Second-order aberration corrected electron energy loss spectroscopy attachment for scanning electron microscopes

Smart acquisition EELS

Quantitative analysis of the effect of probe convergence on electron energy loss spectra of anisotropic materials

A DEC VAXstation 3200 color graphics computer workstation has been interfaced to a Vacuum Generators HB501A Scanning Transmission Electron Microscope (STEM) for on-line image and spectrum acquisition. Electron Energy Loss Spectra (EELS) or Auger spectra may be recorded (serially) using pulse or analog modes (using the voltage to frequency converters supplied by VG). High resolution bright field (BF) / annular dark field (ADF) image pairs may be recorded simultaneously as well as simultaneous pairs of Auger / secondary images. A resolution of 2Å (or better) has been achieved with an experimental pole piece (Cs = 1.2mm. and 0.7mm.). The image quality obtained with this system is greatly improved over the Polaroid system supplied with the microscope.A schematic of the overall system is shown in FIG 1. To avoid possible ground loop noise the entire computer system has been optically isolated from the STEM. There are four 16 bit digital to analog converters (DAC) for controlling the x,y position, the EELS energy and the Auger energy. The output of four detectors is connected back to the computer for pulse counting using a Qbus board manufactured by Codar Technologies. This board has three AMD 9513 counter IC's (with five 16 bit counters each) to count the electron or VFC pulses. The EELS spectra are acquired using two 32 bit counters (16 bit counters concatenated) and may function in a constant dwell time or constant count (constant signal to noise ratio) mode. The Auger and BF/ADF image counters work in a constant dwell time 16 bit mode. The average CPU overhead has been measured at 50 microsec per point in polled mode (images) and 500 microsec in interrupt driven mode (spectra).

We report on first-principles calculations of electron energy-loss (EEL) spectra for bulk group-III nitrides and of spatially resolved EEL spectra for a variety of edge and screw dislocations in GaN. The theoretical bulk low-loss EEL spectra, in the 0--10 eV range, are in good agreement with recent experimental data. We find gap states associated with undecorated full-core dislocations that lead to absorption below the bulk onset energy in low-loss EEL spectroscopy. It is also found that the electrostatic potential at N atoms in the vicinity of an edge dislocation varies by an order of a volt and casts doubt on any simple interpretation of core-loss spectroscopy.

ELS and XPS study of Pd/PdO methane oxidation catalysts

Practical aspects of the quantification of sp2-hybridized carbon atoms in diamond-like carbon by electron energy loss spectroscopy

Enhancement of heterogeneous photo-Fenton performance of core-shell structured boron-doped reduced graphene oxide wrapped magnetical Fe3O4 nanoparticles: Fe(II)/Fe(III) redox and mechanism

FePt nanodendrites with high-index facets as active electrocatalysts for oxygen reduction reaction

One-dimensional Au nanoparticle arrays encapsulated within freestanding SiO2 nanowires are fabricated by thermal oxidation of Au-coated Si nanowires with controlled diameter and surface modulation. The nanoparticle diameter is determined by the Si nanowire diameter and Au film thickness, while the interparticle spacing is independently controlled by the Si nanowire modulation. The optical absorption of randomly oriented Au nanoparticle arrays exhibits a strong plasmonic response at 550 nm. Scanning transmission electron microscopy (STEM)-electron energy loss spectrum (EELS) of nanoparticle arrays confirmed the same plasmonic response and demonstrated uniform optical properties of the Au nanoparticles. The plasmonic response in the STEM-EELS maps is primarily confined around the vicinity of the nanoparticles. On the other hand, examination of the same nanowires by energy-filtered transmission electron microscopy also revealed significant enhancement in the plasmonic excitation in the regions in between the nanoparticles. This versatile route to synthesize one-dimensional Au nanoparticle arrays with independently tailorable nanoparticle diameter and interparticle spacing opens up opportunities to exploit enhanced design flexibility and cost-effectiveness for future plasmonic devices.

The nano-scale chemical distribution and microstructure of a nitride based wear and oxidation resistant coating prepared by unbalanced magnetron sputtering was investigated. The coating consisted of multilayers of CrAlYN/CrN with a partially oxidised CrAlY(O)N/Cr(O)N oxy-nitride surface layer. The multilayer period of both the nitride and oxy-nitride layers was 3.8 ± 0.2 nm. Nano-scale chemical analysis and imaging was performed using sub-nanometer resolution electron energy loss spectroscopic profiling in a spherical aberration corrected scanning transmission electron microscope. Experimentally determined fine edge structure in electron energy loss spectra were in good agreement with theoretically determined spectra, calculated using electron density functional theory. This analysis indicated the CrN layers to be near stoichiometric with a relative Cr/N ratio of 1.05 ± 0.1 while for the CrAlYN layers the best match between the direct chemical analysis and the simulated edges was (Cr 0.5Al 0.5)N. A diffuse interface, ∼ 1 nm wide was observed between the CrAlYN and CrN layers. For the outermost oxy-nitride layer, the chromium to nitrogen ratio remains approximately constant though out the layer, while the aluminium decreases as a function of increasing oxygen content.

Development and application of STEM for the biological sciences

Replica Microscopy and Scanning Electron Microscopy of Laser Impacts on the Skin

Experimental techniques for electron energy loss spectroscopy (EELS) combine high energy resolution with high spatial resolution. They are therefore powerful tools for investigating the local electronic structure of complex systems such as nanostructures, interfaces and even individual defects. Interpretation of experimental electron energy loss spectra is often challenging and can require theoretical modelling of candidate structures, which themselves may be large and complex, beyond the capabilities of traditional cubic-scaling density functional theory. In this work, we present functionality to compute electron energy loss spectra within the onetep linear-scaling density functional theory code. We first demonstrate that simulated spectra agree with those computed using conventional plane wave pseudopotential methods to a high degree of precision. The ability of onetep to tackle large problems is then exploited to investigate convergence of spectra with respect to supercell size. Finally, we apply the novel functionality to a study of the electron energy loss spectra of defects on the (1 0 1) surface of an anatase slab and determine concentrations of defects which might be experimentally detectable.

During the last decade, much effort has been devoted to relations between structure and mechanical properties, particularly in metals. The need for sophisticated structure studies has increased accordingly. Combinations of different types of microscope methods have been tried, for example by performing optical and scanning electron microscopy (SEM) on etched metallographic sections.Particularly in the case of more intricate phase analyses, it is often necessary to add information about the internal structure by means of transmission electron microscopy (TEM). The scope of the present work has been to combine the advantages of the “classical” methods of studying etched surfaces with those of transmission studies of the same field of observation. For that purpose, the scanning transmission electron microscope (STEM) technique is ideal, and has been applied on thin foils, which, after ordinary electro-polishing, were etched (nital, 10 sec.) and thereby given a structure-related surface topography. The microscope used was a JEOL 200B TEM with scanning attachment, operated at 200 kV in emissive SEM, STEM and conventional TEM mode.

Design and aberration study of a new miniature energy analyzer with correctors in a scanning electron microscope