Nonharmonic oscillations of nanosized cantilevers due to quantum-size effects

Using a one-dimensional jellium model and standard beam theory we calculate the spring constant of a vibrating nanowire cantilever. By using the asymptotic energy eigenvalues of the standing electron waves over the nanometer-sized cross-section area, the change in the grand canonical potential is calculated and hence the force and the spring constant. As the wire is bent more electron states fits in its cross section. This has an impact on the spring"constant" which oscillates slightly with the bending of the wire. In this way we obtain an amplitude-dependent resonance frequency of the oscillations that should be detectable.Comment: 6 pages, 5 figure

Coherent two-mode dynamics of a nanowire force sensor

Classically coherent dynamics analogous to those of quantum two-level systems are studied in the setting of force sensing. We demonstrate quantitative control over the coupling between two orthogonal mechanical modes of a nanowire cantilever, through measurement of avoided crossings as we deterministically position the nanowire inside an electric field. Furthermore, we demonstrate Rabi oscillations between the two mechanical modes in the strong coupling regime. These results give prospects of implementing coherent two-mode control techniques for force sensing signal enhancement.Comment: 16 pages, 4 figure

Assessing the Viscoelasticity of Photopolymer Nanowires Using a Three-Parameter Solid Model for Bending Recovery Motion

Photopolymer nanowires prepared by two-photon polymerization direct laser writing (TPP-DLW) are the building blocks of many microstructure systems. These nanowires possess viscoelastic characteristics that define their deformations under applied forces when operated in a dynamic regime. A simple mechanical model was previously used to describe the bending recovery motion of deflected nanowire cantilevers in Newtonian liquids. The inverse problem is targeted in this work; the experimental observations are used to determine the nanowire physical characteristics. Most importantly, based on the linear three-parameter solid model, we derive explicit formulas to calculate the viscoelastic material parameters. It is shown that the effective elastic modulus of the studied nanowires is two orders of magnitude lower than measured for the bulk material. Additionally, we report on a notable effect of the surrounding aqueous glucose solution on the elasticity and the intrinsic viscosity of the studied nanowires made of Ormocomp

Finite Element Analysis Simulations of Micro and Nano-Electromechanical Sensors for Design Optimization

Micro and Nano-electromechanical sensors (MEMS and NEMS) provide a means of actively sensing minute changes in the surrounding environment. Small changes in temperature, momentum, and strain may be sensed in passive modes while greater sensing possibilities exist in active modes. Theoretical femto-gram resolution mass detection and heated element sensing methods may be used while volatile organic compound (VOC) sensing may be achieved when combined with a functionalization layer or device heating. These devices offer a great reduction in cost and offer increased mobility by allowing a lab-on-chip solution for the prospective user while also greatly reducing the amount of energy consumed by current sensor designs and equipment set-ups. Work has been done in our lab on AlGaN/GaN MEMS cantilevers and InN NEMS nanowire sensors for use as NOx and VOC sensing applications. Research and development of optimal mechanical designs for these proposed sensors can be a very iterative, and therefore an expensive process. The devices must be grown (in the case of NEMS) etched, and characterized; a process taking several weeks or months and often involving the use of advanced facilities. Because of this great time and material cost methods are needed to reduce the number of iterations to optimal design and streamline the research and development process to achieve a faster time to end-product. Finite element analysis (FEA) simulations allow the researcher to test hundreds of proposed designs within weeks. Allowing a research and development team to reduce the number of proposed design configurations as well as propose and test the feasibility of new sensor designs for future works. Using full-featured simulation packages such as COMSOL Multiphysics allows a researcher to not only model the mechanical properties of the proposed MEMS/NEMS sensors, but also provides the ability to couple together other attributes of the complete device model such as environmental losses, joule heating effects, and polarization. This can be done either within the simulation software itself, or through coupling with external packages such as MATLAB. Here COMSOL simulations, as well as the simulation methodology, will be presented for the cases of the AlGaN/GaN resonant cantilever sensor as well as the InN nanowire based design. In the case of the AlGaN/GaN MEMS sensor some simulation results will be compared to experimental measurements to show the feasibility of this research step for micro-scale and nanoscale mechanical sensor design

Magnetometry of individual polycrystalline ferromagnetic nanowires

Ferromagnetic nanowires are finding use as untethered sensors and actuators for probing micro- and nanoscale biophysical phenomena, such as for localized sensing and application of forces and torques on biological samples, for tissue heating through magnetic hyperthermia, and for micro-rheology. Quantifying the magnetic properties of individual isolated nanowires is crucial for such applications. We use dynamic cantilever magnetometry to measure the magnetic properties of individual sub-500nm diameter polycrystalline nanowires of Ni and Ni80Co20 fabricated by template-assisted electrochemical deposition. The values are compared with bulk, ensemble measurements when the nanowires are still embedded within their growth matrix. We find that single-particle and ensemble measurements of nanowires yield significantly different results that reflect inter-nanowire interactions and chemical modifications of the sample during the release process from the growth matrix. The results highlight the importance of performing single-particle characterization for objects that will be used as individual magnetic nanoactuators or nanosensors in biomedical applications

Power Spectral Density Analysis of Nanowire-Anchored Fluctuating Microbead Reveals a Double Lorentzian Distribution

In this work, we investigate the properties of a stochastic model, in which two coupled degrees of freedom are subordinated to viscous, elastic, and also additive random forces. Our model, which builds on previous progress in Brownian motion theory, is designed to describe water-immersed microparticles connected to a cantilever nanowire prepared by polymerization using two-photon direct laser writing (TPP-DLW). The model focuses on insights into nanowires exhibiting viscoelastic behavior, which defines the specific conditions of the microbead. The nanowire bending is described by a three-parameter linear model. The theoretical model is studied from the point of view of the power spectrum density of Brownian fluctuations. Our approach also focuses on the potential energy equipartition, which determines random forcing parametrization. Analytical calculations are provided that result in a double-Lorentzian power density spectrum with two corner frequencies. The proposed model explained our preliminary experimental findings as a result of the use of regression analysis. Furthermore, an a posteriori form of regression efficiency evaluation was designed and applied to three typical spectral regions. The agreement of respective moments obtained by integration of regressed dependences as well as by summing experimental data was confirmed