scanning tunneling microscopy biao husces.phys.utk.edu/~dagotto/condensed/hw_2007/672 stm.pdf ·...
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672 Advanced Solid State Physics
Scanning Tunneling Microscopy
Biao Hu
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Outline:
1. Introduction to STM
2. STM principle & working modes
3. STM application & extension
4. STM in our group
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1. Introduction to STM
I. Invented by G.Binnig & H.Rohrer in 1982
II. Richard Feynman’s address: “There’s Plenty of Room at the Bottom” at Caltech in 1959
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Red blood cells(~7-8 µm)
DNA~2-1/2 nm diameter
Things NaturalThings Natural
Fly ash~ 10-20 µm
Atoms of siliconspacing ~tenths of nm
Human hair~ 60-120 µm wide
Ant~ 5 mm
Dust mite
200 µm
ATP synthase
~10 nm diameter
Mic
row
orld
10-2 m
10-3 m
10-4 m
10-5 m
10-6 m
10-7 m
10-8 m
10-9 m
10-10 m
Nan
owor
ld
0.1 nm
1 nanometer (nm)
0.01 µm10 nm
0.1 µm100 nm
1 micrometer (µm)
0.01 mm10 µm
0.1 mm100 µm
1 millimeter (mm)
1 cm10 mm
Visib
le
1,000 nanometers =
Infra
red
Ultra
violet
Soft
x-ra
yMi
crow
ave
1,000,000 nanometers =
Office of Basic Energy SciencesThe Scale of ThingsThe Scale of Things
Things ManmadeThings ManmadeHead of a pin
1-2 mm
Quantum corral of 48 iron atoms on copper surfacepositioned one at a time with an STM tip
Corral diameter 14 nm
Nanotube electrode
Zone plate x-ray “lens”Outer ring spacing ~35 nm
MicroElectroMechanical(MEMS) devices10 -100 µm wide
Carbon nanotube~1.3 nm diameter
Carbon buckyball
~1 nm diameter
Self-assembled,Nature-inspired structureMany 10s of nm
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Scanning Tunneling MicroscopyScanning Tunneling Microscopy
Open Open ““doordoor”” for for nanosciencenanoscience
Nobel PrizeNobel Prize
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2. STM principle & working modesi: Principle:
Fig.1
The wave function of tip and sample overlap.
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In the classically forbidden region:
( ) ( ) ( )⎥⎥⎦
⎤
⎢⎢⎣
⎡ −−=
h
zEmz
φψψ
2exp0 (1)
The tunneling current:
( ) ( ) ( ) zFsFst eEV
zEmEVI φρ
φρ 025.12
2exp −∝⎥⎥⎦
⎤
⎢⎢⎣
⎡ −−∝
h
(2)eV5=φIn gold, , current drops an order of magnitude, gap is changed by
one Å
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ii: Working modes:
••idea for STM, like idea for STM, like ““fingerfinger””, to , to ““touchtouch”” the atomsthe atoms
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(a) Constant current mode
Suited tip; Actuator; Controller.
Vibrational isolation;
Fig. 2
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Atomic sharp Atomic sharp tiptip
electronelectrontunnelingtunneling
piezoelectricspiezoelectrics::move with voltagemove with voltage
STM can image individual atoms!
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(b) Constant height mode
Measure the tunneling current while scanning on a given, smooth x-y-z contour.
The z-position (output of feedback loop) is measured at discrete (x, y)-positions.
line-scan image, grey-scale image or color encoded image.
Observe dynamical processes, but increase the risk of crashing the tip
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3. STM application & extension(a) Reconstruction in Si(111)
The rhombohedral surface unit cell are the corner hole and the 12 maxima, the adatoms.
G. Binnig, H. Rohrer, Ch. Gerber, and E. Weibel, Phys. Rev. Lett. 50, 120 (1983)
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Si(111) surfaceSi(111) surface--7x7 reconstruction7x7 reconstruction
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(b) DNA
Fig. a, Unsmoothed, unfiltered plane-subtracted STM image of DNA ~80x120 Åb. Model of the Van der Waals surface of A-DNA derived from X-ray crystallographic data, scaled to a.
Robert J. Driscoll, Michael G. Youngquist & John D. Baldeschwieler Nature 346294-296 (1990)
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(c) Atom Manipulation and Surface Standing Wave(c) Atom Manipulation and Surface Standing Wave
Quantum Corral of 48 iron atoms on copper surfaceQuantum Corral of 48 iron atoms on copper surfacepositioned one at a time with an STM tip (positioned one at a time with an STM tip (corral diameter 14 nm)corral diameter 14 nm)
G. Binnig, H. Rohrer Rev. Mod. Phys. 71, 324 (1999)
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(d) STM extension
scanning near-field optical microscope (SNOM),
atomic force microscope (AFM),
Maxwell stress microscopy,
scanning electrochemical microscopy et. al.
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4.STM in our groupRecent work:Surface reconstruction of TiO2 (110) by Ti interstitials
STM image of a strand (1.2V; 0.5nA) with the height profiles across (left, dotted line) and along (right) the line defect.
K. T. Park, M. H. Pan, V. Meunier, and E. W. Plummer, Phys. Rev. Lett. 96, 226105 (2006)
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• Sr2RuO4: layered perovskite without copper that exhibits superconductivity
(A)STM image of a 4 by 4 surface area showing extremely large terraces and steps.
(B)Height along the line scan shown in the STM image.
(C)Ball model of the bulk unit cell of Sr2RuO4. Red, strontium; blue, oxygen; and green, ruthenium (in the center of the octahedron).
R. Matzdorf, Z. Fang, Ismail, Jiandi Zhang, T. Kimura, Y. Tokura, K. Terakura, and E. W. Plummer, Science 289, 746 (2000)
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UT STM (SERF 101-E)
mµ
Scan range:xy :12 x12
z: 1.5
Resolution:xy: 0.1nmz: 0.01nm
mµ
mµmµ
Frontview
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Sample stage
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Electronics
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STM scanner
ApplicationsSingle atom or molecule spectroscopy. Atomic resolved spectroscopy maps. The temperature and magnetic field range to study the quantum response of nano-objects. Optical access to the sample in the magnetic field for probing and exciting atoms or molecules.
Low Temperature, High Field STMScanning Tunneling Microscope with extreme stability under extreme conditions
Isolated concrete block with pit
Acoustic isolation room
Dewar / Magnet
Active vibrationisolation
Growth Chamber
ManipulatorAnalysis chamber
Transfer Chamber
Single molecule vibrational spectroscopy: CC22HH22, C, C22DD22Science 280, 1732 (1998)------Stipe and Ho
1 K Stage
300 mKStage
Sample Cleaver
STM Head
Rotation Stage
He3 Pot
He3 Condensor He4 Pot
Heat Switches
Tip
Triangular sapphire rod
Sample Holder
Tube scannerShear stacks
Sample
A CNMS partner instrument built by ORNL, The University of Tennessee, and The University of Houston
Transfer chamber
300 mKstage
1 K stage
Rotating STM
Samplecleaver
Scientific DriversAtomically-resolved topography
and spectroscopy mapsQuantum response at low T and High BReal Space---K space
CapabilitiesLow T - 300 mKHigh B - 9 TeslaSTM rotates in magnetic fieldCryogenic UHV cleavingSample Fabrication in UHV
Nature 415, 412 (2002)– Lang and Davis
Electronic inhomogeneity: BiBi22SrSr22CaCuCaCu22OO8+8+δδ
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Thanks!