Synthesis of nanomaterials by soft chemistry...

Thermoelectricity School

Annecy, June 2014

Synthesis of nanomaterials by soft chemistry

methods for thermoelectric applications

Lorette Sicard

[email protected]

Figure of merit:

Introduction

𝑍𝑇 =𝑆2𝜎

κT

• S: Seebeck coefficient

• σ: electronic conductivity

• κ: thermal conductivity

κ = κe+ κl

S, σ, κ are closely linked properties

Semi-conducting materials

Isolating materials Metals

Carrier concentration (cm-3)

2

S ZT κ

S2

Key issue: to decouple S, σ, κ

• σ • S • ↘ κ

« Phonon glass – Electron crystal »

concept

Strategies to increase ZT:

Engineering the crystal structure at atomic scale

Cage-like materials: skutterudites, clathrates

« rattling » atoms

Complex crystals with defaults: half-Heusler compounds, …

Misfits oxides: cobaltites, …

….

Engineering the material structure at the nanoscale

Low-dimension materials; nanostructuring

3

Introduction

Dramatic change of the DOS by quantum confinement effect

Phonon scattering of phonons at the interfaces Decrease of κ

Increase of S

Low-energy carrier filtering at the boundaries Increase of power factor

Semi-metal to semi-conducting transition

Contribution of nano-engineering:

4

Introduction

Nanostructured materials:

5

From theory…

M. Dresselhaus, Microscale Thermophysical

Engineering, 3 (1999) 100.

…to experiment.

T.C. Harman, Science 297 (2002) 2229

Bi2Te3/Sb2Te3

Super-lattices

ZT = 2.4

Nano_materials

Nano-composites

Nano-composites

PbTe matrix

PbS

PbTe

M.G. Kanatzidis Chem. Mater. 22 (2010) 648.

R. Venkatasubramanian Nature. 413 (2001) 597.

Sb2SexTe1-x

based quantum

dots supperlatices

ZT = 1.6

Introduction

Nanostructured materials in devices:

6

Nano-bulk materials

Nano-composites

Nano-inclusions: LAST (AgPbmSbTem+2), … Phase segregation Chemical engineering approach

Super-lattices Costly physical processes

Sintered nano-particles Physical/chemical processes

Interest restricted to applications at moderate temperature: mostly Bi2Te3, PbTe, CoSb3

Introduction

Outline

I. Fundamentals of soft-chemistry synthesis

II. Reduction in aqueous medium

III. Reduction in organic solution

IV. Solvothermal synthesis

V. Synthesis in confined medium

VI. Decomposition of organometalic complexes

VII. Post-synthesis treatments

Conclusions/Perspectives

Outline

I. Fundamentals of soft-chemistry synthesis 1. Generalities

2. Mechanisms of formation of NPs

3. Chemical reactions involved in the obtention of NPs








I. Fundamentals / 1. Generalities

2 approaches:

volume

powder

nanoparticles

atoms

clusters

Physical methods :

Ball milling

Lithography

Laser ablation

Electroexplosion of a wire

….

Chemical methods :

CVD

Solution chemistry

« Top-down »

« Bottom-up »

Buk-nanomaterial

Sintering at moderateT

7

Advantages and drawbacks of soft-chemistry synthesis

8

Drawbacks:

Advantages:

Easy to perform

Often scalable, high yields

Low temperature, low cost

Versatility over crystalline phase, morphology, size

Good control over particle size, distribution, morphology

Good chemical homogeneity, low strain

Difficulties to control accurately the stoichiometry

Possible oxide/organic coating of the particles

detrimental to densification and electronic properties


General procedure for the obtention of nanomaterials

9

Centrifugation

Structure

XRD • Cristallographic phase • Impurities • Cristallinity • Cristallite size • Defaults, strains TEM • HRTEM • Electronic diffraction

ICP-AES X-ray fluorescence EDX XPS FTIR

Stoichiometry Morphology Physical

SEM TEM

Electronic properties Thermal conductivities


Characterization

10

Characterization mechanisms of formation

Intermediate species in solution • NMR • UV-visible spectroscopy

Intermediate precipitates • XRD • TEM • …

Nucleation/growth • SAXS • UV-visible spectroscopy • Solution chemical analysis

General procedure for the obtention of nanomaterials


Centrifugation

Adapted from V.K. La Mer et R.H. Dinegar, J. Am. Ceram. Soc. 17 (1950) 4847.

Fundamentals of the formation of nanoparticles

time

2. Nucleation

3. Growth

4. Aging

Mo

lecu

lar

sp

ec

ies c

on

cen

trati

on

Nu

mb

er

of

pa

rtic

les

11

1. Induction

1. 2. 3. 4.

1. Induction period

Dissolution of the precursors

I. Fundamentals / 2. Mechanisms of formation of NPs

12

-200

-150

-100

-50

0

50

100

150

200

0 0.5 1 1.5 2

r/rc

DG

Esurface

Evolume Etotal

rc

Nucleation Growth

Nucleus small solid spherical particle

∆𝐺(𝑟) =4π𝑟2𝛾 −4

3𝜋𝑟3 𝑅𝑇𝑙𝑛𝑆

𝑉𝑚

∆𝐺 𝑟 = ∆𝐺𝑆 + ∆𝐺𝑖𝑛𝑡

∆𝐺𝑖𝑛𝑡: free enthalpie of formation of the condensed phase

∆𝐺𝑆: free enthalpie of the surface

𝛾 : surface tension

𝑆 =𝐶𝐿

𝐶𝑆; Vm: molar volume

r

𝑑(∆𝐺 𝑟 )

𝑑𝑟= 0 Critical radius: rc 𝑟𝑐 =

2𝛾

𝑅𝑇𝑙𝑛𝑆

2. Nucleation


3. Growth

13


2 growth models:

Growth limited by the diffusion of species in solution

Growth limited by the precipitation of monomers

14

Growth limited by the diffusion of species in solution

𝐽 =4𝜋𝑟2

𝑉𝑚

𝑑𝑟

𝑑𝑡 The growth rate depends solely of the flux of the

monomers supplied to the particles

𝐽 = 4𝜋𝑟𝐷(𝐶𝑏𝑢𝑙𝑘 − 𝐶𝑠) Fick law ; CS: concentration at the particle surface D: diffusion coefficient

𝑑𝑟

𝑑𝑡=

𝑉𝑚𝐷

𝑟(𝐶𝑏𝑢𝑙𝑘 − 𝐶𝑠)

Growth rate inversely proportional to the radius

𝑑𝜎2

𝑑𝑡= 2𝑉𝑚𝐷 (𝐶𝑏𝑢𝑙𝑘 − 𝐶𝑠) 1 − 𝑟

1

𝑟

<0

The variance of the size distribution ↘ as the particles are growing

If no additional nucleation growth occurs

The smaller the particles are, the faster they grow Focusing effect (dispersion in size ↘)


15

Growth limited by the precipitation of monomers

4. Aging

2 mechanisms:

Coalescence

Ostwald ripening


K; DamKöhler number proportional to diffusion rate/precipitation rate

Competitive effect: dissolution and precipitation

Growth rate: with:

𝐶0𝑆𝑒𝑞

: monomer concentration in solution

𝑘0𝑝: precipitation rate constant of bulk

K low diffusion-controlled growth (focusing effect) K high reaction-controlled growth (focusing effect weakened)

: transfer coefficient

𝑑𝑟∗

𝑑𝜏=

𝑆 − exp (1 𝑟∗ )

𝑟∗ + 𝐾𝑒𝑥𝑝(𝛼 𝑟∗ ) 𝑟∗=

𝑅𝑇

2𝛾𝑉𝑚𝑟

𝜏 =𝑅2𝑇2𝐷𝐶0

𝑆𝑒𝑞

4𝛾2𝑉𝑚𝑡

K=𝑅𝑇

4𝛾𝑉𝑚

𝐷

4𝑘0𝑝

Seed-mediated growth

16

Co65Ni35

Pt/CoNi = 2,5 10-4

dm = 50 nm

Co50Ni50

Pt/CoNi = 0,5 10-2

dm = 7 nm

40 nm40 nm150 nm150 nm

Co80Ni20

homogeneous nucleation

dm = 1400 nm

10-6

10-5

10-4

10-3

10-2

10

100

dm (

nm

)

[Pt]/[Co+Ni] (mol/mol)

3

1

CoNigerme

germegermeCoNim

]NiCo[

]germe[

M

VM6d

Strategies to control the particle size

Control of the size

or Core/shell


17

Conc. and nature of the reactants, nature of the solvent, reaction time

Homogeneous nucleation


hot-injection heating-up

T, P, heating rate, heating mode

Co-precipitation

Heating rate:

Heating mode:

Microwave conventional

Used for polar solvent exclusively

• High heating rate • Uniform heating • High penetration depth of the wave • Rapid reaction (a few minutes) • High yield • Softer conditions can be used

18

2NH3 +CO2

Reactivity of the precursors

Homogeneous nucleation

Urea

Trioctylphosphine telluride

thiourea

+ H2O

Growth oriented by ligands


TiO

iPr

iPrO

iPrO

iPrO

Ti OiPr

iPrO

O

OiPr

O

CH3

CH3

1 acac

4

Ti4+

J. Livage, L’actualité Chimique, 1997

titanium isopropoxide titanium acetate

(Cl-)4Te4+

Tellurium chloride

Use of a hard/soft template

Templating strategies

19

Coalescence:

Electrostatic stabilization:

Steric stabilization:

- - -

- -

- -

- -

- -

- -

- -

- -

- -

- -

Modification of the pH, counter-ion…

Addition of polymer, surfactant Use of chelating agents, solvent

Electro-steric stabilization: - - - -

- -

- -

- - -

- - - - -

-

Templating strategies:

Use of a hard/soft template

Strategies to avoid agregation


20

In summary:

Control of nucleation/growth/aging through the synthesis parameters (T, P,

time, heating rate and mode, precursor nature, additives, …)

linked to the chemical reactions which depends of the nature of the NPs to synthesize

I. Fundamentals / 3. Chemical reactions

a- Oxides

b- Metals

c- Chalcogenides


21

Sol-gel synthesis

a. Synthesis of oxide nanoparticles

Precursors

Sol

Gel Aerogel/Xerogel

Precipitate

Powder

Film

Oxide/glass

Drying Calcination

Condensation

Sol-gel synthesis

Co-precipitation

Specific for oxide synthesis

22

• Dissolution/complexation Mz+ + N H2O [M(OH2)N]z+

• Hydrolysis

[M(OH2)N]z+ + h OH- [M(OH)h (OH2)N-h]z+ + hH2O In basic medium:

• Condensation

M-OH + HO-M M-O-M + H2O oxolation

Aquo complex

M-OH + H2O-M M-OH-M + H2O olation

In the presence of water

From metal alkoxyde precursors

• Hydrolysis

• Condensation

M-OR + H2O M-OH + ROH

M-OH +HO-M M-O-M + H2O

M-OR +HO-M M-O-M + ROH

TEOS

From metal salts

Sol Gel

Hydrolysis rate >> Condensation rate


R: alkyl group

Ca(NO3)2 Co(NO3)2.4H2O

water citric acid

H2O

Dried gel

Poudre

70°C – 3h

130°C, 12h

calcination

400°C

600°C

650°C

800°C

700°C

750°C

Calcination 600°C, Furnace 900°C, 8h

Calcination 600°C, SPS 700°C, 5min

Y. Liu, J. Am. Ceram. Soc., 88 [5] 1337–1340 (2005

Example: preparation of cobaltite Ca3Co4O9

23


24

In the absence of water

Metal halide in alcohol

The oxygen comes from the solvent

MX4 + R-OH RX + M-OH

M-OH +HO-M M-O-M + H2O

Metal halide in ether

R-OR + MX4 RX + M-OR

M-OR +RO-M M-O-M + ROR


25

Co-precipitation method in aqueous solution

Oxide preparation

aq. NiCl2 aq. NH4OH aq. Fe(NO3)3

Ni(NO3)2

Zn(NO3)2

aq. NaOH

Calcination necessary

In aqueous medium

In organic medium

Controlled hydrolysis

Diethyleneglycol:

- high boiling T solvent

- stabilizing agent


26

Mn+ + ne- M0 : E0

M

Xm - ne- Xm-n : E0R < E0

M

N2H4.H2O → N2H5+ + OH-

N2 + 5H+ + 4e− → N2H5+ (ion hydrazinium) E0 = -0,23V

Usual reductants:

• Hydrazine

• Borohydride

Co2(CO)8 → 2Co + 8CO

Reduction

b. Synthesis of metal NPs

Thermolysis

B(OH)4- + 4H2O +8e-

BH4- + 8OH- E = -1,24V at pH = 14

Strong reducing agent


27

E0Te/Te2−=−1.14V

E0Pb2+/Pb =−0.13V

E0Bi3+/Bi=0.200V

E0Te4+/Te=0.53 V

c. Synthesis of metal chalcogenide NPs

Pb2+ + Te2- PbTe

or Pb + Te PbTe

2Bi3+ + 3Te2- Bi2Te3

or 2Bi + 3Te Bi2Te3

Reduction of Te and/or Pb/Bi in some cases

Use of a reductant: often NaBH4 or N2H4

For PbTe: Pb(+II) and Te(+IV) or Te(0)

Precursors:

For Bi2Te3: Bi(+III) and Te(+IV) or Te(0)

2 possible reaction pathways:

Reduction

Example of PbTe and Bi2Te3:


28


In water/organic solvent

At ambiant pressure/solvothermal conditions

In confined medium

Soft template: micelles/microemulsions

Hard template

29

Thermolysis


Te(-II)-TOP complex

Bi(III)/Pb(II) complex with ligands:

=M-S CnH2n+1

=MO2C-CnH2n+1

+

in organic solvent

hot-injection heating-up Microwave

Outline


II. Reduction in aqueous medium 1. Use of organic agents

2. Templating method







Synthesis of Bi2Te3, PbTe, CoSb3 based-NPs

30

II. Synthesis in aqueous medium

Advantages/Drawbacks of reduction in aqueous medium

Advantages:

Very easy to perform

Water = environmental friendly solvent

Low cost reactants

Absence of organic shells in some cases

Drawbacks:

Distribution in size generally high

Agregation difficult to prevent

Surface oxidation possible

31

Strategies to control the morphology and size of the nanoparticules

1. Control of the precursor reactivity and/or particle growth and agregation: Addition of an organic structuring agent

EDTA

Ethylenediaminetetraacetic

disodium salt

Bi3+

Bi(III)/EDTA

complex

Control of the reactivity of ions Control of growth/agregation

Addition of a polymeric agent

Control of growth/agregation by steric effect

2. Control of the NPs form and size by sacrificial templating

PVP

Polyvinyl

pyrrolidone

II. Synthesis in aqueous medium

32

II. Synthesis in aqueous medium / 1. Use of organic agents

W.X. Zhang, Mater. Research. Bulletin 35 (2009) 2009.

Synthesis of PbTe in the absence of an organic agent

Te

aq. KOH

Pb(CH3CO2)2●3H2O

H2O

Agregated NPs 35 nm-sized Polydispersity

Role of the organic directing agent

1. Control of the precursor reactivity and/or particle growth and agregation

1) BiCl3 + Na2TeO3

2) NaBH4

24 hours

Reflux

Preheated H2O

+ NaOH

+ organic agent

Pure Bi2Te3

Influence of the nature of the directing agent

EDTA PVP ethylene diamine

Nanorods d 20-70nm

Agregated nanoparticles

Importance of the directing agent on the growth and aging of the NPs Control over shape and size

33 J.Z. Hu, Phys. Scr. T129 (2007) 120.

Nanotubes d 20-70nm


1) BiCl3 + Na2TeO3

2) NaBH4

Preheated H2O

+ NaOH

+ organic agent

With EDTA

Using Na2TeO3 Using Te

20 nm-sized particles congregated into flakes

Nanotubes d 20-70nm

34 J.Z. Hu, Phys. Scr. T129 (2007) 120.

Importance also of the precursors on the shape and size

Influence of the nature of the directing agent


35 C. Kim, Powder Technol.. 214 (2011) 463.

Bi(NO3)3 in H2O

Ascorbic acid

EDTA

+ aq. NaOH

3h

Te

aq. NaBH4

100°C

Bi2Te3

Bi2Te3

[EDTA] size ↘

Bi2Te3+

Bi2TeO5+Te

Bi2Te3 Bi2Te3

100nm 100nm 100nm 100nm

Influence of the concentration of the directing agent

Tuning of the reaction product Tuning of the size

with the directing agent concentration


BiCl3 in aq. HNO3

+ thioglycolic acid H6TeO6 + H20

=Bi-SCH2CO2H

complex

H20, 70°C

N2H4.H2O

100°C

A. Purkayastha, Adv. Mater. 18 (2006) 496.

36

Multiple role of the directing agent

Bi2Te3 nanorods 54 nm

N. Gaponik, J. Phys. Chem. B 106 (2002) 7177.

Refluxing time in an

aq. thioglycolic acid

solution Thioglycolic acid serves as - directing agent - doping agent

Incorporation of S n-type semi-conductor


37

II. Synthesis in aqueous medium / 2. Templating method

0) NaOH/H20

100°C

1) Na2TeO3+NaBH4

1/2h

2) Pb(CH3CO2).3H2O

t

t=0 Pure Te

1) TeO32- + BH4

- + 2H2O Te + H2BO3- + 2OH- + 2H2

X. Chen, J. Crystal Gowth 311 (2009) 3179.


37

t=0 Pure Te

2) 3Pb2+ + 2BH4- + 6OH- 3Pb + 2H2BO3

- + 5H2

Pb + Te Pb Te

t=0 Te + PbTe

X. Chen, J. Crystal Gowth 311 (2009) 3179.

0) NaOH/H20

100°C

1) Na2TeO3+NaBH4

1/2h

2) Pb(CH3CO2).3H2O

t



37 X. Chen, J. Crystal Gowth 311 (2009) 3179.

t=0 Pure Te

t=0 Te + PbTe

t=48h Pure PbTe

Nanorods

L=0.3-2μm d=50-200nm

Nanorods constituted of NPS (30-50nm)

Absence of organic agents

1) NaOH/H20

100°C

2) Na2TeO3+NaBH4

1/2h

3) Pb(CH3CO2).3H2O

t



Outline









III. Synthesis in organic medium

Advantages of organic solvents over water:

Higher boiling temperature

Favors cristallinity

Some are chelating agents

Control the reactivity of precursors

Orientate the form and shape

Control the dispersity in size

Favors colloidal dispersion

Some are reducing agents

Avoid surface oxidation

38

Drawbacks:

Adsorption of organic species at the particle surface


• Polar solvent, high εr and Tboiling

O H

O

O H O H O H

C H 3

O H O H

T b

( ° C) 198 245 192

1,2 - ethanediol 1 , 2 - butanediol Diethyleneglycol

C H 3

O H

e r

ethanol water

H 2 O

100 78,5

78 , 5 24 38 32 22

39

Polyol synthesis

• Reducing agent

• Polar solvent, high εr and Tboiling

39

• Complexing agent

M

OAc

OH 2

OAc

OH 2

DEG

H 2 O

H 2 O O

O

O

OAc

O

OAc

M

échange

acidobasique M

OH

O

OAc

O

O

O

D. Chiche, Phys. Chem. Chem. Phys., 11 (2009) 11310.

Adsorption on the particle surface

Complex metal ions

Control of nucleation and growth

Avoid surface oxidation

Polyol synthesis


40

Optimisation of the reaction parameters: the case of CoSb3

CoCl2

SbCl3

NaBH4

TetraEG

PVP

Argon

CoCl2 + 2NaBH4 → Co + 2BH3 + 2NaCl + H2

2SbCl3 + 6NaBH4 → 2Sb + 6BH3 + 6NaCl + 3H2

Co+Sb→CoSb (165°C)

CoSb + 2Sb → CoSb3 (T 180°C)

Possibility of obtaining CoSb3 pure and well crystallized with the adequate parameters

15 min

240°C size < 30nm

L. Yang, Materials Letters 62 (2008) 2483–2485

Very well crystallized

tetraEG:


Reaction parameters: T, time, reactant nature, concentration, organic agents…

Influence of temperature

Temperature=

key parameter

41

Possibility of obtaining CoSb3 pure with the adequate parameters

L. Yang, Materials Letters 62 (2008) 2483–2485

CoSb3 is metastable (idem ball milling)

CoSb2 and traces of Co appear with prolonged time

III. Synthesis in organic medium Optimisation of the reaction parameters: the case of CoSb3

Influence of time

CoCl2

SbCl3

NaBH4

TetraEG

PVP

Argon

60 min

tetraEG:

CoSb3 → CoSb2 +Co

Control over stoechiometry

Synthesis of solid solutions: the case of Bi2(Te,Se)3


42 A. Soni, ..M. Dresselhauss Nano Lett. 12 (2012) 1203.

Bi(NO3)3.H2O

K2TeO3.H2O

Na2SeO3

240°C, 4/5h

Bi2Te3 Bi2Te2.7Se0.3 Bi2Se3

Nanoplates

SPS 250°C, 40MPa

1μm 1μm 1μm

1μm

Formation of solid solution with controlled stoichiometry

Different precursors in solution

Orientation of the NPs after pelletization

Te/Se ratio

Outline




IV. Solvothermal synthesis 1. Control of the stoichiometry

2. Control of the morphology

3. Nanoplating





Supercritical

fluid

Solu

tion c

hem

istr

y

Hydrothermal

conditions

water

43

Solvothermal conditions


T > TB in an autoclave P > Patm.

Teflon

liner Steel body

Reactive

solution

Idea: to reproduce the geological conditions

of e and

higher mobility of dissolved species

lower polarity

Equilibrium constants modified (Ke ↗, …)

Modification of the solvent properties modification of chemical reactions

P depends of the volume introduced in the autoclave

44


Versatile method (over cristalline phase, morphology, size)

High cristallinity

Good chemical homogeneity

Excellent control over morphology and particle size distribution

Advantages of solvothermal conditions over ambiant pressure

Same principle as ambiant pressure synthesis:

1. Control of the stoichiometry optimization of the synthesis conditions

2. Control of the morphology use of organic agents sacrificial templating 3. Obtention of nanocomposites by nanoplating

45

1. Control of the stoichiometry

IV. Solvothermal synthesis / 1. Control of the stoichiometry

Phase segregation in the case of CoSb3 ?

J.Q. Li, Mater. Chem. Phys. 112 (2008) 57-62

CoCl2.6H2O

SbCl3

NaBH4

TriEG

290°C

RT

290°C

12h: CoSb3

3 h: CoSb3, Sb, CoSb2

1 h: CoSb3, Sb, CoSb2

Sb CoSb2

CoSb3

Sb + CoSb2 CoSb3

time ↗

Possibility of obtaining CoSb3 pure with the adequate parameters

Optimisation of the synthesis conditions: solvothermal synthesis of CoSb3

46

Possibility of controling the stoichiometry of solid solution

J.Q. Li, Mater. Chem. Phys. 112 (2008) 57-62

NPs size: 10nm

NPs size: 20nm

Evolution of the cell parameter with [Fe]

Vegard law

FeCl3.6H2O

CoCl2.6H2O

SbCl3

NaBH4

TriEG

290°C

Obtention of solid solution: the case of CoSb3-xFex

IV. Solvothermal synthesis / 1. Control of the stoichiometry

47

NaTeO3

Bi(NO3).5H2O

EG

N2H4.H2O

CH3CO2H

PVP

140°C, 1h

1

Growth direction: 112 0 top-bottom facets: 0001 ; side facets 112 0

5 quintuple layers

1.5 unit cell

Q. Yuan, Chem. Commun. 47 (2011à) 12131.

Very well crystallized Bi2Te3 flower-like nanocrystals

Use of organic agents: the case of Bi2Te3 flower-like nanocrystals

Control of the direction growth

2. Control of the morphology

IV. Solvothermal synthesis / 2. Control of the morphology

48

Uniformity in form and size

Role of acetic acid:

Acetic acid: structure directing agent

Role of PVP:

PVP: stabilizing agent

with without

Absence of acetic acid

Self-assembly organisation:

2D-film Honey-comb like spheres

Q. Yuan, Chem. Commun. 47 (2011à) 12131.


49

Templating strategy

Pb(NO3)2

NaOH

Te nanorods

160°C, 6h

Topotactic transformation

J. He, Materials Science in Semiconductor Processing 12 (2009) 217.

Sacrificial templating strategy to control the form and size

Example of the synthesis of PbTe from Te nanorods


50

3. Obtention of nanocomposites by nanoplating

Bulk CoSb3

CoCl2

SbCl3

Absolute ethanol

Ethylenediamine

NaBH4 240°C, 80h

Nanostructuring lowers the thermal conductivity X. Ji, Phys. stat. sol. (RRL) 1 (2007) 229.

Hot pressing

N2, 500°C, 30 min.

NPs precipitates on the bulk

CoSb3 surface

Nanostructing retained

after densification

Formation of nanocomposites

5%nano 20%nano

bulk

IV. Solvothermal synthesis / 3. Nanoplating

Outline





V. Synthesis in confined medium 1. Use of reverse micelles

2. Use of non stabilized biphasic medium




Control of morphology/ size/agregation by : - organic agents - sacrificial templating

Reactions carried out in nano-reactors

V. Synthesis in confined medium / 1. Reverse micelles

reverse micelle

direct micelle

Surfactant

51

Reaction inside the nano-reactor by content exchange

Merged micelles during a few nanoseconds

Content exchange Reaction

M.P. Pileni Nature Materials 2 (2003) 145.

Stable emulsions

1. Use of reverse micelles as nano-reactors

Principle

V. Synthesis in confined medium / 1. Reverse micelles

Modulation of the size of reverse micelles

Modulation of the form of the reverse micelle

52

M.P. Pileni Nature Materials 2 (2003) 145.

w=[H2O] /[AOT]

w=1 w=3 w=5 w=20

Example of Co NPS

Particle size in the nanometer range

Modulation of the size of the NPs to some extend

Modulation of the form of the NPS

Possibility of obtaining solid solutions

use of a ligand as dopant

use of multiple micellar solutions

Difficult to scale up

Advantages:

Drawbacks:

V. Synthesis in confined medium / 1. Reverse micelles Use of a ligand as a dopant

L=thioglycolic acid

After annealing: Bi2Te3 + Bi2Te2S

Micelles of dioctyl sodium sulfosuccinate (AOT) in isooctane

53 A. Purkayastha, Adv. Mater. 18 (2006) 2958.

isooctane

ω=2.4

ω=[H2O] /[AOT]

ω=2.4 ω=4.1

Well crystallized NP Non agglomerated NPs Size with ω (2.5 to 10.4nm)

Incorporation of S from thioglycolic acid Protection against oxidation

AOT

ω=4.1

2.5nm 10.4nm

V. Synthesis in confined medium / 1. Reverse micelles Use of multiple micellar solutions

54 A.J. Karkamkar, M.G. Kanatzidis, J. Am.

Chem. Soc. 128 (2006) 6002.

Reverse micelles of SDS in octane + 1-butanol

SDS: Sodium dodecylsulfate

1) Micellar solution containing Ag(NO3)

+ micellar solution containing K2Sb(C4H2O6)2

+ micellar solution containing Pb(NO3)2

2) Addition of a micellar solution containing Na2TeO3/K2Te

3) Addition of a micellar solution containing NaBH4

AgPb2SbTe4

AgPbSbTe3

AgSbTe2

Formation of pure LAST alloys

d=5.2nm

High atomic order

Nanometric size Well dispersed NPs Size dispersity

d=4.3nm

d=4.6nm

100nm

50nm

50nm

2nm

V. Synthesis in confined medium / 2. Emulsions

Bi3+ Te4+

EDX EDX

J. Fouineau, L. Sicard et al. Chem. Mater. submitted. 55

BiCl3

TeCl4

EG

C12H25SH

2. Use of non-stabilized biphasic medium


Bi3+ Te4+


BiCl3

TeCl4

EG

C12H25SH

Hollow spheres

1 mm 2 mm



Bi3+ Te4+


BiCl3

TeCl4

EG

C12H25SH

Hollow spheres constituted of monocristaline platelets of Bi2Te3

1 mm 2 mm 1 mm 2 mm


+ Bi3+

+ Te4+

Aligned platelets 200 nm

Outline






VI. Decomposition of organometalic complexes 1. Synthesis of simple chalcogenides

2. Synthesis of solid solutions

3. Synthesis of hetero-nanostructures



Reductions

56

VI. Decomposition of complexes

Bi(III) complex

Te(-II) complex

Ligand:

CnH2n+1SH

CnH2n+1CO2H

Te-TOP

Very small nanoparticles (d < 10nm) in the case of hot injection

Monodispersity in size and form

Possibility of tuning the size and form

Colloidal solutions (very well dispersed capped particles) or films

Decomposition of organometalic complexes

Example of Bi2Te3

Advantages:

Presence of an organic shell

Drawbacks:

Heating up or Hot injection Burst of nucleation

Inert atmosphere T150 – 200°C

57

1. Synthesis of simple chalcogenides

M.R. Dyrmier, Small, 5 (2009) 933.

CnH2n+1SH (n=8, 12, 18)

Bi3+--SCnH2n+1 complex

1h

50/150°C

With C12H25SH at 150°C

100nm

Importance of the formation of the Bi-thiol complex:

Well crystallized Bi2Te3 particles

Without thiol

Particle morphology, size, dispersity control

Te(-II)-TOP complex

T = 50/150°C

Synthesis of Bi2Te3 from Bi-thiol complexes

VI. Decomposition of complexes / 1. Simple chalcogenides

58 Possibility of tuning the particle size

M.R. Dyrmier, Small. 5 (2090) 933.

Alkanethiol chain length

C8H17SH C12H25SH C18H37SH

100nm 100nm 100nm

Influence of the capping agent chain length:

T = 50 °C

Influence of the temperature:

Steric protection of the newly formed particles inhibition of particle growth

Particle size (nm) 50°C 150°C

C8H17SH 295 9815

C12H25SH 233 456

C18H37SH 172 527

High temperatures favors growth

The alkanethiol remains adsorbed at the NPs surface


59

High temperature favors growth Change of shape with size (Wulff construction)

J. Urban, J. Am. Chem. Soc. 128 (2006) 3248.

Influence of the temperature:

Bi3+-carboxylate

complex

(CH3CO2-)3 Bi3+

+ oleic acid

Te(-II)-TOP complex

T

T < 170°C Monodisperse cubo-

octahedral NPS

T > 200°C Less monodisperse

cubic NPS Larger size

Synthesis of PbTe from Bi-alcoolate complexes


60

Possibility of tuning the particle size with the ligand

Influence of the oleic acid/Pb acetate ratio

Oleic acid/Pb acetate molar ratio

The size with the addition of oleic acid

J. Urban, J. Am. Chem. Soc. 128 (2006) 3248.

Stability of lead oleate > lead acetate Lead oleate reacts more slowly Less nuclei


High degree of orders ; interesting structures for thermoelectricity

Tape casting of a PbTe colloidal solution

J. Urban, J. Am. Chem. Soc. 128 (2006) 3248. 61

Deposition of QDs lattices


62

Pure I doped-PbTe nanoparticles (4-5% depending on the initial ratio) with tunable size

n-type semi-conductors (non-doped PbTe is p-type) S2σ ↗ with I doping for a same size

Doping of PbTe by iodine

H. Fang, Nano Letters 14 (2014) 1153.

Pb/oleate

complex

in 1-octadecene

Te/I-TOP complex

N2


VI. Decomposition of complexes / 2. Solid solutions

63

Formation of a pure solid solution of AgPbmSbTem+2 (m=1–18)

Synthesis of quaternary nanocrystals

I. U. Arachchige, Adv. Mater. 20 (2008) 3638.

1) Pb(II)oleate

Sb(II) oleate

octadecene

2) Ag-dodecanethiol complex

Te(-II)-TOP complex

N2, 150 °C, 2 min Pure LAST solid

phase

Vegard law


AgPbmSbTem+2

64

Well crystallized Highly monodisperse NPs Diameter = 6.8-8.4nm


AgPbmSbTem+2

mth=2 mexp=2.44

mth=4 mexp=3.96

mth=6 mexp=7.69

mth=8 mexp=9.87

mth=18 mexp=25.7

Morphology of the NPs


65

At 150°C, crystallite size from 6.3 to 14.5nm

Phase separation upon annealing at 150°C within the nanocrystals but no

morphological changes observed

Effect of annealing


AgPb4SbTe6

*: AgSbTe2

#: Ag2Te

@: Sb2Te3

25°C

150°C

400°C


66

PbTe-PbSe core-shell nanostars

M. Scheele, ACS Nano 5 (201) 8541.

Pb/oleate

complex

In diphenylether

Te(-II)-TOP complex

N2 N2

+ Pb/oleate complex

in diphenylether

Se(-II)-TOP complex

PbTe

PbTe-PbSe

Epitaxial growth of PbSe in the [100] direction onto each of 6 the octahedron tips

3. Preparation of hetero-nanostructures

PbTe NPs

VI. Decomposition of complexes / 3. Hetero-nanostructures

67

4. Preparation of composite films

Binary QDs lattice

PbTe (6.5nm) + Ag2Te (3.2nm)

PbTe (10.1nm) + Ag2Te (6.5nm)

PbTe + AgTe colloidal solutions followed by self-organization evaporation

High degree of orders Structure depending upon the NPs size

J. Urban, Nature Mater. 6 (2007) 115.

Modulation of

Measures after N2H4 treatment (see after)

VI. Decomposition of complexes / 3. Hetero-nanostructures

Outline






VI. Decomposition of organometalic complexes 1. Synthesis of simple chalcogenides


3. Synthesis of hetero-nanostructures

VII. Post-synthesis treatments 1. Thermal treatments

2. Chemical treatments


Reductions

68


detrimental to densification and electronic properties

Possible organic/oxide coating: drawback of the solution synthesis Is it a fatality ?

1. Thermal solutions (annealing)

2. Chemical solutions

69

VII. Post-synthesis treatments / 1. Thermal treatments

Insulating

alkanethiol layer

(C18H17SH)

M.R. Dyrmier, Small. 5 (2009) 933.

Hydraulic

press

Use of C18H17SH Particle size (nm)

σ (S cm-1) S (μV K-1) S2σ (μV2cm-1K-1)

Bulk Bi2Te3 12.2 -125 1.9 105

NPs synthesized at T = 50°C

527 5.89 10-1 -85 2.5 103

Poor electronic properties

100 nm

Annealing under N2flow

1. Thermal treatments

NPs obtained by decomposition of organometallic complexes

(Bi-SCnH2n+1 and Te-TOP)

thermal treatment:

350°C, 24h, under N2 flow

Nanostructuration retained

70 M.R. Dyrmier, Small. 5 (2009) 933.

Use of C18H17SH Particle size (nm)

σ (S cm-1)

S (μV K-1)

S2σ (μWcm-1K-1)

NPs before annealing 172 1.07 10-3 -49 2.6 10-6

NPs after annealing 397 30.4 -150 0.69

densification, d 87% after cold compaction

Improvement of the power factor due to • removal of the organic shell • sulfur doping during annealing

Absence of T dependence different from bulk Bi2Te3

at 300 K: κ(NPs) = 0,51 W m-1K-1 << κ(bulk)


71 M.R. Dyrmier, Small. 5 (2009) 933.

Removal of the organic surface layer electronic properties

Keeping nanostructuration layer low κ

Advantages of thermal treatment under N2 flow:

Drawbacks:


Small increase of oxide content

Thermal treatment under N2 flow do not permit to remove the oxide layer

72

Annealing under Ar flow

Y. Zhao, J.S. Dyck, B.M. Hernandez, C. Burda, J. Phys.Chem. C 114 (2010) 11607.

No oxide formation

NPs obtained by decomposition of Bi–thiol (C12H25SH) and Te-TOP complexes

Annealing for 5 hours under Ar flow

Cold-pressing

Vacuum-dried T = 300°C T = 350°C T = 380°C

Bi2Te3

53 nm 62 nm 71 nm 100 nm

Nanostructured materials up to 350°C


73 Y. Zhao, J.S. Dyck, B.M. Hernandez, C. Burda, J. Phys. Chem. C 114 (2010) 11607.

Bi2Te3

Ar flow annealing permits to remove the capping ligand without oxidation

Low σ before annealing σ ↗ with annealing T

n-type semi-conductor S max forT=300°C

Sσ2↗ with annealing T

Simultaneous ↗ of σ and S at annealing T of 300°C

Data non-corrected from radiation loss

Weak ↗ of κL with T due to phonon scattering through nanostructuring Low κL values which increases with annealing


B. Zhang, Appl. Mater. Interf. 2 (2010) 3170.

Bi2Te3 prepared by ball milling treated in a 5%wt HCl solution

Composites of Bi2Te3 in PEDOT:PSS

Removal of the oxide layer

XPS

Acidic treatment to remove the oxide shell:

VII. Post-synthesis treatments / 2. Chemical treatments 2. Chemical treatments

Both and S increase

74

75

Chemical exchange to remove organic ligands:

M. Scheele, Adv. Funct. Mater. 19 (2009) 3476.

1) Exchange of dodecanethiol ligand shell by oleic acid on the surface of nanoparticles obtained by complexes decomposition

2) Hydrazine (or ammoniac) etching treatment Hexane + NPs

N2H4

Hexane

N2H4 + NPs

N2H5+ -O2C17H33

N2H4: - base which can remove the capping agent - reducing agent

sample Resistivity (m cm)

S (μV K-1) (300K)

κ (W m-1 K-1) (200K)

zT (300K)

n-type bulk Bi2Te3 1.4 -180 2.2 0.32

this work 1.3 -80 0.8 0.2

3) SPS treatment (50°C)

Same resistivity as bulk n-Bi2Te3

Lower thermal conductivity.

VII. Post-synthesis treatments / 2. Chemical treatments

76 J.F. Urban J. Am. Chem. Soc. 128 (2006) 3248.

Same resistivity as bulk n-Bi2Te3

Lower thermal conductivity.

N2H4 treatment of a PbTe film followed by thermal treatment

Quantum dots nature preserved with: - hydrazine treatment - thermal treatment up to 200°C (vacuum)

Interparticle distance from 1.8 down to 0.3 nm

N2H4

Insulator σ = 10-13Scm-1

n-type conductor σ x1010-1012

σ ↗

150 °C


SAXS

77 D. Yang, Nanoscale 5 (2013) 7290.

Same crystalline structure Inter-particle distance from 1.4 to <0.3nm

Molecular Metal Chalcogenide complexes (MMC)

Formation of MMC: dissolution in hydrazine of bulk metal chalcogenides in the presence of an excess of chalcogenide

NPs/Hexane

MMC/N2H4

Hexane

N2H4 +

MMC-capped NPs

PbSe obtained by decomposition of complexes (insets) and after MMC treatment (main TEM images)

M.V. Kovalenko, Science 324 (2009) 1417.

20 nm


Use as capping agents

78 D. Yang, Nanoscale 5 (2013) 7290.

VII. Post-synthesis treatments-2. Chemical treatments

n-type (due to MMC) S ↗ when NPs size

(quantum confinement) S ↗ at high T (release

of low energy carriers and ↗ of minority hole carriers)

Electronic properties:

σx108 after MMC treatment

σ=110-320 S cm-1 at 300K

σ ↗ with NPs size σ ↗ with T (low energy

carrier filtering)

low

↗ with NPs size ( interface density)

High ZT

Thermal properties:

Thermoelectric properties:

79

Spin casting

Post-synthesis colloidal atomic layer deposition Removal of the capping agent and engineering stepwise the surface stoichiometry

After 1 cycle

10 nm

After 2-3 cycles

Oleic acid capped PbSe NCs

Connection along the (100) facets first (due to weaker bound oleic ligand)

oxidated surface

non oxidated surface

High electron mobility: 4.5 cm2/(V.s)


S.J. Oh, Nano Letters14 (2014) 1559.

Post-synthesis charge carrier control

80


Advantages of soft-chemistry synthesis:

Variety of chemical routes and strategies to control:

• the cristalline phase

• the stoichiometry

• the morphology

• the particle size, dispersity

Scalable, high yields, low temperature, low cost

Good chemical homogeneity, high cristallinity, low strain

Possibility of designing a high variety of simple or complex materials:

• simple chalcogenides (PbTe, Bi2Te3, CoSb3)

• solid solutions ((Bi,Sb)2Te3, Bi(Te,Se)3, Co (Sb,Fe)3, AgPbmSbTe2+m)

• core-shell NPs

• nanocomposites

Obtention of dense and non oxidized materials through post-treatments

81


Improvement ways:

From « essay-error » to a reasonned approach

Pursuit of efforts to design in a same material both:

• nanostructuring

• chemical stoichiometry (solid solution)

optimization of , S and κ in the same material

Towards advanced materials:

D.-K. Ko, Nano Letters11 (2011) 2841.

Pt nanocubes encapsulated in Sb2Te3

S improved due to filtering of low energy holes but decrease of σ due to mobility reduction Slightly improved power factor

Y. Zhang, Nano Letters. 12 (2012) 1075.

Thank you for your attention Some questions ?

R.J. Mehta, Nature Mater., 11 (2012) 233.

Te/Se-P(C8H17)3 complex

Quick, efficient and scaling up synthesis

Te/Se

(C8H17)3P

Microwave 90-120s

Bi/Sb-S(CH2CO2H) complex

BiCl3/SbCl3

A B + 30-60 s

2-10 g min-1

100 % yield

top-bottom facets: 0001

Single crystals

High crystallinity, shape control

Thioglycolic acid:

directing agent

Sulfur doping via the thioglycolic acid Protection against oxidation thanks to thioglycolic acid Bi2Te3: slight excess of Bi

Energy (eV)

WDX

0.1-O.3 at.% Sulfur controlable through synthesis conditions


After sintering at 300/400°C under vacuum :

Cold-compaction (hydraulic press) and sintering density : 923%

Good compaction

TGA replaced by neodecanoate: n-type

Importance of Sulfur doping

S-doped Bi2Te3 (Bi-rich): n-type

κ: 40-75%

κL: 60-75% lower than bulk materials

attributed to nanostructuring

50nm

Microwave dose (kJ g-1) κL (Wm-1K-1) Bi2Te3

0.59

0.38

50-80

5-10

10-100nm grains 5-50nm inter and intragranular pores

Electronic properties controlled by Sulfur doping

Thermal conductivity controlled by Nanostructuring


Bi2Te3: 1-2 at. % Bi-rich

Bi2Se3: 1-5 at. % Bi-deficient

Sb2Te3: stoeichiometric

0.1-O.3 at.% Sulfur

25% higher than conventional alloys

2-4 times higher than their bulk

counterparts (same composition and

stoichiometry)

High performances nanostructured materials through

- nanostructuring

- doping

Synthesis of nanomaterials by soft chemistry...

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