Contact person: Dr. Mihai Mihaila
Introduced recently [M. Mihaila, US Patent, US 7612551 B2, (2009)], the fluctuation spectroscopy is a method capable to measure the atomic vibration (phonon) spectrum of a conducting material. In addition, the local vibration modes introduced by impurities or crystallographic defects can be observed.
To obtain the phonon spectrum, one measures the frequency spectrum of a fluctuating voltage which develops across the terminals of a resistor/film fabricated from the material whose phonon spectrum is intended to be observed. The measurement system developed in the Nanobiotechnology Laboratory is schematically presented in the attached figure.
The system is controlled by a computer, which is additionally used for data acquisition and signal processing. Current is injected into the resistor to be investigated and the voltage developed across its terminals is amplified and Fourier transformed. In this way, the noise spectrum, SV(f), at a given voltage is obtained. The final result is the dependence of the noise intensity on voltage. Usually, it presents sharp peaks located at voltages corresponding to the phonon energies of the investigated material.
The new method is an electrical one and can be applied at room temperature. It does not require fabrication of a special device and is useful to investigate single small dimensional systems (e.g.: nanowires, nanotubes, etc.).