Surface free energies of electroless Ni–P based composite coatings

Surface free energy of a solid surface gives a direct measure of intermolecular interactions at interfaces and has a strong influence on adsorption and adhesion behaviour. However few data are available for the surface free energies of electroless Ni–P based composition coatings. In this paper, the electroless Ni–P, Ni–P-surfactant, Ni–Cu–P, Ni–P–PTFE and Ni–Cu–P–PTFE composite coatings were prepared under various coating conditions. The chemical compositions, surface morphology and thickness of the coatings were measured using an energy dispersive X-ray microanalysis (EDX), a scanning electron microscope (SEM) and a digital micrometer respectively. The contact angles of water, diiodomethane and ethylene glycol on the coatings were measured automatically using dataphysics OCA-20 contact angle analyser. The surface free energy of the coatings and their components (e.g. dispersion, polar or acid/base portions) were calculated using various methods. The experimental results showed that the incorporation of surfactant or PTFE particles into Ni–P matrixes has a significant influence on the surface free energy of the coatings, while the incorporation of copper into Ni–P matrixes has no significant influence on the surface free energy of the coatings.     

Low-temperature specific heat of Ni–Mn–Ga ferromagnetic shape memory alloys

Results of the low-temperature specific heat measurements (2–80 K) for one austenitic and three martensitic Ni–Mn–Ga ferromagnetic alloys are presented. The alloy compositions are chosen to comprise a wide span of valence electron concentrations e/a=7.3–7.78. Debye temperature (261–345 K) is found to be an increasing function of e/a while the experimental values of the Sommerfeld coefficient (2.9–3.4 mJ/mol K²) appear to be increasing in the martensitic region only. Observation of those trends rekindles the discussion about the role of vibrational and electronic contributions to the lattice instability and transformation mechanism of studied alloys.     

Laser surface alloying of an electroless Ni–P coating with Al-356 substrate

Laser surface alloying of an electroless plating Ni–P coatings on an Al-356 aluminium alloy was carried out using a 1-kW pulsed Nd:YAG laser. The microstructure, chemical composition and phase identification of the alloyed layer were determined using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD), respectively. It was shown that laser surface treatment produced a relatively smooth, crack-free and hard surface layer. The hardness of the surface significantly increased due to the formation of the uniformly distributed fine Ni–Al intermetallic phases. The corrosion behaviour of the surface alloyed specimens in 3.5% NaCl solution at 23 °C was also determined by electrochemical techniques. The laser-alloyed surface showed an improved corrosion and pitting potential compared to the substrate as well as the plated Ni–P coating.     

Influence of the atomic order on the magnetic characteristics of a Ni–Mn–Ga ferromagnetic shape memory alloy

The influence of the atomic order on the magnetic properties has been analyzed in a polycrystalline Ni_49.5Mn_28.5Ga₂₂ ferromagnetic shape memory alloy prepared by arc melting under Ar atmosphere. Different thermal treatments have been performed to modify the order degree of the alloy. The effect of the different thermal treatments on the magnetic and structural characteristics has been analyzed by superconducting quantum interference device (SQUID) and differential scanning calorimetry (DSC) measurements. The magnetic and structural properties of the alloys are modified as a consequence of the atomic order change. The martensitic transformation temperatures increase as long as the order degree increases. On the other side, the Curie temperature and magnetization saturation also reflect the order degree of the alloy but seems to be linked to the particular order of the Mn sub-lattice.     

Annealing effects on the magnetization of Co–Ni–B amorphous nanoparticles

Chemically prepared (Co_xNi_1−x)_1−yB_y (x=0.5, 0.75, 1; y≈0.4) amorphous fine particles were characterized by X-ray diffraction, DTA and TGA, and in situ magnetic measurement as a function of annealing temperature in an inert atmosphere. Magnetic measurement performed in as-prepared and 150°C annealed samples shows an increase of the saturation magnetization and magnetic moment after thermal treatment. Room temperature magnetization increases by factors of 3.5, 1.8, and 1.5, for x=0.5, 0.75, and 1, respectively. These measurements may indicate a local re-ordering of the amorphous phase at temperatures much lower than the full crystallization temperature.     

Improvement of superconducting properties of old Y–Ba–Cu–O specimens by high-energy heavy ion irradiation

Superconducting parameters of different, almost 20 years old Y–Ba–Cu–O samples, prepared in 1987–1988 are investigated. The aim of this research is to find out how a heavy ion beam can enhance the superconducting features of very old and originally not always perfect Y-based specimens. As is observed, their electrical and magnetic characteristics are very sensitive to high-energy Bi-ion irradiation, which results in significant increase of the superconducting parameters. The most important one of them is the global critical current density which is calculated with the help of a new method on the basis of experiments. It can be increased by 18–39%, depending on the original, starting conditions of the samples before the irradiation. At the same time, the average values of intragrain critical current density grows by 37–51%. A slight increase in the critical temperature of 1–2 K was also observed. The experiments on AC susceptibility demonstrate that this irradiation causes to develop faster the total diamagnetic state and decreases the loss. The reason of these effects can be found in the better orientation of crystals, enlargement of microcrystalline aggregates, higher homogenization of the material, thus, in the increase of the superconducting component of samples due to the irradiation.     

An L‐shaped nanoprobe for scanning electrochemical microscopy–atomic force microscopy

We present an L‐shaped nanoprobe for scanning electrochemical microscopy–atomic force microscopy (SECM–AFM) capable of imaging the surface topography and the electrochemical activity of nanostructures of interest. Owing to the geometry of the protrusive peak in the L‐shaped probe, the distance between the probe electrode and the substrate is maintained precisely at ～100 nm during surface scanning. The reduction in electrode‐to‐substrate distance significantly improves the positive feedback current on top of the electrochemically active nanomaterials. The L‐shaped nanoprobe successfully acquired simultaneous a topographical image and an electrochemical current image of individual carbon nanotubes (CNTs) in a two‐dimensional (2D) CNT network.

     

Reaction laser sintering of Ni–Al powder alloys

Laser reactive sintering, i.e., laser-induced self-propagating reaction sintering synthesis was carried out on Ni–Al powder alloys. The exothermic behaviors for the alloys with different Al content were characterized by sintering temperature curves produced from reactive heat. The phases transformed from the sintered alloys were identified by X-ray diffraction. Properties and microstructure of the sintered alloys were studied.     

A new form of the Sutton–Chen potential for the Cu–Ag alloys

The analytic construction of a many-body potential inspired from the Sutton–Chen parametrization is presented for copper and silver. A new approach is used to model the cross interaction for the Cu–Ag alloys. The parameters are fitted to first principles calculations based on the full potential linear plane wave method. The structural properties of the order and disorder Cu–Ag alloys in the B₂and fcc structures are presented for different concentration.     

A comparison study of scratch and wear properties using atomic force microscopy

The patterning technique that uses an AFM (atomic force microscopy) tip as a scratch tool, also known as AFM scratching, has been a vital technique for nanofabrication because of its low cost and potential to reach a resolution into the sub-nanometer domain. The AFM scratching technique was first used to study the scratch characteristics of silicon, with an emphasis on establishing its scratchability or the nanoscale machinability. The effects of the scratch parameters, including the applied tip force and number of scratches, on the size of the scratched geometry were specifically evaluated. The primary property that measures the scratchability was identified and assessed. To illustrate its suitability and reliability, the value of the scratchability, based on the present Si scratching experiments, was compared with the values based on the data available in the literatures for different scratching conditions or for materials other than Si. Since AFM scratching is in some aspects similar to the nanoscale wear test, the scratchability property identified is also compared with two major wear resistance indicators, wear coefficient and hardness. All comparison results indicate that the scratchability property identified, the scratch ratio, is an appropriate manufacturability indicator for measuring the degree of the ease or difficulty of a material scratched by an AFM tip and more suitable than the wear coefficient and hardness to gauge the nanoscale AFM scratchability.     

Detection of magnetic-labeled antibody specific recognition events by combined atomic force and magnetic force microscopy

Atomic force (AFM) and magnetic force microscopy (MFM) were developed to detect biomolecular specific interaction. Goat anti-mouse immunoglobulin (anti-IgG) was covalently attached onto gold substrate modified by a self-assembly monolayer of thioctic acid via 1-ethyl-3-[3-(dimethylamino) propyl] carbodiimide (EDC) activation. Magnetic-labeled IgG then specifically adsorbed onto anti-IgG surface. The morphological variation was identified by AFM. MFM was proved to be a fine assistant tool to distinguish the immunorecognized nanocomposites from the impurities by detection of the magnetic signal from magnetic-labeled IgG. It would enhance the understanding of biomolecular recognition process.     

Numerical study of the hydrodynamic drag force in atomic force microscopy measurements undertaken in fluids

When atomic force microscopy (AFM) is employed for in vivo study of immersed biological samples, the fluid medium presents additional complexities, not least of which is the hydrodynamic drag force due to viscous friction of the cantilever with the liquid. This force should be considered when interpreting experimental results and any calculated material properties. In this paper, a numerical model is presented to study the influence of the drag force on experimental data obtained from AFM measurements using computational fluid dynamics (CFD) simulation. The model provides quantification of the drag force in AFM measurements of soft specimens in fluids.The numerical predictions were compared with experimental data obtained using AFM with a V-shaped cantilever fitted with a pyramidal tip. Tip velocities ranging from 1.05 to 105 μm/s were employed in water, polyethylene glycol and glycerol with the platform approaching from a distance of 6000 nm. The model was also compared with an existing analytical model. Good agreement was observed between numerical results, experiments and analytical predictions. Accurate predictions were obtained without the need for extrapolation of experimental data. In addition, the model can be employed over the range of tip geometries and velocities typically utilized in AFM measurements.     

Effects of microalloying with Cd and Ag on the precipitation process of Al–4Cu–0.3Mg (wt%) alloy at 200°C

The present work investigates the effects of individual and combined additions of Cd and Ag on precipitation processes in an Al–4Cu–0.3Mg (wt%) alloy. Analytical scanning transmission electron microscopy revealed that microalloying with Cd stimulates nucleation of θ′ phase on {001} planes and that Cd-rich particles form on the rim and broad facets of the θ′ platelets. We interpret these observations to suggest that Cd nucleates heterogeneously at the θ′– interface and that θ′ can also nucleate heterogeneously at the Cd– interface. In the quinary alloy, it was observed that Ag and Cd additions seem to work independently resulting in a fine and uniform dispersion of both Ω and θ′. Furthermore, the hardening effect of the {111} Ω phase appears to be more potent than other precipitates formed in this system since the hardness of the quinary alloy was intermediate between the Al–Cu–Mg–Ag and the Al–Cu–Cd alloys.     

Surface adhesion properties of graphene and graphene oxide studied by colloid-probe atomic force microscopy

Surface adhesion properties are important to various applications of graphene-based materials. Atomic force microscopy is powerful to study the adhesion properties of samples by measuring the forces on the colloidal sphere tip as it approaches and retracts from the surface. In this paper we have measured the adhesion force between the colloid probe and the surface of graphene (graphene oxide) nanosheet. The results revealed that the adhesion force on graphene and graphene oxide surface were 66.3 and 170.6 nN, respectively. It was found the adhesion force was mainly determined by the water meniscus, which was related to the surface contact angle of samples.     

Laser‐Raman and atomic force microscopy assessment of the chlorococcalean affinity of problematic microfossils

Organic‐walled microfossils of uncertain origin, classified to an informal group named acritarchs, are most commonly interpreted as the resting cysts of marine eukaryotic phytoplankton. Some acritarchs have recently been interpreted as vegetative cells of chlorococcalean green algae, based on internal bodies that have been interpreted as their asexual reproductive structures (spores). To verify this interpretation, we applied confocal Raman spectroscopy and atomic force microscopy (AFM) to study the ultrastructure and nanostructure of exceptionally preserved acritarchs with internal bodies from the early Silurian cherts (ca 430 Ma‐old) of Frankenwald (Germany). Three‐dimensional Raman mapping showed the spatial distribution of carbonaceous material and other minerals in the walls of the analysed internal bodies and confirmed that these structures are comparable with spores of chlorococcalean microalgae. Our findings document therefore the oldest thus far known vegetative cells of sporulating green algae. The combination of confocal Raman and AFM techniques yielded detailed information about the nanostructure and fossilisation mode of the mineralised organic walls of both the central vesicles and the enclosed spore‐like bodies. Copyright © 2011 John Wiley & Sons, Ltd.     

Chemical surface composition of the polyethylene implanted by Ag ions studied by phase imaging atomic force microscopy

High density polyethylene (HDPE) has been modified by Ag⁺ ion implantation with the energy of 60 keV. The total amount of implanted silver ions was 1, 5 and 12 × 10¹⁵ ions/cm². The surface topography was observed by atomic force microscopy (AFM), while the surface composition changes were detected using phase imaging AFM. Surface topography changes were studied in detail using 3D surface parameters analyses. The average roughness decreased for the implanted HDPE indicating the flattening of the surface. Phase AFM images indicated the homogenization of the polyethylene during ion implantation, while histogram analyses confirmed the change in surface composition.     

XPS study of vanadium–yttrium hydrates

X-ray photoelectron spectroscopy was used to study the chemical composition and valence states of the metal ions in vanadium–yttrium hydrate. The binding energies, FWHM and shape of the main XPS peaks were analyzed. The concentration ratio of tetra- and pentavalent vanadium ions C=V⁴⁺/(V⁴⁺+V⁵⁺), which is an important parameter, deciding the electronic part of total conductivity, was determined before (C=0.14) and after heating at 720 K (C=0.28).     

Imaging of atomic-scale structure of oxide surfaces and adsorbed molecules by noncontact atomic force microscopy

Atom-resolved images of a TiO₂(110)-(1×1) surface and individual formate and acetate ions adsorbed on the surface were obtained by noncontact atomic force microscopy (NC-AFM) in ultrahigh vacuum. In contrast to previous scanning tunneling microscopic studies imaging five-fold coordinated Ti atoms, outermost atoms of bridge-bound oxygen ridges of the surface were resolved as protruding rows by NC-AFM. High-resolution image of the surface revealed that the bridging oxygen atoms on terraces ordered in a (1×1) periodicity. Randomly distributed point and multiple defects of oxygen atoms were also imaged as dark spots. The (2×1) overlayer of formate and acetate ions were resolved as ordered bright spots. Dispersed formate ions at a low coverage were also observed as bright spots between the bridging oxygen ridges along the [001] direction.     

Studying the effects of the addition of TiN nanoparticles to Ni–P electroless coatings

The effects of the addition of nano TiN on the surface morphology, deposition rate, hardness and corrosion properties of Ni–P electroless coatings were studied. Heat treatment was conducted to compare the corrosion and hardness behavior of the coatings before and after heat treatment. It was observed that the incorporation of TiN particles into the coating has an adverse effect on the corrosion properties of the specimens. The hardness of the specimens increased dramatically by adding TiN. Furthermore, the hardness of the specimens increased after conducting the heat treatment. The corrosion and hardness behavior of the Ni–P system after heat treatment largely depended on the temperature of heat treatment. The heat treatment temperatures at which the desired corrosion and hardness properties were expected were determined.     

Ultrastructural organization of premature condensed chromosomes at S-phase as observed by atomic force microscopy

In this study, we used calyculin A to induce premature condensed chromosomes (PCC). S-phase PCC is as “pulverized” appearance when viewed by light microscopy. Then, we applied atomic force microscopy (AFM) to investigate the ultrastructual organization of S-phase PCC. S-phase PCC shows ridges and grooves as observed by AFM. After trypsin treatment, chromosome surface roughness is increased and chromosome thickness is decreased. At high magnification, the ridges are composed of densely packed 30 nm chromatin fibers which form chromosome axis. Around the ridges, many 30 nm chromatin fibers radiate from center. Some of the 30 nm chromatin fibers are free ends. The grooves are not real “gap”, but several 30 nm chromatin fibers which connect two ridges and form “grid” structure. There are four chromatin fibers detached from chromosome: two free straight 30 nm chromatin fibers, one loop chromatin fiber and one straight combining with loop chromatin fiber. These results suggested that the S-phase PCC was high-order organization of 30 nm chromatin fibers and the 30 nm chromatin fibers could exist as loops and free ends.