Developing affordable wet-sample electron microscopy integrated with a temperature controlled sample holder

Scanning electron microscopy (SEM) is widely used to analyze the size, shape and composition of material systems. However, using this tool for analyzing systems such as particles suspended in solution, requires drastic sample alterations, such as precipitation and fixation. Besides altering their environment, this exposes the particles to the harsh conditions within an electron microscope, such as high vacuum and electron beam exposure. To this end, the first goal of this study was to develop methodologies for imaging wet samples using electron microscopy. This is realized by creating a sandwich structure containing the solution of interest between a partially electron transparent window and a silicon substrate. The ability of the developed imaging cells to provide good imaging conditions is demonstrated with a variety of samples including polystyrene spheres, polymeric microgels and spindle shaped nanoparticles. As some of the systems investigated are temperature sensitive, the second goal of the project was to develop a temperature controlled stage that can be integrated with the SEM. In the future this heating stage will be used alongside the wet samples to image microgels above and below their critical solution temperature.https://engagedscholarship.csuohio.edu/u_poster_2015/1030/thumbnail.jp

Characterization of Microgels in Ionic Liquid

Microgels are thermoresponsive polymeric nanoparticles whose size in aqueous solution is dependent on temperature. The microgels were studied using both dynamic light scattering (DLS) and scanning electron microscopy (SEM) to better understand the nanoparticles dynamics. The first part of the study focused on developing a controlled preparation procedure which would generate reproducible SEM images on a wet sample. The ionic liquid was mixed with a dilute solution of microgels and water was dried using nitrogen gas. This technique allowed a large volume of microgels to easily transition from their natural water solvent to a low vapor pressure ionic solvent. The second part of the study attempts to correlate the diffusion found from microgels in ionic liquid using scanning electron microscopy to the statistical average diffusion measured with dynamic light scattering. The microgels in ionic liquid observed with SEM exhibited the same radius that was measured with DLS for microgels in a water based solvent.https://engagedscholarship.csuohio.edu/u_poster_2018/1033/thumbnail.jp

«Il patrimonio culturale tra esigenze di tutela e sua valorizzazione»

Seminario inaugurale del Corso di «Legislazione dei beni culturali, ambientali e turismo

Deducing Shape of Anisotropic Particles in Solution from Light Scattering: Spindles and Nanorods

Depolarized Dynamic light scattering (DDLS) enables to measure in situ rotational and translational diffusion of nanoparticles suspended in solution. Their size, shape, diffusion, and intermolecular interactions can be interred then from DDLS data using various models of diffusion. Incorporating DDLS to analyze the dimensions of easily imaged elongated particles, such as Iron (III) oxyhydroxide Spindles (FeOOH) and gold coated Nanorods, will allow a deeper understanding between rotational/translational diffusion and size distribution of hard-to-image anisotropic wet systems such as micelles, microgels, and protein complexes. The emphasis of this study was to look at the aged FeOOH Spindle sample, and explore the size distribution and modeling of the Nanorod particles. The light scattering results obtained from the basic model of non-interacting prolate ellipsoids offered dimensions similar (within 15%) to the size distribution from the Scanning Electron Microscope (SEM). The results, however, were somewhat different from the original particle size possibly due to sample aging and agglomeration of the FeOOH Spindles. Conversely, the Nanorod dimensions obtained from the Prolate Ellipsoid Model differed by a factor 1.2-2 from the values obtained by Transmission Electron Microscopy and SEM. The significant difference between DDLS and imaging results is due to the nature of the modeling employed (ellipsoid was used to model cylindrically shaped particles with spherical caps).https://engagedscholarship.csuohio.edu/u_poster_2015/1032/thumbnail.jp

P2: Developing Methodologies for Wet-Sample Electron Microscopy Imaging

Scanning Electron Microscopy (SEM) is widely used to analyze the size, shape, and composition of material systems. However, using this tool for analyzing systems such as particles suspended in solution requires drastic sample alterations, such as precipitation and fixation. Besides altering their environment, this exposes the particles to the harsh conditions within an electron microscope, such as high vacuum and electron beam exposure. To this end, the first goal of this study was to develop methodologies for imaging wet samples using electron microscopy. This is realized by creating a sandwich structure containing the solution of interest between a partially electron transparent window and the aluminum stub. The ability of the developed imaging cells to provide good imaging conditions is demonstrated with a variety of samples including polystyrene spheres, polymeric microgels, and spindleshaped nanoparticles. As some of the systems investigated are temperature sensitive, the second goal of the project was to develop a temperature controlled stage that can be integrated with the SEM. In the future, this heating stage will be used alongside the wet samples to image microgels above and below their critical solution temperature.https://engagedscholarship.csuohio.edu/u_poster_2017/1029/thumbnail.jp

Light Scattering Characterization of Elastin-Like Polypeptide Trimer Micelles

Elastin-Like Polypeptides (ELP) can be used to form thermo-reversible vehicles for drug delivery systems. The ELP nanoparticles are composed of three-armed star polypeptides. Each of the three arms extending from the negatively charged foldon domain includes 20 repeats of the (GVGVP) amino acid sequence. The ELP polymer chains are soluble at room temperature and become insoluble at the transition temperature (close to 50 oC), forming micelles. The size and shape of the micelle is dependent on the temperature and the pH of solution, along with the concentration of the Phosphate Buffered Saline (PBS) solvent. The technique of Depolarized Dynamic Light Scattering (DDLS) was employed to study the structure and dynamics of micelles at 62 oC; the solution was maintained at an approximate pH level of 7.3 - 7.5, while varying the concentration of the solvent (PBS). At low salt concentrations (\u3c 15 mM), the micellar size is not very reproducible due to unstable pH levels, arising from low buffer concentration. At intermediate salt concentrations (15 - 60 mM), the system formed spherically-shaped micelles exhibiting a steady growth in the hydrodynamic radius (Rh) from 10 to 21 nm, with increasing PBS concentration. Interestingly, higher salt concentrations (\u3e 60 mM) displayed an apparent elongation of the micelles evident by a significant VH signal, along with a surge in the apparent Rh. A model of micelle growth (and potentially elongation) with increase in salt concentration is considered.https://engagedscholarship.csuohio.edu/u_poster_2016/1038/thumbnail.jp

Comagnetometer probes of dark matter and new physics

We discuss the use of comagnetometry in studying new physics that couples to fermionic spin. Modern comagnetometry is -- in absolute energy units -- the most sensitive experimental technique for measuring the energy difference between quantum states, reaching sensitivities in the $10^{-26}\,$eV range. The technique suppresses the magnetic interactions of the spins, making searches for non-standard-model interactions possible. Many implementations have been developed and optimized for various uses. New physics scenarios which can be probed with comagnetometers include: EDMs, violations of Lorentz invariance, Goldstone bosons of new high-energy symmetries, CP-violating long-range forces, and axionic dark matter. We consider the prospects for improvements in the technique, and show -- based purely on signal-to-noise ratio with existing technology -- that there is room for several orders of magnitude in further improvement. We also evaluate several sources of systematic error and instability that may limit improvements.Comment: Submitted to Journal of Quantum Science and Technology. Version 1 is the manuscript resubmitted following referee reports. Pending final acceptanc