Nanoscale dielectrics

Scientists have manipulating materials such as nanoparticles, single molecules and atoms, in their natural environment by using new generation microscopes to explore the morphology of nanoscale objects. But there are still major hurdles to overcome in measuring the mechanical, chemical, electrical and thermal properties that make each object unique. Scientists working with biological complexes at the nanoscale use chemical labeling by incorporating a visible substance, such as fluorescent dye, into the target object to detect its presence and physical distribution often giving misleading results.
Dielectric materials of nanoscale dimensions have aroused considerable interest. For examples in the semiconductor industry the thickness of gate oxide dielectric material is reaching nanoscale dimensions and the high energy density capacitor industry is currently considering dielectric composites with a polymer host matrix filled with inorganic dielectric nanoparticles or polarizable organic molecules. For the electronic and dielectric properties of materials in the nano-regime surface and interface effects play a dominant role.
Dielectric constant
All objects exhibit a characteristic ‘dielectric constant’, or permittivity, which gives an indication of how the material they are made of reacts to an applied electric field.
In biology, there is also a growing interest in determining the dielectric constant at the nanoscale. Here, the property plays a key role in processes such as membrane potential formation, action potential propagation, and ion membrane transport. Standard thin film characterization techniques are not suited for this purpose as they probe large-areas of the sample.
The local dielectric permittivity of thin films at the nanoscale can be quantitatively measured using by  Electrostatic Force Microscopy based on the detection of the local electric force gradient at different values of the tip sample distance. The value of the dielectric permittivity is then calculated by fitting the experimental points using the Equivalent Charge Method.
Dielectric properties are highly dependent on the behavior of the counter-anions within the film, specifically their position and motion under applied electric fields.
New technique
Scientists at the University of Barcelona (UB) and the Institute for Bioengineering of Catalonia (IBEC), in collaboration with the Centro National de Biotecnologia (CNB-CSIC) in Madrid, have perfected a new technique that uses an electrostatic force microscope (EFM) to unambiguously identify nano-objects with no need for labels. By using EFM, the researchers applied the electric field to the nano-objects using the nano-tip, and sensed the tiny movement of the lever induced by the dielectric responses of the objects. Scientists have quantitatively recognized those made of very similar materials and with low dielectric constants, as is the case with many biological complexes by increasing the electrical resolution of the microscope by almost two orders of magnitude to detect ultra-weak forces.
This method is a non-invasive way of determining the internal state of objects and correlates these with their functions without slicing or labeling.
This will be an invaluable tool for diverse areas of scientific research such as nanomedicine for biomedical diagnostics for quantitative label-free detection of biological macromolecules such as viruses based on their dielectric properties and to detect nanoparticles for environmental monitoring and protection.


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