Transcript Quantum Dots for Sale

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Physics of Low dimensional Materials - 2
Prof.P. Ravindran,
Department of Physics, Central University of Tamil
Nadu, India
&
Center for Materials Science and Nanotechnology,
University of Oslo, Norway
http://folk.uio.no/ravi/cutn/NMNT2016
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Magnetic properties
• Diamagnetism:
Zero-spin systems give rise to circulating currents that oppose
the applied field (negative magnetic susceptibility, Larmor
diamagnetism).
• Paramagnetism:
Free-electrons are magnetically polarized by an external
magnetic field (positive magnetic susceptibility, Pauli
paramagnetism).
• Ferromagnetism:
Spontaneous magnetic ordering due to electron-electron
exchange interactions.
Antiferromagnetism: polarization alternates from atom to atom.
No net macroscopic magnetic moment arises.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Magnetic Interactions



Exchange (electron-electron) interaction (many-particle wavefunction
antisymmetry)
- atomic scales
Dipole-dipole interactions between locally ordered magnetic regions
Dipole interaction energy grows with the volume of the ordered region. The size
of the individual domains is set by a competition between volume and surface
energy effects.
- hundreds of atoms to micron scales
Magnetic Anisotropy energy
Magnetization interacts with angular momentum of the atoms in the crystal.
– many microns
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Super-paramagnetic particles
• Ferromagnetic domains, created by d-electrons exchange interactions,
develop only when a cluster of iron atoms reaches a critical size (ca. microns).
The magnetic moment per atom
decreases toward the bulk value as
cluster size is increased.
Stable
domains
cannot
be
established in crystals that are
smaller than the intrinsic domain
size.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
• Small particles can have very high magnetic susceptibility with
permanent magnetic dipole.
Small clusters consisting of a single ferromagnetic domain
follow the applied field freely (super-paramagnetism).
The magnetic susceptibility of superparamagnetic particles is
orders of magnitude larger than bulk paramagnetic materials.
Ferromagnetic limit
Magnetic response
for particles of
increasing size (Gd
clusters)
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Superparamagnetic separations
Induced magnetic moment:
M  H
Magnetic force:
Fz  M z
B
z
B   0 ( H  M)
Magnetic sorting of cells labeled
with superparamagnetic beads
MFS: microfabricated
ferromagnetic strips
Particle were pulled to point of highest field gradient
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Giant Magnetoresistance
Magnetic hard drives are based on a nanostructured device, called
giant magnetoresistance sensor.
Albert Fert, Peter Grünbers Nobel Prize in Physics 2007
Hitachi hard drive reading head
The magnetization on the surface
of the disk can be read out as
fluctuations in the resistance of
the conducting layer.
Co, magnetic layer
Layers have a width that
is smaller than electron
scattering length.
Cu, electrically conducting layer
NiFe alloy, magnetic layer
An easily re-alignable magnetization
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Giant magnetoresistance occurs when the magnetic layers
above and below the conductor are magnetized in opposite
direction.
Electron
scattering
in
magnetic media is strongly
dependent
on
spin
polarization.
When magnetic layers are
parallely magnetized, only
one spin polarization is
scattered (I,III).
For antiparallel magnetic layers both spin polarizations are
scattered, giving rise to super-resistance (II).
I
II
III
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Quantum Well States and Magnetic Coupling
The magnetic coupling between layers plays a key role in giant
magnetoresistance (GMR), the Nobel prize winning technology used for reading
heads of hard disks. This coupling oscillates in sync with the density of states
at the Fermi level.
(Qiu, et al.
PR B ‘92)
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Spin-Polarized Quantum Well States
Magnetic interfaces reflect the two spins differently, causing a spin
polarization.
Minority spins discrete,
Majority spins continuous
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Giant Magnetoresistance and Spin Dependent Scattering
Parallel Spin Filters 
Resistance Low
Opposing Spin Filters 
Resistance High
Filtering mechanisms
• Interface: Spin-dependent Reflectivity  Quantum Well
States
• Bulk: Spin-dependent Mean Free Path  Magnetic “Doping”
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Magnetoelectronics
Spin currents instead of charge currents
Magnetoresistance = Change of
the resistance in a magnetic field
Giant Magnetoresistance (GMR):
(Metal spacer, here Cu)
Tunnel Magnetoresistance (TMR):
(Insulating spacer, MgO)
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
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Nanoelectronics
• Nanotechnology is the design and construction of
useful technological devices whose size is a few billionths of a
meter
• Nanoscale devices will be built of small assemblies of
atoms linked together by bonds to form macro-molecules and
nanostructures
•Nanoelectronics encompasses nanoscale circuits and
devices including (but not limited to) ultra-scaled FETs,
quantum SETs, spin devices, superlattice arrays, quantum
coherent devices, molecular electronic devices, and carbon
nanotubes.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
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Motivation for Nanoelectronics
Limits of Conventional CMOS technology
• Device physics scaling
• Interconnects
Nanoelectronic alternatives?
• Negative resistance devices, switches (RTDs, molecular), spin transistors
• Single electron transistor (SET) devices and circuits
• Quantum cellular automata (QCA)
New information processing paradigms
• Quantum computing, quantum info processing (QIP)
• Sensing and biological interface
• Self assembly and biomimetic behavior
Issues
• Predicted performance improves with decreased dimensions, BUT
• Smaller dimensions-increased sensitivity to fluctuations
• Manufacturability and reproducibility
• Limited system demonstration
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
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The roadmap
Semiconductor technology trends (ITRS 2006)
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
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P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
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Materials for Si-nanoelectronics
At the origin of Si microelectronics only few elements were necessary for the whole
processes. Current technology requires a much larger number of materials.
Source: Intel
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
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Source: Intel
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
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More Moore -> Beyond Moore
Robert Chau, Intel, ICSICT, 2005
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Critical issues
Channel Electrons
104
4M
29
16M 64M
103
256M
1G
4G
102
16G Memory Capacity/Chip
101
100
10-1
1988
1992
1996
2000
2004
2008
2012
2016
Year
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
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Nano-Device Structure Evolution
Source: Intel
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Si-NW transistor: output characteristics
Lg = 1.3µm; Ø = 26 nm; tox = 300nm SiO2
drain bias Vds [V]
-2
d
S
NW
D
gate
Vg
•Normally-off
drain current Id
V
[A]
Id
0,0
-1
0
+5V; 0 V; -5 V
-500,0n -10 V
-1,0µ
-15 V
20V
;
-Vgs
-1,5µ
-20 V
-2,0µ
•Schottky contacts
Weber, W.M. et al. IEEE Proc. ESSDERC 2006, p. 423 (2006)
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
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Possible Quantum Dot Applications
Single Electron Memory
gate
nanocrystals
SiO2
source
Nanoelectronic Integrated
Circuit (NIC)
Photodetector
Input
Quantum dots or
single electron transistors
as processing elements
drain
gate
Memory
node
Si channel
SiO2
CMOS Drivers providing fan-out
Single “cell” of a Cellular Architecture
Quantum Computation (QBITs)
Quantum Cellular Automata
4
0
Quantum
dots
3
Quantum
dots
1
Tunneling
barriers
2
“1”
“0”
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
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Beyond Moore
Beyond CMOS logic and memory device candidates:
• Nanowire transistors
• CNT transistors
• Resonant tunneling devices
• NEMS devices
• Single electron transistors
• Molecular devices
• Spintronic devices
All those candidates (some of which not yet demonstrated) still suffer from
major reliability and stability problems
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Molecular components
20 nm embedded
GaAs layer after
etching and
deposition of 3 nm
Ti and 7 nm Au.
5 nm embedded
GaAs layer after
etching and
deposition of 2 nm
Ti and 6 nm Au.
OPV11 molecules with simplified phenyl side chains
synthesized by the group of Prof. Dr. E. Thorn-Csányi
at the University of Hamburg)
S. Strobel et al., SMALL 5, 579-582 (2009)
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Cross bar non volatile memory
A crossbar memory – probably the simplest possible functional circuit – is
one of the proposed application of single molecule electronics
V
The current-voltage characteristics of molecules is typically hysteretic, with step-like
nonlinearities and possibly non-symmetric (rectifying) behavior.
G. Casaba et al., IEEE Transactions on Nanotechnology, 8, 369 (2009)
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Problems with single molecule devices
A large variation is found in the IV characteristics between succesive sweeps.
Reasons can be due to:
G17-1c, P03, S05, über Nacht
500p
400p
300p
Current [A]
200p
100p
0
-100p
-200p
-300p
-400p
-500p
-3
-2
-1
0
1
2
3
Voltage [V]
Such variability has to be dealt
at a circuit/architecture level
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016:
0Down (P03:S05-08-)
1Up (P03:S05-08-)
• Configurational changes in
1Down (P03:S05-08-)
single
2Up (P03:S05-08-)
2Down (P03:S05-08-)
molecules
3Up (P03:S05-08-)
• Variation in the number of
3Down (P03:S05-08-)
4Up (P03:S05-08-)
molecules attached to the
4Down (P03:S05-08-)
electrodes
5Up (P03:S05-08-)
5Down (P03:S05-08-)
• Changes in the bond of a
6Up (P03:S05-08-)
single
6Down (P03:S05-08-)
7Up (P03:S05-08-)
molecule to the metal contact
7Down (P03:S05-08-)
•
…
8Up (P03:S05-08-)
8Down (P03:S05-08-)
9Up (P03:S05-08-)
9Down (P03:S05-08-)
10Up (P03:S05-08-)
10Down (P03:S05-08-)
11Up (P03:S05-08-)
11Down (P03:S05-08-)
12Up (P03:S05-08-)
12Down (P03:S05-08-)
13Up (P03:S05-08-)
13Down (P03:S05-08-)
14Up (P03:S05-08-)
14Down (P03:S05-08-)
15Up (P03:S05-08-)
15Down (P03:S05-08-)
16Up (P03:S05-08-)
16Down (P03:S05-08-)
17Up (P03:S05-08-)
17Down (P03:S05-08-)
18Upof(P03:S05-08-)
Physicls
Low dimensional Materials - 2
18Down (P03:S05-08-)
19Up (P03:S05-08-)
Molecular transistor
Once a conducting molecule is set between 2 contacts, an additional electrode has be
introduced as gate. There are various possibilities:
Back gate: a molecule attached to source and
drain electrodes on an oxidized metal or heavily
doped Si gate (substrate). This is the same
configuration of the Thin Film Transistors.
Electrochemical gate: a molecule bridged
between source and drain electrodes in an
electrolyte in which a gate field is applied by a
third electrode inserted in the electrolyte.
Chemical gate: current through the molecule is
controlled via a reversible chemical event, such
as binding, reaction, doping or complexation.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
MRAM chips represent one class of spintronics,
in which the spins of large numbers of
electrons are aligned the same way, as with a
collection of toy tops all spinning clockwise on
the floor.
These so-called spin-polarized electrons typically flow through some part of
the device, forming a spin-polarized current like a polarized beam of light.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
A second class of spintronics: Quantum Spintronics, manipulation of
individual electrons to exploit the quantum properties of spin.
Quantum Spintronics could provide a practical way to carry out
quantum information processing, which replaces the definite 0s and
1s of ordinary computing with quantum bits, or qubits, capable of
being 0 and 1 simultaneously, a condition called a quantum
superposition.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
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Logic with nanomagnets
Information propagation
Inputs
Outputs
The challenges:
How to make signals propagating?
How to write in the magnets?
wires
How to read out the magnets?


Integrated clocking
Localized field from

Hall sensor
In collaboration with M. Becherer and D. Schmit-Lansiedel (TUM) , W. Porod (Notre Dame)
M. Becherer et al., IEEE TRANSACTIONS ON NANOTECHNOLOGY 7, 316 (2008)
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Semiconductor Lasers and LEDs


Various flavours of quantum well
lasers – well established
technology.
Arakawa and Sakaki (1982)
predicted that quantum dot lasers
should be more efficient .
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Quantum dot laser
Optical cavity
Quantum dots of the right size can place
all of the exciton energies at the right
value for lasing.
The QDs are chosen to have a bandgap
that is smaller than that of the medium.
Excitons are stabilized in the optical
cavity, because the electrons are confined
to the low-energy part of the conduction
band and the holes are confined to the
top of the valence band.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Real Quantum Dot Lasers

Innolume GmbH
– QD lasers 1064 –
1320 nm
• QD Laser Inc., Japan
– QD lasers 1.3 and 1.55 µm
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
0-D (Quantum dot)
An artificial atom
 ( E )   ( E  Ei )
E
Ei

P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Quantum cascade lasers
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Quantum Cascade Laser
injector (n-doped)
active
region
3
injector (n-doped)
e
520 meV
2
active
region
60 nm
From IR/MIR/FIT to THz!
J. Faist, F. Capasso, et al. Science 264, 553 (1994)
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
More than Moore
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Interfacing to the real world:
If the interaction is based on a non-electrical phenomenon, then specific
transducers are required. Sensors, actuators, displays, imagers, fluidic or biointerfaces (DNA, Protein, Lab-On-Chip, Neuron interfaces, etc.) are in this
category
Enhancing electronics with non-pure electrical devices:
New devices can be used in RF or analog circuits and signal processing. Thanks to
electrical characteristics or transfer functions that are unachievable by regular
MOS circuits, it is possible to reach better system performances. RF MEMS
electro-acoustic high Q resonators are a good example of this category.
Embedding power sources with the electronics:
Several new applications will require on-chip or in-package micro power sources
(autonomous sensors or circuits with permanent active security monitoring for
instance). Energy scavenging micro-sources or micro-batteries are examples of
this category.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Miniaturization of electron devices




High integration
High speed
Low consumption electric power
Low cost
Miniaturization by top-down method
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Application to electronic devices
Ge
transistor
1950
LSI
1970
Quantum Carbon Point
corral nanotube contact
1980
2000
L.L.Sohn, Nature 394(1998)131
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
February 2003
The Industrial Physicist Magazine
Quantum Dots for Sale
Nearly 20 years after their discovery, semiconductor quantum dots are
emerging as a bona fide industry with a few start-up companies poised to introduce
products this year. Initially targeted at biotechnology applications, such as biological
reagents and cellular imaging, quantum dots are being eyed by producers for eventual use
in light-emitting diodes (LEDs), lasers, and telecommunication devices such as optical
amplifiers and waveguides. The strong commercial interest has renewed fundamental
research and directed it to achieving better control of quantum dot self-assembly in hopes
of one day using these unique materials for quantum computing.
Semiconductor quantum dots combine many of the properties of atoms, such as discrete
energy spectra, with the capability of being easily embedded in solid-state systems.
"Everywhere you see semiconductors used today, you could use semiconducting quantum
dots," says Clint Ballinger, chief executive officer of Evident Technologies, a small start-up
company based in Troy, New York...
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
Quantum Dots for Sale
The Industrial Physicist reports
that quantum dots are emerging
as a bona fide industry.
Emission Peak[nm]
535±10
560±10
585±10
610±10
640±10
Typical FWHM [nm]
<30
<30
<30
<30
<40
1st Exciton Peak
[nm - nominal]
522
547
572
597
627
Crystal Diameter
[nm - nominal]
2.8
3.4
4.0
4.7
5.6
Part Number (4ml)
SG-CdSe-Na-TOL
05-535-04
05-560-04
05-585-04
05-610-04
05-640-04
Part Number (8ml)
SG-CdSe-Na-TOL
05-535-08
05-560-08
05-585-08
05-610-08
05-640-08
Evident Nanocrystals
Evident's nanocrystals can be separated from the
solvent to form self-assembled thin films or
combined with polymers and cast into films for use
in solid-state device applications. Evident's
semiconductor nanocrystals can be coupled to
secondary molecules including proteins or nucleic
acids for biological assays or other applications.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2
EviDots - Semiconductor nanocrystals
EviFluors- Biologically functionalized EviDots
EviProbes- Oligonucleotides with EviDots
EviArrays- EviProbe-based assay system
Optical Transistor- All optical 1 picosecond performance
Telecommunications- Optical Switching based on EviDots
Energy and Lighting- Tunable bandgap semiconductor
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2