Microsoft PowerPoint - Short-SurfPhys2018-2-Structures-.ppt []Nanoscience in Nobel Prize Atomic Arrangements at Surfaces
Scanning Tunneling Microscopy, Electron Diffraction
Surface Electronic States
Surface states Rashba Effect
Topological Surface States
Space-Charge-Layer Transport and Surface-State Transport
Atomic-Layer Superconductivity

φφφ
Surface Tension (N/m) Force, trying to shrink, per unit length at the edge of surface
Surface Energy (J/m2) Energy necessary to create surface of unit area
← Attractive force among atoms and molecules
Surface tension and Balance
cos/ 0 oss
φ=0°wetting φ0° hydrophilic φ>0°dewetting φ> 90° hydrophobic
s Young(-Dupre) Formula
0 Surface energy (tension) of adsorbate
0/S Interface energy between Substrate
Contact angle φ and adsorbate
Substrate
Island
1×1 7×7 1×1 Truncated (Ideal) Surface 7×7 Surface Superstructure (most stable)
diamond Unit cell of diamond lattice
Decrease in number of dangling bonds49→13 → Decrease in surface energy (stabilized
1x1unit cell) Dangling Bonds (Broken Bonds)
Kunio Takayanagi (TIT) 1985
Si(111) Crystal Surface
Pelz & K
©JEOL
Hamers, et al., Phys. Rev. B34 (1986) 5343
STM Image of Si(001)-2×1 Clean Surface Atomic Structure of Si(001)-2×1 Clean Surface
dimer ⇒ ⇒
Ag Adsorption on Si(111)-7×7 Surface
Si(111)-√3×√3-Ag Surface Superstructure
Honeycomb-Chained Triangle (HCT) Structre Toshio Takahashi (ISSP)
- No dangling bonds - Atomically flat - Two-dimensional metal

ev. B 59, 2035 (1999).
Ripples in electron sea, free-electron-like statElectron Standing Wave
S. L. Surnev, et. al. A. A. Sarranin, et. al. S. Takeda, et al.
Si(111) Indium-adsorbed Si(111) surfaces
√7×√3
×√3×√3
Charge-density wave

Wavelength of Electron
de Broglie’s formula
100 V 1.23 1.23 500 V 0.548 0.548
1 kV 0.388 0.388 5 kV 0.173 0.173
10 kV 0.123 0.122 50 kV 0.0548 0.0535
100 kV 0.0388 0.0369 500 kV 0.0173 0.0131
Acc. Voltage λ λ
Atomic-Scale
m peV 2
"for his discovery of the wave nature of electrons “
Prince Louis-Victor Pierre Raymond de Broglie France
Sorbonne University, Institut Henri Poincaré, Paris, France
b. 1892 d. 1987
( )
→

The Nobel Prize in Physics 1915 “for their services in the analysis of crystal structure by means of X-rays”
Sir William Henry Bragg (1862-1942)
William Lawrence Bragg (1890-1971)
The Nobel Prize in Physics 1914 “for his discovery of the diffraction of X-rays by crystals”
Max von Laue (1879-1960)
nd sin2
First Electron Diffraction – Davisson & Germer LEED 75 eV C. Davisson and L. H. Germer, Phys. Rev. 30, 705-740 (1927)
1937 Nobel Prize in Physics Experimental discovery of diffraction of electrons by crystals
Ni Poly-crystal
Ni Single-crystal
30 cm
Au Thin Film :TED
e-
Electron Diffraction by Seishi Kikuchi TED of Mica Thin Film
Discharge Tube
Mag. Field



E10 keV → Grazing Incidence →Forward
Scattering TED Transmission Electron Diffraction
E100 keV → (10 nm ) Thin film specimen → Forward Scattering
LEED Low-Energy Electron Diffraction
E100 eV → Normal Incidence
→ Backscattering
Thin film specimen
Fundamental Spots (Diffraction spots from
bulk crystal)
TED Takayanagi LEED Ino
Si(111)7x7STM
Electron Beam Source –Thermal Electron Gun & Field-Emission Electron Gun-
Thermal EG 1901 Richardson
Field-Emission EG 1968 Crewe Field Emission Tip (W)
Virtual Source 100
Tunneling
Plane wave is impossibleeikz

(μm) 20 0.01 (eV) 2 0.3 at 100 keV 5×105 5 ×108
(A/cm2/st)
l (μm) 0.2 1.3 W (μm) 0.02 0.6
() 2 60
Longitudinal coherence length
Transverse coherence length
At RT
At 440
Melting and Crystallization of Al (20 ML) on Si(111)-7×7
RT deposition: Epitaxial 3D Al growth
Heating to melt Al
Cooling to re-crystalize Al Heating again to re-orient micro crystal Al
Courtesy by Yoshimi Horio


⇒

⇒
hakk 20
Procedure of Structure Analysis: Trial and Error (1) Measure the intensity of each diffraction spot
(2) Assume a model of the atomic arrangement in the unit cell.
(3) Calculate the potential from the model. (4) Fourier transform the to obtain
the crystal structure factor . (5) Compare the calculated with
the measured spot intensity . (6) If they do not agree with each other,
modify the model, and repeat the process (2)-(5) until a satisfactory agreement.
rV
kF
kI
TED Analysis of Si(111)-7x7 Surface Superstructure by Takayanagi etal. Proposal of Structure
Proposed Models for Si(111)-7x7 Surface Superstructure
E. G. McRae, Phys. Rev. B 28, 2305 (1983).
D. J. Chadi, Surf. Sci. 99, 1 (1980).
F. J. Himpsel, Phys. Rev. B 27, 7782 (1983).
W. Moench, Surf. Sci. 86, 672 (1979).
Hatched atoms; raised atoms
Rocking RHEEDSi(111)-√3×√3-Ga
Hanada, T., Daimon, H., and Ino, S: Phys. Rev. B 51:13320 (1993).
In te
n si
T. Shirai, et al., Phys. Rev. B 89, 241403(R) (2014)
Si(111)-7x7 ⇔ 1x1 at 830
864STM

7x7
“1x1”
S. Kitamura et al., Nature 351, 215 (1991). K. Miki et al., Ultramicroscopy 42-44, 851 (1992).
800
S. Ino: JJAP 16, 891 (1977) Si(111)-7x7 ⇔ 1x1 ; 1
S. Hasegawa, et al., Phys. Rev. B 47, 9903 (1993). Phase Transitions 53, 87 (1995).
(3/7, 3/7)
Si(111)-5x2-Au
Off-Bragg Condition (Out-of-Phase Condition)
Harris, Joyce, Dobson 1981
layer-by-layer Grwoth
Mixed Growth
Mode
Mode
Mode
Surface Energy of Substrate Surface Energy of Adsorbate
Surface Energy of Adlayer
Lattice Mismatch
Lattice Match
Lattice Mismatch
Stack up different atoms layer-by-layer ⇒ Artificial materials which do not
exist in nature. (Quantum well structures)
for the discovery of Giant Magnetoresistance"
France Germany Julich
b. 1938 b. 1939
Albert Fert Peter Grünberg
S. Yuasa, et al., Nature Materials 3, 868 (2004).
(TMR) Tunnel magnetoresistance
Parallel M ⇒ Low resistance Anti-parallel M ⇒High resistance
Magnetic head (down sizing and high-density magnetic hard disk)
Fe
Fe
MgO
The Nobel Prize in Physics 2014

2005721
GaN
Without Buffer Layer With Buffer Layer
Release Strain in GaN
ECU Prof. K. Yamaguchi
InAs/GaAs
Photoluminescence Spectrum
Fundamentals of Quantum Mechanics; Wave Nature of E
Qualitative Analysis of Surface Structures
Useful for sample prep
Detailed analysis of surface atomic arrangement ⇒ Kinematical ⇒ Dynamical Claculations
Monitor of dynamical changes in structure
- growth of atomic layers - phase transitions
Summary Electron Diffraction