Daniel J. Masiel

Point Defect Characterization in HAADF-STEM Images Using Multivariate Statistical Analysis

Quantitative analysis of point defects is demonstrated through the use of multivariate statistical analysis. This analysis consists of principal component analysis for dimensional estimation and reduction, followed by independent component analysis to obtain physically meaningful, statistically independent factor images. Results from these analyses are presented in the form of factor images and scores. Factor images show characteristic intensity variations corresponding to physical structure changes, while scores relate how much those variations are present in the original data. The application of this technique is demonstrated on a set of experimental images of dislocation cores along a low-angle tilt grain boundary in strontium titanate. A relationship between chemical composition and lattice strain is highlighted in the analysis results, with picometer-scale shifts in several columns measurable from compositional changes in a separate column.

Laser‐based in situ techniques: Novel methods for generating extreme conditions in TEM samples

The dynamic transmission electron microscope (DTEM) is introduced as a novel tool for in situ processing of materials. Examples of various types of dynamic studies outline the advantages and differences of laser‐based heating in the DTEM in comparison to conventional (resistive) heating in situ TEM methods. We demonstrate various unique capabilities of the drive laser, namely, in situ processing of nanoscale materials, rapid and high temperature phase transformations, and controlled thermal activation of materials. These experiments would otherwise be impossible without the use of the DTEM drive laser. Thus, the potential of the DTEM as a new technique to process and characterize the growth of a myriad of micro and nanostructures is demonstrated. Microsc. Res. Tech., 2009. Published 2009 Wiley‐Liss, Inc.

Silicon-based nanowires from silicon wafers catalyzed by cobalt nanoparticles in a hydrogen environment

We present here the synthesis of silicon-based nanowires directly from silicon wafers at high temperatures and in the presence of cobalt nanoparticles and hydrogen gas. All three ingredients were critical to the growth of Si-based nanowires, which were between 5-60 nm in diameter and microm-mm long. Both heavily coiled and straight Si-based nanowires were made. Experimental evidence suggested that the sources of silicon for the nanowires growth were in the gas phase.

Influence of cathode geometry on electron dynamics in an ultrafast electron microscope

Efforts to understand matter at ever-increasing spatial and temporal resolutions have led to the development of instruments such as the ultrafast transmission electron microscope (UEM) that can capture transient processes with combined nanometer and picosecond resolutions. However, analysis by UEM is often associated with extended acquisition times, mainly due to the limitations of the electron gun. Improvements are hampered by tradeoffs in realizing combinations of the conflicting objectives for source size, emittance, and energy and temporal dispersion. Fundamentally, the performance of the gun is a function of the cathode material, the gun and cathode geometry, and the local fields. Especially shank emission from a truncated tip cathode results in severe broadening effects and therefore such electrons must be filtered by applying a Wehnelt bias. Here we study the influence of the cathode geometry and the Wehnelt bias on the performance of a photoelectron gun in a thermionic configuration. We combine experimental analysis with finite element simulations tracing the paths of individual photoelectrons in the relevant 3D geometry. Specifically, we compare the performance of guard ring cathodes with no shank emission to conventional truncated tip geometries. We find that a guard ring cathode allows operation at minimum Wehnelt bias and improve the temporal resolution under realistic operation conditions in an UEM. At low bias, the Wehnelt exhibits stronger focus for guard ring than truncated tip cathodes. The increase in temporal spread with bias is mainly a result from a decrease in the accelerating field near the cathode surface. Furthermore, simulations reveal that the temporal dispersion is also influenced by the intrinsic angular distribution in the photoemission process and the initial energy spread. However, a smaller emission spot on the cathode is not a dominant driver for enhancing time resolution. Space charge induced temporal broadening shows a close to linear relation with the number of electrons up to at least 10 000 electrons per pulse. The Wehnelt bias will affect the energy distribution by changing the Rayleigh length, and thus the interaction time, at the crossover.

Recognition of melting of nanoparticle catalysts with cubically shaped Co3O4 nanoparticles

Cubically shaped cobalt oxide nanoparticle catalysts were used for the first time to investigate the melting of the nanoparticle catalysts responsible for the synthesis of silica nanocoils at 1050 degrees C and straight nanowires at 1100 degrees C. Cobalt nanoparticles remained morphologically highly anisotropic after the growth of nanocoils at 1050 degrees C, whereas they became predominately spherical after straight nanowires were made at 1100 degrees C. These results strongly indicated that cobalt nanoparticles responsible for the synthesis of straight nanowires were completely molten and that melting occurred to these nanoparticles between 1050 and 1100 degrees C.

The Application of Scanning Transmission Electron Microscopy (STEM) to the Study of Nanoscale Systems

In this chapter, the basic principles of atomic resolution scanning transmission electron microscopy (STEM) will be described. Particular attention will be paid to the benefits of the incoherent Z-contrast imaging technique for structural determination and the benefits of aberration correction for improved spatial resolution and sensitivity in the acquired images. In addition, the effect that the increased beam current in aberration corrected systems has on electron beam-induced structural modifications of inorganic systems will be discussed. Procedures for controlling the electron dose will be described along with image processing methods that enable quantified information to be extracted from STEM images. Several examples of the use of aberration-corrected STEM for the study of nanoscale systems will be presented; a quantification of vacancies in clathrate systems, a quantification of N doping in GaAs, a quantification of the size distribution in nanoparticle catalysts, and an observation of variability in dislocation core composition along a low-angle grain boundary in SrTiO3. The potential for future standardized methods to reproducibly quantify structures determined by STEM and/or high-resolution TEM will also be discussed.

Aerosolization System for Experimental Inhalation Studies of Carbon-Based Nanomaterials

Assessing the human health risks associated with engineered nanomaterials is challenging because of the wide range of plausible exposure scenarios. While exposure to nanomaterials may occur through a number of pathways, inhalation is likely one of the most significant potential routes of exposure in industrial settings. An aerosolization system was developed to administer carbon nanomaterials from a dry bulk medium into airborne particles for delivery into a nose-only inhalation system. Utilization of a cannula-based feed system, diamond-coated wheel, aerosolization chamber, and krypton-85 source allows for delivery of otherwise difficult to produce respirable-sized particles. The particle size distribution (aerodynamic and actual) and morphology were characterized for different aerosolized carbon-based nanomaterials (e.g., single-walled carbon nanotubes and ultrafine carbon black). Airborne particles represented a range of size and morphological characteristics, all of which were agglomerated particles spanning in actual size from the nanosize range (<0.1 μm) to sizes greater than 5 and 10 μm for the particles largest dimension. At a mass concentration of 1000 μg/m3, the size distribution as measured by the inertial impactor ranged from 1.3 to 1.7 μm with a σg between 1.2 and 1.4 for all nanomaterial types. Because the aerodynamic size distribution is similar across different particle types, this system offers an opportunity to explore mechanisms by which different nanomaterial physicochemical characteristics impart different health effects while theoretically maintaining comparable deposition patterns in the lungs. This system utilizes relatively small amounts of dry material (<0.05 g/h), which may be beneficial when working with limited quantity or costly nanomaterials. Copyright 2012 American Association for Aerosol Research

Compressively Sensed Video Acquisition in Transmission Electron Microscopy

Transmission electron microscopy (TEM) is an extremely powerful tool for physical, material, and biological science at the nanoscale. This is especially true for higher-dimensional acquisition modes that produce data beyond the usual two-dimensional images, adding resolution in time, depth (via tomography), scattering angle (through STEM-diffraction, also called 4D STEM), and spectroscopy. Unfortunately, these higher-dimensional modes are extremely bandwidth-hungry. Every added dimension greatly multiplies the number of bytes that need to be captured, with associated increases in acquisition time, sample damage, and equipment expense. This includes, more and more, the equipment needed to transfer, store, and analyze the data. Modern kilohertz-scale cameras are starting to address the issue, but they are not a complete solution, and they can be quite expensive.

Temporal Compressive Sensing Instrumentation for TEM

Advances in compressive sensing (CS) techniques and instrumentation have created a renewed interest in exploring new methods for data collection and post-processing [1,2]. Recently developed Temporal CS (TCS) techniques based on post-specimen, high-speed electrostatic beam deflectors effectively multiply the frame rate of commonly available TEM cameras by pre-compressing video data on the detector prior to readout, enabling much higher frame rates for in situ TEM measurements. In addition to improving camera frame rate, TCS opens up a very powerful set of techniques for electron imaging, diffraction, and spectroscopy by mapping time to other external experimental parameters such as probe position, probe strobe frequency, sample orientation, or sample drift. The TCS system introduced here is capable of precisely modulating or recording these experimental parameters through the same Integrated Timing Unit (ITU) that manages the camera and deflector.

Stroboscopic High-Duty-Cycle GHz Time-Resolved Microscope: Toward Hardware Implementation and Commissioning

1. Euclid TechLabs, 365 Remington Blvd., Bolingbrook, IL 60440, USA 2. Integrated Dynamic Electron Solutions, 5653 Stoneridge Dr., Suite 117, Pleasanton, CA 94588, USA 3. Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA 4. Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, NY 11973, USA * s.baryshev@euclidtechlabs.com