nanochemistry - uzhffffffff-cd8c-a92e-ffff... · nanochemistry andreas borgschulte...

Nanochemistry

Andreas Borgschulte(andreas.borgschulte@empa.ch)

Optical Properties of Nanostructures

CHE729

Mi. 10:00-12:00

Introduction: optical appearance (colors, Maxwell)

Mie-scattering Plasmons

Optical properties of metals Plasmon excitation Nano-plasmonics

Semiconductors Bandstructure of bulk semiconductors Optical properties Nano-semiconductors

Contents of this lecture

Electronic Transitions in UV-Visible Absorptions

VII VIII VIV VV

pictures: wikipedia

Rayleigh-Streuung plusChappuis-Absorption (Ozone)

http://artsci.ucla.edu/BlueMorph/

The STED-Microscope: Nobelprice 2014

Stimulated emission depletion (STED)microscopy is a process that providessuper resolution imaging by selectivelydeactivating fluorophores, so as toenhance the resolution in an area of asample. It was developed by StefanW. Hell and Jan Wichmann in 1994,[2]and was first experimentallydemonstrated by Hell and ThomasKlar in 1999. Hell was awarded theNobel Prize in Chemistry in 2014 forits development. In 1986, V.A.Okhonin (Institute of Biophysics,USSR Academy of Sciences, SiberianBranch, Krasnoyarsk) has patentedthe STED idea. This patent was,perhaps, unknown to Hell andWichmann in 1994

copyright Wikipedia

The STED-Microscope: The idea

Refs.: „STED Mikroskop PSFs“ von Marcel Lauterbach, wikipedia

/E

0B

EjB

BE

jdiv

EPED r

00

HMHB r

00

Fundamentals: The Maxwell equations

Et

Et

jt

Ht

E

2

2

0002

2

22

2

111,1 rr

cn

cEtc

E

EE

rn

nc

nn

ir

0

2

222

1

21

42,

0j

Introduction: optical appearance (colors, Maxwell)

Mie-scattering Plasmons

Optical properties of metals Plasmon excitation Nano-plasmonics

Semiconductors Bandstructure of bulk semiconductors Optical properties Nano-semiconductors

Contents of this lecture

Mie-scattering

Ref: Horiba; wikipedia;

/E

0B

EjB

BE

jdiv

EPED r

00

HMHB r

00

From Maxwell equations to Mie-scattering

Et

Et

jt

Ht

E

2

2

0002

2

22

2

111,1 rr

cn

cEtc

E

EE

iKn r ~

Ref: H. Merkus, Particle size measurements, Springer 2009; G. Mie, Annal. Phys. 4, 377 (1908)

resonant electric

oscillations

Mie- Solution: 22

2122

20

8

SSd

II S1 and S2 are

dimensionless, complex functions

picture: wikipedia

complex refractive index

62

2

24

2212

DnnI

Mie-scattering

Ref: wikipedia; G. Mie, Annal. Phys. 4, 377 (1908) /D

2

1

22

420

sin

sin

8

D

DJ

dDII

Mie-scattering and Fraunhofer approximation:

0

1 1222!

1j

jj

xxxjj

xJ

The difference between Fraunhofer- and Mie-theory is, that Fraunhofer assumes the complete diffracted light to be generated by diffraction only whereas MIE-theory takes into account that especially for transparent (and very small particles get more and more transparent) particles also light caused by refraction, reflection and absorption may end up on the detector.

here S1 and S2 are relatively simple and

Merkus S. 268

From H. G. Merkus, Particle Size measurements, Springer 2009

22

2122

20

8

SSd

II

Fraunhofer-sol.

Mie-sol.

Ref: G. Mie, Annal. Phys. 4, 377 (1908)

Optical properties of Gold nano-particles

=> intrinsic optical properties of Au-nano particles depend on size!

Introduction: optical appearance (colors, Maxwell)

Mie-scattering Plasmons

Optical properties of metals Plasmon excitation Nano-plasmonics

Semiconductors Bandstructure of bulk semiconductors Optical properties Nano-semiconductors

Contents of this lecture

Culturing photosynthetic bacteria through surface plasmon resonance

Ooms, Bajin, and Sinton Appl. Phys. Lett. 101, 253701 (2012)

imeeEx

eeEfxxmxmti

ti

20

0

0

(Ne)-

x(Ne)+

222220

2

222220

220

1

220

1

1

/1

s

s

is

EPNexP

Drude-Lorentz model

0 1 2 3 4 5 6-10

-5

0

5

10

1, 2

22

2

2

22

22

1

0

1

11

int

mne

mne

eeEfxxmxm ti

Metals:

0

p

mNes /2Oscillator strength

R

1

0p

2

2

1~1~

nnR

Reflectance of metals

wikipedia

Plasmon oscillation

An electron gas has a mechanical vibration eigenmode that generates a longitudinal

electromagnetic mode.

Key idea: plasmon is a material resonance.

int

int

1

01

1

0,div0,divdiv

0div

22

22

22

1

1

10

mne

mne

kEkkED

D

p

At p, the electromagnetic wave (field D) is unaffected by the sample

(=> R = 0)

+++++++++++++++++++++

++++++++++++++++++++++++++

++++++++++++++++++

- - - - - - -- - - - - - - - - -

- - - - - - - - - - - -- - - - - - - - - - -

- - - - - - - - -

- - - - - - -- - - - - - - - - -

- - - - - - - - - - - -- - - - - - - - - - -

- - - - - - - - -

- - - - - - -- - - - - - - - - -

- - - - - - - - - - - -- - - - - - - - - - -

- - - - - - - - -

+

=

plasmon oscillation

Plasmon frequency p

discrete positive nuclei positive background

free electron cloud

jellium

Ek

k

E

light is a transverse wave

Electron energy loss Spectroscopy (EELS)

decomposition of MgH2 (insulator)into Mg (metal) and H2

M. Danaie et al. / Acta Materialia 58 (2010) 3162–3172int

22

mne

p

What is a surface wave?

++++++++++++++

++++++++++++++

---------------------------

++++++++++++++

++++++++++++++

++++++++++++++

++++++++++++++

++++++++++++++

++++++++++++++

---------------------------

---------------------------

k

tiziikxEE exp0

light is a transverse wave

tiikxEE exp0

pp c

cnk

c 0,

1

1

k

light in vacuum

surface plasmon

Dispersion relation and phase velocity

no solution!

Excitation of surface plasmon polaritons

Courtesy of Nano-optics @ The Institute of Optics University of Rochester

- - - - - - -- - - - - - - - - -

- - - - - - - - - - - -- - - - - - - - - - -

- - - - - - - - -

Plasmon resonance in nano particles

22

21

232/3

2

m

m RA

A A

wavelength wavelength

S. Underwood and P. Mulvaney. Langmuir 1994,10, 3427Ludovico Cademartiri and Geoffrey A. Ozin, Concepts of

nanochemistry, Wiley VCH Weinheim 2009

SPPmSPP 21

mn

Victor I. Boev, et al. Langmuir 2004, 20, 10268

Shape dependence of plasmon resonance

AgAu

Au Au

Ag Au Aushort rod

Aulong rod

Size dependent properties

Optical properties of Au Clusters

Lycurgus cup (Roman times)Illuminated from behind, the gold nanoparticle-containing dichroic glass that the cup is made from appears deep red in color.

SPPmSPP 21

NOx on BaO catalyst:

Nanoplasmonic Probes of Catalytic Reactions

Elin M. Larsson et al. Science 326, 1091 (2009);

Field enhancement at a metal surface

++++++++++++++

++++++++++++++

---------------------------

++++++++++++++

++++++++++++++

++++++++++++++

++++++++++++++

++++++++++++++

++++++++++++++

---------------------------

---------------------------

k

monochromator

detector analyzer

objective

focus lens

polarizer

sam

ple

Raman Spectroscopy = Inelastic Photon Spectroscopy

06

020

24 10 IIk

dkdI L

energy

Laser line

StokesAnti-Stokes

1W Laser power produces a few Raman phtotons

T. O. Deschaines, D. Wieboldt, Thermo Fisher Scientific, Madison, WI, USA, Application note # 51874

Surface enhanced Raman spectroscopy (SERS)

amplification up to 1014

Surface enhanced Raman spectroscopy (SERS)

250 500 750 1000 1250

0.0

500.0

1.0k

1.5k

2.0k

In

tens

ity (a

rb. u

nits

)

Raman shift (cm-1)

2E-6M solution aq + Ag Nano

solid [Re(py)(CO)3bipy]

2E-6M solution aq

Distance dependence of SERS

RamanLaserRaman EEI Antenna amplifies scattered light

Dipol field decays fast

10

1

arIRaman

a

r

Jon A. Dieringer et al., Faraday Discuss., 2006, 132, 9–26

pyridine adsorbed to AlO coated silver film

Petek, H.; Ogawa, S. Prog. Surf. Sci. 1997, 56, 239−310.Mukherjee, S. et al., Nano Lett. 2012, 13, 240−247.Matthew J. Kale et al. ACS Catal. 2014, 4, 116−128

Direct Photocatalysis by Plasmonic Nanostructures

Hot Electrons Do the Impossible: Plasmon-Induced Dissociation of H2 on Au

Mukherjee, S. et al., Nano Lett. 2012, 13, 240−247.

HD production is a measure for dissociation probability

gasdissdissgasgas HDDHDH 22222

Mukherjee, S. et al.,Nano Lett. 2012, 13, 240−247.

Some molecules examined via SERS would exhibit unexpected vibrational signatures, which were attributed to “chemical-enhancement mechanism”

1st direct evidence: photon-induced desorption of Na atoms from 50 nm Na particles deposited on optically transparent LiF substrates (Hoheisel, W.; et al. Phys. Rev. Lett. 1988, 60, 1649)

direct plasmon driven photocatalysis: Au nanoparticles supported on optically inert SiO2 were active under red light illumination

(600−700 nm) for HCHO oxidation to CO2 at ambient temperatures (Chen, X. et al.,Angew. Chem. 2008, 47, 5353).

rate of ethylene epoxidation (C2H4 + 1/2O2 → C2H4O) executed over Ag nanocubessupported on Al2O3 is significantly enhanced due to low intensity visible light illumination (Christopher, P. et al., Nat. Chem. 2011, 3, 467).

coupling of an aldehyde, amine, and phenylacetylene to produce proparglyamines over Au surfaces (González-Béjar, M. et al., C. Chem. Commun. 2013, 49, 1732).

photo-Fenton reactions on Au (Navalon, S. et al., J. Am. Chem. Soc. 2011, 133, 2218). 9-anthraldehyde oxidation by Au (Wee, T.-L et al. J. Phys. Chem. C 2012, 116, 24373) N−N bond formation to produce p,p′- dimercaptoazobenzene (Sun, M. et al., J. Phys. Chem.

C 2011, 115, 9629). methylene blue decomposition, (Chen, K.-H. et al., J. Phys. Chem. C 2012, 116, 19039) Suzuki coupling (Dhakshinamoorthy, A. et al., Energy Environ. Sci. 2012, 5, 9217)

Summary plasmon chemical enhancement

Matthew J. Kale et al. ACS Catal. 2014, 4, 116−128

Maksym V. Kovalenko ,* Erich Kaufmann , Dietmar Pachinger , Jürgen Roither , Martin Huber , Julian Stangl , Günter Hesser,Friedrich Schäffler , and Wolfgang Heiss, J. Am. Chem. Soc., 2006, 128 (11), pp 3516–3517

Angshuman Nag, Maksym V. Kovalenko, Jong-Soo Lee, Wenyong Liu, Boris Spokoyny, and Dmitri V. Talapin, J. Am. Chem. Soc., 2011, 133 (27), pp 10612–10620

Size dependent properties of semiconductors

Colloidal HgTe Nanocrystals with Widely Tunable Narrow Band Gap Energies: From Telecommunications to Molecular Vibrations

Metal-free Inorganic Ligands for Colloidal Nanocrystals: S2–, HS–, Se2–, HSe–, Te2–, HTe–, TeS32–, OH-, and NH2– as Surface Ligands

Introduction: optical appearance (colors, Maxwell)

Mie-scattering Plasmons

Optical properties of metals Plasmon excitation Nano-plasmonics

Semiconductors Bandstructure of bulk semiconductors Optical properties Nano-semiconductors

Contents of this lecture

Band gap EG

fi

ficV

M

00

2

2

20

0

fi 222220

2

s

0

Indirect band gapOptical constants and band structure of MgH2

J. Is

idor

sson

et a

l. Ph

ys. R

ev. B

, 68,

115

112

(200

3)

Band structure: Bloch functions

airRr /2exp)()( 0

Schrödinger equation

ÜberlappAtom hHH

Tight-binding electronic bandstructure

k = 0

k = /a

k = 0

k = 0 k = /a

E(k)

E0

Example s-orbitals

occu

pied

ban

dsun

occu

pied

ba

nds

gap

= valence band

= conduction band

Bandstructure of semiconductors (Si)

Britney Spears' Guide to Semiconductor Physicshttp://britneyspears.ac/lasers.htm

occu

pied

ban

dsun

occu

pied

ba

nds

gap

= valence band

= conduction band

1 eV

2eV

transmission

energy

Photon induced electronic transition in Si

Photon generated charge carriers in Si

electron-hole (+) in valence band

electron (-) in conduction band

I need a toilet!!!

Mobility of charge carriers

holes are less mobile than

electrons

TkB

ener

gy

EF

EF = Fermi energy = chemical potential of the (free) electrons

Band model of metals and semiconductors

Metals

TkE

B

Gexp

ener

gy

EFEG

insulators

Doping of semiconductors

ener

gy

EF

donor level

Doping of semiconductors: band structure

n-type Si p-type Si

ener

gy

acceptor level

EF

ener

gy

EF

Surface structure of semiconductors: band structure

n-type Si vacuum

vacuum niveau

wor

k fu

nctio

n

- --- - ---

--------- -

++

++

+

applying a voltage

=> MOSFET

U

ener

gy

Nano semiconductors: simple band structure

- ----

++

++

+

- ----

+ +

++

+

depletion length 10…100 nm

dNel 2

2

EF

Depletion lengths: J. H. Luscombe, C. L. Frenzen, Solid-State Electronics 46 (2002) 885T. Wolkenstein Electronic Processes on Semiconductor Surfaces during Chemisorption, Consultance Bureau, NY 1991 (Springer), Wolkenstein 1960

ener

gy

decreasing size

bulk quantum dot

size

Nano semiconductors: quantum confinement

Apapted from: Ludovico Cademartiri and Geoffrey A. Ozin, Concepts of nanochemistry, Wiley VCH Weinheim 2009

Colloidal HgTe Nanocrystals with Widely Tunable Narrow Band Gap Energies

M. Kovalenko, et al. J. Am. Chem. Soc. 2006, 128, 3516-3517

Introduction: optical appearance (colors, Maxwell)

Mie-scattering Plasmons

Optical properties of metals Plasmon excitation Nano-plasmonics

Semiconductors Bandstructure of bulk semiconductors Optical properties Nano-semiconductors

Contents of this lecture

18.02.2015 Introduction 25.02.2015 Measurement of Nanostructures I 04.03.2015 Measurement of Nanostructures II 11.03.2015 Optical Properties 18.03.2015 Surface Science I 25.03.2015 Surface Science II 01.04.2015 Preparation of nano structures I 15.04.2015 Preparation of nano structures II 22.04.2015 Applications I: Catalysis 29.04.2015 Seminars 06.05.2015 Applications II: Wetting, Colloids, Seminars 13.05.2015 Theory, Seminars 20.05.2015 cell biology / Nanotoxicity, Seminars 27.05.2015 Applications III: Energy

Contents of lecture NanoChemistry

andreas.borgschulte@empa.ch