Strain sensing with submicron Al-AlO(x)-Al tunnel junctions.

We demonstrate a local strain sensing method for nanostructures based on metallic Al tunnel junctions with AlO(x) barriers. The junctions were fabricated on top of a thin silicon nitride membrane, which was actuated with an atomic force microscope tip attached to a stiff cantilever. A large relative change in the tunneling resistance in response to the applied strain (gauge factor) was observed up to a value of 37. This facilitates local static strain variation measurements down to approximately 10(-7). This type of strain sensor could have applications in nanoelectromechanical systems used in displacement, force, and mass sensing, for example.

Lateral force microscopy of multiwalled carbon nanotubes.

Carbon nanotubes are usually imaged with the atomic force microscope (AFM) in non-contact mode. However, in many applications, such as mechanical manipulation or elasticity measurements, contact mode is used. The forces affecting the nanotube are then considerable and not fully understood. In this work lateral forces were measured during contact mode imaging with an AFM across a carbon nanotube. We found that, qualitatively, both magnitude and sign of the lateral forces to the AFM tip were independent of scan direction and can be concluded to arise from the tip slipping on the round edges of the nanotube. The dependence on the normal force applied to the tip and on the ratio between nanotube diameter and tip radius was studied. We show that for small values of this ratio, the lateral force signal can be explained with a simple geometrical model.

Electrochemical deposition of polypyrrole nanolayers on discontinuous ultrathin gold films.

Ultrathin layers of polypyrrole (PPy) were electrochemically grown between microelectrodes on a Si/SiO(2) substrate. Conducting nanolayers of PPy are directly grown onto ultrathin discontinuous gold (Au) film between the microelectrodes, with thicknesses in the range 10-100 nm. The system therefore forms a novel (PPy/Au) nanocomposite conductor. Atomic force microscopy (AFM) imaging and conductivity measurements indicate that at all thicknesses a relatively uniform film is formed but with significant roughness that reflects the roughness of the metallic island layer. In PPy/Au films with thickness ∼10 nm, the small barriers around the gold islands dominate the conduction, and as the film thickness increases to 100 nm the intrinsic conductivity of highly doped PPy dominates the charge transport.

Environmental chamber for an atomic force microscope.

A commercial atomic force microscope (AFM), originally designed for operation in ambient conditions, was placed inside a compact aluminum chamber, which can be pumped down to high vacuum levels or filled with a desired gaseous atmosphere, including humidity, up to normal pressure. The design of this environmental AFM is such that minimal intrusion is made to the original setup, which can be restored easily. The performance inside the environmental chamber is similar to the original version.

Imaging the elastic properties of coiled carbon nanotubes with atomic force microscopy

Coiled carbon nanotubes were produced catalytically by thermal decomposition of hydrocarbon gas. After deposition on a silicon substrate, the three-dimensional structure of the helix-shaped multiwalled nanotubes can be visualized with atomic force microscopy. Helical structures of both chiralities are present in the nanotube deposits. For larger coil diameters ( >170 nm), force modulation microscopy allows one to probe the local elasticity along the length of the coil. Our results agree with the classical theory of elasticity. Similar to the case of straight nanotubes, the Young modulus of coiled multiwalled nanotubes remains comparable to the very high Young modulus of hexagonal graphene sheets.