Residue-specific immobilization of protein molecules by size-selected clusters

The atomic force microscope (AFM), operating in contact mode, has been employed in buffer solution to study two proteins; (i) green fluorescent protein (GFP), from the hydromedusan jellyfish Aequorea victoria; and (ii) human oncostatin M (OSM), in the presence of size-selected gold nanoclusters pinned on to a highly oriented pyrolytic graphite substrate. The AFM images have revealed immobilization of single molecules of OSM, which are strongly bound to the gold nanoclusters. Conversely, no strong immobilization has been observed for the GFP, as these molecules were easily displaced by the scanning tip. The contrasting behaviour of the two proteins can be explained by the exposed molecular surface area of their cysteine residues as modelled on the basis of their respective X-ray crystallographic data structures. GFP contains two cysteine residues, but neither is readily available to chemisorb on the gold clusters, because the cysteines are largely inaccessible from the surface of the protein. In contrast, OSM has a total of five cysteine residues, with different degrees of accessibility, which make the protein amenable to anchoring on the nanoclusters. Statistical analysis of the height of the OSM molecules bound to the nanoclusters is in accordance with crystallographic data, and suggests various configurations of the proteins on the clusters, associated with the presence of different cysteine anchoring sites. These results suggest that the three-dimensional conformation of protein molecules is preserved when they are chemisorbed to size-selected gold clusters, thus opening a new route towards oriented immobilization of individual protein molecules.     

Formation of an epitaxial monolayer on graphite upon short-time surface contact with highly diluted aqueous solutions of 1-monostearoylglycerol

Short-time surface contact of highly diluted 1-monostearoylglycerol (1-MSG) aqueous solutions with highly oriented pyrolitic graphite results in the deposition of an epitaxial monolayer that can be detected by atomic force microscopy operating in tapping mode at the graphite-air interface. The monolayer obtained with the racemic mixture is then compared to that obtained with one of the pure enantiomers. The analogous behavior found for aqueous solutions of rac-1-MSG and 3-sn-MSG implies a two-dimensional self-assembly process with chiral discrimination. The results suggest that the monolayer originates from species located at the surface of the deposition drop. They also indicate that the simple experimental procedure reported, or more elaborate Langmuir-Schaefer methods, could be the method of choice to prepare other monolayers of similar surfactants.     

Growth of highly textured aluminum films on LiTaO3 with optimized titanium intermediate layers

Ultra thin titanium films in the range of a few nanometers have been deposited on monocrystalline lithiumtantalate (LiTaO₃) followed by deposition of 400 nm pure aluminum (Al). Texture measurements by means of electron backscatter diffraction show that the thickness of the intermediate titanium (Ti) layer significantly influences texture and grain structure of the overlying Al film. Increasing the thickness of the Ti layer from 0 nm to 20 nm leads to a change of aluminums texture from unoriented polycrystalline over highly oriented in single direction to highly oriented in twin structure.     

Controlled AFM detachments and movement of nanoparticles: gold clusters on HOPG at different temperatures

The effect of temperature on the onset of movement of gold nanoclusters (diameter 27 nm) deposited on highly oriented pyrolytic graphite (HOPG) has been studied by atomic force microscopy (AFM) techniques. Using the AFM with amplitude modulation (tapping mode AFM) we have stimulated and controlled the movement of individual clusters. We show how, at room temperature, controlled detachments and smooth movements can be obtained for clusters having dimensions comparable to or smaller than the tip radius. Displacement is practically visible in real time and it can be started and stopped easily by adjusting only one parameter, the tip amplitude oscillation. Analysing the energy dissipation signal at the onset of nanocluster sliding we evaluated a detachment threshold energy as a function of temperature in the range 300-413 K. We also analysed single cluster thermal induced displacement and combining this delicate procedure with AFM forced movement behaviour we conclude that detachment threshold energy is directly related to the activation energy of nanocluster diffusion and it scales linearly with temperature as expected for a single-particle thermally activated process.     

Room temperature deposition of self-assembled Al nanoclusters on stepped sapphire (0001) surface and subsequent nitridation

Self-assembled growth and nitridation of ultrathin Al nanoclusters on a stepped sapphire (0001) surface were studied by high-resolution X-ray photoemission spectroscopy, atomic force microscopy and low-energy electron diffraction (LEED). Upon room temperature deposition, in the coverage range of ∼ 0.79 to 2.3 monolayer (ML), Al nanoclusters were uniformly nucleated over the entire surface of defect-free atomically smooth terraces as well as step edges. Subsequent nitridation at elevated temperatures by ammonia did not alter the morphology of the nanoclusters. The global morphology of the stepped sapphire (0001) surface such as terrace width, step height and facet orientation had no obvious influence on the nucleation morphology of the nanoclusters in the given Al coverage range. However, local structural defects at the joints of short facets and step edges played a noticeable role on the local morphology of the nanoclusters and subsequently the nitridation chemistry. The Al nanoclusters were uniformly nitridated from surface and downwards through the 3D structures. The LEED pattern indicated a certain degree of crystallinity on the nitridated surface at a nominal Al coverage less than 2 ML, whereas at 2.3 ML Al coverage, the nitridated surface became amorphous. Thus there is a critical coverage for good surface order.     

Nanotube-like structures naturally formed on HOPG surface

Using atomic force microscopy, it has been found that nanotube-like structures can be formed naturally on highly oriented polygraphite (HOPG) surfaces by “peeling” the graphite sheet in air at room temperature. These structures were often distributed near the steps, and are occasionally found on flat terraces. The apparent diameters of these tubes range from several to tens of nanometers. The mechanism of the formation process is discussed.     

Detection of Sodium in Highly Pure Graphite via High-Resolution Electrothermal Atomic Absorption Spectrometry with a Continuous Spectrum Source

This study is dedicated to elucidating the analytical abilities of electrothermal atomic absorption spectrometry with a continuous spectrum source (ETAAS-CSS) to detect the presence of sodium in highly pure graphite powder. In order to plot the calibration dependence for sodium detection, a special technique based on argon dilution of the atomic vapor obtained by introducing the aqueous reference solution in the atomizer is applied. The conditions for thermal pretreatment of highly pure graphite powder and atomization of sodium are established, and the sodium detection threshold is evaluated via ETAAS-CSS (2.6 × 10^–4 ng) as well. The validity of the results is confirmed via the sample variation method.     

Studies on the formability of powder metallurgical aluminum–copper composite

Formability is concerned with the extent of deformation that the materials undergo before failure; thus its investigation is critical for successful processing of materials during bulk deformation. The present investigation has been undertaken to generate the forming limit diagrams for powder metallurgical aluminium–copper composites for different initial relative densities and copper contents. Sintered aluminium–copper composite compacts of 2%, 4% and 6% copper content with different initial relative densities have been prepared by applying recommended powder compaction pressures. The material properties such as apparent strain hardening exponent and strength coefficient were determined using stage wise compression test to generate the formability limit diagram. Densification curves were plotted to investigate the effect of initial relative density and copper content on the pore closure phenomena during deformation. Theoretical and experimental investigations using standard ring compression test were carried out to determine friction factor between tool and work piece interfaces for different initial relative density and copper content. The critical transition densities vide the forming limit diagram were found to be 84%, 85.3%, 86% and 87.5% for pure sintered aluminium, Al–2%Cu, Al–4%Cu and Al–6%Cu composites respectively. The friction factor between tool and work piece interfaces has showed increasing pattern for all the cases with decrease in the initial relative density and increase in the copper content of the composite.     

A graphite nanoeraser

We present here a method for cleaning intermediate-size (up to 50 nm) contamination from highly oriented pyrolytic graphite and graphene. Electron-beam-induced deposition of carbonaceous material on graphene and graphite surfaces inside a scanning electron microscope, which is difficult to remove by conventional techniques, can be removed by direct mechanical wiping using a graphite nanoeraser, thus drastically reducing the amount of contamination. We discuss potential applications of this cleaning procedure.     

Peculiarities of high-temperature properties of HAPG graphite within the melting region

By means of pulse current heating (3–5 μs), specimens of a new highly oriented pyrolytic graphite (the highly annealing pyrolytic graphite, HAPG) within the temperature range 2500–5000 K were investigated. The temperature, electrical resistance (compared to the initial sizes), and Joule energy of heating were measured. The beginning of graphite melting was registered at 4800–5000 K. It was observed that HAPG is characterized by a lower melting heat as compared to other types of graphite.     

Highly c-axis oriented AlN layers grown on c-plane sapphire substrates by radio-frequency sputter epitaxy at 1080 °C

Aluminum nitride (AlN) single-crystalline layers were grown on c-plane sapphire substrates by radio-frequency magnetron sputter epitaxy using N₂/Ar mixture ambient gas and 5-N grade Al target. The crystalline structures of the AlN layers depending on substrate temperature and N₂ composition ratio in ambient gas, were predominantly studied. The crystalline quality of the AlN layer was improved by elevating substrate temperature, and the full-widths at half-maximum (FWHMs) of X-ray rocking curves (XRC) for both symmetric and asymmetric planes of AlN layers grown at N₂ composition ratio of around 25%, became low. The FWHMs of XRC for (0002) diffraction of the AlN layers grown at 1080 °C, were less than 20 arcsec. The surface root-mean-square roughness of such highly c-axis oriented AlN layer was determined by atomic force microscopy, and was increased from 0.6 nm to 1.3 nm when AlN layer thickness was varied from 0.15 to 0.7 μm.     

Self-assembly of vertically aligned nanorod supercrystals using highly oriented pyrolytic graphite

Supercrystallization of CdS nanorods (10 nm x 25 nm) into perpendicular superlattices was obtained by controlled evaporation of a nanorod solution trapped between a smooth substrate and a block of highly oriented pyrolytic graphite (HOPG). Hexagonal oriented domains 2 microm2 in size were routinely obtained on a variety of substrates without external electric fields.     

Effect of electron irradiation on nanogroove-networked single-crystalline and dendritic polycrystalline platinum nanosheets prepared from lyotropic surfactant liquid-crystal templates

Using transmission electron microscopy (TEM) electron irradiation effects were studied for nanogroove-network structured single-crystalline and dendritic polycrystalline Pt nanosheets 50-60 nm in size. These two nanosheets with nearly the same average groove-width or dendritic spacing of 1.3-1.4 nm were prepared from the mixed and single surfactant liquid crystalline templates, respectively. On exposure to electron beam for 20 min at the acceleration voltage of 200 kV, the nanogrooved nanosheets were morphologically little affected, but the dendritic ones were transformed into less branched polycrystalline structures with spacings distributed around ∼1.7 nm. The shape transformation of the latter occurred by the combined mechanism of segmental migration and atomic diffusion. These observations indicate that the nanogrooved Pt nanosheets are highly stabilized by the grooved but crystallographically continuous Pt framework, leading to their extremely high thermo-resistance, in marked contrast to the polycrystalline dendritic structures constructed of crystallographically discontinuous linkages of nanoblocks.     

Hydrogen accumulation in graphite and etching of graphite on hydrogen desorption

Studies of Atomic Hydrogen accumulation in highly oriented pyrolytical graphite (HOPG) have been performed using scanning tunnelling microscope (STM) and atomic force microscope (AFM). It is found that after intercalation atomic hydrogen is stored among graphene layers in H₂ gas form, captured inside graphene blisters. On desorption of hydrogen, some lateral etching of upper graphene layers takes place. Significant information about intake, retention and possibility of manifold accumulation of hydrogen in HOPG has been found.     

Properties of GaAs nanoclusters deposited by a femtosecond laser

The properties of femtosecond pulsed laser deposited GaAs nanoclusters were investigated. Nanoclusters of GaAs were produced by laser ablating a single crystal GaAs target in vacuum or Ar gas. Atomic force and transmission electron microscopies showed that most of the clusters were spherical and ranged in diameter from 1 nm to 50 nm, with a peak size distribution between 5 nm and 9 nm, depending on the Ar gas pressure or laser fluence. X-ray diffraction, solid-state nuclear magnetic resonance, Auger electron spectroscopy, electron energy loss spectroscopy, and high-resolution transmission electron microscopy revealed that these nanoclusters were randomly oriented GaAs crystallites. An oxide outer shell of 2 nm developed subsequently on the surfaces of the nanocrystals as a result of transportation in air. Unpassivated GaAs nanoclusters exhibited no detectable photoluminescence. After surface passivation, these nanoclusters displayed photoluminescence energies less than that of bulk GaAs from which they were made. Our photoluminescence experiments suggest an abundance of sub-band gap surface states in these GaAs nanocrystals.     

Thin films of porphyrin molecules imaged with the atomic force microscope

The assembly of two-dimensional molecular structures of zinc porphyrin molecules arising from the dewetting of a porphyrin solution on mica and graphite is investigated using atomic force microscopy. Both a near equilibrium nucleation and growth process, and a far from equilibrium spinodal dewetting process are observed. Nucleation and growth around pre-existing surface defects on mica produces single layer disks, ∼ 10 μm in diameter, of densely packed molecules. Spinodal dewetting gives rise to the formation of much smaller, single layer, molecular islands of various sizes on both mica and graphite.     

Convex–concave nanostructure transition on highly oriented pyrolitic graphite surface induced by atomic force microscope tip under bias voltage

Convex and concave nanoscale dots were formed on a highly oriented pyrolitic graphite surface in air by an atomic force microscope tip under positively applied bias voltage. It was found that the increasing amplitude or duration of the bias voltage over threshold values can change the convex profiles into concave ones. The threshold voltage duration for the profile transition increases sharply with decreasing amplitude of the voltage and a nonlinear relationship between them was obtained. For enough long duration, there exists a threshold voltage amplitude, about 4.1–5?V in this study, for the profile transition as well.     

Radius and chirality dependent conformation of polymer molecule at nanotube interface

Temperature-dependent conformations of linear polymer molecules adsorbed at carbon nanotube (CNT) interfaces are investigated through molecule dynamics simulations. Model polyethylene (PE) molecules are shown to have selective conformations on the CNT surface, controlled by atomic structures of the CNT lattice and geometric coiling energy. PE molecules form entropy driven assembly domains, and their preferred wrapping angles around large radius CNT (40, 40) reflect the molecule configurations with energy minimums on a graphite plane. While PE molecules prefer 0 degrees wrapping on small radius armchair CNT (5, 5) predominantly at low temperatures, their configurations are shifted to larger wrapping angle ones on a similar radius zigzag CNT (10, 0). A nematic transformation around 280 K is identified through the Landau-de Gennes theory, with molecule aligning along tube axis in extended conformations.     

Optical characteristics of femtosecond laser micromachined periodic structures in Si <100>

A frequency doubled Ti:sapphire laser of 400 nm wavelength, 160 fs pulse width, and 1 kHz repetition rate, combined with a high resolution computer-controlled X-Y stage, was used to direct write periodic structures on Si <100>. Laser pulses of approximately 130 nJ energy were focused using an objective lens of 0.65 NA. Laser micromachining yielded lines of 700 nm width and ablation depths of 600 nm. One- and two-dimensional periodic structures of 5 and 5x5 microm spacing were fabricated, and the structures were characterized by using optical and atomic force microscopy. The light diffraction characteristics of the periodic 1D and 2D patterns were examined. The diffraction properties of the 1D structures were highly dependent upon the light polarization orientation with respect to the micromachining direction.     

A study on the damping capacity of BaTiO<Subscript>3</Subscript>-reinforced Al-matrix composites

To study the damping capacity of BaTiO₃/Al composites, Al composites reinforced with BaTiO₃ powder (average grain sizes: 100 and 1000 nm) were fabricated by the hot-pressing sintering method. The damping properties of pure Al and BaTiO₃/Al composites were investigated and compared based on the dynamic mechanical analysis over a wide range of temperatures (50–285^°C). Compared with pure Al matrix, 1000 nm BaTiO₃/Al composites with 5 and 10% mass fractions of BaTiO₃ exhibited better damping capacity. For 100 nm BaTiO₃/Al composite, its damping capacity is slightly higher than that of pure Al below 145^°C, while it becomes lower above this degree. The damping capacity enhancement of BaTiO₃/Al composites can be explained by the ferroelastic domain damping. Furthermore, 5 and 10% BaTiO₃/Al composites have higher bending strength and hardness than pure Al sample.