Electrostatic force microscopy

Other electrodeless measurements can be made using electrostatic force microscopy, from which it has been deduced [75, 76] that A-DNA exhibits very poor conductance—a conductivity of less than 10 S/cm was suggested. Indeed, no evidence for significant conduction was seen either in A-DNA or in poly(GC). 

The term electrical force microscopy or electrostatic force microscopy (EFM) is used if the detection of the electrical properties like surface potential or charge is based on a force, leading to a d.c. cantilever bending or to a change in the vibration amplitude or frequency of a vibrating cantilever. 

The detection and compensation of the a.c. current is the classical Kelvin method however, the resulting electrostatic forces, i.e. the corresponding cantilever bending, can also be used to establish a potential sensitive feedback. If an a.c. voltage is applied between the tip and the back electrode of the sample instead of using the dither piezo, the Maxwell stress microscopy (MSM) [379-381] or the electrostatic force microscopy (EFM) [317, 382-393] can be performed. 

Lei, C.H. et al.. Conductivity of macromolecular networks measured by electrostatic force microscopy, Appl. Phys. Lett. 83, 482-484, 2003. 

Zdrojek, M. et al.. Comment on Electrostatics of individual single-waUed carbon nanombes investigated by electrostatic force microscopy, Phys. Rev. Lett. 96, 39703,... 

Hassenkam, T., Greve, D.R., and Bjomhohn, T., Direct visualization of the nanoscale morphology of conducting polythiophene monolayers studied by electrostatic force microscopy, Adv. Mater. 13, 631-634, 2001. 

Bergasa F and Saenz J J 1992 Is it possible to observe biological macromolecules by electrostatic force microscopy Ultramicroscopy 42-44 1189... 

D.C. Coffey and D.S. Ginger, Time-resolved electrostatic force microscopy of polymer solar cells. Nat. Mat., S, 735 (2006). 

T.S. Jespersen and J. Nygard, Mapping of individual carhon nanotubes in polymer/nanotube composites using electrostatic force microscopy, App. Phys. Lett., 90,183108-183110 (2007). 

Analogously, in electrostatic force microscopy (EFM) electrostatic forces can be used in the regulation feedback [228, 229], Ferroelectric media can be polarized by a voltage applied to a conductive AFM probe in contact (writing). The surface polarization leads to a long range force that can be detected via interaction with the probe at low bias. This interaction force is used as feedback in noncontact mode (reading). 

Electrostatic Force Microscopy (EFM) allows to obtain information on the surface electrical properties of materials by measuring electric forces between a charged tip and the surface. It is particularly suitable for the study and manipulation of ferroelectric thin films with large surface charge. Interestingly, an EFM can also be used to study the surface properties of dielectric materials, that are polarized by the electric field of the tip. In this mode of operation, the EFM is sometimes called Polarization Force Microscope and can be used to study and image even air-liquid interfaces [64]. 

We have shown how Electrostatic Force Microscopy can be an extremely useful tool to investigate and to modify the electric properties of sample surfaces on a microscopic and even nanoscopic scale and we have presented a phenomenological model to help relating the experimental data to the material properties. Ferroelectric domains can locally be reoriented and their time evolution can be followed, as was shown for PZT. We have also demonstrated how the ferroelectric polymer PVDF-TrFe could be locally modified which can be used to locally vary the optical properties of a LC cell. Finally, we have demonstrated that rubbing polymer substrates can indeed result in electrostatic charging, in particular for PMMA and PI, while no charging is found for PVA. 

M.P. De Santo, R. Barberi and L.M. Blinov would like to thank Taylor and Francis, Ltd, for granting permission to reprint figures from the paper Rubbing-induced charge domains observed by electrostatic force microscopy effect on liquid crystal alignment by I.H.Bechtold, M.P. De Santo, J.J.Bonvent, E.A.Oliveira, R.Barberi and Th.Rasing, Liquid Crystals, (2003), Vol. 30, No. 5, pp. 591-598. 

Electrostatic Force Microscopy Electrostatic force microscopy (EFM) works on the same two-pass measurement technique as MFM. Rather than measure the magnetic force, in EFM a voltage is applied between the tip and the surface. Any deflection in the cantilever can be attributed to locally charged domains on the sample surface. EFM can be used to map electrostatic fields in electronic devices when switched on and off in a technique known as voltage probing. 

Water-dispersable, nanoscaled PAni powder was synthesized and dispersed at Ormecon. The particle size distribution was measured by laser Doppler technique with a Microtrac UPA 150 particle analyzer. Investigations on the morphology of PAni films were made at the University of Copenhagen using atomic force microscopy (AFM) and electrostatic force microscopy (EFM). Pictures were made by Tue Hassenkam with a DI Nanoscope Ilia equipped with an extender module. 

Local Piezoelectric Response and Surface Potential of Dielectric AND Ferroelectric Langmuir-Blodgett Films Studied by Electrostatic Force Microscopy... 

Keywords electrostatic force microscopy, LB films, piezo-effects, ferroelectricity. 

A comparative study of ultrathin dielectric (an azo-compound) and ferroelectric (copolymer P(VDF-TrFE)) Langmuir-Blodgett (LB) films has been carried out by Electrostatic Force Microscopy (EFM). Films were poled locally by a strong d.c. field applied between a conductive tip of an Atomic Force Microscope (AFM) and the bottom A1 electrode. The electrically poled domain was studied by EFM using a weak a.c. electric field and a lock-in amplifier technique. Two modes, a contact and non-contact ones, allowed for the measurement of field a in the air gap between the film and the tip and the piezoelectric distortion of the film due to the d.c. field aligned spontaneous polarization. Simultaneously the topographic relief of the same area was imaged. The results confirm unequivocally a possibility to switch ferroelectric LB film locally by an AFM tip. 

The structural unit of the copolymer -(-CH2-CF2)n-(-CF2-CHF-)m- contains n and m corresponding monomer links. The ferroelectric properties are attributed to transverse dipole moments, formed by positive hydrogen and negative fluorine atoms. Below the temperature of the ferroelectric phase transition (about 80-100°C), the main chain of the polymer is in all-trans form and the dipole moments are parallel, at least, within ferroelectric domains separated fi-om each other by domain walls. The ferroelectric switching is due to an electric field induced, collective flip-flop of the dipoles around the backbone of the polymer. Several recent studies were devoted to a local ferroelectric switching of the domains in cast P(VDF-TrFE) films [6-8]. To this effect, a powerful technique, called Electrostatic Force Microscopy (EFM) [9] was used which was developed for studies of domains in thin ferroelectric films, see papers [10, 11] and references therein. 

EFM Electrostatic force microscopy FAES Flame atomic emission... 

Writing polarization Figure 1.7 Schematic of electrostatic force microscopy (EFM). The electric potential applied to the BaTiOs nanoparticles using a conductive AFM tip has been varied to test its nanometer-scale ferroelectric property. In these experiments, a potential was... 

---