Nanochemistry
Andreas Borgschulte([email protected])
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