We present an improved atomic force microscopy (AFM) method to study the piezoelectric properties of nanostructures. An AFM tip is used to deform a free-standing piezoelectric nanowire. The deflection of the nanowire induces an electric potential via the piezoelectric effect, which is measured by the AFM coating tip. During the manipulation, the applied force, the forcing location and the nanowire's deflection are precisely known and under strict control. We show the measurements carried out on intrinsic GaN and n-doped GaN-AlN-GaN nanowires by using our method. The measured electric potential, as high as 200 mV for n-doped GaN-AlN-GaN nanowire and 150 mV for intrinsic GaN nanowire, have been obtained, these values are higher than theoretical calculations. Our investigation method is exceptionally useful to thoroughly examine and completely understand the piezoelectric phenomena of nanostructures. Our experimental observations intuitively reveal the great potential of piezoelectric nanostructures for converting mechanical energy into electricity. The piezoelectric properties of nanostructures, which are demonstrated in detail in this paper, represent a promising approach to fabricating cost-effective nano-generators and highly sensitive self-powered NEMS sensors.

Current-voltage and Kelvin probe force microscopy (KPFM) measurements were performed on single ZnO nanowires. Measurements are shown to be strongly correlated with the contact behavior, either Ohmic or diode-like. The ZnO nanowires were obtained by metallo-organic chemical vapor deposition (MOCVD) and contacted using electronic-beam lithography. Depending on the contact geometry, good quality Ohmic contacts (linear I-V behavior) or non-linear (diode-like) contacts were obtained. Current-voltage and KPFM measurements on both types of contacted ZnO nanowires were performed in order to investigate their behavior. A clear correlation could be established between the I-V curve, the electrical potential profile along the device and the nanowire geometry. Some arguments supporting this behavior are given based on technological issues and on depletion region extension. This work will help to better understand the electrical behavior of Ohmic contacts on single ZnO nanowires, for future applications in nanoscale field-effect transistors and nano-photodetectors.

No abstract

This study aims to investigate the potential of small densely packed tilted Au nanorods grown on a flexible substrate by physical vapor deposition for strain sensing. By exciting the rods with linearly polarized white light that is perpendicularly impinging onto the sample substrate, interesting plasmonic properties emerge. Electron microscopy characterization shows that the rods are grown at a shallow angle relative to the substrate, as expected for glancing angle deposition conditions. Due to their nonorthogonal orientation, specific coupled multirod plasmon modes are detected for both longitudinal and transverse illumination under illumination normal to the substrate. In a second step, we have performed in situ mechanical tests and showed higher sensitivity to the applied strain for longitudinal E-field directions, which are more strongly affected by changes in inter-rod gaps than for transverse illumination. What is remarkable is that, despite the inherent disorder to this self-assembled system, clear features like polarization dependency and localized surface plasmon resonance (LSPR) wavelength shift with applied strains may be observed due to local changes in the nanorods’ environment. These nanorod coated flexible substrates rank among the most sensitive plasmonic strain sensors in the literature and have potential to be embedded in real strain sensing devices.

We propose to use a parametric amplification regime for small charge or potential difference detection in electric force microscopy. First we give a simple method to accurately estimate the instability domains of the oscillating system. Then we establish general and fully analytical expressions of the parametric amplification gain, and discuss the optimal parameter values which must be used for voltage or charge detection. We show that even in conventional Kelvin probe force microscopy the parametric effect should be taken into account.