1 - The Ohio State University
Download
Report
Transcript 1 - The Ohio State University
Time-Resolved IR and Mass Spectroscopy of
Laser-Ablated Magnesium
Yuki Miyamoto, Chisato Masaki, Naomi Ikeda, Jian Tang
and Kentarou Kawaguchi
Okayama University
67th International Conference on Molecular Spectroscopy, The Ohio State University, USA, June 18 – 22, 2012
Motivation
Group 2 Period 3
12
Mg
Magnesium
24.31
The most abundant
metal in the Universe
Solar-system abundances of the elements
Geochimica et Cosmochimica Acta 46, 2363 (1982)
the 9th in mass fraction and the
8th in atom fraction
Mg ~Si, Fe
•4th abundant in the Earth
•8th abundant in the Earth's crust
•5th abundant in the Ocean
•11th abundant in Human body
Laser Ablation Widely used technique in various fields
Easy (no sample-size requirement, no complicated sample preparation)
Applicable to any material
There are few IR spectroscopic studies on Laser-ablated
metals, although there are many works in optical region.
This study
Time-resolved IR spectroscopy of Laser-ablated Mg
Three Experiments
I. Time-Resolved FTIR spectroscopy
II. Mass measurement using a Q-Mass detector
III.Time-Resolved cw IR laser spectroscopy
Time-Resolved FTIR spectroscopy
Temporal behavior of IR emission/absorption of laser-ablated Mg
2000-4000 cm-1
time resolution ~ μs
freq. resolution ~ 0.01 cm-1
Ablation Laser
Nd:YLF SHG
526.5 nm
1~3 W
1 ~ 3 KHz
FTIR Spectra
12 emission lines
5g-4f
5p-5s
5f-4d
5d-5p
5s-4p
4p-3d
~ 50,000 cm-1
4d-4p
*Mg ground state (2p)6(3s)2
Emission of highly-excited Mg were observed.
Time-Resolved Spectra
Temporal change of 5g-4f transition
Triplet
Singlet
Two distinct components
with different Doppler width were
observed.
•Broad component ~ 0.1 cm-1
Emission Absorption
•Narrow component ~ 0.02 cm-1
Emission only
Why two components?
Origins of atoms
I. Direct desorption
II. Via some reactions ?
•dissociative recombination of molecular ions
Mg2+ + e- 2Mg
•recombination
Mg+ + e- Mg
Further information mass measurement / laser spectroscopy
Mass spectroscopy with Q-Mass
What species are produced by ablation ?
Mass range 1-200
Mass resolution < 1
•Turning On/ Off of ionization filament
neutral / ion
•Effect of residual or leaked air
adding O2 and N2.
Ablation Laser
Nd:YLF SHG
526.5 nm
1~3 W
1 ~ 3 KHz
Mass Spectra
FIL on
Intensity
Intensity
Mg
FIL off
Mg+
22
Mg+ and Mg2+ were observed.
25
26
27
28
FIL off
Intensity
5 10 15 20 25 30 35 40 45 50 55 60
24
Mg2+
0.5mJ/pulse
0
23
47
48
49
50
51
52
Oxygen/Nitrogen
~effect of residual or leaked air
Adding Oxygen
FIL off
FIL off
O2 ~ 10-4 Torr
Intensity
Intensity
MgO+
Mg2+
O2 ~ 10-5 Torr
O2 ~ 10-5 Torr
O2 ~ 10-4 Torr
39
40
41
42
43
47
48
49
50
51
52
*Nitrogen did not effect spectra.
•MgO+ was produced by adding O2 while Mg2+ was destructed.
Time-Resolved IR Laser Spectroscopy
High sensitivity, high resolution
time resolution ~ 0.1 μs
freq. resolution ~ 0.001 cm-1
IR Laser
Fiber laser pumped
PPLN OPO
3~4.5 μm
~200 mW
Ablation Laser
Nd:YLF SHG
526.5 nm
1~3 W
1 ~ 3 KHz
2D Spectra
5g-4f (triplet)
emission
absorption
Stimulated emission
~0.02 cm-1
absorption
~0.2 cm-1
5g-4f (triplet) transition consists
of broad absorption (0.2 cm-1)
and narrow stimulated emission
(~0.02cm-1).
Oxygen
Adding Oxygen
Oxygen
•No significant change by adding oxygen
Broad and Narrow Components
Broad-width component
width 0.1~0.2 cm-1 (10,000~20,000 K)
FTIR Spontaneous emission
Absorption
Laser Only Absorption
Temperature estimated from Doppler width
is comparable to energy of states(~ 70,000 K)
Thermal distributed
direct desorption
Narrow-width component
width 0.02 cm-1
FTIR Spontaneous emission
Laser
Stimulated emission
No dependence on O2
Stimulated emission
Non-thermal distribution
Due to recombination
×Dissociative recombination of Mg2+ or MgO+ should depend on amount of O2
✔Recombination Mg+ + e- Mg*
Only slow Mg+ can recombine with electrons. narrow width emission
Summary
Time-resolved IR spectroscopy and mass spectroscopy were
performed on laser-ablated Mg.
Mass spectra shows that major products are Mg, Mg+ and Mg2+.
By adding O2, MgO+ is produced and Mg2+ is destructed.
Observed IR emission / absorption of Mg were consist of two
components with different Doppler width.
Broad-width component = thermal, Narrow-width component
= Mg++e- recombination.