Mukhles Sowwan

SP1 protein-based nanostructures and arrays.

Controlled formation of complex nanostructures is one of the main goals of nanoscience and nanotechnology. Stable Protein 1 (SP1) is a boiling-stable ring protein complex, 11 nm in diameter, which self-assembles from 12 identical monomers. SP1 can be utilized to form large ordered arrays; it can be easily modified by genetic engineering to produce various mutants; it is also capable of binding gold nanoparticles (GNPs) and thus forming protein-GNP chains made of alternating SP1s and GNPs. We report the formation and the protocols leading to the formation of those nanostructures and their characterization by transmission electron microscopy, atomic force microscopy, and electrostatic force microscopy. Further control over the GNP interdistances within the protein-GNP chains may lead to the formation of nanowires and structures that may be useful for nanoelectronics.

Formation Mechanism of Fe Nanocubes by Magnetron Sputtering Inert Gas Condensation

In this work, we study the formation mechanisms of iron nanoparticles (Fe NPs) grown by magnetron sputtering inert gas condensation and emphasize the decisive kinetics effects that give rise specifically to cubic morphologies. Our experimental results, as well as computer simulations carried out by two different methods, indicate that the cubic shape of Fe NPs is explained by basic differences in the kinetic growth modes of {100} and {110} surfaces rather than surface formation energetics. Both our experimental and theoretical investigations show that the final shape is defined by the combination of the condensation temperature and the rate of atomic deposition onto the growing nanocluster. We, thus, construct a comprehensive deposition rate-temperature diagram of Fe NP shapes and develop an analytical model that predicts the temporal evolution of these properties. Combining the shape diagram and the analytical model, morphological control of Fe NPs during formation is feasible; as such, our method proposes a roadmap for experimentalists to engineer NPs of desired shapes for targeted applications.

Coalescence-induced crystallisation wave in Pd nanoparticles

Palladium nanoparticles offer an attractive alternative to bulk palladium for catalysis, hydrogen storage and gas sensing applications. Their performance depends strongly on surface structure; therefore, nanoparticle coalescence can play an important role, as it determines the resultant structure of the active sites where reactions (e.g. catalysis) actually take place, i.e. facets, edges, vertices or protrusions. With this in mind, we performed classical molecular dynamics (MD) simulations and magnetron-sputtering inert gas condensation depositions of palladium nanoparticles, supported by high-resolution transmission electron microscopy (HRTEM), to study the mechanisms that govern their coalescence. Surface energy minimisation drove the interactions initially, leading to the formation of an interface/neck, as expected. Intriguingly, at a later stage, atomic rearrangements triggered a crystallisation wave propagating through the amorphous nanoparticles, leading to mono- or polycrystalline fcc structures. In the case of crystalline nanoparticles, almost-epitaxial alignment occurred and the formation of twins and surface protrusions were observed.

Inoculation of silicon nanoparticles with silver atoms

Silicon (Si) nanoparticles were coated inflight with silver (Ag) atoms using a novel method to prepare multicomponent heterostructured metal-semiconductor nanoparticles. Molecular dynamics (MD) computer simulations were employed, supported by high-resolution bright field (BF) transmission electron microscopy (HRTEM) and aberration-corrected scanning transmission electron microscopy (STEM) with a resolution ≤0.1 nm in high angle annular dark field (HAADF) mode. These studies revealed that the alloying behavior and phase dynamics during the coating process are more complex than when attaching hetero-atoms to preformed nanoparticles. According to the MD simulations, Ag atoms condense, nucleate and diffuse into the liquid Si nanoparticles in a process that we term “inoculation”, and a phase transition begins. Subsequent solidification involves an intermediate alloying stage that enabled us to control the microstructure and crystallinity of the solidified hybrid heterostructured nanoparticles.

Coalescence behaviour of amorphous and crystalline tantalum nanoparticles: a molecular dynamics study

Porous films of tantalum (Ta) and its oxides exhibit numerous properties suitable for high surface area applications, mainly in the semiconductor and bio-implant industries. Such films can be developed by Ta nanoparticle deposition using DC magnetron sputtering with gas aggregation. In order to engineer films of desirable properties, accurate control and in-depth understanding of the processes and parameters of nanoparticle growth, deposition and coalescence are crucial. Of utmost importance is to control the film’s porosity, since it determines many of the other physical properties. To this end, we performed a number of classical Molecular Dynamics simulations to study the coalescence of two or more Ta nanoparticles. Temperature, relative size and crystallographic orientation, defect content, degree of crystallinity and deposition rate effects were taken into account, and a mapping of the sintering processes was acquired. A broad range of possible interaction mechanisms were observed, from simple nanoparticle reorientation in order to achieve epitaxial configuration, to atomic adsorption, neck formation, twinning within the nanoparticles and full consolidation into a single, larger nanoparticle. The parameters studied are directly linked to experimental deposition parameters; therefore, fitting them accordingly can lead to growth of films with bespoke properties.

Single CuO nanowires decorated with size-selected Pd nanoparticles for CO sensing in humid atmosphere

We report on conductometric gas sensors based on single CuO nanowires and compare the carbon monoxide (CO) sensing properties of pristine as well as Pd nanoparticle decorated devices in humid atmosphere. Magnetron sputter inert gas aggregation combined with a quadrupole mass filter for cluster size selection was used for single-step Pd nanoparticle deposition in the soft landing regime. Uniformly dispersed, crystalline Pd nanoparticles with size-selected diameters around 5 nm were deposited on single CuO nanowire devices in a four point configuration. During gas sensing experiments in humid synthetic air, significantly enhanced CO response for CuO nanowires decorated with Pd nanoparticles was observed, which validates that magnetron sputter gas aggregation is very well suited for the realization of nanoparticle-functionalized sensors with improved performance.

Smart composite nanosheets with adaptive optical properties.

We report efficient design and facile synthesis of size-tunable organic/inorganic nanosheets, via a straightforward liquid exfoliation-adsorption process, of a near percolating gold (Au) thin film deposited onto a branched polyethylenimine (bPEI) matrix. The nanosheets are stiff enough to sustain their two-dimensional (2D) nature in acidic conditions, yet flexible enough to undergo a perfect reversible shape transformation to 1D nanoscrolls in alkaline conditions. The shape transformations, and associated optical property changes, at different protonation states are monitored by transmission electron microscopy (TEM), atomic force microscopy (AFM), UV-visible spectroscopy and zeta potential measurements. Because of their large surface area, both nanosheets and nanoscrolls could be used as capturing substrates for surface-enhanced Raman scattering (SERS) applications.

Analysis Characterization and Some Properties of Polyacrylamide Copper Complexes

The complexation of polyacrylamide (PAam) with Cu+2 metal ions was investigated. The metal complexes were characterized by FTIR, UV-Vis and DSC analysis. The Fourier transform infrared spectroscopy was used to study the characteristic shifts in the maximum absorbance bands of N-H amide C=O and N-H2 absorption bands. UV-Vis spectroscopy was also used to follow the complex formation of PAam-Cu+2. UV-Vis spectroscopy shows the appearance of a new band that was absent both in the polymer and its salt solutions. Thermal analysis of PAam-Cu+2 complexes was studied using DSC. The shifts in Tg values could be attributed to the improvement in the rigidity of PAam in the presence of Cu+2 associated with the polymer chain. Pure polyacrylamide polymer is electrically insular. The electrical conductivity improved by several orders of magnitude after the complexation process. AFM was used to image the surface features of PAam and PAam-Cu+2complex films. The association of polyacrylamide with Cu+2 metal ions at 2.5% (w/w) concentration, showed the formation of large grains with roughness 0.5 µm. Increasing the concentration of PAam-Cu+2 complex up to 25% (w/w), showed different and surprising results: instead of film with large grains, rods 1 µm in diameter were formed.

Nanoparticle design by gas-phase synthesis

Abstract Gas-phase synthesis characterizes a class of bottom-up methods for producing multifunctional nanoparticles (NPs) from individual atoms or molecules. This review aims to summarize recent achievements using this approach, and compare its potential to other physical or chemical NP fabrication techniques. More specifically, emphasis is given to magnetron-sputter gas-phase condensation, since it allows for flexible growth of complex, sophisticated NPs, owing to the fast kinetics and non-equilibrium processes it entails. Nanoparticle synthesis is decomposed into four stages, i.e. aggregation, shell-coating, mass-filtration, and deposition. We present the formation of NPs of various functionalities for different applications, such as magnetic, plasmonic, catalytic and, gas-sensing, emphasizing on the primary dependence of each type on a different stage of the fabrication process, and their resultant physical and chemical properties. Graphical Abstract

Assembly of tantalum porous films with graded oxidation profile from size-selected nanoparticles

AbstractFunctionally graded materials offer a way to improve the physical and chemical properties of thin films and coatings for different applications in the nanotechnology and biomedical fields. In this work, design and assembly of nanoporous tantalum films with a graded oxidation profile perpendicular to the substrate surface are reported. These nanoporous films are composed of size-selected, amorphous tantalum nanoparticles, deposited using a gas-aggregated magnetron sputtering system, and oxidized after coalescence, as samples evolve from mono- to multi-layered structures. Molecular dynamics computer simulations shed light on atomistic mechanisms of nanoparticle coalescence, which govern the films porosity. Aberration-corrected (S) TEM, GIXRD, AFM, SEM, and XPS were employed to study the morphology, phase and oxidation profiles of the tantalum nanoparticles, and the resultant films.Graphical AbstractDesign and assembly of tantalum nanoparticle porous films with a graded oxidation profile perpendicular to the substrate surface were fabricated by magnetron-sputter inert-gas aggregation system. At the top-most layers of the film, the larger free-surface areas of nanoparticles enable the formation of thermodynamically stable Ta2O5.