John L. Stickney
Department of Chemistry
University of Georgia
Athens, GA 30602
Stickney@chem.uga.edu
www.chem.uga.edu/stickney/
Acknowledgments:
People
Dr. Youn-Geun Kim
Madhivanan Muthuvel (Madhi)
Venkatram Venkatasamy (Ram)
Steve Cox
Jay Kim
Nagrrajan Jayaraju (Nag)
Dhego Banga
Deepa Vairavapandian
Chandru Thambidurai
Professor Uwe Happek
Moved on
Dr. Raman Vaidyanathan
Dr. Ken Mathe
Dr. Nattapong Srisook (Natt)
Funding
NSF Materials and Chemistry
NSF DMR NER nanoscale research
DOE, Bio Fuels program
University of Georgia Research Foundation
I have a Dream
That one day all ULSI structures
will be grown from the bottom up,
using solution phase reactions
with atom level control.
The electronic industries are already
working on the 35 nm node, so lateral
size control will be accomplished using
Lithography.
Vertical growth will be accomplished
atomic layer by atomic layer.
Ambient growth of metals and semiconductors
has been demonstrated
(electrodeposition in solution)
using EC-ALE.
Chemistries for the layer by layer
growth of oxides and polymers
are tractable
Zinc Blende
Atomic Layer Epitaxy (ALE): the use of
surface limited reactions to form deposits an
atomic layer at a time.
Atomic Layer Deposition (ALD): Same as
ALE, without emphasizing epitaxy.
Electrochemical Atomic Layer Epitaxy
(EC-ALE): The use of electrochemical surface
limited reactions (UPD or SLR3) for ALE or
ALD.
• UPD: underpotential deposition
Where an atomic layer of one element
deposits on a second at a potential prior to
that needed to deposit on itself
• SLR3:Surface Limited Redox Replacement
Reactions
Use of UPD to form an atomic layer of a
sacrificial metal to limit the deposition of a
more noble metal by redox replacement at
open circuit, to an atomic layer.
Se4+
Se4+
EC-ALE
Layer by layer underpotential
deposition of compound
semiconductors, performed at
room temperature.
Se4+
Se4+
Se4+
Se4+
Se4+
Au
Pb2+
Pb2+
Pb2+
Pb2+
Pb2+
Pb2+
Pb2+
}
One Cycle
of PbSe
Deposition of 200 cycles of CdTe:
0.25 mM TeO2, 10 mM Na2B4O7, 20 mM Na2SO4, E = -400 mM
0.25 mM TeO2, 10 mM Na2B4O7, 20 mM Na2SO4, E = -551
mM
Ultrahigh Vacuum (UHV) System for UHV-EC
x-y-z
Manipulator
AES
LEED
Main
Chamber
AnteChamber
Sample
Transporter
Cryopump
Ion
Pump
Electrochemical
Cell
Pictures of
Ultrahigh Vacuum (UHV) Chamber and Antechamber
1.5 cycle, beginning with Cd, E= -550 mV CdTe 3 x 3
One cycle of CdTe formation:
The bright areas are Cd UPD on Au
Te followed by Cd.
The darker areas are the CdTe
too little Te in first step (0.33 ML). monolayer.
0.44 ML coverage of Te is needed to Cd stripping leaves the 1/3 coverage
form a monolayer of CdTe
Te structure, and pits where there
was only Cd UPD on Au
Compounds, Elements and Structures Formed Using
EC-ALE
II-VI
CdS
CdSe
CdTe
ZnS
ZnSe
ZnTe
HgSe
HgTe
HgS
III-V IV-VI
GaAs? SnS?
GaSb SnSe?
InAs SnTe?
InSb PbS
PbSe
PbTe
Others
In2Se3
CuSe
Sb2Te3
Bi2Te3
Superlattices
InAs/InSb
PbSe/PbTe
HgCdTe
Metals: Pt, Cu
Nanoclusters
In2Se3
PbSe
HgSe
CdTe
Compound
Au
GaAs
GaSb
InP
InAs
InSb
ZnS
ZnSe
ZnTe
CdS
CdSe
CdTe
HgS
HgSe
HgTe
PbS
PbSe
PbTe
SnTe
Band Gap, Lattice Constant, Interatomic
eV
nm
Distance,nm
2.86
1.43
5.653
0.69
6.095
1.28
5.8687
0.36
6.058
0.17
6.4787
3.6-3.8 a 3.814, c 6.257
2.58
5.667
2.28
6.101
2.53 a 4.136, c 6.713
1.74 a 4.299, c 7.010
1.5
6.477
2.5
-0.15
6.086
0
6.42
0.37
5.936
0.26
6.124
0.29
6.46
0.18
6.328
Au Lattice
Mismatch, %
4.29
3.997
4.31
4.15
4.284
4.581
3.814
3.823
4.314
4.136
4.299
4.58
6.83
-0.47
3.26
0.14
-6.78
11.10
10.89
-0.56
3.59
-0.21
-6.76
4.303
4.568
4.197
4.33
4.568
4.475
-0.30
-6.48
2.17
-0.93
-6.48
-4.31
Bohr
Radius,
nm
14
23.3
9.5
35.5
69
1.7
2.8
4.6
3.1
6.1
6.5
39.3
20
46
X-ray Diffraction Pattern for 100 Cycle Electrodeposited PbTe on Au.
Rock salt structure, a = 0.646 nm. Angle of incidence is 1°. The deposit
Is essentially all (200) oriented.
Experimental method of measuring the absorption coefficient
θB eliminates reflection
off of sample surface
Io
I
θB
θB
Io
I
}t
Again, the band gap of even the 100 cycle PbTe deposit is blue shifted
from its bulk value (0.29 eV) due to quantum confinement.
The band gap of even the 50 cycle deposit is blue shifted
from its bulk value (2100 cm-1) due to quantum confinement.
PbSe energy gap data compared to the hyperbolic band
model (Wang et al.) with theoretical film thickness
multiplied by the coverage factor calculated for each film:
Dotted line: using effective mass values of Dalven
Solid line: using effective mass values of Kang et al.
X-ray diffraction of 80 period 4PbTe / 4PbSe superlattice.
Buffer layer is 10 cycle PbSe. Angle of incidence is 1°.
(111)
Period = 4.5 nm
The band gap was found to be to be 0.48 eV. It is blue shifted
from bulk value of PbSe (0.26 eV) and PbTe (0.29eV).
Surface limited redox replacement reaction:SLR3
Replacement of Cu upd by Pt
320 nm×320 nm
105 nm×105 nm
260 nm×260 nm
CV for the upd of Cu on
Au(111) in 0.1M H2SO4 with
0.1M Cu2+,
Cu upd adlayer formed at 0.005
V vs, Cu/0.1 M Cu2+.
Pt submonolayer on Au(111) obtained by replacement of
Cu upd monolayer
S. R. Brankovic, J. X. Wang, R. R. Adžić, Surface
Science 2001, 474, L173.
Experimental
Cu 2+
4+
4+
Pt4+
4+
4+
4+
2+
4+
2+
4+
2 e-
2+
4+
2 e-
2+
2+
2+
4+
4+
2+
2+
2+
4+
4+
2+
2+
2+
2+
2+
2+
2+
2+
2+
2+
2+
2+
2+
Pt monolayer
Iodine
Cu UPD
Gold
Previously Prepared Cu UPD on Au(111) Surface
in 0.05 M H2SO4 with 1mM CuSO4 Solution.
Honeycomb (√3 x √3)R30° Structure
(θCu = 0.67 and θanion = 0.33)
[121]
[121]
Interfacial structure of the Cu UPD on Au(111)
after the first UPD peak:.
top view
side view
- Honeycomb (√3 x √3)R30° structure in which θCu = 0.67 and with
(bi)sulfate anions occupying the centers of the honeycomb (θanion =
0.33)
- Cu-(1x1)structure with (bi)sulfate adsorbed on top of the
copper adlayer.
* Toney, M. F.; Howard, J. N.; Richer, J.; Borges, G. l.; Gordon, J. G.; Melroy, O. R. Phys.
Rev. Lett. 1995, 75, 4472.
LEED Pattern (I)
Clean Au (111)
(1 x 1)
Beam Energy : 55 eV
Cu UPD
(√3 x √3)R30º
Beam Energy : 40 eV
AES (I)
Clean Au (111) vs 1st Cu UPD
(01/21/05)
dN(E)/dE
Clean Au (111)
1st Cu UPD
100
200
300
400
500
600
Electron Energy (eV)
700
800
900
1000
EC-STM Images of Pt Submonolayer on Au(111)
Obtained by Replacement of Cu UPD Monolayer
Iodine-Induced Reordering of Pt
After Iodine
treated
in 0.1 M HClO4 solution at 0.6 V vs. Ag/AgCl
AES (II)
Clean Au (111) vs I / Au (111) vs Cu / I / Au (111)
(05/03/05)
dN(E)/dE
Clean Au (111)
I / Au (111)
I
Cu
Cl
100
200
Cu / I / Au (111)
I
300
400
500
600
700
Electron Energy (eV)
800
900
1000
LEED Pattern (II)
Clean Au (111)
(1 x 1)
Beam Energy : 55 eV
I / Au (111)
(√3 x √3)R30º
Beam Energy : 48 eV
Cu / I / Au (111)
(√3 x √3)R30º
Beam Energy : 48 eV
EC-STM Images of Pt Layer After the
1st Replacement Cycle of UPD Cu with Pt(II)
Iodine modified Pt submonolayer
in 0.1 M HClO4 solution at 0.6 V vs. Ag/AgCl
[121]
[121]
[121]
[121]
[121]
[121]
[121]
High Tunneling Current Reveals Pt with
Au(111)-(1×1) Substrate
10 x10 nm2
10 x10 nm2
10 x10 nm2
OCP change during Exchange with Pt (+2)
Solution
Cycle 1 to 10
Potential change during Pt exchange
2-27-06
0.650
E /V
0.550
0.450
0.350
0.250
0.150
0
100.0
200.0
300.0
t/s
400.0
500.0
600.0
Green -1
Blue -2
.
.
.
OCP change during exchange using Pt (+4)
solution
platinum exchange
22806-pt 1
0.750
0.650
E /V
0.550
0.450
0.350
0.250
0.150
0
25.0
50.0
75.0
100.0
125.0
150.0
t/s
Cycles 1 -4 (top one is first)
EC-STM Images of Pt Layer After the
2nd Replacement Cycle of UPD Cu with Pt(II)
Iodine modified Pt monolayer
in 0.1 M HClO4 solution at 0.6 V vs. Ag/AgCl
High Resolution EC-STM Images of the
Iodine modified Pt Layer on Au(111)
[121]
After 1 min
(√3 x √3)R30°- I
on Pt layer
Iodine modified Pt monolayer
in 0.1 M HClO4 solution at 0.6 V vs. Ag/AgCl
High Resolution EC-STM Images of the
Mobility of Pt-complex
After 1 min
Pt
I
in Iodine and Pt(II) or Pt(VI)-free 0.1 M HClO4 solution
High Resolution EC-STM Images of the
Moire Pattern, (√3 x √3)R30°- I and Pt-Complex
[121]
EC-STM Images of Pt Layer After the
3rd Replacement Cycle of UPD Cu with Pt(II)
Iodine modified Pt layer
in 0.1 M HClO4 solution at 0.6 V vs. Ag/AgCl
[121]