Imaging of Oxide Charges Using The easyPLL From Nanosurf

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Constant Force Gradient Images

Contact Potential Difference


Ultrathin 2.5nm high-k aluminium oxide (Al2O3) films on p-type silicon (001) deposited by atomic layer deposition (ALD) were investigated with noncontact atomic force microscopy (NC-AFM) in ultrahigh vacuum, using a conductive tip.

Constant Force Gradient Images

Constant force gradient images revealed the presence of oxide charges and experimental observations as different tip-sample potentiality were compared with calculations of the electric force gradient based on a spherical tip model. this model could be substantially improved by the incorporation of the image of the tip in the semiconductor substrate.

Contact Potential Difference

Based on the signals of different oxide charges observed, a homogenous depth distribution of those charges was derived. Application of a potential difference between sample and tip was found to result in a net electric force depending on the contact potential difference (CPD) and effective tip-sample capacitance, which depends on the depletion or accumulation layer that is induced by the bias voltage. CPD images could be constructed from height-voltage spectra with active feedback.

AZoNano - The A to Z of Nanotechnology Online - 1ìm x 1ìm topography image of a 2.5 nm Al2O3 film on Si

Figure 1. 1ìm x 1ìm topography image of a 2.5 nm Al2O3 film on Si

Apart from oxide charges large-scale (150 - 300 nm lateral size) and small-scale (50 - 100 nm) CPD fluctuations were observed, the latter showing a high degree of correlation with topography features. This correlation might be a result from the surface-inhibited growth mode of the investigated layers.

Source: Nanosurf

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