486
Y. Yoshida
such “camera”: (1) A mapping technique by focusing the γ-rays down to several
micrometres, and subsequently by measuring either the transmitted γ-rays or the
reemitted conversion and Auger electrons as well as the 6 keV-X-rays as functions
of the positions of the focused 14.4 keV γ-rays on the sample. (2) A direct imaging
technique using a CMOS camera for X-ray imaging (Hamamatsu). In this section, we
are going to explain both methods applied for the diffusion studies on Fe in multicrystalline silicon wafers for silicon solar cells as well as for carbon segregation
process in Fe steel.
9.5.1 Mapping Technique for Mössbauer Spectroscopic
Microscope (MSM)
Recently, a set-up of “3D-Mössbauer Spectroscopic Microscope (MSM)
(Fig. 9.39(a, b))” has been built to investigate the iron contamination in silicon
solar cells in our group [83–90]. The MSM system combines with different evaluation techniques such as a scanning electron microscope (FE-SEM, APCO), an electron beam induced current (EBIC, APCO), an energy dispersive X-ray spectrometer
(EDS, BRUCKER), an electron backscatter diffraction (EBSD, BRUCKER), and a
cylindrical sector electron analyzer (HV-CSA, FOCUS). We show the whole configuration in Fig. 9.39 (b). Furthermore, Fig. 9.40 explains the principle of the MSM: We
use a multi-capillary X-ray lens (MCX, HAMAMATSU) to focus 14.4 keV γ-rays on
a sample mounted on a precision XYZ-θ stage (KOHZU). The electrons and transmitted γ-rays are measured as functions of the sample position by a funnel type MicroChannel-Plate (MCP, HAMAMATSU) and a Si-PIN diode detector (AMPTEK),
respectively. We use a 3.7GBq57 Co-in-Rh source with an active area of 4 mmφ in
diameter (RITVERC) mounted on a moving-coil linear actuator (SMAC) operated
with a constant Doppler velocity corresponding to the isomer shift of a Mössbauer
spectral component. Finally, two different mapping images with 80 × 80 pixels are
created typically for an area of 400 μm × 400 μm or 4 mm × 4 mm corresponding
to each Fe component selectively with a spatial step of 5 or 50 μm, respectively.
In the following, we explain the essential elemental techniques combined in the
Mössbauer Spectroscopic Microscopy (MSM). The whole system can operate by a
LabVIEW program developed within our project. It is crucial to tune a resonance
condition of the γ-ray energy emitted from a
57 Co-in-Rh source to the isomer shift
corresponding to a Mössbauer component to be mapped. First of all, therefore, we
need a precision linear actuator to realize a constant Doppler-velocity operation with
an error of 0.005 mms
−1 for the case of
57 Fe Mössbauer microscope. We use a
moving-coil actuator coupled with a 100 nm-resolution linear encoder (SMAC).
This actuator enables us to operate with either a constant acceleration mode or a
constant velocity mode, as shown in Figs. 9.41(a) and (b), respectively. We obtained
the linewidth error of 0.007 mms
−1 which is sufficiently small for the mapping
Y. Yoshida
such “camera”: (1) A mapping technique by focusing the γ-rays down to several
micrometres, and subsequently by measuring either the transmitted γ-rays or the
reemitted conversion and Auger electrons as well as the 6 keV-X-rays as functions
of the positions of the focused 14.4 keV γ-rays on the sample. (2) A direct imaging
technique using a CMOS camera for X-ray imaging (Hamamatsu). In this section, we
are going to explain both methods applied for the diffusion studies on Fe in multicrystalline silicon wafers for silicon solar cells as well as for carbon segregation
process in Fe steel.
9.5.1 Mapping Technique for Mössbauer Spectroscopic
Microscope (MSM)
Recently, a set-up of “3D-Mössbauer Spectroscopic Microscope (MSM)
(Fig. 9.39(a, b))” has been built to investigate the iron contamination in silicon
solar cells in our group [83–90]. The MSM system combines with different evaluation techniques such as a scanning electron microscope (FE-SEM, APCO), an electron beam induced current (EBIC, APCO), an energy dispersive X-ray spectrometer
(EDS, BRUCKER), an electron backscatter diffraction (EBSD, BRUCKER), and a
cylindrical sector electron analyzer (HV-CSA, FOCUS). We show the whole configuration in Fig. 9.39 (b). Furthermore, Fig. 9.40 explains the principle of the MSM: We
use a multi-capillary X-ray lens (MCX, HAMAMATSU) to focus 14.4 keV γ-rays on
a sample mounted on a precision XYZ-θ stage (KOHZU). The electrons and transmitted γ-rays are measured as functions of the sample position by a funnel type MicroChannel-Plate (MCP, HAMAMATSU) and a Si-PIN diode detector (AMPTEK),
respectively. We use a 3.7GBq57 Co-in-Rh source with an active area of 4 mmφ in
diameter (RITVERC) mounted on a moving-coil linear actuator (SMAC) operated
with a constant Doppler velocity corresponding to the isomer shift of a Mössbauer
spectral component. Finally, two different mapping images with 80 × 80 pixels are
created typically for an area of 400 μm × 400 μm or 4 mm × 4 mm corresponding
to each Fe component selectively with a spatial step of 5 or 50 μm, respectively.
In the following, we explain the essential elemental techniques combined in the
Mössbauer Spectroscopic Microscopy (MSM). The whole system can operate by a
LabVIEW program developed within our project. It is crucial to tune a resonance
condition of the γ-ray energy emitted from a
57 Co-in-Rh source to the isomer shift
corresponding to a Mössbauer component to be mapped. First of all, therefore, we
need a precision linear actuator to realize a constant Doppler-velocity operation with
an error of 0.005 mms
−1 for the case of
57 Fe Mössbauer microscope. We use a
moving-coil actuator coupled with a 100 nm-resolution linear encoder (SMAC).
This actuator enables us to operate with either a constant acceleration mode or a
constant velocity mode, as shown in Figs. 9.41(a) and (b), respectively. We obtained
the linewidth error of 0.007 mms
−1 which is sufficiently small for the mapping