Structure determination by cryoEM at 100 keV.

Electron cryomicroscopy can, in principle, determine the structures of most biological molecules but is currently limited by access, specimen preparation difficulties, and cost. We describe a purpose-built instrument operating at 100 keV-including advances in electron optics, detection, and processing-that makes structure determination fast and simple at a fraction of current costs. The instrument attains its theoretical performance limits, allowing atomic resolution imaging of gold test specimens and biological molecular structure determination in hours. We demonstrate its capabilities by determining the structures of eleven different specimens, ranging in size from 140 kDa to 2 MDa, using a fraction of the data normally required. CryoEM with a microscope designed specifically for high-efficiency, on-the-spot imaging of biological molecules will expand structural biology to a wide range of previously intractable problems.

The effect of work function during electron spectroscopy measurements in Scanning Field-Emission Microscopy.

Electron spectroscopy proves to be a handy tool in material science. Combination of electron spectroscopy and scanning probe microscopy is possible through Scanning Field Emission Microscopy (SFEM), where a metallic probe positioned close to the surface is used as an electron source. However, using this not too much technologically demanding technique, it looks like the compromise between the lateral resolution and spectroscopic clarity must be considered. Here, we demonstrate, using experimental and simulation data, that the spectroscopic information can be understood without the need to grossly deteriorate the potential spatial resolution of the microscope. We prepared a three-section sample with clean W(110), sub-monolayer Cs on W(110) and monolayer of Cs on W(110) on which electron energy loss spectra are obtained via Scanning Probe Energy Loss Spectroscopy (SPELS) measurements. To explain the detected spectra a new model describing SPELS measurements in a SFEM is developed which aids to uncover the origin of spectral features typically detected during experiments. Experimental and simulation data are in a mutual agreement and observed spectral features on different surfaces could be explained. This novel understanding of SPELS can solve the main issue previously related to this technique, and good spatial resolution can be accompanied by the understanding of the measured spectra.

Bamboo and herringbone shaped carbon nanotubes and carbon nanofibres synthesized in direct current-plasma enhanced chemical vapour deposition.

Carbon nanotubes with different structures were catalytically synthesized on Ni coated SiO2/Si substrate in a Direct Current Plasma Enhanced Chemical Vapour Deposition system, in which C2H2 acted as the carbon source and NH3 as the etchant gas. A Scanning Electron Microscope study showed that carbon nanotubes were all vertically aligned with respect to the substrate, with diameters ranging from 10 nm to 200 nm. Different sizes of Ni catalyst particles were observed on the tips of carbon nanotubes. Transmission Electron Microscopy was used to study the morphology of the grown tubes and the results obtained show that the diameters and structures of these carbon nanotubes were closely correlated to the sizes and structures of the Ni nanoparticles. Two main structures namely bamboo shaped carbon nanotubes and herringbone shaped carbon nanofibres were found on the same sample. It is suggested that by controlling the pre-growth condition, desired structure of carbon nanotubes or carbon nanofibres could be produced for practical applications.

Use of Monte Carlo modeling to aid interpretation and quantification of the low energy-loss electron yield at low primary energies.

Experimental low-loss electron (LLE) yields were measured as a function of loss energy for a range of elemental standards using a high-vacuum scanning electron microscope operating at 5 keV primary beam energy with losses from 0 to 1 keV. The resulting LLE yield curves were compared with Monte Carlo simulations of the LLE yield in the particular beam/sample/detector geometry employed in the experiment to investigate the possibility of modeling the LLE yield for a series of elements. Monte Carlo simulations were performed using both the Joy and Luo [Joy, D.C. & Luo, S., Scanning 11(4), 176988 (2005)] to assess the influence of the more recent stopping power data on the simulation results. Further simulations have been conducted to explore the influence of sample/detector geometry on the LLE signal in the case of layered samples consisting of a thin C overlayer on an elemental substrate. Experimental LLE data were collected from a range of elemental samples coated with a thin C overlayer, and comparisons with Monte Carlo simulations were used to establish the overlayer thickness.

Imaging of the boron doping in silicon using low energy SEM.

Scanning electron imaging of plan views of boron-doped patterns in silicon is examined, together with the mechanism of formation of the electronic contrast in this kind of structures. Main to-date published results are critically reviewed and new data are presented concerning the secondary, backscattered and total-emission electron contrasts, including their qualitative and quantitative behaviour, particularly in the low energy range achieved with the help of the cathode lens (the scanning low energy electron microscopy mode, SLEEM). Surface analysis of the structure by means of Auger electron spectrometer has been performed, too, both before and after ion beam bombardment. The scanning electron microscope micrographs, acquired after the oxide mask removal in HF, are examined in a variety of detection modes, aiming at identification of the signal component primarily bearing the contrast. The energy dependence of the contrasts is presented as well as its change owing to alteration in the vacuum conditions. The most important findings include an extremely high contrast obtained in the SLEEM mode and even more enhanced under medium vacuum conditions at which the carbonaceous layer of surface contamination plays its role. The observed phenomena are partly explained in the frame of the "flat band" model of a passivated surface. The increased contrast in the SLEEM mode is understood as connected with the above-surface electric field of the cathode lens, generating space charge layers inside the semiconductor. In addition, charge carriers, injected via the primary electron beam, are considered as influencing the contrast vs. energy dependence.