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.