Qhov zoo ntawm Electron Microscopy vs. Light Microscopy
Electron microscope optical microscope imaging txoj cai zoo sib xws thiab qhov sib txawv
Electron microscope yog ib qho cuab yeej uas hloov lub teeb beam thiab optical lens nrog electron beam thiab electron lens raws li lub hauv paus ntsiab lus ntawm electron optics, kom cov qauv zoo ntawm cov teeb meem tuaj yeem pom nyob rau hauv qhov loj heev.
Kev daws lub zog ntawm lub tshuab ntsuas hluav taws xob yog qhia los ntawm qhov deb me me ntawm ob lub ntsiab lus uas nws tuaj yeem daws tau. Hauv xyoo 1970s, kis tau tus mob electron microscopes muaj kev daws teeb meem ntawm 0.3 nanometers (lub qhov muag tib neeg muaj kev daws teeb meem txog 0.1 millimeters). Tam sim no qhov siab tshaj plaws magnification ntawm electron microscope yog ntau tshaj 3 lab lub sij hawm, thiab qhov siab tshaj plaws magnification ntawm optical microscope yog hais txog 2000 lub sij hawm, yog li cov atoms ntawm tej yam hnyav hlau thiab cov txheej txheem zoo atomic lattice nyob rau hauv crystals yuav ncaj qha soj ntsuam los ntawm electron microscope.
Nyob rau hauv 1931, Knorr-Bremse thiab Ruska nyob rau hauv lub teb chaws Yelemees tau hloov ib tug high-voltage oscilloscope nrog ib tug txias-cathode tawm electron qhov chaw thiab peb electron lo ntsiab muag, thiab tau ib tug magnified duab ntau tshaj kaum lub sij hawm, uas tau lees tias muaj peev xwm ntawm magnifying imaging los ntawm ib tug electron microscope. . . Xyoo 1932, tom qab Ruska txoj kev txhim kho, kev daws teeb meem ntawm lub tshuab hluav taws xob hluav taws xob tau mus txog 50 nanometers, uas yog kwv yees li kaum npaug ntawm lub zog daws teeb meem ntawm lub tshuab ntsuas qhov muag thaum lub sijhawm ntawd, yog li lub tshuab hluav taws xob hluav taws xob pib nyiam tib neeg cov kev xav.
Hauv xyoo 1940s, Hill hauv Tebchaws Meskas tau them nyiaj rau kev sib hloov asymmetry ntawm lub lens electron nrog astigmatist, uas ua rau muaj kev cuam tshuam tshiab hauv kev daws lub zog ntawm lub tshuab ntsuas hluav taws xob thiab maj mam mus txog qib niaj hnub. Nyob rau hauv Tuam Tshoj, ib tug kis tau tus mob electron microscope nrog ib tug daws teeb meem ntawm 3 nanometers tau ntse tsim nyob rau hauv 1958, thiab ib tug loj-scale electron microscope nrog ib tug daws teeb meem ntawm 0.3 nanometers tau ua nyob rau hauv 1979.
Txawm hais tias qhov kev daws teeb meem ntawm electron microscopes yog qhov zoo dua li ntawm optical microscopes, nws yog ib qho nyuaj rau kev soj ntsuam cov kab mob uas muaj sia nyob vim tias electron microscopes yuav tsum ua haujlwm nyob rau hauv lub tshuab nqus tsev, thiab irradiation ntawm electron beams kuj yuav ua rau hluav taws xob puas tsuaj rau cov qauv lom. Lwm yam teeb meem, xws li kev txhim kho qhov ci ntawm rab phom electron thiab qhov zoo ntawm lub lens electron, kuj yuav tsum tau kawm ntxiv.
Lub zog daws teeb meem yog qhov taw qhia tseem ceeb ntawm lub tshuab hluav taws xob hluav taws xob, uas cuam tshuam nrog qhov xwm txheej ntawm lub khob hliav qab lub kaum sab xis thiab lub wavelength ntawm lub teeb hluav taws xob hla ntawm cov qauv. Lub wavelength ntawm pom lub teeb yog li ntawm 300 mus rau 700 nanometers, thaum lub wavelength ntawm lub electron beam muaj feem xyuam rau lub accelerating voltage. Thaum qhov nrawm nrawm yog 50-100 kV, lub teeb hluav taws xob hluav taws xob wavelength yog li 0.0053-0.0037 nm. Txij li thaum lub wavelength ntawm lub electron beam yog ntau me dua lub wavelength ntawm pom lub teeb, txawm yog hais tias lub khob hliav qab ntawm lub electron beam tsuas yog 1 feem pua ntawm cov optical microscope, lub zog daws teeb meem ntawm ib tug electron microscope tseem nyob deb superior rau qhov ntawd. ntawm ib qho optical microscope.
Lub tshuab ntsuas hluav taws xob muaj peb ntu: lub lens raj, lub tshuab nqus tsev thiab lub hwj huam mov txee. Lub lens chim feem ntau suav nrog cov phom hluav taws xob, lub lens electron, cov qauv tuav, fluorescent screen thiab lub koob yees duab mechanism, uas feem ntau yog sib sau ua ke rau hauv lub tog raj kheej los ntawm sab saum toj mus rau hauv qab; lub tshuab nqus tsev yog tsim los ntawm cov tshuab nqus tsev twj tso kua mis, diffusion twj tso kua mis thiab lub tshuab nqus tsev vacuum, thiab lwm yam. Lub raj xa hluav taws xob txuas nrog lub lens chim; lub hwj chim mov txee yog tsim los ntawm high-voltage generator, ib tug excitation tam sim no stabilizer thiab ntau yam kev hloov kho thiab tswj units.
Lub lens electron yog ib qho tseem ceeb ntawm electron microscope chim. Nws siv lub spatial electric teb los yog magnetic teb symmetrical rau lub axis ntawm lub chim rau khoov lub electron trajectory rau lub axis los ua kom pom tseeb. Nws muaj nuj nqi zoo ib yam li cov iav convex lens kom pom cov nqaj, yog li nws hu ua electron lens. . Niaj hnub nimno electron microscopes feem ntau siv electromagnetic lo ntsiab muag, uas tsom cov electrons los ntawm ib tug muaj zog magnetic teb generated los ntawm ib tug ruaj khov DC excitation tam sim no los ntawm ib tug coil nrog ib tug ncej khau.
Cov phom hluav taws xob yog cov khoom siv los ntawm tungsten filament kub cathode, kab sib chaws thiab cathode. Nws tuaj yeem tso tawm thiab tsim cov kab hluav taws xob nrog lub nrawm nrawm, yog li qhov ruaj khov ntawm qhov nrawm nrawm tsis tsawg dua 1/10,000.
Electron microscopes tuaj yeem muab faib ua kis tau tus mob electron microscopes, scanning electron microscopes, reflection electron microscopes thiab emission electron microscopes raws li lawv cov qauv thiab siv. Kev xa cov tshuab hluav taws xob siv hluav taws xob feem ntau siv los soj ntsuam cov khoom siv zoo uas tsis tuaj yeem paub qhov txawv ntawm cov tshuab microscopes; scanning electron microscopes yog siv los soj ntsuam cov morphology ntawm cov khoom nto, thiab tseem tuaj yeem ua ke nrog X-ray diffractometers lossis electron zog spectrometers los tsim electrons. Microprobes rau kev tsom xam ntawm cov khoom muaj pes tsawg leeg; Emission Electron Microscopy rau kev kawm ntawm tus kheej-emitting electron nto.
Qhov projection electron microscope muaj npe tom qab lub teeb hluav taws xob nkag mus rau cov qauv thiab tom qab ntawd siv lub lens electron los ua duab thiab nthuav dav. Nws txoj kev kho qhov muag zoo ib yam li lub tshuab kho qhov muag. Hauv lub tshuab ntsuas hluav taws xob no, qhov sib piv ntawm cov duab cov ntsiab lus yog tsim los ntawm kev tawg ntawm cov kab hluav taws xob los ntawm cov atoms ntawm cov qauv. thinner los yog tsawg dua qhov chaw ntawm cov qauv, cov kab hluav taws xob hluav taws xob tawg tsawg dua, yog li cov hluav taws xob ntau dhau los ntawm lub hom phiaj aperture, koom nrog hauv cov duab, thiab zoo li ci dua hauv daim duab. Conversely, thicker los yog denser qhov chaw ntawm cov qauv tshwm darker nyob rau hauv daim duab. Yog hais tias tus qauv yog tuab heev los yog tuab heev, qhov sib piv ntawm daim duab yuav deteriorate los yog txawm yuav puas los yog puas los ntawm absorbing lub zog ntawm lub electron beam.
Sab saum toj ntawm lub tshuab hluav taws xob xa hluav taws xob lub tshuab hluav taws xob yog lub phom hluav taws xob, cov khoom siv hluav taws xob tau tawm los ntawm tungsten filament kub cathode, dhau los ntawm lub laser, thiab ob lub condenser lo ntsiab muag tsom rau lub teeb hluav taws xob. Tom qab dhau los ntawm cov qauv, cov kab hluav taws xob tau teeb tsa rau ntawm daim iav nruab nrab los ntawm lub hom phiaj lens, thiab tom qab ntawd nthuav tawm cov kauj ruam dhau los ntawm daim iav nruab nrab thiab daim iav projection, thiab tom qab ntawd muab duab rau ntawm lub vijtsam fluorescent lossis cov duab thaij duab qhuav.
Daim iav nruab nrab feem ntau yog kho qhov excitation tam sim no, thiab qhov magnification tuaj yeem hloov pauv tsis tu ncua los ntawm kaum tawm mus rau ntau pua txhiab zaus; los ntawm kev hloov lub focal ntev ntawm daim iav nruab nrab, cov duab electron microscope thiab electron diffraction dluab tuaj yeem tau txais ntawm qhov me me ntawm tib cov qauv. . Txhawm rau kawm cov qauv hlau tuab dua, Fab Kis Dulos Electron Optics Laboratory tau tsim lub tshuab hluav taws xob ultra-high voltage electron microscope nrog qhov nrawm nrawm ntawm 3500 kV. Scanning Electron Microscope Structure Schematic
Lub teeb hluav taws xob ntawm lub tshuab hluav taws xob scanning tsis dhau los ntawm cov qauv, tab sis tsuas yog ntsuas qhov saum npoo ntawm cov qauv kom ua rau cov hluav taws xob thib ob. Ib tug siv lead ua scintillation tso rau ib sab ntawm cov qauv tau txais cov khoom siv hluav taws xob thib ob thiab hloov kho qhov siv hluav taws xob ntawm lub teeb duab raj tom qab kev nthuav dav, yog li hloov qhov ci ntawm qhov screen ntawm lub raj duab. Lub deflection yoke ntawm daim duab tube khaws cia synchronously nrog lub electron beam ntawm tus qauv nto, yog li ntawd lub fluorescent screen ntawm daim duab raj qhia cov duab topographic ntawm tus qauv nto, uas yog zoo ib yam li lub hauv paus ntsiab lus ua hauj lwm ntawm industrial TV.
Qhov kev daws teeb meem ntawm lub tshuab ntsuas hluav taws xob ntsuas hluav taws xob feem ntau yog txiav txim siab los ntawm txoj kab uas hla ntawm lub teeb hluav taws xob ntawm qhov chaw ntawm tus qauv. Qhov kev nthuav dav yog qhov piv ntawm qhov ntsuas amplitude ntawm daim duab raj mus rau qhov ntsuas amplitude ntawm tus qauv, uas tuaj yeem hloov pauv tsis tu ncua los ntawm kaum tawm mus rau ntau pua txhiab zaus. Scanning electron microscope tsis xav tau cov qauv nyias nyias; daim duab muaj zog peb-dimensional nyhuv; Nws tuaj yeem txheeb xyuas qhov sib xyaw ntawm cov teeb meem siv cov ntaub ntawv xws li cov khoom siv hluav taws xob thib ob, cov hluav taws xob nqus hluav taws xob thiab X-rays tsim los ntawm kev sib cuam tshuam ntawm cov kab hluav taws xob nrog cov teeb meem.
Cov phom electron thiab condenser ntawm scanning electron microscope yog roughly tib yam li cov kis tau tus mob electron microscope, tab sis nyob rau hauv thiaj li yuav ua kom lub electron beam thinner, lub hom phiaj lens thiab ib tug astigmatist yog ntxiv nyob rau hauv lub condenser, thiab ob pawg ntawm scanning electrons. uas yog perpendicular rau ib leeg yog ntsia rau hauv lub hom phiaj lens. coil. Cov qauv chamber nyob rau hauv lub hom phiaj lens tsev cov qauv theem uas tuaj yeem txav tau, tig thiab tilted.
