Alternative representation of QW Phase accumulation model
description
Transcript of Alternative representation of QW Phase accumulation model
BiBr e
CiCr e
1/2
1/2
2 ( ) 2integer
3.4 1
2arcsin
B C
B
V
LC
U L
k E d nn
eVE E
E EE E
Alternative representation of QWPhase accumulation model
Dispersion of k(E)
FEVBME
5.5VE eV
2.1gV eV
1/221
2 1
2 2
1/2
22
4 ( )
2
2
2( )
G G G G VBM
G G VBM
G
r V E E V E E
r E V E E r
h GEm
m rk Eh
Synchrotron radiation photoemission spectroscopy
• ISA Aarhus University• Maximum Energy 580 MeV• Max Current 250 mA• Lifetime 15 hours
SGM130-400 eV1010 photons/sec @130 eV
Photoelectron spectroscopy• Core levels
– Chemical reactions/mixing– Growth modes
• Valence bands– Electronic levels relevant for optics
Binding Energy(eV)
sp band
h=130 eV
Secondaryelectrons
Inte
nsity
(arb
. uni
ts) Al2p
h
EF E
vac
Kinetic Energy (eV)
Scanning film thickness by movingwedge through laser or synchrotron beam
Wedge-shaped metal film
18 18 2. . mSample moved into shadow of shield. Evaporation rate ~1 ML per minute Triangular domains ~200 nm
Ag(111) LEED-pattern - only one type of domains
38,80 38,85 38,90 38,95 39,000
5
10
15
20
25Convolution fit ofGauss beamand step functiond=150 m
Si2
p pe
ak h
eigh
t (ar
b. u
nits
)
Sample position (mm)
Width of synchrotron beam
AFM
Film growth - Si2p spectra
102 101 100 99 98
0
2
4
6
8
10
101 100 99 98 97
Growth at 170 KNo annealing
130 eV
Inte
nsity
(arb
. uni
ts)
7x7
Growth at 170 KAnnealing atroom temperature
Binding Energy (eV)
0 2 4 6 8 10 120,01
0,1
1
10 Bulk 300 K Surface 300 K Bulk 170 K Surface 170 K
Inte
nsity
(ar
b. u
nits
)
Coverage (ML)
Growth at 170 K leads to exponential decay of Si2p levels with ~5Å decay rate.Room temperature annealing of the film leads to growth of large atomically flatdomains. Areas with low Ag coverage are formed.
Annealing
3,0 2,5 2,0 1,5 1,0 0,5 0,00
5
10
15
20
25
30
Double peaks
14
2418
1297
5
4210
Cu VBM
Clean Si(111)7x7
Inte
nsity
(ar
b. u
nits
)
Binding Energy (eV)
Cu buffer layerCu wedge under 10-ML Ag film
3 ML Cu: disordered film
6-7 ML Cu: optimum for Ag overlayer
> 7 ML Cu: coupling of overlayerand substrate levels -double peaks -avoided crossings
6 4 2 01
2
3
4
5
6
7
8
9
3 2 1 00,0
0,5
1,0
1,5
2,0
2,5
3,0Ag / 6 ML Cu / Si(111) Valence band 47 eV
20 ML Ag
6 ML Cu
Inte
nsity
(ar
b. u
nits
)
Binding Energy (eV)
Effect of Cu buffer layer
QW levels and film roughness
0 2 4 6 8 10 12 14 16 18 20 22 24-2.5
-2
-1.5
-1
-0.5
0
Thickness (ML)
Bin
ding
Ene
rgy
(eV
)
Film thickness variations expected within probed areaVariations within a few atomic layer give broad peaks in photoemission
Beam size on sample ~1 mm