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نوع زبان: انگلیسی حجم: 0.16 مگا بایت
نوع فایل: اسلاید پاورپوینت تعداد اسلایدها: 23 صفحه
سطح مطلب: نامشخص پسوند فایل: ppt
گروه موضوعی: زمان استخراج مطلب: 2019/05/15 11:23:23

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عبارات مهم استفاده شده در این مطلب

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., electron, specimen, lecture, iv, unit, beam, transmit, energy, scatter, object, light,

توجه: این مطلب در تاریخ 2019/05/15 11:23:23 به صورت خودکار از فضای وب آشکار توسط موتور جستجوی پاورپوینت جمع آوری شده است و در صورت اعلام عدم رضایت تهیه کننده ی آن، طبق قوانین سایت از روی وب گاه حذف خواهد شد. این مطلب از وب سایت زیر استخراج شده است و مسئولیت انتشار آن با منبع اصلی است.

http://srmuniv.ac.in/openware_d_loads/u9Lec5.ppt

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عبارات پرتکرار و مهم در این اسلاید عبارتند از: ., electron, specimen, lecture, iv, unit, beam, transmit, energy, scatter, object, light,

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مشاهده محتوای متنیِ این اسلاید ppt

lecture ۵ principles of electron microscopy sem and tem unit iv lecture ۵ electron microscopy techniques introduction electron microscopes are scientific instruments that use a beam of highly energetic electrons to examine objects on a very fine scale. the main advantage of electron microscopy is the unusual short wavelength of the electron beams substituted for light energy. the wavelengths of about . ۵ nm increases the resolving power of the instrument to fractions unit iv lecture ۵ topography the surface features of an object or how it looks its texture direct relation between these features and materials properties hardness reflectivity …etc. morphology the shape and size of the particles making up the object direct relation between these structures and materials properties ductility strength reactivity …etc. composition the elements and compounds that the object is composed of and the relative amounts of them direct relationship between composition and materials properties melting point reactivity hardness …etc. crystallographic information. how the atoms are arranged in the object direct relation between these arrangements and materials properties conductivity electrical properties strength …etc. unit iv lecture ۵ types there are two main electron microscopy techniques transmission electron microscopy which essentially looks through a thin slice of a specimen. scanning electron microscopy which looks at the surface of a solid object. unit iv lecture ۵ transmission electron microscope tem working concept tem works much like a slide projector. a projector shines a beam of light through transmits the slide as the light passes through it is affected by the structures and objects on the slide. these effects result in only certain parts of the light beam being transmitted through certain parts of the slide. this transmitted beam is then projected onto the viewing screen forming an enlarged image of the slide. tems work the same way except that they shine a beam of electrons like the light through the specimen like the slide . whatever part is transmitted is projected onto a phosphor screen for the user to see. a more technical explanation of typical tems workings is as follows unit iv lecture ۵ working concept of tem unit iv lecture ۵ the virtual source at the top represents the electron gun producing a stream of monochromatic electrons. this stream is focused to a small thin coherent beam by the use of condenser lenses ۱ and ۲. the first lens usually controlled by the spot size knob largely determines the spot size the general size range of the final spot that strikes the sample. the second lens usually controlled by the intensity or brightness knob actually changes the size of the spot on the sample changing it from a wide dispersed spot to a pinpoint beam. the beam is restricted by the condenser aperture usually user selectable knocking out high angle electrons those far from the optic axis the dotted line down the center the beam strikes the specimen and parts of it are transmitted unit iv lecture ۵ this transmitted portion is focused by the objective lens into an image the image is passed down the column through the projector lenses being enlarged all the way. the image strikes the phosphor image screen and light is generated allowing the user to see the image unit iv lecture ۵ specimen interactions and utilization unscattered electrons source incident electrons which are transmitted through the thin specimen without any interaction occurring inside the specimen. utilization the transmission of unscattered electrons is inversely proportional to the specimen thickness. areas of the specimen that are thicker will have fewer transmitted unscattered electrons and so will appear darker conversely the thinner areas will have more transmitted and thus will appear lighter. unit iv lecture ۵ elasticity scattered electrons source incident electrons that are scattered deflected from their original path by atoms in the specimen in an elastic fashion no loss of energy . these scattered electrons are then transmitted through the remaining portions of the specimen. utilization all electrons follow bragg s law and thus are scattered according to wavelength ۲ space between the atoms in the specimen sin angle of scattering . all incident electrons have the same energy thus wavelength and enter the specimen normal to its surface unit iv lecture ۵ these similar angle scattered electrons can be collated using magnetic lenses to form a pattern of spots each spot corresponding to a specific atomic spacing a plane . this pattern can then yield information about the orientation atomic arrangements and phases present in the area being examined. unit iv lecture ۵ inelastically scattered electrons source incident electrons that interact with specimen atoms in a inelastic fashion loosing energy during the interaction. these electrons are then transmitted trough the rest of the specimen utilization all electrons follow bragg s law and thus are scattered according to wavelength ۲ space between the atoms in the specimen sin angle of scattering . all incident electrons have the same energy thus wavelength and enter the specimen normal to its surface unit iv lecture ۵ inelastically scattered electrons can be utilized two ways electron energy loss spectroscopy the inelastic loss of energy by the incident electrons is characteristic of the elements that were interacted with. these energies are unique to each bonding state of each element and thus can be used to extract both compositional and bonding i.e. oxidation state information on the specimen region being examined. kakuchi bands bands of alternating light and dark lines that are formed by inelastic scattering interactions that are related to atomic spacings in the specimen. these bands can be either measured their width is inversely proportional to atomic spacing or followed like …

کلمات کلیدی پرکاربرد در این اسلاید پاورپوینت: ., electron, specimen, lecture, iv, unit, beam, transmit, energy, scatter, object, light,

این فایل پاورپوینت شامل 23 اسلاید و به زبان انگلیسی و حجم آن 0.16 مگا بایت است. نوع قالب فایل ppt بوده که با این لینک قابل دانلود است. این مطلب برگرفته از سایت زیر است و مسئولیت انتشار آن با منبع اصلی می باشد که در تاریخ 2019/05/15 11:23:23 استخراج شده است.

http://srmuniv.ac.in/openware_d_loads/u9Lec5.ppt

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