Thermal Radiation Scanning Tunneling Microscopy

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

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

Scanning Tunnelling Microscopy (STM)

● Tunnelling current through vacuum

● Constant current mode

● Imaging as a function of voltage

● Electronic local density of states (eLDOS)

1 http://en.wikipedia.org/wiki/Scanning_tunneling_microscope2 J. Tersoff, D. R. Hamann, Phys. Rev. B., 31, 805 (1985)

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)

Analogy between STM and TRSTM

● eLDOS● Fermi – Dirac

statistics● Measurement at the

Fermi energy level● Electrons

● EM-LDOS● Bose – Einstein

statistics● Measurement at

chosen wavelength● Phonon and plasmon

enhanced photon scattering

4 R. Hillenbrand, T. Taubner, K. Keilmann, Nature, 418, 159, (2002)5 R. Carminati, J. J. Saenz, Phys. Rew. Lett., 84, 5156 (2000)

Sample Images

● Common optical microscope

● Atomic force microscope

● TRSTM

Origin of the TRSTM Signal

(a) Atomic force microscopy(b) TRSTM image when the tip is scanning 5μm above(c) TRSTM image when the tip and the sample are at room temperature

EM – LDOS Measurement

(a) TRSTM images(b) Numerical calculation of EM – LDOS for different heights and stripe widths

Spatial coherence of thermal emission

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

z – dependence

(a) Image taken with a demodulation frequency of 2Ω(b) Image taken with a band pass filter below the SiC resonance(c) Image taken on a SiO2 substrate

EM – LDOS at the Boundaries

Cavity for surface plasmons

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.

Questions?

Topographical artefact