Hemantha Kumar Wickramasinghe

Apertureless near field optical microscope

We demonstrate a new method whereby near-field optical microscope resolution can be extended to the nanometer regime. The technique is based on measuring the modulation of the scattered electric field from the end of a sharp silicon tip as it is stabilized and scanned in close proximity to a sample surface. Our initial results demonstrate resolution in the 3 nm range--comparable to what can be achieved with typical attractive mode atomic force microscopes. Theoretical considerations predict that the ultimate resolution achievable with this approach could be close to the atomic level.

Scanning Interferometric Apertureless Microscopy: Optical Imaging at 10 Angstrom Resolution

Interferometric near-field optical microscopy achieving a resolution of 10 angstroms is demonstrated. The scattered electric field variation caused by a vibrating probe tip in close proximity to a sample surface is measured by encoding it as a modulation in the optical phase of one arm of an interferometer. Unlike in regular near-field optical microscopes, where the contrast results from a weak source (or aperture) dipole interacting with the polarizability of the sample, the present form of imaging relies on a fundamentally different contrast mechanism: sensing the dipole-dipole coupling of two externally driven dipoles (the tip and sample dipoles) as their spacing is modulated.

Surface investigations with a Kelvin probe force microscope

Abstract The contact potential difference between a reference tip and sample can be measured with high spatial resolution using a modified version of the scanning force microscope. The instrument is comparable to a Kelvin probe but allows the simultaneous imaging of contact potential difference and, in addition, topography. The contact potential difference is not only dependent on the material, i.e. work function, but also on the condition of the surface. Therefore changes in contamination, stress, temperature, the crystalline structure, oxide-layer properties and (trapped) charges can significantly alter the contact potential difference. Initial results concerning these parameters will be presented.