A nearly optimal tip enhanced raman spectroscopy system for UHV

​

The signal to noise ratio in a Tip Enhanced Raman Spectroscopy (TERS) measurement is by nature very low, even though the tip amplifies the Raman signal by many orders of magnitude. This is due to the high lateral resolution and the anyway low intensity of a Raman emission. To keep integration times for the optical measurement low, the optical system must have an as high as possible numerical aperture. The same applies to apertureless SNOM measurements using the same mechanical setup. The sketch on the right shows a setup with a numerical aperture of nearly 1. Almost the whole half sphere above the sample is used as light path.

Such a system working in ultra high vaccum was designed by us in close cooperation with the department of physical chemistry of the Fritz-Haber-Institut in Berlin, Germany (former director was Prof. G. Ertl). The system has following properties:

• • A 5 axis movable stage with a resolution of about 100 nm allows exact mirror positioning to perfectly align STM tip and focal point.
  • Samples and STM tips can be exchanged without breaking the vacuum and without a risk of damage by a specially designed transfer mechanism.
  • For vibrational damping purposes the whole optical and STM setup was designed on a free swinging platform. Light transfer is realized via glass fibers.
  • The STM provides atomic resolution in all three dimensions