An investigation of nickel cobalt oxide nanorings using transmission electron, scanning electron and helium ion microscopy

Nickel cobalt oxide alloy nanorings have been synthesized using a wet chemistry method. Standard characterization techniques such as transmission electron microscopy (TEM) and scanning electron microscopy (SEM) have been used to characterize the nanorings. We, however, also examined the nanostructures in the helium ion microscope (HIM) and employed backscattered ion spectroscopy to determine thickness and composition of the nanostructure. The HIM provides complementary information of the nanostructures and the viability of using it as a tool for magnetic nanoparticle characterization was demonstrated by comparing the results from all three microscopes.

Controlled in situ growth of tunable plasmonic self-assembled nanoparticle arrays

Self-assembled silver nanoparticle (NP) arrays were produced by deposition at glancing angles on transparent stepped Al2O3 templates. The evolution of the plasmonic resonances has been monitored using reflection anisotropy spectroscopy (RAS) during growth. It is demonstrated that the morphology of the array can be tailored by changing the template structure, resulting in a large tunability of the optical resonances. In order to extract detailed information on the origin of the measured dichroic response of the system, a model based on dipolar interactions has been developed and the effect of tarnishing and morphological dispersion addressed.

Imaging of human colon cancer cells using He-Ion scanning microscopy

Due to its low beam current and charge compensation mechanism He-Ion scanning microscopy is a very promising tool for imaging biological cells. However, to obtain relevant information, the method used for sample preparation is also critical. In this work, we have used a Carl Zeiss Orion Plus helium-ion microscope to study the effect of sample gold coating on the morphology of human colorectal adenocarcinoma Caco2 cells. The fixative glutaraldehyde was used and the selective gold coating of the samples was investigated. A comparative study with standard scanning electron microscopy is presented.

Three-dimensional imaging by optical sectioning in the aberration-corrected scanning transmission electron microscope

The depth resolution for optical sectioning in the scanning transmission electron microscope is measured using the results of optical sectioning experiments of laterally extended objects. We show that the depth resolution depends on the numerical aperture of the objective lens as expected. We also find, however, that the depth resolution depends on the lateral extent of the object that is being imaged owing to a missing cone of information in the transfer function. We find that deconvolution methods generally have limited usefulness in this case, but that three-dimensional information can still be obtained with the aid of prior information for specific samples such as those consisting of supported nanoparticles. We go on to review how a confocal geometry may improve the depth resolution for extended objects. Finally, we present a review of recent work exploring the effect of dynamical diffraction in zone-axis-aligned crystals on the optical sectioning process.

Imaging modes for scanning confocal electron microscopy in a double aberration-corrected transmission electron microscope

Aberration correction leads to reduced focal depth of field in the electron microscope. This reduced depth of field can be exploited to probe specific depths within a sample, a process known as optical sectioning. An electron microscope fitted with aberration correctors for both the pre- and postspecimen optics can be used in a confocal mode that provides improved depth resolution and selectivity over optical sectioning in the scanning transmission electron microscope (STEM). In this article we survey the coherent and incoherent imaging modes that are likely to be used in scanning confocal electron microscopy (SCEM) and provide simple expressions to describe the images that result. Calculations compare the depth response of SCEM to optical sectioning in the STEM. The depth resolution in a crystalline matrix is also explored by performing a Bloch wave calculation for the SCEM geometry in which the pre- and postspecimen optics are defocused away from their confocal conditions.