Correlating Nanostructure, Optical and Electronic Properties of Nanogranular Silver Layers during Polymer-Template-Assisted Sputter Deposition

Tailoring the optical and electronic properties of nanostructured polymer-metal composites demonstrates great potential for efficient fabrication of modern organic optical and electronic devices such as flexible sensors, transistors, diodes, or photovoltaics. Self-assembled polymer-metal nanocomposites offer an excellent perspective for creating hierarchical nanostructures on macroscopic scales by simple bottom-up processes. We investigate the growth processes of nanogranular silver (Ag) layers on diblock copolymer thin film templates during sputter deposition. The Ag growth is strongly driven by self-assembly and selective wetting on the lamella structure of polystyrene-block-poly(methyl methacrylate). We correlate the emerging nanoscale morphologies with collective optical and electronic properties and quantify the difference in Ag growth on the corresponding homopolymer thin films. Thus, we are able to determine the influence of the respective polymer template and observe substrate effects on the Ag cluster percolation threshold, which affects the insulator-to-metal transition (IMT). Optical spectroscopy in the UV-vis regime reveals localized surface plasmon resonance for the metal-polymer composite. Their maximum absorption is observed around the IMT due to the subsequent long-range electron conduction in percolated nanogranular Ag layers. Using X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy, we identify the oxidation of Ag at the acrylate side chains as an essential influencing factor driving the selective wetting behavior in the early growth stages. The results of polymer-templated cluster growth are corroborated by atomic force microscopy and field emission scanning electron microscopy.

Formation of Periodically Arranged Nanobubbles in Mesopores: Capillary Bridge Formation and Cavitation during Sorption and Solidification in an Hierarchical Porous SBA-15 Matrix

We report synchrotron-based small-angle X-ray scattering experiments on a template-grown porous silica matrix (Santa Barbara Amorphous-15) upon in situ sorption of fluorinated pentane C5F12 along with volumetric gas sorption isotherm measurements. Within the mean-field model of Saam and Cole for vapor condensation in cylindrical pores, a nitrogen and C5F12 sorption isotherm is well described by a bimodal pore radius distribution dominated by meso- and micropores with 3.4 and 1.6 nm mean radius, respectively. In the scattering experiments, two different periodicities become evident. One of them (d1 = 11.5 nm) reflects the next nearest neighbor distance in a 2D-hexagonal lattice of tubular mesopores. A second periodicity (d2 = 11.4 nm) found during in situ sorption and freezing experiments is traced back to a superstructure along the cylindrical mesopores. It is compatible with periodic pore corrugations found in electron tomograms of empty SBA-15 by Gommes et al. ( Chem. Mater. 2009, 21, 1311 - 1317). A Rayleigh-Plateau instability occurring at the cylindrical blockcopolymer micelles characteristic of the SBA-15 templating process quantitatively accounts for the superstructure and thus the spatial periodicity of the pore wall corrugation. The consequences of this peculiar morphological feature on the spatial arrangement of C5F12, in particular the formation of periodically arranged nanobubbles (or voids) upon adsorption, desorption, and freezing of liquids, are discussed in terms of capillary bridge formation and cavitation in tubular but periodically corrugated pores.

The shape of the orientation distribution of carbon nanotubes in aligned arrays

Recent simulations of vertically aligned carbon nanotube arrays have shown that the shape of the orientation distribution of nanotubes within the array has a drastic effect on the electrical properties of the array. Orienting of shape-anisotropic objects can be carried out in several different ways such as shearing, magnetically steering, or by vibrating the objects. Nevertheless, perfect orientation is difficult if not impossible to achieve. In the case of the growth of carbon nanotube arrays, self-confinement can occur affecting the resultant orientation distribution. Yet so far the shape of the orientation distribution has not been quantified in great detail and it has been mostly assumed to be Gaussian or Lorentzian. In the present work, multi-walled carbon nanotube arrays were grown via aerosol-assisted chemical vapour deposition with iron catalyst and investigated using small-angle X-ray scattering, a method perfectly suited to characterizing the orientation of carbon nanotubes. Using a microfocused X-ray beam of 24 μm x 17 μm in size at beamline P03 of the PETRA III synchrotron storage ring in Hamburg, we determined the orientation distribution of the vertically aligned carbon nanotubes along the film height. Remarkably, the packing density of the carbon nanotubes seems to correlate not only with the width of the distribution but also its shape. The shape of the orientation distribution was then compared to that from different oriented systems. These findings indicate that by using alignment methods that are based on steric interaction between particles, such as shearing or self-confinement during particle growth, the system will reach an alignment with an orientation distribution closer to the Laplace distribution than to the normal distribution. Such a finding has profound implications for simulation studies of mechanical, electrical and other properties of many hierarchical materials.

From Unprintable Peptidic Gel to Unstoppable: Transforming Diphenylalanine Peptide (Fmoc-FF) Nanowires and Cellulose Nanofibrils into a High-Performance Biobased Gel for 3D Printing

The growing interest in gel-based additive manufacturing, also known as three-dimensional (3D) gel-printing technology, for research underscores the crucial need to develop robust biobased materials with excellent printing quality and reproducibility. The main focus of this study is to prepare and characterize some composite gels obtained with a low-molecular-weight gelling (LMWG) peptide called Fmoc-diphenylalanine (Fmoc-FF) and two types of cellulose nanofibrils (CNFs). The so-called Fmoc-FF peptide has the ability to self-assemble into a nanowire shape and therefore create an organized network that induces the formation of a gel. Despite their ease of preparation and potential use in biological systems, unfortunately, those Fmoc-FF nanowire gel systems cannot be 3D printed due to the high stiffness of the gel. For this reason, this study focuses on composite materials made of cellulose nanofibrils and Fmoc-FF nanowires, with the main objective being that the composite gels will be suitable for 3D printing applications. Two types of cellulose nanofibrils are employed in this study: (1) unmodified pristine cellulose nanofibrils (uCNF) and (2) chemically modified cellulose nanofibrils, which ones have been grafted with polymers containing the Fmoc unit on their backbone (CNF-g-Fmoc). The obtained products were characterized through solid-state cross-polarization magic angle-spinning 1H NMR and confocal laser scanning microscopy. Within these two CNF structures, two composite gels were produced: uCNF/Fmoc-FF and CNF-g-Fmoc/Fmoc-FF. The mechanical properties and printability of the composites are assessed using rheology and challenging 3D object printing. With the addition of water, different properties of the gels were observed. In this instance, CNF-g-Fmoc/Fmoc-FF (c = 5.1%) was selected as the most suitable option within this product range. For the composite bearing uCNF, exceptional print quality and mechanical properties are achieved with the CNF/Fmoc-FF gel (c = 5.1%). The structures are characterized by using field emission scanning electron microscopy (FESEM) and small-angle X-ray scattering (SAXS) measurements.

Decoding in-plane orientation in cellulose nanopapers hybridized with tailored polymeric nanoparticles

Biobased cellulose nanofibrils (CNFs) constitute important building blocks for biomimetic, nanostructured materials, and considerable potential exists in their hybridization with tailorable polymeric nanoparticles. CNFs naturally assemble into oriented, fibrillar structures in their cross-section. This work shows that polymeric nanoparticle additives have the potential to increase or decrease orientation of these cellulose structures, which allows the control of bulk mechanical properties. Small amounts of these additives (<1 wt%) are shown to promote the alignment of CNFs, and the particle size is found to determine a tailorable maximum feature size which can be modified. Herein, X-ray scattering allows for the quantification of orientation at different length scales. This newly developed method of measuring cross-sectional orientation allows for understanding the influence of nanoparticle characteristics on the CNF network structure at different length scales in hybrid cellulose-nanoparticle materials, where previously quantitative description has been lacking. It thus constitutes an important foundation for further development and understanding of nanocellulose materials on the level of their nanoscale building blocks and their interactions, which in turn are decisive for their macroscopic properties.

In Situ Study of Structure Formation under Stress in Stretchable Conducting Nanocomposites

One of the major limitations of flexible sensors is the loss of conductivity upon multiple stretching and bending cycles. Conducting fillers with two different geometries, carbon black and carbon nanotubes, were introduced in polydimethylsiloxane (PDMS) for physical insights into the structure formation of nanofillers by the application of periodic tensile stress. The loading of the nanofillers was selected beyond the percolation threshold to determine the cyclic stability of the resulting network channels. The surface chemistry of carbon nanotubes has been varied to understand the interfacial interactions at the molecular length scale. The combination of in situ stretching, annealing, and vis-à-vis conductometry of nanocomposite films with synchrotron-based ultra-small angle X-ray scattering experiments enables us to highlight the importance of the fractal dimensions of nanofillers for the molecular level interactions. The irreversible formation of nanofiller network geometries under cyclic stress and annealing was found to be responsible for the electrical properties of a flexible conducting film.

Insights into the formation of CdSe nanoplatelets using a flow reactor

In recent years, the anisotropic semiconductor nanoplatelets (NPLs) gained interest due to their unique optical properties, which depend primarily on their thickness. However, the formation mechanism behind the zinc blende CdSe NPLs remains unclear. Several theories were presented and discussed, but a concrete mechanism has not yet been found with evidence. Here, we want to present a synthesis of CdSe NPLs in a flow reactor with a liquid precursor, enabling in situ absorbance measurements. The flow reactor allows for more control in obtaining early-stage synthesis samples, which were ex situ examined with optical spectroscopy, transmission electron microscopy, as well as small-angle and powder X-ray diffraction. Our results show that CdSe magic size clusters (MSCs) formed prior to the formation of CdSe NPLs, indicating that these CdSe MSCs are necessary for the initial CdSe NPLs growth.

Light-Induced Transformation of Virus-Like Particles on TiO2

Titanium dioxide (TiO2) shows significant potential as a self-cleaning material to inactivate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and prevent virus transmission. This study provides insights into the impact of UV-A light on the photocatalytic inactivation of adsorbed SARS-CoV-2 virus-like particles (VLPs) on a TiO2 surface at the molecular and atomic levels. X-ray photoelectron spectroscopy, combined with density functional theory calculations, reveals that spike proteins can adsorb on TiO2 predominantly via their amine and amide functional groups in their amino acids blocks. We employ atomic force microscopy and grazing-incidence small-angle X-ray scattering (GISAXS) to investigate the molecular-scale morphological changes during the inactivation of VLPs on TiO2 under light irradiation. Notably, in situ measurements reveal photoinduced morphological changes of VLPs, resulting in increased particle diameters. These results suggest that the denaturation of structural proteins induced by UV irradiation and oxidation of the virus structure through photocatalytic reactions can take place on the TiO2 surface. The in situ GISAXS measurements under an N2 atmosphere reveal that the virus morphology remains intact under UV light. This provides evidence that the presence of both oxygen and UV light is necessary to initiate photocatalytic reactions on the surface and subsequently inactivate the adsorbed viruses. The chemical insights into the virus inactivation process obtained in this study contribute significantly to the development of solid materials for the inactivation of enveloped viruses.

Supraparticles from Cubic Iron Oxide Nanoparticles: Synthesis, Polymer Encapsulation, Functionalization, and Magnetic Properties

Supraparticles (SPs) consisting of superparamagnetic iron oxide nanoparticles (SPIONs) are of great interest for biomedical applications and magnetic separation. To enable their functionalization with biomolecules and to improve their stability in aqueous dispersion, polymer shells are grown on the SPs' surface. Robust polymer encapsulation and functionalization is achieved via atom transfer radical polymerization (ATRP), improving the reaction control compared to free radical polymerizations. This study presents the emulsion-based assembly of differently sized cubic SPIONs (12-30 nm) into SPs with diameters ranging from ∼200 to ∼400 nm using dodecyltrimethylammonium bromide (DTAB) as the surfactant. The successful formation of well-defined spherical SPs depends upon the method used for mixing the SPION dispersion with the surfactant solution and requires the precise adjustment of the surfactant concentration. After purification, the SPs are encapsulated by growing surface-grafted polystyrene shells via activators generated by electron transfer (AGET) ATRP. The polymer shell can be decorated with functional groups (azide and carboxylate) using monomer blends for the polymerization reaction. When the amount of the monomer is varied, the shell thickness as well as the interparticle distances between the encapsulated SPIONs can be tuned with nanometer-scale precision. Small-angle X-ray scattering (SAXS) reveals that cubic SPIONs form less ordered assemblies within the SPs than spherical SPIONs. As shown by vibrating sample magnetometer measurements, the encapsulated SPs feature the same superparamagnetic behavior as their SPION building blocks. The saturation magnetization ranges between 10 and 30 emu/g and depends upon the nanocubes' size and phase composition.

Subcutaneous phaeohyphomycosis caused by Amesia atrobrunnea in Kuwait

The recently described genus Amesia encompasses four species but only Amesia atrobrunnea (=Chaetomium atrobrunneum) is known to be pathogenic to humans. Here, we describe a case of subcutaneous phaeohyphomycosis in Kuwait in an apparently immunocompetent patient diagnosed by direct microscopy of the infected tissue and culture. The identity of A. atrobrunnea was established by typical morphological characteristics and by sequencing of internally transcribed spacer (ITS) region and D1/D2 domains of rDNA. To the best of our knowledge, this is the first report documenting etiologic role of this species in causing a locally invasive subcutaneous infection.

Tailoring of uniaxial magnetic anisotropy in Permalloy thin films using nanorippled Si substrates

In this work the investigation of in-plane uniaxial magnetic anisotropy induced by the morphology due to ion beam erosion of Si(1 0 0) has been done. Ion beam erosion at an oblique angle of incidence generates a well-ordered nanoripple structure on the Si surface and ripple propagates in a direction normal to ion beam erosion. Permalloy thin films grown on such periodic nanopatterns show a strong uniaxial magnetic anisotropy with easy axis of magnetization in a direction normal to the ripple wave vector. The strength of uniaxial magnetic anisotropy is found to be high for the low value of ripple wavelength; it is decreasing with increasing value of ripple wavelength. Similarly, the strength of uniaxial magnetic anisotropy decreases with increasing Permalloy film thickness. Grazing incidence small angle x-ray scattering data reveals an anisotropic growth of Permalloy thin films with preferential orientation of grains in the direction normal to the ripple wave vector. Permalloy thin film growth is highly conformal with the film surface replicating the substrate ripple morphology up to a film thickness of 50 nm has been observed. Correlation between observed uniaxial magnetic anisotropy to surface modification has been addressed.