spektroskopia fotoelektronów w zastosowaniu do izolatorow...
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Spektroskopia fotoelektronów w zastosowaniu do izolatorow topologicznych
Jacek Szade Instytut Fizyki im. A. Chełkowskiego,
Śląskie Międzyuczelniane Centrum Edukacji i Badań Interdyscyplinarnych
Uniwersytet Śląski w Katowicach
Spektroskopia fotoelektronów – krótkie wprowadzenie Wzrost cienkich warstw BixTey
Polikrystaliczne warstwy BixTey na Si(100) Monokrystaliczne warstwy Bi2Te3 na mice Generacja fononów w cienkich warstwach BixTey
Podsumowanie
Photons:
- energy: few eV-103 eV
- polarisation: linear, circular
- UV lamp, x-ray lamp
- synchrotron: VUV, x-ray
sample
Photoelectrons:
detection of intensity in function of:
- kinetic energy
- polarisation of light
- angle (ARUPS, ARXPS)
- spin polarization (SRXPS)
- photon energy (CIS, CFS)
solid, gas in special chambers a spectrum is formed, usually in
function of binding energy
- calculated with the use of work function of the spectrometer
UPS – Ultraviolet Photoelectron Spectroscopy
XPS – X-ray Photoelectron Spectroscopy
ESCA – Electron Spectroscopy for Chemical Analysis
RESPE – Resonant Photoelectron Spectroscopy
Golden Fermi rule
photoelectric current
S
ifiPESpp hHhJ )(2
)(2
,
pAcm
eH
e
vol
PE
dipole interaction
one of the final electronic states with free electron of momentum p and N-1 electrons in atom
initial electronic state set of final possible
quantum states
energy conservation
frozen orbitals approximation
11 NN if
Koopmans theorem
Binding energy derived from the PE spectrum is equal to the initial energy in a non-perturbed atom
S. Hüfner „Photoelectron spectroscopy”
One step model
Koopmans theorem – binding energy is equal to the energy of an orbital
but
one has to take into account that an excited state is measured (photoelectron + photo-hole)
peak position may be different from the orbital energy (relaxation)
additional lines – satellites are present
background
for standard XPS (h up to 1500 eV) mean free path of photoelectrons is less than 2-3 nm
Photoelectron spectroscopy is a surface sensitive technique
photoionisation cross section depends on h and particular atomic orbital
spectrum is different for various excitation energies
XPS spectra can be used for determination of chemical composition
integration of photoemission lines plus photoionization cross sections plus spectrometer transmition function
all elements can be detected except H and He
S. Hüfner „Photoelectron spectroscopy”
Czułość powierzchniowa – zalety:
reakcje na powierzchni reakcje pomiędzy warstwami jeżeli grubość < 3-4 nm możliwość profilowania wgłębnego z dobrą rozdzielczością powierzchni
wady:
reakcja z gazami resztkowymi nawet w UHV konieczność usunięcia zanieczyszczeń z powierzchni:
trawienie jonowe łamanie w próżni drapanie, piłowanie w UHV
Zmiana czułości powierzchniowej:
Zmiana geometrii
Zmiana energii kinetycznej fotoelektronów przez: analizę innej linii fotoemisyjnej o innej energii zmianę energii fotonów
Surface Physics Laboratory at the Silesian Center for Education and
Interdisciplinary Research in Chorzów
Multitechnique UHV (ultra-high vacuum) system XPS – X-ray photoelectron spectoscopy PHI UPS - UV photoelectron spectoscopy PHI AES – Auger electron spectroscopy PHI SEM - Scanning electron microscopy SPM – Scanning probe microscopy (AFM, STM, MFM….) RHK/Prevac MBE - Molecular beam epitaxy (4 efusion cells, 2 electron beam evaporators) Prevac Electron diffractometers (RHEED and LEED) Steib, OCI Surface preparation facilities, cooling and heating in-situ
ToF SIMS – Time of Flight Secondary Ion Mass Spectrometer ION TOF
XPS, UPS – Prevac/VG Scienta
Topological insulator Bi2Te3
Bulk:
- Energy gap – insulator (semiconductor)
- Gap of about 150-170 meV
- Large thermoelectric (Seebeck) coefficient
Surface:
- Dirac states –
- Spin orbit coupling (SOC) drives a band inversion transition at the point
- Topologically protected surface state consisting of a single massless Dirac fermion
•
According to Zhang et al. 2009 for Bi2Se3, point
Chemical bonding
Crystal field
Spin-orbit
ARPES – Angle Resolved Photoemission
Spin Resolved ARPES
According to Alpichshev et al. 2010
Photoelectron spectroscopy Scanning tunelling spectroscopy
Studies of BixTey in the Institute of Physics, University of Silesia
Growth of thin films on Si (100) Different conditions and thickness
Growth of thin films on mica
• Growth by the MBE (Molecular Beam epitaxy)
– Substrate preparation, temperature of the substrate, flux proprtion of the components,…
– Characterization in-situ without the contact of the film with air electron diffraction RHEED (reflective high energy) and LEED (Low energy)
X-ray and ultraviolet photoelectron spectroscopy
AFM microscopy
LC AFM – Local conductivity AFM
Ex-situ characterization
XRD
XRR
Magnetometry (SQUID)
ToF SIMS
Ultrafast optical spectroscopy – le Mans, France
Surface Physics Laboratory at the Silesian Center for Education and
Interdisciplinary Research in Chorzów
Multitechnique UHV (ultra-high vacuum) system XPS – X-ray photoelectron spectoscopy PHI UPS - UV photoelectron spectoscopy PHI AES – Auger electron spectroscopy PHI SEM - Scanning electron microscopy SPM – Scanning probe microscopy (AFM, STM, MFM….) RHK/Prevac MBE - Molecular beam epitaxy (4 efusion cells, 2 electron beam evaporators) Prevac Electron diffractometers (RHEED and LEED) Steib, OCI Surface preparation facilities, cooling and heating in-situ
ToF SIMS – Time of Flight Secondary Ion Mass Spectrometer ION TOF
XPS, UPS – Prevac/VG Scienta
LABORATORIES – SURFACE PHYSICS LABORATORY
SURFACE PHYSICS LABORATORIES @ Chorzów ŚMCEBI, IF, UŚ
MBE – Molecular Beam Epitaxy
Vacuum conditions during the growth process:
UHV ~10-9 - 10-10mbar
Monitored by Residual Gas Analyzer (RGA)
Manipulator:
2-axis manipulator (tilt and rotation)
Shutter for the growth of wedge samples
Possibility of heating and cooling sample
(-120° – 1500ºC)
Preparation and Characterization:
Ar ion gun
RHEED
4-point Resistivity
2 electron beam evaporators (~2000ºC)
4 effusion cells (~1200ºC)
Thickness monitor
Software for the control of the growth process
What we usually grow: Bi, Te, Eu, Mn, Fe, Mo, Cr, Au, Ag, Ta
Typical growth rate 0.01 – 0.03Å/s, typical thicknesses 1-50nm
MULTILAYER DEPOSITION
CO-DEPOSITION
LABORATORIES – SURFACE PHYSICS LABORATORY
SURFACE PHYSICS LABORATORIES @ Chorzów ŚMCEBI, IF, UŚ
XPS (and UPS) – X-Ray (and Ultraviolet) Photoelectron Spectroscopy
CasaXP S (Thi s st ring can be edit ed in CasaXPS.DEF/P rintFootNote.txt)
Eu3d
1190 1180 1170 1160 1150 1140 1130 1120 1110
Bindi ng E nergy (eV)
x 104
6
8
10
12
14
16
18
20
22
24
CPS
Reversible valance transitions of europium
EU 3+ EU 2+
(1) Physical Electronics PHI 5700/660
(2) VG Scienta & Prevac
Monochromatic X-ray, Al, Mg anodes
Several apertures - probe size:
(1) 75 mm, 0.8-2mm
(2) 40-600mm x 4mm
5-axis manipulator (X, Y, Z, tilt, rotation)
Chemical state identification on surfaces
Identification of all elements except for H and He
Quantitative analysis, including chemical state differences
Depth profiling, line scans, chemical mapping
Applicable for a wide variety of materials
Detection limits typically ~ 0.1 at%, down to 100 ppm
Excellent surface sensitivity (~ 3-4 nm information depth)
Eu 3d
Chemical state identification → Evolution of chemical state → Depth profiling and atomic concentration calculations (during occurring processes)
NANOPARTICLES FOR CATALYTIC APPLICATIONS EU-MN THIN FILMS - MULTILAYERED SYSTEM
EU-MN THIN FILMS - MULTILAYERED SYSTEM
Eu-Mn thin
films
grown on Mo
Total thickness
of Eu-Mn layer
~20nm
Grazing angle XPS increase of the surface
sensitivity
λ
e-
λ
analyser
λ - IMFP
XPS regime
- VB states → about 30 Å
UPS regime → about 1-2 Å
TPP2M Quases by S. Tougaard
BixTey on Si (100) Thickness 16-23 nm
Roughness 1-3 nm
RHEED pattern
AFM
XPS analysis
Bi and Te core levels
VB
R. Rapacz, K. Balin, A. Nowak, J. Szade, J. of Cryst. Growth 401, 567-572 (2014)
XPS analysis of the Te 3d i Bi 4f photoemission lines Two chemical states of Te i Bi Grazing angle analysis gives information on localization of additional layers
Superstructure phases of Bi solid solutions in Bi2Te3 Metallic Te forms the layers on the surface
R.J. Cava, J. Huiwen , M.K. Fuccillo, Q.D. Gibson, Y.S. Hor, J. Mater. Chem. C 1 (2013) 3176-3189
Bi2Te3 on mica
Thickness 5-30 nm
Muscovite (KAl2(OH, F)2AlSi3O10)
LEED and AFM in lateral force mode
Single crystalline films starting from 5 nm thickness
Bi2Te3
AFM in UHV
Film 15 nm thick single crystal Stranskii – Krastanov mode of growth Screw dislocation driven growth Precipitations of unknown character
Morphology and local conductance of single crystalline Bi2Te3 thin films on mica
R. Rapacz, K. Balin, M. Wojtyniak and J. Szade
Nanoscale, 2015,7, 16034
Local conductivity AFM
Topography Current Iav = 18.41 nA ; V=5 mV
All values less than 57 % were cut o (the 35.03 nA value). Measured current value did not depend on the height of terraces, but was constant (within 47 % of scale).
Ultrafast spectroscpy for selected films A – BT on Si 10 nm B- BT on Si 15 nm
C – BT on mica 15 nm
Generation of coherent optical phonon A 1g and acoustic phonons
Pump 830 nm Probe 582 nm Transient reflectivity
Acoustic phonons derived from transient reflectivity
Ultrafast light-induced coherent optical and acoustic phonons in few quintuple layers of the topological insulator Bi2Te3 M. Weis, K. Balin, R. Rapacz, A. Nowak, M. Lejman, J. Szade, and P. Ruello Phys. Rev. B 92, 014301 – Published 14 July 2015
1551561571581591600
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Binding Energy (eV)
No
rma
lize
d I
nte
nsity
Fe/Bi2Te3/mika warstwa 0.5nm
Bi2Te3
Fe/Bi2Te3
Fe/Bi2Te3pochylona
5685695705715725735745755765775780
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Binding Energy (eV)
No
rma
lize
d I
nte
nsity
Fe/Bi2Te3/mika warstwa 0.5nm, linia Te 3d5/2
Bi2Te3
Fe/Bi2Te3
Fe/Bi2Te3pochylona
7027047067087107120
0.2
0.4
0.6
0.8
1
1.2
1.4
Binding Energy (eV)
No
rma
lize
d I
nte
nsity
Fe/Bi2Te3/mika warstwa 0.5nm, Fe 2p3/2
Bi2Te3
Fe/Bi2Te3
Fe/Bi2Te3pochylona
Film 0.5 nm Fe/Bi2Te3
Reaction Fe-Te at RT Bi metal layer is formed underneath FeTe
Bi2Te3 Bi2Te3
Fe FeTe Bi
M/BT reactions
3D Render of 129.69 () 3D Render of 208.69 () 3D Render of 152.68 () 3D Render of 152.88 ()3D Render of 129.69 () 3D Render of 208.69 () 3D Render of 152.68 () 3D Render of 152.88 ()3D Render of 129.69 () 3D Render of 208.69 () 3D Render of 152.68 () 3D Render of 152.88 ()
Eu+ Te- Bi- ~1
9n
m
ToFSIMS Time Of Flight Secondary Ion Mass Spectroscopy @Bi+, 30kV, 0.1pA, Fast Imaging Mode, Depth profiling - Cs sputtering at 250V
0 250 500 750 1000 1250 1500 1750 2000
100
1000
10000
100000
Inte
nsity
Sputter time [s]
Eu+
Te-
Bi-Mica
Eu1 63
x 102
25
35
45
55
65
CPS
1140 1130 1120
Bindi ng E nergy (eV)
Bi1 1
x 102
10
15
20
25
30
35
40
CPS
168 166 164 162 160 158 156 154
Bindi ng E nergy (eV)
Te1 32
x 102
20
30
40
50
60
70
80
90
CPS
580 570
Bindi ng E nergy (eV)
Bi4f Eu3d Te3d
Proces utleniania warstwy Eu/BT/mika
czas
Wnioski
Metoda MBE pozwala na uzyskanie dobrej jakości poli- i mononkrystalicznych warstw BixTey w zależności od podłoża
W warstwach osadzanych na Si (100) stwierdzono fazę Bi2Te3 oraz metaliczny Te lub superstrukturę Bi/BiTe w zależności od składu
Warstwy osadzane na mice są monokrystaliczne nawet dla grubości 5 nm
Spektroskopia fotoelektronów wykonana in-situ pozwala rozpoznać stany chemiczne pierwiastków i reakcje zachodzące na granicy warstw
Metoda lokalnego przewodnictwa AFM pozwoliła rozpoznać korelacje morfologii powierzchni i właściwośći elektrycznych
Metoda pump-probe femtosekundowej spektroskopii optycznej wykazała generację spójnych podłużnych fononów optycznych A1g(I) w warstwach zawierających tylko 10 QL
Współpraca
• Pascal Ruello – le Mans, France
• Mariusz Lejman – le Mans, France
• Katarzyna Balin – IF UŚ Chorzów
• Rafał Rapacz – IF UŚ Chorzów
• Marcin Wojtyniak - IF UŚ Chorzów
• Mateusz Weis – IF UŚ Chorzów
• Anna Nowak – IF UŚ Chorzów
• Bartosz Wilk – IF UŚ Chorzów
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