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