Sub Surface Imaging Using a Toroidal Backscattered Electron Energy Spectrometer in a Scanning Electron Microscope

In a SEM, an object under examination is scanned by a focused electron beam, of energy typically 2-30 keV. Some of the incident electrons are scattered out of the sample, carrying with them depth information from the internal structure of the sample. By detecting BSEs in a definite energy range, it is theoretically possible to separate images of individual layers of a three-dimensional sample, ie, perform a kind of instrumental tomography. Additionally, detecting BSEs on an energy separation basis gives another degree of freedom to microscopists to determine greater specimen information. To do this, a suitable BSE energy filter or spectrometer is required.To be effective and produce high quality images, a BSE spectrometer should have a working distance of less than 40 mm. It should be axially symmetric with the electron beam passing through the center of the analyser, impinging on the specimen normal to its surface. The specimen being scanned must be placed in the space free from the analysing field of the spectrometer, which should not introduce any magnetic fields. Using these criteria, computer simulations were performed to determine the equipotentials and trajectories of electrons in cylindrical, hyperbolic, sector spherical and sector toroidal electrostatic energy analysers. The results showed that the above requirements could be satisfied by a toroidal energy analyser, which also has the advantage over the others as to the coupling coefficient, relative aperture dimensions and energy resolution capabilities.</jats:p

A Novel Method for Contactless, Non Destructive Investigation of Semi Conductor Structures in the SEM.

It is known that scanning a focussed laser beam across the surface of a semi conductor wafer, can produce a photon induced voltage (PIV) at electrically active sites. This technique depends upon the incident photons inducing charge carriers, both electrons and holes, on or just below the surface of the semi conductor. These charge carriers drift through the device until they are captured by a defect, at which stage they accumulate, producing a voltage at the surface. These voltages are only associated with a charge carrier capture site, which means that a voltage build up only occurs at a defect. This PIV technique has been used for contactless imaging of semiconductor wafers, allowing easy identification of electrically active sites such as crystallographic defects, imperfections and inhomogenieties on or just below the surface [1,2].Nothing in the above mechanism excludes the use of an electron beam to induce charge carriers and produce an electron induced voltage (EIV).</jats:p

Principles and Possibilities of Backscattered Electron Micro-Tomography in the Scanning Electron Microscope

Multi layer structures are widely used in micro electronics devices and visualisation of their sub surface layers is important to understand the nature and properties of these devices. One of the more common methods of sub surface imaging is ion beam milling, in which sections of the overlaying material are removed to reveal sub surface details. Some disadvantages of this technique are that the equipment required is expensive and the technique is destructive. Another technique is to image a device at different accelerating voltages and determine at which voltage a particular feature is first detected. A major disadvantage of this technique is that the underlying layers are always observed partially obscured by the overlaying material. The development of a non destructive technique for three dimensional characterisation of electronic, physical, compositional and/or topological properties of these structures could be useful.One such technique is micro tomography using the backscattered electron (BSE) signal in the scanning electron microscope SEM [1].</jats:p

Splitting hairs: differentiating between entomological activity, taphonomy, and sharp force trauma on hair

Purpose The analysis of hair can provide useful information for the correct evaluation of forensic cases, but studies of trauma on hair are extremely rare. Hair may present lesions caused by traumatic events or by animals: in fact, signs of sharp force weapons on hair may provide important information for the reconstruction of the manner of death, and, for example, may suggest fetishist practice. This study stemmed from a judicial case where it was fundamental to distinguish between sharp force lesions and insect activity on hair. Methods In order to highlight differences between sharp force lesions and insect feeding activity, different experiments were performed with high power microscopy: hair samples were subjected to several lesions by blunt and sharp force trauma; then samples were used as pabulum for two taxa of insects: the common clothes moth (Tineola bisselliella Lepidoptera, Tineidae) and the carpet beetle (Anthrenus sp., Coleoptera, Dermestidae). Hairs were examined from a macroscopic and microscopic point of view by stereomicroscopy and scanning electron microscopy (SEM): the morphological characteristics of the lesions obtained from the different experimental samples were compared. Results Results show that sharp force trauma produces lesions with regular edges, whereas insects leave concave lesions caused by their “gnawing” activity. These two types of lesions are easily distinguishable from breaking and tearing using SEM. Conclusions This study demonstrates that insect activity leaves very specific indications on hair and sheds some light on different hair lesions that may be found in forensic case