Thermal Radiation Scanning Tunneling Microscopy

1. Yannick De Wilde, Florian Formanek, Remi Carminati, Boris Gralak, Paul-Arthur Lemoine, Karl Joulain, Jean-Philippe Mulet, Yong Chen, Jean-Jacques Greffet Nature, 444, 740, 7 December 2006 Presented by: F. Hakan Köklü Thermal Radiation Scanning Tunneling Microscopy

2. Outline • Scanning tunnelling microscopy basics • Thermal radiation scanning tunnelling microscopy • Analogy between TRSTM and STM • Imaging results – artefact free imaging • Verification of surface states through imaging • Origin of the signal • Conclusions

3. Scanning Tunnelling Microscopy (STM) • Tunnelling current through vacuum • Constant current mode • Imaging as a function of voltage • Electronic local density of states (eLDOS) 1http://en.wikipedia.org/wiki/Scanning_tunneling_microscope 2 J. Tersoff, D. R. Hamann, Phys. Rev. B., 31, 805 (1985)

4. Thermal Scanning Tunnelling Microscopy (TRSTM) • Near field optical microscopy using thermal wavelengths – no external illumination • Includes an atomic force microscopy used in dynamic mode • Electromagnetic local density of states (EM-LDOS) 3 K.Joulain, R. Carminati, J-P. Mulet, J-J. Greffet, Phys. Rev. B, 68, 245405 (2003)

5. EM-LDOS Bose – Einstein statistics Measurement at chosen wavelength Phonon and plasmon enhanced photon scattering Analogy between STM and TRSTM • eLDOS • Fermi – Dirac statistics • Measurement at the Fermi energy level • Electrons 4 R. Hillenbrand, T. Taubner, K. Keilmann, Nature, 418, 159, (2002) 5 R. Carminati, J. J. Saenz, Phys. Rew. Lett., 84, 5156 (2000)

6. Sample Images • Common optical microscope • Atomic force microscope • TRSTM

7. Origin of the TRSTM Signal Atomic force microscopy TRSTM image when the tip is scanning 5μm above TRSTM image when the tip and the sample are at room temperature

8. EM – LDOS Measurement TRSTM images Numerical calculation of EM – LDOS for different heights and stripe widths Spatial coherence of thermal emission

9. z – dependence • Most of the contribution comes from a small part of the tip. • Tip geometry • Demodulation frequency • The contributing part is found to be • 3μ for a demodulation frequency of Ω • 200nm for a demodulation frequency of 2Ω

10. z – dependence Image taken with a demodulation frequency of 2Ω Image taken with a band pass filter below the SiC resonance Image taken on a SiO2 substrate

11. EM – LDOS at the Boundaries Cavity for surface plasmons

12. Conclusions • Thermal near – field optical microscopy with 100nm resolution – 2 orders of magnitude better than far – field microscopy. • First direct experimental demonstration of spatial coherence of thermal emission in the near field. • Qualitative measurement of EM – LDOS.

13. Questions?

14. Topographical artefact