JEOL JSPM-5200 Instructions Manual page 138

■ Principle of SKPM op
Kelvin Force Microscopy (KFM) is designed to observe a surface-potential image of a
specimen by detecting the electrostatic force generated between a cantilever and a
specimen using an AC-mode atomic force microscope (AFM) and controlling the bias
potential of the specimen so that the electrostatic force becomes a minimum.
The following states the principle of KFM.
If U is the potential difference between a cantilever and a specimen, the electrostatic
force generated between them is given by the following equation:
Here, z is the distance between the cantilever and the specimen, and C is the electrostatic
capacitance. An AC voltage with amplitude V
on DC voltage V
This superposed voltage is applied between the cantilever and the specimen. If the
contact potential difference is ∆ φ/q
Fr om the above equati
This equation can be expanded
The Electrostatic force F has both a static component and components at angular
frequ encies ω and 2 ω , as shown in
change of the vibration amplitude (F: Force) of the cantilever and the charac
frequ ency (
Lock-in Amplifier. In the case of Force, the ω component corresponds to
∂
C
(
⋅ −
V
DC
∂
z
In the case of Force gradient the ω component corresponds to
The specimen surface potential is measured by controlling
beco mes zero.
• RE
FERENCE:
Hiroshi Yokoyama, et al., Journal of The Physical Society of
T. Hochwitz, et al., Journal of V
∗
∆φ(units: eV ) is the Work Function Difference (WFD) and ∆φ/q(units: V) is the Contact Potential Difference
(CPD).
TMPM5200-2
eration
∂
1 C
= − ⋅ 2 ⋅
F U
z ∂
2
is given by the following equation:
DC,
= + ⋅
V V V
t DC AC
φ
= − ∆
U V / q
t t
φ
− ∆ + ⋅
V / q V s in
DC AC
on, the el ectrostatic force F is given as follows:
1
(
φ
= − ⋅ − ∆ +
F V / q
DC
2
as follows:
⎡
1
(
φ
= − ⋅ − ∆
F V / q
⎢
DC
2
⎣
∂
C
( )
φ
− ⋅ − ∆ ⋅
V / q V
DC
∂
z
∂
1 C
2 ω
+ ⋅ ⋅ ⋅
V cos 2
AC
∂
4 z
∂
F
: Z-component of Force gradient). The ω component is removed using the
∂
z
)
, as shown in the second term of equation (1).
φ
∆ ⋅
/ q V
AC
and angular frequency ω , superimposed
AC
ω
sin t
∗
, the potential difference U is :
ω
t
∂
C
)
ω 2
⋅ ⋅
V sin t
AC
∂
z
∂
⎤
1 C
)
2 2
+ ⋅ ⎥
V
AC
∂
2 z
⎦
ω
⋅
sin t
AC
（１）
t
equation (1). These components are detected as the
acuum Science Technology, B14,
５ MEASUREMENT OPERATION
t
2
∂
C
( )
φ
⋅ − ∆ V ⋅
V / q
DC AC
∂ 2
z
V so that this
DC
Japan, 49, 281 (1994)
457 (1996)
teristic
.
value
5-75