Gustavo Ardila

Nano‐Newton Transverse Force Sensor Using a Vertical GaN Nanowire based on the Piezotronic Effect

In this paper, we explore the piezotronic effect in a GaN nanowire under a transverse force. The force was applied by bending the end of a single NW using an atomic force microscope (AFM) tip. Our results show that GaN NWs can be used to transduce a shear/bending force into a dramatic current change through the NW due to the piezotronic effect. Owing to the local piezopotential generated by the applied force, the barrier height of the Schottky contact between the GaN NW and the platinum AFM tip can be modulated. Using this transduction mechanism, the transverse force can be correlated to the natural logarithm of the current. Our results indicate that the force sensitivity is about 1.24 ± 0.13 ln(A)/nN, and a force resolution better than 16 nN is demonstrated. The nN sensitivity of GaN NWs shows the potential for piezoelectric semiconductor NWs to act as the main building blocks for micro-/nanometersized force sensor arrays and high spatial resolution artifi cial skin.

Scaling rules of piezoelectric nanowires in view of sensor and energy harvester integration

This paper presents for the first time the scaling rules of piezoelectric nanowires (NWs), as the active transducer element for sensors and mechanical energy harvesters. Moreover, to keep close to realistic structures, non-linear effects associated to large displacements were taken into account, as well as the influence of NW variability, based on experimental data. We demonstrate that well-above-state-of-the-art sensitivities and resolutions can be achieved for sensing applications, and that large energy conversion efficiencies can be obtained for mechanical energy harvesters (about 7 times larger than that of their bulk counterpart).

Optimization of dielectric matrix for ZnO nanowire based nanogenerators

This paper reports the role of selection of suitable dielectric layer in nanogenerator (NG) structure and its influence on the output performance. The basic NG structure is a composite material integrating hydrothermally grown vertical piezoelectric zinc oxide (ZnO) nanowires (NWs) into a dielectric matrix. To accomplish this study, three materials - poly methyl methacrylate (PMMA), silicon nitride (Si3N4) and aluminium oxide (Al2O3) are selected, processed and used as matrix dielectric in NGs. Scanning electron microscopy (SEM) analysis shows the well-aligned NWs with a diameter of 200±50 nm and length of 3.5±0.3 μm. This was followed by dielectric material deposition as a matrix material. After fabricating NG devices, the output generated voltage under manual and automatic bending were recorded, observed and analyzed for the selection of the best dielectric material to obtain an optimum output. The maximum peak-to-peak open-circuit voltage output for PMMA, Si3N4 and Al2O3 under manual bending was recorded as approximately 880 mV, 1.2 V and 2.1 V respectively. These preliminary results confirm the predicted effect of using more rigid dielectrics as matrix material for the NGs. The generated voltage is increased by about 70% using Si3N4 or Al2O3, instead of a less rigid material as PMMA.

High frequency characterization and modeling of single metallic nanowire

The feasibility of using metallic nanowires (NWs) for microwave interconnect application is very attractive. This paper presents RF characterizations of aluminum (Al) nanowires (NWs) up to 65 GHz. Coplanar waveguide (CPW) test structures integrating with NWs of different lengths are designed and fabricated. From the measured S-parameters, the frequency-dependent electrical properties of the NWs can be found. Equivalent-circuit modeling combined with ADS Momentum is used to simulate the CPW devices under test. After comparing the theoretical and measured values, new circuit elements are deduced. From which, contact impedance can be determined accurately. The test setup proposed is useful for determination the actual conductivity and contact impedance of any metallic NW over a wide range of frequencies.