Transcript AC-2 Presentation (with presenter)

Photo-electron spectrometer in air
Model AC-2
The counting mechanism of the photoelectron
and
The application to studies of
The Organic Light Emitting Diode (OLED)
RIKEN KEIKI CO., LTD
1
Contents
1. The outline of AC-2
applications, features
2. The mechanism of counting photoelectrons
How does the open counter detect the electrons in the air?
3. The data analysis
What do the photoelectron spectrums mean?
4. The application to the OLED
The measurements of the IPs and WFs of
the Organic materials.
5. Conclusion
RIKEN KEIKI CO., LTD
2
Contents
1. The outline of AC-2
applications, features
2. The mechanism of counting photoelectrons
How does the open counter detect the electrons in the air?
3. The data analysis
What do the photoelectron spectrums mean?
4. The application to the OLED
The measurements of the IPs and WFs of
the Organic materials.
5. Conclusion
RIKEN KEIKI CO., LTD
3
1. Outline of Spectrometer in Air (PESA)
Photo-Electron
MODEL AC-2
More than 170sets are used in Japan and world market.
36cm
45cm
Light source part
120cm
Measuring part
Mainly applications
Personal computer
Latest applications
•Material research of the OLED .
•Organic transistor
•The quality check of an ITO cleaning.
•Organic solar battery
•The surface research of an MgO film for the PDP. •Catalyst of fuel cell
RIKEN KEIKI CO., LTD
4
The features of AC-2
•Measurements can be done in the air.
Usually a photoelectron spectrometer needs a vacuum.
Because it is very difficult to detect and to count electrons in air.
•The work function and ionization potential can be
measured in the air in very high resolution.
•Measurement of contamination or film thickness on
a sample surface of 1mono layer-20nm.
•Easy operation & short measuring time.
RIKEN KEIKI CO., LTD
5
Contents
1. The outline of AC-2
applications, features
2. The mechanism of counting photoelectrons
We employed the open counter for the detector of AC-2.
3. The data and the analysis
What do the photoelectron spectrums mean?
4. The application to the OLED
The measurements of the IPs and WFs of
the Organic materials.
5. Conclusion
RIKEN KEIKI CO., LTD
6
Conventional methods for detecting electrons
Channeltron
Picoammeter
A pulse of 10 million electrons
Pulse counter
1pA (10-12A )
HV
Sample
Collector
e
Vacuum chamber
UV Light
e
UV light
e
Sample
6.24x106cps (62 million/s)
This method is are
not detected
sensitive
Photoelectrons
enough
photoelectron
as quiteforsmall
amount of
spectroscopy.
electric current.
A photoelectron
isonly
detected
The
This
electrons
device works
strike
the channel
in a vacuum.
walls
as an
electricadditional
pulse. electrons.
and
produce
RIKEN KEIKI CO., LTD
7
The open counter
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
Open counter was invented in 1979 by Uda and Kirihata.
High Voltage Supply
Preamplifier
Scaling
circuit
and Rate meter
Quenching circuit
Anode
Quenching Grid
Suppresser Grid
Suppresser circuit
Display
1 count
e
O2
UV Light
Sample
e
Sample holder
The open counter is employed the photoelectron spectrometer in air. The open
counter is unique counter which can detect and count photoelectrons in the air.
RIKEN KEIKI CO., LTD
8
Structure
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
80mm
High Voltage Supply
Preamplifier
14mm
Scaling
circuit
and Rate meter
Quenching circuit
Anode
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
0 count
The open counter is composed of an anode, a quenching grid,
suppresser grid and electric circuits.
RIKEN KEIKI CO., LTD
9
Structure
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
Preamplifier
Scaling
circuit
and Rate meter
Quenching circuit
Anode
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
0 count
15mm
Sample
Sample holder
The test sample is mounted on the sample stage which is kept at earth potential (0V).
RIKEN KEIKI CO., LTD
10
Structure
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
+2900V
Anode
+100V
+80V
Preamplifier
Scaling
circuit
and Rate meter
Quenching circuit
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
0 count
Sample
Sample holder
Suppresser Grid is kept at +80V, Quenching Grid is +100V, Anode is +2900V.
RIKEN KEIKI CO., LTD
11
Measurement
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
+2900V
Anode
+100V
+80V
Preamplifier
Scaling
circuit
and Rate meter
Quenching circuit
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
0 count
UV Light
Sample
Sample holder
Monochromatized UV photons are used to excite photoelectrons from the sample surface.
RIKEN KEIKI CO., LTD
12
Measurement
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
Preamplifier
+2900V
Anode
+100V
+80V
Scaling
circuit
and Rate meter
Quenching circuit
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
0 count
UV Light
e
Electron
Sample
Sample holder
If the energy of an UV photon(=hn) becomes bigger than a work function of a
sample, a photoelectron is emitted from the sample surface.
RIKEN KEIKI CO., LTD
13
Measurement
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
Preamplifier
+2900V
Anode
+100V
+80V
Scaling
circuit
and Rate meter
Quenching circuit
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
0 count
UV Light
e
Electron
Sample
Sample holder
The electron is accelerated by a weak electric field applied between the sample (0V)
and the suppresser grid kept at +80V.
RIKEN KEIKI CO., LTD
14
Form the O2- ion
N2
N2
e
N2
N2
N2
N2
N2
N2
N2
O2
O2-ion
N2
N2
O2
N2
N2
N2
N2
O2
N2
N2
N2
N2
Sample surface
The electron becomes attached to an oxygen molecule to form O2ion in the air during drift to the counter.
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
RIKEN KEIKI CO., LTD
15
Measurement
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
Preamplifier
+2900V
Anode
Quenching Grid
Suppresser Grid
+100V
+80V
Scaling
circuit
and Rate meter
Quenching circuit
Suppresser circuit
Display
0 count
e
O2
UV Light
Sample
Sample holder
When an O2- ion reaches the inner cylinder of the open counter, the ion is accelerated again by a
strong electric field applied between the quenching grid ( +100V) and the anode kept at +2900V.
RIKEN KEIKI CO., LTD
16
The electron avalanche
Electric
Field
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
Anode surface
N2
O2
N2
N2
N2
N2
N2
O2
N2
N2
N2
O2
N2
N2
N2
N2
N2
N2
N2
N2
N2
O2
e
N2
O2
N2
O2
N2
N2
N2
N2
N2
e
O2
O2-ion
When the O2- ion arrives near the anode, the electron is detached from the O2- ion
and then the electron is accelerated again to the anode.
RIKEN KEIKI CO., LTD
17
The electron avalanche
Electric
Field
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
Anode surface
e
e
e
N2+
N2+
+
O2
N2
N2
N2
N2
O2
N2
e
e
e
N+2
N2
O2
+N
2 e
N2
N2
N2
O2+
e
e
O+2
N+2
e
O2
N2
e e
e
N+2
+N
2e
N2
N2
e
N2+
N2
N2
N2
N2
N2
e
O2
O2-ion
This causes an electron avalanche, which produces many electrons and positive
ions around the anode wire, where only the electrons are collected on the anode.
RIKEN KEIKI CO., LTD
18
Measurement
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
+2900V
Anode
+100V
+80V
Preamplifier
Scaling
circuit
and Rate meter
Quenching circuit
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
10 count
UV Light
Sample
Sample holder
The electron avalanche makes a small electric pulse on anode.
This pulse is detected and counted as one electron.
RIKEN KEIKI CO., LTD
19
Measurement
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
+2900V
+400V
Anode
Preamplifier
Scaling
circuit
and Rate meter
Quenching circuit
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
1 count
UV Light
Sample
Sample holder
When the quenching circuit detects the electric pulse, +400V is applied in place of
+100V to the quenching grid.
RIKEN KEIKI CO., LTD
20
Measurement
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
+2900V
+400V
Anode
Preamplifier
Scaling
circuit
and Rate meter
Quenching circuit
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
1 count
UV Light
Sample
Sample holder
This reduction of the electric field around the anode causes the electron avalanche to be
quenched.
RIKEN KEIKI CO., LTD
21
Measurement
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
+2900V
Anode
+400V
-30V
Preamplifier
Scaling
circuit
and Rate meter
Quenching circuit
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
1 count
UV Light
Sample
Sample holder
On the other hand, -30V is applied in place of +80V to the suppressor grid.
RIKEN KEIKI CO., LTD
22
Measurement
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
Ion
High Voltage Supply
+2900V
Anode
+400V
-30V
Preamplifier
Scaling
circuit
and Rate meter
Quenching circuit
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
1 count
UV Light
Sample
Sample holder
This voltage switch prevents leaving of the positive ions to the sample surface,
and entering of the next O2- ions into the counter during quenching.
RIKEN KEIKI CO., LTD
23
Measurement
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
+2900V
3ms
Anode
+400V
-30V
Preamplifier
Scaling
circuit
and Rate meter
Quenching circuit
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
1 count
UV Light
Sample
Sample holder
Such voltages applied to the quenching grid and suppressor grid are kept for 3msec
i.e. the quenching time.
RIKEN KEIKI CO., LTD
24
Measurement
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
+2900V
3ms
Anode
+400V
-30V
Preamplifier
Scaling
circuit
and Rate meter
Quenching circuit
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
1 count
UV Light
Sample
Sample holder
All positive ions produced around the anode wire arrive and neutralize at the quenching
grid or suppressor grid during quenching time.
RIKEN KEIKI CO., LTD
25
Measurement
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
+2900V
3ms
Anode
+400V
-30V
Preamplifier
Scaling
circuit
and Rate meter
Quenching circuit
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
1 count
UV Light
Sample
Sample holder
If the next electron has emitted from the sample surface, the suppresser grid prevents
entering of the electron during quenching time.
RIKEN KEIKI CO., LTD
26
Measurement
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
+2900V
Anode
+100V
+80V
Preamplifier
Scaling
circuit
and Rate meter
Quenching circuit
Suppresser circuit
Quenching Grid
Suppresser Grid
Display
1 count
UV Light
Sample
Sample holder
After the quenching time (3ms), the initial voltages (+100V and +80V, respectively) are
restored and the quenching procedure is over.
RIKEN KEIKI CO., LTD
27
Measurement
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
High Voltage Supply
Preamplifier
Scaling
circuit
and Rate meter
Quenching circuit
Anode
Quenching Grid
Suppresser Grid
Suppresser circuit
Display
21 count
e
O2
UV Light
Sample
e
Sample holder
Now the counter is ready to count the next electron.
RIKEN KEIKI CO., LTD
28
The calculation of counts
Electron counts may be lost during the quenching time. The
counting rates of electrons are estimated based on the counting
rates of counter pulses by calculation.
NO
N=
1-tNO
NO: Counting rate of counter pulses
N : Counting rate of photo electrons
t :Quenching time
Reference: H.Kirihata, and M.Uda; Rev. Sci. Instrum. 52 (1981) 68.
RIKEN KEIKI CO., LTD
29
Structure and functions of AC-2
optical fiber
deuterium
lamp
grating
monochromator
3.4eV 6.2eV
open
counter
controller
personal
computer
e
sample
photodiode
sample stage
Light source part
Measuring part
: UV light
RIKEN KEIKI CO., LTD
e
: photoelectron
30
Structure and functions of AC-2
optical fiber
deuterium
lamp
grating
monochromator
3.4eV 6.2eV
open
counter
controller
personal
computer
photodiode
sample stage
Light source part
Measuring part
: UV light
RIKEN KEIKI CO., LTD
e
: photoelectron
31
Contents
1. The outline of AC-2
applications, features
2. The mechanism of counting photoelectrons
How does the open counter detect the electrons in the air?
3. The data and the analysis
What do the photoelectron spectrums mean?
4. The application to the OLED
The measurements of the IPs and WFs of
the Organic materials.
5. Conclusion
RIKEN KEIKI CO., LTD
32
(Yield[cps])1/2
Photoelectron Spectrum
Photoemission
Threshold Energy[eV]
Incident Photon Energy [eV]
Yield :: the
counting
rate after
calibtation
Metal
relationship
between
the photon energy and yield 1/2 looks like a linear line.
Semiconductor
yield1/3 gives a (E)
linear
line. of UV-ray (E) x intensity of UV-ray (5.9eV)
counting rate of: photoelectrons
/ intensity
RIKEN KEIKI CO., LTD
33
The relationship between
the threshold energy and the energy diagrams
Vacuum level
Energy
Metal
Conduction Band
Valence Band
Fermi Level
Semiconductor
General material
Lowest unoccupied molecular orbital (LUMO)
Highest occupied molecular orbital (HOMO)
The energy level diagrams of metals, semiconductors and general materials
RIKEN KEIKI CO., LTD
34
The relationship between
the threshold energy and the energy diagrams
Vacuum level
Work
function
Ionization
potential
Work
function
Ionization
potential
Ionization
Work
function
potential
Energy
Metal
Conduction Band
Valence Band
Fermi Level
Semiconductor
General material
Lowest unoccupied molecular orbital (LUMO)
Highest occupied molecular orbital (HOMO)
A work function is an energy difference between a vacuum level and a Fermi level. On the other hand,
the ionization potential is an energy difference between a vacuum level and highest occupied molecular
orbital.
RIKEN KEIKI CO., LTD
35
The relationship between
the threshold energy and the energy diagrams
UV photon
Vacuum level
e
Photoelectron
e
e
Energy
Metal
Conduction Band
Valence Band
Fermi Level
Semiconductor
General material
Lowest unoccupied molecular orbital (LUMO)
Highest occupied molecular orbital (HOMO)
A UV photon excites an electron from the occupied states to the higher energy states than the vacuum level. And this
electron can be emitted from the sample surface. The electron is called the photoelectron.
RIKEN KEIKI CO., LTD
36
The relationship between
the threshold energy and the energy diagrams
UV photon
Vacuum level
e
Photoelectron
e
e
Ionization
potential
Ionization
potential
Ionization
potential
Energy
Metal
Conduction Band
Valence Band
Fermi Level
Semiconductor
General material
Lowest unoccupied molecular orbital (LUMO)
Highest occupied molecular orbital (HOMO)
Therefore, the photoemission threshold energy is the ionization potential.
RIKEN KEIKI CO., LTD
37
The relationship between
the threshold energy and the energy diagrams
UV photon
Vacuum level
e
Photoelectron
e
e
Ionization
Work function
potential
Ionization
potential
Ionization
potential
Energy
Metal
Conduction Band
Valence Band
Fermi Level
Semiconductor
General material
Lowest unoccupied molecular orbital (LUMO)
Highest occupied molecular orbital (HOMO)
We can
The
metal
estimate
is special
the material.
work functions
Because,
or ionization
the energypotentials
of highestofoccupied
the materials
molecular
from orbital
the photoemission
and the Fermi
threshold
level are
energy.
same.
Therefore the photoemission threshold energy of a metal is the work function.
RIKEN KEIKI CO., LTD
38
The shape of a photoelectron spectrum
DOS
Vacuum level
Energy
Potential energy
unoccupied molecular orbital
occupied molecular orbital
Energy level diagram
Reference: M.Uda, Y.Nakagawa, T.Yamamoto, M.Kawasaki,
A.Nakamura, T.Saito, and K.Hirose ”Successive change in
work function of Al exposed to air”, J. Electron. Spectrosc.
and Related Phenom. 88 (1998) 767.
RIKEN KEIKI CO., LTD
39
the relationship between an energy level diagram and
the photoelectron spectrum
DOS
=
dY
dE
Photoemission yield (Y)
0
Photon energy
Potential energy
Energy level diagram
Photoelectron spectrum
The DOS is estimated by the differential of the photoelectron spectrum with respect to the photon energy E.
Reference: M.Uda, Y.Nakagawa, T.Yamamoto, M.Kawasaki,
A.Nakamura, T.Saito, and K.Hirose ”Successive change in
work function of Al exposed to air”, J. Electron. Spectrosc.
and Related Phenom. 88 (1998) 767.
RIKEN KEIKI CO., LTD
40
The difference of a photoelectron spectrum
caused by the thickness of a surface film
-
Incident photon (E)
-
E > sWFs
WFf> WF
Contamination
or
Oxide film
(0-20nm)
Substrate
-
-
WFf
- --
WFs
The cross section of the sample surface covered with a thin film
RIKEN KEIKI CO., LTD
41
The difference of a photoelectron spectrum
caused by the thickness of a surface film
-
Incident photon (E)
-
E > sWFs
WFf> WF
Contamination
or
Oxide film
(0-20nm)
Substrate
-
-
WFf
- --
WFs
When photoelectrons pass through a surface film, some electrons collide with a molecule
forming the surface film, and the photoelectrons are scattered.
So some of photoelectrons can not escape from the sample surface.
RIKEN KEIKI CO., LTD
42
The difference of a photoelectron spectrum
caused by the thickness of a surface film
-
Incident photon (E)
E > sWFs
WFf> WF
Contamination
or
Oxide film
(0-20nm)
Substrate
WFf
- - - --
WFs
So, when the surface film is thick, many photoelectrons can not be emitted from the
sample surface.
RIKEN KEIKI CO., LTD
43
The relationship between the slope and film thickness
- --
WFf
WFs
(Yield[cps])n
-
Large slope
Incident Photon Energy [eV]
- - Thick contamination film
- -- - - - - (Yield[cps])n
WFf
WFs
- - Thin contamination film
- -- - - -
Small slope
WFf
RIKEN KEIKI CO., LTD
WFs
44
Contents
1. The outline of AC-2
applications, features
2. The mechanism of counting photoelectrons
How does the open counter detect the electrons in the air?
3. The data and the analysis
What do the photoelectron spectrums mean?
4. The application to the OLED
The measurements of the IPs and WFs of
the Organic materials.
5. Conclusion
RIKEN KEIKI CO., LTD
45
The applications to the OLEDs
Glass Substrate
ITO transparence anode
Organic layers
Metal cathode
Vacuum Level
WF
LUMO
+
Hole
+
Fermi Level
Photon
Barrier
Ionization
Potential
HOMO
-
ITO
OLED device
Organic
Energy diagram of
ITO and Organic Layer
RIKEN KEIKI CO., LTD
46
Work functions of several metals
Fe
Ni
Cu
Al
Zn
Au
In Air 1)[eV]
4.35
4.25
4.45
3.60
3.80
4.78
In UHV2) [eV]
4.50
5.15
4.65
4.20
5.10
1) M. Uda ; Jpn. J.Appl.Phys. 24,284 (1985)
2) D.E. Eastman ; Phys.Rev. B2, 1 (1970)
RIKEN KEIKI CO., LTD
47
Work functions or Ionization
potentials of EL materials
AC-2 [eV]
UPS 1) [eV]
Alq3
5.84
5.8
a-NPD
5.50
5.4
CuPc
4.99
5.2
1) I.G.Hill and A.Kahn, J.Appl.Phys. 86,4515 (1999)
RIKEN KEIKI CO., LTD
48
The temporal change in the work function of
ITO treated with UV-ozone
Work function (eV)
5.5
UV-ozone 60min
UV-ozone 20min
UV-ozone 10min
UV-ozone 0min
(boiling in IPA )
5.3
5.1
before cleaning
4.9
4.7
0
10
20
30
40
50
60
duration time after treatment (min)
Reference: Y. Nakajima, T. Wakimoto, T. Tuji, T. Watanabe,
M.Uda, The 10th International Workshop on Inorganic and Organic
Electroluminescence (2000.12.4), Hamamatu, Japan.
RIKEN KEIKI CO., LTD
49
Change in WF of Al by Cl2 Contamination
(Yield[cps])0.5
Al exposed mixed gas 20sec
(Cl21.34ppm + air) : 4.33eV
Al in air : 4.05eV
Incident Photon Energy [eV]
RIKEN KEIKI CO., LTD
50
5. Conclusion
1. We can detect and count photoelectrons in the air by
the open counter.
2. We can measure the work function or the ionization
potential of the OLED materials easily.
3. We can estimate the amount of the contamination on
the ITO surface from 1mono-layer to 20nm in the thick.
4. AC-2 is the de facto standard equipment of the work
function measurement on the OLED development.
RIKEN KEIKI CO., LTD
51
References
[1] H.Kirihata, and M.Uda “Externally quenched air counter for low-energy electron
emission measurements”, Rev. Sci. Instrum. 52 (1981) 68.
[2] M.Uda “Open counter for low energy electron detection”, Jpn. J.Appl. Phys. 24
(1985) 284.
[3] T. Noguch, S. Nagashima and M. Uda “An electron counting mechanism for the
open counter operated in air” , Nucl. Instr. Meth. A342 (1994) 521.
[4] S. Nagashima, T. Tsunekawa, N, Shiroguchi, H. Zenba, M. Uda “Double
cylindrical open counter of pocket size”, Nucl. Instr. Meth. A373 (1996) 148.
[5] A. Koyama, M. Kawai, H. Zenba, Y. Nakajima, A. Yoneda and M. Uda “Electron
counting by a double cylindrical open counter in mixtures of N2 and inert gases of
various concentrations” , Nucl. Instr. and Meth. in Phys. Res. A422 (1999) 309.
RIKEN KEIKI CO., LTD
52
References
[6] M.Uda, Y.Nakagawa, T.Yamamoto, M.Kawasaki, A.Nakamura, T.Saito, and
K.Hirose ”Successive change in work function of Al exposed to air”, J. Electron.
Spectrosc. and Related Phenom. 88 (1998) 767.
[7] Y. Nakajima, M. Hoshino, D. Yamashita and M. Uda “ Near Edge Structures of
Tetraphenylporphyrins Measured by PESA and Calculated with DV-Xα” , Adv.
Quantum Chem. 42 (2003) 399.
[8] Y. Nakajima, T. Wakimoto, T. Tuji, T. Watanabe, M.Uda “Measurements of the
work function of ITO Using an electron spectroscopy in air and a contact potential
difference method” ,The 10th International Workshop on Inorganic and Organic
Electroluminescence (2000.12.4), Hamamatu, Japan.
RIKEN KEIKI CO., LTD
53