prof.p. ravindran,folk.uio.no/ravi/cutn/nmnt/5.phys_nanomat2.pdf · 2016. 9. 15. · p.ravindran,...

P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Physicls of Low dimensional Materials - 2

http://folk.uio.no/ravi/cutn/NMNT2016

Prof.P. Ravindran, Department of Physics, Central University of Tamil

Nadu, India

&Center for Materials Science and Nanotechnology,

University of Oslo, Norway

Physics of Low dimensional Materials - 2

1


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.


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


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.


• 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)


Superparamagnetic separations

Magnetic sorting of cells labeled

with superparamagnetic beads

HM

z

BMF zz

)(0 MHB

Induced magnetic moment:

Magnetic force:

Particle were pulled to point of highest field gradient

MFS: microfabricated

ferromagnetic strips


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

Co, magnetic layer

NiFe alloy, magnetic layer

An easily re-alignable magnetization

Cu, electrically conducting layerLayers have a width that

is smaller than electron

scattering length.

The magnetization on the surface

of the disk can be read out as

fluctuations in the resistance of

the conducting layer.


For antiparallel magnetic layers both spin polarizations are

scattered, giving rise to super-resistance (II).

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).

I II III


(Qiu, et al.

PR B ‘92)

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.


Minority spins discrete,

Majority spins continuous

Magnetic interfaces reflect the two spins differently, causing a spin

polarization.

Spin-Polarized Quantum Well States


Filtering mechanisms

• Interface: Spin-dependent Reflectivity Quantum Well

States

• Bulk: Spin-dependent Mean Free Path Magnetic “Doping”

Parallel Spin Filters

Resistance Low

Opposing Spin Filters

Resistance High

Giant Magnetoresistance and Spin -

Dependent Scattering


Giant Magnetoresistance (GMR):

(Metal spacer, here Cu)

Tunnel Magnetoresistance (TMR):

(Insulating spacer, MgO)

Magnetoelectronics

Spin currents instead of charge currents

Magnetoresistance = Change of

the resistance in a magnetic field


22

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.


• Negative resistance devices, switches (RTDs, molecular), spin transistors

• Single electron transistor (SET) devices and circuits

• Quantum cellular automata (QCA)

Limits of Conventional CMOS technology

• Device physics scaling

• Interconnects

Nanoelectronic alternatives?

Issues

• Predicted performance improves with decreased dimensions, BUT

• Smaller dimensions-increased sensitivity to fluctuations

• Manufacturability and reproducibility

• Limited system demonstration

New information processing paradigms

• Quantum computing, quantum info processing (QIP)

• Sensing and biological interface

• Self assembly and biomimetic behavior

23

Motivation for Nanoelectronics


24

The roadmap

Semiconductor technology trends (ITRS 2006)


25


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

26


Source: Intel

27


28

More Moore -> Beyond Moore

Robert Chau, Intel, ICSICT, 2005


29Critical issues

1988

10-1

Year

Ch

an

nel E

lectr

on

s

1992 1996 2000 2004 2008 2012 2016 2020

100

101

102

103

104

16M 64M

256M

1G

4G16G Memory Capacity/Chip

4M


30Nano-Device Structure Evolution

Source: Intel


Lg = 1.3µm; Ø = 26 nm; tox = 300nm SiO2

•Normally-off

•Schottky contacts

-2,0µ

-1,5µ

-1,0µ

-500,0n

0,0

-2 -1 0

-Vgs

-20 V

-15 V

-10 V

+5V; 0 V; -5 V

drain bias Vds

[V]

dra

in c

urr

en

t I d

[A

]

20V;

Weber, W.M. et al. IEEE Proc. ESSDERC 2006, p. 423 (2006)

gate

S D

Vd

Vg

Id

NW

Si-NW transistor: output characteristics

32


Possible Quantum Dot Applications

PhotodetectorInput

Quantum dots orsingle electron transistorsas processing elements

CMOS Drivers providing fan-out

Single “cell” of a Cellular Architecture

Single Electron MemoryNanoelectronic Integrated

Circuit (NIC)

Quantum Cellular Automata

Quantum Computation (QBITs)

“1” “0”

1

23

4

0

source drain

nanocrystalsgate

SiO2

gateMemory

nodeSi channel

SiO2

Quantumdots

Tunnelingbarriers

Quantumdots

33


34

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


35

Molecular components

OPV11 molecules with simplified phenyl side chains

synthesized by the group of Prof. Dr. E. Thorn-Csányi

at the University of Hamburg)

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.

S. Strobel et al., SMALL 5, 579-582 (2009)


36

Cross bar non volatile memory

V

The current-voltage characteristics of molecules is typically hysteretic, with step-like

nonlinearities and possibly non-symmetric (rectifying) behavior.

A crossbar memory – probably the simplest possible functional circuit – is

one of the proposed application of single molecule electronics

G. Casaba et al., IEEE Transactions on Nanotechnology, 8, 369 (2009)


Problems with single molecule devices

-3 -2 -1 0 1 2 3-500p

-400p

-300p

-200p

-100p

0

100p

200p

300p

400p

500p 0Down (P03:S05-08-)

1Up (P03:S05-08-)

1Down (P03:S05-08-)

2Up (P03:S05-08-)

2Down (P03:S05-08-)

3Up (P03:S05-08-)

3Down (P03:S05-08-)

4Up (P03:S05-08-)

4Down (P03:S05-08-)

5Up (P03:S05-08-)

5Down (P03:S05-08-)

6Up (P03:S05-08-)

6Down (P03:S05-08-)

7Up (P03:S05-08-)

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-)

18Up (P03:S05-08-)

18Down (P03:S05-08-)

19Up (P03:S05-08-)

19Down (P03:S05-08-)

20Up (P03:S05-08-)

Cu

rre

nt

[A]

Voltage [V]

G17-1c, P03, S05, über Nacht

A large variation is found in the IV characteristics between succesive sweeps.

Reasons can be due to:

• Configurational changes in

single

molecules

• Variation in the number of

molecules attached to the

electrodes

• Changes in the bond of a

single

molecule to the metal contact

• …

Such variability has to be dealt

at a circuit/architecture level


Molecular transistor

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.

Once a conducting molecule is set between 2 contacts, an additional electrode has be

introduced as gate. There are various possibilities:


MRAM chips represent one class of spintronics,in which the spins of large numbers ofelectrons are aligned the same way, as with acollection of toy tops all spinning clockwise onthe 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.

http://images.google.co.za/imgres?imgurl=http://www.thetaoofmakingmoney.com/wp-content/uploads/images/spinning_top.JPG&imgrefurl=http://www.thetaoofmakingmoney.com/category/consumerism&h=185&w=150&sz=5&hl=en&start=50&um=1&usg=__ao5YI9LUWQvr2vCt_3wf0vWI17Q=&tbnid=uAlx3OeywhzteM:&tbnh=102&tbnw=83&prev=/images?q%3Dtoy%2Btops%26start%3D36%26ndsp%3D18%26um%3D1%26hl%3Den%26sa%3DN









A second class of spintronics: Quantum Spintronics, manipulation ofindividual electrons to exploit the quantum properties of spin.

Quantum Spintronics could provide a practical way to carry outquantum information processing, which replaces the definite 0s and1s of ordinary computing with quantum bits, or qubits, capable ofbeing 0 and 1 simultaneously, a condition called a quantumsuperposition.


41

Logic with nanomagnets

In collaboration with M. Becherer and D. Schmit-Lansiedel (TUM) , W. Porod (Notre Dame)

Outputs

Inputs

Information propagation

The challenges:

How to make signals propagating? Integrated clocking

How to write in the magnets? Localized field from

wires

How to read out the magnets? Hall sensor

M. Becherer et al., IEEE TRANSACTIONS ON NANOTECHNOLOGY 7, 316 (2008)


Semiconductor Lasers and LEDs

Various flavours of quantum well lasers – well established technology.

Arakawa and Sakaki (1982) predicted that quantum dot lasersshould be more efficient .


Quantum dot laser

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.

Quantum dots of the right size can place

all of the exciton energies at the right

value for lasing.

Optical cavity


Real Quantum Dot Lasers

Innolume GmbH

– QD lasers 1064 –1320 nm

• QD Laser Inc., Japan

– QD lasers 1.3 and 1.55 µm


0-D (Quantum dot)

An artificial atom

)()( iEEE

E

Ei


Quantum cascade lasers


Quantum Cascade Laser

60 nm

520 m

eV

3

2

active

region

injector (n-doped)

injector (n-doped)

e

active

region

J. Faist, F. Capasso, et al. Science 264, 553 (1994)

From IR/MIR/FIT to THz!


53

More than Moore

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 bio-

interfaces (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.


Miniaturization of electron devices

High integration

High speed

Low consumption electric power

Low cost

Miniaturization by top-down method


Application to electronic devices

L.L.Sohn, Nature 394(1998)131

Ge

transistor LSIQuantum

corral

Carbon

nanotube

Point

contact

1950 1970 1980 2000


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...


Quantum Dots for Sale

The Industrial Physicist reports

that quantum dots are emerging

as a bona fide industry.

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.

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


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

http://www.evidenttech.com/products/core_evidots/overview.php

http://www.evidenttech.com/products/evifluors.php

http://www.evidenttech.com/applications/eviprobe.php

http://www.evidenttech.com/applications/eviarray.php

prof.p. ravindran,folk.uio.no/ravi/cutn/nmnt/5.phys_nanomat2.pdf · 2016. 9. 15. · p.ravindran,...

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