The most common imaging mode collects low-energy (<50 eV) secondary electrons that are ejected from the k-shell of the specimen atoms by inelastic scattering interactions with beam electrons. Due to their low energy, these electrons originate within a few nanometers from the sample surface. The electrons are detected by an Everhart-Thornley detector, which is a type of scintillator-photomultiplier system. The secondary electrons are first collected by attracting them towards an electrically biased grid at about +400 V, and then further accelerated towards a phosphor or scintillator positively biased to about +2,000 V. The accelerated secondary electrons are now sufficiently energetic to cause the scintillator to emit flashes of light (cathodoluminescence), which are conducted to a photomultiplier outside the SEM column via a light pipe and a window in the wall of the specimen chamber. The amplified electrical signal output by the photomultiplier is displayed as a two-dimensional intensity distribution that can be viewed and photographed on an analogue video display, or subjected to analog-to-digital conversion and displayed and saved as a digital image. This process relies on a raster-scanned primary beam. The brightness of the signal depends on the number of secondary electrons reaching the detector. If the beam enters the sample perpendicular to the surface, then the activated region is uniform about the axis of the beam and a certain number of electrons "escape" from within the sample. As the angle of incidence increases, the interaction volume increases and the "escape" distance of one side of the beam decreases, resulting in more secondary electrons being emitted from the sample. Thus steep surfaces and edges tend to be brighter than flat surfaces, which results in images with a well-defined, three-dimensional appearance. Using the signal of secondary electrons image resolution less than 0.5 nm is possible.
Both use keyword research to uncover popular search terms. The first step for both SEM and SEO is performing keyword research to identify the best keywords to target. The research includes looking at keyword popularity to determine the top keywords or buying keywords that your ideal audience searches for. It also includes looking at keyword competition to see what other brands are targeting the same keywords and determining what you will need to do to compete with those other companies.
Look at your short- and long-term goals to choose whether to focus on organic or paid search (or both). It takes time to improve your organic search rankings, but you can launch a paid search campaign tomorrow. However, there are other considerations: the amount of traffic you need, your budget, and your marketing objectives. Once you’ve reviewed the pros and cons, you can select the search strategy that’s right for you. http://youtu.be/7bNPg8UbhaE