Browsing by Subject "Electrostatic force microscopy"

Now showing 1 - 3 of 3

Open Access
Electrostatic force spectroscopy of near surface localized states
(Institute of Physics Publishing Ltd., 2005) Dâna, A.; Yamamoto, Y.
Electrostatic force microscopy at cryogenic temperatures is used to probe the electrostatic interaction of a conductive atomic force microscopy tip and electronic charges trapped in localized states in an insulating layer on a semiconductor. Measurement of the frequency shift of the cantilever as a function of tip-sample bias voltage shows discrete peaks at certain voltages when the tip is located near trap centres. These discrete changes in frequency are attributed to one by one filling of individual electronic states when the quantized energies traverse the substrate conduction band Fermi energy as the tip-sample voltage is increased. Theoretical analysis of the experiment suggests that such a measurement of the cantilever frequency shift as a function of bias voltage can be interpreted as an AC force measurement, from which spectroscopic information about the location and energy of localized states can be deduced. Experimental results from the study of a sample with InAs quantum dots as trap centres are presented.
Open Access
Reversible electrical reduction and oxidation of graphene oxide
(American Chemical Society, 2011) Ekiz, O. O.; Ürel, M.; Güner, H.; Mizrak, A. K.; Dâna, A.
We demonstrate that graphene oxide can be reversibly reduced and oxidized using electrical stimulus. Controlled reduction and oxidation in two-terminal devices containing multilayer graphene oxide films are shown to result in switching between partially reduced graphene oxide and graphene, a process which modifies the electronic and optical properties. High-resolution tunneling current and electrostatic force imaging reveal that graphene oxide islands are formed on multilayer graphene, turning graphene into a self-assembled heterostructure random nanomesh. Charge storage and resistive switching behavior is observed in two-terminal devices made of multilayer graphene oxide films, correlated with electrochromic effects. Tip-induced reduction and oxidation are also demonstrated. Results are discussed in terms of thermodynamics of oxidation and reduction reactions. © 2011 American Chemical Society.
Open Access
Scanning probe microscopy for optoelectronic characterization at the nanoscale
(2010) Ürel, Mustafa
In this work, we propose methods for electrical characterization of nanostructured surfaces using electrostatic force and tunneling current measurements in scanning probe microscopy. Resolution smaller than 10 nm in electrostatic force microscopy (EFM) is attained and reasons for this attainment is explained in terms of the tip-sample capacitance and mechanical vibrations of tip design. Dynamic measurements are done in EFM using a lumped model for tip-sample electrostatic interaction instead of a simple tip-sample capacitance model. Surface photovoltage measurements are done and assured in EFM using frequency response techniques. Also, combining tunneling current measurements by EFM measurements, optoelectonic properties of graphene/graphene oxide samples are characterized.