On-chip lithium cells for electrical and structural characterization of single nanowire electrodes

A 3-D NanoMagnetoElectrokinetic model for ultra-high precision assembly of ferromagnetic NWs using magnetic-field assisted dielectrophoresis

This report presents a three-dimensional (3-D) magnetoelectrokinetic model to investigate a new approach to magnetic-field assisted dielectrophoresis for ultra-high precision and parallel assembly of ferromagnetic Ni nanowires (NWs) on silicon chips. The underlying assembly methodology relies on a combination of electric and magnetic fields to manipulate single nanowires from a colloidal suspension and yield their assembly on top of electrodes with better than 25 nm precision. The electric fields and the resultant dielectrophoretic forces are generated through the use of patterned gold nanoelectrodes, and deliver long-range forces that attract NWs from farther regions of the workspace and bring them in proximity to the nanoelectrodes. Next, magnetic-fields generated by cobalt magnets, which are stacked on top of the gold nanoelectrodes at their center and pre-magnetized using external magnetic fields, deliver short range forces to capture the nanowires precisely on top of the nanomagnets. The 3-D NanoMagnetoElectrokinetic model, which is built using a finite element code in COMSOL software and with further computations in MATLAB, computes the trajectory and final deposition location as well as orientation for all possible starting locations of a Ni NW within the assembly workspace. The analysis reveals that magnetic-field assisted dielectrophoresis achieves ultra-high precision assembly of NWs on top of the cobalt nanomagnets from a 42% larger workspace volume as compared to pure dielectrophoresis and thereby, establishes the benefits of adding magnetic fields to the assembly workspace. Furthermore, this approach is combined with a strategy to confine the suspension within the reservoir that contains a high density of favorable NW starting locations to deliver high assembly yields for landing NWs on top of contacts that are only twice as wide as the NWs.

Magnetic-field assisted dielectrophoresis delivers ultra-high precision assembly of single nanowires.

Tunable nanomechanical performance regimes in ceramic nanowires

At the macroscopic size regime, ceramic materials exhibit brittle fracture and catastrophic failure when they are subjected to mechanical loads that exceed their characteristic strength. In this report, we present recoverable plasticity in alpha-phase, potassium stabilized manganese dioxide nanowire (α-K_0.13MnO₂ NW) crystals when they are subjected to atomic force microscopy (AFM) based three-point bending tests at very low loading rates. The force-deflection curves and AFM scans obtained from these measurements reveal yielding and extended plasticity in the NWs during the loading process, while the large plastic deformation is recovered spontaneously during the unloading process. However, the same material system exhibits failure via fracture at substantially higher strengths when it is subjected to bending tests at nearly an order of magnitude higher loading rates. These results highlight an important new pathway to controllably tune the nanomechanical performance of these technologically important nanoceramics for application-specific needs: either achieve self-reversible and ultra-large plasticity, or achieve substantially higher fracture strengths that approach the intrinsic limits of the material system.

Plastic recovery and self-healing in longitudinally twinned SiGe nanowires

This paper reports on plastic recovery and self-healing behavior in longitudinally-twinned and [112] orientated SiGe nanowire (NW) beams when they are subjected to large bending strains. The NW alloys are comprised of lamellar nanotwin platelet(s) sandwiched between two semi-cylindrical twins. The loading curves, which are acquired from atomic force microscope (AFM) based three-point bending tests, reveal the onset of plastic deformation at a characteristic stress threshold, followed by further straining of the NWs. This ductility is attributed to dislocation activity within the semi-cylindrical crystal portions of the NW, which are hypothesized to undergo a combination of elastic and plastic straining. On the other hand, the lamellar nanoplatelets undergo purely elastic stretching. During the unloading process, the release of internal elastic stresses enables dislocation backflow and escape at the surface. As a result, the dislocations are predominantly annihilated and the NW samples evidenced self-healing via plastic recovery even at ultra-large strains, which are estimated using finite-element models at 16.3% in one of the tested devices. Finite element analysis also establishes the independence of the observed nanomechanical behavior on the relative orientation of the load with respect to the nanoplatelet. This first observation of reversible plasticity in the SiGe material system, which is aided by a concurrent evolution of segmented elastic and plastic deformation within its grains during the loading process, presents an important new pathway for mechanical stabilization of technologically important group-IV semiconductor nanomaterials.

Brittle fracture to recoverable plasticity: polytypism-dependent nanomechanics in todorokite-like nanobelts

Atomic force microscopy (AFM) based nanomechanics experiments involving polytypic todorokite-like manganese dioxide nanobelts reveal varied nanomechanical performance regimes such as brittle fracture, near-brittle fracture, and plastic recovery within the same material system. These nanobelts are synthesized through a layer-to-tunnel material transformation pathway and contain one-dimensional tunnels, which run along their longitudinal axis and are enveloped by m × 3 MnO₆ octahedral units along their walls. Depending on the extent of material transformation towards a tunneled microstructure, the nanobelts exhibit stacking disorders or polytypism where the value for m ranges from 3 to up to ∼20 within different cross-sectional regions of the same nanobelt. The observation of multiple nanomechanical performance regimes within a single material system is attributed to a combination of two factors: (a) the extent of stacking disorder or polytypism within the nanobelts, and (b) the loading (or strain) rate of the AFM nanomechanics experiment. Controllable engineering of recoverable plasticity is a particularly beneficial attribute for advancing the mechanical stability of these ceramic materials, which hold promise for insertion in multiple next-generation technological applications that range from electrical energy storage solutions to catalysis.

A 3D nanoelectrokinetic model for predictive assembly of nanowire arrays using floating electrode dielectrophoresis

Floating electrode dielectrophoresis (FE-DEP) presents a promising avenue for scalable assembly of nanowire (NW) arrays on silicon chips and offers better control in limiting the number of deposited NWs when compared with the conventional, two-electrode DEP process. This article presents a 3D nanoelectrokinetic model, which calculates the imposed electric field and its resultant NW force/velocity maps within the region of influence of an electrode array operating in the FE-DEP configuration. This enables the calculation of NW trajectories and their eventual localization sites on the target electrodes as a function of parameters such as NW starting position, NW size, the applied electric field, suspension concentration, and deposition time. The accuracy of this model has been established through a direct quantitative comparison with the assembly of manganese dioxide NW arrays. Further analysis of the computed data reveals interesting insights into the following aspects: (a) asymmetry in NW localization at electrode sites, and (b) the workspace regions from which NWs are drawn to assemble such that their center-of-mass is located either in the inter-electrode gap region (desired) or on top of one of the assembly electrodes (undesired). This analysis is leveraged to outline a strategy, which involves a physical confinement of the NW suspension within lithographically patterned reservoirs during assembly, for single NW deposition across large arrays with high estimated assembly yields on the order of 87%.

Intrinsic non-ohmic electronic transport properties of the transparent In-Zn-O compound nanobelts under ohmic contact and out of the space charge limited transport region

It is generally accepted that the nonlinear I-V characteristics for semiconductor nanostructures are mainly induced by the Schottky contacts or by the space charge limited transport mechanism. We perform I-V measurements on undoped and doped In-Zn-O compound nanobelts and confirm that their intrinsic non-ohmic transport behaviors are not caused by these mechanisms. A model based on the hopping assisted trap state electrons transport process is introduced to explain the nonlinear I-V characteristics and to extract their electrical parameters. An understanding of this trap-state influenced carrier transport can advance the progress of nanomaterials applications and enable us to distinguish their intrinsic transport behaviors from contact effects. The results also indicate that the material has good electrical properties and can be used as a potential substitute for In2O3.

Dependence of Young's modulus on the sodium content within the structural tunnels of a one-dimensional Na-ion battery cathode

We report on the Young's modulus (YM) of single-crystalline Na4Mn9O18 (or Na0.44MnO2) nanowires (NWs), which have shown promise as reversible sodium-ion (Na(+)) intercalation cathodes with high capacity and excellent cyclability. In addition, acid treatment of this material yielded proton stabilized Na(0.44-y)MnO2 (y ∼ 0.23) NWs with a 74% increase in the YM. The tight correlation between YM and ionic content within the crystalline tunnels is particularly significant, since it points to the strong dependence of elastic properties on state-of-charge (SOC) within battery materials.

Single nanowire manipulation within dielectrophoretic force fields in the sub-crossover frequency regime

This paper presents the quantitative relationship between the control parameters of a dielectrophoretic (DEP) force field and the resulting electrokinetic region of influence experienced by individual nanowires (NWs) in colloidal suspensions. Our results show that DEP operation at sub-crossover frequencies, which are defined as frequencies slightly below the transition from positive-to-negative DEP, offers a suitable but previously unexplored performance regime for single NW manipulation and assembly. The low-magnitude DEP forces at these frequencies, which are estimated to be 8 orders of magnitude smaller as compared to near-DC frequencies, provide an efficient avenue to controllably extend electrokinetic influence on suspension volumes that present isolated NWs. These results are demonstrated using α-phase manganese dioxide NWs as a model one-dimensional construct. Based on experimentally extracted values for the NW intrinsic conductivity and dielectric permittivity, we employ computational models to explain each of the performance regimes observed in this nanoassembly system. In addition, we use a new approach to estimate the concentration of a NW suspension from experimentally observed data for deposition yields.