify the plasma membrane structure.

Photocurrent near-field microscopy of Schottky barriers.

We used a combination of internal photoemission and of near-field optical microscopy (SNOM) to study the lateral variations in solid interface properties such as energy barriers and electron-hole recombination. In particular we investigated the fully formed Pt-GaP, Au-GaAs, Au-SiNx-GaAs and PtSi-Si Schottky barriers. Our approach enabled us to measure large lateral variations in the photocurrent with spatial resolution on the nanometric scale. Due to the ability of SNOM to supply parallel topographic information, we observed photocurrent variations from zone to zone that only correlated in a few cases with local variations in surface morphology. We assigned the uncorrelated fluctuations to local variations in the interface stoichiometry, the presence of interface states induced by the metallic overlayer and to defect states at the junction. Furthermore, by tuning the photon energy and applied bias we were able to measure the surface distribution of the diffusion length.

Neurone decapping characterization by atomic force microscopy: a topological systematic analysis.

We tested a new approach to cell decapping on rat cerebellar neurones, and observed its effects on cell topography by atomic force microscopy (AFM). The results clearly demonstrate the effectiveness of our decapping approach, and also the ability of AFM to reveal fine details of the decapped cells. Specifically, varying the conditions and duration of the decapping process modifies the extent of the decapping. Such a method can be used to investigate the cytoplasm with surface sensitive techniques.