PZT nanofibers are piezoelectric and can produce a relatively high electrical output under strain that is useful for self-powered nanogenerators. To obtain maximum power output from these devices, their internal impedance needs to be matched with their applicable load impedance. Electrical impedance measurements of PZT nanofibers were performed using a variety of methods over a frequency spectrum ranging from DC to 3.0 GHz. These methods include Conductive AFM and Scanning Microwave Impedance Microscopy. Nanofibers formed by electro-spinning with diameters ranging from 3 to 150 nm were collected and measured. The nanofiber impedance was extremely high at low frequency, decreased considerably at higher frequency and varied with nanofiber diameter as well. The results are applicable for the analysis of many types of nanogenerators and nanosensors including those produced at Stevens.

Electrical Impedance Measurement of PZT Nanofiber sensors are performed and material properties including resistivity and dielectric constant are derived from the measurements. Nanofibers formed by electro-spinning with diameters ranging from 10 to 150 nm were collected and integrated into sensors using microfabrication techniques. The nanosensor impedance was extremely high at low frequencies and special matching circuitry was fabricated to detect output. The resulting impedance measurements are also compared with those of individual nanofibers that were tested using Scanning Conductive Microscopy (SCM) and Conductive AFM.

In this paper, a piezoelectric leaf generator for harvesting wind energy was proposed, fabricated and tested. The leaf generator had a bimorph cantilever structure, with Su-8 as the protective supporting layer, and aligned lead zirconate titanate (PZT) nanofibers as the active layer. Interdigitated electrodes were sputtered on top of the aligned PZT nanofibers to collect the generated charge. After fabrication of the leaf generator, it was tested in a wind tunnel with different wind incident angles and wind speeds. The maximum voltage output of the leaf generator was 820 mV when the wind speed was 17 m/s. The developed leaf generator does not need further bonding to the vibration source, which make it much easier for real applications. In addition, benefited from unique material properties of the PZT nanofiber such as flexible, robust, and high piezoelectric coupling ability, the leaf generator is promising for a high efficiency wind energy harvest.

Thermoelectric oxide nanofibers prepared by electrospinning was expected to have a significantly reduced thermal conductivity compared with their bulk forms. However, the measurement of the thermal conductivity of such a single nanofiber was very difficult because of sample preparation, sample loading and the lack of characterization tools. In this work, a technology that can be used to measure the thermal conductivity of a single nanofiber prepared by electrospinning was developed. A special Si template was designed to collect and transfer the thermoelectric nanofibers prepared by electrospinning. A microelectro-mechanical (MEMS) device was designed and fabricated to measure the thermal conductivity of a single nanofiber. The structure of the MEMS device was specially designed therefore a single nanofiber collected by the special Si template can be transferred onto the MEMS device. A La 0.95 Sr 0.05 CoO 3 nanofiber with the diameter of 290 nm was prepared and characterized by this technology. The measured thermal conductivity of the nanofiber was 2.07 W/m•K, which is 30% lower than that of the bulk form La 0.95 Sr 0.05 CoO 3 previously reported.

A nanoscale active fiber composites (NAFCs) based acoustic emission (AE) sensor with high sensitivity is developed. The lead zirconate titanate (PZT) nanofibers, with the diameter of approximately 80 nm, were electrospun on a silicon substrate. Nanofibers were parallel aligned on the substrate under a controlled electric field. The interdigitated electrodes were deposited on the PZT nanofibers and packaged by spinning a thin soft polymer layer on the top of the sensor. The hysteresis loop shows a typical ferroelectric property of as-spun PZT nanofibers. The mathematical model of the voltage generation when the elastic waves were reaching the sensor was studied. The sensor was tested by mounting on a steel surface and the measured output voltage under the periodic impact of a grounded steel bar was over 35 mV. The small size of the developed PZT NAFCs AE sensor shows a promising application in monitoring the structures by integration into composites.

In this paper, we demonstrate Lead zirconate titanate (PZT) nanofibers as a transducer to generate and detect ultrasound acoustic waves. PZT nanofibers with average diameter of 102nm were fabricated by the electrospinning method. The as-fabricated nanofibers were collected and aligned across a 10 μm silicon trench with Au electrodes. After annealing, the device was tested with the pulse/delay method. Two resonant frequencies, 8 MHz and 13MHz, were detected respectively. By using the Hamilton’s principle for coupled electromechanical systems with properly assumed mode shape, the resonant frequency was caudated. Base on the current testing result, a broadband ultrasound transducer was envisioned.

We present an electrical measurement of elastic modulus of single electrospun lead zirconate titanate (PZT) nanofibers under harmonic vibration using in situ scanning electron microscopy (SEM) equipped with a nanomanipulator. The PZT nanofiber was fabricated using an electrospinning process and collected on a silicon substrate with 10 μm trenches. The individual PZT nanofibers were excited with an oscillating electric field applied by a network analyzer and the resonant frequency was observed through the SEM along with the transfer frequency spectra simultaneously. The elastic modulus was calculated as ∼70 GPa from this resonant frequency using Euler-Bernoulli equation.

We have recently reported on experimental observations of silk-elastin-like protein polymers (SELPs) that self-assembled into 1-dimensional nanofibers on mica surfaces upon application of a mechanical stimulus with atomic force microscopy (AFM) in water. SELPs are genetically engineered block co-polymers made of silk-like blocks (Gly-Ala-Gly-Ala-Gly-Ser) from Bombyx mori (silkworm) and elastin-like blocks (Gly-Val-Gly-Val-Pro) from mammalian elastin. The experiment consisted of adsorbing the protein polymer onto a freshly cleaved mica surface, followed by AFM characterization under different sets of imaging parameters, each of which led to different nanofiber coverage rates. In order to gain further understanding of the factors governing the self-assembly process, we utilized multimodal AFM simulation to formulate and guide the implementation of a suitable force modulation strategy, which allowed us to observe trends of the surface coverage rate as a function of the applied peak forces. The simulations suggest that a nearly linear control of the peak tapping forces can be achieved by following simple scaling laws based on the harmonic oscillator model.

Integration of material composition, microstructure, and mechanical properties with geometry information enables many product development activities, including design, analysis, and manufacturing. In this paper, we propose the modeling of part geometry and microstructure by using a new hierarchical modeling method that utilizes a common geometric model for both macro-scale part geometry and material microstructure. A new surfacelet transform is introduced to model microstructure. The application of image processing methods enables multi-resolution representations of microstructure. Combined with methods from computational materials design, low resolution microstructure representations can be used to compute effective mechanical properties at the macro-scale. Wavelet decomposition was used to generate the low resolution representations. The models and methods are demonstrated with two examples, a simple continuous-fiber-reinforced composite and a nanofiber reinforced polymer material.

Energy harvesting technology that can increase the operation time and decrease the device size is urgently needed in wireless electronics, portable devices, and implantable biosensors. This paper reports the experimental study of electromechanical coupling of PZT (piezoelectric) nanofiber composites which have the potential to be used for energy harvesting. The recorded voltage output was about 6 mV in the experiments. In this paper, we will describe the fabrication of the piezoelectric nanocomposites and demonstrate the characteristics of electro-mechanical coupling using a dynamic mechanical test. The piezoelectric nanocomposite assembly could produce high voltage and power output to be used as a power source, which might be used for wireless sensors, personal electronics, implantable bio-sensors, and bio-actuators.

This paper reports the measurement of the mechanical and piezoelectric properties of Lead Zirconate Titanate (PbZr 52 Ti 48 O 3 , PZT) nanofibers. Partially aligned PZT nanofibers were fabricated by sol-gel electrospinning process. The diameters of the fiber were tuned from 50 to 150 nm by changing the concentration of the sol-gel in the precursor. The fiber consists of nanocrystal grains with average grain size of 10 nm. The Young’s modulus of individual fiber was obtained by nanoscale three-point bending using Atomic Force Microscope (AFM), which was 42.99GPa. Titanium strip was used as the substrate to collect the nanofibers for the three-point bending test to measure the piezoelectric response. The output voltages from the nanofibers under different strain were recorded by Labview, and the highest value of the output voltage was 0.17±0.005V. These results have shown that PZT nanofibers have great potential in nano sensor and actuator applications.

This paper presents the design and development of a fused vision force feedback robust controller for a nanomanipulator used in nanofiber grasping and nano-fabric production applications. The RRP (Revolute Revolute Prismatic) manipulator considered here utilizes two rotational motors with 0.1 μrad resolution and one linear Nanomotor® with 0.25 nm resolution. Weighing just about 30g and having short lever arms (<5cm), the manipulator is capable of achieving well-behaved kinematic characteristics without the backlash in addition to atomic scale precision to guarantee accurate manipulation at the nanoscale. A mathematical model of the nanomanipulator is formulated and both direct and inverse kinematics of the system as well as dynamic equations are presented. A fused force vision feedback based modified optimal robust controller with perturbation estimation for nanomanipulator positioning is then derived and analyzed extensively. Unlike typical macroscale manipulator models and controllers, the controller development is not trivial here due to nanoscale movement and forces, coupled with unmodeled dynamics, nonlinear structural dynamics and mainly lack of position and velocity feedback in this nanomanipulator. Following the development of the fused force vision robust controller, numerical simulations of the proposed controller are preformed to demonstrate the positioning performance capability in nanofiber grasping applications.

Through adaptation of an atomic force microscope, we have developed a peel test at the micro- and nanoscale level that has the capability of investigating how long flexible nanotubes, nanowires, nanofibers, proteins, and DNA adhere to various substrates. This novel atomic force microscopy (AFM) peeling mode extends existing AFM “pushing” and “pulling” force spectroscopies by offering practical knowledge about the complex interplay of nonlinear flexure, friction, and adhesion when one peels a long flexible molecule or nanostructure off a substrate. The static force peeling spectroscopies of straight multiwalled carbon nanotubes suggest that a significant amount of the total peeling energy is channeled into nanotube flexure. Meanwhile dynamic force spectroscopies offer invaluable information about the dissipative physical processes involved in opening and closing a small “crack” between the nanotube and substrate.

Electrospun polyacrylonitrile (PAN) fiber precursor based Carbon Nanofiber (CNF) mats were produced and impregnated with epoxy resin. The mechanical properties of as-prepared nanofibers in the mat and short fiber filled epoxy nanocomposite forms were determined to demonstrate the effect of fiber aspect ratio and interconnecting network on those properties. Our experimental results reveal that epoxy nanocomposites containing Electrospun Carbon Nano Fibers (ECNF) with high fiber aspect ratio and high interconnecting network in the non-woven mat form yield better mechanical properties than those filled with short ECNFs. The ECNF mat in epoxy nanocomposites provides better homogeneity, more interlocking network, and easier preparation than short ECNFs. Mechanical properties of ECNF mat-epoxy nanocomposites, which we obtained using tensile and flexural tests, such as stiffness and modulus increased, while toughness and flexural strength decreased, compared to the neat epoxy resin. Dynamic Mechanical Analysis (DMA) results showed, higher modulus for ECNF mat-epoxy nanocomposites, compared to those for neat epoxy resin and short ECNF-epoxy nanocomposites. The epoxy nanocomposites had high modulus, even though the glass transition temperature, T g values dropped at some extents of ECNF mat contents when compared with the neat epoxy resin. The cure reaction was retarded since the amount of epoxy and hardener decreased at high ECNF contents together with the hindering effect of the ECNF mat to the diffusion of epoxy resin and curing agent, leading to low crosslinking efficiency.