Nanomaterials and their Optical Applications...To use chemical approaches to provide a precise...

[email protected] Lecture 03 http://www.iap.uni-jena.de/multiphoton

Nanomaterials and their Optical Applications Winter Semester 2013

Lecture 03

[email protected]

[email protected] Lecture 03

Module enrolment & Exams 2

Do not forget: module enrolment ( within few weeks)

Examinations date:

Tuesday 11 of February 2013 9-10h30

Exam form: oral or written, it depends on the numbre of student

http://www.iap.uni-jena.de/teaching.html Website for Lecture Materials


Lecture 3: outline 3

Generation of nanomaterials

Top-down

Bottom-up

Characterization of nanomaterials


Generation of nanomaterials 4

Top-down

1. Projection : Optical lithography

2. Direct printing : E-beam, FIB, proton

3. Nanolithography:

a) Two-photon lithography

b) Near-field lithography / soft lithography

c) Plasmon printing

d) Nanosphere litho

e) Dip-pen nanolitho

f) Nanoimprint litho

g) Photonically aligned nanoarray

Bottom up

1. Epitaxial Growth 2. Self organisation

Chapter 3 in Basics of Nanotechnology, , Rubahn

Chapter 11 Nanolithography


Top-down: Lithography 5

Alois Senefelder (1771‐1834)

Lithography stone and mirror-image print of a map of Munich


Top-down: Lithography 6

Photolithography :

• for microstructuring not nanostructure

• For mass production

20 µm


Photolithography 7

The smallest feature:

k: factor between 0.5 and 1.0 that depends on the resist as well as processing procedures NA = n sinθ numerical aperture of the projection lens

http://www.olympusmicro.com/primer/java/nuaperture/


Top-down: Lithography using photoresist 8

1. Substrate : wafer

polycristalline

Much higher solvent solubility

2. Photomask or scanning system

3. Photoresist



Process flow :



Resolution or feature size of photolithography ?

Choose the lowest possible wavelength: UV , 157 nm for Excimer laser • Strong absorption in ambiant air -> in vaccum or nitrogen • Optical components get damaged after few years



Projection methods Photolithography mask

Direct writing approach Ion or electron beam lithography

Introduction to Nanoscience, Lindsay, 2010



Projection methods Photolithography mask

Direct writing approach Ion or electron beam lithography

20 keV electron beam

Why electrons instead of photons ?


Top-down 13

focused ion beam milling FIB

sub-10 nm 3D structuring is feasible Why ion instead of electrons ?

• Ions are positive, large, heavy and slow • Electrons are negative, small, light and fast

MeV protons

1–50 keV


Top-down 14

Focused ion beam milling FIB: gallium ion

Why ion instead of electrons ?

• Ions are positive, large, heavy and slow • Electrons are negative, small, light and fast

1–50 keV

Helium ion microscope

• less damaging to the sample than

Ga ions

• Sub 1 nm features

• it does not suffer from a large

excitation volume, and hence

provides sharp images

Helium ion microscope: A new tool for nanoscale microscopy and metrology B. W. Ward, John A. Notte and N. P. Economou J. Vac. Sci. Technol. B 24, 2871 (2006) http://dx.doi.org/10.1116/1.2357967

liquid metal ion source (LMIS)


Proximity effects… 15

http://www.pbeam.com/theory.php

Poly(methyl methacrylate) (PMMA) is a transparent thermoplastic, often used as a light or shatter-resistant alternative to glass.

… = forward and backward scattering inside the resist

Type of resist


E-beam and FIB systems 16


Nanolithograpjy 17

Top-down

1. Projection : Optical lithography

2. Direct printing : E-beam, FIB, proton

3. Nanolithography:

a) Two-photon lithography

b) Near-field lithography / soft lithography

c) Plasmon printing

d) Nanosphere litho

e) Dip-pen nanolitho

f) Nanoimprint litho

g) Photonically aligned nanoarray

Chapter 11 Nanolithography


Two-photon lithography 18

• To use two-photon excitation instead of UV curing • Three-dimensional fabrication

Webb Lab, Cornell University


The physics behind nonlinear processes

Two-photon absorption already predicted in 1931 by Maria Goeppert-Mayer

The Nobel Prize in Physics 1963

Denk, W. & Svoboda, K., Neuron 18, 351-7 (1997).

Second harmonic generation (SHG) Two-photon fluorescence (TPF) Nonlinear process

Dye molecules (rhodamine 6G) on a sunny day

Linear process the dye will absorbs 1 photon per 1 second

Nonlinear process simultaneously absorbs 2 photons every 10 millions years simultaneously absorbs 3 photons: never in the universe time




Take the simplest atom: hydrogen Put it into an electric field

where α is the answer of the atom to electric field Macroscopic view: N atoms

p Eα=

You end up with a dipole moment

the macroscopic dipole moment (per unit volume) is called the POLARIZATION :

2 30 20 31 0 ...P E E Eε χ ε χε χ= + + +

• 3rd-order : multiphoton absorption, third harmonic generation, coherent anti-Stokes Raman scattering

• 1st-order : absorption and reflection

• 2nd-order: SHG, sum and difference frequency generation, hyper-Rayleigh

Microscopic view: 1 atom

Electric susceptibility

Permittivity of free space




Scattering (elastic) Absorption (non elastic)

Absorption

the incoming light bounces off an object in many different directions

the incoming light hits an object and causes its atoms to vibrate, converting the

energy into heat which is radiated

ω

ω 2ω

Ground state

Virtual state

SHG

ω

ω

Real state

< 2ω

Ground state

Non-radiating relaxation

2-photon fluorescence

Energy diagram

No photobleaching Less heating




Scattering (elastic) Absorption (non elastic) Non resonant excitation Resonant

Excitation and emission spectra

Laser pump

(> 450 nm) 800 850 900 400 425 450

SHG 2-photon fluorescence


Two-photon lithography 23

• Key: to develop two-photon absorbing material • Organic chromophores • Organic-inorganic hybrid materials • To take advantage of quenching: above a certain threshold only

the polymerization occurs

features of 200 nm


Near-field lithography 24

Scanning probe methods:

STM pulls away atoms from the surface but let it bound to it (Xenon

atom on a nickel surface)

Nature 344, 524 - 526 (05 April 1990)

SNOM: Near-field scanning optical microscopy

wikipedia

Features of 70 nm Features of 120 nm

Single-photon Two-photon


Near-field phase-mask soft-lithography 25

features of 90 nm


Plasmon printing 26

features of 12-50 nm


Nanosphere lithography 27

DOI:10.1039/C0AN00053A (Minireview) Analyst, 2010, 135, 1483-1489

features of 43 nm


Dip-pen Nanolithography 28

Science 29 January 1999: Vol. 283 no. 5402 pp. 661-663 DOI: 10.1126/science.283.5402.661

features of 70 nm

To produce structure of one molecule thickness


Nanoimprint lithogrpahy 29

features of 25 nm

• High throughput • Low-cost • Non optical method • Based on the etching


Photonically aligned nanoarrays 30


Bottom-up approaches 31

1. Thin film technology: epitaxial growth

2. Nanochemistry • Self-assembled molecular monolayers

• Reverse micelle synthesis • Colloidal synthesis


Thin film technology 32

2 issues • oxygen at 300K, 1015 molecules strike each centimeter of the surface per second at a

pressure of 10−6 Torr (1 Torr beeing 1/760 of a standard atmosphere) • Thus, if a surface is prepared so as to be absolutely clean, a vacuum of 10−9

Torr is required • the growth pattern of deposited material on the underlying surface

• Thus lattice matching is required

Simple techniques: • Thermal evaporation: The material to be evaporated is placed in a tungsten

“boat” (a container that also serves as a resistive filament) and is heated electrically

• Sputtering is another approach for depositing thin films. It uses a beam of energetic ions to bombard the surface of the material to be deposited and literally chips it away so that chunks of the material fly from the source to the sample to be coated.


Bottom-up: epitaxial growth 33

Sputtering or evaporation of one material to generate another or the same material while maintening the crystal structure

1. Metal-organic chemical vapor deposition (MOCVD) 2. Molecular beam epitaxy (MBE) 3. Chemical Beam epitaxy 4. Liquid-phase epitaxy

In contrast to molecular beam epitaxy (MBE) the growth of crystals is by chemical reaction and not physical deposition. This takes place not in a vacuum, but from the gas phase at moderate pressures (10 to 760 Torr). As such, this technique is preferred for the formation of devices incorporating thermodynamically metastable alloys, and it has become a major process in the manufacture of optoelectronics

1.Metal-organic chemical vapor deposition (MOCVD)



2. Molecular beam epitaxy (MBE)

Prasad, Nanophotonics, chap. 7 : § 7.1.1



Lattice matching: avoid stress in the material

Lattice constant =constant distance between unit cells in a crystal lattice

Revise: crystallography !



Distributed Bragg mirror

http://www.rp-photonics.com/

An Open Access Encyclopedia for Photonics and Laser Technology


Other epitaxy techniques 39

Liquid-phase epitaxy: dipping process

robust and cheap

Less control on the crystal orientation leading to poor surface quality

Chemical beam epitaxy: combination of MBE and MOCVD

High-vaccum chamber with metal-organic precursor

Laser-assisted vapor deposition : laser ablation of a solid target

for deposition of film and nanoparticles


Bottom-up approaches 40

1. Epitaxial Growth

• Molecular beam epitaxy (MBE)

• Metal-organic chemical vapor deposition (MOCVD)

• Chemical beam epitaxy, Liquid-phase epitaxy, Laser-

assisted vapor deposition

2. Nanochemistry • Self-assembled molecular monolayers

• Reverse micelle synthesis • Colloidal synthesis


Why nanochemsitry ? 41

Challenge To use chemical approaches to provide a precise control of composition, size and shape of the

nanomaterials product formed

Capabilites of nanochemistry:

• Preparation of nanoparticles of a wide range of metals, semiconductors, glasses, polymers, …

• Preparation of multilayer structures, core-shell type of nanoparticles

• Nanopatterning of surfaces, surface functionalization and self-assembling of structures on this

patterned template

• Organization of nanoparticles into periodic or aperiodic functional structures

• In situ fabrication of nanoscale probe, sensors and devices


Outlook 42

M. Reed et al. “Observation of discrete electronic states in a zero-dimensional semiconductor nanostructure,” Physical Review Letters, 60, 6, 535–537, 1988.

Helium ion microscope: A new tool for nanoscale microscopy and metrology B. W. Ward, John A. Notte and N. P. Economou J. Vac. Sci. Technol. B 24, 2871 (2006)

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