ABSTRACT
We report the working of a novel detector design based on a Bessel Box (BB) electron energy analyser in a scanning electron microscope (SEM). We demonstrate the application of our detector for elemental identification through Auger electron detection in an SEM environment and its potential as a complementary technique to energy dispersive X-ray (EDX) spectroscopy. We also demonstrate energy-filtered secondary electron imaging of a copper-on-silicon sample using an electron pass energy of 12 eV. LAY DESCRIPTION: Advancements in the field of the Scanning Electron Microscopy have been one of the major nanotechnology enablers. A Scanning Electron Microscope (SEM) generates a magnified image of the sample by bombarding it with an electron beam and detecting the electrons that scatter off the surface along with the electrons that are generated in the sample. Conventional detectors such as the Everhart-Thornley detector (ET) or through-the-lens (TTL) detectors, either offer little to no energy analysis (ET) or limited energy filtering capability (e.g the low-pass energy filter in TTL). This information is crucial to interpret the image of the sample under study. What is needed is a smart and compact detector that can detect electrons and furnish energy inside the SEM chamber. Here, we report a novel secondary electron (SE) detector design with energy analysis capability for use in scanning electron microscopes. The detector is based on the design of a Bessel Box (BB) energy analyser. We have designed and experimentally tested it in an SEM environment. The band-pass filter action of the detector enables the BB to be operated at a selected energy and allows a narrow window of energies to be detected for generating energy-filtered images.
ABSTRACT
The effect of gallium ion concentrations (0.5 and 2%) on the morphologies, structural and optical properties of Ga-doped ZnO nanostructures are presented. Ga-doped ZnO nanostructures were synthesized on silicon substrates by simple thermal evaporation process using metallic zinc and Ga powders in the presence of oxygen. Interestingly, it was observed that Ga-ions incorporation in ZnO nanomaterials play an important role on the growth kinetics and hence on the morphologies of as-grown Ga-doped ZnO nanostructures. It was seen that at low Ga-concentration, needle-shaped Ga-doped ZnO nanostructures are formed, presumably by subsequent stacking of hexagonal plates. However, when increasing the Ga-concentration, multipods of Ga-doped ZnO were grown. In addition to the morphologies, incorporating Ga-ions into ZnO also affect the room-temperature photoluminescence properties. Therefore, at lower Ga-ion concentration, an intense UV emission was observed while at high Ga-concentration a deep level emission was seen in the room-temperature photoluminescence spectra. This research demonstrates that by controlling the Ga-ion concentration the morphologies and optical properties of ZnO nanomaterials can be tailored.
ABSTRACT
The sensitivity of Monte Carlo estimates of backscattering coefficients η to the accuracy of their input data is examined by studying the percentage change in η due to changes of 10% and 20% in the differential elastic scattering cross-section dσ/dΩ and corresponding changes in the stopping power S(E) in the primary energy range 200-10,000 eV. To a good approximation equivalent elastic and inelastic scattering changes produce equal and opposite shifts in η, a result consistent with predictions of transport theory. For medium to high atomic numbers an x% error in the specification of either S(E) or dσ/dΩ produces a percentage change in η significantly less than x%, while at low atomic number Δη/η increases approximately linearly with ln E so that Monte Carlo predictions are then more sensitive to parameter precision at high energy.
ABSTRACT
Even though the Schottky emitter is a high-brightness source of choice for electron beam systems, its angular current intensity is substantially lower than that of thermionic cathodes, rendering the emitter impractical for applications that require high beam current. In this study, two strategies were attempted to enhance its angular intensity, and their experimental results are reported. The first scheme is to employ a higher extraction field for increasing the brightness. However, the tip shape transformation was found to induce undesirably elevated emission from the facet edges at high fields. The second scheme exploits the fact that the angular intensity is proportional to the square of the electron gun focal length [Fujita, S. & Shimoyama, H. (2005) Theory of cathode trajectory characterization by canonical mapping transformation. J. Electron Microsc. 54, 331-343], which can be increased by scaling-up the emitter tip radius. A high angular current intensity (J(Omega) approximately 1.5 mA sr(-1)) was obtained from a scaled-up emitter. Preliminary performance tests were conducted on an electron probe-forming column by substituting the new emitter for the original tungsten filament gun. The beam current up to a few microamperes was achieved with submicron spatial resolution.
ABSTRACT
The secondary electron (SE) yield, delta, was measured from 24 different elements at low primary beam energy (250-5,000 eV). Surface contamination affects the intensity of delta but not its variation with primary electron energy. The experiments suggest that the mean free path of SEs varies across the d bands of transition metals in agreement with theory. Monte Carlo simulations suggest that surface plasmons may need to be included for improved agreement with experiment.
ABSTRACT
The electron backscattering factor was measured from 24 different elements at low primary beam energy (250-5,000 eV). The results were compared with Monte Carlo simulations from a variety of freely available programs and an in-house developed program. The results suggest that a thin film of oxide can modify the backscattering factor at low primary energy. In addition, a number of problems have been identified with the freely available programs.
