Jennifer L. Gray

Thinning of large mammalian cells for cryo-TEM characterization by cryo-FIB milling.

Focused ion beam milling at cryogenic temperatures (cryo‐FIB) is a valuable tool that can be used to thin vitreous biological specimens for subsequent imaging and analysis by cryo‐transmission electron microscopy (cryo‐TEM) in a frozen‐hydrated state. This technique offers the potential benefit of eliminating the mechanical artefacts that are typically found with cryo‐ultramicrotomy. However, due to the additional complexity in transferring samples in and out of the FIB, contamination and devitrification of the amorphous ice is commonly encountered. To address these problems, we have designed a sample cryo‐shuttle that directly and specifically accepts Polara TEM cartridges to simplify the transfer process between FIB and TEM. We optimized several parameters in the cryo‐FIB and cryo‐TEM processes using the quality of the samples’ ice as an indicator and demonstrated high‐quality milling with large mammalian cells. By comparing the results from HeLa cells to those from Escherichia coli cells, we discuss some of the artefacts and challenges we have encountered using this technique.

Ferrocene and Inconel assisted growth of dense carbon nanotube forests on copper foils

Aligned growth of carbon nanotubes on copper substrates has been achieved using a nickel-based catalyst, Inconel, which is first deposited on the copper foil substrate before the growth of nanotubes via thermal chemical vapor deposition (CVD). An additional catalyst, iron, is supplied by mixing ferrocene with the carbon feedstock, xylene, during the CVD growth. For specific ranges of the film thickness, 10–12 nm, and under certain growth conditions, dense, aligned growth of carbon nanotubes is observed. This technique represents a relatively simple process for direct growth of carbon nanotubes on copper substrates without the need for additional barrier layers and plasma-enhanced CVD techniques. Scanning electron microscopy was used to qualitatively evaluate the density of the nanotubes and the tendency to align in a direction perpendicular to the substrates. Transmission electron microscopy and Raman spectroscopy were used to examine the structure and quality of the nanotubes, as well as the composition ...

Fabrication of discrete gallium nanoislands on the surface of a Si(001) substrate using a focused ion beam

A gallium focused ion beam (FIB) has been used to implant Ga at specific sites on the surface of undoped Si(001) substrates. Upon annealing at 600 °C, discrete nanoscale surface islands form within the FIB patterned regions when the total Ga ion dose, or fluence, is greater than 1.0 × 10(16) ions cm( - 2). The number of islands depends on the size of the irradiated region and a single island can be achieved for a FIB milled region that is 100 nm × 100 nm. The average sizes of the islands were found to range from 24.5 nm when exposed to a total ion dose of 1.2 × 10(16) ions cm( - 2) to 45 nm for a dose of 3.0 × 10(16) ions cm( - 2). We have confirmed that these surface islands are metallic Ga by performing a selective chemical etch that removes the islands and by transmission electron microscopy characterization. These patterned Ga surface templates could serve as nucleation sites for the lateral arrangement of discrete quantum dot structures.

3D Imaging of Biological Cells Using a CryoFIB/SEM and a CryoTEM

The emerging discipline of cryo-electron tomography provides unique opportunities to determine 3dimensional (3D) cellular architectures in their native conditions. However, one major limitation, specimen thickness, has hindered its broader application in cellular structural biology, since it’s performed in TEM by tilting the specimen through a series of angles. Thinning a biological sample using cryo-ultramicrotomy and a diamond knife has yielded limited success due to technical difficulties and artifacts associated with this mechanical sectioning method [1]. It has been shown that a dual beam system consisting of a scanning electron microscope (SEM) and focused ion beam (FIB) used under cryogenic conditions can successfully mill biological samples for use in cryoTEM. This technique eliminates the cutting artifacts that are associated with ultramicrotomy, while thinning specimens enough for electron tomography [2, 3].

Growth of Carbon Nanotubes on Copper Substrates Using a Nickel Thin Film Catalyst

Carbon nanotubes with their attractive properties, one-dimensional geometry, and their large aspect ratio are ideal candidates for a variety of applications including energy storage, sensing, nanoelectronics, among others. We have studied the growth of carbon nanotubes on copper substrates using a nickel thin film as a catalyst. The catalyst was sputtered in a chamber with a base pressure in the ultra-high-vacuum regime. By adjusting the sputtering parameters, the effects of the morphology and the thickness of the nickel catalyst on the growth of carbon nanotubes have also been investigated. Multiple hydrocarbon sources as carbon feedstock (methane, acetylene and m-xylene), corresponding catalyst precursors and varying temperature conditions were used during chemical vapor deposition (CVD) process to understand and determine the best conditions for growth of carbon nanotubes on copper. Correlation between the thickness of the thin film nickel catalyst and the carbon nanotube diameter is also presented in the study. Characterization techniques used to study the morphology of the CNTs grown on copper include SEM, TEM, HRTEM, Raman Spectroscopy. Results of these studies are outlined and discussed.