optically-induced structural change in graphite yoshida lab. naoki hosoya 1 [1]ramani k. raman,...
TRANSCRIPT
![Page 1: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/1.jpg)
Optically-Induced Structural Change
in Graphite
YOSHIDA Lab.
Naoki HOSOYA
1
[1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan,
Teng Yang, Savas Berber, and David Tománek,
Phys. Rev. Lett. 101 077401 (2008).
![Page 2: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/2.jpg)
Contents
2
Introduction・ Structural Change
・Graphite-Diamond Transition
・ Previous Research of Optical Irradiation to Graphite
・ This Letter
Main Issue・Ultrafast Electron Crystallography (UEC)
・ Equilibrium
・Near-Equilibrium
・ Far-from-Equilibrium
・ Further Elucidation
・ Calculations
Summary
![Page 3: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/3.jpg)
Structural Change (SC)
3
Temperature-induced SC Pressure-induced SC Electric / Magnetic field-induced SC
Optically-induced SCUltrafast and efficient
・ Development of materials for optical memory
・Material Design without changing chemical composition
・ Building new concept for material science
![Page 4: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/4.jpg)
4
Graphite-Diamond Transition
Graphite-Diamond transition by temperature or/and pressure.
This can be induced by optical irradiation to Graphite.
[2] T. Meguro et al., Appl Phys. Lett. 79, 3866 (2001)[3] H. Nakayama and H. Katayama-Yoshida, J. Phys. Condens. Matter 15, R1077 (2003)
Graphite Diamond
![Page 5: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/5.jpg)
Previous Researches ofOptical Irradiation to Graphite
Photo-induced melting[2] S. Ashitkov et al., JETP Lett. 75, 87 (2002).
[3] D.H. Reitze, H. Ahn, and M.C. Downer, Phys. Rev. B 45, 2677 (1992).
Generation of coherent phonon[4] T. Mishima, K. Nitta, and Y. Masumoto, Phys. Rev. B 62, 2908 (2000).
[5] K. Ishioka, M. Hase, M. Kitajima, and K. Ushida, Appl. Phys. Lett. 78, 3965 (2001).
Auger decay process[6] H. Nakayama and H. Katayama-Yoshida, J. Phys. Condens. Matter 15, R1077 (2003)
By observing changes in the electronic properties
(Indirect observation of atomic motion)
5
![Page 6: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/6.jpg)
This Letter
First direct determination
of
by
for
6
Optically induced structural change in graphite
Ultrafast electron crystallography (UEC) and ab initio DFT calculation
Graphite-diamond transition
![Page 7: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/7.jpg)
Sample : Highly oriented pyrolytic graphite (HOPG)
Pump : A mode-locked Ti-Sapphire laser pulse
Probe : A photo generated electron beam
Feature of using electron beam Short wavelength (λe = 0.069 Å) Large scattering cross section Femtosecond temporal resolution
Direct observation of atomic motion of carbon
7
Ultrafast Electron Crystallography (UEC)
The layered structurte of graphite
![Page 8: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/8.jpg)
Left : Diffraction pattern of graphite
Right : Layer density distribution function (LDF), obtained via Fourier transform of the diffraction pattern.
8
Equilibrium regime (not excited)
The peaks are good agreement with the structure of bulk graphite
The decay of LDF peaks suggest a probing depth of ≈ 1 nm.
![Page 9: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/9.jpg)
9
Near-equilibrium (weakly-excited)
Dropping the intensity of all 3 maxima
[7] T. Kampfrath et al., Phys. Rev. Lett. 95, 187403 (2005)
Recent Report :・ Generation of coherent phonons with E2g symmetry.[4][5]
・ Phonon relaxation times is 7 ps.[7]
Direct measure of the phonon-phonon interaction.
Out-of-plane displacement of the atoms.
8ps
![Page 10: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/10.jpg)
10
Far-from-equilibrium (strongly-excited)
Why saturate ?
− Metastable structure.
Expansion of interlayer distance
(6% at F = 40 mJ/cm2)
Why expansion ?
− Effect of rise surface potential.
Lattice vibration :
linearly increasing (Near-equilibrium)
saturation (Far-from-equilibrium)
![Page 11: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/11.jpg)
Maximum of surface potential Vs ≈ 12 VContraction of interlayer distance ≈ 6%.
The potential rise Vs yields an internal field of E ≈ 1.2 V/Å (probe depth ≈ 1nm), which causes Coulomb stress.
11
Effect of surface potential
![Page 12: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/12.jpg)
12
Further elucidation of the structural change
The time evolution of the LDF curves at F = 77 mJ/cm2.
New peak at R ≈ 1.9 Å appears.
Diamond peak R ≈ 1.99 Å
The transient sp3-like structure emerged.
![Page 13: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/13.jpg)
13
Calculation technique
ab initio DFT calculation in the LDA Slab model in hexagonal graphite . The ABINIT code. 64 Ry energy cutoff. Troullier-Martins pseudopotential (norm conseriving). Ceperley-Alder form of the exchange-correlation functional. Brillouin zone of the 4 atoms bulk unit cell. 24×24×12 k-point.
Density of states (solid line)
Fermi-Dirac distribution at 0 K (dashed line)
at kBT = 1.0 eV (dotted line)
Total charge density ρ(r) at 0 K
![Page 14: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/14.jpg)
Calculation of the effect of temperature instead of electron excitation
kBTe = 1.0 eV (≈ 10000K)
Δρ (r) = ρ(r; kBTe) − ρ(r; 0)
Increase of the population of C2pz orbitals.
→ Increase of layer attraction
Decrease of the population of in-layer bonding-states.
→ Expansion of in-layer
Global structure optimization calculation result
Contraction of interlayer distance by 1.5%
14
Effect of temperature
![Page 15: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/15.jpg)
Charge separation by the laser pulse induces the Coulomb stress.
To take the effect into account,
the charge distribution is created following below scheme.
Contraction of interlayer distance by 2-3 %
Combined with the result of previous page (1.5% contraction),
the contraction of the interlayer distance by ≈ 5% can be explained.
15
Effect of Coulomb stress
1.2 V/Å
-
+
![Page 16: Optically-Induced Structural Change in Graphite YOSHIDA Lab. Naoki HOSOYA 1 [1]Ramani K. Raman, Yoshie Murooka, Chong-Yu Ruan, Teng Yang, Savas Berber,](https://reader031.vdocuments.site/reader031/viewer/2022032106/56649e605503460f94b5b457/html5/thumbnails/16.jpg)
Summary
The first direct determination of structural changes induced in graphiteby a femtosecond laser pulse using UEC.
Graphite is driven into a transient state with sp3-like character.
The main forces of this structural change are the modified force field in the excited state andthe Coulomb stress.
Issue : More precise theoretical analysis
(e.g. Molecular Dynamics using time-dependent DFT)
16