scanning tunnelling microscope

7/21/2019 SCANNING TUNNELLING MICROSCOPE

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Merve Ayvaz

Boazii University4.05.2011

SCANNING TUNELINGMICROSCOPE (STM)

ChE 592

1


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STMSTM can produce atomic resoution ima!es o" metaic

or semiconductor sur"aces #$ making ee!trons

t"nne #et$een a metai! %ro#e &the ti%' an(the s"r)a!eunder!oin! t%e scan (t%e sampe)&

T%e tip is attac%ed to pie'oeectric cr$stas %ic%it% t%e %ep o" eectronic "eed#ac* contro canposition t%e tip precise$ reati+e to t%e sampe

#eneat% it&

,urin! t%e scan t%e tip is ordinari$ *ept #eteen -and 1-.A aa$ "rom t%e sampe&

Si (111) ima!e#ond en!%t #ondan!e

*ei(en University+ ,nstit"teo) -h si!s

/


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IN0ENTION O STMT%e in+ention o" t%e topo!ra2ner #$ 3oun! et a& in

145/&

Eectron tunnein! e6periments reported #$ Tea!uein 1457&

Topo!ra2ner as a de+ice t%at used a pie'oeectric

dri+er to scan a sur"ace %ose pro#e restedappro6imate$ 188nm a#o+e t%e sampe sur"ace&Usin! a 2ed emission current induced #$ app$in!a positi+e +ota!e o" a "e *0 to t%e sampe t%etopo!ra2ner coud produce a sur"ace ima!e it% a

atera resoution o" 988nm&Tea!ue:s e6periments demonstrated +acuum

tunnein! #eteen to !od eectrodes& Tea!ue:sapparatus aoed 2ne ad;ustment o" t%e !apidt% #ut did not %a+e a raster scan mec%anism&



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IN0ENTION O STM=inni! and Ro%rer com#ined t%ese tec%noo!ies

to create t%e STM&


9


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>o STM or*s=asis p%enomenon is ?uantum mec%anica

tunnein!&A +er$ sma current i @o #eteen a s%arp

meta pro#e tip and t%e sur"ace o" aneectrica$ conducti+e materia&

T%e tip is positioned ;ust a "e nanometersaa$ "rom t%e sampe sur"ace i&e& no contactis made #eteen t%e tip and t%e sampe&

(1) Pie'oscanner(/) Metaic tip(


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"ant"m Me!hani!a "nneing

Metas are not touc%in! no current i @o

t%rou!% t%e #atter$&Eectrons can mo+e +er$ easi$ and ?uic*$ "rom

one end o" t%e meta to t%e ot%er&

T%e eectrons are "ree to mo+e around t%e meta

#ut cannot ea+e it&University o) 3is!onsinB


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%en t%e metas are #rou!%t to!et%er #ut are not

?uite touc%in! a sma eectric current can #emeasured&

T%e current !ets ar!er t%e coser t%e metas are#rou!%t to!et%er unti it reac%es its ma6imum

+aue %en t%e metas are touc%in!&T%e metas must #e on$ 18 an!stroms apart to

produce detecta#e tunnein! current&


University o) 3is!onsin5


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An eectronDs ener!$ can #e spit into to

contri#utions *inetic ener!$ and potentia ener!$&Finetic ener!$ (t%e ener!$ o" motion) is ar!e "or

eectrons mo+in! "ast and sma "or eectronsmo+in! so$&

Potentia ener!$ is t%e ener!$ a+aia#e "or aneectron to con+ert to *inetic ener!$ i" it mo+esaon! an eectric 2ed&

Lar!e potentia ener!$ #eteen t%e to metas

tends to *eep eectrons inside t%eir respecti+emeta&



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Eectrons %a+e #ot% a partice and a a+e

nature&So e s%oud picture t%e eectron as a coud&

%en t%e coud coides it% t%e #arrier part o"

t%e coud ma$ penetrate it&




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One o" t%e metas is t%e sampe #ein! ima!ed(sampe) and t%e ot%er meta is t%e pro#e (tip)&

A o" t%e tunnein! eectrons i pass t%rou!%atom at t%e end&

T%is "eature eads to t%e atomic resoutioncapa#iities o" t%e microscope&




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=ardeen:s Tunnein! T%eor$

=ardeen:s tunnein! t%eor$ as pu#is%ed in14B1 and appied to t%e scannin! tunnein!microscope in 147< #$ Terso and >amann&

T%e tip and sampe are suHcient$ "ar apart

T%e #ias (potentia dierence #eteen t%e tipand t%e sampe) is o enou!%&

C. . Chen.+ ,ntro("!tion to /!anning11


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T%e space containin! t%e STM is di+ided into tore!ions the sam%e region+ an( the ti% region&


Ass"m%tion 1T%e eectroneectroninteraction can #e

i!nored&

C. . Chen.+ ,ntro("!tion to /!anning1/


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Considerin! tip and sampe in isoation rat%er t%an

as parts o" t%e STM in order to estimate t%ecurrent t%rou!% t%e tipsampe ;unction&

0tip(r) 8 "or r in t%e sampe re!ion

0sam(r) 8 "or r in t%e tip re!ion


C. . Chen.+ ,ntro("!tion to /!anning1amann ormuaTerso and >amann deduced a use"u rueo"t%um#

t%e tunnein! current is proportiona to t%e part o"t%e eectronic densit$ at t%e center o" t%e tip due tot%e sampe a+e"unctions at t%e ?uasiermi ener!$&

C. . Chen.+ ,ntro("!tion to /!anning/8


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>amann T%eor$

T%e tip (ar#itrar$ s%ape) is assumed to %a+e aoca sp%erica radius o" cur+ature R& T%enearest tipsampe distance is d&

Predominant tip state in tunnein! is sor#ita

C. . Chen.+ ,ntro("!tion to /!anning/1


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Instrumentation/M in!"(e6

a s%arp pro#in! tipa pie'oeectricscannin! unita coarse positionin!

unita +i#ration isoationsta!ea set o" eectronics

C. . Chen.+ ,ntro("!tion to /!anning//


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TipPreparation

Ma -an!k ,nstit"te )or /oi( /tate/

scanning tunnelling microscope

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