EINFÜHRUNG NANOMATERIALIEN
Is it possible to fabricate nanostructures using simple physical methods?
“Simple physical method“ : Sputtering
Sputtering:
- What is sputtering
- What is a glow discharge
- Magnetronsputtering, ion beam sputtering
- Reactive and non-reactive sputtering
PES:
- The photoelectric effect
- Light sources
- Penetration depth
- Application of ESCA and Valence band to nanoscience
Examples of nanomaterials we can do/have done/are doing
Examples of possible experiments to be done in the practicum
Experimental set-up: The SPUTTERING CHAMBER
10-7 mbar
10-6
Thin film deposition
Nanostructured films
By SPUTTERING
mbar
10-10 mbar
In-situ characterization:
By PHOTOELECTRON SPECTROSCOPY
1
What is Sputtering?
Sputter:
to spit
particles von
of food
or saliva
Sputtering:
Zerstäubung
Festkörpern
noisily
from the mouth
durch Ionenbeschuss
How do we produce the ions we need? Glow discharge
Current
emission
area
Abnormal glow
V
Cathode area
A
Current
emission
area = Cathode
area
2
What happens inside the glow discharge?
+
+
-
Magnetron sputtering
Higher efficiency at lower gas pressure
Plasma is confined to cathode
3
Ion beam sputtering
Ion source
Extractor
Ion beam
Substrate
target
Non-reactive Sputtering
Noble gas: Ar
Substrate
Thin film of
target
material
4
Reactive Sputtering
Noble gas: Ar
+ reactive gas:
O2, N2, CH4, usw…
Substrate
Thin film
different
than target
material
Example I: Reactive Sputtering with Al target in Ar/O2 mixture
Control on parameters gives control on surface morphology
-Temperature of substrate
-Gas pressure, gas mixture
-Biasing of substrate
-relative position of substrate/magnetron
-Continuos (DC) or pulsed (AC, RF...) discharge...
5
LOTTUS EFFECT
Lotus plants have
superhydrophobic surfaces.
As a result, the surfaces stay dry
even during a heavy shower.
What's more, the droplets pick up
small particles of dirt as they roll,
so that the lotus leaves are
self-cleaning.
LOTTUS EFFECT
6
Example II: Co-Sputtering with Ti and Ag targets in Ar/N2 mixture
Ti
Ag
Ti + N reacts to TiN
Ag remains pure
TiN and Ag are inmiscible
Possible applications:
1. Thin films as substitution for
liquid lubricants.
Lubricity would be provided by
the soft cluster phase, while
the hard matrix would protect
against wear.
2. Optical applications
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Example III: growth of carbon nanotubes
Hohe Temperatur: 500-1100°C
Produkte
M
M-C
substrate
substrate
M
substrate
(M= Fe, Co, Ni…)
Si (a. i.)
Buffer Layer
Catalyst: Fe
(TiN, TiO2, Al2O3)
Annealing
C2H2
Metal-substrate interaction
Metal-C interaction
Nanotube characteristics
8
Experimental set-up II: the PHOTOELECTRON SPECTROMETER
10-7 mbar
10-6 mbar
10-10 mbar
Photoemissionspektroskopie: Grundlagen
Ekinetisch= hω-Ebindung - φ
9
Photoemissionspektroskopie: Lichtquellen
Röntgenstrahlen
UV-Photon
XPS: X-ray photoemission spectroscopy
oder
ESCA (Electron Spectroscopy for Chemical Analysis)
Al (1486eV), Mg (1253eV)
UPS: UV Photoemission
Spectroscopy
He (21.2 und 40.8 eV),
Ne (16.8 und 26.9 eV)
Synchrotron-Strahlung:
Erlaubt eine kontinuierliche
Variation der Lichtenergie
Photoemissionspektroskopie: Oberflächenempfindlich Methode
Nur Elektronen aus
oberflachennahen
Schichten treten aus
(starke Wechselwirkung
der Elektronen mit dem
Festkörper)
1. Studium der elektronischen Eigenschaften von Festkörperoblerflächen
2. Oberflächen müssen rein sein: Präparation unter Ultrahochvakuumbedingungen
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Beispiele
Au: [Xe] 4f14 5d10 6s1
4f
4f5/2
Orbital
Energie (eV)
1s
2s
2p1/2
2p3/2
3s
3p1/2
3p3/2
3d3/2
3d5/2
4s
4p1/2
4p3/2
4d3/2
4d5/2
4f5/2
4f7/2
5s
5p1/2
5p3/2
80725
14353
13734
11919
3425
3148
2743
2291
2206
762.1
642.7
546.3
353.2
335.1
87.6
83.9
107.2
74.2
57.2
XPS
hν=1253.6 eV
4f7/2
4d
4p
4s
4p1/2
4d5/2
4d3/2
4p3/2
5s
5p
800
600
400
200
0
Binding Energy (eV)
F
UPS (He I)
hν=21.2 eV
EF
EF
10
8
6
4
2
0
-2
Binding Energy (eV)
10
8
6
4
2
0
-2
Binding Energy (eV)
11
ESCA
Electron Spectroscopy for Chemical analysis
XPS
hν=1253.6 eV
Fe 2p
Fe 2p3/2
Fe 2p1/2
Fe
Fe
730
725
720
2+
3+
715
710
705
Binding Energy (eV)
Valenzband
UPS
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PAST AND FUTURE
PRACTICUM EXPERIMENTS
Why is there no CNT growth when we use Si covered with Al as substrates?
Fe
Al2O3
Si
CVD IDENTISCH
Gas, Temp, Zeit
Fe
TiO2
Si
13
Our next experiment…
Coverage of CNTs with different
materials is different. Why?
CNT surface should be inert… or
not?
In-situ PES for the
study of
CNT/coating
interfaces
Al2O3
Elektronenstruktur von Kohlenstoff: 1s 2 2s 2 2p 2
s
pz
py
-308.2 eV
sp 3
sp 3
sp 3
px
-11.8 eV
-19.2 eV
sp3
2p
2s
1s
-13.9 eV
sp3
Hybridisierung sp3
1s
14
Hybridisierung und Bindungen
H
sp3
H
H
σ
C
C
H Ethan
H
sp2
1xp
π
H
H
H
σ
C
H
C
H
Ethylen
sp
2xp
π
H
σ
C
C
π
H
Acetylen
Allotrope Formen von Kohlenstoff
Elektronen fest in
Kovalente Verbindungen
(σ-Bindungen)
C
C
C
C
C
C
C
C
Diamant sp3
Isolator
C
C
C
C
C
C
C
C
C
C
C
C
Elektronen fest
in σ-Bindungen
aber “frei” in πBindungen
Graphit sp2
Leiter
15
Allotrope Formen von Kohlenstoff
Fullerene
1985
Diamant sp3
Graphit sp2
Amorph
sp2/sp3
Nanotubes - 1991
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