Right! Each person, we are living a short time – about 100 year, just a dot in a endless line. Sooner or later, people might disappear, for new creature in the new earth. What we try to do now is trying to extend the very very short time of human-life.
Then, some people may think, why we need to care about such “far” thing? Far? Is it far? Tsunamis, floods, fires, polution are far?

NO! Not at all!

When I was in college, there was a seminar of recycling waste as fuel, well, not only biogas but also other waste, the presenter was a professeur from Japan. He said some people thought to save the world, we might need to back to the old time. However, the fact is, we could never be back to the ancient time, and we never want to, never!

Then what we should do?

“Save the world!”.

Sound hard.

Too hard.

I remember the news on our TV these recent days, many bad things have been happening. Some forests are in danger by the people who are in charged of taking care of them! The beautiful land with river, trees, animal in TN is going (or might be going) to be destroyed to mining the bauxite…

Governments, in general, they are thinking of the future of the countries, of course. But for how far? Some next generations or the long-life of the people, or human.

Or they just want to get as much as possible for their countries in some next generations only?…

But not only government. The awareness of people, it is better, but not enough to save the world.

My family, for example, when I talked about this, they just say, it is a long time. Just live your life. Be a good girl now and then.

Is it all for everything? Then what is the meaning of life?

Obviously, we want to do many things not only for ourselves but for the world. But it looks like we put ourselves at first.

That’s the bad point…

And I am, too… As any people. Usually put myself over others…

…

WISH YOU LUCK ENOUGH TO RECOVER FAST, MOTHER EARTH!

Và vì lý do trên, nên mình sẽ post từ từ, không lấy nguyên một bài của wiki mà lấy từng đoạn, cho đến khi hoàn chỉnh.

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SEM – The scanning electron microscope

From Wikipedia, the free encyclopedia

SEM opened sample chamber

The scanning electron microscope (SEM) is a type of electron microscope that images the sample surface by scanning it with a high-energy beam of electrons in a raster scan pattern. The electrons interact with the atoms that make up the sample producing signals that contain information about the sample’s surface topography, composition and other properties such as electrical conductivity.

The types of signals produced by an SEM include secondary electrons, back scattered electrons (BSE), characteristic x-rays, light (cathodoluminescence), specimen current and transmitted electrons. These types of signal all require specialized detectors for their detection that are not usually all present on a single machine. The signals result from interactions of the electron beam with atoms at or near the surface of the sample. In the most common or standard detection mode, secondary electron imaging or SEI, the SEM can produce very high-resolution images of a sample surface, revealing details about 1 to 5 nm in size. Due to the way these images are created, SEM micrographs have a very large depth of field yielding a characteristic three-dimensional appearance useful for understanding the surface structure of a sample. This is exemplified by the micrograph of pollen shown to the right. A wide range of magnifications is possible, from about x 25 (about equivalent to that of a powerful hand-lens) to about x 250,000, about 250 times the magnification limit of the best light microscopes. Back-scattered electrons (BSE) are beam electrons that are reflected from the sample by elastic scattering. BSE are often used in analytical SEM along with the spectra made from the characteristic x-rays. Because the intensity of the BSE signal is strongly related to the atomic number (Z) of the specimen, BSE images can provide information about the distribution of different elements in the sample. For the same reason BSE imaging can image colloidal gold immuno-labels of 5 or 10 nm diameter, that would otherwise be difficult or impossible to detect in secondary electron images in biological specimens. Characteristic X-rays are emitted when the electron beam removes an inner shell electron from the sample, causing a higher energy electron to fill the shell and release energy. These characteristic x-rays are used to identify the composition and measure the abundance of elements in the sample.

History

The first SEM image was obtained by Max Knoll, who in 1935 obtained an image of silicon steel showing electron channeling contrast.^[1] Further pioneering work on the physical principles of the SEM and beam specimen interactions was performed by Manfred von Ardenne in 1937,^[2][3] who produced a British patent^[4] but never made a practical instrument. The SEM was further developed by Professor Sir Charles Oatley and his postgraduate student Gary Stewart and was first marketed in 1965 by the Cambridge Instrument Company as the “Stereoscan”. The first instrument was delivered to DuPont.

Scanning process and image formation

In a typical SEM, an electron beam is thermionically emitted from an electron gun fitted with a tungsten filament cathode. Tungsten is normally used in thermionic electron guns because it has the highest melting point and lowest vapour pressure of all metals, thereby allowing it to be heated for electron emission, and because of its low cost. Other types of electron emitters include lanthanum hexaboride (LaB₆) cathodes, which can be used in a standard tungsten filament SEM if the vacuum system is upgraded and field emission guns (FEG), which may be of the cold-cathode type using tungsten single crystal emitters or the thermally-assisted Schottky type, using emitters of zirconium oxide.

The electron beam, which typically has an energy ranging from a few hundred eV to 40 keV, is focused by one or two condenser lenses to a spot about 0.4 nm to 5 nm in diameter. The beam passes through pairs of scanning coils or pairs of deflector plates in the electron column, typically in the final lens, which deflect the beam in the x and y axes so that it scans in a raster fashion over a rectangular area of the sample surface.

When the primary electron beam interacts with the sample, the electrons lose energy by repeated random scattering and absorption within a teardrop-shaped volume of the specimen known as the interaction volume, which extends from less than 100 nm to around 5 µm into the surface. The size of the interaction volume depends on the electron’s landing energy, the atomic number of the specimen and the specimen’s density. The energy exchange between the electron beam and the sample results in the reflection of high-energy electrons by elastic scattering, emission of secondary electrons by inelastic scattering and the emission of electromagnetic radiation, each of which can be detected by specialized detectors. The beam current absorbed by the specimen can also be detected and used to create images of the distribution of specimen current. Electronic amplifiers of various types are used to amplify the signals which are displayed as variations in brightness on a cathode ray tube. The raster scanning of the CRT display is synchronised with that of the beam on the specimen in the microscope, and the resulting image is therefore a distribution map of the intensity of the signal being emitted from the scanned area of the specimen. The image may be captured by photography from a high resolution cathode ray tube, but in modern machines is digitally captured and displayed on a computer monitor and saved to a computer’s hard disc.

(to be continued…)

I believe at first, people pass by this blog as my introduce in my Yahoo360 blog. For the reason, the language (you may think) I should write is in Vietnamese, my mother tongue. However, as my aim for this blog is “doc” and “tech”, I would like to use English mostly, or, back and forth between the two languages. Hopely, one day I could open to the third language!

Anyway, welcome you to my blog, and thank you for your time to pass by. This is just the beginning, so there are many things to do. I hope when I start, I could get your comments and ideas on each topics, any ideas, but please do not use so “bad” words (for example: “sh!t” is sometimes fine, but “f**ck” is not welcomed here!).

Alright, I would stop my first entry in this blog here. Hope to be back soon and get your comments soon!

Thanks all,

Trang