nano-Dielectric Spectroscopy set-up



The overwhelming interest in nanostructured materials during the last years has highlighted the lack of spatial resolution in BDS measurements. As a result, an experimental method that combines the BDS advantages with the outstanding spatial resolution of the Atomic Force Microscope (AFM) has been developed by combining standard AFM equipments in with a dedicated lock-in amplifier.
In this approach (see Figure below), a sinusoidal voltage Vac(f) is applied to the AFM conductive probe, while maintained a few nanometers above the sample, and the harmonic components of the photodiode signal at 2f (the oscillation amplitude, |VPh|, and the phase) are measured. The characteristics of this signal are originated in the electrical properties of the sample film, including dissipative effects.

This set-up allows to determine the local dielectric relaxation behavior of thin films, with up to 20 nm lateral resolution, in a frequency range from 1 to 1MHz.

INSTRUMENT CHARACTERISTICS

Atomic Force Microscope: MultiMode Bruker

  • Temperature range 260-450 K, stability better than 1 K


Low-noise Lock-in amplifier: SRS865A SRS

  • Frequency range: 1e-3 - 4e6 Hz, 10MOhm input impedance

  •  Noise: 2.5 nV/sqr(Hz) @ 1 kHz and 10 nV/sqr(Hz) @ 10 Hz


Samples: Thin films on conductive support

  • A topographic AFM image is adquired and afterwards the dielectric relaxation spectrum in a given sample location is obtained by placing the conductive tip-apex at a small vertical distance from the film surface, typically in the range 10-30 nm.

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