quantum dots 100 gbit/s - portal ifgwlenz/escola de inverno 2014/quantum dots.pdf · quantum dots...

Erbium

Optical fibers

Solitons

100 Gbit/s

Waveguides

Solitons

New Material

Nonlinear

Ultrafast

Quantum dots

Optical switch

C.L.Cesar

UNICAMP

Quantum Dots

Carlos Lenz Cesar

lenz@ifi.unicamp.br

Carlota Perez: Technological Revolutions and Financial Capital

5 Revolutions - ~ 60 years total cycle

1. Industrial Rev. – England – 1771

2. Steam and rail-road – England – 1829

3. Steel and eletricity – England+USA+Germany – 1875

4. Oil, cars and mass production – USA – 1908

5. Information and comunications – USA – 1971

Financial crisis

Periphery deployment

No funds for other techwave up to this point

Bell Labs na Revolução da Informação

Beginning 20th century - Telephone calls < 30 km .

1913 - De Forest sell triode vacuum tube patent to AT&T

San Francisco 1915 World Fair 1st Transcontinental Call

Amplification, amplification, amplification!

Repercussions: AT&T became a monopoly

Alexander Bell

Theodor VailThomas Atson

1925: Bell Labs became a company

AT&T and Western Electric only costumers

Bell labs hired PhDs:

Millikan main provider

13 Nobel laureates

Shockley - Stanford

Silicon Valley

1947 marvelous yearSolid State: Transistor - Bardeen + Brattain + Shockley

Information Theory – Claude Shannon

Traitorous 8

Fairchild – 1957

Importance of Bell Labs – 1983 AT&T breakup

Vacuum tubes

Photovoltaics

Transistor

Satellites communicatios

Cell phone

Laser – semiconductors

Optical fibers

Ultrafast lasers

Non linear optics

Information theory

C

UNIX

13 Nobel laureates

Clinton Davisson – 1937

Bardeen + Brattain + Shockley – 1956

Phil Anderson – 1977

Penzias + Wilson - 1978

Steven Chu – 1997

Stormer + Laughlin + Tsuj - 1998

Boyle + Smith – 2009

The beggining: 1971 first INTEL chip

1946 – ENIAC

1951 – Texas Instruments

1958 – Noyce & Kilby (Nobel 2000) 1st integrated circuit

1968 - INTEL – 1968 Robert Noyce e Gordon Moore

Robert NoyceGordon Moore

IBM XT – 1983

Hardware

Apple 1977

INTEL 1971

Microsoft 1975

IBM PC 1981

IBM AT 286 1984

IBM 386 – 1991

IBM 486 – 1993

Software

2004 – Facebook

1994 – Netscape

1993 – Mosaic

1998 – Google

1995 Amazon

1975 – Microsoft

2004 – Firefox

Optical Network

1994 – calls by OF > electronic calls

1988 – 1st TAT EDFA

1975 OF communication

1970 Optical Fiber

1987 – Optical Amplifier

Amplification, amplification, amplification!

Optical Erbium Doped Fiber Amplifier

Bell Labs and Brazil

IFGW Founders

José Ellis Ripper Filho Rogério Cerqueira LeiteSérgio Porto

Charles Shank:

diretor

Brito Cruz: 1986-1987

Hugo Fragnito: 1987-1989

Carlos Lenz: 1988 – 1990

Photonics for communications: ultrafast lasers,

Semicondutors, Non linear optics, Optical fibers,

Optical amplifiers

Quantum Dots in UNICAMP

Started with CdTe 1990

PbTe 1995

Colloidal 1999

Laser Ablation 2001

Teses sobre Quantum Dots disponíveis no site do IFGW

Orientação: Lenz

Doutorado

Carlos Roberto M. de Oliveira 1995

Gastón E. Tudury 2001

André A. de Thomaz 2013

Diogo B. Almeida 2014

Mestrado

Cristiane O. Faria 2000

Antônio Á. R. Neves 2002

Wendel L. Moreira 2005

Gilberto Júnior Jacob 2005

Diogo B. Almeida 2008

Outras teses Dr. recomendadas:

Eugenio Rodrigues Gonzales 2004

Lázaro A. Padilha Jr. 2006

Smaller cord -> higher frequency -> higher E -> smaller l

Quantum Dots: size controlled color!

Quantum confinement

En

erg

y

Quantum dot diameter

Quantum Dot: quantum confinement and size

Espectro de Absorção

400 800 1200 1600 2000

Comprimento de onda (nm)

Ab

so

rção

Absorption spectra

Wavelength (nm)

1989 1995

Right wavelength: optical properties tuning

End of controversy quantum confinement vs stechoimetric variation

CdTe Coloidal Quantum Dots Produced at UNICAMP

Applications and

Technological Importance

Switching:

Ultrafast Optical Devices

Optical Communication - On the edge

Typical optical fiber attenuation

Bandwidth for 1 dB/km losses

Dl = 750 nm DnDt = 0.44

Total Capacity of only one fiber

1014 = 100 Tbit/s

750 nm

Wavelength: 1.5 or 1.3 m

High Optical Nonlinearity

resonant:

non resonant:

Ultrafast Response time < 3 ps

resonant:

non resonante:

Devices always based on Dn or D

Optical Device Material Requirements

Compatible with Optical fibers

Dn or D Response time

Dilemma

vs

D~4nm

D~20nm

Quantum Dots

E

E

abs

abs

Quantum dots (QD’s): dilemma solution

-1000 0 1000 2000 3000 4000 5000

Dt = 2.5 ps

Dt = 1.0 ps

Dt = 0.5 ps

Tra

nsie

nt

Tra

nsm

issio

n

Delay (fs)

1 Tbit/s optical device?

High nonlinearity & ultrafast response time:

CdTe quantum dot

Padilha et al, Appl. Phys. Lett. 86 (16), 161111 (2005)

Aplicações dos PQs

Óptica não-linear:

Fótons Portadores

•Células fotovoltaicas (energia solar)

•Chaveamento óptico

•Sistemas de 2 níveis (computadores quânticos)

Portadores Fótons

•LEDs

•Displays

Fótons Fótons•Marcadores Fluorescentes (aplicações biológicas)

•Iluminação

Incandescente LED LED + PQs

Aplicações PQs

Óptica não-linear:

Fótons Portadores

•Células fotovoltaicas (energia solar)

•Chaveamento óptico

•Sistemas de 2 níveis (computadores quânticos)

Portadores Fótons

•LEDs

•Displays

Fótons Fótons•Marcadores Fluorescentes (aplicações biológicas)

•Iluminação

Processos que precisam de alta

eficiência de fluorescência

Precisamos da passivação para aumentar a eficiência dos pontos

quânticos

-

+

Capa de outro

material

X. Wu et al,

Nature Biotech.

21, 41 - 46 (2003).

No photobleaching!

One laser to excite all colors

Physics of the Quantum Dots

Particle in a box

Quantum Confinement: Simple Model

Free electron function Free electron energy

c cBulk: Ywave = eik•R

• uBloch E= Eg+ h2 k2 /(2m* )

Quantum dot: Ywave = x(R) • uBloch E= Eg+ Econf

cc cc

Envelope function Confinement energy

Infinite spherical well

spherical Bessel function Boundary condition

c c

x(R) = jn(kR) • Ynm(q, f) jn(ka) = 0 Econf = h2 kroot

2 /(2m*)

)( )( 2

ml,n,ln,ml,n,esf2

2

rFErFUm

h

Spherical Bessel Functions Roots

0 2 4 6 8 10-0.4

0.0

0.4

0.8

2P

1F

2S1D

1P

1S

j3

j2

j1

j0

j l (x)

X

Regras de seleção: 1-fóton

n n nuxY

in z fin n n n z n

n n n z n

e u u e

u e u

x x

x x

Y Y

Função de onda:

2

in z finF e Y Y

Transição intersubbanda

Transição interbanda

Transição Intersubbanda

0

1

2

0

1

2

Transição só é possível se níveis excitados

estiverem populados

in z fin n n n z ne u u ex x

Y Y

Transição Interbanda

0

1

2

0

1

2

0nD

in z fin n n n z ne u e ux x

Y Y

2

val val b b b b cond cond

b b

u e u u e uF

E

x x x x

D

0val b b co val b b con ndb

u u u ue ex x x x

0valval b b b b condcondb

u e u u e ux x x x

Regras de seleção: 2-fótons

0

0

2

val b b coval b b cond

b b

val b b co

nd

val b b cd

b

nn

b

o d

e

E

u u u e u

u e u u uF

e

E

x x x x

x x x x

D

D

22

val b b cond val b b cond

bval co

b bn

bdu e

e

E Eu

eF

x x x x x x x x

D D

1nD

0

1

2

0

1

2

Absorção de 2-fótons

Fit a cryostat at the System and gain a Spectral platform with spatial resolution

FL

IM

Ti:Saphire

405 nm

Spectrometer

Vacuum

Pump

He lineMicroscope body

Translation stage Adapted plate

Cooled sample

High NA but long working distance: we used NA=0.6 with WD = 3mm

Small cryostat to fit under a Zeiss LSM 780 upright

Main Issues

Small copper piece to bring the sample closer to optical window

Mirrored microscope coverslip

Colloidal QDs film with ureia small crystals

Light collection must be done in backscatered geometry.Sample deposited on a mirror to enhance light collection efficiency.

Spatial/optical resolution

Green: QDs fluorescencePurple: urea SHG

Pump: Ti:Saphire laser

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

2.1 2.3 2.5 2.7 2.9 3.1 3.3

Inte

ns

ity (

a.u

.)

Energy (eV)

PL SHG

0

500

1000

1500

2000

2500

3000

3500

2.3 2.5 2.7 2.9 3.1 3.3

Inte

ns

ida

de

(u

.a.)

Energia (eV)

1 fóton

2 fótons

CdTe quantum dot 1 and 2 photons PLE at 40 K

0

1

2

0

1

2

0

1

2

0

1

2

1nD 0nD

Stress Induced Phase Transition

PbTe CdTe

Colloidal vs Doped Glass QDs

Confinement Models

??

1Pe

1Se

1Plh

1Phh

1Slh

1Shh

450 550 650 7500

10

20

30

40

Absorption spectrum

1Phh

-1Se??

1Sso-1Se

1Phh-1Pe

1Slh-1Se 1Shh-1Se

Wavelength (nm)

Ab

sorp

tion

coef

fici

ent

(cm

-1)

2.0 2.4 2.8 3.2

PLE Transitions assignement

hev

en1 -

eo

dd

1

hev

en1 -

eo

dd

1

soo

dd

1 -

eev

en1

ho

dd

2 -

eev

en1

ho

dd

1 -

eev

en1

Energy (eV)

1S

1S

1P

1P

1D

1D

fm

p 2

0

2

fin ini F Ffin ini nn ll mm

Optical Transition Selection Rules

Quantum Confinement: Full k P Hamiltonian Model

two subspaces: r = space inside a cell (Bloch);

R = space between cells (envelope)

( ) P P

m

r R 2

02

dot

potential

lattice

potential

Spin-orbit

interaction

H = (

P P P P

m

r r R R

2 2

0

2

2

) + Vspheric + Vperiodi + (

V P S

m c

per r

0

)

comutes with:xxx comutes with:xxx

L Lr R

L Sr

Conclusions:

[F ,H] = 0 where

F L L SR r F = good quantum number

More*: H r H r( ) ( )

Y Y( ) ( ) r r parity well defined

* Germanium model

Band Structure K·P

LR = 0 LR = 1 LR = 2 LR = 3

J = 2

1

Conduction Band

(Lr = 0)

21 2

1

23

23

25

25

27

J = 2

1

Split off band

(Lr = 1)

21 2

1

23

23

25

25

27

J = 2

3

Valence Band

(Lr = 1) 23

21

23

25

21

23

25

27

23

25

27

29

Parity = LR + Lr

SOVC

F 1,2

11,

2

30,

2

1

21

SOVC

F 0,2

12,

2

31,

2

1

21

SOVVC

F 1,2

13,

2

31,

2

32,

2

1

23

32

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

2 2 2 2C V V SO

F

,R

J L

Optical transitions in the full

model

pE

= odd operator so:

only even to odd or odd to even transitions are allowed

1Plh

1Slh

1Phh

1Shh

1Pe

1Se

F = 3/2 even2

Full ModelSimple Model

F = 3/2 odd1

F = 3/2 odd2

F = 3/2 even1

F = 1/2 odd1

F = 1/2 even1

2.0 2.4 2.8 3.2

PLE Transitions assignement

hev

en1 -

eo

dd

1

hev

en1 -

eo

dd

1

soo

dd

1 -

eev

en1

ho

dd

2 -

eev

en1

ho

dd

1 -

eev

en1

Energy (eV)

Anis

otr

opy

l = 0

Osc

illa

tor

stre

ngth

(a.

u.)

l = 0.2

l = 0.4

0.75 1.00 1.25 1.50 1.75

l = 1

p = piso

+ l(ptrue

-piso

)

Energy ( eV )

PbTe Quantum Dots Physics

Breathing

Modes

Pump&Probe: Coherent Phonons

-2 0 2 4 6 8 10 120

10

20

30

40

50

60

DT

/T ·1

0-6

Delay (ps)

2 4 6 8

40

41

42

43

Detector

E. R. Thoen et al; “Coherent Acoustic Phonons

in PbTe Quantum Dots”, Appl. Phys. Lett. 73,

2149 (1998)

Coherent Phonons frequency

Simple Model:

1.40 1.45 1.50 1.55 1.60

0.50

0.52

0.54

0.56

0.58

0.60

0.62

0.64

n (

TH

z)

Wavelength (m)

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.80

2

4

6

8

10

experim.Range of

spectral widthTypical pulse

Wavelength (m)

(

cm

-1)

2 soundV

R

17 cm-1 to 20 cm-1

Sine Cosine

Impulse K - change

Excitation and phase

1.40 1.45 1.50 1.55 1.60

-0.2

-0.1

0.0

0.1

0.2

Phas

e (r

ad)

Wavelength (m)

Phase 0o cosine Excitation

Damping Time

1.4 1.5 1.6

0.2

0.4

0.6

0.8

1.0

Anisotropic band

calculation

Experimental data

SAXS data

Parabolic band approximation

n (

TH

z)

Wavelength (m)

Sphere Acoustic Modes APL 73, 2149-2151 (1998)

022

2

l

)uu

u

()(t

1.40 1.45 1.50 1.55 1.600.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

( b )

Dam

p t

ime

(ps)

Wavelength (m)

Coherent Phonons: pump & probe detection

-2 0 2 4 6 8 10 120

10

20

30

40

50

60

DT

/T

·10

-6

Delay (ps)

2 4 6 8

40

41

42

43

Coherent Phonons: amplitude

6104.4 A

A

00

22,)(

r

r

E

E

rrE

conf

conf

PKr

r

r

rK

r

rrK

V

VKP

3

1

1)(

0

3

03

0

30

3

0

D

dr

dE

rP

dEdrrPPdV

conf

conf

2

2

4

1

4

2

0

0

2

2

1

2

1

E

EE

E

A

A

T

T

TotTot

Critiscim to kp Models

Parabolic and kP Models are not good enough for very

small quantum dots

Energy Dispersion

Bulk energy dispersion calculated by

Prof. Guimarães USP/UNICAMP

Modelo Unidimensional

com solução analítica

Cadeia de poços unidimensionais

Solução analítica

Estrutura de bandas

Estados confinados

Energia de confinamento

Heuristic Model

e 0 nnj ka k

a

E

ek

e 0 nnj ka k

a

SOk

E

E

No YesE

HHk

LHk

1 HH 3 LH

3 HH 1 LH

9 j k a j k a +

+j k a j k a = 0 ??

FCS

Fluorescence Correlation Spectroscopy

Fluorescence Correlation Spectroscopy FCS

(1 m)3 = 1 femtoliter mass spectrometry?

Hydrodynamic radius

extracted from

diffusion time

Rodamine

Home made CdSe Quantum dot

R = 1.9 nm

Quantum Dot Fabrication

Etanol + MPS

Alvo

giratório

53

2 n

m

Laser

Lente

cilíndrica

Lâminas de

microscópio

SHSiCH3O

CH3O

CH3O

Ambas precisam de estabilização:

AMA (solúvel em água) MPS (solúvel em etanol)

Fluxo de

Argônio

Te

NaBH4

Te2- Cd(ClO4)2+ AMA Cd2+ + AMA-

Agitador magnético

+ Aquecimento

Laser Ablation in Liquids

Vaccum versus liquid laser ablation

SAITO, K. et al. Appl. Surf. Sci. 197, 56-60, ( 2002)

Laser Ablation in Vacuum

Ti:Sapphire, 800 nm,

(30mJ/pulse, 100fs, 10Hz)

~ 38 TW/cm2

Experimental set up

substrate

Lower bkg pressure

Higher nr. of pulses

QD growth on

substrate

COALESCENCE

target

Higher bkg pressure

Lower nr. of pulses

QD Growth at vapor

phase

HRTEM (LME-LNLS) PbTe QDs images

Quantum dot doped Glass

Growth Kinectics: How to Control Size and Dispersion

0 10 20 30 40 50 60

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Siz

e D

isp

ersi

on

[l

n 2

]

CdTe0.6

S0.4

CdTe0.3

S0.7

Heat Treatment Time [min]

Size dispersion vs time:

SAXS study

Glass and QD elements

melted together 1200 oC:

transparent glass

Thermal annealing 460 - 560 oC:

QD’s development - time

Results

SAXS show nucleation&growth

happening simultaneously

Double annealing method suggested:

first (460oC): only nucleation

second (560oC): only growth

- New method produced 6% size

dispersion QD’s

Thanks for the attention

The End!!