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RAMAN SCATTERING IN MoS2, MoSe2 AND α-MoTe2 AT HIGH PRESSURES
S. Sugai, T. Ueda, K. Murase
To cite this version:
S. Sugai, T. Ueda, K. Murase. RAMAN SCATTERING IN MoS2, MoSe2 AND α-MoTe2 AT HIGH PRESSURES. Journal de Physique Colloques, 1981, 42 (C6), pp.C6-320-C6-322.
�10.1051/jphyscol:1981693�. �jpa-00221630�
JOURNAL DE PHYSIQUE
CoZloque C6, suppZdment au n o 12, Tome 42, de'cembre 1981 page C6-320
RAMAN SCATTERING IN MoSZ,MoSe2 AND a-MoTe2 AT H I G H PRESSURES
S. sugai*, T . Ueda and K. Murase
Department of Physics, Osaka University, l'o'oyonaka, S60 Japan.
A b s t r a c t . - L a t t i c e v i b r a t i o n s under h y d r o s t a t i c high p r e s s u r e , up t o 180 kbar, were i n v e s t i g a t e d i n t h e layered m a t e r i a l s , 2H-MoS , 2H-MoSe2 and a2H-MoTe by Raman s c a t t e r i n g . Including t h e r i g i d l a y e r moie, one A and two E - 2' modes were observed i n each m a t e r i a l . The energy of t h e r i i 8 d l a y e r mo%g r a p i d l y increased with p r e s s u r e , but t h e i n c r e a s e became slow above 50 kbar.
The p r e s s u r e dependences of t h e i n t e r l a y e r s h e a r f o r c e c o n s t a n t and i n t r a - l a y e r s h e a r f o r c e c o n s t a n t were obtained using a l i n e a r chain model.
The Group V I t r a n s i t i o n metal, molybdenum dichalcogenide MoX2 has t h e t y p i c a l ZH-type l a y e r s t r u c t u r e . The 2H-MoX2 contains two l a y e r s i n a u n i t c e l l , and t h e r e f o r e t h e r i g i d l a y e r mode i s observable by o p t i c a l spectroscopy, and t h e weak van d e r Waals i n t e r l a y e r binding f o r c e can be i n v e s t i g a t e d . Applying hydro- s t a t i c p r e s s u r e , t h e i n t e r l a y e r d i s t a n c e r a p i d l y d e c r e a s e s and i n t e r l a y e r binding f o r c e i n c r e a s e s .
The c r y s t a l s t r u c t u r e o f 2H-MoS2, 2H-MoSe2 and aZH-MoTe2 i s t h e hexagonal 4
D6h. The long wavelength o p t i c a l phonons a r e Alg + A 2 U + B I U + 2BZg + Elg + E l u + 2E2g + E2 u. The A E and E -modes a r e Raman a c t i v e . One B and one E -
l g ' l g 2g 2g 2g
mode (E 2) a r e t h e r i g i d l a y e r modes. The l a t t i c e v i b r a t i o n has been measured by 22
Raman scattering,''') i n f r a r e d spectroscopy1-4) and neutron s c a t t e r i n g 5 ) a t atmos- p h e r i c p r e s s u r e . The A and E - modes i n 2H-MoS2 have been measured under high
6 ) 1 g 2g
p r e s s u r e .
The h y d r o s t a t i c high p r e s s u r e was generated by a diamond a n v i l c e l l . The p r e s s u r e was measured by a wavelength s h i f t of a ruby R1 fluorescence l i n e
(dI?/dX = 2 . 7 4 kbar / A). The Raman s c a t t e r i n g experiment was executed i n a back s c a t t e r i n g c o n f i g u r a t i o n using a 5145 A argon ion l a s e r average power 100 mW, and a double holographic g r a t i n g monochrometer, Spex 1400. The A and E - modes a r e
1 g 2g
observable i n t h i s c o n f i g u r a t i o n .
Figures l ( a ) - (c) show t h e observed p r e s s u r e dependence of t h e phonon energies. The e n e r g i e s of r i g i d l a y e r modes i n c r e a s e r a p i d l y with p r e s s u r e , but t h e i n c r e a s e decreases above 50 kbar. The e n e r g i e s a t atmospheric p r e s s u r e a r e i n good agreement with Wieting, e t a l l s and t h e p r e s s u r e c o e f f i c i e n t of t h e A and E - modes n e a r atmospheric p r e s s u r e i s i n good agreement with Bagnall, e t
1 g 2g
"Present address: Div.Engineering, Brown U n i v e r s i t y , Providence, RI 02912 Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981693
a1 I s d a t a . 6, These r e s u l t s a r e summarized i n Table I .
Many models have been proposed t o calcu- l a t e t h e phonon energy. I n t h i s paper, t h e simple l i n e a r chain model proposed by Wieting 7 ) was adopted. The s h e a r and compressive f o r c e c o n s t a n t s between t h e chalcogen planes o f t h e neighboring l a y e r s a r e expressed by C; and c:,
r e s p e c t i v e l y . The s h e a r and compressive f o r c e c o n s t a n t s between t h e molybdenum and chalcogen planes i n a l a y e r a r e expressed by C: and cC w'
r e s p e c t i v e l y . The energy of t h e A and E 1 g
modes a r e 2g-
PRESSURE( kbar)
Fig. 1 (a)
PRESSURE( kbar)
where M and M a r e t h e atomic masses o f molyb- m
denum and chalcogen, and M = MmMJ(Mm+2Mx). The shear f o r c e c o n s t a n t C: r a p i d l y i n c r e a s e s with p r e s s u r e a s shown i n Fig. 2. The r a t i o of t h e
i n t e r l a y e r s h e a r f o r c e c o n s t a n t C: and t h e i n t r a l a y e r shear f o r c e c o n s t a n t C: r a p i d l y i n c r e a s e s with p r e s s u r e , but t h e value i s only 8%, even a t 150 kbar. Evidence of a phase t r a n s i t i o n was n o t observed i n t h e p r e s s u r e range of t h i s experiment.
The authors a r e g r a t e f u l t o S . Uchida and S. Tanaka f o r supplying MoS2 and MoSe2
c r y s t a l s . Fig. l ( b )
C6-322 JOURNAL DE PHYSIQUE
-
0 2 0 4 0 6 0 8 0
PRESSURE (Ubar)
IIIIIIIIIII
'0 40 80 120 160 200 PRESSURE ( kbar)
Fig.2 : P r e s s u r e dependence of t h e
- i n t e r l a y e r f o r c e c o n s t a n t .
Table 1 : The phonon e n e r g i e s , t h e f o r c e c o n s t a n t s and t h e i r p r e s s u r e d e r i v a t i v e s .
Fig. l ( c )
F i g . 1 : P r e s s u r e dependence of t h e phonon e n e r g i e s i n 2H-MoS2 ( a ) , i n 2H-MoSe2 (b) , and a2H-MoTe2 ( c ) .
References
1) T. J . Wieting and J . L . V e r h l e , Phys. Rev. C1971) 4286.
2) T . J . Wieting, A. G r i s e l and F. Levy, Physica (1980) 337.
3) G. Lucovsky, R. M. White, J . A. Benda and J . F. R e v e l l i , Phys. Rev, - 87 Cl973) E 2g
b w
W - a p
33.5 0.45 5.8
26 0.36
27.5 0.37
3859.
4) S . Uchida and S . Tanaka, J. Phys. Soc. Japan, 45 (1978) 153.
51 N . Wakabayashi, H. G. Smith and R . M. Nicklow, Fhys. Rev. B12 (1975) 659.
6) A. G. Bagnall, W. Y . Liang, E. A. Marseglia and B. ~ e l b e r , P h y s i c a (1980) 343.
7) T. J . Wieting, S o l i d S t a t e Commun. 12 (1973) 931.
E 2g
a w
W - a P Y
387 0.19 0.21 283 0.23 234 0.26
#
MoS MoSe2 clMoTe2
A 1 g
a w
W - a P Y
cm-I cm-I k b a r - I 413.5 0.40 0.42
244 0.31
174 0.26
MoS MoSeZ aMoTe2
a (Cb/Cw)
a P
~ X I O - ~
5 9
- Cb Cw 1 . 6 x 1 0 - ~ 1 . 8 3.5
a c:
3-F
110 210 230
c;
1 . 5 ~ 1 0 ~ 1 . 4
1.1 C;
dyne 2 . 7 ~ 1 0 3 2.6 3.9
a c:
-
a P 1 1 dyne Cm- kbar-
7 0 8 0 110
