Size and shape distributions of primary crystallites in titania aggregates

The primary crystallite size of titania powder relates to its properties in a number of applications. Transmission electron microscopy was used in this interlaboratory comparison (ILC) to measure primary crystallite size and shape distributions for a commercial aggregated titania powder. Data of four size descriptors and two shape descriptors were evaluated across nine laboratories. Data repeatability and reproducibility was evaluated by analysis of variance. One-third of the laboratory pairs had similar size descriptor data, but 83% of the pairs had similar aspect ratio data. Scale descriptor distributions were generally unimodal and were well-described by lognormal reference models. Shape descriptor distributions were multi-modal but data visualization plots demonstrated that the Weibull distribution was preferred to the normal distribution. For the equivalent circular diameter size descriptor, measurement uncertainties of the lognormal distribution scale and width parameters were 9.5% and 22%, respectively. For the aspect ratio shape descriptor, the measurement uncertainties of the Weibull distribution scale and width parameters were 7.0% and 26%, respectively. Both measurement uncertainty estimates and data visualizations should be used to analyze size and shape distributions of particles on the nanoscale.

Superplastic behavior of silica nanowires obtained by direct patterning of silsesquioxane-based precursors

Silica nanowires spanning 10 μm-deep trenches are fabricated from different types of silsesquioxane-based precursors by direct e-beam patterning on silicon followed by release through deep reactive ion etching. Nanowire aspect ratios as large as 150 are achieved with a critical dimension of about 50 nm and nearly rectangular cross-sections. In situ bending tests are carried out inside a scanning electron microscope, where the etch depth of 10 [Formula: see text] provides sufficient space for deformation. Silica NWs are indeed observed to exhibit superplastic behavior without fracture with deflections reaching the full etch depth, about two orders of magnitude larger than the nanowire thickness. A large-deformation elastic bending model is utilized for predicting the deviation from the elastic behavior. The results of forty different tests indicate a critical stress level of 0.1-0.4 GPa for the onset of plasticity. The study hints at the possibility of fabricating silica nanowires in a monolithic fashion through direct e-beam patterning of silsesquioxane-based resins. The fabrication technology is compatible with semiconductor manufacturing and provides silica nanowires with a very good structural integrity.

A deep etching mechanism for trench-bridging silicon nanowires

Introducing a single silicon nanowire with a known orientation and dimensions to a specific layout location constitutes a major challenge. The challenge becomes even more formidable, if one chooses to realize the task in a monolithic fashion with an extreme topography, a characteristic of microsystems. The need for such a monolithic integration is fueled by the recent surge in the use of silicon nanowires as functional building blocks in various electromechanical and optoelectronic applications. This challenge is addressed in this work by introducing a top-down, silicon-on-insulator technology. The technology provides a pathway for obtaining well-controlled silicon nanowires along with the surrounding microscale features up to a three-order-of-magnitude scale difference. A two-step etching process is developed, where the first shallow etch defines a nanoscale protrusion on the wafer surface. After applying a conformal protection on the protrusion, a deep etch step is carried out forming the surrounding microscale features. A minimum nanowire cross-section of 35 nm by 168 nm is demonstrated in the presence of an etch depth of 10 μm. Nanowire cross-sectional features are characterized via transmission electron microscopy and linked to specific process steps. The technology allows control on all dimensional aspects along with the exact location and orientation of the silicon nanowire. The adoption of the technology in the fabrication of micro and nanosystems can potentially lead to a significant reduction in process complexity by facilitating direct access to the nanowire during surface processes such as contact formation and doping.

Lateral resolution of nanoscaled images delivered by surface-analytical instruments: application of the BAM-L200 certified reference material and related ISO standards

The certified reference material BAM-L200, a nanoscale stripe pattern for length calibration and specification of lateral resolution, is described. BAM-L200 is prepared from a cross-sectioned epitaxially grown layer stack of AlxGa1-xAs and InxGa1-xAs on a GaAs substrate. The surface of BAM-L200 provides a flat pattern with stripe widths ranging down to 1 nm. Calibration distances, grating periods and stripe widths have been certified by TEM with traceability to the length unit. The combination of gratings, isolated narrow stripes and sharp edges of wide stripes offers plenty of options for the determination of lateral resolution, sharpness and calibration of length scale at selected settings of imaging surface-analytical instruments. The feasibility of the reference material for an analysis of the lateral resolution is demonstrated in detail by evaluation of ToF-SIMS, AES and EDX images. Other applications developed in the community are summarized, too. BAM-L200 fully supports the implementation of the revised International Standard ISO 18516 (in preparation) which is based on knowledge outlined in the Technical Report ISO/TR 19319:2013.

On the role of surface composition and curvature on biointerface formation and colloidal stability of nanoparticles in a protein-rich model system

The need for a better understanding of nanoparticle-protein interactions and the mechanisms governing the resulting colloidal stability has been emphasised in recent years. In the present contribution, the short and long term colloidal stability of silica nanoparticles (SNPs) and silica-poly(ethylene glycol) nanohybrids (Sil-PEG) have been scrutinised in a protein model system. Well-defined silica nanoparticles are rapidly covered by bovine serum albumin (BSA) and form small clusters after 20min while large agglomerates are detected after 10h depending on both particle size and nanoparticle-protein ratio. Oppositely, Sil-PEG hybrids present suppressive protein adsorption and enhanced short and long term colloidal stability in protein solution. No critical agglomeration was found for either system in the absence of protein, proving that instability found for SNPs must arise as a consequence of protein adsorption and not to high ionic environment. Analysis of the small angle X-ray scattering (SAXS) structure factor indicates a short-range attractive potential between particles in the silica-BSA system, which is in good agreement with a protein bridging agglomeration mechanism. The results presented here point out the importance of the nanoparticle surface properties on the ability to adsorb proteins and how the induced or depressed adsorption may potentially drive the resulting colloidal stability.

Impact of polymer shell on the formation and time evolution of nanoparticle-protein corona

The study of protein corona formation on nanoparticles (NPs) represents an actual main issue in colloidal, biomedical and toxicological sciences. However, little is known about the influence of polymer shells on the formation and time evolution of protein corona onto functionalized NPs. Therefore, silica-poly(ethylene glycol) core-shell nanohybrids (SNPs@PEG) with different polymer molecular weights (MW) were synthesized and exhaustively characterized. Bovine serum albumin (BSA) at different concentrations (0.1-6 wt%) was used as model protein to study protein corona formation and time evolution. For pristine SNPs and SNPs@PEG (MW=350 g/mol), zeta potential at different incubation times show a dynamical evolution of the nanoparticle-protein corona. Oppositely, for SNPs@PEG with MW≥2000 g/mol a significant suppression of corona formation and time evolution was observed. Furthermore, AFM investigations suggest a different orientation (side-chain or perpendicular) and penetration depth of BSA toward PEGylated surfaces depending on the polymer length which may explain differences in protein corona evolution.