New insights into subsurface imaging of carbon nanotubes in polymer composites via scanning electron microscopy.

Despite many studies of subsurface imaging of carbon nanotube (CNT)-polymer composites via scanning electron microscopy (SEM), significant controversy exists concerning the imaging depth and contrast mechanisms. We studied CNT-polyimide composites and, by three-dimensional reconstructions of captured stereo-pair images, determined that the maximum SEM imaging depth was typically hundreds of nanometers. The contrast mechanisms were investigated over a broad range of beam accelerating voltages from 0.3 to 30 kV, and ascribed to modulation by embedded CNTs of the effective secondary electron (SE) emission yield at the polymer surface. This modulation of the SE yield is due to non-uniform surface potential distribution resulting from current flows due to leakage and electron beam induced current. The importance of an external electric field on SEM subsurface imaging was also demonstrated. The insights gained from this study can be generally applied to SEM nondestructive subsurface imaging of conducting nanostructures embedded in dielectric matrices such as graphene-polymer composites, silicon-based single electron transistors, high resolution SEM overlay metrology or e-beam lithography, and have significant implications in nanotechnology.

Gold nanoshell assembly on a ferritin protein employed as a bio-template.

Gold nanoshells around 26 nm in diameter with a 7 nm thick wall were fabricated in an aqueous solution using pre-reconstituted ferritin proteins as a removable bio-template. The synthesis of gold nanoshells was initiated by planting gold nanoparticle seeds in the hydrophilic three-fold channels of the ferritin protein. The process was facilitated by the energetically favorable gold-sulfur bonds formed at the cysteine residues lining these channels.

A quantitative assessment of carbon nanotube dispersion in polymer matrices.

Quantifying the nature and extent of the dispersion of nanomaterials in polymer matrices is the important first step in understanding the relationship between the nanoscale structure and the bulk scale functional performance of nanocomposites. We present here a methodology for using scanning electron microscope images of nanocomposites taken under high accelerating voltages to quantify four parameters that relate to the dispersion of the nanomaterial. This image analysis methodology is general and applicable to images from other microscopes as well. The analysis performed here was done on representative local areas of six samples to determine the effects of processing conditions, matrix chemistry, and carbon nanotube composition on the level of dispersion. Future work will involve expanding this analysis to rapidly cover larger areas and reducing the data in a manner that is similar to the approach of small angle scattering studies.

Very long single- and few-walled boron nitride nanotubes via the pressurized vapor/condenser method.

A new method for producing long, small-diameter, single- and few-walled, boron nitride nanotubes (BNNTs) in macroscopic quantities is reported. The pressurized vapor/condenser (PVC) method produces, without catalysts, highly crystalline, very long, small-diameter, BNNTs. Palm-sized, cotton-like masses of BNNT raw material were grown by this technique and spun directly into centimeters-long yarn. Nanotube lengths were observed to be 100 times that of those grown by the most closely related method. Self-assembly and growth models for these long BNNTs are discussed.

Cobalt oxide hollow nanoparticles derived by bio-templating.

We present here the first fabrication of hollow cobalt oxide nanoparticles produced by a protein-regulated site-specific reconstitution process in aqueous solution and describe the metal growth mechanism in the ferritin interior.

Plastic tip arrays for force spectroscopy.

The mechanical stability and viability of molecules investigated with the atomic force microscope (AFM) continue to be limiting factors in the duration of force spectroscopy measurements. In an effort to circumvent this problem, we have fabricated an all-plastic array of over 30 000 tips with dimensions similar to common AFM probes using silicon micromolding techniques. This approach enables rapid fabrication of tip arrays with improved properties, as compared to tip arrays made entirely of silicon.