Experimental Indication of Quantum Mechanical Effects in Surface Enhanced IR-Spectroscopy?
The conduction electrons of metal nanoparticles can be collectively excited by incident electromagnetic radiation. Their resonance frequency strongly depends on the geometric dimensions of the particles and can be tuned from the classical radio frequencies up to the visible range. Such resonantly excited localized surface plasmon resonances (LSPR) are accompanied by an electromagnetic nearfield enhancement which is concentrated at the surface. In the infrared (IR) spectral range these huge local fields can be applied to the enhancement of infrared vibrations of molecules. Using this technique, which is called surface enhanced infrared spectroscopy (SEIRS), with gold nanostripes, attomol sensitivity has been achieved .
In this contribution we show first results of the resonant signal enhancement of the carbon monoxide (CO) stretching vibration of physisorbed CO multilayers on micrometer-long gold nanoantennas on silicon substrates under ultrahigh vacuum (UHV) conditions. We cooled the sample to about 18 K to allow multilayer adsorption of CO gas.
The preliminary results show signal changes with increasing CO layer thickness which exhibit a behavior differing from classical expectations and are in accord to recent quantum mechanical predictions . In the near future we will conduct systematic experiments to prove the origin of these deviations.
KeywordsCarbon Monoxide Radio Frequency Silicon Substrate Metal Nanoparticles Electromagnetic Radiation