Upload
doanquynh
View
216
Download
1
Embed Size (px)
Citation preview
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
ECE 5320 Lecture #10
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Synthetic Methods of Semiconductor NP and Applications
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
* Terminology
Nanoparticle : small particles in the size-range of 1~999 nm (most general term)
Nanocrystal : nanoparticles having a unique crystallinity
Quantum Dot : nanocrystals showing the quantum size effect (usually < 10 nm)
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Perspectives on the Physical Chemistry of Semiconductor Nanocrystals
Optical absorption vs. size of CdSe. Density of state
A.P. Alivisatos, J. Phys. Chem. 1996, 100, 13226.
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Photocurrent (photovoltaic cell, sensor) CB E (hv)
bandgap
Small bandgap -7 high conductivity VB (because of easy electron jumping)
: 102 ~ 10-4 S/cm
* Bandgap for bulk semiconductor
1 eV = 1.602177 x 10-19 J (96.485 kJ/mol)
Solid State electronic Devices, 5th edition, New Jersey: Prentice Hall, 524.
Si 1.11 eV CdS 2.42 eV
Ge 0.67 eV CdSe 1.73 eV
TiO2 3.2 eV GaP 2.26 eV
ZnO 3.2 eV GaAs 1.43 eV
NP Band Gap
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Photochemical reactions (Energy conversion reactions)
Mn+
- Photo-induced chemical reaction
hv e- M0 Light energy (hv)
Xn- or
h+
X0
chemical energy
electric energy
- Light-Emitting Devices (LED, ELD, .)
NP Band Gap
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Photoinduced chemical reactions vs. relaxation
CB
e- B B-
+ e-
[red]
- e-
[ox] A A+
h+
VB
Lifetime of excited state : ~ns (too short to show any photoinduced chemical reactions)
NP Band Gap
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Mediators to increased excited state life-time & enhance the efficiency
Pt
Electron acceptor (removes e- from the excited state) TiO2
RuO2 Electron donor (removes hole from the excited state)
CB
e- A B-
RuO2 Pt
h+ A+ B
VB
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Synthesis of Titania(TiO2) Nanoparticles
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Synthesis of Titania Hydrolysis & condensation of Ti(OR)4
Ti(OR)4 H2O Ti(OH)n(OR)4-n
-Ti O Ti - TiO2
1.0 50
E. A. Barringer et al., J. Am. Ceram. Soc. 1982, 65, C-199. E. A. Barringer and H. K. Bowen, Langmuir, 1985, 1, 414. J. H. Jean et al., Langmuir, 1986, 2, 251.
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Synthesis of Titania . / Reaction in microemulsions (micelle)
V. Chhabra et al., Langmuir, 1995, 11, 3307.
Source : TiCl4 Surfactant : Triton X-100* Co-surfactant : n-hexane Oil phase : cyclohexane
size : 15 30 nm
* Triton X-100 - Polyoxyethylene isooctylphenyl ether
O OH
n Schematic diagram showing the preparation of TiO2 particles in microemulsions.
530 890 TiO2(amorphous) TiO2(anatase) TiO2(rutile)
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Synthesis of Titania
E. Joselsevich et al., J. Phys. Chem., 1994, 98, 7628.
- TiCl4 / cetyldiemthylbenzyl ammonium chloride in benzene
H3C(H2C)15 N
CH3
CH3 Cl-
UV
- Size : 9 0.5 UV / Blue
. / Synthesis in aerosols
M. Visca and E. Matijevic, J. Colloid Interface Sci., 1979, 68, 308.
Ti(OEt)4 or Ti(OiPr)4 0.06 ~ 0.6 TiO2
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Synthesis of Cadmium Chalcogenide
(CdS and CdSe) Nanoparticles & Nanocrystals
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Cd chalcogenide nanoparticles
1. Reaction in homogeneous system E Matijevic et al., J. Colloid Interface Sci., 1982, 86, 476.
Cd2+ (Cd(NO3)2, 10-3 M) +
pH < 1 CdS particles ( ~ 1 )
TAA (thioacetamide)
S H3C C NH2
TAA CH3CN + 2H+ + S2- Rate-determining step ; the generation of S2-
If pH < 1
If pH is high (basic) Slow generation of S2-, CdS size can be controlled
Fast generation of S2-, CdS size cannot be controlled
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Cd chalcogenide nanoparticles
In the case of CdSe,
selenourea + Cd2+ CdSe pH ~ 4.5
Se H2N C NH2 H2NCN + 2H + Se
+ 2-
Rate-determining step ; the generation of Se2-
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Cd chalcogenide nanoparticles 2. Homogeneous reaction with stabilizer (surfactants)
G. Chiu, J. Colloid Interface Sci., 1981, 83, 309.
Cd2+ H2S (g)
EDTA CdS monodisperse size (10-4 ~ 10-3 M )
EDTA = ethylenediaminetetraacetic acid
O O N N
OH HO
O O T. Sugimoto et al., J. Colloid Interface Sci., 1996, 180, 305.
Gelatin - anticoagulant (to prevent aggregation) - up to 10-1 M
HO OH
Cd-EDTA + TAA Monodisperse CdS (~0.5 um) 1 wt% gelatin
S H3C C NH2
TAA
CH3CN + 2H+ + S2-
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Cd chalcogenide nanoparticles T. Sugimoto et al., Colloids Surf. A: Physicochem. Eng. Aspects., 1998, 135, 207.
Detailed mechanism study on CdS formation
* Ligands : amines and acids N
TMD H2N NH2 trimethylenediamine
H2N N,N-dimethylethylenediamine
H
DMED
H N H N
N
DETA H2N NH2 N H
NH2
di(ethylene)triamine TETA
2
tri(ethylene)tetraamine
N NH2 O
TAEA NH2
H2N
tri(ethylamine)amine
AA NH2 O
aspartic acid
OH HO
NTA N
O OH
O O
EDTA N
N O
O
HO O HO
O
OH OH nitrilotriaceticacid
HO OH ethylenediaminetetraacetic acid
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Cd chalcogenide nanoparticles
Mn+ + L ML, K = [ML]
If K increases, more stable M-L complex
For nanosize products: 10 < log K < 18 (optimizing value)
[Mn+] [L]
i) log K < 10, too fast growth II) log K > 18, too slow growth S
H3C C NH2 100
60 8 hr
A : TAEA D : DETA N : NTA
Cd2+ + S2- CdS
Cd-L
Yiel
d (%
)
25 2 min
25 1 hr
E : EDTA
rate = k[Cd-L]
rate (Cd)
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Cd chalcogenide nanoparticles 3. CdS formation in organized media
1. Ionically conductive polymer film
M. A. Fox and A.J. Bard et al., JACS, 1983, 105, 7002.
[(-CF2-CF2)m(CF-CF2-)]n
(O-CF2-CF-CF3)l
O-CF2-CF2-SO3H
Cd2+ H S 2 Nafion film (125 type) ( ~ 0.13 mm )
1.0 M pH1
CdS nanoparticle in Nafion (< 1 )
Nafion CdS in Nafion
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Cd chalcogenide nanoparticles
Methylviologen (MV)
+ e- MV+ H3C N X-
N CH3 X-
colorless Violet color
CB e-
Nafion film
MV2+
Solution hv
h+
CdS
MV+ VB
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Cd chalcogenide nanoparticles 3.2. Bilayer lipid membrane
J. H. Fendler et al., JACS, 1988, 110, 1012.
Teflon
bilayer film
Cd2+ solution H2S(g)
4 ~ 5 nm CdS ( ~ nm )
Cd2+ H S 2
bilayer ZnS, Cu2S, PbS, In2S3,
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Cd chalcogenide nanoparticles 3.3. Langmuir-Blodgett (LB) films
LB film Multiple dip Multilayer generation
J. H. Fendler et al., J. Phys. Chem., 1994, 98, 2735.
H2S(g)
air CdS generation
Cd2+ in H2O
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Cd chalcogenide nanoparticles 3.4. CdS clusters encapsulated in Zeolites
Zeolites have ion exchange ability
Cd2+ cation
H2S (g) Zeolite CdS within Zeolite cavity (
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Synthesis of CdSe Quantum Dots
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Brus, Alivisatos, and Bawendi
L. E. Brus A. P. Alivisatos M. G. Bawendi
Louis Brus 1965 Rice University
1969 Columbia University (Ph.D) Gas phase photodissociation
1973 ~ 1996
Bell Labs. Study of short lived intermediates nano-size material (1986: CdS, CdSe, )
1996~ Columbia Univ.
A. Paul Alivisatos 1981 University of Chicago (Chemistry)
1986 U. C. Berkeley (Ph.D.), Photophysics of electronically excited molecules
1986 ~1988
AT&T Bell labs.
1988~ U. C. Berkeley
Moungi G. Bawendi Harvard University (Arts)
1988 University of Chicago (Chemistry, Ph.D) Lattice model for polymer solution
1988 ~1989
AT&T Bell labs.
1990~ MIT
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
CdS nanoparticles
R. Rossetti and L. E. Brus, JCP, 1983, 79, 1086.
CdS prepd in aq. solution ( ~ 3.5 nm )
max = 440 nm
12.5 nm Still stable in solution
max > 500 nm
1 day aging pH = 3
quantum-size bulk Quantum-size effect (absorption band gap) was first observed!
R. Rossetti and L. E. Brus, JCP, 1985, 82, 552.
Na S solution in MeOH rapid mixing 2 ( 5 ml of 6.6 10-3 M )
+ Cd(ClO4)2 solution
( 100 ml of 3 10-3 M )
CdS ( ~ 5.4 nm) 23
rapid mixing - 77 CdS ( ~ 2.8 nm)
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
CdS nanoparticles
L. E. Brus, J. Chem. Phys., 1984, 80, 4403.
Particle-in-a-box 0 < x < a , V = k(x)
Particle(e-)-in-a-sphere model boundary condition : 0 < x < r
r 0 a
L. E. Brus et al., J. Phys. Chem,, 1986, 90, 3393. Luminescence at 10 K
no band edge luminescence deep trap luminescence ( surface defect site emission )
featureless and broad emission
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
CdSe nanoparticles Easy to see CdS
Band gap = 2.42 eV UV region
CdSe Band gap = 1.73 eV
Vis. region
& detect !!
L. E. Brus et al., J. Chem. Phys., 1986, 85, 2237.
1. Cd(ClO4)2 in MeOH ( - 80) xs. H2Se in iso-PrOH ( - 80) injection
In alcohol, small CdSe
2. Cd(ClO4)2 in H2O (23) xs. H2Se in H2O (23) injection
In water, large CdSe ( > 5 nm)
Small refers to CdSe colloid at -80. Large refers to CdSe colloid at 23. The vertical scale for Large is expended 5 500nm. The mass of CdSe in the optical path is nominally the same in both spectra.
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Size Control of CdSe nanocrystals Arrested pprreecciippiittaattiioonn ( rreeaaccttiioonn in ccoonnffiinneedd rreeggiioonn )
- J. H. Fendler et al., JCS CC., 1984, 90.
P. Lianos & J. K. Thomas, Chem. Phys. Lett., 1986, 125, 299. Y. Wang & N. Herron, J. Phys. Chem., 1987, 91, 257.
- A. P. Alivisatos & L. E. Brus et al., JACS, 1988, 110, 3046. AOT ( Aerosol-OT) : sodium bis(2-ethylhexyl)sulfosuccinate
O +Na -O3S
[H2O] CH3 CH3
O
O
AOT / H2O / Heptane
Cd(ClO4)2 in aq. solution Se(TMS)2 in heptane
W = [AOT] Se Si CH3 H3C Si
CH3 CH3
Color change : from yellow to orange ( red )
Se(TMS) 2
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Size Control of CdSe nanocrystals
A. P. Alivisatos & L. E. Brus et al., J. Chem. Phys., 1988, 89, 4001. Electronic state of CdSe quantum dots (calculation)
Energy level diagram for a spherical cluster of CdSe 45 in diameter, from elementary theory. Dotted lines are bulk band edges. The straight arrow shows the HOMO-LUMO transition. The wiggly arrows indicate the probable nonradiative decay times. labels spin- orbit split-off states. (inset) Stick diagram of the energies at which optical transitions occur within the MO model. The arrow denotes the HOMO-LUMO transition.
A. P. Alivisatos & L. E. Brus et al., J. Chem. Phys., 1988, 89, 5979. Pressure dependent HOMO-LUMO transition energy due to surface deformation from zinc blend to wurzite
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Enhancement of Quantum Efficiency Core/Shell nanocrystals
A. Henglein et al. JACS, 1987, 109, 5649. - inorganic ions (NaOH + Cd2+) can enhance PL.
M. G. Bawendi & L. E. Brus et al., Phys. Rev. Lett., 1990, 65, 1623. Low temp. photoluminescence experiments of CdSe QD
- low temp. : ~ 15 K , PL > 0.1 ( = 10 % ) - absorption & emission moves together tendency.
M. G. Bawendi & L. E. Brus et al., JACS, 1990, 112, 1327. - CdSe/ZnS, prepared from AOT inversed micelle, can emit PL at room temp.
ZnS
CdSe Core-shell structure
ZnS CdSe ZnS Band-edge Emission
Energy trap !!
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Enhancement of Quantum Efficiency Pyrolysis Method to Prepare High Quality CdSe QDs
C. B. Murray, D. J. Morris, and M. G. Bawendi, JACS, 1993, 115, 8706. Pyrolysis of organometallic precursors
dimetylcadmium Me2Cd
Cd2+ or Cd0
TOP-Se / TOPO ( solvent & ligand )
P Se P Se
O2
trioctylphosphine (TOP) O P
trioctylphosphine oxide (TOPO, mp ~ 60)
Nearly monodispersed size Soluble in hexane, benzene, CHCl3, ...
Stable at 350 Nice crystal (wurzite)
Strong band-edge emission at room temp! PL = ~ 10 % at room temp.
= ~ 100 % at low temp.
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Enhancement of Quantum Efficiency = O P Pyrolysis & Overcoated Structure
M. G. Bawendi & L. E. Brus et al., J. Phys. Chem., 1996, 100, 468.
ZnS
CdSe CdMe2 + TOP-Se CdSe TOPO 350
ZnMe2 (TMS) S 2 300 stirring
at 100 PL > ~ 50 %
Fluorescence Absorption
(CdSe)ZnS
(CdSe)ZnS
Fluorescence of (CdSe)ZnS
(CdSe)TOPO
(CdSe)TOPO
TEM picture of (CdSe)ZnS nanocrystals. This picture is 95 95 nm.
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Enhancement of Quantum Efficiency CdS
CdSe A. P. Alivisatos et al., JACS, 1997, 119, 7019.
10 nm
A B
Absorption (dashed) & PL (solid) spectra of two series of core/shell nanocrystals.
Q.Y. : quantum yield of photoluminescence. : number of monolayers of shell growth.
All spectra were taken at a concentration corresponding to an optical density (OD) of roughly 0.2 at the peak of the lowest energy feature in the absorption spectrum. Figure A : 30 CdSe core diameter series. Figure B : 23 CdSe core diameter series.
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Enhancement of Quantum Efficiency
CdSe
ZnS
M. G. Bawendi et al., J. Phys. Chem. B, 1997, 101, 9463.
Figure 1. Absorption spectra for CdSe (dashed) & CdSe/ZnS (solid) dots with dia-meters measuring (a) 23, (b) 42, (c) 48, and (d) 55 . Figure 2. PL spectra for CdSe (dashed) & CdSe/ZnS (solid) dots with the following core sizes : (a) 23, (b) 42, (c) 48, and (d) 55 . The PL spectra for the overcoated dots are much
Figure 1 Figure 2
more intense owing to their higher quantum yields : (a) 40, (b) 50, (c) 35, and (d) 30.
Full color display could be possible !!
small size large size
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Applications 1. Biological labeling
Organic dyes - photochemically unstable Serious photobleaching
5-Fluorescein (FITC) Rhodamine Red-X
- broad emission band ( baseline width > 200 nm ) Multi-site monitoring is hard
QDs - photochemically stable
no photobleaching - narrow emission band ( baseline width < 60 nm )
CdSe InP InAs
Simultaneous multi-site monitoring
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Applications
Shuming Nie et al., Science, 1998, 281, 2016.
= HS OH O
Color luminescence images obtained from (A) original QDs, (B) mercapto- solubilized QDs, and (C) QD-IgG conjugates. The images were directly
CdSe ZnS recorded on color photographic film
(ASA-1600) with a 15-s exposure by a 35-mm camera that was attached to a Nikon inverted optical microscope. Continuous-wave excitation at 514.5 nm was provided by an Ar ion laser. There are emission color differences among single QDs.
mercaptocacetic acid
A. P. Alivisatos et al., Science, 1998, 281, 2013.
< ~ 10 % PL
Si O
O
O HS =
Cross section of a dual- labeled sample examined with a Bio-Rad 1024 MRC CLSM with a 40 oil 1.3 numerical aperture objective. The mouse 3T3 fibroblasts were grown and prepared as described. A false-colored image was obtained with
ZnS
CdSe
(3-mercaptopropyl) trimethoxysilane
363-nm excitation, with simultaneous two-channel detection (522DF 35-nm FWHM narrow-pass filter for the green, and a 585-nm long-pass filter for the red). Image width: 84 mm.
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Applications org. soluble
CdSe
B. Dubertret & D. J. Norris et al., Science, 2002, 298, 1759. QD labeling of Xenopus embryos at different stages phospholipid
CdSe
Water- soluble micellar structure PL : 50 ~ 70 %
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Applications 2. Display (LED, ELD)
LED : LLiigghhtt--Emitting Diode Epoxy matrix
containing CdSe
GaN Blue LED
Using high PL efficiency By changing the ratio of various size CdSe in epoxy resin, LED color can be easily tuned
M. G. Bawendi et al., Adv. Mater., 2000, 12, 1102.
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Applications
ELD : EElleeccttrroo-Luminescent Device Electric E. Light E.
ZnS CdSe
e- hv
TOPO-capped CdSe/ZnS
M. G. Bawendi et al., Nature, 2002, 420, 800. - Sandwich-type - mono-layered device - EL = ~ 0.52% at 10 mA/cm2
h+
hole transporter
- Luminescence efficiency 1.6 cd/A at 2000 cd/m2
Ag Mg:Ag
40 nm Alq3 QD monolayer
35 nm TPD ITO
Glass
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Applications
3.Photovoltaic device (solar cell) Light E.
A. P. Alivisatos et al., Science, 2002, 295, 2425. (A) 7 7 nm
Electric E.
(B) 7 30 nm (C) 7 60 nm
e- hv
Electrical energy
A
h +
(D) 10 10 nm CdSe in P3HT (E) 7 60 nm CdSe in P3HT
Al External Circuit
CdSe/P3HT Blend
PEDOT:PSS ITO Substrate
EQEs of 7-nm-diameter nanorods with lengths 7, 30, and 60 nm. The intensity is at 0.084 mW/cm2 at 515 nm.
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Large Scale Synthesis & Water-soluble QDs
Scale of conventional method; up to ~ 102 mg
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Conventional Pyrolysis Method
J. Am. Chem. Soc., 1993, 115, 8706
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Surface Passivation with higher bandgap Inorganic Shell (TYPE I)
Reason ? - CdSe QDs ensemble as-prepared can have PL QY of ~70%
-+ High PL QY for most cases !!! however, - Low processibility of bare CdSe QDs
-+ Surface alkyl chains, PL loss on surface ligand exchange - Low photochemical stability of bare CdSe QDs
-+ PL loss on the exposure to UV irradiation (oxidation of Se)
Approach ? - Heteroepitaxial growth of inorganic shell (CdS, ZnS, ZnSe)
having low lattice mismatch to core QDs.
TOPO
TYPE I core-shell Confinement of CdSe ZnS Organic Ligand
CdSe
both h+ and e- in the core ZnS core shell
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Conventional Synthetic Method to Prepare Core-Shell Semiconductor QDs
Injection of Se-precursor
Dropwise addition of Zn-/S-precursors
stoichiometric stoichiometric
Hot Cd-precursor
solution CdSe CdSe-ZnS
Isolate CdSe QD
Cd-precursor Se-precursor
CdSe Zn-/S-precursors
CdSe-ZnS
Similar approaches have been used to prepared CdSe/CdS, CdSe/ZnSe
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Problem of Previously Known Inorganic Shell Passivation Technique
1. Extensive purification step to remove unreacted precursors
2. Dropwise addition of a precursor mixture
3. Hard-to-handle dangerous and pyrophoric metal-precursor
Very expensive materials!! -+ Bottleneck of large scale synthesis of
Core-shell semiconductor QDs
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Successive injection of Precursors in One-Pot
One-Pot Method with Temperature-Controlled Precursor Injection
Fast Injection of excess Se-precursor
Fast injection of excess Zn-precursor
Hot Cd-precursor
solution CdSe CdSe-ZnSe Product isolation
Cd-precursor Se-precursor
CdSe CdSe-ZnSe
Zn-precursor
No isolation
* Expected advantages of low temperature shell precursor injection (1) quenching of seed growth & no new nuclei formation (2) swift & large amount of precursor injection (3) high reproducibility
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Temporal Evolution of PL of QDs
(a) (b) 1.0
CdSe 1.05
PL In
tens
ity (a
.u.)
CdSe/ZnSe
0.8
1.0 0.3 min 1 min 3 min 5 min
PL In
tens
ity (a
.u.)
0.6
0.8
1.00 592 nm 568 nm
0.6 10 min 20 min 70 min
0.2
0.4 0.95 560 565 570 575 580 585 590 595
No ZnSe peak 0.2
0.4
400 450 500 550 600
Wavelength (nm) 650
0.0 0.0 400 450 500 550 600 650 700
Wavelength (nm) (a) Temporal PL evolution of CdSe QDs. CdSe
size increases slowly between 3 and 20 min after TOPSe injection. Arrow indicates slow
(b) Temporal PL evolution of CdSe /ZnSe QDs during ZnSe shell growth.
growth region during CdSe growth.
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Multi-gram scale Production
Characteristic of SIPOP process Kim, J. I. et al. Adv. Func. Mater. 2006, 16, 2077.
13 g CdSe/ZnSe 13 g CdSe/ZnSe from one-pot synthesis
(b) (a)
: room temperature precursor injection large scale synthesis ?
from one-pot synthesis
50 nm (c)
0.3 2
0.2
1
0.1
Abso
rban
ce (a
rb. u
nits
)
PL In
tens
ity (n
orm
aliz
ed)
400 500 600
Wavelength(nm) 700
0.0 0
unit : mm under UV
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
TEM images of CdSe and CdSe/ZnSe QDs
(a) CdSe (b) CdSe/ZnSe
Short axis Short axis D = 4.5 nm, = 0.37 D = 5.6 nm, = 0.23
10 nm
JEM-3000F
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
XPS and ICP-AES
Zn 2p1 Zn 2p3 (a) (b) 1.0 [Cd]/([Cd]+[Zn])
[Zn]/([Cd]+[Zn])
Cou
nts /
s
0.6
0.8
Mol
. fra
ctio
n
CdSe/ZnSe
0.2
0.4
1050 1040 1030 1020 Binding energy (eV)
1010
CdSe
0
CdSe-ZnSe cluster
10 20 30 40 50 60 0.0
(a) XPS data for CdSe and CdSe/ZnSe QDs. No zinc 2p1 and 2p3 peaks were observed
(b) Typical ICP-AES results during ZnSe shell growth. 4 molar excess zinc precursor was
time (min
in CdSe QDs. used for ZnSe shell.
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Proposed ZnSe Shell Growth Mechanism
Temperature-Controlled One-Pot Process ; let QDs remain in quasi-eq. state, followed by
precursor injection under temperature-controlled condition
Quasi-Equilibrium Condition
Se-precursor +
Cd-precursor
Cd-prec [Cd]
280 oC CdSe CdSe
Swift injection of Zn-precursor
at < 50 oC Quasi-Equilibrium
Condition
Zn-prec [Zn]
240 oC CdSe CdSe
Cd-prec [Cd]
ZnSe ZnSe
[Cd] : Cadmium active species [Zn] : Zinc active species
Cd-prec : Cadmium precursor Zn-prec : Zinc precursor
Influx of precursors outflux of precursors
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Instability of selenide surface
Se is easy to be oxidized with O2 Very sensitive to surface modification
Hard to make stable water-soluble QDs having high quantum yields
No isolation of core seems to be better process. Core-double shell structure has been suggested:
CdSe/ZnSe/ZnS
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
CdSe/ZnSe/ZnS QDs via SiPOP process (Successive Injection of Precursor in One-Pot)
excess Zn(UD)2
excess S
Cd(SA)2
excess Se
MPA MPA MPA
CdSe CdSe-ZnSe CdSe-ZnSe-ZnS
Hydrophobic ligand, i.e. SA, TOPO, and ODA Hydrophilic ligand, i.e. MPA
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
CdSe/ZnSs/ZnS QDs via SiPO process
PL In
tens
ity (n
orm
aliz
ed)
CdSe-ZnSe-ZnS
Abso
rban
ce (a
.u.)
CdSe-ZnSe
500 550 600 Wavelength (nm)
650 700
CdSe
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
CdSe/ZnSs/ZnS QDs via SiPOP process
toluene water toluene water toluene water
90
70
80 toluene
toluen
PL q
uant
um e
ffici
ency
(%)
water 50
40 toluene
30
20
60
0
10 water water
CdSe-ZnSe-ZnS CdSe-ZnSe CdSe
toluene water toluene water toluene water
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
How large scale SiPOP process can be extended?
Semiconductor Quantum Dot
???? L 100 mL ~500 mg
3 L ~13 g
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
Semiconductor Quantum Dot
Semi--PPiilloott Scale 20 L Reactor (103 times bigger than normal lab. reaction scale)
100 ~ 1000 g scale synthesis
Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320
200 g of CdSe--ZnSe QDs was prepared from one bbaattcchh reaaccttiioonn
Semiconductor Quantum Dot
Slide Number 1Synthetic Methods of Semiconductor NP and Applications Slide Number 3Slide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Synthesis of TitaniaSynthesis of TitaniaSynthesis of TitaniaSlide Number 13Cd chalcogenide nanoparticlesCd chalcogenide nanoparticlesCd chalcogenide nanoparticlesCd chalcogenide nanoparticlesCd chalcogenide nanoparticlesCd chalcogenide nanoparticlesCd chalcogenide nanoparticlesCd chalcogenide nanoparticlesCd chalcogenide nanoparticlesCd chalcogenide nanoparticlesSlide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Slide Number 31Slide Number 32Slide Number 33Slide Number 34Slide Number 35Slide Number 36Slide Number 37Slide Number 38Slide Number 39Slide Number 40Slide Number 41Slide Number 42Slide Number 43Slide Number 44Slide Number 45Slide Number 46Slide Number 47Temporal Evolution of PL of QDsMulti-gram scale ProductionTEM images of CdSe and CdSe/ZnSe QDsXPS and ICP-AESProposed ZnSe Shell Growth MechanismSlide Number 53CdSe/ZnSe/ZnS QDs via SiPOP process(Successive Injection of Precursor in One-Pot)Slide Number 55CdSe/ZnSs/ZnS QDs via SiPOP processSlide Number 57Slide Number 58Slide Number 59