Surface and Interface Properties of Semiconductor Quantum Dots by Raman Spectroscopy

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1 Surface and Interface Properties of Semiconductor Quantum Dots by Raman Spectroscopy Austin 30. Juni 2015 Dietrich R.T. Zahn chemnitz.de/physik/hlph

2 Contents Ternary QDs in Glass Matrix Colloidal CdSe QDs QDs Prepared by Langmuir Blodgett Technique Enhanced Raman Spectroscopy

3 Raman Spectroscopy (from Wolfgang Richter)

4 Most Important Contributors Alexander Milekhin Institute of Semiconductor Physics Novosibirsk Volodymyr Dzhagan Institute of Semiconductor Physics, Kiev now TU Chemnitz Yuriy Azhniuk Institute of Electron Physics, Uzhhorod Oleksandr Stroyuk and Alexandra Raevskaya Institute of Physical Chemistry, Kiev

5 Properties of Semiconductor Quantum Dots Size-dependence of bandgap and other properties. Typical compounds: CdSe, CdS, ZnO, PbS CuInS2, CuxS, Cu2ZnSnS4 Ge, Si Typical size: 1-10 nm

6 CdSe Quantum Dots

7 Quantum Dot LEDs and Displays CES 2015: What the Heck Are Quantum Dots? The next big thing for 2015, we ll likely be told at CES, will be the quantum dot TV. Sounds pretty space agey, for sure.

8 Applications: Photovoltaics

9 Contents Ternary QDs in Glass Matrix Colloidal CdSe QDs QDs Prepared by Langmuir Blodgett Technique Enhanced Raman Spectroscopy

10 Ternary CdSSe Quantum Dots in a Glass Matrix 2.8 nm 2.7 nm 2.5 nm 2.3 nm 7.5 nm 4.8 nm 3.1 nm 2.3 nm Average radii can be derived from the absorption spectra using the effective mass approximation. (A.Efros and Al.Efros, 1979)

11 Determination of the CdS1 xsex Quantum Dot Composition Resonant Raman scattering conditions are required to record the Raman spectra of diluted nanocrystals since their amount in the total scattering volume is very small (usually below 1 %) LO1 CdSe-like phonon LO2 CdS-like phonon Accuracy in x: 0.03

12 Influence of Glass Matrix Pressure Nanocrystals grown in a glass matrix are under additional pressure due to the difference of thermal expansion coefficients of the QDs and the matrix pressure 0.5 GPa phonon frequency increase by 2 4 cm 1

13 Phonon Confinement r = 2.2 nm r = 4.8 nm I( ) j A j dqc( 0, q) j ( q) 0 / 2 Raman shift / cm -1 I.H. Campbell, P.M. Fauchet, Sol. St. Comm. 58, 739 (1986) 2

14 Surface Phonons in CdS1 xsex Nanocrystals LO with confinement taken into account surface phonon contribution

15 Contents Ternary QDs in Glass Matrix Colloidal CdSe QDs QDs Prepared by Langmuir Blodgett Technique Enhanced Raman Spectroscopy

16 Resonant Raman Spectra in CdSe Quantum Dots Detailed Structure of the Spectrum Intensity / arb.un. Intensity / arb.un. TO 173 (14) 20 nm 5 nm LO+SO 400 (22) SO 196 (20) LO 206 (10) Raman shift / cm -1 2LO 412 (15) HFS HFS Types of vibrational modes: TO transversal optical SO surface optical LO longitudinal optical HFS high-frequency shoulder; possible origin: (i) phonon DOS; (ii) LO+acoustic modes; (iii) surface Se vibrations Raman shift / cm -1 V. Dzhagan, M. Valakh, A. Milekhin, D.R.T. Zahn, E. Cassette, C. Javaux, T. Pons, B. Dubertret. J. Phys. Chem. C 117 (2013)18225

17 Core/Shell Quantum Dots Core Shell QDs CdS CdSe Reasons to form core/shell: improved stability; increased PL efficiency; reduced blinking (intermittency of the photon emission by single NCs); reduced Auger recombination and enhanced multiple exciton recombination.

18 Raman Spectra of CdSe/CdS Core/Shell QDs 1 nm CdS shell 3 nm CdS shell V. Dzhagan, M. Valakh, A. Milekhin, D.R.T. Zahn, E. Cassette, C. Javaux, T. Pons, B. Dubertret. J. Phys. Chem. C 117 (2013)18225

19 Effect of the Inorganic Shell on the Phonon Spectra Intensity, arb. un. LO CdSe CdSe CdSe/ZnS T=100K exc =442 nm Narrowing ofthe core phonon peak upon shel deposition indicates the increase ofthe phonon lifetime. 2LO CdSe Raman shift, cm -1 V.M. Dzhagan, M.Ya. Valakh, A.E. Raevskaya, A.L. Stroyuk, S.Ya. Kuchmiy, D.R.T. Zahn. Nanotechnology 18 (2007) V.M. Dzhagan, M.Ya. Valakh, O.E. Raevska, O.L. Stroyuk, S.Ya Kuchmiy, and D.R.T Zahn. Nanotechnology 20 (2009)

20 Ultra small QDs (magic size clusters) Number of atoms = 64, e.g. Cd 32 S 32 d = nm A.E. Raevskaya, O. L. Stroyuk, D.I. Solonenko, V.M. Dzhagan, D. Lehmann, S.Ya Kuchmiy, V.F. Plyusnin, D.R.T. Zahn, Journal of Nanoparticle Research (2014) 16:2650

21 Raman Spectra of normal vs. ultra small QDs S. Kilina et al. J. Am. Chem. Soc. 2009, 131, V.M. Dzhagan, M.Ya. Valakh, C. Himcinschi, A.G. Milekhin, D. Solonenko, N.A. Yeryukov, O.E. Raevskaya, O.L. Stroyuk, D.R.T. Zahn, J. Phys. Chem. C, (2014) 118 (33), 19492

22 Contents Ternary QDs in Glass Matrix Colloidal CdSe QDs QDs Prepared by Langmuir Blodgett Technique Enhanced Raman Spectroscopy

23 Quantum Dot Formation: Langmuir Blodgett Technology

24 Quantum Dot Formation: Langmuir Blodgett Technology Molecule of metal behenate oxygen carbon metal Monolayers of organic material are deposited from the surface of a liquid onto a solid substrate by immersing the substrate into the liquid.

25 Quantum Dot Formation: Langmuir Blodgett Technology NCs NC materials: Sulphur Selenium thermal annealing CdS(Se), PbS(Se), ZnS(Se), CuS(Se), Ag2S, ZnO

26 CdSe QDs: Scanning Electron Microscopy 20 MLs of organics, T =150 С CdSe NCs 1 МL CdSe NC size 6nm 1 monolayer of NCs

27 SEM images of mesa structures having different areal densities of PbSe NCs (light spots): (a, b) NCs/μm2; (c, d) 100 NCs/μm2; and (e, f) 15 NCs/μm2. The rectangular areas shown in panels a, c, and e are plotted enlarged in panels b, d, and f, respectively. The laser spots (illuminated areas) are shown schematically by circles. Published in: Alexander G. Milekhin; Nikolay A. Yeryukov; Larisa L. Sveshnikova; Tatyana A. Duda; Sergey S. Kosolobov; Alexander V. Latyshev; Nikolay V. Surovtsev; Sergey V. Adichtchev; Cameliu Himcinschi; Eduard I. Zenkevich; Wen-Bin Jian; Dietrich R. T. Zahn; J. Phys. Chem. C 2012, 116, DOI: /jp210720v Copyright 2012 American Chemical Society

28 Room temperature micro-raman spectra of (curve 1) 3-dimensional PbSe NC layers measured with nm and (curves 2 4) PbSe NC single layers with different NC densities measured with nm. Open circles and thin dashed lines represent the results of fitting with Lorentzian line shapes. Vertical dashed lines are guides to the eye. Published in: Alexander G. Milekhin; Nikolay A. Yeryukov; Larisa L. Sveshnikova; Tatyana A. Duda; Sergey S. Kosolobov; Alexander V. Latyshev; Nikolay V. Surovtsev; Sergey V. Adichtchev; Cameliu Himcinschi; Eduard I. Zenkevich; Wen-Bin Jian; Dietrich R. T. Zahn; J. Phys. Chem. C 2012, 116, DOI: /jp210720v Copyright 2012 American Chemical Society

29 Contents Ternary QDs in Glass Matrix Colloidal CdSe QDs QDs Prepared by Langmuir Blodgett Technique Enhanced Raman Spectroscopy

30 Conventional vs Resonant Raman Scattering by QDs ZnS NCs ZnO NCs Raman intensity/ cts/mw/s 2,5 2,0 1,5 1,0 0,5 0,0 LO LO(X) +TA(X) x100 T=300K =325nm =514.5nm 2LO Raman shift/ cm -1 Raman intensity/ a.u. 1LO(A 1 ) T=300K 4 x x Raman shift/ cm -1 enhancement factor of 10 3

31 SERS by QDs on Arrays of Gold Nanoclusters Fabrication of Au nanocluster arrays NC formation 31

32 SERS Substrates: Au Nanocluster Arrays 10µm

33 SERS Substrates: Au Nanocluster Arrays LSP resonance energy decreases with increasing Au nanocluster size D=110nm 130nm 150nm Milekhin et al., Thin Solid Films (2013)

34 SERS Substrates: Au Nanocluster Arrays CdSe 1ML (6nm) SERS enhancement factor is at least 2x103

35 Polarization Dependent Enhancement of SERS in Au Dimer Arrays d NC =90 nm gap=10nm P P SERS by optical phonons in CdSe QDs on the array of Au dimers is polarization dependent

36 CdSe QDs near single Au Dimers P 100 nm

37 Raman Spectroscopy on QDs delivers: Composition Strain Intermixing at Interfaces Surface and Interface Contributions Electron Phonon Coupling Phonon Lifetime Single QD Spectra Published in: Volodymyr M. Dzhagan; Mykhailo Ya. Valakh; Alexander G. Milekhin; Nikolay A. Yeryukov; Dietrich R.T. Zahn; Elsa Cassette; Thomas Pons; Benoit Dubertret; J. Phys. Chem. C 2013, 117, DOI: /jp Copyright 2013 American Chemical Society

38 Financial Support

39 Semiconductor Physics Group Volodymyr Dzhagan Alexander Milekhin