- Email: [email protected]
Raman spectroscopy and FTIR spectroscopy studies of Mn-doped CdSe QDs at different particles size
Accepted Manuscript Title: Raman Spectroscopy and FTIR Spectroscopy Studies of Mn-doped CdSe QDs at Different Particles Size Authors: Nor Aliya Hamizi, Mohd Rafie Johan, Zaira Zaman Chowdhury, Yasmin Abdul Wahab, Yarub Kahtan Abdul-Rahman Al-Douri, Asmalina Mohamed Saat, Omid Akbarzadeh Pivehzhani PII: DOI: Reference:
S0030-4026(18)31737-6 https://doi.org/10.1016/j.ijleo.2018.10.214 IJLEO 61840
To appear in: Received date: Accepted date:
28 September 2018 31 October 2018
Please cite this article as: Hamizi NA, Rafie Johan M, Zaman Chowdhury Z, Wahab YA, Abdul-Rahman Al-Douri YK, Saat AM, Pivehzhani O, Raman Spectroscopy and FTIR Spectroscopy Studies of Mn-doped CdSe QDs at Different Particles Size, Optik (2018), https://doi.org/10.1016/j.ijleo.2018.10.214 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Raman Spectroscopy and FTIR Spectroscopy Studies of Mndoped CdSe QDs at Different Particles Size
SC RI PT
Nor Aliya Hamizi1*, Mohd Rafie Johan1, Zaira Zaman Chowdhury1, Yasmin Abdul Wahab1, Yarub Kahtan Abdul-Rahman Al-Douri1, Asmalina Mohamed Saat2, Omid Akbarzadeh Pivehzhani1 E-mail:
[email protected]*,
[email protected],
[email protected],
[email protected], [email protected], [email protected], [email protected]
Nanotechnology & Catalysis Research Centre, Deputy Vice Chancellor (Research & Innovation) Office,
N
1
Fax: +603 7967 6556
U
Tel: +603 7967 6959
2
A
University of Malaya, 50603 Kuala Lumpur, MALAYSIA.
Universiti Kuala Lumpur Malaysian Institute of Marine Engineering Technology (UniKL MIMET)
D
32200 Lumut Perak, MALAYSIA.
M
Department, Dataran Industri Teknologi Kejuruteraan Marin, Bandar Teknologi Maritim, Jalan Pantai Remis,
Abstract
TE
In this paper, we exclusively report on raman spectroscopy and fourier-transform infrared (FTIR)
EP
spectroscopy results and analysis of zinc blende manganese-doped cadmium selenide quantum dots (Mn-doped CdSe QDs) that synthesized using inverse Micelle technique with physical size ranging
CC
from 3 to 14 nm. Two significant peaks were observed correspond to the raman scattering by longitudinal optical (LO) of phonon and its first overtone (2LO) which located near ~ 200 and 400
A
cm-1 under an exposure of 532 nm incident laser The role of oleic acid acid as a surfactant and capping agent shows in FTIR spectra. Keywords: cadmium selenide; quantum dots; manganese doped; semiconductor; chemical synthesis; raman spectroscopy; FTIR spectroscopy PACS numbers: 73.67. Kv, 81.07.Ta 1
1. Introduction Mn-doped CdSe QDs (zinc blende) was a tremendously significant to the semiconductor research since Mn incorporation into CdSe QDs promised a high-density
SC RI PT
diluted semiconductor for spintronic application and provide good traps for excitation
electrons which significant for electronic and optoelectronic devices [1]. The band gap tunability can be achieved by tuning size of the QDs [2] to target a specific application requirement. Furthermore, the intrinsic optical properties of CdSe QDs is reported to be
tailored by the introduction of transition metal dopant (i.e. Mn, Mg and Zn) [3, 4]. The
U
integration of size variation and introduction of transition metal dopant in CdSe QDs system
N
drawn a great attention to the outcome analysis and how it can be manipulate to the specific
A
application direction [5]. Come to realize the important of phonon scattering analysis &
M
organic capping structure analysis, alongside with the other analysis such optical and
D
structural properties, we here present the raman scattering techniques and FTIR spectroscopy
EP
2. Experimental
TE
analyses.
CC
Mn-doped CdSe QDs were prepared using Mn-Cd and Se as precursors. 0.5g of Mn acetate and 0.5 g of CdO, 25 ml of paraffin oil and 15 ml of oleic acid were loaded in a three
A
neck round bottom flask. The mixture was placed into glove box in vacuum condition. The solution was heated to 160 ◦C and stirred until the CdO was completely dissolved and a light yellowish homogeneous solution was obtained. Then, 0.079 g of Se in 50 ml of paraffin oil was carefully heated in a glove box under vacuum condition to 220 ◦C with rapid stirring in another three neck round bottom flask. The solution turned light orange and then wine red. 2
Then about 5ml of Mn-Cd solution was swiftly injected into the Se solution during rapid stirring. The temperature dropped to 210 ◦C immediately after the injection, then rose to 220 ◦C. The temperature was maintained at 220 ◦C for the growth of CdSe QDs at different times,
SC RI PT
i.e. 0, 0.2, 0.5, 1, 5, 16, 46 and 90 mins. Finally, the precipitate was isolated from solvents and unreacted reagent via centrifugation, further washed with methanol several times and was dried in the vacuum oven at 50 ◦C.
The particles size determination of Mn-doped CdSe QDs was performed using High-
resolution Transmission Electron Microscope (HRTEM) LEO LIBRA instrument operating
U
at 120 kV. Infrared spectra of Mn-doped CdSe QDs samples are taken using a Perkin Elmer
N
2000 Fourier Transform Infrared spectroscopy (FTIR) wavenumber region between 4000
A
and 400 cm-1. The raman scattering behavior will be observed using Horiba Scientific Xplora
TE
3. Results and Discussions
D
M
Micro-raman Spectroscopy with 532 nm laser source wavelength.
Mn-doped CdSe QDs samples are successfully synthesized with physical size ranging
EP
from 3 to 14 nm (Fig 1). The XRD difractogram shows three well-defined peaks were
CC
observed at 2θ = 24.7 º, 41.6 º and 49.3 º correspond to (111), (220) and (311) planes
A
respectively (Fig 2) is an evidence of zinc blende structure QDs.
3
SC RI PT U
N
Figure 1: HRTEM image of Mn-doped CdSe QDs with QDs size distribution (insert) at (a)
CC
EP
TE
D
M
A
0 and (b) 90 mins reaction time
A
Figure 2: XRD patterns of Mn-doped CdSe QDs sample
Further analysis on optical and vibrational properties of Mn-doped CdSe QDs various sizes are studied using Raman spectroscopy. Fig. 3 shows the Raman spectra of Mn4
doped CdSe QDs of 0 to 90 min samples. Two significant peaks were observed correspond to the scattering by the longitudinal optical (LO) of phonon and its first overtone (2LO) which located near ~ 200 and 400 cm-1 under an exposure of 532 nm incident laser. The LO and
SC RI PT
2LO peaks were observed to behave red-shifted with respect to the excitation wavelength as
tabulated in Table 1 Furthermore, the overall LO of Mn-doped CdSe QDs shows strong blueshift compared to the LO for and pure CdSe QDs of 3.15 nm particle diameter (206 cm-1) [6] and bulk CdSe QDs (210 cm-1) [7]. Both of these raman-shifts are induced by phonon confinement. Furthermore, this red-shift behavior may contributed by lattice strain induced
U
by the doping of Mn mechanism into CdSe QDs [8]. These two factors may also lead to the
N
domination of anti-Stoke`s shift in highest occupied molecular orbital and lowest un-
A
occupied molecular orbital (HOMO-LUMO) transition for 16, 46 and 90 mins samples
M
respectively [7].
D
In addition, Mn-doped CdSe QDs exhibits extremely broader LO (~100 cm-1) peak
TE
compared to bulk CdSe (~5 cm-1) [7] which can induced by combination factor of phonon confinement, band gap structural disorder and QDs sizes distribution that are all is a function
EP
of QDs sizes growth and Mn-doped factor [6, 9].
CC
On the other hand, there was a slight increase in LO line width as the QDs size reduced. The increment is believe to be arises from the low-wavenumber side induced by the
A
negative dispersion of phonon branch away from the zone-centre optical phonon as proposed in Brillouin zone [10]. It is also reported that the line width increases are prominent for QDs with size below 10 nm [11]. This which is contradic with Mn-doped CdSe QDs raman analysis which shows of constant increase in LO line width for QDs size 11 to 14 nm (1690 mins) which similarly observed for QDs with below size of 10 nm. 5
Equally important, the peak shoulder features at low wavenumber of LO peak observed in each Raman spectra. This surface optical (SO) phonon mode are observed in wide range of QDs semiconductors which is also contributed by the phonon confinement
SC RI PT
phenomenon of LO phonon with non-zero angular momenta (Trallero et al., 1998). Then
again, the Mn-doped as a lattice strain inducer can influence the formation of this SO features [12].
The intensity ratio of 2LO and LO (𝐼2𝐿𝑂 /𝐼𝐿𝑂 ) reported to be strongly related to the electron-phonon coupling strength in QDs [13]. As for Mn-doped CdSe QDs the 𝐼2𝐿𝑂 /𝐼𝐿𝑂
U
not varied much change (~0.32- 0.37), which indicated that electron-phonon coupling in Mn-
A
CC
EP
TE
D
M
A
N
doped CdSe QDs were not affected much with QDs size variations [13].
6
SC RI PT U N A M D TE EP
A
CC
Figure 3: Raman scattering spectra of Mn-doped CdSe QDs at various reaction times
7
Table 1: Raman scattering parameters and excitation wavelengths for various sizes of Mndoped CdSe QDs samples 𝐼2𝐿𝑂 /𝐼𝐿𝑂
QDs physical size
LO
2LO
(nm)
(cm-1)
3
205.3
410.0
5
205.6
410.7
8
206.2
411.5
9
206.6
412.3
10
207.0
412.9
0.33
11
207.8
12
208.3
14
208.8
0.37 0.36 0.33
0.34
414.0
0.32
415.0
0.33
A
413.4
D
M
0.37
N
U
SC RI PT
(cps)
TE
The surface analysis of Mn-doped CdSe QDs performed by observing the FTIR transmittance spectra of Mn-doped CdSe QDs samples, paraffin oil and oleic acid (Fig. 4).
EP
Mn-doped CdSe QDs samples spectra exhibits a well defined peak of triplet band located at
CC
2855, 2925 and 2956 cm−1 correspond to CH2 stretching (sp3) which might act as surface termination of these QDs by functional groups [14]. The band at 722 cm−1 corresponding to
A
CH2 vibrational mode [5]. The peak at 1377cm−1 shows the CH3 bending in paraffin oil. C– N stretching behavior can be shown by a peak at 1463cm−1. In addition, the presence of IR peak at 1712 cm−1 indicates the signatures of capping agent, oleic acid bounded to the surface of Mn-doped CdSe QDs. On the basis of the FTIR data, the surface of the CdSe QDs is 8
mainly coated with oleic acid ligand. Flexible organic molecules provide repulsive interactions between the QDs in methanol, thus preventing aggregation. A small peak shifting (~0.1 – 2 cm-1) towards larger wavenumber observed as the QDs sizes increase.
SC RI PT
Small peak shift towards larger wavenumber also observed in Mn-doped CdSe QDs
FTIR peaks as compared to pure CdSe QDs [16], particularly for triplet band of CH2
A
CC
EP
TE
D
M
A
N
U
stretching.
Figure 4: The FTIR pattern of paraffin oil, oleic acid and Mn-doped CdSe QDs at various reaction time
9
4. Conclusion FTIR spectra confirmed the oleate-capping introduced to the surface of Mn-doped CdSe QDs which act as the surface passivator which reduced the particle interfacial electron and hole
SC RI PT
trapping phenomenon. The phonon confinement observed in Mn-doped CdSe QDs from the blue-shift behavior of LO and 2LO compared to pure CdSe QDs.
Acknowledgement
This work was financially supported by Postgraduate Research Grant (PG084-2012B) and
U
MyBrain15 scholarship by government of Malaysia. The authors gratefully acknowledge the
A
N
financial support.
D
M
References
S. C. Erwin, L. J. Zu, M. I. Haftel, A. L. Efros, T. A. Kennedy, and D. J. Norris, Nature. 436 (2005).
[2]
A. P. Alivisatos, Science. 271 (1996).
[3]
Y. M. Sung, W. C. Kwak, & T. G. Kim, Crystal Growth & Design, 8(4), 1186-1190 (2008).
CC
EP
TE
[1]
W. C. Kwak, Y. M. Sung, T. G. Kim, and W. S. Chae, Appl. Phys. Lett. 90, (2007).
[5]
N. A. Hamizi, (2017). Synthesis And Characterization Of Mn-Doped CdSe Quantum Dots Via Inverse Micelle Technique (Doctoral dissertation). University of Malaya, Kuala Lumpur, Malaysia.
A
[4]
[6]
A. M. Kelley, Q. Dai, Z. J. Jiang, J. A. Baker & D. F. Kelley, Chemical Physics, 422, 272-276 (2013).
10
V. Plotnichenko & Y. Mityagin, Sov. Phys. Solid State, 19(9), 1584-1586 (1977).
[8]
C. Barglik-Chory, D. Buchold, M. Schmitt, W. Kiefer, C. Heske, C. Kumpf, ... & M. Lentze, Chemical physics letters, 379(5-6), 443-451 (2003).
[9]
N. H. Patel, M. Deshpande, S. V. Bhatt, K. R. Patel & S. Chaki, Advanced Materials Letters, 5, 671-677 (2014).
SC RI PT
[7]
[10] H. Bilz, & W. Kress, Springer Series in Solid State Sciences (1979).
[11] A. K. Arora, M. Rajalakshmi, T. Ravindran, & V. Sivasubramanian, Journal of Raman Spectroscopy, 38(6), 604-617 (2007).
U
[12] T. Muck, J. W. Wagner, L. Hansen, V. Wagner & J. Geurts, Journal of Applied Physics, 95(10), 5403-5407 (2004).
A
N
[13] M. Klein, F. Hache, D. Ricard, & C. Flytzanis, Physical Review B, 42(17), 11123 (1990).
M
[14] G. B. Deacon, S. J. Faulks, & G. N. Pain, (1986). Advances in organometallic chemistry, 25, 237-276 (1986).
TE
D
[15] L. R. Becerra, C. B. Murray, R. G. Griffin, & M. G. Bawendi, The Journal of chemical physics, 100(4), 3297-3300 (1994).
A
CC
EP
[16] N. A. Hamizi & M. R. Johan, Materials Chemistry and Physics, 124(1), 395-398 (2010).
11
S0030-4026(18)31737-6 https://doi.org/10.1016/j.ijleo.2018.10.214 IJLEO 61840
To appear in: Received date: Accepted date:
28 September 2018 31 October 2018
Please cite this article as: Hamizi NA, Rafie Johan M, Zaman Chowdhury Z, Wahab YA, Abdul-Rahman Al-Douri YK, Saat AM, Pivehzhani O, Raman Spectroscopy and FTIR Spectroscopy Studies of Mn-doped CdSe QDs at Different Particles Size, Optik (2018), https://doi.org/10.1016/j.ijleo.2018.10.214 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Raman Spectroscopy and FTIR Spectroscopy Studies of Mndoped CdSe QDs at Different Particles Size
SC RI PT
Nor Aliya Hamizi1*, Mohd Rafie Johan1, Zaira Zaman Chowdhury1, Yasmin Abdul Wahab1, Yarub Kahtan Abdul-Rahman Al-Douri1, Asmalina Mohamed Saat2, Omid Akbarzadeh Pivehzhani1 E-mail:
[email protected]*,
[email protected],
[email protected],
[email protected], [email protected], [email protected], [email protected]
Nanotechnology & Catalysis Research Centre, Deputy Vice Chancellor (Research & Innovation) Office,
N
1
Fax: +603 7967 6556
U
Tel: +603 7967 6959
2
A
University of Malaya, 50603 Kuala Lumpur, MALAYSIA.
Universiti Kuala Lumpur Malaysian Institute of Marine Engineering Technology (UniKL MIMET)
D
32200 Lumut Perak, MALAYSIA.
M
Department, Dataran Industri Teknologi Kejuruteraan Marin, Bandar Teknologi Maritim, Jalan Pantai Remis,
Abstract
TE
In this paper, we exclusively report on raman spectroscopy and fourier-transform infrared (FTIR)
EP
spectroscopy results and analysis of zinc blende manganese-doped cadmium selenide quantum dots (Mn-doped CdSe QDs) that synthesized using inverse Micelle technique with physical size ranging
CC
from 3 to 14 nm. Two significant peaks were observed correspond to the raman scattering by longitudinal optical (LO) of phonon and its first overtone (2LO) which located near ~ 200 and 400
A
cm-1 under an exposure of 532 nm incident laser The role of oleic acid acid as a surfactant and capping agent shows in FTIR spectra. Keywords: cadmium selenide; quantum dots; manganese doped; semiconductor; chemical synthesis; raman spectroscopy; FTIR spectroscopy PACS numbers: 73.67. Kv, 81.07.Ta 1
1. Introduction Mn-doped CdSe QDs (zinc blende) was a tremendously significant to the semiconductor research since Mn incorporation into CdSe QDs promised a high-density
SC RI PT
diluted semiconductor for spintronic application and provide good traps for excitation
electrons which significant for electronic and optoelectronic devices [1]. The band gap tunability can be achieved by tuning size of the QDs [2] to target a specific application requirement. Furthermore, the intrinsic optical properties of CdSe QDs is reported to be
tailored by the introduction of transition metal dopant (i.e. Mn, Mg and Zn) [3, 4]. The
U
integration of size variation and introduction of transition metal dopant in CdSe QDs system
N
drawn a great attention to the outcome analysis and how it can be manipulate to the specific
A
application direction [5]. Come to realize the important of phonon scattering analysis &
M
organic capping structure analysis, alongside with the other analysis such optical and
D
structural properties, we here present the raman scattering techniques and FTIR spectroscopy
EP
2. Experimental
TE
analyses.
CC
Mn-doped CdSe QDs were prepared using Mn-Cd and Se as precursors. 0.5g of Mn acetate and 0.5 g of CdO, 25 ml of paraffin oil and 15 ml of oleic acid were loaded in a three
A
neck round bottom flask. The mixture was placed into glove box in vacuum condition. The solution was heated to 160 ◦C and stirred until the CdO was completely dissolved and a light yellowish homogeneous solution was obtained. Then, 0.079 g of Se in 50 ml of paraffin oil was carefully heated in a glove box under vacuum condition to 220 ◦C with rapid stirring in another three neck round bottom flask. The solution turned light orange and then wine red. 2
Then about 5ml of Mn-Cd solution was swiftly injected into the Se solution during rapid stirring. The temperature dropped to 210 ◦C immediately after the injection, then rose to 220 ◦C. The temperature was maintained at 220 ◦C for the growth of CdSe QDs at different times,
SC RI PT
i.e. 0, 0.2, 0.5, 1, 5, 16, 46 and 90 mins. Finally, the precipitate was isolated from solvents and unreacted reagent via centrifugation, further washed with methanol several times and was dried in the vacuum oven at 50 ◦C.
The particles size determination of Mn-doped CdSe QDs was performed using High-
resolution Transmission Electron Microscope (HRTEM) LEO LIBRA instrument operating
U
at 120 kV. Infrared spectra of Mn-doped CdSe QDs samples are taken using a Perkin Elmer
N
2000 Fourier Transform Infrared spectroscopy (FTIR) wavenumber region between 4000
A
and 400 cm-1. The raman scattering behavior will be observed using Horiba Scientific Xplora
TE
3. Results and Discussions
D
M
Micro-raman Spectroscopy with 532 nm laser source wavelength.
Mn-doped CdSe QDs samples are successfully synthesized with physical size ranging
EP
from 3 to 14 nm (Fig 1). The XRD difractogram shows three well-defined peaks were
CC
observed at 2θ = 24.7 º, 41.6 º and 49.3 º correspond to (111), (220) and (311) planes
A
respectively (Fig 2) is an evidence of zinc blende structure QDs.
3
SC RI PT U
N
Figure 1: HRTEM image of Mn-doped CdSe QDs with QDs size distribution (insert) at (a)
CC
EP
TE
D
M
A
0 and (b) 90 mins reaction time
A
Figure 2: XRD patterns of Mn-doped CdSe QDs sample
Further analysis on optical and vibrational properties of Mn-doped CdSe QDs various sizes are studied using Raman spectroscopy. Fig. 3 shows the Raman spectra of Mn4
doped CdSe QDs of 0 to 90 min samples. Two significant peaks were observed correspond to the scattering by the longitudinal optical (LO) of phonon and its first overtone (2LO) which located near ~ 200 and 400 cm-1 under an exposure of 532 nm incident laser. The LO and
SC RI PT
2LO peaks were observed to behave red-shifted with respect to the excitation wavelength as
tabulated in Table 1 Furthermore, the overall LO of Mn-doped CdSe QDs shows strong blueshift compared to the LO for and pure CdSe QDs of 3.15 nm particle diameter (206 cm-1) [6] and bulk CdSe QDs (210 cm-1) [7]. Both of these raman-shifts are induced by phonon confinement. Furthermore, this red-shift behavior may contributed by lattice strain induced
U
by the doping of Mn mechanism into CdSe QDs [8]. These two factors may also lead to the
N
domination of anti-Stoke`s shift in highest occupied molecular orbital and lowest un-
A
occupied molecular orbital (HOMO-LUMO) transition for 16, 46 and 90 mins samples
M
respectively [7].
D
In addition, Mn-doped CdSe QDs exhibits extremely broader LO (~100 cm-1) peak
TE
compared to bulk CdSe (~5 cm-1) [7] which can induced by combination factor of phonon confinement, band gap structural disorder and QDs sizes distribution that are all is a function
EP
of QDs sizes growth and Mn-doped factor [6, 9].
CC
On the other hand, there was a slight increase in LO line width as the QDs size reduced. The increment is believe to be arises from the low-wavenumber side induced by the
A
negative dispersion of phonon branch away from the zone-centre optical phonon as proposed in Brillouin zone [10]. It is also reported that the line width increases are prominent for QDs with size below 10 nm [11]. This which is contradic with Mn-doped CdSe QDs raman analysis which shows of constant increase in LO line width for QDs size 11 to 14 nm (1690 mins) which similarly observed for QDs with below size of 10 nm. 5
Equally important, the peak shoulder features at low wavenumber of LO peak observed in each Raman spectra. This surface optical (SO) phonon mode are observed in wide range of QDs semiconductors which is also contributed by the phonon confinement
SC RI PT
phenomenon of LO phonon with non-zero angular momenta (Trallero et al., 1998). Then
again, the Mn-doped as a lattice strain inducer can influence the formation of this SO features [12].
The intensity ratio of 2LO and LO (𝐼2𝐿𝑂 /𝐼𝐿𝑂 ) reported to be strongly related to the electron-phonon coupling strength in QDs [13]. As for Mn-doped CdSe QDs the 𝐼2𝐿𝑂 /𝐼𝐿𝑂
U
not varied much change (~0.32- 0.37), which indicated that electron-phonon coupling in Mn-
A
CC
EP
TE
D
M
A
N
doped CdSe QDs were not affected much with QDs size variations [13].
6
SC RI PT U N A M D TE EP
A
CC
Figure 3: Raman scattering spectra of Mn-doped CdSe QDs at various reaction times
7
Table 1: Raman scattering parameters and excitation wavelengths for various sizes of Mndoped CdSe QDs samples 𝐼2𝐿𝑂 /𝐼𝐿𝑂
QDs physical size
LO
2LO
(nm)
(cm-1)
3
205.3
410.0
5
205.6
410.7
8
206.2
411.5
9
206.6
412.3
10
207.0
412.9
0.33
11
207.8
12
208.3
14
208.8
0.37 0.36 0.33
0.34
414.0
0.32
415.0
0.33
A
413.4
D
M
0.37
N
U
SC RI PT
(cps)
TE
The surface analysis of Mn-doped CdSe QDs performed by observing the FTIR transmittance spectra of Mn-doped CdSe QDs samples, paraffin oil and oleic acid (Fig. 4).
EP
Mn-doped CdSe QDs samples spectra exhibits a well defined peak of triplet band located at
CC
2855, 2925 and 2956 cm−1 correspond to CH2 stretching (sp3) which might act as surface termination of these QDs by functional groups [14]. The band at 722 cm−1 corresponding to
A
CH2 vibrational mode [5]. The peak at 1377cm−1 shows the CH3 bending in paraffin oil. C– N stretching behavior can be shown by a peak at 1463cm−1. In addition, the presence of IR peak at 1712 cm−1 indicates the signatures of capping agent, oleic acid bounded to the surface of Mn-doped CdSe QDs. On the basis of the FTIR data, the surface of the CdSe QDs is 8
mainly coated with oleic acid ligand. Flexible organic molecules provide repulsive interactions between the QDs in methanol, thus preventing aggregation. A small peak shifting (~0.1 – 2 cm-1) towards larger wavenumber observed as the QDs sizes increase.
SC RI PT
Small peak shift towards larger wavenumber also observed in Mn-doped CdSe QDs
FTIR peaks as compared to pure CdSe QDs [16], particularly for triplet band of CH2
A
CC
EP
TE
D
M
A
N
U
stretching.
Figure 4: The FTIR pattern of paraffin oil, oleic acid and Mn-doped CdSe QDs at various reaction time
9
4. Conclusion FTIR spectra confirmed the oleate-capping introduced to the surface of Mn-doped CdSe QDs which act as the surface passivator which reduced the particle interfacial electron and hole
SC RI PT
trapping phenomenon. The phonon confinement observed in Mn-doped CdSe QDs from the blue-shift behavior of LO and 2LO compared to pure CdSe QDs.
Acknowledgement
This work was financially supported by Postgraduate Research Grant (PG084-2012B) and
U
MyBrain15 scholarship by government of Malaysia. The authors gratefully acknowledge the
A
N
financial support.
D
M
References
S. C. Erwin, L. J. Zu, M. I. Haftel, A. L. Efros, T. A. Kennedy, and D. J. Norris, Nature. 436 (2005).
[2]
A. P. Alivisatos, Science. 271 (1996).
[3]
Y. M. Sung, W. C. Kwak, & T. G. Kim, Crystal Growth & Design, 8(4), 1186-1190 (2008).
CC
EP
TE
[1]
W. C. Kwak, Y. M. Sung, T. G. Kim, and W. S. Chae, Appl. Phys. Lett. 90, (2007).
[5]
N. A. Hamizi, (2017). Synthesis And Characterization Of Mn-Doped CdSe Quantum Dots Via Inverse Micelle Technique (Doctoral dissertation). University of Malaya, Kuala Lumpur, Malaysia.
A
[4]
[6]
A. M. Kelley, Q. Dai, Z. J. Jiang, J. A. Baker & D. F. Kelley, Chemical Physics, 422, 272-276 (2013).
10
V. Plotnichenko & Y. Mityagin, Sov. Phys. Solid State, 19(9), 1584-1586 (1977).
[8]
C. Barglik-Chory, D. Buchold, M. Schmitt, W. Kiefer, C. Heske, C. Kumpf, ... & M. Lentze, Chemical physics letters, 379(5-6), 443-451 (2003).
[9]
N. H. Patel, M. Deshpande, S. V. Bhatt, K. R. Patel & S. Chaki, Advanced Materials Letters, 5, 671-677 (2014).
SC RI PT
[7]
[10] H. Bilz, & W. Kress, Springer Series in Solid State Sciences (1979).
[11] A. K. Arora, M. Rajalakshmi, T. Ravindran, & V. Sivasubramanian, Journal of Raman Spectroscopy, 38(6), 604-617 (2007).
U
[12] T. Muck, J. W. Wagner, L. Hansen, V. Wagner & J. Geurts, Journal of Applied Physics, 95(10), 5403-5407 (2004).
A
N
[13] M. Klein, F. Hache, D. Ricard, & C. Flytzanis, Physical Review B, 42(17), 11123 (1990).
M
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