Introduction
The local probe of matter-light interaction is recently advancing due to the development of scanning probe techniques. Approaching a metallic tip to surfaces allows to dramatically enhance the light scattering cross section. Pronounced nonlinearities, single molecule spectroscopy with a lateral resolution of 10nm and second harmonic generation are demonstrated.
TERS setup
Our setup consists of separate scanning and coarse stepping stages for the tip and the sample. The TERS setup is attached to our high efficiency Raman setup. All components are prepared for use at low temperature and high magnetic fields.
The scanner and stepper including controler and basic software have been delivered from attocube (ANC150 and 200). This saved quite some time. The tip design is used as developed by F.J. Giessibl (Regensburg). The tips are prepared/edged inhouse by T. Lampe. The space for the setup is limited to the sample space of the cryostat. Therefore we presently investigate different horizontal and vertical tip arrangements as well as glues.
The tip-sample distance is controlled by a frequency modulation scheme using the phase shift of the oscillating cantilever as the input of a digital two-phase Log-In (Ithaco 3961B) that directly calculates A*cos(phi), with the amplitude A and the phase shift (phi).
This signal is integrated and feed back to the extremely stable signal source (Rohde&Schwarz, SMY01). The electronic circuit and integrator corresponds to several OP amps and a resistor/capacitor network. Recently we use an SRS SIM960 PID controller to stabilize the tip-surface separation.
Force probe, AFM tip on a quartz
tuning fork.
(T. Lampe, IPKM, TUBS; Design F. J. Giessibl,
Augsburg)
Initial setup in an early stage (November 2006) including the coarse sample approach (Attocube) und distance control. The AFM head is fixed on an optical rail on top of the electronics to be attached to the Raman spectrometer. (V. Gnezdilov, IPKM, TUBS)
Seth White with the more recent
setup: The tuning fork is tuned!
This includes the integrator and preamp from SRS.
Low temperature setup
For low temperatures we use a Cryovac large diameter cryostat (previously installed for the large pressure cell). The large aperture and size of the window allow an easy access to the measurement unit.
