ece 5320 lecture #10 - uh engineering information ...ecnfg/w5l2.pdfnp band gap material science of...

Material Science of Thin Films, ECE 6348 Stanko R. Brankovic ECE 5320

ECE 5320 Lecture #10


Synthetic Methods of Semiconductor NP and Applications


* 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)


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.


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


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


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


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


Synthesis of Titania(TiO2) Nanoparticles


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.


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)


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


Synthesis of Cadmium Chalcogenide

(CdS and CdSe) Nanoparticles & Nanocrystals


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



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-


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-


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



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)


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



Methylviologen (MV)

+ e- MV+ H3C N X-

N CH3 X-

colorless Violet color

CB e-

Nafion film

MV2+

Solution hv

h+

CdS

MV+ VB


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,


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


Cd chalcogenide nanoparticles 3.4. CdS clusters encapsulated in Zeolites

Zeolites have ion exchange ability

Cd2+ cation

H2S (g) Zeolite CdS within Zeolite cavity (


Synthesis of CdSe Quantum Dots


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


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)


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


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.


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


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


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 !!


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.


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.


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.


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


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


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.


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 %


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.


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


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.


Large Scale Synthesis & Water-soluble QDs

Scale of conventional method; up to ~ 102 mg


Conventional Pyrolysis Method

J. Am. Chem. Soc., 1993, 115, 8706


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


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


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


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


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.


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


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


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.


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


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


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


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


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


How large scale SiPOP process can be extended?

Semiconductor Quantum Dot

???? L 100 mL ~500 mg

3 L ~13 g



Semi--PPiilloott Scale 20 L Reactor (103 times bigger than normal lab. reaction scale)

100 ~ 1000 g scale synthesis


200 g of CdSe--ZnSe QDs was prepared from one bbaattcchh reaaccttiioonn


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

ece 5320 lecture #10 - uh engineering information ...ecnfg/w5l2.pdfnp band gap material science of...

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