Spektroskopia fotoelektronów w zastosowaniu do izolatorow topologicznych

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1 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 Bi x Te y Polikrystaliczne warstwy Bi x Te y na Si(100) Monokrystaliczne warstwy Bi 2 Te 3 na mice Generacja fononów w cienkich warstwach Bi x Te y Podsumowanie

2 Photons: - energy: few ev-10 3 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 UPS Ultraviolet Photoelectron Spectroscopy XPS X-ray Photoelectron Spectroscopy a spectrum is formed, usually in function of binding energy - calculated with the use of work function of the spectrometer ESCA Electron Spectroscopy for Chemical Analysis RESPE Resonant Photoelectron Spectroscopy

3 J p ( h ) 2 S Golden Fermi rule p 2, S H PE i ( f i h ) photoelectric current H vol PE e m c e dipole interaction set of final possible quantum states A p one of the final electronic states with free electron of momentum p and N-1 electrons in atom frozen orbitals approximation f initial electronic state N 1 N 1 i energy conservation Koopmans theorem Binding energy derived from the PE spectrum is equal to the initial energy in a non-perturbed atom

4 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) S. Hüfner Photoelectron spectroscopy background peak position may be different from the orbital energy (relaxation) additional lines satellites are present

5 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 S. Hüfner Photoelectron spectroscopy 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 all elements can be detected except H and He integration of photoemission lines plus photoionization cross sections plus spectrometer transmition function

6 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

7 Zmiana czułości powierzchniowej: Zmiana geometrii Zmiana energii kinetycznej fotoelektronów przez: analizę innej linii fotoemisyjnej o innej energii zmianę energii fotonów

8 Surface Physics Laboratory at the Silesian Center for Education and Interdisciplinary Research in Chorzów ToF SIMS Time of Flight Secondary Ion Mass Spectrometer ION TOF 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 XPS, UPS Prevac/VG Scienta

9 Bulk: Topological insulator Bi2Te3 - Energy gap insulator (semiconductor) - Gap of about 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

10 According to Zhang et al for Bi 2 Se 3, point Chemical bonding Crystal field Spin-orbit

11 ARPES Angle Resolved Photoemission Spin Resolved ARPES

12 cording to Alpichshev et al Photoelectron spectroscopy Scanning tunelling spectroscopy

13 Studies of Bi x Te y 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

14 Surface Physics Laboratory at the Silesian Center for Education and Interdisciplinary Research in Chorzów ToF SIMS Time of Flight Secondary Ion Mass Spectrometer ION TOF 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 XPS, UPS Prevac/VG Scienta

15 LABORATORIES SURFACE PHYSICS LABORATORY MBE Molecular Beam Epitaxy Vacuum conditions during the growth process: UHV ~ mbar 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 ( ºC) 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 MULTILAYER DEPOSITION CO-DEPOSITION What we usually grow: Bi, Te, Eu, Mn, Fe, Mo, Cr, Au, Ag, Ta Typical growth rate Å/s, typical thicknesses 1-50nm SURFACE PHYSICS Chorzów ŚMCEBI, IF, UŚ

16 LABORATORIES SURFACE PHYSICS LABORATORY XPS (and UPS) X-Ray (and Ultraviolet) Photoelectron Spectroscopy (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) mm 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) Eu3d NANOPARTICLES FOR CATALYTIC APPLICATIONS EU-MN THIN FILMS - MULTILAYERED SYSTEM EU-MN THIN FILMS - MULTILAYERED SYSTEM Reversible valance transitions of europium x 10 4 Eu-Mn thin films grown on Mo Total thickness of Eu-Mn layer ~20nm 24 Eu 3d CPS EU 2+ EU Bin d i ng E nerg y (ev) CasaXP S ( Th i s st rin g can b e ed it ed in CasaXP S.D EF/P rin tfo o tn o te.txt) Chemical state identification Evolution of chemical state (during occurring processes) Depth profiling and atomic concentration calculations SURFACE PHYSICS Chorzów ŚMCEBI, IF, UŚ

17 Grazing angle XPS increase of the surface sensitivity analyser λ e - λ λ - IMFP XPS regime - VB states about 30 Å UPS regime about 1-2 Å TPP2M Quases by S. Tougaard

18 Bi x Te y on Si (100) Thickness nm Roughness 1-3 nm RHEED pattern AFM

19 XPS analysis Bi and Te core levels R. Rapacz, K. Balin, A. Nowak, J. Szade, J. of Cryst. Growth 401, (2014) VB

20 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

21 R.J. Cava, J. Huiwen, M.K. Fuccillo, Q.D. Gibson, Y.S. Hor, J. Mater. Chem. C 1 (2013) Superstructure phases of Bi solid solutions in Bi 2 Te 3 Metallic Te forms the layers on the surface

22 Bi 2 Te 3 on mica Thickness 5-30 nm Muscovite (KAl 2 (OH, F) 2 AlSi 3 O 10 )

23 LEED and AFM in lateral force mode Single crystalline films starting from 5 nm thickness

24 Bi 2 Te 3 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 Bi 2 Te 3 thin films on mica R. Rapacz, K. Balin, M. Wojtyniak and J. Szade Nanoscale, 2015,7, 16034

25 Local conductivity AFM

26 Topography Current I av = na ; V=5 mv All values less than 57 % were cut o (the na value). Measured current value did not depend on the height of terraces, but was constant (within 47 % of scale).

27 Ultrafast spectroscpy for selected films A BT on Si 10 nm B- BT on Si 15 nm C BT on mica 15 nm

28 Pump 830 nm Probe 582 nm Transient reflectivity Generation of coherent optical phonon A 1g and acoustic phonons

29 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, Published 14 July 2015

30 Normalized Intensity Normalized Intensity Normalized Intensity 1.6 Fe/Bi2Te3/mika warstwa 0.5nm 1.6 Fe/Bi2Te3/mika warstwa 0.5nm, linia Te 3d5/2 1.4 Fe/Bi2Te3 pochylona 1.4 Fe/Bi2Te3 pochylona Fe/Bi2Te Bi2Te3 0.6 Fe/Bi2Te Bi2Te Binding Energy (ev) Binding Energy (ev) Fe/Bi2Te3/mika warstwa 0.5nm, Fe 2p3/2 Bi2Te Fe/Bi2Te3 pochylona Film 0.5 nm Fe/Bi 2 Te 3 Reaction Fe-Te at RT Bi metal layer is formed underneath FeTe Fe/Bi2Te3 708 Binding Energy (ev) Fe Bi FeTe Bi 2 Te 3 Bi 2 Te 3 M/BT reactions

31 ~19nm Intensity ToFSIMS Time Of Flight Secondary Ion Mass 30kV, 0.1pA, Fast Imaging Mode, Depth profiling - Cs sputtering at 250V Bi - Te - Eu Eu+ Te- Bi- Mica Sputter time [s]

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34 CPS CPS CPS Bi4f Te3d Eu3d czas x x 10 2 x Bindi ng E nergy (ev) Bindi ng E nergy (ev) Bindi ng E nergy (ev) Proces utleniania warstwy Eu/BT/mika

35 Wnioski Metoda MBE pozwala na uzyskanie dobrej jakości poli- i mononkrystalicznych warstw Bi x Te y w zależności od podłoża W warstwach osadzanych na Si (100) stwierdzono fazę Bi 2 Te 3 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

36 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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