Electrochemical process for thermoelectric nanowire...

Pr Clotilde Boulanger Groupe « Chimie et Electrochimie des Matériaux »

Institut Jean Lamour– UMR CNRS , Université de Lorraine

Electrochemical process for

thermoelectric nanowire fabrication

2

Outlines

Nanowires Synthesis without porous template

Membrane-based synthesis approach

Principles of Electroplating

V2VI3 films: some examples

Synthesis of V2VI3 nanowires in Alumina membrane

Experimental parameters

Characterizations

Synthesis of V2VI3 nanowires in Polymeric membrane

Experimental parameters

Characterizations

Nanostructured and complex structures: some examples

Summary

3

Enhancement of conversion efficiency

nano-objects, nano-structures

• quantum confinement effect

• phonons scattering

Aims and motivations

Nanowire electrodeposition

Template synthesis or self-assembly growth

Z = α 2 (e+p).r

Szymczak, J. et al.

Electrochemistry Communications, 2012

Synthesis of Te in RTIL

4

Nanostructured TE compounds

=e+p

A.I.Boukai and al.,Nature, vol 451 (2008) A.I.Hochbaum and al., Nature, vol 451 (2008)

decrease of lattice thermal conductivity

boundary scattering of phonons

The dimensionality of the material :

a new variable to tune the thermoelectric properties

Example nanowires of Silicon

ZT @ 200K : 200 fold increase !

changes in density of

electronic states

5

How ?

Synthesis of thermoelectric nanowires

Synthesis without porous

template Electrochemical synthesis on Highly

Oriented Pyrolytic Graphite

Menke et al. Langmuir, 2006, 22, 10564

Solution phase growth process (polyol

method)

M Chen Mat Res Bull.2005

Direct Growth of Semiconductor

Nanowires by stress-induced mass flow

along grain boundaries in the

polycristalline film Shim, Nanoletters 2009

Nucleation of Bi2Te3

along step edges

and coalescence

6

Membrane-based synthesis approach Martin, Charles, Science; 1994

Pressure injection process :

Technique consists in the pressure injection into an alumina template

with molten Bi2Te3 liquid

Electroplating of nanowires through porous template

P. Jones, T. Huber

ICT 2006

How ?

Synthesis of thermoelectric nanowires

7

Electroplating: an attractive route

Advantages over thermally driven techniques

• More cost-effective

– Non intensive equipment

– Low temperature

– Absence of vacuum

• Thickness control by consumed charge

– From tens of nm to hundreds of µm

– Interesting growth rates

• Wide range of compositions

• Limitation of interdiffusion and chemical reaction

• Scalability (large or small areas)

• Epitaxial deposition (uniform growth)

• Considerably simpler but necessity of electroanalytical study

8

V

A

C

E

R

E

W

i i

Te+I

V

Bi3+

potentiostat

e

e

Electroplating: principle

Creation of solid materials directly from

electrochemical reactions onto substrate materials

Reduction of ionic precursors in aqueous, non

aqueous, ionic liquids, or molten salts But also deposit by oxidation

Mn+ + ne- M°

electrons

from an external source (electroplating)

in potentiostatic mode Efixed i=f(t)

in galvanostatic mode Ifixed E=f(t)

from a chemical reductor (electroless deposition)

No external source, more difficulty to control

the thickness and uniformity of the deposits

9

Factors of electrocrystallization

Electrical parameters:

• E potential

• I current density

• Q consumed charge

Electrode parameters:

• Type of substrate

• Geometry

• Surface roughness

Electrolyte parameters:

• Nature and Concentration

• Support electrolyte

• Additives

• Temperature

Mass transfer parameters:

• Mode (convection, diffusion)

• Hydrodynamic conditions

V

A

C

E

R

E

W

i i

Te+IV

Bi3+

potentiostat

e

e

10

Electrode – Electrolyte interface

Electroplating : Interfacial reaction between an electrode and a solution

Electrode =

Electronic conductor

- Metal

- Semi Conductor

- Conducting polymer

Bulk solution =

Ionic conducting medium:

- electrolyte solution

- molten salt

- solid electrolyte

Migration

Solvated

ion

Solvated

ion

Double layer

Mass transport

Charge transfer + desolvatation

Nucleation

Growth

Adsorption

adion

Surface diffusion

Incorporation

atom

S

S

S

Bulk solution Electrode

11

Current – potential relationship

Mn+ + ne- M°

characterized by Nernst Law

If E app < Eeq electrodeposition current

= Eapp(I) - Eeq

0

00

/

M

M

MMeq

a

aLn

nFRTEE

n

n

linear region i=io (nF/RT)

Charge transfer control

exponential region

Mixed control

Charge and mass transfer

Mass transfer control

Limiting current density region

cu

rre

nt d

en

sity

potential

Ilim =f(|Mn+|sol)

M° Mn+ + ne-

Eeq

Buttler-Volmer

12

Current – potential relationship

Cyclic Voltammetry curves potential

potential

Cu

rre

nt d

en

sity

Stirred solution

Unstirred solution

ilim

ip

Cu

rre

nt d

en

sity

13

Electrochemical window

H

Li

Na Mg

Be

K

Rb

Cs

Fr

Ca

Sr

Ba

Ra

Sc

Y

La

Ac

Ti

Zr

Hf

Rf

V

Nb

Ta

Db

Cr

Mo

W

Sg

Mn

Tc

Re

Bh

Fe

Ru

Os

Hs

Co

Rh

Ir

Mt

Ni

Pd

Pt

Uun

Cu

Ag

Au

Uuu

Zn

Cd

Hg

Uub

Ga

In

Tl

B

Al

Ge

Sn

Pb

C

Si

As

Sb

Bi

N

P

Uuq

Se

Te

Po

O

S

Br

I

At

F

Cl

Kr

Xe

Rn

Ne

Ar

He

Ce

Th

Pr

Pa

Nd

U

Pm

Np

Sm

Pu

Eu

Am

Gd

Cm

Tb

Bk

Dy

Cf

Ho

Es

Er

Fm

Tm

Md

Yb

No

Lu

Lr

Electrodeposited metal in aqueous medium Limitation by hydrogen evolution (E~-1.2 V) H2O + 1e-

½ H2 + OH-

14

Nucleation

Real surfaces : defects on crystal face nucleation sites for electrodeposition

N N0At

N N0

Edge dislocation with

the surface

Vacancy in terrace

Adatom

(same kind as bulk atoms)

Kink, step in the edge

Monoatomic step

Vacancy in the edge

Screw dislocation

Impurety

adsorbed atom

Perfect flat surface

Adatom on terrace

N0 = total number of sites (maximum possible number of nuclei

per unit surface)

A = nucleation rate constant

N = N0[1- exp (-At)]

A and At>>1

A and At <<1

immediate activation of all reaction sites

and constant number of nuclei

increase of nuclei number

during the growth process

15

Growth

lateral (k2) and vertical (k1)

growths

Depend on the affinity :

Metal – Metal

Metal - Substrate

Growth

Growth

3D Pyramidal nucleus

2D Cylinder nucleus

16

Nucleation – growth

Z3 =overlap of nuclei

Slowing down of nucleation and current

Z1 =double layer

charging current

Z2 = i

- growth of independant nuclei

- increase in nb of nuclei

Potentiostatic current-time transients

i=f(t)

im

tm

im

ifree

Z4 = diffusion of ions in solution

Limiting current

Exemple of 3D nucleation limited by diffusion

Electrochemist point of view

17

Current time transients

t0

t1

t2

0

0,2

0,4

0,6

0,8

1

0 0,5 1 1,5 2 2,5 3

t/tmax

(i/i

max)²

Nucléation instantanée 3D

Nucléation progressive 3D

t0

t1

t2

3D Nucleation 2D Nucleation Instantaneous nucleation

immediate activation of all reaction sites

and constant number of nuclei

Progressive nucleation

increase of nuclei number during the

growth process

t 0

t 1

t 2

t 0

t 1

t 2

0

0,2

0,4

0,6

0,8

1

0 0,5 1 1,5 2 2,5 3

t/tmax

i/i m

ax

Nucléation instantanée 2D

Nucléation progressive 2D

Theoretical models of nucleation

18

Electrocrystallization

Schematic présentation of grain

structures of electrodeposited films

Arrow: increase of the given parameter

in determining grain sizes

But also

- Chelates

- Other C+ et A-

- Substrate

- pH

- Adsorbed species

Operating conditions over electrodeposit structure

E

19

Simplified diagram of electrocrystallization types

Proposed by Winand J. Appl. Electrochem., 21, 377 (1991)

after work of Fischer Electrochimica Acta, 2, 50 (1960)

Jdl: limiting current density

FI: Field oriented Isolated crystals

BR: Basis oriented Reproduction

FT: Field Orientated Texture

UD: Unoriented Dispersion

FI or

no

deposit

Dendrites

Bad

crystallization

Hydrogen

evolution

Important parameters:

- Ratio J/Jlim (or J / |Mn+|)

- inhibition intensity

Inh

ibitio

n inte

nsity

20

Conditions

Conducting surface as a seed layer

Good resist adhesion on the substrate

Easy access to recesses of plating solution

Compatibility of plating solution with substrate materials

Uniform current distribution on the substrate surface

Dependence of shape and size of the deposits over the

surface characteristics of the substrate

Further studies on the fundamentals of the nucleation and

growth

to understand the preferential deposition on a particular site

of the electrode substrate

21

Electrochemistry for TE compounds

Chronological research on TE powder and layers

1990 1995 2000 2005 2010

Bi2Te3 Takahashi

Magri

Surfactant adding Molten salt

powder

Bi2Te3 Panson

Bi2Se3 Torane

PbTe

PbSe

PbSeTe Streltsov

Saloniemi

1964

BiSb Povetkin

Bi2(SeTe)3 Martin Gonzalez

Michel Sb2Te3

(BiSb)2Te3 Leimkuhler

Nedelcu

Organic medium

Ionic liquid

CoSb

CoSb3 Sadana

22

Chronological research on TE nanowires

1998

Bi Chien

2000 2005 2010

Growth rate tuning

Control of stoichiometry

Polymeric membrane

2003

BiSb

Bi2(SeTe)3

(BiSb)2Te3 Martin Gonzalez - Prieto

1999

Bi2Te3 Sapp

CoSb3 Prieto

2004

PbTeSe Sima

Anodized Aluminium Membrane

23

F. Xiao, C. Hangarter, B. Yoo, Y. Rheem, K.H. Lee, N.V. Myung, Recent progress in electrodeposition

of thermoelectric thin films and nanostructures, Electrochimica Acta 53 (2008) 8103-17.

C. Boulanger, Thermoelectric material electroplating: a historical review, Journal of Electronic Materials

39, 9 (2010) 1818-1827

Electroplating of V2VI3 compounds

Reduction of tellurite ions (TeIV) in presence of Bismuth

2Bi3+ + 3xTe+IV + 18 e- → Bi2Te3

2Bi3+ + 3xTe4+ + 3(1-x)Se4+ + 18 e- → Bi2(TexSe1-x)3

2(1-x)Sb3+ + 2xBi3+ + 3Te4+ + 18 e- → (Sb1-xBix)2Te3

p-type ternary compound

n-type ternary compound

24


Dissolved precursors: Bi3+, Sb3+, Te+IV, Se+IV Bi2O3, Bi(NO3)3, Bi°, Sb2O3, Te, TeO2, K2TeO3, NaSeO3,

Weak solubilities of ions → acidic electrolyte

• HNO3 but also HClO4, H2SO4, HCl + NH4F, HNO3 + H3PO4

For Sb3+, necessity of chelating agent (tartrate / citrate)

Electrolytes enriched in Bismuth:

Bi/Te or (Te+Se) = 0.75 -1.33 to compare with 0.66

Substrate: conductors not attacked by H+

Au, Pt, Mo, Ti, stainless steel, Ni, Bi2Te3

Bismuth Nickel-Chrome Tantalum Tungsten Titanium Gold

25

Electrodeposition approach

Electrochemical study

investigation of electrolyte behaviour through

voltametric techniques onto microelectrodes

Electrodeposition onto electrodes

potentiostatic and galvanostatic deposition

(control of E, I, electrolyte composition)

Characterization of deposits

• Composition (EPMA, XFS), structure (DRX), morphology

(SEM, AFM)

• Transport properties (Hall effect, Van der Pauw), Seebeck

effect

• Contactless methods (Spectroscopic ellipsometry)


26

Electrodeposition of Films

Tuning of the composition of electroplated films in aqueous medium :

n-type semiconductor

Bi2-xTe3+x % at. Te>62

Bi2Te2.7Se0.3

ZnO:Al

p-type semiconductor

Bi2+xTe3-x % at. Te<58

Bi0.5Sb1.5Te3

in liquid ionic medium :

Doping with heavy elements such

as Rare Earths (RE) elements

Bi-Te-La

« high cathodic stability, Liquid at room

temperature,high thermal stability »

1-ethyl,1-octylpiperidinium

bis(trifluoromethylsulfonyl)imide

Formation of (Bi1-xSbx)2Te3

0.5 < x < 1

0 2 4 6 8 10 12 14 16 18 20 22 24 260

2

4

6

8

10

12

14

16

18

20

22

y= 0,8281x + 0,52701

R2=0,9987

Ato

mic

% o

f B

i in

film

Atomic % of Bi in electrolyteSb2Te3

BiSbTe3

Bi0.5Sb1.5Te3

Solid solution

between Sb2Te3 and Bi2Te3

27

[Bi3+]=[HTeO2+] = 10-3 M

[HTeO2+] = 10-3 M

[Bi3+] = 10-3 M HNO3 1N

single phase in acidic medium

-200 0 200 400 600 800 1 000-16

-8

0

8

16

24

Inte

nsité

(m

A)

Potentiel (mV/ECS)

Electroplating of Bi2Te3

-0,4 -0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2-4

-2

0

2

4

6

8

10

12

14

Te

j (m

A/c

m²)

E (V/Ag/AgCl)

-0,4 -0,2 0,0 0,2 0,4 0,6-4

-2

0

2

4

6

8

10

12

14

Bi

% (2)

j (m

A/c

m²)

E (V/Ag/AgCl)

2Bi3++3HTeO2++18 e- +9H+ Bi2Te3+6H2O

HNO3 1N

HNO3 1N

Magri J. Mater. Chem 6, 1996

Bi 3+ Bi°

Te+IV Te°

Bi2Te3 Bi3+, Te+IV

Bi2Te3

Bi° Bi 3+

Te+IV Te°

28

-400 -200 0 200 400 600

-600

-400

-200

0

200

400

600

800

1000

E (mV/ECS)

i (µA) Bi/Te = 1/2

Bi/Te = 2/3

Bi/Te = 1

Bi/Te = 4/3

Bi/Te = 2

[HTeO2+] = 10-3 M

Potential range : -20 to -200 mV/SCE

Existence of single phase compounds

BixTey

Bi/Te =

4/3

BiTe E=-90mV/ECS

Bi/Te =

1/2

BiTe2

E=-125mV/ECS BiTe2

Bi/Te =

2/3

Bi2Te3

Bi2Te3 Bi4Te3

Bi/Te =

1

Bi2Te3

Bi2Te3

Bi/Te =

2/3

Bi2Te3

Bi2Te3

Bi/Te =

1

Bi2Te3

Bi2Te3


J Crystal Growth,277, 2005, 274

E (mV/SCE)

29

[HTeO2+] = 10-2 M

[Bi3+] = 10-2 M -0,3 -0,2 -0,1 0,0

-2,4

-2,2

-2,0

-1,8

-1,6

-1,4

-1,2

-1,0

-0,8

-0,6

-0,4

-0,2

0,0

J (m

A/

cm2)

E (V/ECS)

Bi 3+,Te+IV

Bi2Te3


HNO3 1N

Potentiostatic mode Galvanostatic mode

Bi2-xTe3+x

J. Crystal Growth, 277 (2005) 274.

30

Preferential orientation

Pole figure analysis fiber texture Bi2Te3

(11.0)

ab

c

xyz Te(1)

Bi

Te(2) Bi

Te(1)

ch

rhomboedral R-3m

layered structure: anisotropy of properties

Sab ~ Sc

rab ~ 1/4 -1/6 . rc

ab ~ 2 . c

orientation knowledge importance


ZT (basal plane) = 2 x ZT(along c axis)

Journal of Crystal Growth 296, 2006, 227-233

31

39°

10.10

11.0 11.0

60 65 %Te 55

Bi 2,25 Te 2,75 Bi 2,00 Te 3,00 Bi 1,75 Te 3,25

Gro

wth

axis

10.0

ch


J. Crystal Growth 296, 2006, 227

ZT (basal plane) = 2 x ZT(along c axis)

Better electrical conductivity, Favorable to thermoelectric properties

growth in the direction of basal planes

32

Electroplating of Bi2Te3 layers

Journal of Crystal Growth, 277 (2005) 274-283.

33

Arabic gum : decrease of the surface roughness

No surface contamination

Without gum With gum

AFM (10x10 µm²)

569 nm 51 nm

0 nm 0 nm

RMS = 92 nm RMS = 9,4 nm

Bi 1,8 Te 3,2 Bi 2,0 Te 3,0 Bi 2,2 Te 2,8

S (µV/K) without gum

S (µV/K) with Arabic gum

r (µ.m)

ZT

(cm²/V.s)

n (1020 cm-3)

-75

-167

15

0.59

8

3.5

-65

-115

30

0.25

8

5

-50

-56

28

0.07

12

5

Addition of organic species in electrolytes

[Bi]/[Te] = 1 [Te] = 10-2 M

-0.25A/dm2 < J < -0.10A/dm2

with = 1 W/m.K (Z=S²/r)

34

Instantaneous nucleation : immediate

activation of all reaction sites and constant

number of nuclei

Progressive nucleation : increase

of nuclei number during the growth

process

2

maxmax

2

max t

t2564.1exp1

t/t

9542.1

i

i

2

2

maxmax

2

max t

t3367.2exp1

t/t

2254.1

i

i

3D

²ln btat

i

3

²ln dtc

t

i

2D

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2 2.5 3

(i/i m

ax)²

t/tmax

instantaneous nucleation progressive nucleation

with arabic gum with SDS

Potential influence Surfactant influence


35

Electroplating of Bi0.5Sb1.5Te3

-300 -250 -200 -150 -100 -50 0 50 100 150 200

-2,4

-2,2

-2,0

-1,8

-1,6

-1,4

-1,2

-1,0

-0,8

-0,6

-0,4

-0,2

0,0

Bi0,5

Sb1,5

Te3

BixSb

yTe

z

0,5Bi3+

+ 1,5Sb3+

+ 3TeIV+

+ 18e-

xBi3+

+ ySb3+

+ zTeIV+

+ (3x+3y+4z)e-

Bi2Te

3 2Bi3+

+ 3TeIV+

+ 18e-

Te° TeIV+

+ 4e-

c3

c2

c1

J/m

A.c

m-2

E/mV (vs. ECS)

2(1-x)Sb3+ + 2xBi3+ + 3Te4+ + 18 e- (Sb1-xBix)2Te3

HClO4 1M + Tartaric Acid 0.1 M

C2 two phases BixSbyTez + Te°

Bi-Sb-Te

([Bi]+[Sb])/[Te]=1

[Sb]/[Bi]=3 – [Te]=10-2M

1M HClO4-0,1M C4H6O6

C1 two phases Bi2Te3 + Te°

C3 single phase Bi0.5Sb1.5Te3

E (mV/SCE)

36

•E=-0.17 V/SCE

•([Bi]+[Sb])/[Te] = 1

•[Sb]/[Bi]: from 1 to 10

-0,30 -0,25 -0,20 -0,15 -0,10 -0,05 0,00 0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

zone 3 zone 2 zone 1

Com

po

sitio

n o

f film

s

Potential (V/SCE)

Bi Sb Te

Formation of (Bi1-xSbx)2Te3

0.5 < x < 1

0 2 4 6 8 10 12 14 16 18 20 22 24 260

2

4

6

8

10

12

14

16

18

20

22

y= 0,8281x + 0,52701

R2=0,9987

Ato

mic

% o

f B

i in

film

Atomic % of Bi in electrolyte

Sb2Te3

BiSbTe3

Bi0.5Sb1.5Te3

Solid solution

between Sb2Te3 and Bi2Te3

20 30 40 50 60 70 80

Bi-Sb-Te

Te°

Te°

01.2

321

.10

12.5

12.5

10.1

910

.19

02.1

002

.10

02.1

0

20.5

20.5

20.5

00.1

500

.15

11.0

11.0

10.1

010

.10

10.1

0

01.5

01.5

zone 2

E=-0,1 V/ECS

zone 3

E=-0,17 V/ECS

01.5 zone 1

E=-0,02 V/ECS

2 (Cu

=1,54056 Å)

E=-0.17 V/SCE

E=-0.1 V/SCE

E=-0.02 V/SCE


Thin Solid Films 483, 2005, 44

37

SEM: morphology

Cross section Top view

Rough surface

Dendritic layer


Winand J. Appl. Electrochem., 21, 377 (1991)

Fischer Electrochimica Acta, 2, 50 (1960)

FI or

no

deposit

Dendrites

Powder

Bad

crystallization

Hydrogen

evolution Important parameters:

- Ratio J/Jlim (or J / |Mn+|)

- inhibition intensity

Inh

ibitio

n inte

nsity

J/Jlim

Jlim: limiting current density

Diagram of electrocrystallization types

Too high J / |Mn+|

38

Direct mode on

stainless steel

Pulsed mode on

stainless steel

Pulsed mode on

gold

[Sb]/[Bi]= 3 [Sb]/[Bi] = 8 [Sb]/[Bi] = 8

(Bi0.25Sb0.75)2Te3 (Bi0.17Sb0.83)2Te2.99 (Bi0.25Sb0.75)2Te3

annealing 1 h at 250°C 1 h at 250°C 2 h at 480°C

Seebeck

coefficient (µV/K) 190 138 108

resistivity (µΩ.m) 545 123 9

power factor

(µW/K2.m) 66 155 1350

pulsed electroplating in galvanostatic mode 1.9 mM Bi – 5.6 mM Sb - 10 mM Te 0.1 M HT HNO3

EC or IC

tc

toff

0

I (mA) ou E (mV)

t (s)

ton + toff

ton Jm = Jc

Pulse deposition

recovery of species

during rest time

Technique for improving the morphology of electroplated films

Modification of the nucleation and the grain size


J. Applied Electrochem 36, 2006, 440

39

Towards application

Thick films :

Li & al, Chem. Mater. 18, 3627 (2006)

Electrolyte :

BiO+ = 13 mM HTeO2+ = 10 mM

HNO3 pH = 0 With Ethylene Glycol 10-40 %

Potentiostatic and Galvanostatic syntheses thickness up to 350 µm

Growth speed :

Between 4 to 12.5 µm/h

Good adhesion on the

substrate

Use of ethylene glycol

not suitable for an

industrial application

Properties As

deposited

After heat

treatment (2h at 300°C)

Seebeck

coefficient (µV/K)

-70 -125

Electrical resistivity (µΩ.m)

22 25

Power factor (10-4 W/m.K²)

2.20 6.00

40

Thick films :

Glatz & al, Electrochim. Acta 54, 755 (2008)

Electrolyte :

Bi2O3 = 93 mM TeO2 = 80 mM HNO3 pH = 0

Mixed method : potential deposition pulses and zero current resting pulses

Zero current resting pulses allow the

electrolyte homogenization at the

electrode surface

Towards application

41

Thick films :

Glatz & al, Electrochim. Acta 54, 755 (2008)

Electrolyte :

Bi2O3 = 93 mM TeO2 = 80 mM HNO3 pH = 0

Mixed method : potential deposition pulses and zero current resting pulses

Great speed of growth

Use of a pulse method

Growth rate up to 50 µm.h-1

Seebeck coefficient :

- 40 µV/K for the Te-rich compound

+ 55 µV/K for the Bi-rich compound

Towards application

42

Towards application

No modification of the electrolyte concentration

even after 100 h

Constant stoichiometry = f(t) = f(thickness)

Interest of anode to maintain the concentration

of cations in the electrolyte

i

V

A

Working

electrode

Counter Electrode

: Soluble anode

Improvement:

soluble anode of Bi2Te3 electrolyte auto-regeneration

Tests for binary Bi2Te3 depositions

1

2

3

4

5

Cross section composition

for one film:

1 : 37,96%Bi ; 62,04%Te

2 : 38,00%Bi ; 62.00 %Te

3 : 36,58%Bi ; 63,42%Te

4 : 37,83%Bi ; 62,17%Te

5 : 37,58%Bi ; 62,43%Te

average : 37,38%Bi ; 62,62%Te 0,82

43

MM130902_01

Operations: Background 0.457,1.000 | Strip kAlpha2 0.500 | Import

MM130902_01 - File: MM130902_01.raw

Lin

(C

ou

nts

)0

10000

20000

30000

40000

50000

60000

70000

80000

90000

100000

110000

120000

130000

140000

150000

160000

170000

180000

190000

200000

2-Theta - Scale

15 20 30 40 50 60 70 80 90

SEM Surface

Roughness < 1 µm

2h 16 h 16 h

Linear growth rate

Efficiency ~100 %

6,6 µm/h 450 µm

- Columnar structure

- Compact and dense layers

Deposition time (h)

Thickness

(µm)

6.6379x - 0.1495 R² = 0.9984

0

50

100

150

200

250

300

350

400

450

500

0 20 40 60 80

[Bi]/[Te] = 1 [Te] = 2. 10-2 M

J = 2 A/cm2 J. Electronic Matetrials in press 2014

Towards application

20 30 40 50 60 70 80 90 100 110

01.5

00.1

5+

11.6

02.1

010.1

0

20.5

11.0

11.1

5 01.2

0+

12.5

21.1

0

30.0

substrat

film

110

44

V

A

CE

RE

W

i i

Te+IV

Bi3+

potentiostat

e e

Sputtered layer

Membrane

Electrodeposition of TE nanowires

3 HTeO2+ + 18 e- + 2 Bi3+ + 9 H+ Bi2Te3 + 6 H2O

45


The used templates

The anodic membranes: porous anodized aluminium oxide films AAO

Anodization of high purity

aluminium in mineral acid

Presence of insulating, dense oxide

layer (called barrier layer) separating the

aluminium substrate and the porous

oxide film

thinning the barrier layer*

Geometric parameters (pores size,

radius, density) linked to anodization

parameters (electrolyte, anodizing

voltage)

* N. Stein et al., Electrochimica Acta,2002

46

Porous structure ~ a honeycomb array

High pore density > 109 pores/cm²

Range of thickness = 10 – 100 µm

Commercial products (filtration) = interconnection between nanopores

Cross section* Top view

*Sander, Advanced Mat. 2002

The most popular template in the literature but …

The thermal conductivity of AAM overwhelms that of the NW/ template composites

Anodic membranes: porous anodized aluminium oxide films (AAO)


The used templates

47


Electrocrystallization

NUCLEI

GROWTH

FILLING

UPPER LAYER

Filling time

Time (s)

Curr

ent

density m

A/c

m2

At imposed potential, transient time current curve

48

Bi2Te3

Electroplating of V2VI3 nanowires in AAO

1999 Sapp Nanoletters, 11, 402

Galvanostatic deposition into commercial Anodized Alumina Membrane = 200 nm

I = 3.5 mA/cm² |Bi|/|Te| = 25/33 mM

49

Bi2Te3

1999 Sapp Nanoletters 11, 402

Galvanostatic deposition into Alumina Anodised Membrane = 200 nm

2001 Prieto J.A.C.S, 123, 7160 2002 Sander Advanced Mat. 14, 665 =45 nm L= 70 µm FR

= 70-80% E = -0.46 V /Hg/HgSO4 |Bi|/|Te| = 75/100 mM

as- deposited annealed

2003 Sander Chem. Mater.,15, 335 Annealing 400°C 3h

E = -0.46 V /Hg/HgSO4 |Bi|/|Te| = 75/100 mM

2003 Martin Gonzalez Nanoletters, 7, 973 =50 /200 nm L= 20 µm FR = 75%

E = 0 V /Ag/AgCl |Bi| / |Te|+|Se| = 7.5 / (9+1) mM

Bi2(TeSe)3

(BiSb)2Te3

2003 Martin Gonzalez Advanced Mat, 15, 1003 =40/200 nm L= 30/16 µm FR = 80/75%

E = -0.17 V /Hg/HgSO4 |Bi|+|Sb| /|Te| = (19+56)/100 mM

Electroplating of V2VI3 nanowires in AAO

50

Growth rate tuning of V2VI3 nanowires

2006 Li Nanotechnology, 17, 1706 Pulsed deposition : recovery of species during rest time

E = -1.3 V Au/Cgraph ton = 3 ms, toff = 10 ms |Bi| /|Te| = 10/15 mM

= 40/60 nmstronger orientation (015)

2008 Lee Nanotechnology, 19 , 365701 Pulsed deposition

Longer rest time higher preferred orientation

lower Seebeck coefficient, higher Te content

Bi2Te3

Problems for electroplating nanowires :

- inhomogeneous growth rates between pores

- eventual composition gradient due to different diffusion coefficients of the ions

constant replenishment of electroactive species

AAO

51

2006 Wang J.Phys. Chem. B 110, 12974. rotation of AAM template

E = -0.14 V/SCE |Bi| /|Te| = 2.5/3.3 (a) or 7.5/10 mM (b)




Bi2Te3



- eventual composition gradient due to different diffusion coefficients of the ions.


Reduced variation of composition

along the wires

AAO

52

2006 Wang J.Phys. Chem. B. 110, 12974 = 200 nm rotation of AAM template


2007 Trahey Nanoletters, 7, 2535 Pulsed deposition+ Low T (1-4°C) FR 93 %,

= 35 nm E = -0.42 V /MSE ton = 1s + Erest = -0.3V toff = 2s |Bi|/|Te| = 7.5/10 mM



Bi2Te3



- eventual composition gradient due to different diffusion coefficients of the ions.


Uniform growth front

Highly oriented wires

AAO

53

Electrodeposition of nanowires in organic medium

2010 Cagnon, Nielsch, Bourgault Phys. Status Solidi B 247, 1384

= 50 nm DMSO or EG

Higher temperature 110°C , strirring, galvanostatic deposition

AAO

PbSe

Sb2S3

54

1999 Behnke 18th ICT

125 mM Citrate 0.196M citric acid - 688 mM Co – 6 mM Sb

First attempts

Electroplating of other TE nanowires

2003 Prieto J. Am. Chem. Soc. 125, 2388

2006 Keyani Applied Phys. Letters 89, 233106

Potentiostatic deposition in DMSO in AAO

Hybrid device: BiSb NW – Bulk Te

50 mM Bi – 30 mM Sb

BiSb :

CoSb3 :

AAO

55

TE properties of V2VI3 nanowires

Characterization of a single NW

2005 Zhou Appl. Phys. Lett .87, 133109 2009 Mavrokefalos J. Appl. Phys. 105, 104318 annealing

Characterization of NW bundles 2009 Mannam

J. Elec. Soc 156, B871

r + Seebeck

2004 Borca Tasciuc Appl. Phys. Lett. 85 6001

Photothermoelectric technique

2010 Chen J. Phys. Chem. C, 114, 3385

r + Seebeck + LFA

56

Nanostructures as efficient TE materials

Zhou, APL, 2005

ZT (@ 300K ) ≈ 0.02

“High ZT can potentially be obtained in Bi2+XTe3−x nanowires

with an optimized atomic ratio”

Bismuth Telluride: first results

BUT !!!

57

Properties of Nanowires

Experimental values of Seebeck coefficient for Bi2Te3 nanowires

Large dispersion of the literature data :

Difficulties of measurements

Composition of the nanostructures

Crystallinity of the samples

Global composition Ø

(nm)

L

(µm)

Elaboration

mode

Bundle B /

Individual I

Template

Seebeck

Coefficient

(µV/K)

Orientation Reference

Bi2Te3 50 100 Potentiostatic B - AAO +270 Wang J. Appl. Phys.

2004, 96, 615

Bi2Te3 200 55 Liquid injection B - AAO -100 (110) Jones

Proceeding ICT 2006

Bi2Te3/Bi2,38Te2,62 40 50 Galvanostatic

Potentiostatic B - AAO + 12/+33 (110)

Lee , Nanotechnology

2008, 19, 365701

Bi2,25Te2,75/Bi1,50Te3,50 20 / Potentiostatic B - AAO +117/-318 (110) Mannam J. Elec Soc.

2009, 156, B871

Bi2Te3 50 25 Galvanostatic B - AAO + 45 / 55 Lee, Phys Status solidi

2010, 4, 43

Bi2Te3 60 200 Pulsed

Potentiostatic B – AAO (015)

LI , Nanotechnology

2006, 17, 1706

Bi1.85Te3.15 120 / Potentiostatic B and I – AA0 -65 (110) Chen, J. Phys. Chem

2010 , 114, 3385

Bi2,3Te2,7/Bi2,7Te2,3 50 / Galvanostatic I - AAO + 260/-25 (110) Zhou , Appl. Phys. Lett.

2005, 87, 133109

Bi2,15Te2,85 55 / Galvanostatic I - AAO -70 Mavrokefalos , J. Appl.

Phys. 2009, 105, 104318

58

Properties of single crystalline nanowires

N Peranio, E Leister, W Töllner, O Eibl, K Nielsch Adv. Funct. Mater. 2012, 22, 151–156

59

Bassler, S.; Bohnert, T.; Gooth, J.; Schumacher, C.; Pippel, E.; Nielsch, K., Thermoelectric

power factor of ternary single-crystalline Sb2Te3- and Bi2Te3-based nanowires.

Nanotechnology 2013, 24, 495402

Millisecond pulse voltages for electroplating

Diameter 80 nm and 200 nm

Compound Bi15Sb29Te56

p type

S= + 156µV/K

PF 1750µW.K-2m-1

Compound Bi38Te55Se7

p type

S= -115 µV/K

PF 2820 µW.K-2m-1

Increase of PF after annealing under Te atmosphere

AAO


60

AAO


61

AAO


62

Polymeric membranes (PC): ( = 30, 60, 90, 120 nm, L = 30 µm)

Lower than Anodized Alumina Membrane

No Heat leakage in micro scale Peltier TE devices

Disk diameter = 50

mm

e =

6 -

30 µ

m Pores : 30nm<d<120nm

Top view of porous membrane

after partial chemical etching

(diameter 60nm)

Pores with no tilt and regular shape

Nanowires growth vertically to the substrate Ideal configuration for TE devices

Tuning of the pore diameter by calibrated etching rates

Pores density : 108 to 109 pores/cm²

Maximum aspect ratio : 1/1000

Electrodeposition of nanowires into polymeric membrane

Coll. Dr. E. Toimil Molares

GSI, Darmstadt, Germany

Commercial products :

with PVP hydrophilic

treatment

63

n-type p-type

Conditions :

Output powers

filling ratio

nanowire density 108 - 109cm2

Thermal gradient

Contact resistance

Direct integration of nanowire in legs of Peltier device

Concept of microdevice

64

Optimization of the filling ratio

Improvement: Limiting factors:

Electrolyte impregnation

Improved value (at Ø 60 nm)

Lower growth rate:

DMSO (50 % v/v)

Pulsed deposition

Wetting agent:

DMSO (50 % v/v)

Pretreatment:

short sonication

Inhomogeneous growth

rate between pores

40 % 80 %

Initial value (at Ø 60 nm)

&

HNO3 0.5M;

[Bi3+] = 10 mM

[TeIV] = 10 mM J Electr Mat, 39, 2010, 2043

65

Electrodeposition of V2VI3 nanowires

Electrocrystallization : the filling ratio

E = -100 mV/Ag/AgCl

PC + Platinum layer

Filling time Filling ratio

without DMSO 831 s 50,6 %

with DMSO 7138 s 79,4 %

Without DMSO:

HNO3 0.5M;

[Bi3+] = 10 mM

[TeIV] = 10 mM

With DMSO:

DMSO 50% vv;

HNO3 0,5M;

[Bi3+] = 10 mM

[TeIV] = 10 mM

DMSO: lower growth rate of NWs leading to a higher filling ratio

E = -100 mV/ AgCl/Ag°

C. Frantz Journal of Electronic Materials, 39, 2010

66

Scan rate:

5 mV/s

C1

C2 C3

MC1

A3 A2

MA1

Te° BixTey

Votammetric behavior on Pt-coated membrane electrodes pore = 60 nm

HNO3 1M, DMSO 50%v/v [TeIV]=10-2M and [Bi3+]/[TeIV] = 1.5

Electrodeposition of Bi2Te3 nanowires

TeIV + 4e- → Te0

2Bi3+ + 3TeIV + 18e- ↔ Bi2Te3

Bi3+ + 3e- ↔ Bi0

67


E=-150mV

Bi : 42,8%at.,Te : 57,2%at. Bi : 34,8%at., Te : 65,2%at. Bi : 40,8%at., Te : 59,2%at.

Influence of the applied potential (E)

E=-100mV E=-75mV

Enrichement of Bi for more negative applied potential

(Bi2,04Te2,96) Stoichiometric compound at -100mV

pore = 60 nm

68 Fig7. EDX mapping and Bright Field images (a) along the nanowire,

(b) of the nanowire head.

1) 45.3 Bi at.%

2) 43.2 Bi at.%

4) 40.6 Bi at.%

3) 40.8 Bi at.%

5) 40.2 Bi at.%

6) 40.6 Bi at.%

7) 40.2 Bi at.%

1

2

4

6

5

3

7

a) b)

40.2 Bi at.%

40.6 Bi at.%

40.2 Bi at.%

40.2 Bi at.%

40.8 Bi at.%

Fig7. EDX mapping and Bright Field images (a) along the nanowire, (b) of the nanowire head.

1) 45.3 Bi at.%

2) 43.2 Bi at.%

4) 40.6 Bi at.%

3) 40.8 Bi at.%

5) 40.2 Bi at.%

6) 40.6 Bi at.%

7) 40.2 Bi at.%

1

2

4

6

5

3

7

a) b)45.3 Bi at.%

43.2 Bi at.%

200nm

Zoom : cap

Enrichment of Bi

Form texture

Change of cation diffusion

28.9 Bi at.%

35.0 Bi at.%

40.2 Bi at.%

39.1 Bi at.%

36.3 Bi at.%

200nm

Zoom : bottom

Enrichment of Te

Polyphased state

Bi2Te3 Te°

Poly-crystalline

…

Composition profile


Efixed=-100 mV/Ag/AgCl

Electrochimica Acta, 69, 2012, 30

Corrected with an initial

pulse (E=-300mV; t=2s)

69

(01.5)

(01.5)

(01.5)

(01.5)

[01.5]*

Nanowire

Crystallinity

Single crystal with defaults and strains

Preferential growth (01.5)


70

Bi2Te3 nanowires : Bundle characterization

Homemade setup for thermoelectric characterizations of ultra-thin devices

Heat flux generated by two Peltier modules

Macroscopic thermocouples as surface temperature probes

Measurements of :

Seebeck coefficient

Output power

Internal resistance

Coll: Dr L Gravier Switzerland

71


Sample connected to a load circuit

Access to conversion efficiency

η = Pout / Pin = … effective ZT

When the load circuit is open, measure of voltage taking into account T

Seebeck coefficient

Output power measured = f(load resistance /internal resistance ratio) at room

temperature

Specific curve of generator

Exhibit a maximum output power

Access to the internal resistance equal to the load resistance

o n-type thermoelectric generator

Coll: Dr L Gravier Switzerland

72

S = -54.81 ± 0,1 µV/K

Rint = 6.85 mΩ

ΔT = 1.52°C

Example of Bi1,75Te3,25 nanowires

synthesized in Millipore filtration

membranes with 200nm pore diameter,

6µm thickness


Sample connected to a load circuit

Access to conversion efficiency

η = Pout / Pin = … effective ZT

When the load circuit is open, measure of voltage taking

into account T

Seebeck coefficient

Output power measured = f(load resistance /internal

resistance ratio) at room temperature

Specific curve of generator

Exhibit a maximum output power

Access to the internal resistance equal to the

load resistance

o n-type thermoelectric generator

73

With DMSO

Without DMSO

Witness : Ni

n-type TE generator

Internal resistance reduced with DMSO

Lower Pout in aqueous electrolyte

C. Frantz et al. Journal of Electronic Materials, 39, 2010


74

-140 -120 -100 -80 -60 -40 -20 0

-60

-50

-40

-30

-20

-10Pores diameter

50 nm

220 nm

Se

eb

ec

k V

olt

ag

e [

V

/K]

Electrodeposition Voltage [mV/Ag/AgCl]

Seebeck coefficient evolution = f(E electroplating)

Seebeck coefficient with more cathodic

conditions

trend linked to the change of composition

nanowires

At -50mV highest Seebeck coefficient

corresponding to the n-type Te-rich compound

At -125mV, Seebeck coefficient negative even

if the composition is Bi-rich

due to defaults in the material

Seebeck coefficient f(pore diameter)

Te-rich

Bi-rich

Bi2Te3 Bi2.08Te2.92 Bi1.57Te3.43

Bi1.75Te3.25


75

Composition of the electrolyte

Overall cathodic reaction

xBi+3 + ySb+III + zTe+IV + (3x+3y+4z)e- BixSbyTez

Acidic medium : Nitric acid 1M

Chelating reagent : tartaric acid C4H6O6 (0.6M)…[Sb2(C4H4O6)2]2+

Synthesis of (Bi1-xSbx)2Te3 nanowires

76

Voltammetric study Whatman PC membranes, pores diameter = 50nm, thickness = 8µm

Electroplated at different potentials between 75 and -150mV

Bismuth depletion

Antimony enrichment with more cathodic polarization

Tellurium depletion

Voltamperometric response within porous

membrane TEM / Calibrated EDX measurements

Synthesis of (Bi1-xSbx)2Te3 nanowires

77

Bi0.5Sb1.5Te3 nanowires

HRTEM analyses

1 0 n m

3.6Å

(009)

Growth according to (00l) planes

Growth perpendicularly to the basal

planes

Observation of twin grain boundaries

Whatman PC membranes, pores diameter = 50nm, thickness = 8µm

Cation concentration : |TeIV| = 10mM with (Bi+Sb)/Te = 1 and Sb/Bi = 6

E = -100mV

10Å

(003)

10Å (003)

78



Bi0.5Sb1.5Te3 nanowires: Bundle characterization

Seebeck measurements

With non homogeneous upper layer : Very high resistance

(>100kΩ)

Not suitable for application

S= 540 +/-120 µV/K

R=159+/- 3 k

79



Seebeck measurements

Composition S (µV/K) ΔT (°C) R (mΩ) P (nW)

Bi0.4Sb1.14Te3.46 21.5 ±

0.07 1.8 6.32 ± 0.004 60

Bi0.3Sb1.59Te3.11 14.6 ± 0.1 1.55 37.7 ± 0.1 3.4

Bi0.48Sb1.76Te2.76 9.1 ± 0.04 1.89 5.73 ± 0.01 13

With non homogeneous upper layer : Very high

resistance (>100kΩ)

Not suitable for application

With Electroplated copper upper layer

High decrease of the internal resistance

Positive Seebeck coefficient corresponding to p-type nanowires

Seebeck coefficient depend on the nanowires composition

Possible contribution of copper explaining the lowered values of Seebeck coefficient

Bi0.5Sb1.5Te3 nanowires: Bundle characterization

80

Nanostructured and complex V2VI3 compounds

2005 Lim Advanced Mater., 17, 1488

bundles of BiSbTe/ Bi2Te3 nanowires / patterned within the same AAM

ECD suitable method for fabrication of TE nanodevices

2005 Wang Microelectronic Engineering 77 223

Design of TE micro-generator, composed of n-type and p-type Bi2Te3 nanowire array

81

2005 Xu J Solid State Chem., 178, 2163

Heterostructure Polyaniline (low ) / encapsulated Bi2Te3 into AAM

Goal : stronger confinement effect


82

2008 Li Crystal growth and design, 8, 771

Bi2(TeSe )3 and (BiSb)2Te3 nanotubes

electroplating onto surface / wall pores of AAM sputtered by gold

with a wall thickness of 40-70 nm modulated by the electroplating time


83

Electroplating of V2VI3 superlattices

2007 Yoo Advanced Mater., 19, 296

Pulsed deposition in PC membrane:

nanowires Bi2Te3/(Bi0.3Sb.0.7)2Te3

from a unique solution by adjusting

potentials

2008 Wang J. Phys. Chem. C., 112, 15190

Pulsed deposition in AAM :

nanowire Bi2Te3/Sb

min period: 10 nm

84

Summary

Electroplating: convenient route for thermoelectric compounds

Synthesis of films and nanowire arrays

Thickness from tens to hundreds of µm, growth rates

Wide range of compositions: binaries and ternaries

Template synthesis: AAO or Polymeric membranes

Optimized membrane filling ratio (electrolyte, T, pulse, sonication)

Comprehensive study

Voltammetric study knowledge of operating conditions for

stoichiometric film or NW

Determination of diffusion coefficients to monitor stoichiometry

Characterization

Morphology, stoichiometry, orientation

• Homogeneous composition over the thickness

• Preferential growth: films [110], NW: [110] and [015];

Importance of electrocrystallization - crystallinity : internal resistance

85

85

GSI Helmholtzzentrum für Schwerionenforschung GmbH (Darmstadt, Allemagne) Providing of Polycarbonate foil and irradiation

Dr E. Toimil-Molares

Laboratoire d’Etude des microstructures et de mécanique des matériaux (Metz,

France) Texture and Transmission Electron Microscope (TEM) Dr Bolle Dr Zhang

Acknowledgments

Haute Ecole d'Ingénierie et de Gestion du Canton de Vaud,

Yverdon, Suisse

Dr L. Gravier

86

Dr V. Richoux

Dr S. Michel

Dr N. Stein

Dr A. Zimmer

Pr J.M. Lecuire

Dr L. Scidone

Dr D. Del Frari

Dr S. Diliberto

Dr C. Frantz

Dr P. Magri

Past and present

Contributors

Electrochimie des Matériaux

J. Schoenleber Dr J. Szymszack

Dr S Legeai

Financial

supports

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