What are the differences between SEM and TEM imaging?
The differences of SEM and TEM imaging:1. Resolution: TEM has much higher resolution than SEM. The current TEM system can inspect in atom level, which is in the range of 1nm or less. But the resolution of SEM is about tens of nm for common materials.2. Information obtained from sample: TEM can show many characteristics of the sample, such as morphology, crystallization, stress or even magnetic domains (holography). But common SEM can only show the morphology of samples.3. Sample preparition: the sample preparition of SEM is much simpler. Many materials could be directed loaded in SEM for inspection. Some insulating materials need additional coating, which can be simply done by PVD. But TEM sample need to be thinned to thickness of 100 nm or less. The thinning procedure is very time consuming. It can be done by mechanical polishing, which takes one day or a few days to prepare a sample. Alternatively, it can be done by focused ion beam (FIB) system in higher resolution. But the cost of a FIB system is even higher than that of a SEM.4. Cost of machine: The cost of TEM is much higher than SEM (two or three times higher)5. Health effect: due to the existence of very high energy electron beam, TEM has more detrimental effect on human health.
Why does TEM have higher resolution than SEM?
I figured I would clear this up. First lets talk about the other two answers, what does TEM stand for again? NOT, tunneling electron microscope, TEM actually is transmission electron microscopy. SEM is scanning electron microscopy.Now how are these two things different? Really the only fundamental difference is how are you looking at the sample. As it would imply transmission "transmits" through the sample, so basically you pass an electron beam through the sample and can measure the relative absorption through different phases. Now for SEM if you look at a basic diagram of an SEM set up you can see the geometry of the system is slightly different, in fact you are no longer transmitting through the sample, but rather you are looking at the emission of secondary electrons that are being emitted from the excitation induced by the electron beam itself! Now this is kind of the cool difference, TEM typically what we will do is microtome the sample, basically get the sample thin enough to transmit. We basically can ignore a sample thickness for SEM since we are reading emission patterns from the surface topography.Why use one versus the other? TEM can get slightly smaller in dimension, but honestly not by that much. Very fancy SEM set ups can measure to roughly 1 nm which is right along the minimum scale for differentiation between phase separated domains. Below this typically corresponds to ordered arrangments of atoms (crystals, exotic hydrogen bonding states... DNA!). Someone who works with this a little more than I can probably get a little more technical about the advantages of one versus the other.Source: I do polymer morphology characterization through x-ray scattering and electron microscopy.
What are the advantages of a light compound microscope over an electronic microscope?
A light compound microscope is not capable of the very high resolution and magnification of an electron microscope. A practical resolution limit is about 0.2 micrometers and a practical maximum magnification of about 1000x. However this covers an awful lot of samples, and there are some definite advantages.It is easier to use than an electron microscope, and certainly cheaper.The images you get are in colour, since you are normally using white light as the illumination source, whereas electron microscopes do not produce images in colour (#1). If you are using a chemical stain to enhance some feature, then you can see the colour of the stain. If you are using a fluorescence microscope then you see the fluorescence in colour.Samples are just placed on the stage in ambient air, so you can view samples either dry or wet, or suspended in a liquid. In a compound microscope, samples are usually mounted on a glass slide and may be under a glass coverslip.You can view some specimens live.If specimens are too thick for the light to penetrate, they may need to be sectioned into thin slices (typically in the range 1 - 10 micrometers), which can then be viewed. In some cases this can be done with a razor blade, or a microtome if you need thinner sections. For a transmission electron microscope, specimens often need to be prepared as very thin slices (typically less than 0.1 micrometer thick), and this can be a much more complicated procedure than for a light microscope, especially for materials and geological samples.In electron microscopes, the samples are placed in a vacuum and are bombarded with a beam of electrons. Therefore, in general, the preparation methods for the specimens that you want to image are more exacting than for light microscopes. However light microscopes are normally very useful for initial examination of specimens before they are prepared for the electron microscope, and even during the preparation procedure.(#1 Some electron microscope images you see on the Web look great in colour but they have been colorised to enhance them — the original images would have been in monochrome.)
If I read 40 pages per day for the next 4 months will I see an improvement in my vocabulary?
You sure will! But if you really want to improve your vocabulary, read so-called English Literature some of the time. This, in the broad sense, includes American Literature at the very least. I don’t want to run through a list of all the English-speaking countries (including India, which has a genuine literature in English), but they would all be on it. The reason I suggest this is because of a basic principle in foreign-language teaching which applies to us native speakers too: the most improvement comes from giving a student what he or she already knows plus alpha (alpha being what the student doesn’t know; it should be a fraction of the book read). When I read my first 19th-century novel on my own, as (in public school terms) a first-year high school student, my vocabulary shot up. It was “Jane Eyre,” and though I was a guy, I came to just love it. But I needed to use a dictionary at first. By the end of the novel, I didn’t need the dictionary. So all reading of decent writing is good for your vocabulary, but something fine and a little challenging (with the plus-alpha factor) is best.
What are some things I can make slides of for a low-resolution (child's) microscope?
There are numerous specimens you can use for this purpose, including (but not restricted to) the following list:Pond water sample (this is a favourite amongst many budding microscopists, as it contains numerous micro-organisms for exploration of the micro-world)Blood Sample (a drop of blood on a slide to allow observation of the red & white blood cells)Cheek cell scrapings [use a blunt toothpick to gently do this, & spread the smear onto a clean glass slide - you may need to stain the cells (with food colouring, etc) as they are transparent under the microscope]Onion epidermis (this allows you to visualize the epidermal cells & is often utilized to provide a first glance into the world of cells)Section of a Leaf - this allows you to explore the stomata on the underside of the leaf, or a transverse section for exploring the inner leaf structure (you’ll need a microtome to section the leaf to such a thickness for this though, while you can find some pretty cheap & handy microtomes on eBay, etc)Pollen grains (from flowers such as Hibiscus, etc)Dust Mite (if you can find it, which is relatively common)Section of a plant stem (e.g. celery)etcThese are just some of the numerous projects you may wish to consider trying out with your microscope to explore the micro-world. Enjoy! :)